Abstract
Rate constants are measured for the addition reactions of 1-hydroxy-1-cyclohexyl (1HC) and 2-hydroxy-2-propyl (2HP) radicals to 7 alkenes and for the 1-electron reduction of 16 organic dyes by 1HC, and a subset of 5 of these dyes by 2HP. This was done to determine to what extent the many reported rate constants for reactions of 2-hydroxy-2-propyl radicals (2HP) may be used to predict the rates of reactions of other tertiary α-hydroxy-alkyl radicals, and to give a better understanding of the factors that control dye reduction. The dyes were chosen to represent a wide range of dye types (azo, anthraquinone, phthalocyanine, triaryl-methane, indocyanine and azine dyes). Radicals were produced by laser flash photolysis of the corresponding tertiary α-hydroxyketone giving carbonyl and tertiary α-hydroxy-alkyl radicals. Control experiments with a bis-acylphosphine oxide were carried out which clearly demonstrated that the carbonyl radicals did not interfere with the kinetics. On average the addition and reduction rate constants for 1HC are only 20% lower than for 2HP. Larger decreases are observed for sterically congested alkenes due to the increased steric bulk of 1HC. The rate constants for 1-electron reduction of the dyes are in the range 4 × 107 to 6 × 109 mol−1 l s−1 and may be predicted, reasonably well using the Marcus equation with a reorganisation energy, λ = 182 kJ mol−1.
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H. F. Gruber, Photoinitiators For Free Radical Polymerization Prog. Polym. Sci. 1992 17 953–1044
See Landolt-Börnstein Radical Reaction Rates in Liquids, ed. H. Fischer, Springer Verlag, Berlin, 1995, volume IIb, pp. 2233–2275
S. N. Batchelor and H. Fischer, Radical Addition Rates to Alkenes by Time-Resolved CIDNP: 2-Hydroxy-2-Propyl Radicals J. Phys. Chem. 1996 100 9794–9799
S. Jockusch, M. S. Landis, B. Freiermuth and N. J. Turro, Photochemistry and Photophysics of Alpha-Hydroxy Ketones Macromolecules 2001 35 1619–1626
F. Wilkinson, Diffuse Reflectance Flash-Photolysis J. Chem. Soc., Faraday Trans 2 1986 82 2073–2081
J. P. Fouassier, D. Ruhlmann, B. Graff, F. Morlet-Savary and F. Wieder, Excited State Processes in Polymerisation Photoinitiators Prog. Org. Coat. 1995 25 235–271
P. Hunt, D. R. Worrall, F. Wilkinson and S. N. Batchelor, Quantitative Rate Constants For Radical Reactions in the Nanopores of Cotton J. Am. Chem. Soc. 2002 124 8532–8533
S. Jockush and N. J. Turro, Radical Addition Rate Constants to Acrylates and Oxygen: α-Hydroxy and α-Amino Radicals Produced by Photolysis of Photoinitiators J. Am. Chem. Soc. 1999 121 3921–3925
R. Martschke, R. D. Farley and H. Fischer, Rate constants for the addition of 2-hydroxy-2-propyl radicals to alkenes in solution studied by laser flash photolysis Helv. Chem. Acta 1997 80 1363–1374
K. Vacek, J. Geimer, D. Beckert and R. Mehnert, Radical Generation from Photoinitiator (IC 2959) Decomposition and Radical Addition to Acrylate. A laser photolysis fourier transform electron paramagnetic resonance study J. Chem. Soc., Perkin Trans. 2 19902469–2471
S. G. Lias, J. E. Bartmess, J. F. Liebmann, J. L. Holmes, R. D. Levin and W. G. Maillard, Gas-Phase Ion and Neutral Thermochemistry J. Phys. Chem. Ref. Data Suppl. 1988 17 1 1–861
H. Fischer and L. Radom, Factors Controlling the Addition of Carbon-Centred Radicals to Alkenes - an Experimental and Theoretical Perspective Angew. Chem., Int. Ed. 2001 40 1340–1371
R. L. Reeves, M. S. Maggio and S. A. Harkaway, A Critical Spectrophotometric Analysis of the Dimerization of Some Ionic Azo Dyes in Aqueous Solution J. Phys. Chem. 1979 83 2359–2368
J. Shore and D. Patterson, in Colorants and Auxiliaries Volume 1 Colorants, ed. J. Shore, Soc. of Dyers And Colourists, Manchester1990, p. 1-72
U. Kolczak, G. Rist, K. Dietliker and J. Wirz, Reaction Mechanism of Monoacyl - and Bisacylphosphine Oxide Photoinitiators Studied by 31P-, 13C-, and 1H-CIDNP and ESR J. Am. Chem. Soc. 1996 118 6477–6489
R. A. Marcus, Electron Transfer Reactions in Chemistry: Theory and Experiment (Nobel Lecture) Angew. Chem., Int. Ed. Engl. 1993 32 1111–1121
L. Eberson, Electron Transfer Reactions in Organic Chemistry, Springer Verlag, Berlin, 1987
P. Wardmann, Reduction Potentials of One-Electron Couples Involving Free Radicals in Aqueous Solution J. Phys. Chem. Ref. Data 198941637–1755
G. Klopman and N. Doddapaneni, Electrochemical Behavior of Cis and Trans Azobenzenes J. Phys. Chem. 1974 78 1825–1828
J. L. Bragger, A. W. Lloyd, S. H. Soozandehfar, S. F. Bloomfield, C. Marriotta and G. P. Martin, Investigation into the Azo Reducing Activity of a Common Colonic Microrganism Int. J. Pharm. 1997 157 61–71
S. N. Guha and J. P. Mittal, Pulse Radiolysis Study of One-Electron reduction of Safranine T J. Chem. Soc., Faraday Trans. 1997 93 3647–3652
C. M. Carliell, S. J. Barclay, N. Naidoo, C. A. Buckley, D. A. Mulholland and E. Senior, Microbial Decolorization of a Reactive Azo-Dye Under Anaerobic Conditions Water SA 1995 21 61–69
S. Okubayshi, A. Yamazaki, Y. Koide and H. Shosenji, Effects of Cylodextrin on the Electrolytic Reduction of an Anthraquinone Dye J. Soc. Dyers Col. 1999 115 312–317
H. A. Schwarz and R. W. Dobson, Reduction Potentials of CO2− and the Alcohol Radicals J. Phys. Chem. 1989 93 409–414
J. T. Edwards, Molecular Volumes and the Stokes-Einstein Equation J. Chem. Ed. 1970 47 261–270
S. N. Batchelor and H. Fischer, Time Resolved CIDNP Investigation of the Cross-Relaxation Mechanism of 1H Nuclear Polarization J. Phys. Chem. 1996 100 556–564
P. Neta and H. Levanon, Spectrophotometric Study of Radicals Produced by Reduction of Syn-Azobenzene and Anti-Azobenzene J. Phys. Chem. 1977 81 2288–2292
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Dedicated to the memory of Nobel Laureate, Lord George Porter FRSC FRS OM.
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Hunt, P., Worrall, D.R., Wilkinson, F. et al. Quantitative rate constants for the reaction of dyes and alkenes with α-hydroxyalkyl radicals, measured by laser flash photolysis. Photochem Photobiol Sci 2, 518–523 (2003). https://doi.org/10.1039/b212051h
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DOI: https://doi.org/10.1039/b212051h