- The Presence of Two Reactive Intermediates in the Photolysis of N-Bromosuccinimide: Kinetic Proofs
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The direct photolysis of N-bromosuccinimide in the presence of an olefin (to scavenge bromine and its atoms) was shown to products the ring-opened product β-bromopropionamide from two reactive intermediates as confirmed by kinetic analysis of competing reactions of the ring opening and addition to benzene.The reactive intermediates were assigned to the succinimidyl radical and the precursor in agreement with the previous publication.The plots of relative quantum efficiencies of β-bromopropionamide against benzene concentrations were shown to be consistent with mathematical predictions derived from the proposed reaction scheme.These established that while both the precursor and succinimidyl radical underwent the ring-openning reaction, only the latter showed the reactivity of attacking benzene.The precursor can be either another state of the succinimidyl radical or an excited state of NBS; evidence to distinguish between these is not available.It is surmised that failure to recognize the presence of the precursor in the direct photolysis of N-bromosuccinimide has contributed to the protracted controversy in the current literatures.
- Chow, Yuan L.,Zhao, Da-Chuan
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- A convenient and practical method for conversion of primary alkyl chlorides to highly pure bromides (≥99%)
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Repeated treatment (second after the aqueous work-up) of primary alkyl chlorides with ten equivalents (each) of lithium bromide in 3-pentanone at 120 °C for a total of five hours gave the corresponding bromides in excellent yield (86-96%) and with high chemical purity (≥99%).
- Li,Singh,Labrie
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p. 733 - 743
(2007/10/02)
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- Kinetics of radical-initiated chain bromination of 2-methyl-2-propanol by N-bromosuccinimide in water
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The kinetics and product distribution of the radical chain bromination of 2-methyl-2-propanol (RH) by N-bromosuccinimide (SBr) in water have been studied by pulse-radiolytic and γ-radiolytic methods in order to obtain key data for the reactivity of the succinimidyl radical, S?. The products of the reaction after γ-radiolysis are dependent on the concentration of RH, being essentially made up of equal amounts of (CH3)2C(OH)CH2Br and succinimide at [RH] > 0.5 M, while the hydrolyzed ring-opened product, 3-bromopropionamide, increases at the expense of (CH3)2C(OH)CH2Br when the RH concentration is lowered. The chain-propagating steps R? + SBr → RBr + S? (i) and S? + RH → SH + R? (ii) of the S? mediated chain reaction had rate constants ki = (1.8 ± 0.3) × 108 (determined in three ways) and kii = (1 ± 0.5) × 107 M-1 s-1 (determined in four ways), respectively, whereas the corresponding rate constants for the Br? mediated chain under the same conditions were 2.5 × 109 and (5 ± 3) × 103 M-1 s-1. Under pulsed conditions with initial radical concentrations around 10-4 M, the chain length is ≈10. The ratio between kii and the rate constant for ring opening of S?, kiii (S? → ?CH2CH2CONCO), was determined to be 77 M-1, significantly higher than the corresponding value with neopentane as substrate and with dichloromethane as solvent (0.10 M-1). The kii value places S? as having significantly lower reactivity than OH? in hydrogen atom abstraction reactions, whereas a theoretical estimate based on electron affinities puts it in between Cl? and OH?, i.e. at higher reactivity than OH?. This provides kinetic evidence for the II nature of ground state S?. It was also established that Br? complexes rather strongly to SBr according to SBr + Br? → SBr2? (iv). As kiv = (4-7) × 103 M-1 and SBr2? is probably unreactive, the propagation rate of a bromine atom chain is expected to decrease with increasing SBr concentration.
- Lind, Johan,Jonsson, Mats,Xinhua, Shen,Eriksen, Trygve E.,Merényi, Gábor,Eberson, Lennart
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p. 3503 - 3510
(2007/10/02)
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- Electrochemical studies on haloamides. Part II. Electrochemical reduction of N-(1-acetoxy-2,2,2-trichloroethyl)-ω-bromoalkanamides
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The electrochemical reduction of haloamides Br(CH2)nCONHCH(OCOCH3)CCl3 2 - 5 in N,N-dimethylformamide solutions containing tetraethylammonium perchlorate as supporting electrolyte has been investigated at a mercury cathode.Acrylamide 2a, acetoxy- and chloro-amides 3a,b - 5a,b and lactames 3d - 5d were isolated after macroscale electrolysis carried out at a potential corresponding to the first voltammetric peak.The electron exchange between electrode and substrate produces a two-electron cleavage of a C-Cl bond in the CCl3 group, followed by β-elimination of acetate ion.The formation of substituted amides 3a,b - 5a,b was related to the reactivity of acetate and chloride ions as nucleophiles, that of acrylamide 2a and lactams 3d - 5d to the reactivity of acetate ion as a base.
- Casadei, M. A.,Inesi, A.
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- Process for the production of halogenated carboxylic acid amides
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A process for the production of halogenated carboxylic acid amides wherein an amide of the unsaturated aliphatic carboxylic acid is reacted with an anhydrous hydrogen halide and an epoxide compound is added to the reaction mixture and after cooling, the precipitated halogenated carboxylic acid amide is separated.
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