The Radiation Chemistry of Aqueous Solutions of Chloral Hydrate and of Bromal Hydrate

Abstract

The radiation chenlistry of aqueous solutions of chloral hydrate and of bronlal hydrate has been further investigated. T h e electrical conductivity method of Andrews and Shore (1) was used to follow the appearance of acid. T h e yield of acid was found to be dependent on the dose rate, contrary t o the conclusion reached by Andrews and Shore but in agreement with the results of other workers. A reexamination of Andrews and Shore's paper indicates that a n incorrect interpretation was made of their data and reveals that, in fact, their data also indicate a dose rate dependence for the yield of acid. A free radical mechanism is proposed which is in good agreement with the obscrved dependence of the rate of formation of acid upon the dose rate and upon the solute concentration in both the presence and in the absence of oxygen.Several reports have been published on the radiation chemistry of aqueous solutions of chloral hydrate (1-6) and of bron~al hydrate (6-11). There is general agreenlent that one of the main products is the corresponding hydrohalic acid. In the earliest reported work, that of Andrews and Shore (1) on aqueous chloral hydrate solutions, the appearance of hydrochloric acid was followed by ineasureinent of the electrical conductivity of the solution. A siinilar method was used by I-Iilsenrod (4). In the other worlr referred to, the production of acid was followed by titration with standard base. Andrews and Shore (1) interpreted their results in a manner which indicated that theG value (number of illolecules of product per 100 eV of energy absorbed) of I-IC1 was independent of dose rate. I-Iilsenrod (4) did not investigate the dose rate dependence. In contrast, all of the other worlters (2, 3, 5 , 6) reported a dose rate dependence, the G value being approxiinately inversely proportional to the square root of the dose rate. A siinilar dose rate dependence was found for aqueous solutions of broinal (6-9).No satisfactory explanation for this large discrepancy in the dose rate dependence has been offered. While.it seeins unliltely, a possible explanation is that the different behavior reported arises because of the methods used to follow the appearance of the hydrohalic acid. The electrical conductivity method is not very specific, since the appearance of any electrolyte will result in an increase in electrical conductivity. The titration nlethod is more specific, since it will respond only to acidic products. I t should be noted that Andrews and Shore (1) did do sonle chloride analysis and PI-I measurements which indicated that the electrical conductivity measured by t h a n was due mainly to hydrochloric acid. By titration with a base, they found that the anlount of total acid present was solnewhat larger than that which would be expected if only hydrochloric acid was responsible for the electrical conductivity. Similarly, Woods and Spinks (7), and I-Ieusinger et al. (8)

MEAN LIFETIME OF FREE RADICAL CHAINS IN 60Co γ-IRRADIATED CHLORAL HYDRATE AND BROMAL HYDRATE SOLUTIONS

“…The results for the chloral hydrate solutions presented in Table I indicate that r , kt, and k, are not very pH dependent. This is consistent with the mechanism proposed by the present authors for the irradiation of solutions of chloral hydrate and of bromal hydrate (2). Similarly the variation of 7 either with dose rate or with concentration is qualitatively consistent with the proposed reaction scheme (2).…”

“…This point, which was not made in ref. 2, is further support for the reaction scheme proposed by the present authors (2). The effect of a decreased dose rate would be to lower the concentration of ii.…”

Decomposition of chloral hydrate in aqueous solution by the action of ultrasound

“…ultrasound, regardless of the concentration of oxygen gas dissolved in the solutions. These results are different from those observed in radiolysis by McIntosh et al 4 They reported that in the case of radiation-induced decomposition of aqueous solution of chloral hydrate the rate is proportional to [Ch]0•39/0•66, where I is the intensity of rays.…”