Selective oxidations by nitrosating agents - Part 1: Oxidations of ketones in concentrated sulfuric acid

Selective oxidations by nitrous acid in aqueous sulfuric acid towards alkyl side chains of enolizable ketones are reported. The conversion reagents-products in different experimental conditions is explored and the reaction path of the compounds involved as intermediates is tested. Side-chain oxidations are particularly successful for substrates with one site or with equivalent sites of oxidation. Thus, 95% of benzoylformic acid from acetophenone and 60% of 1,2-cyclohexanedione from cyclohexanone are obtained at similar to 78 and at similar to 40% H2SO4, respectively. Kinetic (k(obs)) and thermodynamic (k degrees) rate constants of acetophenone are also determined, the latter by using the acidity dependence of the rates, the equilibria involving the reacting species and the departure from the ideality of the catalytic acid system. Details of the process between enolizable ketones and electrophilic species in concentrated aqueous acid solutions are discussed. (c) 2005 Elsevier B.V. All rights reserved.