Hydrocarbons acetoxylation

More information has appeared concerning the nature of the side reactions, such as acetoxylation, which occur when certain methylated aromatic hydrocarbons are treated with mixtures prepared from nitric acid and acetic anhydride. Blackstock, Fischer, Richards, Vaughan and Wright have provided excellent evidence in support of a suggested ( 5.3.5) addition-elimination route towards 3,4-dimethylphenyl acetate in the reaction of o-xylene. Two intermediates were isolated, both of which gave rise to 3,4-dimethylphenyl acetate in aqueous acidic media and when subjected to vapour phase chromatography. One was positively identified, by ultraviolet, infra-red, n.m.r., and mass spectrometric studies, as the compound (l). The other was less stable and less well identified, but could be (ll). 

Similar acetoxylations have been reported for several other aromatic ethers, amines and polynuclear hydrocarbons and more complex reaction products have also been identified, although kinetic data are lacking. 

Acetoxylation of Alkenes, Dienes and Aromatic Hydrocarbons 61.3.4.3.1 Vinyl acetate from ethytene... 

As an example, it has been suggested 37-) that many anodic substitution reactions of aromatic hydrocarbons are ECEC processes, as shown below for anodic aromatic acetoxylation Eqs. (2-5) ) ... 

Table 1 Isomer Ratios for Oxidative Acetoxylation or Aromatic Hydrocarbons...

Acetoxylation of hydrocarbons. I n a paper of 1923Dimroth reported preliminary observations on the oxidation of aromatic hydrocarbons and olefins with lead tetraacetate. Toluene, he found, affords benzyl acetate in very low yield oxidation of diphenylmethane and triphenylmethane proceeded more readily but offered nothing of preparative promise. Dimroth observed also that anethole reacts to give in small yield a product of addition of two acetoxyl groups to the olefin linkage. 

Rudolf Criegee worked for the doctorate with Dimroth at Wurzburg on the mechanism of diazo coupling, but the results were initially recorded only in his dissertation (1925). He then undertook a comprehensive investigation of the reaction of lead tetraacetate with olefins and aromatic hydrocarbons and in 1930 at the age of 28 presented the results in his first publication, a40-page nnu/en paper. The results were hardly commensurate with the effort and experimental skill evident from the paper. Cyclohexene reacted in part by addition of two acetoxyl groups, as noted by Dimroth, to give a mixture of cis and trans products (2), and in part by... 

Under slightly different conditions, using 1,3-propanedithiol, acyloins and acyloin acetates lead to the formation of 1,3-dithianes where hydrogen has replaced the hydroxyl or acetoxyl groups . Hydrolysis to the ketone provides a method of converting acyloins to ketones and desulphurization allows conversion of acyloins to hydrocarbons (equation 10). Reduction of l,l-dimethyl-5-hydroxysila-4-cycloheptanone gave l,l-dimethylsila-4-cycloheptanone by this method (equation 11) . A similar reaction is believed to be involved in the action of D-proline reductase . ... 

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