ISSN:
1434-193X
Keywords:
Phenacyl halides
;
Hydrogen donor
;
Bond dissociation enthalpies
;
Lignin
;
DFT
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
-The reduction of α-X-acetophenones (X = PhO, Br, Cl), as model compounds for lignin liquefaction studies, has been investigated in the presence of a hydrogen-donating solvent such as 9,10-dihydroanthracene (AnH2) or 2-propanol, between 373 and 573 K. With α-phenoxyacetophenone (PAP) in AnH2, acetophenone and phenol have been obtained with high selectivities. The mechanism involves the reverse radical disproportionation (RRD) with AnH2. Hydrodebromination of α-bromoacetophenone (BrAP) is quantitative at 423 K using AnH2 as a reducing agent. Now, the hydrogen transfer proceeds by an uninhibited radical chain mechanism with anthracenyl radicals as the chain carriers. For the kinetic analysis, the C-X (X = Br, Cl) bond dissociation enthalpies (BDEs) have been determined by means of very low pressure pyrolysis to give BDE(C-Br) = 271 kJ mol-1 and, as a lower limit, BDE(C-Cl) ≈ 309 kJ mol-1, at 298 K. The BDEs are quite at variance with recently published insights derived from an electrochemical study. For comparison, density functional theory calculations (DFT) have been performed.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
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