3043
THEy RADIOLYSIS OF 2-PROPANOL
The y Radiolysis of 2-Propanol. V.1.
Oxidation by Carbon Tetrachloride
by Cecelia RadlowskiIb and Warren V. Sherman Department of Physical Science, Chicago State College, Chicago, Illinois
60631
(Received January $1, 1970)
Dilute solutions of carbon tetrachloride in 2-propanol have been subjected to W o y irradiation. Reduction of the solute to chloroform and hydrogen chloride was observed with the concomitant oxidation of the solvent to acetone in accord with the stoichiometry: CCL (CH&CHOH-L CHC& HCl (CH3)2CO. The 100eV yields were independent of initial carbon tetrachloride concentration in the range 1 x 10-2 to 2 x 10-1 M but showed a first-order dependence on 2-propanol concentration when the system was diluted with 2-methyl2-propanol. A chain mechanism is indicated by the magnitude of G(products); inhibition by 0 2 is consistent with free radical intermediates being involved. The observed dose-rate dependence is in accord with free radical chain carriers undergoing second-order termination. The data are consistent with the chain propagation steps, CCl3 (CH&CHOH -* CHCls (CH3)dOH (3) and (CH&COH CCla --c (CHJ2C0 HCl CCb (4), with k s = 3 M - 1 sec-1 and k3 < k+
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The original motivation for an examination of the radiation chemistry of 2-propanol solutions of carbon tetrachloride was to gain further information concerning the scope of the recently radical-initiated chain oxidation of primary and secondary aliphatic alcohols which occurs under alkaline conditions. It was thought that carbon tetrachloride would fulfill the criteria set115 for compounds that would enter into electron transfer with the ionized form of the a-hydroxymethyl radical (generated by free radical attack on the alcohol solvent) and thus effect a chain oxidation reaction analogous to that obtained with alkyl and aryl monobromides and monoiodides. It has long been knowns that carbon tetrachloride undergoes slow decomposition in basic alcoholic solution. In the present work i t was found that 2-propanol solutions containing 0.1 M carbon tetrachloride and 0,l M potassium hydroxide could be stored for several days without the occurrence of a significant amount of chemistry. However, on deaerating (flushing with nitrogen or pumping on a vacuum line), a relatively rapid reaction set in.’ Because of this instability of 02-free alkaline carbon tetrachloride solutions a quantitative study of their radiation chemistry was not attempted. Preliminary experiments on the radiolysis of neutral solutions of carbon tetrachloride, however, indicated some interesting chemistry, and hence study of the system was continued. Some time ago, Hannerz,S in search of a potential y-ray dosimetry system involving the production of acid in proportion to absorbed dose, briefly surveyed the radiolysis of 50 vol % mixtures of carbon tetrachloride with primary and secondary alcohols. Although the very large 100-eV yields of hydrochloric acid observed are an asset for such a chemical dosimeter, Hannerz concluded that “insufficient stability to impurities preclude an extended use of these systems for dosimetric purposes.” I n the present study the data for dilute deaerated solutions of
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carbon tetrachloride in 2-propanol show that although certain criteria for a sensitive chemical dosimeter are met (large 100-eV yields, direct proportionality of yield to exposure time when subjected to constant radiation intensities, yield reproducibility), observation of a dependence of yield-dose upon radiation intensity is not consistent with the requirements of a useful dosimeter. In connection with the present study, the earlier work of Minderg on the radiolysis of polychlorinated hydrocarbons in alcohols should be cited.
Experimental Section Materials. 2-Propanol (Baker Spectrophotometric reagent) was used as received; the only impurity detected by glc analysis was acetone (
