Scheme 1.

Methyldiazene synthetic scheme. Hydroxylamine-O-sulfonic acid (3) was synthesized as a white precipitate after reaction of chlorosulfonic acid (1) and hydroxylamine (2, where the N atom was either ¹⁵N or ¹⁴N). N-methylhydroxylamine (5) was synthesized by the reduction of nitromethane (4, where the N atom was either ¹⁴N or ¹⁵N and the C atom was either ¹²C or ¹³C). Methyldiazene (6) was prepared by the base-catalyzed reaction of hydroxylamine-O-sulfonic acid (3) with N-methylhydrolyamine (5), and the gas was isolated by freezing. See Materials and Methods for details.