Thiazole-5-sulfonic acids, preparation

Direct sulfonation of thiazole, as well as of 2-substituted thiazoles, leads mostly to substitution m the 5-position (330-332). 4-Thiazole sulfonic acid has been prepared through direct sulfonation of 2.5-dibromothiazole with subsequent Rane% Ni reduction (330). Sulfonation of 2.5-dimethyl- and 2-piperidyl-5-methylthiazoles affords the corresponding 4-sulfonic acids as barium salts (247). The 2-hydroxy group facilitates the sulfonation (201. 236). When the 4- and 5-positions are occupied direct sulfonation can occur in the 2-position. 5-hydroxyethyl-4-methyl-2-thiazole sulfonic acid has been prepared in this manner (7). 

Although sulfonation of thiazole only takes place under forcing conditions, it is possible to prepare 5-thiazole sulfonic acids using SO3 as sulfonating agent. The reaction must be carried out using three equivalents of sulfur trioxide. The use of one equivalent of sulfur trioxide leads exclusively to the formation of the thiazolium salt <87KGS1353>. 

Various types of dyes are prepared from dehydrothiotoluidine. The free base or its sulfonic acid is diazotized and coupled with various naph-tholsulfonic acids such as, for example, e acid (l-naphthol-3,8-disul-fonic acid). The resulting dye is characterized by its high purity of color and can be discharged to a pure white. Such red direct dyes are sold under various names, and are usually referred to as dyes of the erika red type. (Erika Z is the combination from dehydxothioxylidine and e acid. l-Naphthol-3,6-disulfonic acid gives a very similar dye.) In addition to the true azo dyes from dehydrothiotoluidine, two other products are made which are important yellow dyes. One of these dyes is the naphthamine yellow NN (also called chloramine yellow) (Kalle), formed from dehydrothiotoluidinesulfonic acid by oxidation with sodium hypochlorite. The other is thiazole yellow or Clayton yellow, which is made by combining the diazo compound of dehydrothiotoluidinesulfonic acid with a second molecule of the same compound to form a diazoamino compound. 

Ring opening of l,3-thiazole-5(4ff)-one 91 with a-aminoalkyl esters 92 in the presence of 1-hydroxybenzotriazole and iV-ethyl diisopropylamine gives the endothiotripeptide 93 (Eq. 32) [54]. The starting compound 91 is prepared by the ( )-camphor-10-sulfonic acid-catalyzed cydization of endodipeptide.The reaction with 92, where a bulky alkyl group is introduced to the carbon atom... 

Padwa and co-workers used pyrrolothiazole 108 (R = Me) to prepare sulfone 109 (Fig. 4.38). However, attempts to extmde sulfur dioxide from 109 to form the novel dipole 110 were unsuccessful. Gyorgyde and colleagues converted a series of 2-substituted 3-acyl-l,3-thiazolidine-4-carboxylic acids 111 into the corresponding pyrrolo[l,2-c]thiazoles 113 via munchnones 112, which were trapped with DMAD (Fig. 4.39). 

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