Nitrous acid reacts with all classes of amines. The nature of products obtained from these reactions depends on whether the amine is primary, secondary or tertiary. It also depends on whether the amine is aliphatic or aromatic. Aliphatic primary amines react with nitrous acid $(NaN{O}_2+HCl)$  to form alcohol as the major product. In addition to alcohol, alkene and alkyl halide are also formed as minor products. Certain cyclic primary amines undergo either ring expansion or ring contraction on treatment with nitrous acid. This reaction is called Demjanov ring expansion or contraction.