Formamidine disulfide

In many cases, the a-haloketone does not appear to be an intermediate in this reaction, since reagents such as sulfur trioxide, sulfuric, or 60% nitric add lead to 2-aminothiazole but with lower yields (11 to 43%). Formamidine disulfide [-S-C(=NH)NH2]2, a product of the oxidation of thiourea, seems to be the intermediate in this reaction, since upon treatment with ketones, it gives 2-aminothiazole (604). However, the true mechanism of this reaction has not yet been completely elucidated. 

However, Sahasrabudhey thinks that the compound formed from 5-amino-1,2,3,4-thiatriazole does not have the composition CSN2H3CI, but (CSN2H4C1)2, and is in fact the dihydrochloride of formamidine disulfide, the oxidation product of thiourea. This con-... 

Formamidine disulfide (103) was also formed when 5-aminothiatriazole (10) was allowed to react with thiobenzoyl chloride in acetonitrile without addition of base (81BSB89>. Beer and Hart found that 5-aminothiatriazole (10) reacted with acetyl chloride or acetic anhydride to give 3,5-diace-tamido-l,2,4-thiadiazole (104 R = Me) while neither a thiapentalene (102) nor 5-acetamido-thi-atriazole was observed (Scheme 18) <77CC143). In contrast, L abbe and Vermeulen isolated 2,5-dimethyl-l,6-dioxa-6a-/, -thia-3,4-diazapentalene (102 R = Me) together with the 1,2,4-thiadiazole... 

Azzaroni etal. [163] have used STM to study electrochemical reactivity of thiourea toward Au(lll). Sequential STM imaging has shown that thiourea adsorbs as striped arrays that evolve to the hexagonal close-packed structure when surface charge density is decreased. The transient hep structure undergoes electrooxidation to formamidine disulfide, which slowly yields adsorbed sulfur. Adsorption of thiourea on the pc-Au electrode from KCIO4 solutions has also been studied [164]. The film pressure and the Gibbs surface... 

On treatment of 5-amino- and 5-alkylamino-thiatriazoles with concentrated hydrochloric acid, formamidine disulfide dihydrochlorides (54) are formed, along with 50% hydrolysis leading to hydrazoic acid, carbon dioxide and hydrogen sulfide. It is postulated that hydrazoic acid reduces the positive ion presumably formed by ring cleavage of the thiatriazole in the presence of the strong acid (equation 26) (64AHC(3)263). 

When R = Me, a mixture of the pentalene and of 1,2,4-thiadiazole (58) was obtained (equation 29). In the absence of base, HC1 was liberated which caused decomposition of 5-aminothiatriazole to formamidine disulfide (equation 26). 

It appears that the main reaction product of OsO with thiourea is [Os(thio)s], together with formamidine disulfide, via initial formation of [Os02thio4]. The earlier-reported species [Os(thio)j](OH)Cl3 is likely to have contained the osmium(III) species. Salts of [Os(thio)< ] with [Cr(NH3)2(SCN)4] and [Cr(SCN)5] have been isolated using OSO4, thiourea and the complex anion in HC1. [Os(thio) ](SnCl3)2Cl has been reported ESCA data on [Os(thio)j]Cl3 have been given. 

A transient red color observed during the oxidation of thiourea by nitrous acid to formamidine disulfide [(NH2)2CSSC(NH2)2] is the S-nitroso compound [(NH2)2CSNO]. The decomposition of this intermediate, equation (21), involves two pathways, one involving the reversible... 

C10H2 8Cl6N S2Te, Bis(N,N -diethyl) formamidine disulfide hexachloro-tellurate, 46B, 67... 

Fischer indole synthesis, 91-95 Formamidine disulfide, salts of, 281, 282 Formazans, oxidation of, 37 Furans, alkyl-, ring-opening of, 63... 

The kinetics of the coherent synchronous reactions of HP decomposition and oxidation of pyridine derivatives has been reported. Regioselective oxidation of the pyridine derivatives were studied and conditions have been optimized for the production of 4-vinylpyridine, 4-vinylpyridine oxide, 2,2 -dipyridyl, and pyridine. A probable synchronized reaction mechanism has been suggested for the decomposition of HP and the free radical chain oxidation of pyridine derivatives. It is suggested that the hydroperoxy radical (H02-radical) plays a key role in this reaction mechanism. The activation energy has been calculated for the elementary steps of the dehydrogenation of 4-ethylpyridine. Oxidation of formamidine disulfide with HP in acidic medium results in the formation... 

Thiourea acts as a mild reductant (E° = 0.427 V) for transition metal complexes and is oxidized to formamidine disulfide. Thiourea is an excellent ligand for many metal ions, especially for those of the platinum metals.88 Therefore, in most of its redox reactions, thiourea acts simultaneously as a reductant and as a ligand. For example, OSO4 reacts with thiourea in sulfuric acid to form [Osfthiole] and formamidine disulfide.89 Addition of [NH4][Tc04] to a solution of thiourea in a mixture of ethanol and hydrochloric acid results in the formation of the homoleptic thiourea complex of technetium(in), [Tc(thio)6] ". An X-ray structure study of the isolated product, [Tc(thio)6]Cl3-4H20, has shown that the six thiourea ligands are S-bonded to the metal. 

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