Effect of reaction pH and CuSO4 addition on the formation of catechinone due to oxidation of (+)-catechin

• Published in: International journal of cosmetic science Vol. 35; no. 4; pp. 362 - 367
• Main Authors: Matsubara, T., Wataoka, I., Urakawa, H., Yasunaga, H.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-08-2013; Wiley Subscription Services, Inc
• Subjects: (+)-catechin; Aqueous solutions; biobased material; Catechin - chemistry; catechinone; Copper Sulfate - chemistry; CuSO4; Dyes; hair dyestuff; Hydrogen-Ion Concentration; Oxidation; Oxidation-Reduction; CuSO4; pH; (+)-catechin; catechinone; hair dyestuff; biobased material
• ISSN: 0142-5463; 1468-2494
• DOI: 10.1111/ics.12051

Synopsis
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 Cu2+ 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 ‐ Cu2+ 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.
Résumé
Le produit de l'oxydation du (+)‐catechin, catechinone, est un nouveau colorant plus sûr pour la teinture des cheveux. Il a été préparé chimiquement à partir de (+)‐catechin dans une solution aqueuse avec du gaz O2 dans une gamme pH de 7.1–11.7. Le taux et la quantité de la formation de colorant augmentent avec le pH. La dissociation du groupe de l'hydroxyl de la partie catechol du (+)‐catechin est considérable pour l'oxydation du (+)‐catechin, et encourage la production de la teinture. Cela est dû à la plus grande réactivité du (+)‐catechin déprotonisé avec le O2. La production de catechinone est accélérée par l'addition de CuSO4, et le taux de la production atteint son maximum à pH = 8.8. Les complexes (+)‐catechin ‐ Cu2+ sont formés, et la formation encourage l'oxydation de la partie catechol du (+)‐catechin à pH ≤ 8.8. Néanmoins, le complexe devient trop stable pour continuer la réaction de l'oxydation à pH > 8.8.