Kinetics and Mechanism of Synthesis of Carboxyl-Containing N-Vinyl-2-Pyrrolidone Telehelics for Pharmacological Use

It was found that sulfanylethanoic and 3-sulfanylpropanoic acids are effective regulators of molecular weight with chain transfer constants of 0.441 and 0.317, respectively, and show an unexpected acceleration effect on the radical polymerization of N-vinyl-2-pyrrolidone, initiated by 2,2’-azobisisobutyronitrile. It was determined for the first time that the thiolate anions of mercapto acids form a high-temperature redox initiating system with 2,2’-azobisisobutyronitrile during the radical polymerization of N-vinyl-2-pyrrolidone in 1,4-dioxane. Considering the peculiarities of initiation, a kinetic model of the polymerization of N-vinyl-2-pyrrolidone is proposed, and it is shown that the theoretical orders of the reaction rate, with respect to the monomer, initiator, and chain transfer agent, are 1, 0.75, 0.25, and are close to their experimentally determined values. Carboxyl-containing techelics of N-vinyl-2-pyrrolidone were synthesized so that it can slow down the release of the anticancer drug, doxorubicin, from aqueous solutions, which can find its application in the pharmacological field.

Rhodium-Catalyzed Synthesis of Organosulfur Compounds Involving S-S Bond Cleavage of Disulfides and Sulfur

Organosulfur compounds are widely used for the manufacture of drugs and materials, and their synthesis in general conventionally employs nucleophilic substitution reactions of thiolate anions formed from thiols and bases. To synthesize advanced functional organosulfur compounds, development of novel synthetic methods is an important task. We have been studying the synthesis of organosulfur compounds by transition-metal catalysis using disulfides and sulfur, which are easier to handle and less odiferous than thiols. In this article, we describe our development that rhodium complexes efficiently catalyze the cleavage of S-S bonds and transfer organothio groups to organic compounds, which provide diverse organosulfur compounds. The synthesis does not require use of bases or organometallic reagents; furthermore, it is reversible, involving chemical equilibria and interconversion reactions.

Kinetic and mechanistic studies of the reactions of 2-mercaptoethanol and thioglycolic acid with a Co(III)-bound superoxide complex

In acid media ([H+] = 0.01–0.06 M), 2-mercaptoethanol (HSCH2CH2OH, abbreviated as MERCAP) and thioglycolic acid (HSCH2COOH, abbreviated as TGA) reduce the superoxo complex [(en)(dien)CoIII(O2)CoIII(en)(dien)]5+ (1) to the corresponding peroxo complex [(en)(dien)CoIII(μ-O2)CoIII(en)(dien)]4+ (2). The observed rate (ko), although proportional to both [MERCAP] and [TGA], is higher for TGA than for MERCAP, which is contrary to the expected trend on the basis of standard reduction potential (–0.14 versus –0.26 V, respectively). Moreover, ko values decrease with increasing media ionic strength (I) and [H+] and thus, thiolate anions are supposed to be the reactive forms of the reductants. Under the experimental conditions, the concentrations of such reductants (–SCH2CH2OH and HOOCCH2S–, respectively) from MERCAP (pKa = 9.7) and TGA (pKa1, pKa2 = 3.53, 10.10) are very small. However, for TGA, the tautomerization between HSCH2COO– and –SCH2COOH (pKi = 7.0) plays a significant role in increasing the concentration of HOOCCH2S–. The rates of both of the reactions are limited by the rate of solvent diffusion and this fact is also supported by the relatively low activation energy (Ea), for the reactions. The Ea values for the reactions with MERCAP and TGA are close enough (29.6 ± 1.3 and 27.0 ± 0.4 kJ M−1 respectively) to suggest a common reaction mechanism for both.

Preparation of phthalocyanines fused with four tetrathiafulvalene units via the functional group transformation of tetrakis(o-xylylenedithio)phthalocyanines with toluene/aluminum chloride

Tetrakis(o-xylylenedithio)phthalocyanine 5 and its nickel complex 5-Ni were treated with aluminum chloride in toluene to eliminate the peripheral o-xylylene groups. The thiolate anions generated from 5 and 5-Ni were reacted with carbonyldiimidazole to produce phthalocyanines 6 and 6-Ni with four 1,3-dithiole-2-one rings, respectively. Phthalocyanine 7a having four ethylenedithiotetrathiafulvalene units was prepared via the condensation of 6-Ni with ethylenedithio-1,3-dithiole-2-thiones. The reaction of 6-Ni with bis(methylthio)-1,3-dithiole-2-thiones gave phthalocyanine 7b with the corresponding TTF units. The structures of the products were determined by 1 H NMR and MALDI-TOF-MS. Their electrochemical and optical properties were examined by cyclic voltammetry and UV-vis spectroscopy.

Aggregation of Hydrogen Bonded Dimeric Tri-Organotin Amino Substituted Pyrimidine-2-Thiolates

The synthesis of six tri-organotin compounds with 4-amino and 4,6-diaminopyrimidine-2-thiolate is described. The compounds have the general formula R3Sn(thiolate) where R = Me, Bu, or Ph. The compounds are investigated by a variety of spectroscopic techniques both in solution and in the solid state. The environment around the tin centres proves to be tetrahedral with monodentate thiolate anions as is inferred from the infrared and NMR spectra. The coordination sphere is not affected even by the presence of DMSO as solvent. In the solid state, the crystal structure determination of the trimethyl and triphenyltin derivatives of the 4,6-diaminopyrimidine-2-thiolate ligand, reveal an association into centrosymmetric dimers through N–H⋯N hydrogen-bonding interactions leaving the organotin site practically unaffected. However, in addition to the classical hydrogen bonding, weaker N–H⋯RS and N–H⋯Rπ interactions are also present and play an important role in determining further aggregation of these dimers which gives rise to a three-dimensional polymeric structure in the case of the trimethyltin and a layer of dimers in the case of the triphenyltin derivative, respectively.