| dc.description.abstract | The thesis entitled "Studies on Oxidation of Naphthols using Tetrachloro-o-benzoquinone" consists of three chapters and an Appendix.
Chapter I is a brief introduction to the chemistry of oxidative coupling of phenols. Use of quinones as phenol oxidative coupling reagents has been emphasised.
Chapter II deals with a study of the rearrangement observed during the oxidation of naphthols using tetrachloro-o-benzoquinone (1) and is divided into three sections.
Section I is a brief introduction to the present investigation and describes the earlier work on the reaction of naphthols with the quinone 1. The oxidation of ?-naphthol with the quinone 1 has been reported to give 2,2-(tetrachloro-o-phenylenedioxy)naphthalen-1(2H)-one (2). ?-Naphthol, on the other hand, was found to give a mixture of 2 and 1,1-(tetrachloro-o-phenylenedioxy)naphthalen-2(1H)-one (3). The formation of 2 in the oxidation of ?-naphthol suggested involvement of a rearrangement. In the present investigation this unusual oxidation has been studied using different substituted naphthols.
The naphthols required for this study fall into four main classes viz.,
(i) 8-alkyl (methyl, isopropyl and t-butyl)-2-naphthols,
(ii) 3-alkyl (methyl, isopropyl and t-butyl)-2-naphthols,
(iii) 3-alkyl (methyl, isopropyl and t-butyl)-1-naphthols, and
(iv) 2-naphthols having electron withdrawing (-NO?, -Cl and -Br) and electron donating (-OMe) groups at 6 position.
These naphthols were synthesised either by reported or new methods which are described in Section II.
The study of the reaction of the above-mentioned naphthols with the quinone 1 is elaborated in Section III. The reaction, in general, afforded the corresponding phenylenedioxy-naphthalenone (3) as major products. Only t-butyl group exerts pronounced steric influence on the rearrangement observed in the reaction of ?-naphthol with the quinone 1. Both electron withdrawing (-Cl) and electron donating (-OMe) groups at 6 position do not favour the rearrangement.
The reaction of 3-t-butyl-1-naphthol furnished the rearrangement product viz., 3-t-butyl-1,1-(tetrachloro-o-phenylenedioxy)naphthalen-2(1H)-one, besides the expected 3-t-butyl-2,2-(tetrachloro-o-phenylenedioxy)naphthalen-1(2H)-one. The major product of the reaction was, however, the para-coupled product viz., 3-t-butyl-4,4-(tetrachloro-o-phenylenedioxy)naphthalen-1(4H)-one. 3-Isopropyl-1-naphthol afforded a mixture of 3-isopropyl-2,2-(tetrachloro-o-phenylenedioxy)naphthalen-1(2H)-one and 3-isopropyl-4,4-(tetrachloro-o-phenylenedioxy)naphthalen-1(4H)-one, but no rearrangement product.
A probable mechanism involving the intermediacy of a tetrachlorocyclohexadienone has been suggested to explain the observed results.
Chapter III comprises two sections.
A brief introduction to the chemistry of quinone methide is presented in Section I.
Section II deals with the studies on the reaction of a few methylnaphthols with the quinone 1. This study was initiated with a view to exploring the possibility of generating quinone methides by this method. Reaction of 1-methyl-2-naphthol (4) with the quinone 1 in refluxing benzene gave the spirodimer (5) of 1,2-naphthoquinone 1-methide and a yellow solid to which the structure of 5,6,7,8-tetrachloro-1,4-benzodioxan-2-spiro-1'-naphthalen-2'-one (6) was assigned on the basis of spectral data. Catalytic hydrogenation of the benzodioxan 6 furnished a mixture of 1-methyl-2-naphthol (4) and tetrachlorocatechol, supporting the assigned structure.
A mechanism involving the initial formation of 1,2-naphthoquinone 1-methide followed by cycloaddition of the quinone 1 has been suggested for the formation of 6. The reaction of the naphthol 4 with the quinone 1 at room temperature resulted in the formation of 1-methyl-1-(1-methyl-2-naphthyloxy)naphthalen-2(1H)-one, besides the spirodimer (5) and the benzodioxan (6).
Among the other naphthols studied, 4-methyl-2-t-butyl-1-naphthol afforded, on reaction with the quinone 1, 5,6,7,8-tetrachloro-1,4-benzodioxan-2-spiro-1'-naphthalene-3-t-butyl-4'-one suggesting the initial formation of 1,4-naphthoquinone-4-methide. Reaction of 2-methyl- and 4-methyl-1-naphthols gave the corresponding phenylenedioxynaphthalenones, resulting from coupling at the unsubstituted 4 and 2 positions respectively.
The results obtained in the attempted synthesis of 1-[(2-hydroxy-3,4,5,6-tetrachlorophenoxy)methyl]-2-naphthol involving condensation of the tetrahydropyranyl ether of 1-bromomethyl-2-naphthol with tetrachlorocatechol in acetone in presence of potassium carbonate, are described in the Appendix. The reaction unexpectedly gave the spirodimer (5) as the major product in addition to two yellow solids. Based on spectral data and on mechanistic grounds, tentative structures have been assigned to these compounds. | |
