Methyl nitrite

Structure

At room temperature, methyl nitrite exists as a mixture of cis and trans conformers. The cis conformer is 3.13 kJ mol⁻¹ more stable than the trans form, with an energy barrier to rotation of 45.3 kJ mol⁻¹. The cis and trans structure have also been determined by microwave spectroscopy (see external links).

Synthesis

Methyl nitrite can be prepared by the reaction of silver nitrite with iodomethane: Silver nitrite (AgNO₂) exists in solution as the silver ion, Ag⁺ and the nitrite ion, NO₂⁻. One of the lone pairs on an oxygen from nitrite ion attacks the methyl group (—CH₃), releasing the iodide ion into solution. Unlike silver nitrite, silver iodide is highly insoluble in water and thus forms a solid. Note that nitrogen is a better nucleophile than oxygen and most nitrites would react via an S_N2-like mechanism and the major product would be nitromethane. For example, sodium and potassium nitrite reacting with iodomethane would produce mostly nitromethane, with methyl nitrite as the minor product. However, the presence of the silver ion in solution has a stabilizing effect on the formation of carbocation intermediates, increasing the percent yield of methyl nitrite. In either case, some nitromethane and methyl nitrite are both formed.

The figure shows the two gas-phase structures of methyl nitrite, as determined by IR and microwave spectroscopy.

This compound is produced by the combustion of unleaded petrol, and might be a cause of the decline of insects, and hence that of the house sparrow and other songbirds in Europe.