O-Nitrosation

Alcohols react readily with acidified aqueous nitrous acid solutions to generate alkyl nitrites. The reaction sets up an equilibrium, which can be driven to the right by the use of a large excess of the alcohol or by removal of the alkyl nitrite by distillation, since alkyl nitrites have lower boiling points than do the corresponding alcohols. These reactions are O-nitrosation reactions and were first demonstrated by Allen who showed that a chiral alcohol gave the corresponding alkyl nitrite without racemization. Similarly, the reverse reaction, the hydrolysis of alkyl nitrites, occurs by N–O bond fission, again shown by the retention of configuration and by absence of an excess of 18 O in the alcohol product when the hydrolysis is carried out in 18 O-enriched water. There is much kinetic evidence that suggests that carboxylic acids undergo nitrosation reactions generating nitrosyl carboxylates, which can act as nitrosating reagents just as is the case for the in situ generation of nitrosyl halides and other derivatives. There have been no significant developments in this area either in mechanistic or synthetic studies since 1988, so the earlier account, gives the presently known position.