SPECIFIC RATE CONSTANT FOR URETHAN CLEAVAGE

The kinetics of binding of imidazole to ferriprotoporphyrin IX (hemin) in aqueous ethanol has been studied at 25° using the temperature jump technique. The reaction was studied quantitatively as a function of acid concentration using the pH scale developed by Bates et al. for mixed solvent systems. The results can be explained by a mechanism in which the imidazolium ion binds to hemin with a specific rate constant of (4 ± 2) × 106 M−1 s−1 and imidazole binds with a rate constant of (3 ± 0.3) × 104 M−1 s−1. The dissociation constant for the imidazolium ion was determined by acid–base titration to be 1.8 × 10−7 M, and a dissociation constant for the hemin of 2.3 × 10−7 M was determined by spectrophotometric titration in a solvent containing 44.5 weight % of ethanol. The latter dissociation involves the proton on a solvent ligand.

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Facet-dependent performance of BiOBr for photocatalytic reduction of Cr(vi)

RSC Advances ◽

10.1039/c5ra18768k ◽

2016 ◽

Vol 6 (3) ◽

pp. 2028-2031 ◽

Cited By ~ 25

Author(s):

Zao Fan ◽

Yubao Zhao ◽

Wei Zhai ◽

Liang Qiu ◽

Hui Li ◽

...

Keyword(s):

Electric Field ◽

Rate Constant ◽

Photocatalytic Reduction ◽

Specific Rate ◽

Internal Electric Field ◽

Specific Rate Constant

BiOBr dominated with {110} facets giving a specific rate constant 3 times as high as BiOBr with {001} facets, and its much stronger internal electric field was believed to be the main reason.

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A STUDY OF SOME REACTIONS OF THE CYCLOPENTYL RADICAL

Canadian Journal of Chemistry ◽

10.1139/v65-075 ◽

1965 ◽

Vol 43 (3) ◽

pp. 570-581 ◽

Cited By ~ 11

Author(s):

Alvin S. Gordon

Keyword(s):

Hydrogen Atom ◽

Kinetic Parameters ◽

Rate Constant ◽

Energy Of Activation ◽

Radical Reactions ◽

Specific Rate ◽

Exponential Factor ◽

Allyl Radical ◽

Specific Rate Constant ◽

Activated Complex

The specific rate constant for opening the cyclopentyl radical has been determined to be 1014.5 exp –37 700/RT s−1. The energy of activation indicates that any eclipsed pairs of H atoms in the cyclic radical are not de-eclipsed in the activated complex. No evidence for the resulting five-membered linear radical can be found, only evidence for its breakdown products, allyl radical and ethylene.The disproportionation/combination ratio for methyl and cyclopentyl radicals is about 0.3. The energy of activation for methyl abstracting a hydrogen atom from cyclopentane has been confirmed as about 9.5 kcal/mole.Cyclopentyl radical also loses a hydrogen atom to form cyclopentene. The kinetic parameters are difficult to obtain because of radical–radical reactions which form cyclopentene. An analysis of the results indicates an energy of activation at least equal to that for opening the cyclopentyl ring.Evidence is presented to support the view that the cyclopentyl radical loses a molecule of hydrogen to form the resonance-stablized cyclopentenyl radical with an energy of activation close to that for opening the ring, and a pre-exponential factor about 1/10 of that for the opening of the ring.

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