REARRANGEMENT STUDIES WITH C¹⁴. X. ETHANOL-2-C¹⁴ FROM THE IRRADIATION OF ETHANOL-1-C ¹⁴ WITH Co⁶⁰ GAMMA RAYS

Abstract

The irradiation of aqueous solutior~s of ethanol-1-C1", containing about 2% ethanol by weight, with up to 58.0 million rads of CoGo y-rays lecl to the formation of up to 0.49y0 ethanol-2-C14 in the alcohol recovered after irradiation. The G value of this isotope position rearrangenlent was about 0.04 and amounted to approximately 2% of the G value for the total amount of ethanol decomposed. Possible mechanisms for the rearrangement are discussed.In a review in 1956, Collinson and Swallow (1) pointed out that radiolysis of alcohols follows the general pattern of a fission of an a-carbon -hydrogen bond to give a n a-hydroxyallcyl radical \\-hich can either dimerize to a glycol or be further oxidized t o a carbonj-1 compound. In the case of ethanol, this generalization can be applied to account satisfactorily for the formation of the chief products derived from the ethanol, namely, acetaldehyde and 2,3-butanediol (2-6).While a number of minor products have been quailtitatively estimated for the radiolysis of pure ethanol with a-particles (3), the irradiation of dilute aqueous solutions of ethanol with X or Coca y-raja was reported to give, besides hydrogen and hydrogen peroxide, only acetaldehyde in the presence of oxygen and acetaldehyde and 2,3-butanediol in deaerated solutions (2, 5, 6). The organic products can, therefore, be regarded as being formed from the a-hydroxyethyl radical. The most recently suggested mechanism for the radiolysis of aqueous solutions of ethanol postulated reactions of H or OH radicals with the solute t o give a-hydroxyethyl froin the breaking of an a-carbon -hydrogen bond (6). No rupture of the carbon-oxygen bond was envisaged. In the present study, dilute aqueous solutions of ethanol-1-C14 was irradiated with Co60 y-rays to ascertain whether any isotope position rearrangement to ethanol-2-C14 would result. Detection of such a rearrangement could possibly be regarded as indicating some rupture of the carbonoxygen bond to give an ethyl radical followed by a 1,2-hydrogen shift in the radical analogous to 1,2-hydride shifts observed in certain reactions involving the ethyl c a t' ion (7,8,9). X stock solution containing 2.O2Y0 ethanol by weight was made up with distilled water and e t h a i~o l -l -C~~. "Its C14 content was about 10 pc/ml. Three-milliliter aliquots were placed ill 4-ml glass vials, stoppered and sealed with wax, and then irradiated a t room temperature in fixed positions near a 90-curie CoGo source. The dose rates were measured by determining the ferric ions formed upon irradiating solutions of ferrous an~inonium sulphate (10). Under the conditions of the present experiments, the dose rates were of the order of 1200 rads/minute.After irradiation, the samples were analyzed for total decomposition of ethanol and for the presence of isotopically rearranged ethanol-2-C1" in the recovered alcohol. Before and after irradiation, equal aliquots of the solution were diluted with exactly the same amounts of absolute ethanol as a carrier. The diluted solutions were converted...