Peracetic acid, pyrolysis

Sauers (1959) has now oxidised camphor directly to the a-campholide by means of peracetic acid. It is also of interest to note that Otvos et al (i960) have shown, using labelled. - CH2C 02H (lkc), that in the pyrolysis of the calcium salt of homocamphoric acid to camphor, it is the labelled carboxyl group that is lost. 

V-oxides of alkaloids could be easily prepared using w-chloroperbenzoic or peracetic acids 17, 24). On pyrolysis of the (V-oxide of dimethylodecodine a mixture of products was obtained, and only dimethyldecodine (14) could be characterized. 

C. A. McDowell and J. B. Farmer, Fifth Symposium (International) on Combustion, p. 453, op. ciL, have shown the formation of peracetic acid as the principal initial product in the photosensitized and thermal oxidation of acetaldehyde. (See also earlier papers of McDowell and Farmer.) J. Grumcr, ibid, p. 447, also showed that, at low O2 content, C2H4, C He, CO, CH4, CH,OH, CHsCHO, and CH,CH2CHO were important products from propane pyrolysis in the range 350 to 475 C. He also found considerable amounts of acetic acid from the oxidation of CHaCHO in mixtures at 130 to 450 C having about 3 per cent O2. Such I0W-O2 mixtures are, of course, ideal for observing sensitized pyrolysis reactions. 

The synthesis of the initial compound (277) can be effected in three ways (Scheme 106). The first of them consists in the reduction with alkali metals and alcohol of 2,6-dimethoxynaphthalene (280) [79, 950, 951]. The second method starts from 6-methoxytetralin (275) which, on treatment with lead tetraacetate, gives the acetate (276) which forms compound (274) when acetic acid is split out oxidation of the latter with perbenzoic acid and pyrolysis leads to the desired product (277) [952, 953]. The most suitable method for large amounts proved to be the third method, starting from 6-methoxy-1-tetralone (272), the synthesis of which has been described in Chapter II (Scheme 1). The tosylhydrazone (273) obtained from it, on being heated with sodium glycolate and subsequently distilled in vacuum over potassium bisulfate gives the tetraene (274), which, on oxidation with peracetic acid and treatment of the reaction product with hydrochloric acid forms the ketone (277) [954]. 

Another way to get citronellol is by the reductive dimerization of isoprene with formic acid and triethylamine using a 1% pcdladium phosphine catalyst [32]. The two head-to-tail dimers are formed in up to 79% yields, which can easily be separated from the head-to-head and tail-to-tail dimers by conversion with aqueous hydrochloric acid, yielding 7-chloro-3,7-dimethyl-l-octene. Hydroboration and pyrolysis of this chloro derivative produces a 1 3-mixture of a- and jS-citronellol. The mono-chloro compound can also be oxidized with tert- mty peracetate and a cuprous bromide catalyst to the chloroacetate, which is reduced with LiAJH4 and pyrolyzed to linalool in 64% overall yield. 

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