- Medium effects on the α-effect in DMSO-H2O mixtures - Comparative studies of p-nitrophenyl benzoate and acetate - Dissection of ground-state and transition-state effects
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In a study of the origin of the α-effect and its dependence on the nature of the reaction medium as well as structural effects, we report herein a kinetic study of the reactions of p-nitrophenyl benzoate (PNPB) with butan-2,3-dione monoximate (Ox-, α-nucleophile) and p-chlorophenoxide (p-ClPhO-, the reference nucleophile) in dimethyl sulfoxide (DMSO)-H2O mixtures of varying compositions at 25.0 ± 0.1°C. The second-order rate constants (kN) decrease modestly on addition of DMSO to the medium up to 10 mol% DMSO but increase significantly beyond that point for both nucleophiles. Ox- is more reactive than p-ClPhO- in all solvent mixtures studied (i.e., the α-effect). The α-effect increases as the DMSO content in the medium increases up to 40 mol% DMSO and then decreases beyond that point resulting in a bell-shaped α-effect profile. The bell-shaped α-effect profile obtained for the current reaction is similar to that found previously for the corresponding reaction of p-nitrophenyl acetate (PNPA), differing notably however, in the magnitude of the α-effect beyond 40 mol% DMSO. The PNPB/p-ClPhO- reaction gains greater rate enhancement than the PNPA/p-ClPhO- reaction in the DMSO-rich region, resulting in the smaller α-effect for PNPB beyond 40 mol% DMSO. It is proposed that the observed modulation of the α-effect by the solvent medium is explicable as a ground-state effect in the H2O-rich region and a transition-state effect in the DMSO-rich region.
- Um, Ik-Hwan,Shin, Young-Hee,Han, Jeong-Yoon,Buncel, Erwin
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Read Online
- Dual photoredox/palladium-catalyzed C-H acylation of 2-arylpyridines with oxime esters
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An unprecedented dual photoredox/palladium-catalyzed iminyl-radical-mediated C-C bond cleavage and directed ortho C-H acylation of 2-arylpyridines by using oxime esters is described. Oxime esters can serve as efficient acyl sources through formation of the corresponding acyl radicals by photoredox-catalyzed iminyl-radical-mediated C-C bond cleavage. This redox-neutral protocol features excellent regioselectivity, a broad substrate scope, and good functional-group tolerance with respect to both components, giving a broad range of aryl ketones with generally good yields.
- He, Bin-Qing,Gao, Yuan,Wang, Peng-Zi,Wu, Hong,Zhou, Hong-Bin,Liu, Xiao-Peng,Chen, Jia-Rong
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supporting information
p. 373 - 377
(2020/09/11)
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- Reactivity studies of carbon, phosphorus and sulfur-based acyl sites with tertiary oximes in gemini surfactants
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Kinetic studies of the reactions of tertiary oximes (monoisonitroso acetone; MINA and butane 2,3 dione monooxime; BDMO) with some carboxylate (p-nitrophenyl acetate and p-nitrophenyl benzoate), phosphate (p-nitrophenyl diphenyl phosphate and bis (2,4-dini
- Gupta, Bhanushree,Sharma, Rahul,Singh, Namrata,Karpichev, Yevgen,Satnami, Manmohan L.,Ghosh, Kallol K.
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p. 632 - 642
(2013/08/23)
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- Kinetic study of the reactions of p-nitrophenyl acetate and p-nitrophenyl benzoate with oximate nucleophiles
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The reactions of p-nitrophenyl acetate (PNPA) and p-nitrophenyl benzoate (PNPB) with α-nucleophile oximates, that is, butane 2,3-dione monoximate, pralidoximate, and other oximates have been studied in the presence of different cationic surfactants. The f
- Tiwari, Shuchi,Kolay, Sancheeta,Ghosh, Kallol K.,Kuca, Kamil,Marek, Jan
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experimental part
p. 57 - 64
(2009/04/18)
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- The effect of acyl substituents on the α-effect: Contrasting α-effect profiles for reactions of 4-nitrophenyl substituted benzoates with neutral and anionic nucleophiles
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The magnitude of the α-effect for reactions of 4-nitrophenyl substituted benzoates with a pair of anionic nucleophiles is independent of the electronic nature of the acyl substituent, while the one for the corresponding reactions with a pair of neutral nucleophiles increases as the acyl substituent changes from a strong electron withdrawing substituent to electron donating ones.
- Um, Ik-Hwan,Han, Hyun-Joo,Chung, Eun-Kyung
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p. 8051 - 8053
(2007/10/03)
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- Synthesis, structure, and acylating properties of 1-aroyloxy-4,5-dimethyl- 1,2,3-triazoles
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Lead tetra-acetate oxidation of α-hydroxyimino aroylhydrazones of biacetyl (1) gives 1-aroyloxy-4,5-dimethyl-1,2,3-triazoles (2), the structures of which were confirmed by X-ray analysis. A mechanism for this reaction is discussed. The products (2) are effective aroylating agents for the amino function under mild conditions.
- Theocharis,Maroulis,Hadjiantoniou-Maroulis,Alexandrou
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p. 619 - 621
(2007/10/02)
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