Methyltrioctyl phosphonium methyl carbonate [P8881]+[MeOCO2]- was prepared by the alkylation of trioctyl phosphine with the non toxic dimethyl carbonate. This salt was a convenient source to synthesize different ionic liquids where the methyltrioctyl phosphonium cation was coupled to weakly basic anions such as bicarbonate, acetate, and phenate. At 90-220 °C, all these compounds [P8881]+X-; X=MeOCO2; HOCO2; AcO; PhO] were excellent organo-catalysts for the transesterification of dimethyl- and diethyl-carbonate with primary and secondary alcohols, including benzyl alcohol, cyclopentanol, cyclohexanol, and the rather sterically menthol. Conditions were optimized to operate with very low catalyst loadings up to 1 mol% and to obtain non symmetric dialkyl carbonates (ROCO2R’; R= Me, Et) with selectivity up to 99% and isolated yields > 90%. The catalytic performance of the investigated ionic liquids was discussed through a cooperative mechanism of simultaneous activation of both electrophilic and nucleophilic reactants.
Carbonate, Acetate and Phenolate Phosphonium Salts as Catalysts in Transesterification Reactions for the Synthesis of Non Symmetric Dialkyl Carbonates
SELVA, Maurizio;NOE', Marco;PEROSA, Alvise;GOTTARDO, MARINA
2012-01-01
Abstract
Methyltrioctyl phosphonium methyl carbonate [P8881]+[MeOCO2]- was prepared by the alkylation of trioctyl phosphine with the non toxic dimethyl carbonate. This salt was a convenient source to synthesize different ionic liquids where the methyltrioctyl phosphonium cation was coupled to weakly basic anions such as bicarbonate, acetate, and phenate. At 90-220 °C, all these compounds [P8881]+X-; X=MeOCO2; HOCO2; AcO; PhO] were excellent organo-catalysts for the transesterification of dimethyl- and diethyl-carbonate with primary and secondary alcohols, including benzyl alcohol, cyclopentanol, cyclohexanol, and the rather sterically menthol. Conditions were optimized to operate with very low catalyst loadings up to 1 mol% and to obtain non symmetric dialkyl carbonates (ROCO2R’; R= Me, Et) with selectivity up to 99% and isolated yields > 90%. The catalytic performance of the investigated ionic liquids was discussed through a cooperative mechanism of simultaneous activation of both electrophilic and nucleophilic reactants.File | Dimensione | Formato | |
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