L-Hydroxypyridine-2-thione

Sulfhydryl groups usually make a molecule polarographically active in alkaline solution where the anodic wave is caused by the formation of a mercurous salt. This is, for example, found for the anodic wave of l-hydroxypyridine-2-thione.314 In acid medium heteroaromatic mercapto compounds are mostly found on the thio-carbonyl forms. Few of these compounds have been investigated. 

In contrast to the oxidative generation of radicals described above, redactions of alkyl iodides nsing tris(trimethylsilyl)silane also produces alkyl radicals under conditions suitable for Minisci-type substitution. Carboxylic acids (a-keto acids) are also useful precursors for alkyC° and/or acyC radicals via silver-catalysed peroxide oxidation, or from their l-hydroxypyridine-2-thione derivatives, the latter in non-aqueous conditions. 

The A -oxides of pyridine, quinoline, and benzoquinoline are antibacterial provided that an ionizable group is present in the 2-position to make chelation possible. A mercapto-group has been found best for this purpose. Thus 2-mercaptopyridine-A-oxide (l-hydroxypyridine-2-thione) 2.26) (pyrithione, Omadine ) is as intensely antibacterial as oxine. Although the chelated... 

Zinc pyrithione l-Hydroxypyridine-2-thione, zinc salt mercaptopyridine W-oxide, zinc salt 13463-41-7... 

Silver(I) complexes with mixed donor S, 0-ligands have been described with 1-hydroxypyridine-2-thione (261),1437,1438 cyclo-L-methionylglycine,1439 acyclic polyethers (262),1440-1442 dithio- and trithio-oxalate,1443 or chlorosulfate.1444... 

Isoxazolo[4,5-c]pyridines have been converted into thiazolo[5,4-(>]pyridines by three methods. Catalytic hydrogenation of compound (616) using palladium on carbon (10%) in aqueous sodium hydroxide at 50 psi followed by neutralization with HC1 to selectively cleave the isoxazole ring afforded 6-chloro-3-(l-iminoethyl)-4-hydroxypyridine-2-thione (617) (57%) <90JCS(P1)1477>. Animation of the thione moiety of the imine (617) with hydroxyamine-Osulfonic acid and subsequent cyclization affords 6-chloro-4-hydroxy-3-methylisothiazolo[5,4-<5 pyridine (618) (57%) (Scheme 78). 

Decompositions of Bis(cyclopropylacetyl) Peroxides, Bis(cyclopropylalkyl)diazenes, and Cyclopropylalkyl Esters of l-Hydroxypyridine-2(1 0-thione... 

A new decarboxylative route to free radicals, which has proved particularly successful in preparative work, embodies the thermal (or photochemical) decomposition reaction of 1-hy-droxypyridine-2(l/f)-thione esters 23 with tributyltin hydride, /er/-butanethiol, or a similar hydrogen donor.These esters can be easily prepared from acyl halides and the sodium salt of l-hydroxypyridine-2(l//)-thione, or from the carboxylic acid, dicyclohexylcarbodiimide and l-hydroxypyridine-2(l/f)-thione. The intermediate radicals were readily reduced to the corresponding hydrocarbons 24 in efficient chain reactions with organotin hydrides or thiols as reaction partners, and the proportion of rearranged to unrearranged products could be controlled by the choice of hydrogen donor, its concentration and the temperature. This system was sufficiently quantitative and well behaved for use in kinetic studies, and the rate constants of the (S-scission reactions of the listed cyclopropylmethyl species were determined. 

An alternative procedure for reductive decarboxylation without the use of trialkyltin hydrides as hydrogen atom donors has been developed Alkane carboxylic acid esters derived from AT-hydroxypyridine-2-thione decomposed to alkyl radical, which can readily accept a hydrogen atom from t-BuSH (equation 74) to give alkanes. This reaction can be conveniently performed as a one-pot experiment wherein the acid chloride of an alkane carboxylic acid, the sodium salt of thiohydroxamic acid, t-BuSH and 4-dimethyl-aminopyridine (DMAP) in benzene solution are heated to reflux. This procedure works well for COOH groups attached to primary and secondary carbon atoms. Instead of AT-hydroxypyridine-2-thione, one can use other thiohydroxamic acids, viz. iV-hydroxy-AT-methylthiobenzamide, 3-hydroxy-4-methylthiazole-2(3if)-thione (equation 75) and l-iV-hydroxy-3-AT-methylbenzoylenethiourea for decarboxylation reactions. 

Reszka, K. J. and Chignell, C. F., Photochemistry of 2-mercaptopyridines. 3. EPR study of photoproduction of hydroxyl radicals by N-hydroxypyridine-2-thione using 5,5-dimethyl-l-pyrroline N-oxide in aqueous-solutions Photochem. Photobiol, 61, 269, 1995. 

Barton, D. H. R. and Samadi, M., The invention of radical reactions. 25. A convenient method for the synthesis of the acyl derivatives of N-hydroxypyridine-2-thione, Tetrahedron, 48, 7083,1992. Garner, R, Anderson, J. T. and Dey, S., S-(l-oxido-2-pytidinyl)-l,l,3,3-tetramethylthiouronium hexafluorophosphate a new reagent for preparing hindered barton esters,/. Org. Chem., 63,5732,1998. Prabhakar, S., Lobo, A. M., and Santos, A., A, Convenient method for the synthesis of N-hydroxy thiobenzamides (C-arylthiohydroxamic acids). Synthesis, 829,1984. 

Related Reagents. Carbon Disulfide A(-Hydroxypyridine-2-thione l,l -Thiocarbonyldiimidazole p-Tolyl Chlorothionocar-bonate Phenyl Chlorothionocarbonate. 

The PE spectra of hydroxy- and mercapto-pyridines have been examined, together with the model iV-alkyl and S- or O-alkyl compounds, to elucidate the tautomeric equilibria in the vapor phase (77JCS(P2)1652) (Section 2.04.4.2). Figure 21 and Table 13 show details of the PE spectra of l-methylpyridin-2-one, 2-methoxypyridine and the tautomeric mixture at equilibrium of pyridin-2-one and 2-hydroxypyridine. This indicates that there is approximately 25% of oxo form present once adjustment has been made for the expected influence of methylation, similar measurements reveal ca. 10% of the thione form in the mercapto-thione equilibrium. Other spectra indicate that 3- and 4-hydroxy- and 3- and 4-mercapto-pyridine exist in the vapor phase with less than 5% of the alternative tautomer present. 

Reactions of 3-hydroxy-6-methyl-2(lfl)-pyridinethione with 1,3-dibromo-propanes in methanol in the presence of sodium methylate yielded betaines (205) (70ACS2949). 9-Hydroxy-3,4-dihydro-2f/-pyrido[2,l-6][1,3]-thiazinium bromide was obtained in the reaction of 3-hydroxypyridine-2(lH)-thione and l-bromo-3-chloropropane in boiling toluene [81JCR(S)208]. 

E. Aminyl Radicals from A -Hydroxypyridine-2(l//)thione Carbamates. 11... 

Abbreviations used pop, dianion of pyrophosphite (P20,.iH2 ) pep, dianion of /u.-methylenebis(phosphite) im, anion of imidazole 4-mpyt, anion of 4-methylpyridine-2-thioI pyt, anion of pyridine-2-thiol pyms, anion of pyrimidine-2-thione bttz, anion of l,3-benzothiazole-2-thiol form, anion of di-p-tolylformamidine dpb, N,W -diphenylben-zamidine mhp, anion of 6-methyl-2-hydroxypyridine chp, 6-chloro-2-hydroxypyridine and dpt, 1,3-diphenyltriazen. 

Studies of the generation of hydroxyl radicals by photocleavage of the N-O bonds in A -hydroxypyridine-2(1 0-thione, and N-hydroxy-2(l//)-pyridone have been reported. Alternative photochemical sources of hydroxyl radicals are 4-mercaptopyridine-A -oxides. ... 

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