Amino-aromatic sulphonic acids, reactions

Diazotization.—Like aniline and other aromatic primary amines they undergo diazotization. The resulting diazo compounds undergo the various diazo reactions (p. 601) by means of which the naphthalene group becomes coupled as an azo compound with other naphthalene or benzene rings. These azo compounds are dyes. The most important dyes of this group are derived from mixed amino and sulphonic acid or mixed amino and hydroxyl derivatives of naphthalene and will be considered a little later. Not only, however, may the naphthylamines >deld diazo compounds and through them azo compounds but they may be coupled as azo compounds with a diazotized benzene compound. 

Studies in aromatic sulphonation include full details of the rearrangement of sodium 1-naphthylsulphamate into the 4-sulphonate in dioxan-sulphuric acid, where S-studies show that the reaction is partly intramolecular. There are few syntheses of natural products offering an opportunity for employing aromatic sulphonation as an essential step, though a recent synthesis of the demethyl derivative establishes the structure of aeruginosin B as 2-amino-6-carboxy-10-methylphenazinium-8-sul-phonate. Ionization of aromatic sulphonic acids in aqueous sulphuric acid has been studied by u.v. spectroscopy, showing that the benzo-phenone H% and the acidity functions are followed substituent effects are small (Hammett p-value 0.7 0.2). 

The displacement of aromatic amino groups by sulphite, to form a sulphonic acid (or a sulphonate salt), gives rise to the genetic hazard of sulphites. Deamination or dehalogen-ation of the aromatic rings in nucleosides is a very facile reaction in which sulphonic acid salts are produced, either in vivo or in vitro192 199. For example, cytosine reacts with sodium sulphite to form the 6-sulphonate, by deamination, as shown in equation 28. 

Various dehydrating agents—concentrated sulphuric acid, zinc chloride, phosphorus pentoxide—can be used. Sulphuric acid, although perhaps the most convenient, has the disadvantage that it tends to sulphonate the aromatic substances employed. At a low temperature, however, diphenylmethane can be obtained from benzyl alcohol and benzene. At 140° phosphorus pentoxide condenses benzene and diphenylcarbinol to triphenylmethane (see B., 7,1204). Not only substituted benzyl alcohols, but even mandelic acid can be brought within the scope of the reaction, while in place of benzefte its nitro, amino or phenolic derivatives may be used. 

Dehydroabietic acid can undago typical aromatic substitution reactions (e.g. acylation, chlorosulphonation, sulphon-ation and nitration) with prefoential functionalization of the more reactive 12 position, followed in some cases by the 14 position. These reactions were first exploited in the 1930s-1940s [5, 12-14]. The nitration of dehydroabietic acid (Fig. 4.6) was one of the first reactions studied because of the synthetic vCTsatility of the nitro group, namely as precursor of amino groups [14]. More recently, this reaction has been optimized using less harsh conditions [15,16]. 

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