Side chain nitration of polymethylbenzenes in nitric acid-acetic anhydride mixtures

Abstract

Product distributions resulting from nitration of polymethylbenzenes in nitric acid-acetic anhydride mixtures have been determined by gas chromatography. Nitration of a methyl group occurs in all the substrates studied; such nitration occurs only at a methyl group para to the methyl most activated to ipso nitration. These results support the view that side chain nitration occurs through the diene intermediates which lead to ring acetoxylation.

Nitration of the tetramethylbenzenes in acetic anhydride. Formation and rearomatization of adducts

“…Moreover, the adducts, when isolated, were prone to decomposition via rearomatization, particularly so when allowed to warm to room temperature, and this complicated the investigation of their physical properties and reactions. The failure of previous attempts (7) to detect the tetramethylbenzene adducts is easily understood. There are two different ipso positions (I and 2) in prehnitene which are of comparable reactivity.…”

“…However, this was likely formed from the 2,5 adduct, a secondary acetate, which by elimination of nitrous acid can form the aryl acetate without rearrangement. In the earlier work (7) on nitration of the tetramethylbenzenes aryl acetate was obtained from each substrate. Here rearomatization of the adducts occurred during the reaction and/or on work-up.…”

“…In acetic anhydride solution iyso-nitration leads to the formation of 1,4-acetoxynitro adducts which, in favourable cases, may be isolated (2-4) but which are prone to undergo rearomatization leading to 'abnormal' nitration products (2-6). In an earlier study of the nitration of the tetramethylbenzenes in acetic anhydride substantial amounts of aryl acetates and side-chain nitro derivatives were found (7). In the cases of 11-xylene and pseudocumene (1,2,4-trimethylbenzene) it was shown (2b, i, k) that such derivatives are secondary products obtained via the formation and rearomatization of adducts (Scheme 1) and it seemed clear that adducts must be formed in the cases of the tetramethylbenzenes although attempts to detect them were not successful (7).…”

“…In an earlier study of the nitration of the tetramethylbenzenes in acetic anhydride substantial amounts of aryl acetates and side-chain nitro derivatives were found (7). In the cases of 11-xylene and pseudocumene (1,2,4-trimethylbenzene) it was shown (2b, i, k) that such derivatives are secondary products obtained via the formation and rearomatization of adducts (Scheme 1) and it seemed clear that adducts must be formed in the cases of the tetramethylbenzenes although attempts to detect them were not successful (7). The high yields of 'abnormal' products obtained, reaching 75% in the case of prehnitene (1,2,3,4-tetramethylbenzene), and (Table 1) predictions based on partial rate factors for attack at ipso, ortlzo, meta, and yam positions (8) indicated that potentially large amounts of adducts should be found with the tetramethylbenzene substrates.…”

Ipso nitration. XX. Nitration of 5-tert-butyl-1,2,3-trimethylbenzene in acetic anhydride. Formation and rearomatization of adducts

“…Thus it is clear that the nitrite 5 is the major primary aromatic product over the complete acidity range investigated. Benzyl nitrite itself is known to undergo autodecomposition to benzaldehyde (16) and benzaldehydes often accompany benzylic products obtained from rearomatization of diene adducts (3,4,11,17). The benzyl alcohol 8 which was obtained on work-up of the reaction to which 0.057, sulfuric acid had been added also appears to have been formed from 5.…”