Special reactions/tests for Urea, Formamide, Oxamide, Salicylamide, Succinimide, Phthalimide

Urea

Urea nitrate and oxalate: Take a concentrated solution of urea, to one portion, add a few drops of con. HNO₃: the white crystalline urea nitrate (m.p. is 163°) is precipitated; to another portion, add con. Oxalic acid solution and scratch with a glass rod. White crystals of urea oxalate (m.p. is 171°) are separated. In an excess of water both salts dissolve.

Biurate reaction: Take 0-2 g of urea into a dry test-tube and heat gently above the melting point. NH₃ is evolved. After 2 minutes the liquid rapidly solidifies with the formation of biuret.

2NH₂CONH₂à NH₂CONHCONH₂ + NH₃

Dissolve the solid residue in a few ml. of warm 10% NaOH solution. Stand it to cool and add 1 drop of dil. CuSO₄ solution. A purple coloration is obtained. A pink/purple coloration is due to containing two -CONH- groups attached to one another, or to the same carbon atom or nitrogen atom. Therefore the same colouration is also given by malonamide, oxamide and by proteins/peptides.

Urease test: Urease enzymes can hydrolys Urea to Ammonium carbonate. The reaction is specific. It is used for solutions of urea to which the biuret test cannot be applied.

Action of hypobromite: Add sodium hypobromite solution to a solution of urea. The brisk effervescence is given.

NH₂CONH₂ + 3NaOBr à N₂ + CO2 + 3NaBr + 2H₂O

Formamide

Boil 1 ml of formamide in a test-tube. NH₃is evolved from it.  CO is produced, but cannot be ignited in the presence of the NH₃.

Oxamide

Biuret test: Oxamide does not need any preliminary treatment to proceed with the test. Shake 1 g of oxamide with 1ml of 10% NaOH solution. Add 1 drop of very dilute CuSO₄ solution to it and mix well. A pink coloration is produced.

Sulphuric acid test: Heat 0-3 g of Oxamide with con. H₂SO₄. CO and CO₂ are evolved.

Salicylamide

FeCl₃ coloration: Take the solid into a test tube. Add FeCl₃ solution and shake. An intense violet coloration is produced as the Phenolic groups are present.

Succinimide

Reduction: Take about 1 g of succinimide and an equal amount of Zn dust into a dry hard-glass test tube and mix well. Heat strongly. Soak a pinewood splinter in con.HCl and place it in the mouth of the tube. The splinter is turned red by the vapour of pyrrole which is formed by reduction.

Fluorescein reaction: Take about 1 g of Succinimide, 1 g of resorcinol and 2 drops of con. H₂SO₄ into a dry test tube and fuse all of it together. Cool and add water. Then add NaOH solution in excess. A green fluorescent solution is produced.

Phthalimide

Phthalein reaction: Take about 1 g of Phthalimide, 1 g of phenol and 2 drops of con. H₂SO₄ into a dry test-tube and fuse all together very gently. Let it cool and add water. Then add NaOH solution in excess. A red coloration is produced which is decolorized by acids.

Fluorescein reaction: Repeat the above test, using resorcinol instead of phenol. A green fluorescent solution is produced on the addition of NaOH solution.