Sulphonic acids, 1-Naphthalenesulphonic acid

P-Bromonaphthalene. The preparation from p-naphthylamine, which has carcinogenic properties, is avoided by the use of 2-naphthylamine-1-sulphonic acid ( 2-amino-1-naphthalenesulphonic acid ) the latter is obtained commercially by cautious treatment of p-naphthol with sulphuric acid—the SOjH group first enters the 1-position—followed by the Bucherer reaction. Diazotisation and reaction with cuprous bromide yields 2-bromonaphthalene-l-sulphonic acid heating with sulphuric acid eliminates the sulphonic acid group to give 2-bromonaphthalene. 

Reductive desulphonation of naphthalenesulphonic acids is also observed [84]. The 1-sulphonic acid substituent in a wide range of sulphonated naphthylamines is removed by reduction at mercury in aqueous sodium hydroxide [85], Reductive... 

Naphthalenesulphonic Acids, C10H7.SO3H.—The effect of the temperature at which sulphonation is carried out on the position taken by the entering group, is well shown in the case of naphthalene. When the hydrocarbon is heated with concentrated sulphuric acid at 80°, the chief product of the reaction is the a-acid at 160° the /3-acid is chiefly formed. The acids form hygroscopic crystals. They are prepared in large quantities in the manufacture of the naphthols and the naphthylamines. 

Many steroid secondary alcohols are resistant to acid-catalysed dehydration, but can be converted into olefins by elimination reactions of their sulphonate esters, usually the toluene 3 -sulphonate ( tosylate ) or methanesulphonate ( mesylate ). These elimination reactions always accompany attempted nucleophilic substitution of the sulphonate (p. 41), and can be made to predominate by appropriate choice of reaction conditions. Activated alkaline alumina has been used to prepare A - and AH-olehns from the sulphonates of 3 - [131] and i2a-alcohols [132]. In the latter case the naphthalene-i-sulphonate was most effective, and the methanesulphonate distinctly less so, suggesting that steric acceleration occurs with the more bulky naphthalenesulphonate [ 132c]. This view is strengthened by the enhanced efficiency of elimination of a i2a-sulphonate in the presence of a 17a-methyl group, which increases the compression at C(i2) [132b]. The mechanism and stereochemical features of these heterogeneous reactions have not been described in detail. 

The reactions of the naphthalenesulphonic adds are similar to those given above under benzenesulphonic add. It is still to be mentioned that the a-add is converted into the /8-add by heating with concentrated sulphuric add to almost 2000 a reaction which is explained by the feet that the sulphonic add decomposes in the small amount of water always present, into naphthalene and sulphuric acid, and that the former is then sulphonated to the /8-add at the higher temperature (2000). The sulphonation of naphthalene to the a-and /3-adds is carried out on the large scale in technical operations, since when fused with sodium hydroxide these adds yield naphthols of great importance for the manufacture of dyes. The next preparation deals with this reaction. 

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