PHOTOCHEMISTRY 37 



A* -^ A + hvf, 



A* -^ A', 



A' -> A, 

 A* + Co^sl -^ A + C2H5 + I, 

 A' + C2H5I -^ A + C2H5 + I. 



Photoaiitooxidations of reactive reducing agents are sensitized by a 

 wide variety of dyes and pigments (Hurd and Livingston, 1940). These 

 reactions occur in aqueous solutions or in organic solvents, such as 

 methanol or acetone. In cases where the kinetics have been studied in 

 detail, they appear to be complex, and in no case has a completely satis- 

 factory mechanism been proposed. These reactions are produced by 

 either visible light or ultraviolet radiation, depending chiefly on the 

 absorption spectra of the sensitizers. 



Sensitized photochemical redox reactions are of great importance in 

 biology, the outstanding example being photosynthesis by green plants 

 (Rabinowitch, 1945). Photodynamic action and certain pathological 

 skin reactions (Blum, 1941) are also of interest. The oxidative inactiva- 

 tion of enzymes is sensitized by riboflavin (Galston and Baker, 1949) as 

 well as by certain dyes. 



REFERENCES 



Alyea, H. N., and H. L. J. Backstrom (1929) The inhibitive action of alcohols on the 

 oxidation of sodium sulfite. J. Am. Chem. Soc, 51: 90-109. 



Bamford, C. H., and R. G. W. Norrish (1938) Primary photochemical reactions. 

 XII. The effect of temperature on the quantum yield of the decomposition of 

 di-M-propyl ketone in the vapour phase and in solution. J. Chem. Soc, 1544- 

 1554. 



Bateman, L., and G. Gee (1948) A kinetic investigation of the photochemical oxida- 

 tion of certain nonconjugated olefins. Proc. Roy. Soc. London, A195: 376-391. 



Bawn, C. E. H. (1948) The chemistry of high polymers. Interscience Publishers, 

 Inc., New York. 



Berthoud, A., and H. Bellenot (1924) Recherches sur la reaction photochimique du 

 brome ou de I'iode avec I'oxalate de potassium. Helv. Chim. Acta, 7: 307-324. 



Berthoud, A., and C. Urech (1930) Isomerisation photochimique de I'acide allo- 

 cinnamique en presence de I'iode. J. chim. phys., 27: 291-307. 



lilum, H. F. (1941) Photodynamic action and diseases caused by light. Reinhold 

 Publishing Corporation, New York. 



Bodenstein, M., and H. Liitkemeyer (1924) Die photochemische Bildung von 

 Bromwasserstoff. Z. physik. Chem., 114: 208-236. 



Honhoeffer, K. F., and L. Farkas (1928) Der Reaktionsmechanismus des photo- 

 chemischen Jodwas.serstoffzerfalls. Z. physik. Chem., 132: 235-256. 



Bowen, E. J., and A. H. Williams (1939) Photooxidation of hydrocarbon .solutions. 

 Trans. Faraday Soc, 35: 765-771. 



Biicher, T., and J. Kaspers (1947) Photochemische Spaltung des Kohlenoxydmyo- 

 globins durch ultraviolette Strahlung (Wirksamkeit der durch die Protein- 

 komponente des Pigments absorbierten Quanteu). Biochim. et Biophys. Acta, 

 1:21-34. 



