Analytical chemistry Trinidad & 

Tobago Lab resources
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Qualitative organic analysis reagents


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

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Preparation of laboratory reagents


Check below for preparation of Specific organic reagents


CLASS AND GROUP REACTIONS


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.

Aldehydes

1. Schiffs reagent.(fuchsin aldehyde reagent)
2. Fehlings solution.
3. Ammoniacal silver nitrate solution.(Tollens reagent)

Esters and anhydrides

1. Hydroxamic acid test.
Esters react with hydroxylamine in the presence of sodium hydroxide to form the sodium salt of the corresponding hydroxamic acid. On acidification and addition of ferric chloride the magenta-coloured iron (III) complex of the hydroxamic acid is formed.

( 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 with reaction.
2. Acetyl chloride or benzoyl chloride.
3. Hydrochloric acid / zinc chloride reagent.(Lucas Test)

(Lucas Test - differentiate between primary, secondary, and tertiary alcohols)
Dissolve 68g of anhydrous zinc chloride in 50ml conc. HCl in ice bath with stirring and 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. Hinsburg Test. Acetyl, benzoyl, or benzenesulphonyl or p-toluebesulphonyl chloride as reagent.(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%.

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Preparation of organic reagents



Ammoniacal silver nitrate.
(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.

Barfoed's reagent

To 100 ml of dilute acetic acid , add 6.5 g of cupric acetate.

Benedicts reagent.

Solution A: Dissolve 8.65g of CuSO4.5H2O in 75 ml of H2O.
Solution B: Dissolve 86.5 g of sodium citrate and 50 g of anhydrous Na2CO3 in 400 ml H2O.

Pour Solution A slowly into Solution B and make up the volume to 500 ml . Mix well.

Bradys reagent (2,4 DNPH)

(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.

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.

Ferric chloride (Neutral)

Dissolve FeCl3 in water. Add NH4OH dropwise till there is a start of precipitation. Filter. Use filterate as neutral FeCl3 solution.
Precipitation indicates that HCl produced by hydrolysis of FeCl3 has been neutralized and added ammonium hydroxide is reacting with FeCl3 to precipitate Fe(OH)3)

Iodine reagent.

Dissolve 20g KI and 10g iodine crystals in 100ml water.

Jones reagent.

The Jones Reagent is a mixture of chromic trioxide or sodium dichromate in diluted sulfuric acid, which forms chromic acid in situ.
The unknown is first dissolved in acetone and the reagent added to the mixture.

Mix 25g of chromium trioxide (chromic anhydride CrO3) with conc. sulphuric acid to a paste (use ice bath), then dilute with water to 75mls to make the regent.

1. Dissolve 10 mg (solid) or 2 drops (liquid) of the unknown substance in 0.8 mL to 1 mL of pure acetone.
2. Add 1 drop of Jones reagent and shake.
3. Look for a color change from orange-yellow to green.

Molischs reagent.

20% soln. in naphthol. Dissolve 20g of 1-naphthol in 100ml ethanol.

Nesseler's reagent .

Dissolve 5g of KI in minimum amount of water. To it add saturated solution of HgCl2 till a faint permanent red precipitate is formed. Mix it with 40 ml of 50% aqueous KOH solution. Allow the precipitate to settle. Dilute to 100 ml with water. Allow it to stand overnight and filter. Filterate is nesseler's reagent.

Ninhydrin solution.

Dissolve 0.2 g of ninhydrin in 100 ml of rectified spirit (alcohol).

Schiff's 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.

Tollens reagent.

Add sodium hydroxide soln. to silver nitrate soln. to form a ppt. then add dilute ammonia soln. until ppt. dissolves.



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Signature: Dhanlal De Lloyd, Chem. Dept, The University of The West Indies, St. Augustine campus
The Republic of Trinidad and Tobago.
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