Synthesis of Diazeniumdiolates from the Reactions of Nitric Oxide with Enolates

Abstract

Reactions of nitric oxide with enolates derived from aliphatic methyl ketones containing α-methylene or α-methine groups and with enolates derived from α,α‘-dimethylene or α,α‘-dimethine ketones yield mono- or bis(diazeniumdiolate) products. Diazeniumdiolation occurs in the following order:  α-methine > α-methylene > α-methyl. The amount of the base used alters the extent of diazeniumdiolation and the course of the reaction. Mono- and bis(diazeniumdiolate)-substituted methyl ketones are cleaved in the presence of excess base before and after the subsequent diazeniumdiolation of the α-methyl group. Similar to the trihalogenated methyl groups in the base-assisted halogenation reactions of methyl ketones, the bis(diazeniumdiolate)-substituted α-methylene and α-methyl groups act as leaving groups in the presence of excess base. The reaction of nitric oxide with a (∼20:80, cis/trans) mixture of 2,6-cyclohexananone yields the cis and trans isomers of 2,6-dimethylcyclohexanone-2,6-bis(diazeniumdiolate) in 12.9% and 57.6% yield. Single-crystal X-ray diffraction data determined for potassium cis-2,6-dimethylcyclohexanone-2,6-bis(diazeniumdiolate), cis-14b, reveal that the N2O2- substituent is planar with considerable delocalization of a double bond over the anionic four-atom group. Except for one of the diazeniumdiolate products, namely, potassium propanoate 2,2-bis(diazeniumdiolate), 8b, all are stable in neutral and basic aqueous media. Compound 8b slowly decomposes in neutral aqueous solution releasing nitrous oxide and nitric oxide gases but is stable in basic aqueous media. Differential scanning calorimetry data measured for the diazeniumdiolate products indicate that they decompose exothermally with most of them undergoing explosive decomposition at moderately high temperatures (181−274 °C)