Qualitative organic analysis reagents

This page gives info on the preparation of the reagents and solutions used in organic qualitative analysis:
reagents specific to determination by class reactions and group analysis

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Preparation of laboratory reagents

CLASS AND GROUP REACTIONS Class reactions Special reagents Unsaturation 1. Bromine in carbon tetrachloride. ( 2%-3% ) 2. Potassium permanganate solution. ( 2% Aqueous ) Saturated hydrocarbons. 1. Fuming sulphuric acid. (20% free SO2) Halogens 1. Alcoholic silver nitrate solution. (2% in abs. Alcohol) 2. Sodium iodide in acetone. (7.5g. in 50ml. AR acetone) Aldehydes and ketones 1. 2:4 Dinitrophenylhydrazine. (Method 1. Suspend 2.0g. of 2:4 dinitrophenylhydrazine in 100ml. of methanol. Cautiously and slowly add 4.0ml. of conc. Sulphuric acid. Filter if nessary.) Method 2. Dissolve 0.25g. of the reagent in a mixture of 42ml. conc.HCl and 50ml. of water by warming on a water bath; dilute to 50 ml. with distilled water.This reagert is more suitable for water soluble aldehydes and ketones since alcohol is abscent. Aldehydes 1. Schiffs reagent.(fuchsin aldehyde reagent) Method (1) Dissolve 0.2g. of pure p-rosaniline hydrochloride in 20ml. freshly prepared saturated aqueous solution of solphur dioxide. Dilute to 200ml. and keep in tightly stoppered bottle. Method (2) Add 2g. of sodium bisulphite to a solution of 0.2g.of p-rosaniline hydrochloride and 2ml. of conc. HCl in 200ml. of water. 2. Fehlings solution. Solution no. 1. Dissolve 34.64g. of AR copper sulphate crystals in water containing a few drops of dilute sulphuric acid and dilute to 600ml.) Solution no. 2. Dissolve 60g. of NaOH and 173g. of sodium potassium tartrate in water and dilute to 500ml. Keep the two solutions separately in tightly stoppered bottles and mix exactly equal volumes immediately before use. 3. Ammoniacal silver nitrate solution.(Tollens reagent) Solution A. (3g. of silver nitrate in 30ml. of water) Solution B. (3g. of NaOH in 30ml. of water) Mix equal volumes of A and B (1ml) and add dilute ammonia solution drop by drop until the silver oxide is just redissolved. Use this as the reagent. Esters and anhydrides 1. Hydroxamic acid test.( 5% ferric chloride added in presence of 0.5N hydroxylamine hydrochloride in 95% ethanol and 6N sodium hydroxide solution.) 2. Saponification; saponification equivalent.(Aqueous sodium hydroxide method and the diethylene glycol method) Alcohols 1. Sodium together with reaction 2. 2. Acetyl chloride or benzoyl chloride. 3. Hydrochloric acid / zinc chloride reagent.(Lucas Test - differentiate between primary, secondary, and tertiary alcohols) Dissolve 68g (0.5mole) of anhydrous zinc chloride in 52.5g (0.5mole) conc. HCl with cooling to avoid loss of hydrogen chloride. Ethers 1. Sodium.(no reaction) 2. Acetyl chloride.(no reaction) 3. Hydriodic acid.- constant boiling point 126-128oC.- fission of ester Carboxylic acids 1. Sodium bicarbonate and sodium hydroxide solution.(5% solutions) 2. Neutralisation equivalent. Phenols 1. Sodium bicarbonate and sodium hydroxide solution.(soluble in 5% sodium hydroxide and insoluble in 5% sodium bicarbonate) 2. Bromine in carbon tetrachloride and bromine water.(substitution reactions) 3. Ferric chloride solution.( yield intense colours-5%solution) Amines 1. Acetyl, benzoyl, or benzenesulphonyl or pToluebesulphonyl chloride.(for primary and secondary amines) 2. Nitrous acid.(Prepare in situ - add HCl and 10% cold sodium nitrite solution) Nitro compounds 1. Zinc and ammonium chloride solution. 2. Tin and hydrochloric acid. Amides 1. Dilute sodium hydroxide solution.(10% solutions) 2. Dilute sulphuric acid. Boil with 10% solution) Nitriles 1. Dilute sodium hydroxide solution.(30-40%) boil. 2. Dilute sulphuric acid.(50-70%) boil. Sulphonic acids 1. Sulphur present. 2. Sodium bicarbonate and sodium hydroxide solution. 3. S-Benzoyl-iso-thiuronium chloride. 4. Neutralisation equivalent. Sulphonamides 1. Sulphur and nitrogen present. 2. Sodium hydroxide solution. 3. Sulphuric acid, 70-80%. Back to Top SPECIFIC GROUP REAGENTS REAGENTS SPECIFIC TO FUNCTIONAL GROUPS: Ammoniacal silver nitrate. Add conc ammonia to bench silver nitrate (0.1M) until the initially formed ppt. Just disappears. Bradys reagent (2,4 DNPH) Dissolve 40g of 2, 4 dinitrophenylhydrazine in 80ml conc. Sulphuric acid. Cool and add 900ml methanol and 100ml water. Iodine reagent. Dissolve 20g KI and 10g iodine crystals in 100ml water. Jones reagent. Mix 25g of chromium trioxide (chromic anhydride CrO3) with conc. sulphuric acid to a paste, then dilute with water to 75mls. Molischs reagent. 20% soln. in naphthol. Dissolve 20g of 1-naphthol in 100ml ethanol. Tollens reagent. Add sodium hydroxide soln. to silver nitrate soln. to form a ppt. then add dilute ammonia soln. until ppt. Dissolves. delloyd.50megs.com Back to Top