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Title: Nanosecond flash studies of reduction of benzophenone by aliphatic amines. Quantum yields and kinetic isotope effects

Abstract

Nanosecond flash photolysis, steady irradiation, and deuterium substitution studies have been carried out on solutions of benzophenone with added reductants. Quantum yields (phi/sub ketyl/) for reduction in benzene of benzophenone triplet to ketyl radical, based on phi = 2 for benzhydrol (I), were approx. 1 for cyclohexane (II), tert-butylamine (III), 2-aminobutane (IV), cyclohexylamine (V), di-n-propylamine (VI), and triethylamine (VII), approx. 0.7 for 1,4-diazabicyclo(2.2.2)octane (VIII), and approx. 0 for tert-butyl alcohol (IX). Thus, quenching, without radical formation by H abstraction from N and/or ..cap alpha..-C, does not occur with common aliphatic amines but does with Dabco (VIII). The latter quenching is markedly increased by small additions of acetonitrile; the flash spectrum from this compound indicates formation of a triplet amine CT complex or radical ion pair. Triplet-reductant interaction rate constants, k/sur ir/, are high for the amines (approx. 10/sup 8/-10/sup 9/ M/sup -1/ s/sup -1/) but also show significant deuterium kinetic isotope effects: 1.9 with III-N-d/sub 2/; 1.4 with IV-N-d/sub 2/; 1.2-1.3 with IV-..cap alpha..-C-d. It is proposed that k/sub ir/ measures H atom abstraction, favored in the transition state by an initial charge-transfer interaction. Overall steady irradiation quantum yields of reduction by amines, phi/sub Red/, are much lower than phi/submore » ketyl/. This is attributed to disproportionationreactions of ketyl and alkylaminyl radicals for primary and secondary amines, and, possibly, aminoalkyl radicals for tertiary amines. In the case of tert-butylamine, the rate constant for disproportionation is obtained from the decay kinetics of ketyl radical and leads to phi/sub Red/ in agreement with that directly measured.« less

Authors:
; ;
Publication Date:
Research Org.:
Brandeis Univ., Waltham, MA
OSTI Identifier:
6520378
DOE Contract Number:  
EY-76-S-02-3117
Resource Type:
Journal Article
Journal Name:
J. Am. Chem. Soc.; (United States)
Additional Journal Information:
Journal Volume: 103:5
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BENZOPHENONE; PHOTOLYSIS; DEUTERIUM; ISOTOPE EFFECTS; AMINES; BENZENE; CYCLOHEXANE; EXPERIMENTAL DATA; PULSED IRRADIATION; RADICALS; REDUCTION; SCINTILLATION QUENCHING; TRIPLETS; ALKANES; AROMATICS; CHEMICAL REACTIONS; CYCLOALKANES; DATA; DECOMPOSITION; HYDROCARBONS; HYDROGEN ISOTOPES; INFORMATION; IRRADIATION; ISOTOPES; KETONES; LIGHT NUCLEI; MULTIPLETS; NUCLEI; NUMERICAL DATA; ODD-ODD NUCLEI; ORGANIC COMPOUNDS; PHOTOCHEMICAL REACTIONS; STABLE ISOTOPES; 400500* - Photochemistry; 400302 - Organic Chemistry- Isotope Effects- (-1987)

Citation Formats

Inbar, S, Linschitz, H, and Cohen, S G. Nanosecond flash studies of reduction of benzophenone by aliphatic amines. Quantum yields and kinetic isotope effects. United States: N. p., 1981. Web. doi:10.1021/ja00395a009.
Inbar, S, Linschitz, H, & Cohen, S G. Nanosecond flash studies of reduction of benzophenone by aliphatic amines. Quantum yields and kinetic isotope effects. United States. https://doi.org/10.1021/ja00395a009
Inbar, S, Linschitz, H, and Cohen, S G. 1981. "Nanosecond flash studies of reduction of benzophenone by aliphatic amines. Quantum yields and kinetic isotope effects". United States. https://doi.org/10.1021/ja00395a009.
@article{osti_6520378,
title = {Nanosecond flash studies of reduction of benzophenone by aliphatic amines. Quantum yields and kinetic isotope effects},
author = {Inbar, S and Linschitz, H and Cohen, S G},
abstractNote = {Nanosecond flash photolysis, steady irradiation, and deuterium substitution studies have been carried out on solutions of benzophenone with added reductants. Quantum yields (phi/sub ketyl/) for reduction in benzene of benzophenone triplet to ketyl radical, based on phi = 2 for benzhydrol (I), were approx. 1 for cyclohexane (II), tert-butylamine (III), 2-aminobutane (IV), cyclohexylamine (V), di-n-propylamine (VI), and triethylamine (VII), approx. 0.7 for 1,4-diazabicyclo(2.2.2)octane (VIII), and approx. 0 for tert-butyl alcohol (IX). Thus, quenching, without radical formation by H abstraction from N and/or ..cap alpha..-C, does not occur with common aliphatic amines but does with Dabco (VIII). The latter quenching is markedly increased by small additions of acetonitrile; the flash spectrum from this compound indicates formation of a triplet amine CT complex or radical ion pair. Triplet-reductant interaction rate constants, k/sur ir/, are high for the amines (approx. 10/sup 8/-10/sup 9/ M/sup -1/ s/sup -1/) but also show significant deuterium kinetic isotope effects: 1.9 with III-N-d/sub 2/; 1.4 with IV-N-d/sub 2/; 1.2-1.3 with IV-..cap alpha..-C-d. It is proposed that k/sub ir/ measures H atom abstraction, favored in the transition state by an initial charge-transfer interaction. Overall steady irradiation quantum yields of reduction by amines, phi/sub Red/, are much lower than phi/sub ketyl/. This is attributed to disproportionationreactions of ketyl and alkylaminyl radicals for primary and secondary amines, and, possibly, aminoalkyl radicals for tertiary amines. In the case of tert-butylamine, the rate constant for disproportionation is obtained from the decay kinetics of ketyl radical and leads to phi/sub Red/ in agreement with that directly measured.},
doi = {10.1021/ja00395a009},
url = {https://www.osti.gov/biblio/6520378}, journal = {J. Am. Chem. Soc.; (United States)},
number = ,
volume = 103:5,
place = {United States},
year = {Wed Mar 11 00:00:00 EST 1981},
month = {Wed Mar 11 00:00:00 EST 1981}
}