| dc.description.abstract | The thesis entitled "Studies in Oxidation of Aromatic Substrates" is divided into four chapters.
Chapter I starts with a brief review of the reactions of organic substrates with peroxydisulphate. This chapter describes the investigation carried out on the oxidation of aromatic substrates with peroxydisulphate in the presence of metal ions like copper(II), iron(III), silver(I), cerium(IV), nickel(II) or cobalt(II). The present investigation was motivated by a desire to optimise the yields of the single products which could be formed from the aromatic substrates by oxidation. It is observed that:
(a) Halophenols are oxidised in excellent yield to the corresponding p-quinones in the presence of copper(II) salt.
(b) Electron-rich benzylic hydrocarbons are converted to the carbonyl compounds in the presence of copper(II) ions in aqueous acetonitrile medium.
(c) Oxidation of benzylic hydrocarbons, in general, in the presence of metal ions like iron(III), copper(II), cobalt(II) or nickel(II) gives the corresponding benzyl acetates and carbonyl compounds in aqueous acetic acid medium. In aqueous acetonitrile medium, carbonyl compounds are formed in good yields.
(d) Oxidation of naphthalene and substituted naphthalenes in the presence of copper(II) yields 1,4-naphthoquinones (8–66%). 1-Substituted naphthalenes give a mixture of 2- and 5-substituted 1,4-naphthoquinones. The formation of 2-substituted 1,4-naphthoquinones involves a 1,2-shift, which has been recognised as a general feature of cation radical involvement (previous work from this laboratory).
In these copper-promoted peroxydisulphate oxidations, it is proposed that SO?•? formed from thermal decomposition of peroxydisulphate converts Cu²? to Cu³? species and the latter is involved in the oxidation of aromatic substrates to aromatic cation radicals.
Chapter II describes some of the oxidation of aromatic substrates with hydrogen peroxide–hydrochloric acid. The present study shows that:
(a) 1-Naphthol, substituted 1-naphthols and 1-naphthylamine are converted into 1,4-naphthoquinones in 60–85% yield.
(b) 4-t-Butyl or 4-t-pentyl-o-cresol gives 2-chloro-6-methyl-1,4-benzoquinone (50–55%) and 2,6-disubstituted phenols give 2,6-disubstituted 1,4-benzoquinones (47–51%).
Chapter III deals with the oxidation of aromatic substrates by lead(IV) acetate. A number of halophenols are oxidised to yield mixtures of products. The products have been separated and characterised. The present investigation highlights the fact that the product composition is solvent-dependent (contrary to the literature reports):
(a) Oxidation of 2,4-dihalo-1-naphthols gives 4-halo-1,2-naphthoquinone and 2-halo-1,4-naphthoquinones. The former is the predominant product.
(b) 2-Alkyl-1-naphthols give a mixture of 1,4-naphthoquinones and o-naphthoquinol acetate, whereas 4-alkyl-1-naphthols give 1,2-naphthoquinone diacetate and p-naphthoquinol acetate.
(c) 2-Bromo-6-t-butyl-p-cresol gives a mixture of products, the formation of one of which involves a new 1,2-shift.
(d) With naphthalene, lead(IV) acetate and aluminium chloride give 1-acetoxynaphthalene (10%) and 1,2,3,4-tetrachloro-1,2,3,4-tetrahydronaphthalene (8%).
Chapter IV is concerned with the oxidation of phenols by periodic acid:
(a) The present study shows that oxidation of halonaphthols and halophenols gives a mixture of 1,4-quinones and 1,2-quinones in good yields, the former products being the predominant ones.
(b) Oxidation of 2,6-dibromo-4-t-butylphenol and its analogues gives a mixture of products. The results are interpreted on the basis of involvement of radicals.
(c) Oxidation of 2,2?-dihydroxy-1,1?-binaphthyl with periodic acid gives a 9-membered keto lactone I. The formation of the keto lactone I provides an insight into the mechanism of the oxidation of phenols by periodic acid. | |
