Date of Award
Doctor of Philosophy
The reduction of (.)C(CH(,3))(,2)OH and (.)CH(CH(,3))OC(,2)H(,5) radicals by V(H(,2)O)(,6)('2+) forms the respective organic products, (CH(,3))(,2) CHOH and (C(,2)H(,5))(,2)O and the V('3+) ion. The kinetics of these reactions were studied by a method of chemical competition using the homolytic decomposition of the corresponding organo(pentaaquo)chromium(III) complex. The rate constants are 2.1 x 10('5) M('-1)S('-1) for (.)C(CH(,3))(,2)OH, which is found to be independent of H('+) and ionic strength, and 5.9 x 10('4) M('-1)S('-1) for (.)CH(CH(,3))OC(,2)H(,5) at 25(DEGREES)C. The former reaction studied in 92% D(,2)O has K = 3.6 x 10('4) M('-1)S('-1). The mechanism invoked is either (1) hydrogen atom abstraction by the radical form a vandium-bound water molecule or (2) formation of a seven-coordinate organovanadium intermediate followed by its rate-limiting acidolysis;The rate constants of the reactions between the Co('II)(14aneN(,4))('2+) complex and the same aliphatic radicals were determined in the same manner, being 8.8 x 10('6) M('-1)S('-1) for (.)C(CH(,3))(,2)OH and 1.7 x 10('6) M('-1)S('-1) for (.)CH(CH(,3))OC(,2)H(,5) (at 25(DEGREES)C, 0.2M H('+), 0.5M ionic strength). These reactions are believed to occur by formation of an organocobalt transient which subsequently decomposes to yield (CH(,3))(,2)CO from (.)C(CH(,3))(,2)OH, and CH(,3)CHO and C(,2)H(,5)OH from (.)CH(CH(,3))OC(,2)H(,5);Organoperoxycobaloximes are subject to decomposition in^aqueous perchloric acid. The complexes examined are^(1) ROOCo(dmgH)(,2)Py with R = 2-propyl, 2-butyl, cyclopentyl,^benzyl and d(,7)-2-propyl and (2) (CH(,3))(,2)CHOOCo(dmgH)(,2)L with L =^pyridine, piperidine, water and ammonia. Their decomposition leads^to H(,2)OCo(dmgH)(,2)L('+) and a mixture of ketone and hydroperoxide.^Kinetic studies were carried out at 25.0(DEGREES)C, (mu) = 1.0M in the H('+)^range 0.010-0.98M. The disappearance of the organoperoxy^complexes obeys a rate law with k(,obsd) = kH('+)/(K(,H)('-1) + H('+)). K(,H) isthe equilibrium constant for the protonation of the oxime oxygens.The decomposition process is rate-limiting and consists of twoparallel pathways leading to ketone and hydroperoxide, respectively.The relative yields of the organic products afford the individual rateconstants for their formation. The ketone pathway shows anappreciable kinetic isotope effect: k(,H)/k(,D) = 8.9 (+OR-) 1.5, suggestingC-H bond breaking promotes the cleavage of the oxygen-oxygenbond. The formation of hydroperoxide, favored by the complexes;with better electron-donating groups, is best accounted by the protonation of the cobalt-bound oxygen atom promoting the Co-O bond cleavage;('1)DOE Report IS-T-1031. This work was performed under ContractNo. W-7405-Eng-82 with the Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Chen, Jwu-Ting, "Kinetic and mechanistic studies of the reactions of selected aliphatic radicals with metal complexes and the decomposition of organoperoxy cobalt complexes " (1982). Retrospective Theses and Dissertations. 8337.