Issue 5, 1985

Aromatic sulphonation. Part 92. Sulphonation of the three methylphenols and the six dimethylphenols in concentrated aqueous sulphuric acid; and the lsomerization of some of the resulting sulphonic acids and of m-xylene-2-and o-xylene-3-sulphonic acid

Abstract

The isomer distributions for the mono- and di-sulphonation of the three methylphenols in 81.6–90.0% sulphuric acid and of the six dimethylphenols in 84.9% sulphuric acid at 35 °C have been determined by means of 1H n.m.r. spectroscopy. Products that would result from demethylation, disproportionation, or ipso-substitution have not been observed. The monosulphonation isomer distribution of each of the three methylphenols is independent of the sulphuric acid concentration. 2,4-Dimethylphenol in 84.9% H2SO4yields 19% 5- and 79% 6-sulphonic acid, and 2,6-dimethylphenol yields 28% 3- and 72% 4-sulphonic acid. With the phenols (2), (3), (5), and (7), which have positions both ortho and para to the –OH substituent available for sulphodeprotonation, the yield of ortho-substitution is relatively high, viz. 44, 45,36, and 27%, respectively. The mono- and di-sulphonic acids of which the sulpho group is between the –OH and an –Me group are unstable under the reaction conditions employed, with the exception of the 3,5-dimethylphenol-2-sulphonic acid. It is proposed that their isomerization proceeds by protiodesulphonation followed by resulphonation to yield the more stable sulphonic acid isomer(s). From a kinetic analysis of the calculated first-order rate coefficients for protiodesulphonation, it is concluded that the unprotonated substrate species is the entity undergoing the protiodesulphonation.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1985, 669-675

Aromatic sulphonation. Part 92. Sulphonation of the three methylphenols and the six dimethylphenols in concentrated aqueous sulphuric acid; and the lsomerization of some of the resulting sulphonic acids and of m-xylene-2-and o-xylene-3-sulphonic acid

H. J. A. Lambrechts, Z. R. H. Schaasberg-Nienhuis and H. Cerfontain, J. Chem. Soc., Perkin Trans. 2, 1985, 669 DOI: 10.1039/P29850000669

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