Effect of Ultrasound on Ester Hydrolysis in Binary Solvents

Abstract

We have investigated the kinetics of the acid-catalyzed hydrolysis of ethyl, propyl, and butyl acetates in aqueous binary mixtures of ethanol and of 1,4-dioxane without sonication and under ultrasound at 22 kHz. Various rate enhancements were found in the region from pure water up to 50 wt % ethanol and 60 wt % dioxane. The calorimetric measurements performed in the same region indicated an insignificant effect of the solvent composition on the ultrasonic power. It was concluded that the sonochemical acceleration of ester hydrolysis in ethanol-water and 1,4-dioxane-water mixtures may be interrelated with the destruction of the molecular structure of the binary solvent and essentially with the perturbation of hydrophobic solute-solvent interactions. The ultrasonic acceleration of polar homogeneous reactions takes place in the bulk reaction medium. This implies the presence of acoustic-field sonochemistry besides the generally accepted hot-spot sonochemistry.

Ultrasonic-assisted derivatization reaction of amino acids prior to their determination in urine by using single-drop microextraction in conjunction with gas chromatography

“…Values in parentheses represent the relative abundance. tion bubble, where transient hot spots with locally extremely harsh conditions occur, are generally accepted as the origin of the chemical effects [35,36]. Another beneficial effect of ultrasonication compared to the corresponding silent reaction is the efficient removal of bubbles from the bulk solution.…”

Ultrasonic detection of hydrophobic interactions: a quantitative approach

“…For the acid-catalyzed hydrolysis of ethyl acetate we observed a similar dependence of the sonication effect on solvent composition. [19,20] These results initially led us to think that sonication effects were merely related to a perturbation of the solvent system. However, on replacing ethyl acetate with more hydrophobic esters, we observed a dramatic change in the dependence of the sonication effect on solvent composition, which obliged us to revise our early point of view.…”

“…Solute-solvent interactions in these complicated systems proved to be particularly important in clarifying the matter. [20,23] Recent spectroscopic, X-ray diffraction, and mass spectrometric investigations have shed light on the structure of ethanol-water solutions. [30][31][32] It has been concluded that small additions of ethanol in the range of 0 < X E < 0.08 (X E being the ethanol molar ratio) exert a strong structure-making effect accompanied by an increase in the self-association of water.…”

“…Our contribution to HI studies consists in applying power ultrasound to kinetic investigation of polar (ionic) homogeneous reactions in solutions, mainly in ethanol-water binary mixtures. [19][20][21][22][23] Ultrasonic acceleration effects on chemical processes are widely exploited both in the laboratory and industrial practice. [24][25][26] Sonication mostly affects reaction rates, yields, and in some cases the ratios of reaction products.…”

“…Sonication studies of solvolysis/hydrolysis reactions in aqueousorganic binary solvents have brought to light specific solutesolvent interactions and hydrophobic effects that are not manifested in conventional kinetic investigations. [19][20][21][22][23][27][28][29] It was concluded that in these cases the sonochemical effects may be related to the perturbation of the molecular structure of the solvent and, more critically, to the destruction of hydrophobic solute-solvent interactions.…”