Preparation of 2,2,2(2H3)‐diazoethane

Abstract 2,2,2(2H3) Ethyl‐N‐nitroso‐p‐toluenesulfonamide 6a, prepared in three steps from trideuteroacetonitrile 2a (overall yield 71%), has been subjected to alkaline decomposition to give after co‐distillation with ether/n‐hexane solutions of 2,2,2(2H3)‐diazoethane 1a. As shown by quantitative studies and from NMR and mass spectra, respectively, carboxylic acids were completely converted by 1a under mild reaction conditions into highly labelled (>96% d3, (<0.3% d0) 2,2,2(2H3)‐ethyl esters. The ready preparation of 1(2H1,2)‐ethyl 4‐nitrobenzoate 15 from 9 and unlabelled 1b under H/D exchange conditions illustrates the possibility of further introduction of 2H or 3H into an ethyl group. The molar extinction coefficient of 1a, b has been determined (ϵ (470 nm)=8.4).