Kinetic studies of Dakin oxidation of o- and p-hydroxyacetophenones

Abstract

Rates of oxidation of aqueous o-, and p-hydroxyacetophenone with alkaline hydrogen peroxide to yield catechol and hydroquinone, respectively, have been followed spectrophotometri-cally. Both ketones showed smooth pseudo first-order behaviour, the ortho isomer yielding rate constants in the range 2.6 to 6.6 × 10−2 min−1 at 0 °C, and the para isomer of 0.73 to 7.10 × 10−2 min−1 at 35 °C for the concentrations of hydrogen peroxide and base used. The order in hydrogen peroxide was, unexpectedly, found to be 1.4. A simple test established that this fractional order was probably not the result of hydrogen peroxide involvement in simultaneous first- and second-order processes of differing rates. Other plausible pathways to explain this are proposed.

Tandem Payne/Dakin Reaction: A New Strategy for Hydrogen Peroxide Detection and Molecular Imaging

“…Zuschriften and NH 2 )atthe ortho position of aryl aldehydes (for example, salicylaldehyde), in which the ortho-OH could form an intramolecular hydrogen bond to activate the aldehyde. [13] However,t he reaction still requires alkaline conditions, which are not suitable for direct application in live-cell imaging.I nP ayne oxidation, H 2 O 2 can be activated by the in situ formation of ap eroxyimidic acid from its basecatalyzed addition to nitrile.A sr eported by Bach, the electron-deficient trichloroacetonitrile (CCl 3 CN) could afford as ufficiently reactive peroxytrichloroacetimidic acid under physiological conditions. [14] Therefore,w er easoned that at andem Payne/Dakin reaction should activate both H 2 O 2 and aldehyde,r espectively,t op rovide an ovel and biocompatible strategy for specific H 2 O 2 detection (Scheme 2b).…”

Tandem Payne/Dakin Reaction: A New Strategy for Hydrogen Peroxide Detection and Molecular Imaging

“…A century ago, Dakin reported the transformation of aryl aldehyde into phenol mediated by hydrogen peroxide under strongly basic conditions . In 1977, Hocking found that the Dakin reaction could be accelerated by the presence of electron‐donating substituents (such as OH and NH 2 ) at the ortho position of aryl aldehydes (for example, salicylaldehyde), in which the ortho ‐OH could form an intramolecular hydrogen bond to activate the aldehyde …”

On the mechanism of alkaline hydrogen peroxide oxidation of the lignin model p-hydroxyacetophenone

“…Hydroquinone monoacetate was obtained as previously described (5). Commercial peracetic acid (32%) was analyzed for acid equivalence by titration with sodium hydroxide solution, for peroxide concentration by titration with permanganate solution (17), and for total oxidizing ability by addition of potassium iodide and subsequent titration with thiosulphate (18).…”

“…The fraction of reactant remaining was calculated from the relative peak heights. Previous studies had indicated that the peak height was a reliable measure of the relative amount of substance in solution (5,12). Occasionally impurities caused decomposition of the peroxide to oxygen, which resulted in a rapid loss of resolution and collapse of the methyl resonances.…”

“…Hocking (5) showed earlier that the rate of reaction of the lignin model p-hydroxyacetophenone @HAP) with a 100-fold excess of aqueous alkaline hydrogen peroxide depended on the concentration of hydrogen peroxide to the power 1. 4.…”