Aliphatic nitro compounds

i) Vapour phase nitration of alkanes

Hydrocarbons when heated with forming nitric acid at 693 - 793 K, are converted to nitro alkenes. Nitration of methane end lower members can be carried out by this nitration technique.

This direct nitration of alkanes is relatively more difficult in comparison to the nitration of arenes. Hence this method has no significance as a laboratory method but may be of commercial importance in the bulk production of small nitro alkanes

Since the process occurs at high temperature therefore, C - C bond of alkenes also undergo cleavage at this temperature and a mixture of nitro alkenes are formed.

For e.g.,

ii) Treatment of alkyl halides with alcoholic silver nitrate

Iodo alkanes on treatment with alcoholic AgNO₂ gives 80% of nitroalkanes and 20% alkyl nitrites.

This method is primarily used to prepare primary nitro compounds. Secondary and tertiary halides give major proportion of alkenes due to b-elimination reaction.

Hence 2^o and 3^o nitro alkenes are not prepared by this method.

If alkyl bromides or iodides are treated with alkali nitrites, the major with alkali nitrites, the major product is alkyl nitrite with nitro alkanes as the minor product.

Even NaNO₂ or KNO₂ give a fairly good yield (60%) of nitro compound if the reaction is carried out in solvents like dimethyl formamide (DMH) or dimethyl sulphoxide (DMSO).

iii) Oxidation of t-alkyl amines with KMnO₄

In this reaction, the amine must be primary and -NH₂ group should be attached to a tertiary carbon.