2-Pyridinethiones

Sulfur Substituents. Acetylation and alkylation of pyridinethiones usually take place on sulfur (39). An exception to this is 4-pyridinethione [19829-29-9] which is acetylated on nitrogen. Displacement of thioethers can be achieved with hydroxide or amines (eq. 13) (40). Thioether functional groups can also be removed by reduction (39). 

Oxidation of a pyridinethione gives the corresponding sulfonic acid, eg, 6-carboxy-2-pyridinesulfonic acid [18616-02-9] from 6-carboxy-2-pyridinethione [14716-87-1] (eq. 14) (41). 

Pyridinethiones acylation, 2, 357 alkylation, 2, 357 aromaticity, 2, 148 protonation, 2, 357 tautomerism, 2, 356 Pyridine-2-thiones aromaticity, 2, 156 basicity, 2, 157 oxidation, 2, 357 N-oxide, sodium salt biocide, 1, 399 synthesis, 2, 360... 

Mercaptopyridine iV-oxide sodium salt (pyridinethione or pyrithione sodium salt) [3811-73-2] M 149.1, m 250°(dec), pK] -1.95, pK2 4.65. When recrystd from water it assayed as 98.7% based on AgNO titration [Krivis et al. Anal Chem 35 966 1963, see also Krivis et al. Anal Chem 4 1001 1976 and Barton and Crich J Chem Soc. Perkin Trans I 1603, 1613 1986]. 

Glutaconaluehyde Enol Benzoates " and 1-Substituted 3-Formyl-2(1H)-Pyridinethiones " Prepared from Glutaconaldehyde Anion and Its... 

The 3-formyl-2(IH)-pyridinethiones were prepared by reaction of glutaconaldehyde anion with the corresponding isothiocyanates (RN—C==S). 

A stereoselective radical reaction of the ester of M-hydroxy-2-pyridinethione (see also Sect. 4.1) to chiral vinylphosphine oxides has also been described and moderate to good diastereomeric ratios have been obtained for the compound 112 [70] (Scheme 33). 

CgH7NS = l-methyl-2(lH)-pyridinethione),1257 [Ag(C7N2S2)2]Br,1258 and [AgBr(mbi)] (mbi = methyl-2-thiobenzimidazole) have been reported.12... 

N-Hydroxythiopyridone 2(1H)-Pyridinethione, 1-hydroxy- (8,9) (1121-30-8) Dicyclohexylcarbodiimide highly toxic. Carbodiimide, dicyclohexyl- (8) Cyclohexanamine, N,N -methanetetraylbis- (9) (538-75-0)... 

The sequence carbon radical —> imine —> amine is illustrated in equation 30. Irradiation of the pyridinethione 64 (R = cyclohexyl) with the light of a tungsten lamp generates the cyclohexyl radical 65, which was trapped as the imine 67 in the presence of the diazirine 66. The imine was finally hydrolysed to cyclohexylamine80. 

Another related example can be found in the series of copper complexes with the bis(imino)-3-formyl-l-phenyl-pyridinethione ligands shown in Scheme 18.180 Both Cu(I) and Cu(II) complexes can be prepared with this type of ligands. 

As far as one can tell from the rather limited data, and as we shall see later, much the same factors as listed above appear to be at work in deciding the amount of thiol form in 2- and 4-pyridinethione tautomerism. 

Application of pulsed ion gas-phase cyclotron resonance (ICR) spectroscopy to proton affinities of the derivatives 2-methoxypyridine and N- methylpyridin-2-one confirm previous deductions on the enthalpy of 2-hydroxypyridine-pyridin-2-one tautomerism (76JA6048), provided that the difference between the influences of O-methylation on 2-hydroxypyridine and A-me thy lat ion in pyridin-2-one are taken into account. These measurements have been further clarified and extended to other gas phase basicity measurements (79JA1361). A similar estimation of the gas phase basicities of 2- and 4-pyridinethiols and 2- and 4-pyridinethiones confirms that the thiol form is predominant in the gas phase (77TL1777), in line with previous studies involving mass spectrometric deuterium isotope studies (75BSB465). Photoelectron spectroscopy has also been employed in such studies (see Section 2.04.3.6 and Figure 21 for details) <77JCS(P2)1652>. 

Protonation of pyridinethiones and quinoline-4-thione occurs at sulfur, giving the corresponding mercapto-pyridinium and -quinolinium cations (65JCS3825, 62JCS3127). 

The a- and y-pyridinethiones can be oxidized to the corresponding sulfonic acids, e.g. (134), by reagents such as alkaline permanganate, nitric acid and peracids (67FES1069). Thioether oxidation gives the corresponding sulfone, e.g. (135 Scheme 125). 

Pyridinethiones and thiols are readily oxidized to the corresponding disulfides by reagents such as hydrogen peroxide, potassium ferricyanide and bromine, e.g. Scheme 126 (70JCS(C)1530). Treatment of acridine-9-thione with sulfuric acid gives acrid-9-one. 

The synthesis of chloromethylthio heterocycles, e.g., 127 had been described by Goralski and Burk193 in the reaction of benzothiazole-2-thiones, 2-pyridinethiones, and 2-quinolinethiones with chlorobromomethane. In the case of l,3,4-thiadiazole-2,5-dithione, the reaction was made with the preformed alkali metal salt. 

Pyridines and azines with a- or 7-mercapto groups exist predominantly in the pyridinethione, etc., forms, e.g. as (855) rather than in the mercapto form (854). This behavior is analogous to that of the corresponding hydroxypyridines (Section 3.2.3.7) see also Section 2.2.5.1. 

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