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Author Topic: reaction of aniline with H2SO4?  (Read 27233 times)

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reaction of aniline with H2SO4?
« on: August 15, 2007, 01:37:28 AM »

plz tell me what will be the reaction of aniline when added to sulfuric acid?
and I want to ask what are the important points in the Carbylamine test and Hinsberg's test?I mean, what should be the expected results of these tests?and what are its goalS??

thank you!! :)


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Re: reaction of aniline with H2SO4?
« Reply #1 on: August 15, 2007, 07:08:54 AM »

Aniline with H2SO4 gives the sulfate or bisulfate of the anilinium ion:

C6H5NH2 + H2SO4 ---> [C6H5NH3]+ + [HSO4]-

The anilinium ion, having a positive charge, is unlike aniline very slow to react with electrophiles llike SO3 or NO2+ to give sulfonic acid or nitro-compounds. So a mixture of H2SO4 and HNO3 will not nitrate aniline.

For this reason to nitrate or sufonate aniline we convert it first to acetanilide C6H5NHCOCH3 which being virtually non-basic does not protonate completely in concentrated H2SO4. Also it is less reactive than aniline so less likely to oxidise or polysubstitute. Then the acetyl group is removed by base hydrolysis:

C6H5NH2 + (CH3CO)2O ---> C6H5NHCOCH3 + CH3COOH

C6H5NHCOCH3 + HNO3 (in conc. H2SO4) ---> O2NC6H4NHCOCH3 + H2O

O2NC6H4NHCOCH3 + OH- ---> O2NC6H4NH2 (nitroaniline)+ CH3COO-

Carbylamine test is a test for primary amines. In the presence of strong alkali these react with chloroform to give an isonitrile RNC, these used to be called carbylamines. Isonitriles have a powerful, distinctive foul smell. The main problem is that so powerful is the pong that traces of primary amine in a secondary or tertiary one will give a positive test!

RNH2 + CHCl3 + 3OH- ---> RNC + 3Cl- + 3H20

Hinsberg test involves reacting an amine with a sulfonyl chloride.

A primary amine gives a sulfonamide which still has a proton on N and is weakly acidic, so dissolves in NaOH solution:

RNH2 + C6H5SO2Cl ---> RNHSO2C6H5 +HCl

RNHSO2C6H5 + OH- ---> RN-SO2C6H5 (soluble in water) + H2O

A secondary amine gives a sulfonamide with two organic groups on N and no prton, so it does not dissolve in water:

R2NH + C6H5SO2Cl ---> R2NSO2C6H5 (non-ionic, water-insoluble).

A tertiary amine does not react at all and is recovered on adding base.

Hope that helps!


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