Alkoxy-1,2,3,4-thiatriazoles

Similar decomposition of alkylthio- and alkoxy-thiatriazoles should yield thiocyanates and cyanates, but they may rearrange to the isocompounds and polymerize (see Sections IV, D and V). 

The highly explosive 5-chloro-l, 2,3,4-thiatriazole (prepared from thiophosgene and sodium azide) has been used for the preparation of 5-substituted 1,2,3,4-aminothiatriazoles and certain 5-alkoxy-thiatriazoles (Section 4.19.7). Great care should be exercised in handling any reaction product of thiophosgene and azide ion. In particular the reaction of 5-chloro-l,2,3,4-thiatriazole with azide ion yielded a product assumed to be 5-azido-l,2,3,4-thiatriazole which gave rise to explosion as a suspension in water (61J0C1644>. 

The thermal degradation of isotopically labeled 5-isobutoxy-thiatriazole15 and the kinetics of the decomposition of 5-alkoxy thiatriazoles have been studied16 (Section III, A). 

Xanthogenhydrazides, RO-CS NHNH2, give 5-alkoxy-l,2,3,4-thiatriazoles on treatment with nitrous acid, and dithiocarbazinic esters, RS-CS-NHNH2, give 5-alkylmercapto-l,2,3,4-thiatriazoles. ... 

Sodium azide does not react with carbonyl sulfide to form 5-hydroxy-1,2,3,4-thiatriazole, nor with carboxymethyl xanthates, RO-CS SCH2COOH, to form 5-alkoxy-l,2,3,4-thiatriazoles. The latter, however, could be prepared from xanthogenhydrazides (RO-CS NHNH2) and nitrous acid. They are very unstable and may decompose explosively at room temperature only the ethoxy compound (6) has been examined in detail. This is a solid which decomposes rapidly at room temperature and even at 0°C is transformed after some months into a mixture of sulfur and triethyl isocyanurate. In ethereal solution at 20° C the decomposition takes place according to Eq. (16)... 

The first synthesis of ethyl cyanate48 from 5-ethoxythiatriazole49 was briefly mentioned in the previous review of thiatriazoles.1 The thiatriazole decomposes smoothly in ethereal solution at 20° with formation of nitrogen, sulfur, and ethyl cyanate. Although several other methods are now available for the preparation of both alkyl and aryl cyanates the thiatriazole method prevails as the most generally applicable for the thermally and chemically sensitive alkyl cyanates, since the only by-products are inert—sulfur and nitrogen. Thus a number of 5-alkoxy,50-54 5-aryloxy,55-57 and 5-aralkoxythiatriazoles12,53 have been prepared. 

The only data on hand to distinguish between the two mechanisms are the kinetic studies of Jensen on a variety of 5-alkoxy- and on 5-phenoxy-l,2,3,4-thiatriazoles. The energies of activation and the activation entropies are nearly the same for all compounds studied = 24-6 kcal mole" and = 4-4 e.u. Jensen interprets this as indicating a stepwise mechanism, in which thioacyl azide is formed in... 

Of the higher aza-compounds, only derivatives of 1,2,3,4-thiatriazole are well defined, but even here alkyl derivatives decompose at or below 0 C, though 5-aryl- and amino derivatives are generally fairly stable. Many other derivatives are, however, dangerously explosive, for example the 5-chloro and thiolate derivatives. The controlled decomposition of 5-alkoxy-l,2,3,4-thiatriazoles (for example the 5-ethoxy-derivative in ether at 20 C) has been recommended as the best preparation of pure alkyl cyanates thermal decomposition of 5-aryl compounds gives the corresponding nitrile. ... 

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