Aspects of Phenol Oxidation

Monaghan, Francis (1977) Aspects of Phenol Oxidation. PhD thesis, University of Glasgow.

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In an extension of previous studies on the rate of autoxidation of l-alkyl-2-naphthols, the synthesis and study of a series of related l-aralkyl-2-naphthols was undertaken. Preparation of 1-trityl-2-naphthol from o-naphthofuchsone was reinvestigated. Initial attempts to prepare o-naphthofuchsone by reaction of 2-naphthol with Ph2CCl2 in the presence of AICI3 led to formation of 12-phenyl-12H-benzo[a]xanthene. A successful preparation involved the dehydration of 1-diphenylhydroxy methyl-2-naphthol which was prepared in high yield from the methyl ester of 2-hydroxy-1-naphthoic acid by reaction with PhMgBr. Reaction of the stable o-quinone methide with PhMgBr gave l-trityl-2-naphthol. The related 1-(1,1-diphenylethyl)- and diphenylmethyl-2-naphthol were prepared from o-naphthofuchsone by reaction with MeMgl and NaBH4 respectively. None of these three naphthols showed any tendency to autoxidise although they were considered to experience an unfavourable peri interaction the magnitude of which would be similar to, if not greater than, that in related l-alkyl-2-naphthols which had proved to be highly susceptible to autoxidation. The solution IR spectra of these three compounds revealed that there was total intramolecular hydrogen bonding in each case. The previously studied l-benzyl-2-naphthol which is also stable to autoxidation under the standard conditions showed approximately one third of the molecules had intramolecularly H-bonded hydroxyl groups. Prolonged treatment of l-benzyl-2-naphthol with oxygen with or without a catalytic amount of Co(acac)3 led to the formation of 1-benzyl-1-(1-benzyl-2-naphthyloxy)naphthalen-2(lH)-one and a mixture of ketol isomers, 1-benzyl-1-hydroxynaphthalen-2(iH)-one and 2-benzyl-2-hydroxynaphthalen-1(2H)-one. The identity of these species was confirmed by the independent synthesis of the dimer by potassium ferricyanide oxidation of l-benzyl-2-naphthol and of the ketol mixture by sodium periodate oxidation and by Wessely oxidation of l-benzyl-2-naphthol. Attempts to oxidise l-benzyl-2-naphthol to an o-quinone methide using dichloro-dicyanobenzoquinone led to the formation of the above O-C dimer. Attempts to prepare the benzoate of 1-hydroperoxy-1-isopropyl-naphthalen-2(1H)-one repeatedly led to the isolation of 1-benzoyloxy-l-isopropoxynaphthalen-2(1H)-one. Thermolysis of 1-hydroperoxy-1-isopropylnaphthalen-2(1H)-one itself proceeds by a radical pathway with evolution of a gas. The latter part of the thesis describes work intended to explore the range of application and the stereospecificity of various reagents which epoxidise alpha,beta-unsaturated ketones in which the faces of the enone are not equivalent. Three enone types were investigated: 1-alkyl-l-hydroxynaphthalen-2(1H)-ones, 4-hydroxy-2,4,6-trialkylcyclohexadienones and 4-alkyl-4-hydroxynaphthalen-1(4H)-one. Preparation of 1-hydroxy-1-isopropylnaphthalen-2(lH)-one was achieved by autoxidation of 1-isopropyl-2-naphthol followed by reduction of the hydroperoxide by dimethyl sulphide. 1-Hydroxy-1-methylnaphthalen-2(1H)-one was prepared by chromium trioxide or peroxyacetic acid oxidation of 1-methyl-2-naphthol. On heating with molybdenum hexacarbonyl both these ketols undergo ketol rearrangement, the latter more slowly than the former, and in both cases this rearrangement precludes epoxidation by t-butyl hydroperoxide catalysed by Mo(CO)6.1-Hydroxy-1-isopropylnaphthalen-2(1H)-one was reduced to a single diol by sodium borohydride. Reaction of the diol with t-BuOOH and V0(acac)2 or with m-chloroperoxybenzoic acid led to a mixture of hydroxyketones containing an epoxide which is probably 2-hydroxy-2-isopropylnaphthalen-2(1H)-one-3,4-epoxide formed after unexpected oxidation of the diol and ketol rearrangement. The in situ generation of singlet oxygen, using CeO2 and H2O2, provides a convenient route to hydroperoxycyclohexadienones from mesitol and 2,6-di-t-butyl-4-mathylphenol. Attempts to prepare 4-hydroperoxy-2,4,6-tri-t-butylcyclohexadienone by this method led to recovery of starting material. 2,6-Di-t-butyl-4-hydroperoxy-4-methyl-cyclohexadienone was also prepared by base-catalysed oxygenation. Reduction of these hydroperoxides with dimethyl sulphide gave the corresponding hydroxydienones. Attempted epoxidation of 2,6-di-t-butyl-4-hydroxy-4-methylcyclohexadienone with t-butyl hydroperoxide and Mo(CO)6 led to a complex mixture which showed evidence for the presence of an epoxide but which could not be separated. Attempted epoxidation of 2,6-di-t-butyl-4-hydroxy-4-methylcyclohexadienone and 4-hydroxy-2,4-6-trimethylcyclohexadienone with alkaline hydrogen peroxide were unsuccessful. Epoxidation of 4-hydroxy-4-methylnaphthalen-l(4H)-one, prepared by singlet oxygen oxidation of 4-methyl-1-naphthol followed by reduction, with both alkaline hydrogen peroxide and m-chloroperoxy-benzoic acid led to the same epoxide, both reactions proceeding with high stereoselectivity. The discussion of these new results is preceeded by an Introduction reviewing previous work on phenol oxidations of various types and enone epoxidations with particular regard to steric control.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1977
Depositing User: Enlighten Team
Unique ID: glathesis:1977-78769
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 14:55
Last Modified: 30 Jan 2020 14:55

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