On the photoreactivity of vitamin K compounds

Abstract

AbstractRate constants for conversion of vitamin K1‐and K2‐derived 1,3‐quinone methides into 1,2‐quinone methides have been measured in CH3CN solutions in the presence of Brönsted acids and bases. Second‐order rate constants approach the diffusion‐controlled limit and are essentially independent of the (acid or base) strength of the catalyst. On the other hand, rate constants for triplet quenching of 2‐methyl‐3‐undecyl‐1,4‐naphthoquinone, used as model compound, are presented and compared with data for 1,4‐naphthoquinone and 2‐methyl‐1,4‐naphthoquinone. A significant decrease in reactivity is observed as the number of alkyl substituents in the quinoid moiety increases, which is attributed to the concomitant increase in triplet π,π* character. Correlation of rate constants for physical quenching, by aromatic hydrocarbons and dimethylsulfoxide, with the electron affinity of the (ground state) quinone and ionization potential of the quenchers suggests quenching by charge‐transfer interactions. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 839–844, 2008