Pyridines mercapto

With mercapto pyridine, mercapto quinoline and derivatives... 

Table 11 summarizes the main results on the tautomerism of mono-hydroxy-, -mercapto-, -amino- and -methyl-azines and their benzo derivatives, in water. At first sight the equilibrium between 2-hydroxypyridine (71) and pyridin-2-one (72) is one between a benzenoid and a non-benzenoid molecule respectively (71a 72a). However, the pyridinone evidently... 

In comparison with mercapto-, hydroxy-, and amino-pyridines, methylpyridines should show an even greater tendency to exist in the methyl form [instead of as pyridmethines (297)] than do the amino compounds to exist as such. If the methyl carbon atom carries an electron-withdrawing group, it might be expected that structures of type 297 would be stabilized. Fused benzo groups should also tend to stabilize the methine form, and tautomerism involving 298 has, in-... 

The methods outlined, of course, are readily applicable to a wide variety of substituted heterocycles like the carboxyl, hydroxy and mercapto derivatives of pyridines, pyridine 1-oxides, pyrroles, etc. The application to amines and to diaza compounds such as pyrimidine, where the two centers are basic, is obvious except that now 23 takes the role of the neutral compound, 21 and 22 the roles of the tautomeric first conjugate bases, and 20 the role of the second conjugate base. Extensions to molecules with more than two acidic or basic centers, such as aminonicotinic acid, pyrimidinecarboxylic acids, etc., are obvious although they tend to become algebraically cumbersome, involving (for three centers) three measurable Kg s, four Ay s, and fifteen ideal dissociation constants (A ), a total of twenty-two constants of which seven are independent. 

Figure 15 Molecular structure of Ph2SnCl(MP) with the atom numbering scheme, (AMP = 2-mercapto pyridine). ...

In the context of studies on the coordination of organotin(IV) moieties by thiolic S and heterocyclic N atoms, diorganotin(IV) complexes of 2-mercapto-pyridine, R2Sn(SPy)2 and R2SnCl(SPy), have been characterized in the solid state and in solution. The structure of the latter complex (R = Ph) was determined by XRD (Figure 17). The crystal is monoclinic in the space... 

Another class of new ligands was prepared in quantitative yields by Feringa et al., in 1997, by reaction between a-mercapto acids, aniline and 2-pyridine-carboxaldehyde." These pyridyl-substituted thiazolin-4-one ligands were further involved in the copper-catalysed conjugate addition of ZnEt2 to 2-cyclohexenone,... 

The supported aqueous phase methodology was applied to the system Pd(OAc)2/5 TPPTS, a catalytic precursor for the Trost-Tsuji reaction. The characterization of the solid by 31P MAS NMR confirms the presence of Pd°(TPPTS)3 as the main surface species. The catalytic properties of the solid were tested for the allylic substitution of E-cinnamylethylcarbonate by different nucleophiles such as ethyl acetoacetate, dimethyl malonate, morpholine, phenol, and 2-mercapto-pyridine. The absence of palladium leaching was demonstrated, and having solved the problem of water leaching from the solid to the organic phase, the SAP-Pd catalyst was successfully recycled several times without loss in its activity. It was used in a continuous flow experiment which... 

Finally, we note that Karelson et al. [295] have used the D02 model with small cavity radii to consider aqueous solvation effects on other tautomeric equilibria of substituted pyridines. In particular, they examined methyllmethylene, amino/imino, hydroxy/oxo, and mercapto/thiono substitution at the 2-, 3, and 4-positions of pyridine. They observed methyl/methylene equilibria to be only slightly perturbed by aqueous solvation. Amino/imino equilibria were slightly more perturbed, followed by hydroxy/oxo equilibria. Mercapto/thiono equilibria were very significantly affected by aqueous solvation Karelson et al. predicted pK shifts of up to 16 units. This sensitivity of the thiono group to solvation is also discussed in the next section. Overall, the tautomeric equilibria of 3- and 4-substituted pyridines were more sensitive to aqueous solvation than were those of 2-substituted pyridines. 

Several crown ethers that possess side chains with terminal mercapto groups enhance the rate of transesterification of amino-acid p-nitrophenyl esters. Matsui and Koga (1978) reported the reactions of a number of amino-acid p-nitrophenyl ester hydrobromides dissolved in mixtures of ethanol and dichloromethane (1 4) and buffered with acetic acid and pyridine (pH 4.60 in... 

Abstract This presentation is a brief review on the resnlts of our work on iodine interaction with thioamides, selenoamides and amides. The thioamides, benzothia-zole-2-thione (BZT) (1), 6-n-propyl-2-thiouracil (PTU) (2), 5-chloro-2-mercap-tobenzothiazole (CMBZT) (3), N-methyl-benzothiazole-2-thione (NMBZT) (4), benzimidazole-2-thione (BZIM) (5), thiazolidine-2-thione (TZD) (6), 2-mercapto-pyridine (PYSH) (7), 2-mercapto-nicotinic acid (MNA) (8), 2-mercapto-benzoic acid (MBA) (9) and 2-mercapto-pyrimidine (PMT) (10) react with producing three type of complexes of formulae [(HL)IJ(l2) (HL= thioamide and n= 0, 1), [(HL) [I3 ] and [(HL-L)]+[l3 ]. The interaction of seleno-amides, derived from, 6-n-propyl-2-thiouracil (RSelJ) (R= Me- (11), Et- (12), n-Pr- (13) and i-Pr- (14)) with I, have also been studied and produced the complexes [(RSeU)IJ of spoke structure. These complexes are stable in non-polar solvents, but they decompose in polar solvents, producing dimeric diselenide compounds or undertake deselenation. 

The structure of the compound consists of two residues, one cationic (PYS-PYSH)+, containing the S-S bond linking the two 2-mercapto-pyridine molecules one of which is protonated and Ij as a counter anion. In the crystal lattice there are four symmetry-independent cation-anion pairs. There are only a few crystal structures reported in the literature containing open chain stable cations of DS-SD dimers, such as the monocationic [(C HgN S-SNjC Hj) ) ) [15]. The two I-I bond distances of the Ij" in the four components of complex (26) are 2.887(4) and 2.944(3) A in component a, 2.874(4) and 2.957(3) A in b, 2.968(3) and 2.862(3) A in c and 2.855(4) and 2.927(3) A in d, respectively, indicating a slight asymmetry of I3 in this complex (covalent hnear asymmetric). 

The ring closure of 5-alkylated 3-mercapto-1,2,4-triazoles to thiazolo[3,2-h][l,2,4]triazoles was reported a long time ago. Thus, treatment of 131 with acetic anhydride/pyridine (heat) yields 132 (50BRP634951). 

Table 11 summarizes the main results on the tautomerism of mono-hydroxy-, -mercapto-, -amino- and -methyl-azines and their benzo derivatives, in water. At first sight the equilibrium between 2-hydroxypyridine (71) and pyridin-2-one (72) is one between a benzenoid and a non-benzenoid molecule respectively (71a 72a). However, the pyridinone evidently has a continuous cyclic p- orbital system, containing six it- electrons, the usual aromatic count, if the carbonyl group contributes none. This assumption implies the formula (72b), from which by redistribution of electrons we arrive at (72c), which has the same benzenoid system as (71a). Further canonical forms (71b, 71c) can be drawn of (71) which correspond to the non-benzenoid forms of (72). The elusive property of aromaticity is therefore possessed by both tautomers, although not necessarily by both equally. When the carbonyl oxygen of (72) is replaced by less electronegative atoms, as in the imine tautomers of amino heterocycles, or the methylene tautomers of methyl derivatives, the tendency towards polarization in forms corresponding to (72b) and (72c) is considerably less, and the amino and methyl tautomers are therefore favoured in most instances. 

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. 

UV and pKa measurements show that pyridine-3-thiol and quinoline-3-thiol occur predominantly in the zwitterion form, e.g. (133) (76AHC(S1)144). Quinolines carrying a mercapto group on the benzo ring exist in the zwitterion or the zwitterion extended quinone form to a larger extent than do the analogous hydroxy compounds (63AHC(S1)400). 

Einen einfachen Zugang zu 4(5)-(Mercapto-thiocarbonyl)-imidazolen ermoglicht die Umsetzung von Natrium-imidazoliden in Dimethylsulfoxid oder der freien Imidazole mit Na-triumhydroxid in Pyridin oder Methyl-pyridinen mit Schwefelkohlenstoff699. Fiir Imidazol selbst wurde nur eine Ausbeute von 2% beschrieben. Mit 2-substituierten bzw. 2,4(5)-disub-stituierten Imidazolen liegen die Ausbeuten dagegen zwischen 60 und 90%. 

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