ABSOLUTE KINETICS OF HYDROGEN ABSTRACTION FROM ALPHA-TOCOPHEROL BY SEVERAL REACTIVE SPECIES INCLUDING AN ALKYL RADICAL

被引:87
作者
EVANS, C
SCAIANO, JC
INGOLD, KU
机构
[1] UNIV OTTAWA,OTTAWA CARLETON CHEM INST,OTTAWA K1N 6N5,ONTARIO,CANADA
[2] NATL RES COUNCIL CANADA,INST MOLEC SCI,OTTAWA K1A 0R6,ONTARIO,CANADA
关键词
D O I
10.1021/ja00038a021
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Laser flash photolysis and competitive techniques have been employed to study the reactions of alpha-tocopherol with various radicals and ketone triplets in solution. For example benzophenone triplets abstract hydrogen with rate constants of 5.1 x 10(9) and 3.7 x 10(9) M-1 s-1 in benzene and benzene/1.3 M methanol. Similar near-diffusion-controlled values were obtained for several other ketone triplets, as well as tert-butoxyl and 4-methoxybenzoyloxyl radicals. Deuterium kinetic isotope effects are frequently very small, reflecting the expected lack of selectivity of fast reactions. The reactivity of the 5-hexenyl radical toward alpha-tocopherol was examined by studying the competition of this process with the radical cyclization to the cyclopentylmethyl radical. The value of (1.7 +/- 0.2) x 10(6) M-1 s-1 (at 70-degrees-C in benzene) for this hydrogen atom abstraction from alpha-tocopherol makes this process exceptionally fast in comparison with the limited available rate data for reactions of carbon-centered radicals with other phenols.
引用
收藏
页码:4589 / 4593
页数:5
相关论文
共 55 条
[31]   FREE-RADICAL CLOCKS [J].
GRILLER, D ;
INGOLD, KU .
ACCOUNTS OF CHEMICAL RESEARCH, 1980, 13 (09) :317-323
[32]   INHIBITED AUTOXIDATION OF STYRENE .1. DEUTERIUM ISOTOPE EFFECT FOR INHIBITION BY 2,6-DI-TERT-BUTYL-4-METHYLPHENOL [J].
HOWARD, JA ;
INGOLD, KU .
CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 1962, 40 (09) :1851-&
[33]  
HOWARD JA, 1984, RADICAL REACTION R B, V13
[34]   VITAMIN-E REMAINS THE MAJOR LIPID-SOLUBLE, CHAIN-BREAKING ANTIOXIDANT IN HUMAN-PLASMA EVEN IN INDIVIDUALS SUFFERING SEVERE VITAMIN-E-DEFICIENCY [J].
INGOLD, KU ;
WEBB, AC ;
WITTER, D ;
BURTON, GW ;
METCALFE, TA ;
MULLER, DPR .
ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS, 1987, 259 (01) :224-225
[35]   KINETICS AND EQUILIBRIA IN THE SYSTEM BR + CH3OOH REVERSIBLE HBR + CH3OO - AN UPPER LIMIT FOR THE HEAT OF FORMATION OF THE METHYLPEROXY RADICAL [J].
KONDO, O ;
BENSON, SW .
JOURNAL OF PHYSICAL CHEMISTRY, 1984, 88 (26) :6675-6680
[36]   PRIMARY PHOTOCHEMICAL PROCESSES IN AROMATIC MOLECULES .6. ABSORPTION SPECTRA AND ACIDITY CONSTANTS OF PHENOXYL RADICALS [J].
LAND, EJ ;
PORTER, G ;
STRACHAN, E .
TRANSACTIONS OF THE FARADAY SOCIETY, 1961, 57 (11) :1885-&
[37]   EXTINCTION COEFFICIENTS OF TRIPLET-TRIPLET TRANSITIONS [J].
LAND, EJ .
PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL AND PHYSICAL SCIENCES, 1968, 305 (1483) :457-&
[38]  
MACHLIN LJ, 1980, VITAMIN E
[39]   OPTICAL-SPECTRA OF TOCOPHEROXYL MODEL RADICALS [J].
MUKAI, K ;
WATANABE, Y ;
ISHIZU, K .
BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 1986, 59 (09) :2899-2900
[40]  
Nygaard OF, 1983, RADIOPROTECTORS ANTI