Sulfonation of 1- and 2-naphthol and their methanesulfonate esters with sulfur trioxide. The influence of initial sulfation on the sulfo-product composition

Article abstract of DOI:10.1002/recl.19931120302

The sulfonation of 1- and 2-naphthol with sulfur trioxide in C(2)H3NO2 has been studied by using 1H NMR. 1-Naphthol (1) yields, upon reaction with 1.0 mol-equiv of SO3, a mixture of 2- and 4-sulfonic acids (2- and 4-S); upon increasing the reaction temperature, the relative amount of 2-S increases.Upon reaction with 4.0 mol-equiv of SO3, the initially observed products are the hydrogen sulfate 1-O,2,4-S3 and some corresponding sulfonic anhydrides.After prolonged reaction times, some 1-O-4,7-S3 is formed. 2-Naphthol (3), upon reaction with 1.0 mol-equiv of SO3, yields a 85:15 mixture of 1-S and 8-S, whereas upon reaction with 2.0 mol-equiv of SO3, a 8:14:78 mixture of 5-S, 6-S and 8-S are formed.Sulfonation of 3, either by (i) reaction with 1.2 and, subsequently, an additional 2.0 mol-equiv of SO3, or (ii) by direct addition of 4.0 mol-equiv of SO3, yields a mixture of the carbyl sulfates 5-5-S and 5-6-S and the hydrogen sulfate 3-O,6,8-S3, the relative yield depending on the method used.The results are discussed in terms of initial formation of the corresponding naphthyl hydrogen sulfates and on the basis of a comparison with the reactions of 1- and 2-naphthyl methanesulfonates, the chosen model compounds for the hydrogen sulfates, with SO3.