Mercaptotetrazoles

In addition to chemical and spectral sensitizers, several other classes of chemical compounds are added to emulsions before coating. Additives are used to facihtate coating operations, eg, surfactants (qv) and viscosity enhancers to reduce spontaneous development ia unexposed regions, eg, tetraazaiadenes and mercaptotetrazoles and to reduce abrasion and permit high temperature processing, eg, aldehydes (qv). 

Accordingly, 5-substituted-amino-l,2,3,4-thiatriazoles (Tables III and IV) are formed quite generally from 4-substituted-thiosemicarb-azides. When the substituent is an aryl group these initial products are isomerized to 5-mercaptotetrazoles on treatment with alkali whereas this is not the case when the substituent is an alkyl group. 

As shown by Oliveri-Mandalli,and by Lieber et al., 5-sub-stituted-amino-l,2,3,4-thiatriazoles are also formed by reaction of isothiocyanates with hydrazoic acid. When sodium azide is used instead of the free acid the isomeric mercaptotetrazoles are formed. 

Sodium l-methyl-5-mercaptotetrazolate reacts with species 194 to yield the neutral complex 195 (99P749). Similar species are known [96JGS(D)1011, 98IGG873)]. 

In a purer state, it may be prepd by acidifying the Na salt of mercaptotetrazole with sulfuric acid (see below). Forms salts, some of which are si expl (see below)... 

Sodium Mercaptotetrazole. NaCHN4S, mw 124.11, N 45.15% colorl needles. Can be prepd by adding to the prod of the reaction between methylmercaptotetrazole and aq hydriodic acid a sufficient amt of soda soln to make the reaction si alkaline (Ref 2). The resulting cryst compd cont 1.5 mols of w. It is sol in w and ale, less sol in abs ale, insol in eth. May be obtd in a very pure state by dissolving in w and pptg with eth. Such crysts would give pure 5-mercaptotetrazole on acidification with sulfuric acid Refs 1) Beil 26,409 2) M. Freund T. 

Several classes are known. Dimroth-type rearrangements occur by ring opening and reclosure so that one ring atom changes places with an exocyclic atom. The rearrangement of 5-phenylaminothiatriazole to l-phenyl-5-mercaptotetrazole in basic solution is reversible (Scheme 74). As the anion, the tetrazole system is the more stable whereas as the neutral species, the thiatriazole is more stable... 

The rearrangement of 5-phenylaminothiatriazole to l-phenyl-5-mercaptotetrazole in basic solution A58 has been shown to be reversible59 (Scheme 4). The mercaptotetrazole (11) rearranges rapidly in refluxing... 

N,C2H4N402 mw 148.16 N 37.82% white cryst (from ethanol) mp 120° (starts to sinter at 110°). V sol in ethanol, eth, chlf, benz, ligr and w, Prepn is by treating 5-methyl mercaptotetrazole with aq sulfuric acid. The compd forms several expl salts ... 

Hydroxy- and 5-mercaptotetrazoles and their mono-N1 -substituted derivatives can be involved into keto-enol and thiol-thione tautomeric equilibria (Equation 7). This is the reason for significant differences in chemical and physical properties of these compounds from other 5R-tetrazoles. 

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