Photolysis of α-Diazo Ketones in the Gas Phase Monitored by Fourier Transform Infrared Spectrometry

Article abstract of DOI:10.1021/jo00152a023

3-Diazo-2-butanone (1),2,2,5,5-tetramethyl-4-diazo-3-hexanone (2), and 2-diazocyclohexanone (3) were photolyzed in the gas phase at low pressure.The course of the reactions was followed by FT IR spectroscopy.The Wolff rearrangement occured to an extent of 70percent for 1 and of about 40percent for 2; the resulting ketenes were respectively somewhat photolabile and photostable.The ketene from 3 was quite unstable to photolysis, although it could be indentified in the early part of the reaction.For irradiations at the laser line λ = 457,9 nm, the ratio of photolysis rates k₁/k₂ was at least 300, which suggests a concerted mechanism for the rearrangement of 1.Photolysis of 1 in the presence of argon to increase intermolecular collisions raised the production of dimethylketene to over 95percent.In contrast, the Wolff rearrangement of 2 occured in the gas phase but not in solution.The gas-phase reaction path may have its origin in the excited vibrational states of an electronic isomer of 2 or in those of the corresponding carbene.