Mastering Chemistry Help

Reaction of nitrous acid with Aromatic Primary amines At 273 - 278 K, atomic primary amines react with sodium nitrite and dilute HCl, to give aromatic diazonium salts. For example, aniline forms benzene diazonium chloride. Aromatic diazonium salts are stable only at low temperature. Hence at higher temperature, aromatic primary amine gives phenols. Reaction of nitrous acid with Aromatic Primary amine Aliphatic diazonium salts are highly unstable and hence alcohols are obtained when aliphatic primary amines are reacted with nitrous acid.

Chemical properties of amines In most of its reaction, amines act as a nucleophile or a base due to lone pair on nitrogen. In aromatic amines, due to resonance, the -NH 2 group make the ring more susceptible to electrophilic substitution at ortho and para position. Important reactions of amines are classified as :   1. Salt formation Amines are soluble in mineral acids and carboxylic acids, due to the formation of soluble ammonium salts. RNH 2 + HCl  ------->  RNH 3 + Cl - C 6 H 5 NH 2 --------> C 6 H 5 NH 3 + Cl - 2. Alkylation Alkyl halides when react with primary or secondary amines undergo nucleophilic substitution. When HX is removed, secondary or tertiary amine formed will again reacts with alkyl halide froming tertiary amine and finally quaternary ammonium salt.   3. Acylation 4. Reaction with carbonyl compounds 5. Carbylamine reaction 6. Reaction with nitrous acids With nitrous  acid primary, secondary and ter...

Reaction of Amine with Carbonyl compunds Only primary amines react with aldehydes and ketones and condensation products are obtained. These condensation products are known as imines or Schiffs bases. R-CHO (aldehyde) + RNH 2   ---------> RCH = N-R (aldimine) R 2 CO (ketone) + R-NH 2 --------> R 2 C = N-R (ketimines) Imines can be reduced to secondary amines. This reaction, in turn, can be used to convert a primary amine to secondary amine. RCH = NR  ------ (H 2 / Ni) -----> R-CH 2 -NH-R  (Secondary amine) R 2 C = N-R ------ (H 2 / Ni) -----> R 2 CH-NH-R For more visit P roperties of Amines

Acylation of amines mechanism Both aliphatic and aromatic primary and secondary amines undergo N-acetylation. This acetylation can be effected using acid halides or anhydrides in presence of a base (pyridine) and the product obtained is an amide. Base remove HCl and prevent protonation of amine. Acylation of primary amine Acylation of Secondary amine Since amides formed are not basic, they do not under go further actylation. Acid chlorides are stronger acetylating agent than acetic anhydride. In tertiary amines there is no replaceable hydrogen and they do not undergo acylation. 

Physical Properties of Amine 1. Physical state of Amine Lower amines are gases while higher members are mostly liquids. Amines are almost unpleasant, having fishy smell. In the pure state amines are colourless, but in certain case they become coloured due to oxidation and mixing of impurities. 2. Boiling point In amines, there are polar N-H bonds. Hence, in general they are polar. More over, in amines, inter molecular hydrogen bonds are present, leading to high boiling points in comparison to corresponding hydrocarbons of the same molar mass. Primary and secondary amines can form hydrogen bonding hence they higher boiling points than isomeric tertiary amines. 3. Solubility in water All the three classes of amines can form hydrogen bond with water. Hence they are soluble in water. But higher amines are least soluble due to the non-polar effect of big alkyl groups. Due to weaker hydrogen bonds solubility of amines in water is less than that of alcohols.

Distinction between primary, secondary and tertiary amine Using Carbylamine Reaction Primary amine (both aliphatic and aromatic) when warmed with chloroform and alcoholic KOH, gives isocyanides ( carbylamines ). This is called c arbylamine reaction . Carbylamines has an offensive smell. This reaction is answered only by primary amine and hence to distinguish primary amine from other classes of amines . In general R-NH 2   +  CHCl 3   +  3KOH  --------->  RNC (carbylamine) +  3KCl + 3H 2 O

Distinction between primary, secondary and tertiary amine Using Hinsberg  reagent Three classes of amines are distinguished by Hinsberg reagent test . The Hinsberg reagent is benzene sulphonyl chloride (C 6 H 5 SO 2 Cl). 1. Reaction of Hinsberg reagent with Primary amine A primary amine forms a precipitate of N-alkyl benzene sulphonamide with Hinsberg reagent. This precipitate is soluble in alkali. RNH 2 (primary amine)  +  C 6 H 5 SO 2 Cl ( Hinsberg reagent ) ------------>  R-NH-SO 2 -C 6 H 5   ------(NaOH)---> R-N - Na + -SO 2 C 6 H 5 (soluble) 2. Reaction of Hinsberg reagent with secondary amine   Secondary amine reacts with Hinsberg reagent to form a precipitate N,N-dialkyl benzene sulphonamide. But this precipitate is insoluble in alkali. R 2 NH (secondary amine)  +  C 6 H 5 SO 2 Cl ( Hinsberg reagent ) ------------> R 2 NSO 2 C 6 H 5 (precipitate)  -----(NaOH)---> insoluble (no reaction) 2. Reac...