Air-free ethyl iodide has been photolyzed both in the pure liquid state and in cyclohexane sulution, using light of 2537 A.The composition of the product mixture was independent of the extent of photolysis and in the case of pure ethyl iodide was ound to be: C?H4, 38.8; C2H6, 26.0; 12, 24.2; HI, 11.3; H1, 0.03 mole %. By the use of initially added H I and Iz it has been shown that the ratio CgH4/C2H6 is a linear function of Iz/HI. mole fraction, the ratio C2H4/C2Hs was depressed below the value predicted by the linear function, due to decrease in the C2H4 yield, which is constant a t lower H I concentrations. -4 tnechanism has been proposed and tested in which the primnry act is dissociation of the C-I bond. It is further proposed that diffusion-controlled reactions occur between the ethyl radicals and iodine atoms yielding for recombination & = 0.60, for ethylene and for hydrogen iodide & = 0.19, and for diffusion apart into the steady state 6 3 = 0.21. The effect of high concentrations i i f hydrogcn ioditlc i i t o diminiili c$, and 4. by intervention in the diffusioiicontrolled processes.IVhen H I exceeded 3 X IntroductionThe quantum yield for production of iodine in photolysis of pure liquid ethyl iodide a t 2537 A. is 0.2G2 gram atom. Many previous investigations have considered iodine to be the only significant iodine-containing product, and have therefore taken this quantum yield to be equal to that for decomposition of ethyl iodide. Studies of the absorption spectrum3 have indicated that the primary process is the rupture of the C-I bond. By use of

Benzil has been irradiated in cyclohexane solution. The principal products are: benzoic acid; benzal-dehyde; phenyl cyclohexyl ketone; benzoin; benzoin benzoate; a compound tentatively identified as desyl benzoyloxydesyl ether; another compound not yet identified; and approximately one-third of the reacted benzil that was not accounted for. A small amount of unsaturation is also found. As long as there is enough benzil present (presumably to absorb all of the light) the benzil disappearance is linear with time. All products appear at the shortest times checked and so cannot be secondary products. If one neglects the benzoic acid approximately 19% of the benzoyl groups that react do so in the form of benzoyl radicals. No evidence for phenyl radical formation was found. The upper limit for the quantum yield of benzil disappearance at 366 mμ is 0.25. The benzoic acid does not arise directly during the photolysis but only when the solution is exposed to oxygen during the work-up. Preliminary experiments in cumene solution have shown that the amount of benzil lost for the same length of irradiation increases by a factor of about 1.5. In 2-propanol solution the increase is by a factor of 2.5. When 2-propanol is the solvent, a new product appears which is most probably the dimer of the ketyl radical which is formed when an excited benzil abstracts a hydrogen atom. This product is very unstable.

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Benzil is photoreduced in neat triethylamine and mixtures of triethylamine and 2-propanol. In neat 2-propanol the principal products are; benzil pinacol, 20%; benzoin benzoate, 19%; benzoin, 18%; and benzoic acid, 12%. When the amine concentration is as low as 0.2 mM the benzil pinacol formation is almost completely suppressed. At amine concentrations higher than 0.36 mM the principal product is benzoin, 80%. At intermediate amine concentrations benzoin benzoate is important. The rate of benzil disappearance reaches a maximum and then declines as either the benzil concentration in triethylamine is increased or the amine concentration in 2-propanol is increased.4-Hydroxybenzil is not photoreduced by 2-propanol. It is reduced by triethylamine. The quantum yield of disappearance is 0.04 at a concentration of 47.8 mM and in solutions containing at least 0.36 M of amine. 4-Hydroxybenzoin is the principal product but at low starting 4-hydroxybenzil concentrations 4,4′-dihydroxybenzil is important. A rate maximum is also observed in this case.4,4′-Dihydroxybenzil is not photoreduced by 2-propanol. It does undergo photoreaction in neat triethylamine but no products were isolated.Triethylamine also appears to suppress biacetyl pinacol formation in the photoreaction of biacetyl with 2-propanol.

Benzil has been irradiated in 2-propanol and in cumene with a mercury lamp filtered through Pyrex. The principal products are benzoin, 1,2,3,4-tetraphenyl-2,3-dihydroxybutane-1,4-dione (3), benzoin benzoate, benzaldehyde, benzoic acid, 1,2,3,4-tetraphenyl-2,3-dihydroxybutane-1,4-dione dibenzoate (5), and some unidentified high molecular weight compounds. The yield of 3 is strongly dependent on initial benzil concentration and temperature and on the solvent used. The quantum yield of benzil disappearance depends on initial benzil concentration to a lower limit which varies with solvent. At an initial benzil concentration of 0.083 moles/l, the quantum yield of benzil disappearance is 0.11 in 2-propanol and 0.018 in cyclohexane. Compound 3 does not appear to be formed by a coupling of the appropriate ketyl radicals, as in the benzophenone case but instead, a complex is formed between a benzil molecule and the ketyl radical. Compound 3 decomposes at temperatures as low as 25°. The principal path for the formation of benzaldehyde and benzoyl radicals is the dissociation of the ketyl radical. Excited benzil abstracts a hydrogen from 2-propanol at least ten times faster than it dissociates into two benzoyl radicals.