38836-40-7Relevant academic research and scientific papers
Catalysis by Aliphatic Thiols in Photoreduction of Benzophenone by Amines and Alcohols
Stone, Paul G.,Cohen, Saul G.
, p. 1719 - 1725 (1981)
The quantum yield of photoreduction of benzophenone by aliphatic thiol is low, ca. 0.03.However, the photoreduction by primary and secondary aliphatic amines, which contain α-C-H (and N-H), is markedly catalyzed by low concentrations (ca. 1E-2 M) of aliphatic thiol, while it is retarded by aromatic thiol.The catalysis is greater at high concentrations of ketone and amine and passes through a maximum with increasing concentration of thiol.Photoreduction by tertiary amines is retarded by both aromatic and aliphatic thiols. tert-Butylamine and aniline, which lack α-C-H, lead to ketyl and N-centered aminyl radicals, which disproportionate, regenerating ketone and amine.These amines retard photoreduction by amines which possess α-H, and aliphatic thiol greatly decreases this retardation.Acceleration by thiol is ascribed to a sequence of hydrogen atom abstractions, by N-centered aminyl radical from thiol, with rate constant >1E5 M-1s-1, and by thiyl radical from α-C of amine, with rate constant >1E3 M-1s-1.These reactions convert a disproportionating N-centered radical to a reducing C-centered radical.The tert-butylamine-retarded reduction by benzhydrol, but not that by 2-propanol, is accelerated by aliphatic thiol.Retardation and acceleration by thiols in photoreduction by amines and alcohols are discussed in terms of competing free radical reactions and are related to the S-H bond strengths of aromatic and aliphatic thiols, the reactivities of the related thiyl radicals, the ease of abstraction of H from α-C of alcohols and amines, and the reactivities of α-hydroxyalkyl and α-aminoalkyl radicals.
Site-specific catalytic activities to facilitate solvent-free aerobic oxidation of cyclohexylamine to cyclohexanone oxime over highly efficient Nb-modified SBA-15 catalysts
Ding, Wei,Mao, Liqiu,Peng, Haoyu,Yin, Dulin,Zhong, Wenzhou
, p. 3409 - 3422 (2020/06/09)
The development of highly active and selective heterogeneous catalysts for efficient oxidation of cyclohexylamine to cyclohexanone oxime is a challenge associated with the highly sensitive nitrogen center of cyclohexylamine. In this work, dispersed Nb oxide supported on SBA-15 catalysts are disclosed to efficiently catalyze the selective oxidation of cyclohexylamine with high conversion (>75%) and selectivity (>84%) to cyclohexanone oxime by O2without any addition of solvent (TOF = 469.8 h?1, based on the molar amount of Nb sites). The role of the active-site structure identity in dictating the site-specific catalytic activities is probed with the help of different reaction and control conditions and multiple spectroscopy methods. Complementary to the experimental results, further poisoning tests (with KSCN or dehydroxylation reagents) and DFT computational studies clearly unveil that the surface exposed active centers toward activation of the reactants are quite different: the surface -OH groups can catch the NH2group from cyclohexylamine by forming a hydrogen bond and lead to a more facile cyclohexylamine oxidation to desired products, while the monomeric or oligomeric Nb sites with a highly distorted structure play a key role in the dissociation of O2molecules beneficial for insertion of active oxygen species into cyclohexylamine. These catalysts exhibit not only satisfactory recyclability for cyclohexylamine oxidation but also efficiently catalyze the aerobic oxidation of a wide range of amines under solvent-free conditions.
