title: Effect of reaction pH and CuSO4 addition on the formation of catechinone due to oxidation of (+)-catechin.
abstract: A novel hair dyeing technique being milder and safer for a human body is desired. The oxidation product of (+)-catechin, catechinone, was invented as a safer dyestuff for hair colouring under such the situation. The preparation of catechinone by a chemical oxidation is a practical way and the objective of the study is clarify the effect of the solution pH and in the presence or absence of Cu(2+) on the formation rate and yield of catechinone in order to improve the efficiency of the dye formation. The catechinone formation was monitored by ultraviolet-visible spectroscopy. Catechinone was prepared chemically from (+)-catechin in aqueous solution with O2 gas introduced over a pH range of 7.1-11.7. The rate and amount of the dye formation increase with increasing pH. Dissociation of the hydroxyl group of the catechol part of (+)-catechin is significant for the oxidation of (+)-catechin and promotes the dye production. This is because the deprotonated (+)-catechin has a higher reactivity with O2 . The production of catechinone is accelerated by the addition of CuSO4 and the production rate reaches the maximum at pH = 8.8. (+)-Catechin - Cu(2+) complexes are formed and the formation promotes the oxidation of the catechol part of (+)-catechin at pH ≤ 8.8. On the other hand, the complex becomes too stable to proceed for the oxidation reaction at pH > 8.8.
authors.affiliation: Department of Biobased Materials Science, Kyoto Institute of Technology, Kyoto, Sakyo-ku, Matugasaki, Gosyokaido-tyo, 606-8585, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Matsubara
authors.forename: I
authors.initials: I
authors.lastname: Wataoka
authors.forename: H
authors.initials: H
authors.lastname: Urakawa
authors.forename: H
authors.initials: H
authors.lastname: Yasunaga
mesh_terms: D002392:Catechin / Q000737:chemistry*; D019327:Copper Sulfate / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction
chemical_list: D002392:Catechin; D019327:Copper Sulfate
keywords: (+)-catechin; CuSO4; biobased material; catechinone; hair dyestuff; pH