Aliphatic primary amines react with nitrous acid in cold condition to give aliphatic diazonium salts which exist only as transient intermediates, quickly decomposing into a nitrogen molecule and carbonium ion. Aromatic amines react with nitrous acid to give aromatic diazonium salt which are stable for short time and slowly decompose even at low temperatures, hence are immediately used after preparation they are also stable due the resonance of its ion.