Methyldiazonium

Methyldiazonium is an organic compound consisting of a methyl group attached to a diazo group. This cationic chemical is the conjugate acid of diazomethane, wih an estimated pKa<10.
 * Methyldiazonium acidity equilibrium.png

It is an intermediate in methylation reactions of diazomethane with acidic hydroxyl compounds, such as conversion of carboxylic acids to methyl esters and phenols to methyl ethers.
 * Diazomethanemethylation.png

It has been implicated as the metabolite of N-nitrosodimethylamine responsible for the observed carcinogenicity of that compound.
 * Ndma activ.svg