Oxidation Studies of Perfumery Phenols Found in Indian Spices

The quantitative aspects of the oxidation of phenols to the corresponding quinones have been studied and reported in literature but there are few reports of the kinetic, thermodynamic and mechanistic studies of the oxidation of phenols.This chapter deals with the oxidation of some perfumery phenols found in Indian spices by a variety of inorganic and organic oxidants using kinetic methods.

The oxidation of the perfumery isomeric phenols, Eugenol (4-Allyl-2-methoxy phenol) and Isoeugenol (2-Methoxy-4(prop-1-en-1-yl) phenol) has been carried out using 1) inorganic oxidants,KBrO3,KIO3 and K2S2O8 in acidic medium and 2)N-Bromosuccinimide and Sodium chloro(4-methylbenzene-1-sulfonyl)azanide (Chloramine T) in alkaline medium.These phenols are found in the Indian spices,clove (Syzygium aromaticum), nutmeg (Myristicafragrans), Cinnamon (Cinnamomum zeylanicum) and Basil (Tulsi) (Ocimum basilium) and are used in the manufacture of perfumes,fragrances and flavouring agents.

The oxidation was studied under first order kinetic conditions with respect to the oxidant ie.[oxidant]<<[phenol].For both the phenols studied,the oxidation rate increased with phenol concentration but decreased with oxidant concentration.The sequences of oxidation rates of the phenols for the different oxidants has been explained on the basis of their steric factors,isomeric and structural features. From the variation of oxidation rate with temperature, the energy of activation and other thermodynamic activation parameters were evaluated and interpreted in terms of the molecular dynamics of the oxidation process.Suitable reaction mechanisms have been suggested for the oxidation of the phenols under study.