3, 5-dimercapto structure

The tautoraerism of certain difunctional derivatives of l-thia-3,4-diazole has received considerable attention. Pala assigned structure 156 to 2,5-dimercapto-l-thia-3,4-diazole on the basis of infrared spectral data, and Thorn" reached the same conclusion by comparing its ultraviolet spectrum (measured in ethanol) with those of the four possible methylated derivatives. However, the infrared spectrum of a chloroform solution of the parent compound showed bands at 2600-2550 cm indicating an SH group and the probable occurrence of form 157 under these conditions, and this conclusion is supported by the occurrence of SH bands in solid state spectra obtained by Swiss investigators. For a summary of earlier work on these compounds, see reference 187. 

Tungsten, tris(2,3-dimercapto-2-butenedinitrile)-structure, 1,63 Tungsten alkoxides physical properties, 2,346 synthesis, 2,339... 

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... 

Mono- and di-thiocyanato-1,2,4-thiadiazoles, obtained by the stepwise action of cyanogen bromide on barium 3,5-dimercapto-l,2,4-thiadiazole, and on 5-chloro- and 5-hydroxy-3-mercapto-1,2,4-thiadiazole, are somewhat labile. The structures of certain of their transformation products (e.g. mono- and di-sulfides), which may have one of several isomeric forms, are not fully elucidated. The reactivity of their cyano group, resembling that in cyanogen halides, is noteworthy it is easily removed by the action of alkalis, the parent thiol being regenerated.202... 

Trimercaptosulfonium salts were prepared by reacting CI>S 1 salts with excess H2S248 [Eq. (4.67)]. According to calculation, the pyramidal structure of C3v symmetry is the energy minimum structure with the S—H bonds pointing toward the top of the pyramid. The corresponding dimercapto(methyl)sulfonium salts were also synthesized in an analogous way.249 The products were transformed into chlorothio derivatives [Eq. (4.68)]. 

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). 

Potential 2-hydroxy- and 2-mercapto-l,3,4-thiadiazoles have been examined both by infrared and by ultraviolet spectra in the solid state and in solution by Sheinker et They concluded that these compounds exist in the 2-oxo and 2-thione forms, respectively. To 2,5-dimercapto-l,3,4-thiadiazole the 2-mercapto-5-thione structure (155) was given. The structure of this compound has been the subject of some controversy. Stanovnik and TiSler have added some valuable arguments to the discussion. They measured the pKfl values of 155, its iV-methyl, iV -phenyl, and iV -phenyl-/S-methyl derivatives (156), and of the conjugate acids of these and the S-methyl derivative (pKn ) (Table III). In all compounds 156 with R = H, the infrared spectrum showed an absorption band near 2300 cm characteristic of the SH group. They also had pK i values near —1.5, Avhich in connection with the infrared evidence was taken as characteristic of an SH group in this situation. Since the 2,5-dithiol structure is excluded by ultraviolet spectral evidence, the 2-mercapto-5-thione structure (155) seems rather well established. It has previously been shown bj Thorn to predominate in chloroform solution, whereas he concluded that the dithione form (157) should predominate in ethanol solution. However, the pK i value for 155, — 1.36, makes it rather probable that Thorn used the monoanion of 155 instead of the acid itself for spectral comparison, and in that case his conclusions have a very weak foundation. 

Two water-soluble analogs of dimercaprol have been studied as lewisite antidotes, namely meio-2,3-dimercaptosuccinic acid (DMSA) and 2,3-dimercapto- 1-propane sulfonic acid (DMPS) (see review by Aposhian, 1993). Their structures are as follows ... 

The reaction of toluene-3,4-dithiol(3,4-dimercaptotoluene) and antimony trichloride in acetone yields a yellow solid Sb2(tdt)3, where tdt is the toluene-3,4-dithiolate anionic ligand (51). With the disodium salt of maleonitriledithiol ((Z)-dimercapto-2-butenedinitrile), antimony trichloride gives the complex ion [Sb(mnt)2]- , where mnt is the maleonitriledithiolate anionic ligand. This complex has been isolated as a yellow, crystalline, tetraethyl ammonium salt. The structures of these antimony dithiolate complexes have apparendy not been unambiguously determined. 

Tetrols Having Two Additional, Like Substituents. A cyclohexanetetrol disubstituted with substituent Y, of the type CaHa(OH)4Y2, can have three structures, and the predicted number of diastereoisomers is 20 ortho, 20 meta, and 14 para. Known compounds of this type include dimercapto-,... 

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