Hydrogen atom abstraction from Acetone

An alternative possible route for the formation of carbamoyl radicals may involve a hydrogen atom abstraction from formamide by the excited acetone molecule in its triplet, state (45, 57). Ketonic compounds at this state of excitation mainly if the excitation is of an n - -7r transition, are known to be hydrogen atom abstraction agents, due to the electron deficient oxygen in the excited state. Thus, the formation of carbamoyl radicals through the second route may be summarized by the following scheme ... 

R CHORj. Such radicals have been formed by hydrogen atom abstraction from the ether by radicals produced from thermal decomposition of peroxides (67, 75, 76). Similar radicals may be produced in photochemical processes, either by direct irradiation (29, 54), or by the use of a photosensitizer or a photoinitiator, such as acetone or benzophenone (21, 64, 66). The ether radicals once produced, participate in a variety of chemical reactions. It might be noted that resonance forms as illustrated... 

The generation of such a radical was effected through hydrogen atom abstraction from N-acetylglycine ethyl ester by a photoexcited acetone molecule. This radical can add to olefins yielding the corresponding derivatives of the higher alpha amino acids (70),... 

The first-order ft-scission of the ferf-butoxy radical is one of the oldest radical clock reactions and has been used for over 50 years for the measurement of the relative rates of hydrogen abstraction from organic compounds (AH) in solution (Scheme 10.14). At low conversions, when the concentration of AH has not appreciably changed, the ratio of the rate constants for hydrogen atom abstraction, kAH> and /3-scission, kp, can be determined simply by analysis for acetone and ferf-butyl alcohol formation in the reaction. This is most conveniently achieved by gas chromatography ... 

The light-induced addition of 2-pyrrolidone to olefins when induced directly by light leads to traces only of the desired 1 1 adducts. On the other hand, when acetone is used as a photosensitizer for this reaction it results in relatively high yields of the 1 1 adducts and may be exploited for synthetic purposes in some cases. As in the case of y-butyrolactone the initiation step can be regarded involving a hydrogen atom abstraction process from the lactam by the excited acetone molecule,... 

Propanol. 2-Propanol was chosen as a model for a simple alcohol. Irradiation under vacuum gave hydrogen and acetone as major products along with smaller amounts of methane, acetaldehyde, carbon monoxide, tert-butyl alcohol, and ethanol. These minor products must arise mainly from acetone. Acetaldehyde may be formed either by direct photolysis of 2-propanol, hydrogen atom abstraction by acetyl radical, or /3-scission of the 2-propyloxy radical. The formation of tert-butyl alcohol implies the presence of methyl and 2-hydroxy-2-propyl radicals. 

CH3F (trace). Pyrolysis of sodium trifluoroacetate alone yields trifluoro-acetyl fluoride and trifluoroacetic anhydride pyrolysis of sodium trifluoroacetate in the presence of sodium hydroxide, however, does appear to give difluorocarbene since tetrafluoroethylene is produced in at least 32% yield. Data from kinetic studies on hydrogen atom abstraction by Me and CFa (generated by photolysis of acetone and hexafluoroacetone, respectively) from methyl trifluoroacetate and methyl fluoroformate have been presented and discussed. ... 

Studies in the photoinitiation of polymerization by transition metal chelates probably stem from the original observations of Bamford and Ferrar [33]. These workers have shown that Mn(III) tris-(acety]acetonate) (Mn(a-cac)3) and Mn (III) tris-(l,l,l-trifluoroacetyl acetonate) (Mn(facac)3) can photosensitize the free radical polymerization of MMA and styrene (in bulk and in solution) when irradiated with light of A = 365 at 25°C and also abstract hydrogen atom from hydrocarbon solvents in the absence of monomer. The initiation of polymerization is not dependant on the nature of the monomer and the rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation and the initiation species is the acac radical. The mechanism shown in Scheme (14) is proposed according to the kinetics and spectral observations ... 

If the primary chemical process is still abstraction of a hydrogen atom to produce the benzophenone ketyl radical, one would expect to observe some mixed pinacol product arising from coupling of the benzophenone ketyl and acetone ketyl radicals,... 

The photoreductions of a number of carbonyl compounds with either lowest mr or jiji triplet states in the presence of tributyltinhydride are reported24. The carbonyl compounds include cyclohexanone and acetone which possess nrr lowest-energy triplets, and 2-acetonaphthone, 1-naphthaldehyde and 2-naphthaldehyde which possess lowest-energy mr triplets. In the case of the two njr triplets, a simple mechanism is proposed which involves the abstraction of a hydrogen atom from the tributyltinhydride by the triplet state... 

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