Abstract:Thermolysis of benzophenone O-benzoyloxime leads to the formation of NH3, CO2, benzene, biphenyl, benzophenone, benzanilide, benzonitrile, benzoic acid, 2-phenylbenzoxazole, salicylaldehyde and its p-isomer. Analogous results were also obtained on thermolysis of acetophenone O-benzoyloxime. Similarly, benzophenone and/or acetophenone O-benzyloximes give pyrolysis products of the same nature in addition to others corresponding to the benzyl moiety. Thermolysis of deoxybenzoin oxime gives NH3, toluene, benzonitr… Show more
“…A priori, several pathways can be used to explain the product formation in MeOH, including bond homolysis (Scheme A), , bond homolysis followed by ET (Scheme B), nucleophile-induced mesolytic cleavage (Scheme C), and nucleophilic addition followed by a [1,3]-proton transfer and elimination (Scheme D). 4 …”
The mechanistic aspects of the photosensitized reactions of a series of oxime ethers were studied by steady-state (product studies) and laser flash photolysis methods. Nanosecond laser flash photolysis studies have shown that chloranil-sensitized reactions of the oxime ethers result in the formation of the corresponding radical cations. The radical cation species react with nucleophiles such as MeOH by clean second-order kinetics with rate constants of (0.7-1.4) x 10(6) M(-1) s(-1). Only a small steric effect is observed in these reactions, which is taken as an indication that the reaction center is not the O-alkyl moiety, but rather somewhere else in the molecule. Product studies in a polar nonnucleophilic solvent (MeCN) revealed that in order for the oxime ether radical cation to react more readily, alpha-protons must be available on the alkyl group. The O-methyl (1), O-ethyl (2), and O-benzyl (3) acetophenone oximes all reacted readily to give acetophenone oxime as the major product (as well as an aldehyde derived from the O-alkyl group), whereas O-tert-butyl acetophenone oxime (4) did not. The product formation can be explained by a mechanism that involves electron transfer followed by proton transfer (alpha to the oxygen) and subsequent beta-cleavage. When using 3 in MeOH, a change in the product formation is observed, the most important difference being the presence of benzyl alcohol rather than benzaldehyde as the major product. On the basis of the data from LFP and steady-state experiments, it is suggested that the competing mechanism under these conditions involves electron transfer, followed by a nucleophilic attack on the nitrogen, a MeOH-assisted [1,3]-proton transfer, and subsequent loss of benzyl alcohol. This mechanism is supported by DFT (B3LYP/6-31G) and AM1 calculations.
“…A priori, several pathways can be used to explain the product formation in MeOH, including bond homolysis (Scheme A), , bond homolysis followed by ET (Scheme B), nucleophile-induced mesolytic cleavage (Scheme C), and nucleophilic addition followed by a [1,3]-proton transfer and elimination (Scheme D). 4 …”
The mechanistic aspects of the photosensitized reactions of a series of oxime ethers were studied by steady-state (product studies) and laser flash photolysis methods. Nanosecond laser flash photolysis studies have shown that chloranil-sensitized reactions of the oxime ethers result in the formation of the corresponding radical cations. The radical cation species react with nucleophiles such as MeOH by clean second-order kinetics with rate constants of (0.7-1.4) x 10(6) M(-1) s(-1). Only a small steric effect is observed in these reactions, which is taken as an indication that the reaction center is not the O-alkyl moiety, but rather somewhere else in the molecule. Product studies in a polar nonnucleophilic solvent (MeCN) revealed that in order for the oxime ether radical cation to react more readily, alpha-protons must be available on the alkyl group. The O-methyl (1), O-ethyl (2), and O-benzyl (3) acetophenone oximes all reacted readily to give acetophenone oxime as the major product (as well as an aldehyde derived from the O-alkyl group), whereas O-tert-butyl acetophenone oxime (4) did not. The product formation can be explained by a mechanism that involves electron transfer followed by proton transfer (alpha to the oxygen) and subsequent beta-cleavage. When using 3 in MeOH, a change in the product formation is observed, the most important difference being the presence of benzyl alcohol rather than benzaldehyde as the major product. On the basis of the data from LFP and steady-state experiments, it is suggested that the competing mechanism under these conditions involves electron transfer, followed by a nucleophilic attack on the nitrogen, a MeOH-assisted [1,3]-proton transfer, and subsequent loss of benzyl alcohol. This mechanism is supported by DFT (B3LYP/6-31G) and AM1 calculations.
“…The cleavage of benzyl-O bond into iminoxyl and benzyl radical occurs under the photolysis conditions. A recent report has shown that benzophenone-O-benzyloxime forms bibenzyl by the free radical dimerization of the benzyl radicals, produced as a result of the homolysis of the benzyl-O bond, when heated in a sealed tube at 200°C [36]. The preferential cleavage of C-O bond (bond energy 68 kcal/ mol) over N-O bond (48 kcal/mol) may be attributed to the resonance stabilization of benzyl radicals.…”
ChemInform Abstract Thermolysis of the oximes (I) yields products, e.g. (II)-(V), which are formed via homolysis of the N-O and O-Bz bond. In the case of the oxime (VI) the N-O rather than the O-Bz bond undergoes homolysis and products such as (VII)-(X) are generated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
