Topic 16 Organic chemistry, hydrocarbons, food tests, biochemistry
Updated 2008-09-27
Please send comments to: J.Elfick@uq.edu.au
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Table of contents
16.1.0 Organic chemistry
16.1.1 Acyclic hydrocarbons, alkanes,alkenes, alkynes
16.1.3.1 Alcohols,phenols, thiols, ethers,epoxy compounds, acetates (ethanoates) benzoyls, acetals
16.1.1b Ethane (C2H6) prepare ethane
16.1.5.3 Salts, organic salts, e.g. sodium ethanoate (sodium acetate) (CH3COONa) ammonium acetate (CH3COONH4)
16.1.5.5 Acyl halides (group: --CO.X, X = halogen atom) acid chloride, acid chlorides group: (-COCl ) suffix: -oyl chloride
16.1.5.6 Amides, acid amides group: (-CONH2, RCONH2) suffix: -amide
16.1.5.6.1 Acrylamide, 2-Propenamide,ethylene carboxamide, acrylic amide, vinyl amide
16.1.5.7 Acid anhydrides, acyl anhydrides, anhydrides [RCO-O-COR' (R(C=O)O(C=O)R')]
16.1.5.8 Imides (imido group: -CONHCO-) (R1CO-NH-COR2)
16.2.2 Halogen compounds, haloalkanes (alkyl halides) halogen derivatives
16.2.3 Organometal compounds (prefixing the metal with organo-)
16.2.3.1 Carbides (C4-) (carbon + metal)
16.2.4 Nitrogen compounds, one atom of nitrogen
16.2.4.2 Nitriles (acid nitriles, alkyl cyanides, cyanides)(-CN, RC=-N) (cyanide ion: CN-)
16.2.4.2.1 Cyanamides (inorganic, CN22-) ionization reaction of methylamine, cyanic acid, melamine
16.2.4.3 Amines, aliphatic amines (RNH2-, R = alkyl group) ionization reaction of methylamine
16.2.4.3a Imines (imino group: --NH-- in a ring, or =NH)
16.2.4.4 Nitroalkanes (nitroparaffins) (CnH2n+1NO2)
16.2.4.5 Nitrites (NO2-, dioxonitrate ion, salts or esters of nitrous acid, O=NOH) Nitrites group: (-C=N) suffix: -nitrite
16.2.4.6 Oximes (hydrox- imino- alkanes) (group: C:NOH)
16.2.4.7 Cyanocrylates [(CH2)C(CN)COOR] "Superglue"
16.2.5 Nitrogen compounds, two or more nitrogen atoms
16.2.6 Phosphorous compounds
16.2.8 Sulfur compounds
16.2.10 Coal tar products
16.3.1.0 Aldehydes, ketones, quinones, aldehydes group: (-CHO) suffix: -al
16.3.1.1 Carbohydrates
16.3.5.0 Fluorescent liquids
16.4.1 Test organic acids and alcohols
16.4.2 Prepare ethanoic acid (acetic acid) ionization reaction
16.4.3 Prepare ethanedioic acid-2-water (oxalic acid) ionization reaction
16.4.4 EDTA, ethylenediaminetetraacetic acid, C10H16N2O8
9.137 Tests for fats and oils
3.79 Make soap from fats
16.4.5 Tests for proportion of fats in foods
16.4.6 Test gases from burning hydrocarbons
16.4.7 Tests for saturated hydrocarbons, bromine water test
16.4.8 Tests for saturated hydrocarbons, alkaline potassium manganate (VII) solution
16.4.9 Tests for saturated hydrocarbons, acidified potassium manganate (VII) solution
16.5.1.0 Esters, derivatives of fatty acids (RCOOR') Esters group: (-COOR) suffix: -oate
16.9.0 Food, plants
3.95.0 Breakdown large molecules to small molecules
3.100.0 Building up molecules
9.7 Food tests
16.1.1 Acyclic hydrocarbons, alkanes, alkenes, alkynes
16.1.1.1 Alkanes (CnH2n+2) paraffins
16.1.1a Methane (CH4) prepare methane gas
16.1.1a.1 Natural gas
16.1.1a.2 Reaction of methane with chlorine
16.1.1b Ethane (C2H6), prepare ethane
16.1.1c Propane (C3H8)
16.1.1d Butane (C4H10), prepare butane
16.1.1e Pentane (C5H12)
16.1.1f Hexane (C6H14)
16.1.1g Heptane (C7H16)
16.1.1h Octane (C8H18), octane number
16.1.1.2 Alkenes (CnH2n)olefins
16.1.1.2.1 Prepare ethene (ethylene) gas
16.1.1.2.2 Dienes, isoprene units
16.1.1.3 Alkynes (CnH2n-2)acetylenes
16.1.1.3.1 Prepare ethyne (acetylene) gas
16.1.3.1 Alcohols,phenols, thiols, ethers,epoxy compounds, acetates (ethanoates) benzoyls, acetals
16.1.3.1.1 Alcohols, Alcohols group: (-OH) suffix: (ol) primary, secondary and tertiary aliphatic alcohols
16.1.3.1.2 Prepare sodium ethoxide
16.1.3.2 Phenols (group: OH-C in a benzene ring) (phenol = C6H5O6)
16.1.3.3 Thiols, mercaptans, thio alcohols,Thioalcohols group: (-SH) suffix: -thiol (SH in an organic compound)
16.1.3.4 Ethers (group: --O-- in organic compound)
16.1.3.5 Epoxy compounds (O atoms in CCO ring)
16.1.3.6 Acetates (ethanoates) ROAc
16.1.3.7 Benzoyl group, benzene carbonyl group C6H5CO--
16.1.3.8 Acetals (alcohol + aldehyde) RCH(OR')2
16.1.12 Fractional distillation of crude oil
16.1.13 Prepare triodomethane (iodoform)
16.1.14 Prepare trichloromethane (chloroform)
16.1.12 Fractional distillation of crude oil
16.1.12.1 Petroleum gas (methane, ethane, propane, butane)
16.1.12.2 Naphtha (ligroin) processed to make gasoline
16.1.12.3 Petrol, "gas", gasoline, motor fuel
16.1.12.4 Kerosene, kerosine, paraffin oil, jet engine fuel, tractor fuel
16.1.12.5 Diesel oil, gas oil or diesel distillate, diesel fuel, heating oil
16.1.12.6 Lubricating oil, motor oil, grease
16.1.12.7 Paraffin wax, heavy gas, fuel oil
16.1.12.8 Residuals, bitumen, "tar", asphalt, waxes, petroleum jelly
16.2.8 Sulfur compounds, For the "thio" prefix, replace oxygen by sulfur, e.g. thiobenzamide PhC(=S)NH2
16.2.8.1 Isothiocyanates (old name: mustard oil) (RN=C=S) mustards [X(CH2.CH2)2S]
16.2.8.2 Sulfides: RSR (R not equal to H) (old name: thioethers)
16.2.8.3 Sulfonic acids, group: R-SO2OH, e.g. methanesulfonic acid, CH3SO2OH, salts or esters called sulfonates
16.2.8.4 Sulfonium compounds: R3S+, e.g. trimethylsulfonium chloride [(CH3)3S]+Cl-
16.2.8.5 Thiocyanates: [RC(=O)SN] salts and esters of thiocyanic acid HSCN, e.g. methyl thiocyanate CH3SC =- N
16.2.8.6 Silicones: polymeric unbranched siloxanes, formula (-OSiR2-)n (R not equal to H)
16.2.8.7 Siloxanes
16.2.8.9 Sulfoxide, dimethyyl sulfoxide, DMSO (CH3)2SO, C2H6OS
16.1.3.3 Thiols, thio-alcohols
16.3.1.0 Aldehydes, ketones, quinones, aldehydes group: (-CHO) suffix: -al
See also: Metaldehyde
16.3.1 Prepare ethanal (acetaldehyde) with potassium dichromate
16.3.2 Prepare ethanal with potassium manganate (VII) (potassium permanganate, Condy's crystals)
16.3.3 Oxidation of methanol to methanal using platinum catalyst
16.3.4 Oxidation of glucose with sodium hydroxide and methylene blue, blue bottle experiment
16.3.5 Silver mirror test for aldehydes, Tollens' test for acetaldehyde
16.3.6 Silver mirror test for aldehydes, Tollens' test for glucose
16.3.7 Fehling's test for aldehydes in solution
16.3.8 Ketones, group: (>C=O) suffix: -one
16.3.9 Diacetyl, 2,3-butanedione
16.3.10 Quinones, contains C=O group in unsaturated ring, e.g.cyclohexandiene-1,4-dione
9.140 Tests for reducing sugars and aldehydes, test for simple sugars, Fehling's test
16.3.5.0 Fluorescent liquids
16.3.5.1 Aesculin (Escalin)
16.3.5.2 Amido phthalic acid and amido-tarephthalic acid
16.3.5.3 Eosin (Eosine)
16.3.5.4 Fluorescein
16.3.5.5 Fraxin
16.3.5.6 Magdala red
16.3.5.7 | Quinine
16.3.5.8 Safranin (safranine, safranin O, basic red 2)
16.4.1 Test organic acids and alcohols
16.4.1.1 Carboxylic acids, fatty acids and their salts, Carboxylic acids group: (-COOH) suffix: -oic acid
16.4.1.1.1 Dicarboxylic acids, two carboxyl groups (-dioic acid)
16.4.1.1.2 Tricarboxylic acids, citric acid
16.5.1.0 Esters, derivatives of fatty acids, derivatives of fatty acids (RCOOR') Esters group: (-COOR) suffix: -oate
16.5.1 Prepare ethyl chloride
16.5.1.1 Ethyl acetoacetonate (ethyl 3-oxobutanoate)
16.5.2 Prepare esters, ethyl acetate (ethyl ethanoate)
16.5.4 Hydrolysis of esters
16.5.5 Prepare esters, methyl salicylate (oil of wintergreen)
16.5.6 Prepare esters, amyl acetate (pear oil)
16.5.7 Prepare ethyl butyrate
16.5.8 Prepare ethyl acetate (ethyl ethanoate)
16.5.9 Prepare methyl chloride
16.6.1.1 Tests for proteins, peptides, amino acids
16.6.1 Tests for proteins, heat test for proteins
16.6.1.1 Tests for proteins, peptides, amino acids
16.6.2 Tests for proteins, burning test for proteins
16.6.3 Prepare protein solutions
16.6.4 Tests for albumin and gelatine
16.6.5 Tests for proteins, biuret test
16.6.6 Tests for proteins, xanthoproteic test
16.6.7 Tests for proteins, Millon's test
16.6.8 Tests for proteins, Albustix test strips
16.6.9 Nitrogen in an organic compound, Kjeldahl method
16.6.10 Tests for proteins, Sakaguchi's arginine test
16.6.11 Tests for sulfur in proteins
16.6.12 Proteins are amphoteric
16.6.13 Urea forms biuret
16.6.14 Reactions of urea with sodium hypochlorite
16.6.15 Reactions of urea with nitrous acid
16.6.16 Reactions of urea with soda lime
16.6 17 Hydrolysis of urea with urease
16.6.18 Urea acts as a base
16.8.1.1 Aromatic hydrocarbons
16.8.1 Reactions of benzene
16.8.2 Prepare ferric tannate with tea leaves
16.8.3 Extraction of caffeine and benzoic acid from soft drinks, e.g. cola and lemonade
16.9.0 Food, plants
9.7 Food tests
16.9.1 Burn carbohydrates, fats and proteins
16.9.2 Heat food with copper (II) oxide
19.2.1.6 Antioxidants
16.1.0 Organic chemistry
See diagram 16.0.0: Organic chemistry functional groups | See diagram 16.0.1: Tetrahedral geometry of carbon, methane molecule, isobutyl alcohol
Organic chemistry is the chemistry of carbon compounds. Hydrocarbons contain carbon and hydrogen only. The main types are the alkanes, alkenes and alkynes. In alkenes and alkynes, addition reactions occur at the double bond or =--s bond.
Be careful! When heating organic chemicals, do not point the test-tube towards anyone! Organic compounds may suddenly vaporize and spurt out of the test-tube!
1. Classification by molecular framework
1.1 Acyclic compounds have chains of unbranched or branched carbon atoms
1.2 Carbocyclic compounds have rings of carbon atoms
1.3 Heterocyclic compounds have rings of carbon atoms with one atom in a ring not carbon, e.g. O, N, S
2. Classification by functional group, e.g. hydroxyl group, OH, is characteristic of alcohols
16.1.1 Acyclic hydrocarbons, alkanes, alkenes, alkyne
See diagram 16.1.1: Alkanes, alkenes, alkynes | See also 10.6.3: Distil crude oil and collect the fractions
Alkanes, alkenes, alkynes or their derivatives are aliphatic compounds, i.e. non-cyclic organic compounds. Acyclic molecules have carbon atoms in chains but not in rings. The chains may be unbranched or branched. Aromatic compounds contain a benzene ring in the molecule. Hydrocarbon compounds contain only hydrogen and carbon. Hydrocarbons are usually colourless and have low solubility in water.
Hydrocarbons may be:
1. saturated, i.e. have only single bonds, or unsaturated, i.e. contain multiple bonds, e.g. double bond, triple bond,
2. aliphatic (alkane) or aromatic (arenes, benzene). Crude oil is a mixture of hydrocarbons.
16.1.1.1 Alkanes (CnH2n+2) paraffins
The first 10 unbranched alkanes and molecular formula: methane (CH4) ethane (C2H6) propane (CH3H8) butane (CH4H10) pentane (CH5H12) hexane (CH6H14). heptane (CH7H16) octane (CH8H18) nonane (CH9H20) decane (CH10H22).
1. Alkanes (paraffins) are saturated hydrocarbons, i.e. all single bonds between C atoms, have formula CnH2n+2 and names end in "ane". The names of unbranched alkanes come from the number of carbon atoms. The name of branched alkanes come from the longest chain of carbon atoms. The hydrocarbon branches, alkyl groups, symbol R, are formed by removing one hydrogen atom from the alkane and named by changing the "ane" to "yl", e.g. methane, CH4 to methyl, CH3-, also "Me". The carbon atoms of the longest continuous name are numbered starting at the end of the chain closest to the first branch, e.g. an eight carbon chain with an ethyl group attached to carbon 5 and a methyl group attached to carbon 3 and carbon 4 is called 5-ethyl-3,4-dimethyloctane.
2. Cycloalkanes are saturated hydrocarbons with a ring of carbon atoms, e.g. cyclopropane (the simplest) cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane. The position of branches depends on the alphabetical order of the branch names so that highest in order is attached to carbon 1, e.g. 1-ethyl-2-methylcyclopropane. Alkanes are usually associated with natural petroleum deposits and can be distilled from petroleum.
3. Alkanes burn in oxygen to give carbon dioxide and water.
4. Candle wax is a mixture of different alkanes that are solid at room temperature.
16.1.1a Methane (CH4) prepare methane gas
See diagram 16.0.1: Tetrahedral geometry of carbon, methane molecule
Methane is the simplest alkane. It is colourless and odourless and found in natural gas and bubbles of methane in swamp water. Fire damp, which causes explosions in coal mines, is a mixture of methane and air. Methane is found in large quantities usually associated with petroleum. It has largely displaced town gas produced from coal. Methanogenic bacteria live in swamps and in the human gastrointestinal tract where they liberate methane causing flatulence. After carbon dioxide, methane produced by bacteria in rice paddies may be the second most important greenhouse gas made by man. They produce methane gas anaerobically (without oxygen) by removing the electrons from hydrogen gas. The electrons and H+ ions from hydrogen gas are used to reduce carbon dioxide to methane. H+ ions combine with the oxygen from carbon dioxide to form water and electrons move through the steps of an anaerobic electron transport system to the phosphorylate of ADP to form ATP. Methane, is a simple asphyxiant.
1. Prepare methane gas
See diagram 13.1.0: Collect insoluble gases over water
Heat 20 g of sodium acetate-3-water in a Pyrex test-tube until the salt becomes anhydrous. Grind the cooled salt with an equal amount of soda lime [NaOH + Ca(OH)2] granules in a mortar and pestle. Mix thoroughly and place the mixture in a Pyrex test-tube. Heat the test-tube and collect the gas over water.
Be careful! If you do not pull out the delivery tube, heating the water stops or the water will be "sucked back" into the hot test-tube! For safety, wrap the test-tube in wire gauze.
CH3COONa + NaOH---> CH4 + Na2CO3
sodium acetate + sodium hydroxide---> methane + sodium carbonate
2. Tests for methane gas: Light the gas in the test-tube with a glowing splint. The gas burns with a clear flame.
CH4 + 2O2 --> CO2 + 2H2O
3. Repeat the experiment using glacial acetic acid soaked in glass wool + soda lime.
16.1.1a.1 Natural gas
Natural gas consists of about 90% methane together with varying proportions of ethane, propane, butane, nitrogen and carbon dioxide. Methane is odourless but during manufacture a rotten egg rank smelling compound, usually a mercaptan, e.g. captan (ethane thiol or ethyl mercaptan) is added so that the presence of the gas can be easily detected. Incomplete combustion yields carbon monoxide. Natural gas should burn with a 90% blue flame. Check the colour of the flame in the pilot light. If the flame appears yellow, the gas is probably contaminated by condensates during manufacture so contact the gas distribution authority for advice. Similarly, see assistance if you find yellow condensate when you wipe the wall, or a shadow behind pictures on the wall, or a black smudge on the bottom of cooking pots. Be careful! Do not search for a gas leak with a lighted match or lighted tape! Use a soap solution.
16.1.1a.2 Reaction of methane with chlorine
When a mixture of an alkane and chlorine gas are stored at low temperature in the dark no reaction occurs. At high temperatures or in sunlight, a substitution exothermic reaction called chlorination occurs to produce chloromethane, methyl chloride and HCl.
CH4 + Cl2---> CH3Cl + HCl
Excess chlorine can produce dichloromethane (methylene chloride) trichloromethane (chloroform) and tetrachloromethane (carbon tetrachloride).
16.1.1b Ethane (C2H6) prepare ethane
Colourless and odourless gas which has properties similar to methane.
Prepare ethane
See diagram 13.1.0-4: Collect insoluble gases over water | See diagram 16.1.1: Ethane
(This experiment was called the "wet asbestos method" because asbestos wool, now not allowed in schools, was used to soak up the methyl iodide in the test-tube.)
Pour 2 cm methyl iodide in a test-tube. Add 5 g of copper turnings and push it down firmly with a spatula. Set up the apparatus and heat the mixture.
2CH3I + 2Cu---> C2H6 + Cu2I2
16.1.1c Propane (C3H8)
LPG, LP gas (liquefied petroleum gas, bottled gas, propane C3H8, butane C4H10) b.p. -42.2oC. Liquefied Petroleum Gas (LPG) is a clean burning fuel and is stored in gas cylinders as bottled gas. LP gas. Bottled gas is a simple asphyxiant. It consists of propane (about 95%) together with varying proportions of butane, propylene and butylene. A rank smelling compound is added so that the presence of the gas can be easily detected. Incomplete combustion yields carbon monoxide. Do not search for a gas leak with a lighted match or lighted taper. Use a soap solution.
16.1.1d Butane (C4H10) prepare butane
b.p. -0.5oC, relative density 0.60 at 0oC, is stored as liquid under pressure in steel cylinders giving Calor gas and cigarette lighter gas, cigarette lighter fuel is 90% butane, isomer isobutane.
Prepare butane
See diagram 13.1.0-4: Collect insoluble gases over water | See diagram 16.1.1: Butane
(This experiment was called the "wet asbestos method" because asbestos wool, now not allowed in schools, was used to soak up the ethyl iodide in the test-tube.)
Pour 2 cm ethyl iodide in a test-tube. Add 5 g of copper turnings and push it down firmly with a spatula. Set up the apparatus and heat the mixture.
2C2H5I + 2Cu ---> C4H10 + Cu2I2
16.1.1e Pentane (C5H12)
b.p. 36.3oC, relative density 0.63, is made by distillation of petroleum.
16.1.1f Hexane (C6H14)
b.p. 68.7oC, relative density 0.66, exists as five compounds with same formula, normal hexane, n-hexane, in petrol and petroleum ether solvent, colourless liquid ethereal odour. "Shellite" (Australia) is 60% hexane and 40% heptane.
16.1.1g Heptane (C7H16)
b.p. 98oC, relative density 0.68, nine isomers, normal heptane has similar properties to normal hexane.
16.1.1h Octane (C8H18) Octane number
See diagram 16.1.1h: Octane number
b.p. 126oC, relative density 0.702 at 20oC, exists as eighteen compounds, in petroleum. Isomeric with iso-octane, 2,2,4-trimethylpentane (CH3)3CCH2CH(CH3)2.
Octane number
See also: 32.5.5.5: Spark plugs, pre-ignition
Some hydrocarbons with unbranched carbon chains prematurely explode in the cylinder and produce an audible knocking sound or "ping" sound. A scale of "knock property" has isooctane (2,2,4-trimethylpentane) at 100 (a good fuel) and heptane at 0 (a poor fuel). So gasoline with octane number 80 has the same properties as a mixture of 80% isooctane and 29% heptane. Octane number is the percentage of iso-octane normal heptane mix with the same knocking behaviour of the fuel being tested, so it indicates the knock rating of a motor fuel. A high octane fuel has a longer self-ignition delay in a motor car engine.
A high octane rating of a fuel means that it has less tendency to preignite in a high compression engine. Preignition means that, before the spark plug has fired, the fuel air mixture burns because of the heat created in the cylinder by compression.
Engine compression ratio 4:1 5:1 6:1 7:1 8:1 9:1 10:1 11:1 12:1
Octane number to be knock-free 60 73 81 87 91 95 98 100 102
16.1.1.2 Alkenes (CnH2n) olefins
ethene (ethylene) (H2C=CH2) amylene, propadiene (allene) (R2C=C=CR2) dienes buta-1,2-diene (CH3CH=C=CH2) amylene
See diagram 16.1.1: Cyclodienes, cis-trans alkenes
1. suffix: -ene for C=C (olefin, olefins, olefines) are unsaturated hydrocarbons with at least one double bond between C atoms, C=C, have formula CnH2n. Alkenes include ethene (ethylene, C2H4, CH2=CH2) ethenyl (vinyl CH2=CH-) 3-propenyl (allyl, CH2=CH-CH2-) e.g. vinyl chloride (chlorethene, CH2CHCl) allyl chloride (3-chloropropene CH2=CH-CH2Cl). (In the textile trade "olefin" refers to synthetic fibre, polyolefin fibre, that are long-chain polymers of ethylene or propylene, i.e. polyethylene (polypropylene, PP). Alkenes decolorize acidified potassium permanganate solution and bromine solution.
2. The cycloalkenes, cycloolefins, are closed chain, non-aromatic forms, e.g. cyclopropene, CH.CH.CH2, cyclobutene, cyclopentene, cyclohexene.
16.1.1.2.1 Prepare ethene (ethylene) gas
See also 3.32: Prepare gases with a gas generation apparatus
1. Slowly add 10 mL of concentrated sulfuric acid to 5 mL of ethyl alcohol and 1 g of powdered aluminium sulfate in the gas preparation apparatus. Be careful!
Pass the gas formed through sodium hydroxide solution to remove sulfur dioxide and carbon dioxide. Collect the gas over water. Heat only if necessary. Pass through sulfuric acid as dehydrating agent.
CH3CH2OH ---> H2C=CH2 + H2O
2. Prepare ethene (ethylene) from ethanol (Breakdown of ethanol to ethene (ethylene, H2C=CH2).
See also 3.96: Breakdown of ethanol to ethene (ethylene)
Alkanes (paraffins) are saturated hydrocarbons.
Ethene (ethylene, H2C=CH2) gas is a plant growth substance. It is produced in wounded, diseased and ripening tissues where it reacts with auxins to induce fruit ripening and abscission of leaves or diseased parts. It is used to ripen stored fruit artificially, e.g. bananas.
Put some cleaned and dried unglazed porcelain chips in a flask. Add 10 mL of pure ethanol (absolute alcohol). Slowly pour 30 mL of concentrated sulfuric acid down the sides of the flask. Be careful! Shake the flask gently under cool water to avoid alcohol being carbonized because of increase in temperature. Fit the flask with a thermometer and a delivery tube inserted in a 2-hole rubber stopper. Heat the flask to raise the temperature quickly to 170oC, then control at 170oC. This heating procedure is used to increase the use ratio of ethanol and decrease by-products. Wait until exclusion of the air in the flask and then collect the produced ethene gas over water. Concentrated sulfuric acid and sodium hydroxide solution can be used to absorb and remove the small quantities of the ethyl ether (sulfuric ether) vapour, carbon dioxide and sulfur dioxide present in the produced ethene.
C2H5OH(l) ---> C2H4(g) + H2O
---170oC.
3. Prepare ethene (ethylene) from ethanol, alternative method
See diagram: 16.10.3
Absorb ethanol in cotton wool and push this to the bottom of a hard-glass test-tube. Pack small pieces of unglazed porcelain in the middle of the test-tube. Fit a delivery tube to collect ethene gas over water. First heat the porous pot strongly and then heat gently the cotton wool to produce some ethanol vapour. This vapour breaks down over the hot porous pot to produce ethene gas and water vapour. The temperature should be above 170oC otherwise the reaction produces dimethyl ether. Collect the ethene over water. Be careful! Disconnect the delivery tube when you stop heating, to avoid a suck back of water onto the hot porous pot.
16.1.1.2.2 Dienes, isoprene units
A diene, alkadiene, has 2 double bonds in the molecule. A cumulated diene has double bonds next to each other. A conjugated diene has 2 double bonds separated by a single bond, e.g. buta-1,3-diene (CH2:CHCH:CH2) Isoprene, 2-methylbuta-1,3-diene, CH2:C(CH3)CH:CH2. Also, cyclodienes: 1,3-cyclohexadiene, 1,4-cyclohexadiene. Also, the 5-carbon isoprene unit in natural products consists of a four carbon chain and a one carbon branch at C2, i.e. [C(CC)CC], e.g. terpenes have linked isoprene units, natural rubber. Rosin is a solid amber residue made by the distillation of turpentine using pine stumps. Turpentine contains the terpene called pinene, C10H16.
16.1.1.3 Alkynes (CnH2n-2) acetylenes
1. acetylenes: ethyne (acetylene) C2H2 (HC =-- CH) isoprene, methylene
suffix: -yne for C=-C (acetylenes) are unsaturated hydrocarbons with at least one triple bond (=--) between C atoms, include ethyne C2H2 (acetylene, HC=-CH) 3-propargyl (propargyl, HC=-C-CH2-). Alkynes decolorize acidified potassium permanganate solution and bromine solution.
2. The cycloalkynes, are closed chain, non-aromatic forms, e.g cyclooctyne, C8H12 (the smallest form).
16.1.1.3.1 Prepare ethyne (acetylene) gas
See diagram 16.01.5
Early bicycle lamps used this reaction. However, the calcium carbide used to decompose in moist air to produce the unpleasant odour of acetylene. This decomposition could be lessened by pouring petroleum over the calcium carbide to exclude air and moisture.
1. Put sand in a dry test-tube and add pieces of calcium dicarbide (calcium carbide). Add water drop by drop. Collect the gas over water.
CaC2 + 2H2O ---> C2H2 + Ca(OH)2
calcium dicarbide + water ---> ethyne (acetylene) + calcium hydroxide
2. Tests for ethyne (acetylene): Light the gas in the test-tube with a glowing splint. The gas burns with a smoky flame.
16.1.3.0 Alcohols, phenols, thiols, ethers, epoxy compounds, acetates (ethanoates) benzoyls, acetals
Alcohols, R-OH, are compounds in which a functional group, the hydroxyl group, -OH, is attached to a saturated carbon atom, e.g. R3COH, "hydroxyl" refers to the radical HO-. The "alcohol" in alcoholic beverages is ethanol, ethyl alcohol, CH3CH2OH
See diagram 16.0.1: isobutyl alcohol
Alcohols (ROH) (-ol) alkanols, e.g. methanol (methyl alcohol) (CH3OH) ethanol (ethyl alcohol) (C2H5OH) propanol has 2 isomers:
1. propan-1-ol, 1-propanol (n-propyl alcohol) (CH3CH2CH2OH)
2. propan-2-ol, 2-propanol (iso-propyl alcohol) [CH3CH(OH)CH3] 1-butanol, n-butyl alcohol (CH3CH2CH2CH2OH) 2-butanol, sec-butyl alcohol [CH3CH(OH)CH2CH3] 2-methyl-1-propanol, isobutyl alcohol [CH3CH(CH3)CH2OH].
Primary alcohols RCH2OH, Secondary alcohols R2CHOH, Tertiary alcohols R3COH
Dihydric alcohols, glycols, diols, have two hydroxy groups on different carbon atoms, e.g. ethane-1,2-diol, ethylene glycol, glycol (HOCH2CH2OH) butane-1,4-diol [HO(CH2]4OH]
Trihydric alcohols, e.g. propane-1,2,3,-triol, glycerol [HOCH2CH(OH)CH2OH]
16.1.3.1.1 Alcohols, primary, secondary and tertiary aliphatic alcohols
See also 3.38: Carbon dioxide and fermentation for brewing
1. Primary alcohols, e.g. methanol (methyl alcohol, CH3OH) propanol (isomer propan-1-ol, n-propyl alcohol, CH3CH2CH2OH) and butan-1-ol (1-butanol, n-butanol, CH3(CH2)3OH) have two hydrogen atoms attached to the carbon atom attached to the hydroxyl group (-OH). So they all have -CH2OH in their molecules. They can be directly oxidized to aldehydes or carboxylic acids using oxidizing agents.
(O)R1-CH(OH)-R2 ---> R1-C(O)-R2(O)R-CH2OH ---> R-CHO(O)R-CHO ---> R-COOH
2. Secondary alcohols, e.g. propan-2-ol (CH3)2CHOH, isopropyl alcohol (rubbing alcohol) and secondary butyl alcohol, butan-2-ol (CH3CH2CH[CH3]OH) [ or CH3CH(OH)C2H5] have one hydrogen atom attached to the carbon atom attached to the hydroxyl group (-OH). So they all have (-CHOH) in their molecules. They can be slowly oxidized to ketones.
(O)R1-CH(OH)-R2 ---> R1-C(O)-R2
3. Tertiary alcohols, e.g. 2-methylpropan-2-ol, 2-methyl-2-propanol (CH3)3COH, tertiary butyl alcohol has no hydrogen atom attached to the carbon atom attached to the -OH group. So they all have -COH in their molecules.
4. To one drop of each alcohol in three test-tubes, add saturated potassium manganate (VII) solution drop by drop with shaking. If decolorization occurs, continue additions until pink coloration persists as shown by spot testing on filter paper. Add one drop of concentrated sulfuric acid and resume drop by drop addition of potassium manganate (VII). No decolorization occurs with tertiary alcohols. The colour eventually fades with secondary alcohols, but persists with primary alcohols.
16.1.3.1.2 Prepare sodium ethoxide
Sodium ethoxide is the salt of a weak acid, ethanoic acid, and a strong base, sodium hydroxide.
Add a pinhead size piece of sodium to 1 mL of ethyl alcohol.
Tests for hydrogen:
Na(s) + 2C2H5OH(l) ---> 2C2H5ONa(s) + H2(g)
sodium + ethanol ---> sodium ethoxide + hydrogen
Evaporate the sodium ethoxide solution to form white crystals. Add drops of water and test for litmus that turns blue.
16.1.3.2 Phenols
See diagram 16.1.4.3: Phenols, coniferyl alcohol (p-coumaryl alcohol) urushiol, organohalogens
See also 19.2.1.6: Antioxidant phenols, antioxidants, vitamin E, beta-carotene
See also 19.2.1.7: Cholesterol
1. Phenols, Ar-OH, are compounds with an hydroxyl group attached to an aromatic ring, e.g. benzene, 2-napthol. Phenols (hydroxyl group -OH) connected to a carbon atom in a benzene ring, benzene-OH, hydroxybenzenes, e.g. "phenol", carbolic acid (C6H5OH) p-chlorophenol (C6H4ClOH) 2,4,6-tribromophenol (C6H2Br3OH) 2-napthol, beta-napthol, napthalen-2-ol (C10H7OH) p-nitrophenol. Cresols, monomethylphenols, epoxy compounds, e.g. 1,2-epoxypropane, catechol [C6H4(OH)2] pyrocatechol, 1,2-dihydroxybenzene, 2-hydroxy phenol, urushiol (C6H4(OH)2).
2. The methylmethionine and asparagusic acid, alpha-aminodimethyl-gamma-butyrothetin, in asparagus may produce methanethiol, dimethyl disulfide and dimethyl sulfone in people who eat asparagus. However, less than 50% of adults can smell these compounds in the urine.
3. Organohalogens, e.g. 2,4,6-trichlorophenol, 2,4,6-tribromianisole, 2,4,6-trichloroanisole
chlorophenol compounds + filamentous fungi --> 2,4,6-trichloroanisole
16.1.3.3 Thiols
See diagram 16.1.4.3: Thiophenol (phenyl mercaptan) | See diagram 16.13.6.6: Metam, zineb
Thiols, thio-alcohols (RSH, R not equal to H) (sulfhydryl group: -SH, characteristic of thiols) (suffix: -thiol) [old name: mercaptans, because react with mercuric ion to produce mercaptides (RS)2Hg], e.g. methanethiol, methyl mercaptan (CH3SH) ethanethiol (MeCH2SH) ethyl mercaptan (ethanethiol or ethan-ethiol or captan) (C2H5SH) 1-butanethiol, n-butyl-mercaptan (CH3CH2CH2CH2SH) thiophenol, phenyl mercaptan Ph-SH, sodium thiolate: (RS-Na+) thiols, RS-H, are oxidized to disulfides, RS-SR
16.1.3.4 Ethers
Compounds in the form: R1OR2 (R not equal to H) where R1 may or may not be the same as R2, e.g. the anaesthetic diethyl ether. Ethers (ROR') (CnH2n+2O) alkyl ethers, ethoxethane ether, e.g. dimethyl ether (CH3OCH3) diethyl ether, ether anaesthetic (C2H5OC2H5,CH3CH2OCH2CH3)
16.1.3.5 Epoxy compounds
Have an oxygen atom attached to two carbon atoms of a carbon chain or ring system, so are cyclic ethers, e.g. 1,2-epoxypropane.
16.1.3.6 Acetates (ethanoates) ROAc, salt or ester of ethanoic acid (acetic acid)
As a salt: sodium acetate, sodium ethanoate (CH3COONa). As an ester: ethyl ethanoate (CH3COOC2H5)
16.1.3.7 Benzoyl group, benzene carbonyl group C6H5CO-
e.g. benzoyl chloride (C6H5COCl)
16.1.3.8 Acetals (alcohol + aldehyde) RCH(OR')2,
e.g. "acetal", 1,1-diethoxy ethane [CH3CH(OC2H5)2] Hemiacetals: [RCH(OH)R'] Di-methyl acetals: [RC(OMe)2R'] Di-ethyl acetals: [RC(OEt)2R']
16.1.5.3 Salts, e.g. sodium ethanoate (sodium acetate) (CH3COONa) ammonium acetate (CH3COONH4)
16.1.5.5 Acyl halide, acid chloride, Acid chlorides group: (-COCL ) suffix: -oyl chloride
acyl chloride (RCOCl) e.g. ethanoyl chloride (acetyl chloride) (CH3COCl)
16.1.5.6 Amides, acid amides (-amide) (amide group: -CONH2, RCONH2)
See diagram 16.13.4.7: Carbamates, carbaryl, methiocarb
See diagram 16.13.8.0: Deet, DMP dimethylphthalate
e.g. urea (H2NC=ONH2) [IUPAC: Do NOT distinguish amides with NH2, NHR, NR2 groups by the terms "primary, secondary, tertiary".]
(primary amides RCONH2) e.g. alkanamides: ethanamide (acetamide) (CH3CONH2) propanamide (C2H5CONH2)
(secondary amides, N-substituted amides RCONHR')
(tertiary amides RCNR'R") secondary or tertiary amides have the prefix N, e.g. N-ethylethanamide CH3CONHCH2CH3, N.N-dimethylmethanamide HCON(CH3)2 (the polymer group -CO-NH-) (inorganic amides, e.g. KNH2)
carbamates: esters of carbamic acid [H2NC(=O)OH] methiocarb,
urethanes [R2NC(=O)OR', where R' not = H, R= ethyl], e.g. polyurethane resins, cyanides, imidesisocyanates, quinines, carbamide (urea) [CO(NH2)2] carbazole C12H9N, Deet
16.1.5.6.1 Acrylamide, 2-Propenamide, ethylene carboxamide, acrylic amide, vinyl amide
CH2CHCONH2, poison, harmful if swallowed, inhaled or absorbed through skin, affects central and peripheral nervous systems and reproductive system, causes irritation to skin, eyes and respiratory tract, suspected cancer hazard depending on level and duration of exposure, possible birth defect hazard, thermally unstable, can polymerize explosively if heated to the melting point, most common in overcooked french fries and potato chips, also burned toast and burned high carbohydrate foods.
16.1.5.7 Acid anhydrides, acyl anhydrides, anhydrides [RCO-O-COR' (R(C=O)O(C=O)R')]
e.g. ethanoic anhydride (acetic anhydride) [(CH3CO)2O] ethanoic anhydride [CH3(C=O)O(C=O)CH3] trifluoroethanoic propanoic anhydride [CH3CH2(C=O)O(C=O)CF3]
16.1.5.8 Imides (R1CO-NH-COR2) (imido group: -CONHCO-)
e.g. glutemide (C13H15NO2) the polymer group (-CO-NR-CO) polyimides, N-(trichloromethylthio) cyclohex-4-ene-1,2-dicarboyimide
16.1.12 Fractional distillation of crude oil
Fractional distillation of crude oil: petroleum gas (LPG) naphtha, petrol (gasoline) kerosene (paraffin oil) diesel oil, lubricating oil (motor oil) paraffin wax (fuel oil) residuals (bitumen, "tar", asphalt, waxes)
16.1.12.1 Petroleum gas (methane, ethane, propane, butane)
Mix of 1 to 4 carbon atoms, boiling range < 40oC. Liquefied under pressure as LPG (liquefied petroleum gas)
16.1.12.2 Naphtha (ligroin) processed to make gasoline
Mix of 5 to 9 carbon atoms, alkanes, boiling range 60oC to 100oC
16.1.12.3 Petrol, "gas", gasoline, motor fuel
Mix of C6H14 to C11H24, 5 to 12 carbon atoms, alkanes and cycloalkanes, boiling range 40 to 205oC
16.1.12.4 Kerosene, kerosine, paraffin oil, jet engine fuel, tractor fuel
Mix of C12H26 to C15H32, 10 to 18 carbon atoms, alkanes and aromatics, boiling range 175oC to 325oC
16.1.12.5 Diesel oil, gas oil or diesel distillate, diesel fuel, heating oil
Mix of C15H32 to C18H38, 12 or more carbon atoms, alkanes, boiling range 250oC to 350oC
16.1.12.6 Lubricating oil, motor oil, grease
Mix of C16H34 to C24H50, 20 to 50 carbon atoms, alkanes and cycloalkanes and aromatics, boiling range 300oC to 370oC
16.1.12.7 Paraffin wax, heavy gas, fuel oil,
Mix of C20H42 and higher hydrocarbons, 20 to 70 carbon atoms, alkanes and cycloalkanes and aromatics, boiling range 370oC to 600oC
16.1.12.8 Residuals, bitumen, "tar", asphalt, waxes
A mix of C24H50 and higher hydrocarbons, multiple-ringed compounds, 70 or more carbon atoms, boiling range > 600oC
Petroleum jelly is a saturated semi-solid of crystalline and liquid hydrocarbons, carbon numbers < C25, made by dewaxing paraffinic residual oil.
Naptha, "Greek fire", was an inflammable bituminous substance used in warfare.
16.1.13 Prepare triodomethane (iodoform)
See 5.4.8: Iodine solution | See diagram 16.2.2: Halogen compounds, haloalkanes
Add five drops of iodine solution to five drops of ethanol. Add drops of dilute sodium hydroxide solution until the brown colour of iodine disappears. Examine the crystals under a microscope.
C2H5OH + 4I2 + 6NaOH---> HCOONa + 5NaI + 5H2O + CHI3
ethanol + iodine + sodium hydroxide---> sodium methanoate (sodium formate) + sodium iodide + water + triodomethane (iodoform)
16.1.14 Prepare trichloromethane (chloroform)
See diagram 16.1.7: Prepare chloroform | See also 16.2.2: Halogen compounds, haloalkanes
Bleaching powder is usually a mixture of calcium chlorate (I) [basic calcium chloride, calcium hypochlorite] calcium chloride and calcium hydroxide prepared by passing chlorine gas through a calcium hydroxide solution. Calcium chlorate (I) oxidizes ethanol to ethyl aldehyde. Aldehydes or ketones have a hydrogen atom attached to the carbon atom attached to the carbonyl group, C=O.
This hydrogen atom can be replaced by a halogen atom to form halogen compounds. If a molecule contains three such hydrogen atoms, e.g. ethanol and propanone (acetone) molecule, a trihalide may be formed, e.g. trichloromethane (chloroform, CCl3).
H3C-C(O)-R + 3OX---> X3C-C(O)-R
ketone or aldehyde hypochlorite---> trihalide
The trihalide decomposes in a basic solution to a haloform (CHX3) e.g.:
CHCl3C-C(O)-R(l) + OH-(aq)---> CHCl3(l) + RCOO-(aq)
Reactions of ethyl alcohol with bleaching powder
C2H5OH(l) + Cl2(g)---> CH3CHO(l) + 2HCl(aq)
ethyl alcohol + chlorine---> ethyl aldehyde
CH3CHO(l) + 3Cl2(g)---> CCl3CHO(l) + 3HCl(aq)
2CCl3CHO(l) + Ca(OH)2(aq)---> 2CHCl3(l) + (HCOO)2Ca(aq)
Decomposes trichloromethane to calcium formate
Ca(OH)2 (aq) + 2HCl(aq)---> CaCl2(aq) + 2H2O(l)
Reactions of acetone with bleaching powder
CH3COCH3 + 3Cl2---> CCl3COCH3+ 3HCl
2CCl3COCH3 + Ca(OH)2---> 2CHCl3+ (CH3COO)2Ca
Ca(OH)2 + 2HCl---> CaCl2 + 2H2O
Be careful! Do not allow any flames in the laboratory!
Grind together in a mortar and pestle 5 g bleaching powder and 10 mL water. Put the mixture into the test-tube of the gas preparation apparatus. Cool the test-tube. Add either 4 mL ethanol in 2 mL water or 4 mL propanone (acetone) in 2 mL of water. Swirl the contents of the test-tube and keep it cool. Use an electric water bath to warm the temperature to 55oC. Water and trichloromethane condense in the receiving test-tube leaving a solution of calcium salts in the test-tube. Add water to the distillate and separate the trichloromethane with a separating funnel.
16.2.2 Halogen compounds, haloalkanes (alkyl halides) halogen derivatives
See diagram 16.1.1: Haloalkanes: Methyl chloride, methylene chloride, chloroform, carbon tetrachloride
See diagram: 16.13.5.0: Bifenox, dicofol, naled, trichlorophon, tetrachlorvinphos
See diagram 16.13.7.7: MCPA, 2,4-D, 2,4,5-T, picloram
Acyl halides, acid halides (RCOX, RCO. halogen atom, R = organic group) (acetyl = CH3CO-) Haloforms: trihalomethanes CHX3, Alkanes react with chlorine and bromine (halogens) in ultraviolet light to give haloalkanes, e.g. 2-chloropropane.
1. Chlorine: acyl chlorides, acid chlorides (acyl = RC=O-) ethanoyls (-COCl) (-oyl chloride) ethanoyl chloride (acetyl chloride) (CH3COCl) chloroform CHCl3, chloromethane (methyl chloride) (CH3Cl) ethylene dichloride (1,2-dichloroethane, Freon 150) (ClH2C-CH2Cl) chloroethene (vinyl chloride) (CH2:CHCl) tetrachloromethane (carbon tetrachloride) (CCl4) phosgene (carbonyl dichloride) COCl2, chlorine + sulfur: thiophosgene (thiocarbonyl dichloride) (CSCl2) chlorine + OH: dicofol, MCPA, 2,4-D, 2,4,5-T, chlorine + N: Bifenox, chlorine + P: trichlorophon, tetrachlorvinphos
2. Iodine: iodoform (tri-iodomethane) (CHI3) iodoethane (CH3CH2I)
3. Bromine: bromoform (CHBr3) ethyl bromide (bromoethane) (C2H5Br) ethylene dibromide (1:2-dibromoethane) Halons (fire extinguishers): Halon-1211 bromochlorodifluoromethane (CBrClF2) Halon-1301 bromotrifluoromethane (CBrF3)
(4. Fluorine: fluoroform (CHF3) tetrafluoroethene (CF2CF2) polytetrafluoroethene (PTFE, Teflon) (-[CF2-CF2]x-)
Chlorofluorocarbons, CFCs (old name = Freons): CFC-11 trichlorofluoromethane (CCl3F) CFC-12 dichlorodifluoromethane (CCl2F2)
16.2.3 Organometal compounds (prefixing the metal with organo-)
e.g. organomagnesium compounds, MeMgI iodo(methyl)magnesium, Et2Mg diethylmagnesium
16.2.3.1 Carbides (C4-) (carbon + metal)
e.g. aluminium carbide (Al4C3) chromium carbide Cr3C2, iron carbide Fe3C (cementite) silicon carbide SiC, also dicarbides (C22-) e.g. calcium dicarbide (calcium carbide, carbide, calcium acetylide, ethnide) (CaC2)
Iron carbide is formed with carbon monoxide when iron oxide is heated with charcoal.
3Fe2O3 +11C --> 2Fe3C + 9CO (g)
16.2.4 Nitrogen compounds, one atom of nitrogen
See 16.1.5.6: Amides
16.2.4.2 Nitriles (acid nitriles, alkyl cyanides, cyanides)(-CN, RC=-N) (cyanide ion: CN-)
e.g. ethane nitrile (methyl cyanide, ascetonitrile) (CH3C=--N) 5-methoxyhexanenitrile [CH3C(OCH3)HCH2CH2CH2C=--N] acrylonitrile for making Orlon (vinyl cyanide, 1-cyanoethene) (CH2=CH-C=-N)
16.2.4.2.1 Cyanamides (inorganic, CN22-) ionization reaction of methylamine
See diagram 16.13.4.7: Melamine
cyanic acid (fulminic acid) (HOC =-- N) (cyanates, fulminates) Isocyanic acid (H-N=C=O) isocyanates (isocyanate group: -NCO, HN=C=O) isocyanides (HN=--C) hydrocyanic acid (HC=--N)
CaCn2 + H2O + CO2 --> H2NCN + CaCO3
calcium cyanamide + water + carbon dioxide --> cyanamide + calcium carbonate
(NH2)2CO --> HCNO + NH3
urea --> cyanic acid + ammonia
6HCNO --> C3H6N6 + 3CO2 (polymerization reaction)
cyanic acid --> melamine + carbon dioxiode
6(NH2)CO --> C3H6N6 +6NH3 + 3CO2
Melamine, 1,3,5-triazine-2,4,6-triamine, is 66% nitrogen w/w and is used in the plastics industry.. Unfortunately, its high nitrogen content has been the reason for its use as a powdered milk pollutant in China resulting in death and kidney problems in young babies due to the formation of kidney stones.
16.2.4.3 Amines, aliphatic amines (RNH2-, R = alkyl group) ionization reaction of methylamine
Primary amines: RNH2, NH2-= amino group, e.g. methylamine (CH3NH2) ethylamine (CH3CH2NH2)
Secondary amines: R2NH, NH = imino group, e.g. dimethyl amine [(CH3)2NH] diethylamine
Tertiary amines: R3N, trimethylamine [(CH3)3N] triethylamine, methylamine hydrochloride
Ionization reaction of methylamine
CH3NH2 + H2O <--> CH3NH3+ + OH-
16.2.4.3a Imines
See diagram 16.13.4.7: Schiff base,azomethine
imino group = ring containing -NH- or =NH linked to C] (RN=CR', where R = H or hydrocarbyl, e.g. ethyl-) e.g. 0-benzoquinonedimine
imine primary RC(=NH)R’ imino-, -imine
imine secondary RCH=NR’ imino-, -imine
16.2.4.4 Nitroalkanes (nitroparaffins) (CnH2n+1NO2)
nitromethane (CH3NO2) nitroethane, urea (carbamide)
16.2.4.5 Nitrites (NO2-, dioxonitrate ion, salts or esters of nitrous acid, O=NOH)
e.g. sodium nitrite and potassium nitrite as meat curing agents
16.2.4.6 Oximes (hydrox- imino- alkanes)
(-CNOH group) (ketone or aldehyde + hydroxylamine - water) (RCNOHR')
e.g. ethanal oxime (acetaldehyde oxime, AAO) (CH3CH=NOH)
16.2.4.7 Cyanocrylates [(CH2)C(CN)COOR]
e.g. "Superglue": Me or Et ester
16.2.5 Nitrogen compounds, two or more nitrogen atoms
1. Azide compounds: (N3- or -N3, -N=N+N-, usually attached to carbon) e.g. sodium azide NaN3, phenyl azide or azidobenzene PhN3, diazine (diimide) (HN=NH)
also, salts of hydrazoic acid, HN3. e.g. sodium azide NaN3.
2. Azo compounds: derivatives of diazene (diimide) HN=NH, with both hydrogens substituted by hydrocarbyl groups, e.g. azobenzene or diphenyldiazene PhN=NPh.
hydrazone (ketone + hydrazine N2H4 - water) (RC=NNH2R')
3. Diazo compounds: (RN=NR') e.g. diazomethane (CH2=N2) diazonium compounds [(RN =- N+) Cl-]
4. Phenylhydrozone [RC=N(NH)(Phenyl group)R'] (ketone or aldehyde + phenylhydrazine [C6H5(NH)NH2] - water) 2,4-dinitrophenylhydrozone, semicarbazone [RC=N(NH)CO(NH2)R']
16.2.6 Phosphorous compounds
Organophosphates, acephate, dichlorvos, dimethoate, malathion (maldison) parathion
See diagram 16.13.6.1: Benomyl, captan, glyphosate, paraquat
1. Phosphonic acid, orthophosphorous acid [HP(=O)(OH2) H3PO3]
2. Phosphonoglycine, N-(phosphonomethyl) glycine, Glyphosate (in "Roundup" weedicide) C3H8NO5P
3. Organic phosphates: acephate, diazinon, dichlorvos, dimethoate, malathion (maldison) naled, parathion
16.2.8 Sulfur compounds, For the "thio" prefix, replace oxygen by sulfur, e.g. thiobenzamide PhC(=S)NH2
16.2.8.1 Isothiocyanates (old name: mustard oil) (RN=C=S) mustards [X(CH2.CH2)2S]
16.2.8.2 Sulfides: RSR (R not equal to H) (old name: thioethers)
e.g. diallyl sulfide (garlic smell) [CH2=CHCH2)2S] or inorganic salts of hydrogen sulfide. Most people who eat asparagus notice a smell, the over-boiled cabbage smell, in their urine because of sulfur compounds, e.g. dimethyl sulfide, dimethylsulfone.
sulfimides (sulfilimines): H2S=NH
16.2.8.3 Sulfonic acids HS(=O)2OH
16.2.8.4 Sulfonium compounds: R3S+, e.g. trimethylsulfonium chloride [(CH3)3S]+Cl-
16.2.8.5 Thiocyanates: [RC(=O)SN] salts and esters of thiocyanic acid HSCN, e.g. methyl thiocyanate CH3SC =- N
16.2.8.6 Silicones: polymeric unbranched siloxanes, formula (-OSiR2-)n (R not equal to H)
16.2.8.7 Siloxanes
Saturated silicon-oxygen hydrides with chains of alternating silicon and oxygen atoms, e.g. unbranched [H3Si(OSiH2)nOSiH3] branched [H3Si(OSiH2)nOSiH(OSiH2OSiH3)2]. "Volasil" is octamethylcyclotetrasiloxane. Dimethylpolysiloxane is an anti-caking agent, emulsifier and anti-foaming agent.
16.2.8.8 Thiols, thio-alcohols See 16.1.3.3
16.2.8.9 Sulfoxide, dimethyyl sulfoxide, DMSO (CH3)2SO, C2H6OS
16.2.10 Coal tar products
Chemicals produced from destructive distillation of coal when making coke for steel production. Many organic compounds can be isolated by distillation of coal tar but many are now made from petroleum or natural gas. The residue of coal tar distillation is called pitch and is used for road tar and waterproofing of roof material. The residue of petroleum distillation is called asphalt but also called "tar".
Coal tar products include:
1. hydrocarbon oils, e.g. benzene, toluene, xylene,
2. phenols, e.g. carbolic acid, and
3. bases. e.g. pyridine.
Coal tar paints resist heat and moisture. Coal tar wood preservatives, e.g. creosote, are use for soap, sheep dip, railway sleepers, telegraph poles. Coal tar dyes, called azo dyes, are made from azobenzene and were used as food colourings
16.3.1 Prepare ethanal (acetaldehyde) with potassium dichromate
Add two drops of 0.1 M potassium dichromate solution to two drops of ethanol and ten drops of dilute sulfuric acid. Heat gently. The orange potassium dichromate solution turns green showing the presence of Cr3+. The reaction forms ethanal then ethanoic acid (acetic acid). Note the odour of an acetaldehyde.
C2H5OH + (O) ---> CH3CHO + H2O
ethanol + (oxygen) ---> ethanal + water
CH3CHO + (O) ---> CH3COOH
ethanal + (oxygen) ---> ethanoic acid
K2Cr2O7 + 4H2SO4 + 3CH3CH2OH ---> K2SO4 + Cr2(SO4)3 + 7H2O + 3CH3CHO
16.3.1a Aldehydes, ketones, quinones
Aldehydes (-CHO) (-al) alkanals, e.g. methanal (formaldehyde) (CH2=O, HCHO) ethanal (acetaldehyde) (CH3CHO)
Aldehydes are compounds in the form RC(=O)H, where a carbonyl group is bonded to one hydrogen atom and to one R group. Aldehydes contain the aldehyde group (-CHO) which is a carbonyl group (C=O) with a hydrogen atom attached to the carbon atom. Methanal (HCOH, formaldehyde) and ethanal (CH3CHO, acetaldehyde) are the simplest aldehydes (RCHO, alkanals). Aldehyde names end with "-al". Aldehydes are reducing agents and can be detected with Tollens' test or Fehling's test. Most monosaccharides and disaccharides can act as reducing agents, but not sucrose, and can be detected by Fehling's test or Benedict's test.
16.3.5.1 Aesculin (escalin)
It is a glucoside from the horse chestnut Aesculus hippocastanum. It is used to identify Enterococcus bacteria. It gives pale blue colour by reflected light and straw colour by transmitted light.
16.3.5.2 Amido phthalic acid and amido-tarephthalic acid
It gives pale violet colour by reflected light and pale yellow colour by transmitted light. Amido-tarephthalic acid gives bright green colour by reflected light and pale green colour by transmitted light.
16.3.5.3 Eosin (eosine)
It gives yellow green colour by reflected light and orange colour by transmitted light. It is formed by reaction of bromine with fluorescein. “Eosin Y” has yellowish colour, and “eosin B” (Acid red) has bluish colour. It is used as a counterstain to haematoxylin for microscopic examination. Eosin, an acidic dye, stains cytoplasm stained pink-orange and hematoxylin, a basic dye, stains nuclei blue or purple where nucleic acids mainly occur. Eosin stains red blood cells intensely red.
16.3.5.4 Fluorescein
See diagram 16.3.1.1.2.1
It gives intense green colour by reflected light and orange yellow colour by transmitted light. It is 1,3-dihydoxybenzene phthalein, 2-(6-hydroxy-3-oxo-xanthen-9-yl) benzoic acid, C20H12O5, red crystals that can dissolve in alkali to form a red colour and green fluorescence.
16.3.5.5 Fraxin
It gives blue green colour by reflected light and pale green colour by transmitted light. It is a colourless glucoside found in the bark of the ash tree, Fraxinus. Fraxin and esculin are two coumarins found in Actinidia chinensis and Actinidia deliciosa (kiwi fruit, Chinese goosberries).
16.3.5.6 Magdala red
It gives opaque scarlet colour by reflected light and brilliant carmine colour by transmitted light.
16.3.5.7 Quinine
It gives pale blue colour by reflected light and no color by transmitted light. It is an alkaloid from the bark of Cinchona and Remijia in South America. It was formerly an antimalarial medicine and is still used for treatment of some heart conditions. As a medicine it was taken in carbonated mineral water but nowadays is still taken as a beverage called "tonic water" which is valued for its slightly bitter taste. Tonic water is not a medicine.Fluorescence spectroscopy can be used to determine the percentage quinine content in commercial samples of tonic water or bitter lemon. by comparing the fluorescece of a sample in ultraviolet light to the fluorescence of a standard quinine sulphate solution containing 10mg of quinine sulphate in 1L of deionized water.
16.3.5.8 Safranin (safranine, safranin O, basic red 2)
It gives yellow red colour by reflected light and crimson colour by transmitted light. It is a biological stain colouring all cell nuclei red. It is used as a counterstain in a Gram stain in microbiology. It can also be used for the detection of cartilage and mucin and as a redox indicator in analytical chemistry. Safranines are the azonium compounds of symmetrical 2,8-dimethyl-3,7-diamino-phenazine.
16.3.2 Prepare ethanal with potassium manganate (VII) (potassium permanganate, Condy's crystals)
Add one drop of 1% potassium manganate (VII) to five drops of ethanol and ten drops of dilute sulfuric acid. Heat gently. The purple colour disappears as potassium manganate (VII) solution is reduced to manganese (II) sulfate. Note the odour of an acetaldehyde.
CH3CH2OH + (O) ---> CH3CHO + H2O
2KMnO4 + 3H2SO4 + 5CH3CH2OH ---> K2SO4 + 2MnSO4 + 8H2O + 5CH3CHO
16.3.3 Oxidation of methanol to methanal using a platinum catalyst
See diagram 16.3.3: Be careful! This experiment may be too dangerous for your school. Test the experiment in the science preparation room before demonstrating it in the classroom. Do not let anyone look down into the flask if the experiment appears not to be working!
Put 10 mL methanol in a flask and heat briefly with a Bunsen burner. Heat a piece of platinum wire connected to a copper wire until it is red-hot. Hook a copper / platinum wire inside the flask to start the reaction. You can reheat the wire if the reaction does not start. The reaction continues till all the MeOH is used up. To stop the reaction, remove the catalyst platinum wire catalyst. Be careful!
The methanol is oxidized to methanal when the vapour reaches a certain concentration accompanied by a loud "whoosh" sound as the vapour burn and leaves the flask. The copper T-piece acts as a chimney allowing entry of air when the vapour bums. The Pt wire changes from red-hot to silver.
CH3OH + ˝ O2---> CH2O + H2 (Pt catalyst)
CH2O + O2 ---> CO2 + H2O (Pt catalyst)
16.3.4 Oxidation of glucose with sodium hydroxide and methylene blue, blue bottle experiment
In a sodium hydroxide solution, the aldehyde glucose is oxidized by oxygen gas (dioxygen) to gluconic acid (d-gluconic acid, CH2OH(CHOH)4COOH) and then forms sodium gluconate. Methylene blue acts as an oxygen transfer catalyst and is reduced to colourless leucomethylene blue. Leucomethylene blue is then oxidized by oxygen in the air to methylene blue again. Methylene blue is a thiazine dyestuff, C16H18ClN3S, 3,7-bis-(dimethylamino)-phenothiazin-5-ium chloride. Methylene blue is blue when oxidized and colourless when reduced
1. Solution 1: Add 2.5 g glucose (dextrose) + 2.5 g sodium hydroxide + 1 mL 0.1% solution methylene blue to 500 mL water. Solution 2: Add 5 g glucose + 5 g NaOH + 1 mL 0.1% solution methylene blue to 500 mL water. Note that the blue colour of Solution 2 disappears faster than in Solution 1. The blue colour appears at the surface of the solutions because of oxygen in the air. Shake the flasks and the blue colour returns.
2. Solution 2: Dissolve 0.05 g of methylene blue in 50 mL 0.1% ethanol. Solution 2: Dissolve 6 g of sodium hydroxide (or 8 g potassium hydroxide) in 300 mL water in a conical flask at room temperature above 25oC. Stir to dissolve then the add 5 mL of Solution 1. The blue solution turns colourless. Close the flask and shake to dissolve air in the solution, or pour the solution from a height. The colour changes to blue then fades back to colourless. Repeat the shaking many times and note the colour changes. Leave the solution for some hours and shake again. The solution turns yellow and no colour change occurs after shaking.
Repeat the experiment but instead of shaking the flask, pass nitrogen gas or natural gas through the solution. No colour change occurs because oxygen was not dissolved as in the shaking.
3. Repeat with other dyes:
3.1 Phenosafranine solution is red when oxidized and colourless when reduced. Use 6 drops of 0.2% solution in water that becomes pink on shaking and colourless when standing, after some time.
3.2 Phenosafranine, 6 drops of 0.2% solution in water, and methylene blue, 20 drops of 0.1% solution in ethanol, becomes pink on shaking and purple with more shaking then blue. On standing the sequence of colours reverses.
3.3 Indigo carmine solution becomes red-brown on gentle shaking and pale green on more shaking. On standing the sequence of colours reverses.
3.4 Resazurin (red to colourless) is dark blue when first added to the solution to be tested then becomes pale blue then becomes purple-pink on shaking.
16.3.5 Silver mirror test for aldehydes, Tollens' test for acetaldehyde
Be careful! Silver salts are expensive! Do not keep the Tollens' reagent after the test because it can explode on standing. Prepare the Tollens' reagent, just before doing the test and after doing the test wash the unused Tollens' reagent down the sink with lots of water. Do this test in a fume cupboard.
To prepare Tollens' reagent, add 1 drop of dilute sodium hydroxide solution to 1 mL silver nitrate solution and when a brown precipitate of silver oxide forms add drops of dilute ammonia solution, NH3(aq) ("ammonium hydroxide") solution until the brown precipitate dissolves. Clean a test-tube with water and acetone. Add Tollens' reagent then 3 drops of acetaldehyde. Warm the test-tube in a beaker of water and a silver mirror of silver deposits. You can "silver plate" small objects or coins.
CH3CHO(aq) + Ag2O(s)---> CH3COOH(aq) + 2 Ag(s)
16.3.6 Silver mirror test for aldehydes, Tollens' test for glucose
Dissolve 2.8 g of silver nitrate in 170 mL of deionized water to prepare an approximate 0.1 mol per litre solution. Dissolve 3.7 h potassium hydroxide in 85 mL of deionized water to prepare an approximate 0.8 mol per litre solution. Dissolve 0.75 g of glucose in 17 mL deionized water. Add drops of 880 ammonia to the silver nitrate solution in a test-tube until a brown precipitate forms. Continue adding about 5 mL of the 880 ammonia until the precipitate dissolves leaving a colourless solution of Tollens' reagent containing the ion Ag(NH3)2+(aq). Add the glucose solution to the Tollens' reagent and shake the test-tube until the solution turns brown then forms a silver mirror on the inside of the test-tube. The aldehyde glucose reduces the Ag+(aq) ions to silver metal. Pour the contents of the test-tube down the sink and flush it down the sink with plenty of water.
C6H12O6, i.e. as aldehyde CH2OH(CHOH)4CHO(aq) + 2Ag(NH3)2+(aq) + 3OH-(aq)---> 2Ag(s) + CH2OH(CHOH)4CO2-(aq) + 4NH3(aq) + 2H2O(l)
Show that this test reaction does not occur with propanone, a ketone.
16.3.7 Fehling's test for aldehydes in solution
16.3.1a Aldehydes, ketones, quinones | See also 16.3.1.1.1: Ketones | See diagram 16.3.2.0: Sugars
1. Fehling's reagent consists of two solutions: Fehling's A solution (Fehling's 1 solution) and Fehling's B solution (Fehling's 1 solution)
Add Fehling's B solution to 1 mL of Fehling's A solution until the blue precipitate just dissolves to give a deep blue solution. Add 3 drops acetaldehyde solution and boil the solution until the red copper (I) oxide precipitate indicates the presence of a reducing agent.
CH3CHO(aq) + 2CUO ---> CH3COOH + Cu2O(s)
2. Add drops of methanal (formaldehyde) solution (formalin) HCHO, to a test-tube one quarter filled with Fehling's reagent and heat to boiling. Note the yellow then orange then red precipitate of copper (I) oxide. The copper from the copper (II) sulfate solution has been reduced from copper (II) to copper (I). Methanal is a strong reducing agent. The ketones do not react with Fehling's reagent. Be careful! Formaldehyde as at concentrations above 0.1 ppm in air it can irritate the eyes and mucous membranes, cause headaches, difficulty breathing or aggravate asthma symptoms. Students should not do this test.
3. Add drops of formalin to a test-tube one quarter filled with Fehling's A and B solutions and heat to boiling. Note the yellow then orange then red precipitate of copper(I) oxide. The copper from the copper(II) sulfate solution has been reduced from copper(II) to copper(I).
4. Repeat the experiment using acetaldehyde instead of formalin. Note the similar reaction. In this reactions, the aldehyde is oxidized to carboxylic acids and the Cu2+ ion (cupric ion) complexioned with tartrate ion is reduced to Cu+ ion (cuprous ion).
RCHO + 2Cu2+ + 4OH- ---> RCOOH + Cu2O + 2H2O
5. Fehling's reagent is a solution of copper (II) sulfate (cupric sulfate) and potassium sodium tartrate in alkali is used as an oxidizing agent to detect reducing sugars, e.g. (+) glucose, fructose and aldehydes, e.g. methanal (formaldehyde). The deep blue Fehling's solution is reduced to a yellow-red (brick-red) precipitate of copper (I) oxide.
6. Benedict's test is more sensitive than Fehling's test, and is easier to do because only one solution is needed, but it may be more expensive.
7. A reducing sugar acts as a reducing agent by giving electrons to other molecules. Reducing sugars are monosaccharides or disaccharides with a free ketone group, -CO-, e.g. fructose, or a free aldehyde group, -CHO, e.g. glucose. So fructose is a ketose or ketohexose and glucose is an aldose or aldohexose. Sucrose is not a reducing sugar because of the linkage of aldehyde and ketone groups between the component sugars glucose and fructose.
Tests for reducing sugars use mixtures of mild oxidizing agents
Fehling's test for reducing sugars and aldehydes uses a tartrate ion-Cu2+ complex
Benedict's test for reducing sugars uses a citrate ion-Cu2+ complex. Nowadays, Benedict's test is used instead of Fehling's test for detecting reducing sugars. Tollens test for aldehydes, the silver mirror test, uses Ag+ in ammonia solution.
Oxidation of aldose sugars: RCH=O + 2Cu2+ (blue solution) + 5OH- --> R(C=O)O- + Cu2O (red precipitate) + 3H2O
16.3.8 Ketones (=CO) (-one)
e.g. propanone (acetone) (CH3C=OCH3)
Ketones have a carbonyl group (C=O) bonded to two carbon atoms in the form R2C=O, but neither R may be H. Ketones contain the ketone group (-CO-). It is a carbonyl group with two single bonds to other carbon atoms. Propanone (acetone, CH3COCH3) and butanone (CH3COC2H5, methyl ethyl ketone) are the simplest saturated ketones (R1COR2). Ketone names end with "-one". Ketones cannot be detected with Tollens' test or Fehling's test.
16.3.9 Diacetyl, 2,3-butanedione
See also: Butanedione
Diacetyl, CH3COCOCH3, is used in the popcorn industry to give a butter or butterscotch flavour to popcorn sold in bags. However, workers in the popcorn industry have reported medical problems with their respiratory systems, particularly the lungs, leading to workers compensation. Heating bags of popcorn in a microwave oven may lead to similar problems. The popcorn industry is considering not using diacetyl in bagged products.
16.3.10 Quinones
See diagram 16.1.4.3: Quinones
See also 16.3.5.0: Polycyclic aromatics
C=O groups in an unsaturated ring, as 1,2-quinones and 1,4-quinones, cyclic dione structure, conjugated diketones, e.g. benzoquinone, by conversion of -CH= groups into -C(=O)- groups, "quinone": cyclohexadiene-1, 4-dione, 1,4-benzoquinone is the simplest quinone, C6H4O2, all are coloured, many are plant pigments, e.g. lawsone from Lawsonia inermis the orange dye henna, and juglone from walnut shells, Juglans regia, formed from oxidation of hydroquinone and in pecan nuts, and are used in dyes, hydroquinone, 1,4-dihydroxybenzene, used in photography developer, also coenzymes Q in animal and plant cells and plastoquinones involved in photosynthesis, also vitamin K. Juglone, C10H6O3, is produced by some trees in the walnut family, e.g. black walnut, Persian walnut, butternut, and pecan and is leached or released into the soil. Juglone has fungicidal and insecticidal properties but it is toxic to many plant species.
16.5.1.0 Esters, derivatives of fatty acids (RCOOR') Esters group: (-COOR) suffix: -oate
Esters (RCOOR', R(C=O)OR') (-oate) derivatives of fatty acids: ethyl ethanoate (ethyl acetate) (CH3COOC2H5, CH3C=OOCH2CH3) [glyceride (acyl glycerol) fatty acid ester of glycerol: HOCH2CH(OH)CH2OH] Esters include methyl buranoate apple, ethyl methanoate rum essence, ethyl butanoate pineapple oil, pentyl ethanoate banana, octyl butanoate orange, methyl salicylate oil of wintergreen, amyl acetate pear oil.
16.5.1 Prepare ethyl chloride
Ethyl chloride C2H5Cl is an alkyl halide.
See also 16.2.2: Halogen compounds, haloalkanes (alkyl halides) | See diagram 1.13: Smelling chemicals
Pour ethyl alcohol or methylated spirit into a test-tube. Note the odour. Test the liquid with litmus paper. No colour change occurs. Add dilute hydrochloric acid. Heat the mixture gently by putting the test-tube in hot water. Smell any gas coming from the test-tube.
Be careful! Do not inhale gases directly from the test-tube. Fan the gas towards the nose with the hand and sniff cautiously. If no odour is detected, move closer and try again.
Cool the mixtures and add drops of concentrated sulfuric acid. Heat the mixture gently by putting the test-tube in hot water.
Be careful! Smell for not more than one second. The gases may cause general anaesthesia. Note the sweet "ethereal" smell.
The heated sulfuric acid acts as a catalyst.
HCl(aq) + C2H5OH(l) ---> C2H5Cl(g) + H2O(l)
hydrochloric acid + ethanol ---> ethyl chloride + water
16.5.1.1 Ethyl acetoactonate (ethyl 3-oxobutanoate)
ethyl ethanoate + sodium ethoxide --> ethyl acetoacetonate (3-oxobutanoate), CH3COCH2COOC2H5 (acetoacetic ester) (hydrolysis + acid) --> acetoacetic acid (3-oxobutanoic acid) CH3COCH2COOH (unstable beta-keto acid)
CH3COCH2COOH → CH3COCH3 + CO2
acetoacetic acid --> acetone + carbon dioxide
16.5.2 Prepare esters, prepare ethyl acetate (ethyl ethanoate) 1
Alcohols react with organic acids to produce esters and water. Esters are non-electrolytes, so they must be heated to speed the reaction. Sulfuric acid is used for a dehydrating agent and catalyst to join the other portions of the reactant alcohol and acid to produce the ester. Ethyl ethanoate (ethyl acetate, acetic ether [CH3COOC2H5]) is a colourless liquid with a fruity smell used as a solvent for lacquers and paints. Esters of low molecular mass have fruity smells and are found in flavours and perfumes. The semi-structural formula is R1COOHR2. R = alkyl groups, e.g. R1 = CH3 and R2 = C2H5. Heating a mixture of ester and water produces a mixture of alkanoic acid and alkanol in an equilibrium mixture.
Mix other organic acids with an alcohol.
Add drops of concentrated sulfuric acid then heat the test-tube gently in hot water. Note the odour of the ester, e.g. pentyl ethanoate smells of apricots and octyl acetate smells of oranges. Add five drops of ethanoic acid (glacial acetic acid) to five drops of ethyl alcohol with one drop of concentrated sulfuric acid as a catalyst. Heat the test-tube gently. Note the fruity odour of ethyl acetate and the sharp odour of acetic acid.
alkanol + alkanoic acid <---> ester + water
R1COOH + R2OH <---> R1COOR2 + H2O
organic acid + alcohol <---> ester + water
CH3COOH + C2H5OH <---> CH3COOC2H5 + H2O
ethanoic acid + ethanol <---> ethyl ethanoate + water
(acetic acid + ethyl alcohol <---> ethyl acetate + water)
16.5.4 Hydrolysis of an ester
See also 12.12.0: Soaps and detergents
1. Add acid to an ester.
The H+ of the acid catalyses the hydrolysis.
CH3COOC2H5 + HOH (H2O) ---> CH3COOH + C2H5OH
2. Add alkali to an ester. This is called saponification because the reaction is used to prepare soap.
CH3COOC2H5 + NaOH ---> CH3COONa + C2H5OH
16.5.5 Prepare esters, methyl salicylate (oil of wintergreen)
Methyl salicylate (oil of wintergreen, HOC6H4COOMe) has the odour of "oil of wintergreen" used for liniments. Add 1 g of salicylic acid to a mixture of 1 mL of methyl alcohol and three drops of sulfuric acid in a test-tube. Heat the test-tube gently and note the odour of the ester produced by the reaction.
methyl alcohol + salicylic acid ---> methyl salicylate (oil of wintergreen)
16.5.6 Prepare esters, amyl acetate (pear oil)
Amyl acetate (pear oil, pentyl ethanoate, CH3COOC5H11) has the odour of bananas or pears. Mix 5 mL of ethanoic acid (acetic acid) 3 mL of pentan-1-ol (amyl alcohol, n-pentyl alcohol, C5H11OH) and 1 mL of sulfuric acid in a test-tube. Heat the test-tube gently and note the odour of the ester produced by the reaction.
amyl alcohol(l) + acetic acid ---> amyl acetate (banana or pear oil)
16.5.7 Prepare ethyl butyrate (pineapple oil)
Ethyl butyrate has the odour of pineapples. Mix in a test-tube 1 mL of concentrated sulfuric acid and 2 mL of ethanol. Add 2 mL of n-butyric acid (butanoic acid, C3H7COOH). It smells like rancid butter. Heat the test-tube gently and note the odour of the ester produced by the reaction.
ethyl alcohol + butyric acid (l) ---> ethyl butyrate (pineapple oil)
16.5.8 Prepare ethyl acetate
1. Repeat the above experiment with two drops of glacial ethanoic acid (acetic acid) in place of the ethanol. Connect a delivery tube from the test-tube to a solution of limewater. Tests for carbon dioxide during the reaction. The odour of acetic acid disappears. The reaction produces ethyl acetate.
2. Mix 2 mL ethyl alcohol with 3 mL acetic acid in a test-tube. Add 3 drops concentrated sulfuric acid. Heat the mixture gently by immersing the test-tube in hot water. Cautiously note the odour of the ethyl acetate produced and compare it with the odours of ethyl alcohol and acetic acid. Ethyl acetate has a fragrant odour different from the wine-like odour of ethyl alcohol and the sharp odour of acetic acid.
[heated with sulfuric acid] ethyl alcohol (l) + acetic acid (aq) ---> water (l) + ethyl acetate(aq)
16.5.9 Prepare methyl chloride
Pour 5 mL methyl alcohol and 5 mL ethyl alcohol into separate test-tubes. Note their odours. Drop small pieces of red and blue litmus paper into each liquid. Add to each about 5 mL of dilute hydrochloric acid. If you see no visible signs of reaction, warm each mixture gently by standing the tube in hot water for 5 minutes. Cautiously smell any gas that may be coming from the test-tubes.
Be careful! Sulfuric acid is a corrosive chemical!
Cool the mixtures and add a few drops of concentrated sulfuric acid to each test-tube. If you see no visible signs of reaction, warm each mixture gently by standing the tube in hot water for 5 minutes. Cautiously smell any gas that may be coming from the test-tubes. Avoid smelling for more than one second any gases liberated, since one of them can cause general anaesthesia when inhaled in sufficient quantity. Although there is no apparent reaction when hydrochloric acid is mixed with either of the two alcohols, after heating the mixture with concentrated sulfuric acid, a reaction occurs shown by the production of a gas with a sweetish "ethereal" smell.
[heated with sulfuric acid] methyl alcohol(l) + hydrochloric acid(aq) ---> water(l) + methyl chloride(g)
16.6.1 Tests for proteins, heat test for proteins
See also 16.3.6.0: Proteins, peptides, amino acids
Proteins decompose when heated to form carbon and a mixture of gases. One gas is usually ammonia. Proteins are slightly soluble in cold water, but are more soluble in hot water. When the hot solution is cooled, it may set like a jelly. Heat proteins until they char. Smell the gases that form
16.6.2 Tests for proteins, burning test for proteins
Burn feathers or hairs and note the gases that form. These proteins contain sulfur. Try the same test on samples of fats and carbohydrates to observe if the results are different enough to detect proteins.
16.6.3 Prepare protein solutions
Shake the white of an egg in its own volume of water. Squash peas in water, filter and use the filtrate Prepare a gelatine solution from a commercial "jelly" preparation Collect solid proteins, e.g. hair, feathers. Test on a microscope slide: plant juices, meat, soup, pieces of tissue, sunflower seed.
16.6.4 Tests for albumin and gelatine
1. Heat albumin and gelatine in separate test-tubes. They decompose when heated, producing carbon and a mixture of gases one of which usually, but not always, is ammonia.
2. Add small quantities of albumin and gelatine to water. Shake. Warm the mixture and allow to cool. They are sparingly soluble in cold water but are more soluble in hot water. When the hot solution is cooled, it may set like a jelly.
3. Add to small quantities of albumin and gelatine to Biuret solution, potassium hydroxide solution and then a few drops of copper (II) sulfate solution. They produce a deep blue violet colour when treated with solution of copper (II) sulfate and an alkali. This is called the Biuret test for proteins.
4. Add drops of Millon's solution to albumin and gelatine and warm. They produce a white precipitate, a brick-red colour develops on warming the mixture.
16.6.5 Tests for proteins, biuret test
Biuret, NH2CONHCONH2, is formed from heated urea, crystallizes as NH2CONHCONH2.H2O Alkaline solution of biuret gives red-violet colour with copper (II) sulfate solution because of reaction with peptide bonds but no reaction if solution contains amino acids. The concentration of the colour is proportional to the amount of protein so the biuret test is approximately quantitative. So if the sample contains soluble protein, the reagent turns from light blue to purple but if the reagent remains light blue, the sample does not contain protein.
1. Add an equal volume of 40% sodium hydroxide solution to any protein solution, e.g. egg albumin, dried milk, gelatine. Add drops of dilute copper (II) sulfate solution with a light blue colour. The reaction produces a violet colour.
2. Add an equal volume of 1% potassium hydroxide solution + a few drops of 1% copper sulfate solution to the sample solution. If the solution turns purple, protein is present in the sample.
16.6.6 Tests for proteins, xanthoproteic test
Do protein tests on plant material by using expressed juice, aqueous extracts, pieces of tissue, or on a microscopic slide on which thin slices or sections of the tissue are placed. To a protein solution add one third of that volume of concentrated nitric acid. Heat gently to boiling with care. The precipitate changes from white to yellow. Cool the mixture under the tap and add drops of concentrated ammonia solution. The reaction produces an orange colour. Positive results come from proteins containing an aromatic group, e.g. phenylalanine, tyrosine, tryptophane.
16.6.7 Tests for proteins, Millon's test
Add drops of Millon's reagent and heat.
Be careful! Millon's Reagent contains mercury (I) nitrate in nitrous acid. This document does not recommend the use of mercury salts in school experiments. However, the amount of mercury (I) nitrate in drops of Millon's Reagent is very small.
Add drops of Millon's reagent to equal number of drops of a protein solution. Proteins form a white precipitate that turns pink when heated. A brick-red precipitate indicates the presence of the amino acid tyrosine.
16.6.8 Tests for proteins, Albustix test strips
Albustix strips are test papers dipped into buffered tetrabromophenol blue solution as an indicator solution. The indicator on the Albustix strip can combine with proteins. This change will in turn change the colour of the strip from yellow to shades of green. They are used by doctors to test the proteins present in a sample of human urine both quickly and semi-quantitatively. Protein in the urine may suggest kidney disease in which the glomerular membrane allows passage of serum albumin and some serum globulin from the plasma resulting in oedema. Thestest is most sensitive to albumin.. Normal urtine contains 20 mg / 100 L . Dip an Albustix strip in a protein solution and observe the change in its colour.
16.6.9 Nitrogen in an organic compound, Kjeldahl method
Be careful! Do this experiment in a fume cupboard.
Add 10 mL of concentrated sulfuric acid to 0.5 g of urea in a long necked flask (Kjeldahl Flask). Add potassium hydrogen sulfate to raise the boiling point of the acid and complete the decomposition of the protein. Boil in a fume cupboard for 10 minutes. Leave to cool then add 100 mL water. Add strong sodium hydroxide solution (30%) and anti-bumping granules. Distil the mixture. Tests for ammonia in the distillate. For volumetric titration, pass all the ammonia through 1 M acid solution. The ammonia neutralizes some acid. Titrate the acid left over with an alkali to find how much acid used by the ammonia.
Repeat the experiment with 5 g egg albumin (egg white).
H2SO4(aq) + 2NH3(g) ---> (NH4)2SO4(aq)
16.6.10 Tests for proteins, Sakaguchi's arginine test
Make a 5 mL test solution alkaline with drops of sodium hydroxide solution. Add 5 drops of 2% alpha-naphthol in alcohol solution the one drop of sodium hypochlorite or bleaching powder solution. A carmine colour indicates the presence of arginine.
16.6.11 Tests for sulfur in proteins
Add drops of lead acetate solution to 5 mL of egg albumen test solution. Then add sodium hydroxide solution until the lead hydroxide precipitate forms then dissolves. Heat to boiling. A brown-black precipitate of lead sulfide indicates the presence of the amino acid cystine.
16.6.12 Proteins are amphoteric
Amino acids are amphoteric in that they contain both acidic and basic groups in their molecules. Proteins dissolve in alkalis and in concentrated solutions of acids. In alkaline solutions proteins are negatively charged. In strongly acid solutions proteins are positively charged. They are uncharged at the iso-electric point and are precipitated. At pH higher than the iso-electric point, a protein acts as an acid. At pH lower than the iso-electric point the protein acts as a base. When acting as an acid a protein forms a fast colour with a basic dye, e.g. methylene blue. When acting as a base, a protein reacts with an acid dye, e.g. eosin.
To show the amphoteric nature of a protein, prepare four test-tubes, two containing eosin, and two containing Millon's reagent methylene blue.
1. Add a white feather or white wool to each test-tube. Add 3 drops of acetic acid to one eosin solution and 3 drops of concentrated ammonia solution (ammonium hydroxide) to the other eosin solution. Leave to stand for five minutes. Wash the feather or wool and note the fast dyeing in the eosin and acid solution. The protein acted as a base in the presence of the acid, and reacted with the acid dye eosin.
2. Add 3 drops of acetic acid to one of the methylene blue solutions and 3 drops of concentrated ammonia solution (ammonium hydroxide) to the other methylene blue solution. Leave to stand for five minutes. Wash the feather or wool or feather and note the fast dyeing in the alkaline solution. The protein acts as an acid in alkaline solution and reacts with the basic dye methylene blue.
16.6.13 Urea forms biuret
Heat some crystals of dry urea slowly in a test-tube until the liquid which forms solidifies again as the white solid biuret. Dissolve the biuret in water for use in the biuret reaction.
2NH2.CO.NH2 ---> NH2.CO.NH.CO.NH2 + NH3
16.6.14 Reactions of urea with sodium hypochlorite
Dissolve crystals of urea in the minimum amount of water. Add drops of sodium hypochlorite solution. Nitrogen gas forms. Carbon dioxide gas also forms but it dissolves in the alkaline solution.
NH2.CO.NH2 + 3NaOCl ---> N2 + 2H2O + 3NaCl + CO2
16.6.15 Reactions of urea with nitrous acid
Add an equal volume of dilute hydrochloric acid to a saturated solution of sodium nitrite. Cool under the tap. When the effervescence has moderated, add drops of a solution of urea. Nitrogen gas forms.
NH2.CO.NH2 + 2HNO2 ---> 2N2 + CO2 + 3H2O
16.6.16 Reactions of urea with soda lime
Heat a mixture of urea and soda lime. Test the gas formed for ammonia.
NH2.CO.NH2 + 2NaOH ---> 2NH3 + Na2CO3
16.6.17 Hydrolysis of urea with urease
Dissolve urea crystals in water. Add a tablet of urease or soya flour and keep at 40oC. for a minute. Tests for ammonia. The enzyme, urease, hydrolyses the urea
NH2.CO.NH2 + H2O ---> 2NH3 + CO2
16.6.18 Urea acts as a base
Add an equal volume of concentrated nitric acid to a saturated solution of urea. The white precipitate is urea nitrate, NH2.CO.NH2.HNO3.