Abnormal Solvent Effects on Hydrogen Atom Abstraction. 3. Novel Kinetics in Sequential Proton Loss Electron Transfer Chemistry

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TypeArticle
Journal titleJournal Of Organic Chemistry
ISSN00223263
Volume70
Issue22
Pages89828990; # of pages: 9
AbstractA prolonged search involving several dozen phenols, each in numerous solvents, for an ArOH/2,2-diphenyl-1-picrylhydrazyl (dpph) reaction that is first-order in ArOH but zero-order in dpph has reached a successful conclusion. These unusual kinetics are followed by 2,2'-methylene-bis(4-methyl-6-tert-butylphenol), BIS, in five solvents (acetonitrile, benzonitrile, acetone, cyclohexanone, and DMSO). In 15 other solvents the reactions were first-order in both BIS and dpph (i.e., the reactions followed "normal" kinetics). The zero-order kinetics indicate that in the five named solvents the BIS/dpph reaction occurs by sequential proton loss electron transfer (SPLET). This mechanism is not uncommon for ArOH/dpph reactions in solvents that support ionization, and normal kinetics have always been observed previously (see Litwinienko, G.; Ingold, K. U. J. Org. Chem. 2003, 68, 3433 and Litwinienko, G.; Ingold, K. U. J. Org. Chem. 2004, 69, 5888). The zero-order kinetics found for the BIS/dpph reaction in five solvents, S, imply that BIS ionization has become the rate-determining step (rds, rate constants 0.20-3.3 s-1) in the SPLET reaction sequence: S + HOAr S- HOAr SH+ + -OAr SH+ + OAr + dpph- S + OAr + dpph-H, where ArOH = BIS. Some properties specific to BIS that may be relevant to its relatively slow ionization in the five solvents are considered.
Publication date
Linkhttp://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/jo051474p
AffiliationNational Research Council Canada; NRC Steacie Institute for Molecular Sciences
Peer reviewedNo
Identifier10008226
NPARC number12327132
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Record identifier98c89724-c94a-4173-bd21-0b35ec4b5808
Record created2009-09-10
Record modified2016-05-09
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