Sulfonation of 1, 2‐(methylenedioxy)benzene, 1, 2‐(ethylenedioxy)benzene, 2‐methylanisole, 2, 3‐dihydrobenzofuran, chromane, benzo‐15‐crown‐5 and dibenzo‐30‐crown‐10 in concentrated sulfuric acid and with sulfur trioxide

Abstract

AbstractThe sulfonation of 1, 2‐(methylenedioxy)benzene (2), 1,2‐(ethylenedioxy)benzene (3), benzo‐15‐crown‐5 (4), 2‐methylanisole (5), 2,3‐dihydrobenzofuran (7), 2, 3‐dihydrobenzopyran (chromane, 8) and dibenzo‐30‐crown‐10 (9) in concentrated sulfuric acid and with sulfur trioxide mainly in nitromethane has been studied. Upon dissolution in sulfuric acid, 3 yields a mixture of 3‐3‐sulfonic acid (3‐3‐S) and 3–4‐S in a ratio of 0.8, independent of the H2SO4 concentration. In sulfuric acid with a concentration greater than 83% H2SO4, the two monosulfonic acids both eventually yield 3‐3,5‐S2. The ratio of rate coefficients of sulfonation of 3‐3‐S and 3‐4‐S is approximately 70. The reaction of the crown ethers 4 and 9 in sulfuric acid leads to formation of 4‐4‐S and to an equimolar mixture of 9‐4,4′‐S2 and 9‐4,5′‐S2, respectively.Sulfonation of 5 in 85 and 98% H2SO4 yields a mixture of 5–4‐S and 5‐5‐S in a ratio of approximately 7:1 and 11:1, respectively; in 98% H2SO4, these products are converted into 5‐4,6‐S2 and 5‐3,5‐S2, respectively. On dissolving 5 in 105% H2SO4, the initially observed product is 5–4,6‐S2, which exhibits O demethylation.Sulfonation of both 7 and 8 in 85% H2SO4 yields a mixture of 4‐S and 6‐S in an initial ratio of 1.4. These acids eventually yield 7‐4,6‐S2 and 8‐4,6‐S2. The rate coefficients of sulfonation of 7‐6‐S and 8‐6‐S are both approximately 50 times those of the corresponding 4‐sulfonic acid isomers. Upon sulfonation with 1.0 equiv of SO3 in nitromethane, all the substrates studied yield the corresponding 4‐sulfonic acid. Upon reaction with 2.0‐4.0 equiv of SO3, 2, 3, 7 and 8 all yield the 4,6‐S2 almost quantitatively; 4 does not yield any disulfonic acid. Reaction of 9 with ≥2.0 equiv of SO3 yields a 1:1 mixture of 4,4′‐S2 and 4,5′‐S2.The routes of the sulfonation of 1,2‐(methylenedioxy)‐ (2) and 1, 2‐(ethylenedioxy)benzene (3) and their monosulfonic acids have been compared with those of 1,2‐dimethoxybenzene (1) and its 4‐sulfonic acid and the differences are discussed in terms of the Curtin‐Hammett principle. The differences observed between the mono‐ and disulfonation of 2,3‐dihydroxybenzofuran (7) and 2,3‐dihydrobenzopyran (8) on the one hand and those of 2‐methylanisole (5) on the other are discussed along similar lines.