Aromatic reactivity. Part LI. Nitrosodesilylation as a route to nitrodesilylation products from aryltrimethylsilanes and nitric acid in acetic anhydride

Abstract

A detailed study of the reaction between p-tolyltrimethylsilane and nitric acid in acetic anhydride has shown that the formation of the nitrodesilylation product, p-nitrotoluene, takes place predominantly, and possibly exclusively, via nitrosodesilylation. Thus, (i) when the mixture of nitric acid and acetic anhydride was heated briefly to 100° then used at 15°, the ratio of nitrodesilylation to nitration product (2-nitro-4-trimethylsilyltoluene) was 90, (ii) when the mixture was made up and used at 15° the ratio was 0·64, (iii) when the mixture was made up and used at 15° but with urea present, the ratio was 0·14, and (iv) when the mixture was made up at 15° and nitrous fumes were dissolved in it before use at 15° the ratio was 4·8. With a solution of nitrous fumes in acetic acid–acetic anhydride, only the nitrodesilylation product was formed. The p-nitrotoluene formed in the reaction with solutions of acetyl nitrate or dinitrogen pentoxide also seems to be produced predominantly and exclusively through nitrosodesilylation.

The reactions between nitric acid and phenyltrimethylsilane, m-methyl-, m-chloro-, or p-chloro-phenyltrimethylsilane in acetic anhydride have been more briefly studied, but the results are again consistent with the assumption that the formation of nitrodesilylation products involves initial nitrosodeilylation. In the reaction with a solution of nitrous fumes in acetic acid–acetic anhydride, p-tolyl- is ca. 50 times as reactive as phenyl-trimethylsilane.