New approach to the synthesis of 1,3-dioxolanes

Abstract

Application of ethanol to the synthesis of 1,3-dioxolanes by the condensation of carbonyl compounds with vicinal diols results in a high yield of the reaction product and considerably reduces the duration of the process. It is assumed that the effect of the ethanol is caused by the adduct formation with carbonyl compounds (hemiacetals) which behave as active intermediates of the condensation. A cyclic ketal of acetone with glycerol obtained with the help of ethanol was used as a basis component in the synthesis of a series of ketals substituting diol or carbonyl components by transketalyzation mechanism proceeding without water liberation.Cyclic ketals and acetals (1,3-dioxolanes), condensation products of carbonyl compounds with vicinal di-or polyols, are used in practice as semiproducts and auxiliary substances in the synthesis of polymers, rubber goods and paint-and lacquer materials, perfumes and cosmetics. Recently they attracted additional interest due to the possibility of application in the petrol for improving the octane characteristics, increasing the phase stability of the alcohol-containing gasoline, and decreasing the toxicity of the exhaust gases [1]. The most detailed studies of cyclic ketals as fuel components included the ketals based on glycerol, ethylene glycol and lower ketones (acetone, methyl ethyl ketone, cyclohexanone.The main source of glycerol is the processing of fats and oils, in particular, the production of biologic diesel oil from plant triglycerides, mainly from the colza oil. The growing scale of this production surpasses the demand for crude glycerol that frequently is forcedly regarded as waste. New way of glycerol utilization in the framework of the same production as biodiesel would improve the economy of the process and approach it to the modern ecologic standards. This goal requires a development of new approach to the synthesis of cyclic ketals (1,3-dioxolanes) from glycerol and the other di-and polyols.The dilos condensation with carbonyl compounds providing 1,3-dioxolanes is an acid-catalyzed equilibrium process that can be shifted to the side of the reaction products by the elimination of the formed water. OH OH OH + R 2 CO Catalyst O O OH + R 1 R 2 H 2 O I _ IIIR 1 = R 2 = Me (I); R 1 = Me, R 2 = Et (II); R 1 ,R 2 = (CH 2 ) 5 (III); catalyst H 2 SO 4 , HCl, TsOH etc.Ketones as a rule form with water azeotropic mixtures, therefore the elimination of water can be performed by azeotropic drying. The water content in the mixture with acetone does not exceed fractions of a percent, therefore the azeotropic elimination of water requires in this case a prolonged boiling of the reaction mixture (~40 h) [2]. The chemical binding of water seems more effi cient. In the system glycerol-acetone-Ac 2 O 4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane (I) formed in 93% yield at boiling the reaction mixture over 3 h. The catalyst formed in situ (AcOH) does not require the neutralization for it can be removed by distillation. However therewith along-

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