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The photooxidation of mono- and dimethylnaphthalenes by singlet oxygen

✍ Scribed by C. J. M. van den Heuvel; H. Steinberg; Th. J. de Boer

Publisher
Elsevier Science
Year
2010
Tongue
English
Weight
515 KB
Volume
99
Category
Article
ISSN
0165-0513

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✦ Synopsis

Abstract

The reactions of singlet oxygen with all possible isomers of mono‐ and dimethylnaphthalenes as well as with 1,4,6,7‐tetramethylnaphthalene have been studied. Apart from 2‐methylnaphthalene, which does not react under our reaction conditions, attack on 1,4‐ and in some cases also on 5,8‐positions results in the formation of endoperoxides (epidioxides). In the case of 1,4‐dihydro‐2,3‐dimethyl‐1,4‐epidioxynaphthalene there is a subsequent reaction step with singlet oxygen which introduces an allylic hydroperoxy function.

The structures of the endoperoxides were established by means of NMR. A simple volumetric method was employed to measure the relative reaction rates. Rate constants (15°C) for the mono‐ and dimethylnaphthalenes vary over a range of 10^3^ M^−1^s^−1^. The differences in reactivity can be logically explained by the activating effect of the methyl substituents.

On heating, the endoperoxides decompose quantitatively back to starting materials.

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