Perthiocyanic acid

Persulfo-cyansaure, /. perthiocyanic acid, per-sulfocyanic acid, -molybditnsaure, /. per-thiomolybdic acid, tbiopermolybdic acid, -zyansaure, /. perthiocyanic acid. Perthiokoblensaure, /. perthiocarbonic acid, penianisch, a. Peru, Peruvian. 

Xanthanwasserstoff, m, xanthan hydride (perthiocyanic acid, CaHaNaSs). 

Amino and 5-amino-l,2,4-thiadiazoles both exist predominantly in the amino forms. The IR spectrum of 5-mercapto-l,2,4-thiadiazole does not show a clear SH absorption as would be expected for structure 6 and therefore the thione tautomers 7 and 8 have been suggested (Scheme 2). Similarly, IR evidence suggests that perthiocyanic acid exists as the dithione 9 as opposed to stmcture 10 <1984CHEC(6)463>. 

The interconversion between dithiazoles and thiadiazoles and the relationship between iso-perthiocyanic acid (294) and perthiocyanic acid (14) have been elucidated <82AHC(32)285>. A mixture... 

Synthesis from Thiocyanic Add (Isoperthiocyanic and Perthiocyanic Acids)... 

In the present account, isoperthiocyanic and perthiocyanic acid are formulated as 144 and 147, respectively. The salient facts supporting these structures are briefly discussed in Section III, J,l. 

Wohler143 first described the formation, from concentrated aqueous thiocyanic acid, of a compound, C2H2N2S3 later named isoperthiocyanic acid, and now formulated as 3-imino-5-thiono-l,2,4-dithia-zolidine (144). Solutions of isoperthiocyanic acid in alkali deposit sulfur this redissolves presently giving a liquid containing144-147 the salt of an isomeric acid, later named perthiocyanic acid, for which the 3,5-dimercapto-l,2,4-thiadiazole structure is now accepted (see Section III, J, 1). This acid, isolated from its barium salt by treatment with mineral acid and ether extraction,144,145 readily reverts to isoperthiocyanic acid,144 but fairly stable specimens are obtainable under carefully controlled conditions.148 148... 

The reaction has been further employed to convert 3-alkylthio-5-chloro- into 3,5-di(alkylthio)-l,2,4-thiadiazoles of unequivocal structure their identity with the di-S-alkyl derivatives of perthiocyanic acid has served to establish the structure of th latter91 (see Section III,J,I). 

Alkylation of mercapto groups in 1,2,4-thiadiazoles proceeds normally.71, 72 The reaction has provided authentic specimens of 3,5-di-methyl(or dibenzyl)mercapto-l,2,4-thiadiazoles, the identity of which with the /S-alkylation products of perthiocyanic acid provided evidence concerning the structure of the latter compound90 (see Section III,... 

The structure (342 R,R = Me or PhCH2) of the di- -ethers of perthiocyanic acid has been confirmed by Goerdeler and his co-workers.91 These compounds, which are the products of the alkylation of perthiocyanic acid (340) or its salts,144,147 were unequivocally synthesized (t) by the interaction of 3-alkyl(or aralkyl)thio-5-chloro-l,2,4-thiadiazoles (344 R = Me or PhCH2) with the appropriate thiols (R SH)91, and (ii) by alkylation of the monoethers (345 R = Me or... 

In the case of 5-thio derivatives, the IR spectra show no clear SH absorption as would be anticipated for (17a), and the thione structure (17b) or (17c) was tentatively assigned (Scheme 10) (73CJC2353). The IR spectrum in Nujol of perthiocyanic acid is considered to indicate that the dithione structure (18a) is favored over (18b) (63JCS3168). 

In 1821 Wohler discovered that a solid deposited from concentrated aqueous solutions of thiocyanic acid. The solid, which was called isoperthiocyanic acid (3-imino-5-mercapto-1,2,4-dithiazole) (361), formed a new product perthiocyanic acid (3,5-dimercapto-l,2,4-thiadiazole) (18) when treated with alkali and then acid. On storage perthiocyanic acid (18) readily reverted to isoperthiocyanic acid (361) (65AHC(5)119). The mechanisms of these interconversions are still not known with certainty but the transformations outlined in Scheme 130 are suggested. Wohler proposed the initial formation of a dimer of thiocyanic acid for which structure (359) appears resonable. Addition of the imine function of (359) to the nitrile function of HSCN would produce the trimer (360) which could readily eliminate hydrogen cyanide to produce isoperthiocyanic acid (361). 

Hantzsch s first important research was the synthesis of pyridine from acetoacetic ester and aldehyde ammonia, a general method of synthesis of pyridine derivatives. Coumarone, discovered by Fittig and Ebert (see p. 768), was (with some derivatives) synthesised by Hantzsch, who called it the fur-furane of the naphthalene series . He synthesised thiazole, and benzene, pyridine, and thiophen derivatives from derivatives of pentamethylene, and pyrrole, investigated tetrazoles, and perthiocyanic acid C2N2S3H2 (discovered by Wohler), giving it a cyclic structure." ... 

The dipotassium sail of 3,5-dimercapto-l,2,4-thiadiazole ( perthiocyanic acid ) (36) is most conveniently prepared by refluxing a solution of (31) in methanol with sulphur. The salt is readily chlorinated to the stable bis(sulphenylchloride) (37). The observations supplement and further clarify previous work on the synthesis of 1,2,4-thiadiazoles from thiocyanic acid (see Volume 1, p. 448 and ref. 15). 

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