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The synthesis of 3-pyridinols carrying alkyltelluro, alkylseleno, and alkylthio groups is described together with a detailed kinetic, thermodynamic, and mechanistic study of their antioxidant activity. When assayed for their capacity to inhibit azo-initiated peroxidation of linoleic acid in a water/chlorobenzene two-phase system, tellurium-containing 3-pyridinols were readily regenerable by N-acetylcysteine contained in the aqueous phase. The best inhibitors quenched peroxyl radicals more efficiently than alpha-tocopherol, and the duration of inhibition was limited only by the availability of the thiol reducing agent. In homogeneous phase, inhibition of styrene autoxidation absolute rate constants k(inh) for quenching of peroxyl radical were as large as 1 x 10(7) M(-1) s(-1), thus outperforming the best phenolic antioxidants including alpha-tocopherol. Tellurium-containing 3-pyridinols could be quantitatively regenerated in homogeneous phase by N-tert-butoxycarbonyl cysteine methyl ester, a lipid-soluble analogue of N-acetylcysteine. In the presence of an excess of the thiol, a catalytic mode of action was observed, similar to the one in the two-phase system. Overall, compounds bearing the alkyltelluro moiety ortho to the OH group were much more effective antioxidants than the corresponding para isomers. The origin of the high reactivity of these compounds was explored using pulse-radiolysis thermodynamic measurements, and a mechanism for their unusual antioxidant activity was proposed. The tellurium-containing 3-pyridinols were also found to catalyze reduction of hydrogen peroxide in the presence of thiol reducing agents, thereby acting as multifunctional (preventive and chain-breaking) catalytic antioxidants.

Group 14 element derivatives of carbotelluroates, RCOTeMPh 3 (M = Ge, Sn, Pb), were synthesized as stable compounds by reacting sodium carbotelluroates with Ph 3 MCl and were characterized by IR and 1 3 C and 1 2 5 Te NMR spectra. Their molecular structures were revealed by X-ray molecular analysis. The C=O...Sn distance in RCOTeSnPh 3 was found to be shorter than the C=O...Ge distance in RCOTeGePh 3 , despite the fact that the atomic radius of Sn is larger than that of Ge. A similar shortening of the nonbonding distance was observed for the corresponding selenium derivatives. Molecular orbital calculations of model compounds, i.e., CH 3 COEM(CH 3 ) 3 (E = Se, Te; M = Ge, Sn, Pb), at the B3LYP/LANL2DZ+p level also supported this shortening of the C=O...Sn distance. NBO (natural bond orbital) analyses of the model compounds showed that two types of orbital interactions, n O →σ * M E and n O →σ * M C (E = S, Se, Te; M = Ge, Sn, Pb), are important in these carbochalcogenoates. Furthermore, the former interaction has a greater role in the case of carbothioates, whereas the latter is dominant in carbotelluroates.

Selenothioic acid S-alkyl esters were synthesized from the reaction of terminal acetylenes with n-butyllithium, selenium, and alkanethiols in moderate to high yields. The use of substituted benzene...

Thiocarboxylic acids, such as selenocarboxylic acids, exist predominantly in the thioxo form (RCSOH, thion acid) in polar solvents such as tetrahydrofuran (THF) at temperatures below −50 °C. Tellurocarboxylic acids (5) were observed for the first time by acidolysis of the corresponding cesium tellurocarboxylates with hydrogen chloride. The telluroic acids (6) exist predominantly in the telluroxo form (RCTeOH, telluron acid) in THF at temperatures below −70 °C. Telluron acids were reddish to blue violet for the aliphatics (R = alkyl) and dark green for the aromatics (R = aryl) and reacted with aryl isocyanates at −70 °C to give crystalline acyl carbamoyl tellurides in good yields.

[structure: see text]. We found that the C=O.Sn distance in RCOSSnR'3 was shorter than the C=O.Ge distance in RCOSGeR'3 and theoretically confirmed that the orbital interactions between the nonbonding orbitals on the carbonyl oxygen (n(O)) and the sigma*(SnS) orbitals were important in regard to the shortness.

Selenotellurocarbamic acid Te-alkyl esters were isolated for the first time in yields of 20−40% from the reaction of acyl isoselenocyanates with tellurols.