Abstract
The sulfonation of 1‐ and 2‐naphthol with sulfur trioxide in C^2^H~3~NO~2~ has been studied by using ^1^H NMR. 1‐Naphthol (1) yields, upon reaction with 1.0 mol‐equiv of SO~3~, 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 SO~3~, the initially observed products are the hydrogen sulfate 1‐O,2,4‐S~3~, and some corresponding sulfonic anhydrides. After prolonged reaction times, some 1‐O‐4,7‐S~3~, is formed.
2‐Naphthol (3), upon reaction with 1.0 mol‐equiv of SO~3~, yields a 85: 15 mixture of 1‐S and 8‐S, whereas upon reaction with 2.0 mol‐equiv of SO~3~, a 8: 14: 78 mixture of the 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 SO~3~, or (ii) by direct addition of 4.0 mol‐equiv of SO~3~, yields a mixture of the carbyl sulfates 5‐5‐S and 5‐6‐S and the hydrogen sulfate 3‐O,6,8‐S~3~, 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 SO~3~.