'The photolysis of azoisopropane has been reinvestigated in a n attempt to obtain a better understanding of the discrepancies fo~uid between the behavior of sec-propyl radicals produced from this source (1) and other sources under similar esperimental conditions. Analytical difficulties encountered in an earlier investigation (1) were avoided through the extensive use of gas chromatography.I t was found necessary t o include an internal conversion reaction among the primary > EdisYoc~ation An explanation of this observation remains a matter of conjecture though a tentative suggestion is offered. The data also leads to results in agreement with those found for other azo compounds and in agreement with the rates of reactions of sec-propyl radicals obtained from other sources under similar conditions. IXTRODUCTIONRecent studies of the rates of reactions of sec-propyl raclicals (2, 3, 4) present a slightly clifferent picture to that obtained by Durhaln and Steacie ( I ) in the photolysis of azoisopropane. T o some extent these differences can be traced back to the analytical difficulties encountered by Durllam and Steacie. Since many of these difficulties can now be avoided, a reinvestigation of the photolysis of azoisopropane, making extensive use of gas chromatography, was undertalien. A further reason for the reinvestigation was the rather poor agreement a t lower temperatures between the mechanism proposed and the experimental data obtained by Durham and Steacie (I).The high-vacuum apparatus was in g e~~e r a l of the design ~~s u a l l y employed in these laboratories; hou-ever, stopcoclcs and oil diffusion pumps were used in order t o obt aln ' a mercury-free s).stem. Part of the analytical line, consisting of a simple mercury-containing system usecl to handle noncondensable reaction products, was connected to the nlercuryfree system in the manner described by McElcheren, Wijnen, and Steacie (5).T h e quartz reaction cell, 10 cm in length with a volume of 180 cc, was ellclosed in a thermostatted hot box in which the temperature could be controlled to within 1/2O C. A mecliun~ pressure I-Ianovia S500 mercury arc \\,as enlployed as the light source. This, in conjunction with the filter A described by Iiasha ( G ) , supplied incident radiation consisting of the 3662.9 A and 3663.3 A lines. The ultraviolet absorption spectrum of azoisopropane shows one large bancl extending from 2900 A to 3900 A with a flat maximum a t 3540 A. A 935 phototube positionecl behind the reaction cell and outside the hot box was coupled to a sensitive galvanon~eter to measure the transmitted intensity. By using azomethane in the reaction cell as an actinometer and making the assun~ption that, with this compound, aN2 = 1 (7), it was possible to correlate directly the difference in galvanolneter reaclings obtained with the empty cell and the filled cell ~vith the nu~nber of quanta absorbed per cubic centimeter per second. The error introduced into the actinometer l~Wiz?tz~scribt received AZLPZLS~ 5. 1960.

Acknowledgments. -The authors wish to express their appreciRtion to R, Dessauer, L. Cescon, and c.Yembrick for bringing the present problem to their attention and for supplying most of the compounds used in this study. The aid of J. M. White in carrying out these experiments is gratefully acknowledged.We also thank v. I?. Hanson for the construction of the flash photolysis apparatus and €3. R. Stevens for assistance.The oxidation of tris(2-1iiethyl-4-diethyla1ni1iophenyl)iiietha~~e by photogenerated 2-(o-chlorophenyl)-4,5-dipheiiylimidaxolS1 radical (L . ) was studied by flash photolysis.occurs at an unprotonnted amino nitrogen of the leuco dye and is responsible for the first oxidation step. Subsequent reactions do not involve the L . radical and depend only on the structure of the leuco dye and environmental effects.An electron-exchange reaction involving L The influence of pH on both the course and rate of the dye-forming reaction is discussed.

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