An Efficient and Chemoselective Procedure for Acylal Synthesis
A novel heterogeneous efficient procedure has been developed for the chemoselective synthesis of acylals (1,1-diacetates) under solvent-free conditions. A novel catalyst prepared by the sulfuric acid catalyzed copolymerization of p-toluenesulfonic acid and paraformaldehyde displays extremely high activities for the title reactions, affording average yields over 90% within several minutes. A comparative study showed that the novel catalyst has much higher activity than other catalysts used for this purpose. Besides, the novel catalyst displays chemoselectivity for the protection of aldehydes in the presence of ketones. In addition the high acidity (4.0 mmol/g), thermal stability (200 ºC) and easy reusability make the novel catalyst one of the best choices for the process.
A new approach to the synthesis of diacetals (diketals) pentaerythritol catalyzed by SO3H-functionalized ionic liquids
Abstract In this article, an efficient, simple and environmentally friendly approach to the synthesis of diacetals (diketals) pentaerythritol using SO 3 H-functionalized ionic liquids (ILs) as catalysts was reported. The ILs show high catalytic activity and reusability with good to excellent yields of the desired products. Hammett method has been used to determine the acidity order of these ionic liquids and the results are consistent with the catalytic activities observed in acetalization reaction. Maximum product yield of 93% was observed on using [PSPy][OTf] as catalyst and it can be reused at least 8 times without obvious activity loss.
Sterol metabolism. XLI. Cholesterol A-ring autoxidations
Abstract Chromatographic and spectral evidence is adduced for the presence of cholest-5-en-3-one, cholest-4-en-3-one, and cholest-4-ene-3,6-dione in samples of cholesterol aged naturally in air or subjected to irradiation in air by 60 Co gamma radiation. These findings establish an additional mode of air oxidation of cholesterol to A-ring 3-ketones. Moreover, the oxidation by air of cholest-5-en-3-one induced by 60 Co gamma radiation yielded cholest-4-en-3-one, cholest-4-ene-3,6-dione, and the epimeric 3-oxocholest-4-ene-6-hydroperoxides. Cholest-4-en-3-one was not altered by irradiation in air, nor was cholesterol isomerized to cholest-4-en-3β-ol upon irradiation. From these observations it is deduced that the radiation-induced A-ring dehydrogenation of cholesterol yields initially cholest-5-en-3-one which upon isomerization yields cholest-4-en-3-one not further oxidized and which by a second oxidation yields the epimeric 3-oxocholest-4-ene-6-hydroperoxides which decompose to cholest-4-ene-3,6-dione.