Abstract
When ultrasonic irradiation is applied to chemical reactions, the reaction rates are often increased. The application of ultrasonics, therefore provides an alternative mode of acceleration reaction rates which is complementery to conventional methods. The effects of ultrasound on the solvolysis of 2-ch1oro-2-methylpropane were investigated. The ultrasonic source employed in this study were the Decon bath (FS300), operating at a fixed frequency and power (45± 5KHz at 200 watts) and the more controllable Sonicator cup-horn (W-225R), again operating at a fixed frequency (20KHz) with the advantage of power control. Solvolyses were carried out in aqueous alcohol (ethanol, i-propanol and t-butanol) mixtures of various composition and the kinetics monitored conductiometrically.It was found that the ultrasonic rate constants were higher than the non-ultrasonic rate constants for each percentage aqueous solvent. The effect of ultrasound on the rate was found to be greater in solvents of higher alcohol content and in the case of
(I) ethanol-water mixtures in the Decon bath at 250C
and
(II) t-butanol-water mixtures in the Sonicator cup-horn (150C-300C), a maximum in the rate enhancement was obtained at the solvent composition corresponding to maximum structuredness. Also, as the reaction temperature was lowered, the effect of acceleration on reaction rate induced by the ultrasound increased. The relevance of these results have been interpreted in terms of the thermodynamic parameters and discussed in terms of ultrasonically induced cavitation within the solvent and disruption of hydrogen bonded structure. Evidence exists to suggest that solvolysis under ultrasound has become more SN2 like in character and that there is, a drastic change in behaviour of the profile for this solvolysis.
| Date of Award | 1985 |
|---|---|
| Original language | English |
| Supervisor | Timothy Mason (Supervisor) & John P Lorimer (Supervisor) |