Mechanism sulphonation, aromatic

The mechanism of aromatic sulphonation is complex and may vary, e.g. with the concentration of water or oleum in the acid, the temperature, and the hydrocarbon. One active agent is SO3, and one simplified route may be ... 

The mechanism of aromatic sulphonation is broadly analogous to that previously described for aromatic nitration and halogenation and may be represented in the following way, the neutral sulphur trioxide molecule functioning as the electrophilic species. Sulphonation differs from nitration and halogenation, however, in that the overall reaction is reversible. 

A kinetic study of the desulphonation of 2-naphthylamine-l-sulphonic acid by hydrochloric, sulphuric and phosphoric acids showed the rate to be proportional to the concentration of hydrogen ions and the aromatic and a mechanism involving the formation of 1-naphthylsulphamic acid was proposed702. 

A further route to compounds with an aromatic ring A lies in an unusual acid-catalysed rearrangement of steroidal A -3-ketones. Testosterone (35) is reported to give the 4-methyl aromatic compound (36) with trichloroacetic anhydride in the presence of toluene- -sulphonic acid [178]. The mechanism of this reaction is not clear. 

A mechanism of action for the r-deficient 2-heteroaryl derivatives was postulated based upon the reaction of 6-(2-pyridyl)methylene penicillanic acid sulphone (28) with sodium methoxide (Scheme 6.14) [46]. Chen and co-workers proposed that after bimolecular interaction between the enzyme and (28), an aromatic acyl-enzyme ester (76) is obtained. This conjugated... 

Important for industry is the reaction of the substitution of a nilro group by a sulphonic group as was described in Vol. I (pp. 201, 207). The mechanism of the reaction is now given in the chapter dedicated to the manufacture of TNT and other higher nitrated aromatics. 

Aromatic sulphonic acids (X = SO3H) for example, are isomerized in this way. The change of position in the aromatic ring of the tertiary alkyl groups and bromine likewise cannot be confined as intramolecular mechanism with successive 1,2-shifts of the migrating group. Thus, the interconversions of ortho- and para-disubstituted benzenes with substituents of the above type proceed faster than their conversion into a thermodynamically more stable meta isomer... 

Sulphonation of aromatic compounds takes place using oleum or sulphuric acid containing excess of sulphur trioxide. Mechanism of sulphonation involves the following steps. 

The carbonyl group of aromatic aldehydes with electron-withdrawing substituents on the aromatic ring may, contrary to previous reports, act as a dienophile in a Diels-Alder reaction, giving dihydropyran derivatives, e.g. (128). Toluene-4-sulphonic acid catalyses several of these reactions and it is clear that two mechanisms must operate for this type of cycloaddition (thermal [4 +2], and acid-catalysed). 

Chen, Y., Wu, Z., and Yu, K., Effect of Mechanism of Concrete Admixtures Based Aromatic Hydrocarbon Sulphonate, 9th Int. Congr. Chem. Cements, New Delhi, IV 550-556 (1992)... 

Reaction at Sulphur.—The oxidation of benzo[6]thiophens to sulphoxides by t-butyl hypochlorite has been studied. In the presence of a ruthenium catalyst, dibenzothiophen was oxidized by oxygen to the sulphone. The reactions of benzo[ >]thiophen 1,1-dioxides with various reagents such as amines, amino-alcohols,3-aminopropylsilanes, and aromatic sulphonyl chlorides have been studied. Four detailed papers on the reaction of dibenzophenonium salts with aryl-lithiums have appeared in which the mechanism of ligand exchange was elucidated. " ... 

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