3073-51-6Relevant articles and documents
Effects of Structure on Rates and Quantum Yields in Photoreduction of Fluorenone by Amines. Catalysis and Inhibition by Thiols
Stone, Paul G.,Cohen, Saul G.
, p. 3435 - 3440 (1982)
Rate constants, kir, quantum yields, φred, and effects of thiol have been studied in the photoreduction of fluorenone by amines in benzene.Hydroxyethylamines show increased φred as compared with unsubstituted ethyl analogues, φred ca.0.8 with triethylamine, but ca.2, the maximum theoretical value, with triethanolamine and 2-(diethylamino)ethanol.Abstraction is predominantly from unsubstituted ethyl groups in the latter, and increased kir and φred are attributed to solvation by hydroxyl, present only at the reaction site, of polar intermediates or transition states.Secondary amines have high kir and low φred, 0.01-0.2, attributed to predominant abstraction of H from N and disproportionation of ketyl and aminyl radicals.This reduction is strongly catalyzed by aliphatic thiol, as aminyl radical abstracts H from S and thiyl radical abstracts H from α-C of amine.Primary amines have low kir and φred.This reduction is not catalyzed by thiol, indicating that H is not abstracted by triplet fluorenone from N of primary aliphatic amines.Aniline inhibits this reduction, but aniline plus thiol leads to strong catalysis.Triplet fluorenone abstracts H from N of aniline, anilino radical abstracts H from S of thiol, and thiol abstracts H from α-C of amine, leading to effective reduction.Thiol catalysis may be diagnostic for the formation of aminyl radicals.Inhibition and catalysis by thiols are discussed.
Vanadium(I) chloride and lithium vanadium(I) dihydride as epimetallating reagents for unsaturated organic substrates: Constitution and mode of reaction
Eisch, John J.,Fregene, Paul O.,Doetschman, David C.
experimental part, p. 2825 - 2835 (2009/04/07)
Subvalent vanadium(I) salts, of empirical formulas, VCl, vanadium(I) chloride and LiVH2, lithium vanadium(I) dihydride, can be conveniently prepared in THF solution, starting at -78 °C, by treating either VCl3 or VCl4 with an appropriate number of equivalents of nBuLi. As judged by the stability of solutions or solid samples of LiVH2, the preparation of LiVH2 from VCl4 is the preferred method. Individual physical characterization of solid samples of VCl or of LiVH2, admixed with their LiCl by-product, was carried out after removal of all volatiles in vacuo and by the following measurements: 1) gasometric protolysis with glacial acetic acid and measurement of the H 2 evolved in the oxidation of VI to VII; 2) infrared spectroscopic search for V-H bands; and 3) examination for unpaired electrons by EPR activity. Such measurements applied to VCl lend strong support for a VI oxidation state but only probable evidence for paramagnetism and for the association of VCl units. Similar measurements applied to LiVH 2 give unambiguous gasometric and IR evidence favoring the LiVH 2 stoichiometry and the biradical nature of the VH2 anion with a linear array of H-V-H atoms. Chemical characterization of both VCl and LiVH2 toward individual organic substrates, such as olefins, ketones, epoxides and organic halides, yielded convincing evidence that organic radical mechanisms are involved, both for the proven biradical, LiVH2, as well as for the diamagnetic VCl. Finally, the question of why LiVH2 prepared from VCl4 is more stable than the LiVH2 obtained from VCl3 is addressed in terms of the actual coordination sphere of the VH2 anion in THF solution and in the solid state. Preliminary studies comparing the reactivities of LiVH2 and LiCrH2 toward organic substrates indicate that LiVH2 is the distinctly more moderate and usefully selective reductant. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
Facile reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by an aqueous TiCl3/NH3 system: Selectivity and scope
Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
, p. 3326 - 3335 (2007/10/03)
A simple and rapid procedure for the almost quantitative reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by use of TiCl3/NH3 in aqueous methanol solution is reported. The reducing system distinguishes between different classes of aldehydes and/or ketones, and many functionalities that usually do not survive under reducing conditions are tolerated well. The concept of reversal of chemoselectivity has also been developed. A mechanism based on two sequential one-electron transfers from TiIII to the carbonyl carbon atom is proposed, the second SET becoming operative only in the presence of ammonium ion (either added or formed in situ). Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
