Alcohols In Ionic Liquids Research Articles

Synthesis of esters in ionic liquids: The effect of vinyl esters and alcohols

Free Candida antarctica lipase B (CALB) was successfully applied to catalyzing the synthesis of alkyl esters by transesterification from vinyl esters and alcohols in ionic liquids based on 1-alkyl-3-methylimidazolium cations ([bmim +] and [omim +]) and the hexafluorophosphate anion ([PF 6 −]). First, the variables affecting the performance of CALB in transesterification reactions in ionic liquids, temperature and pH, were studied, choosing the synthesis of butyl butyrate in [bmim +][PF 6 −] as reaction model. An increase in the rate of butyl butyrate synthesis in [bmim +][PF 6 −] was observed as the temperature was increased from 30 to 70 °C, while the optimal pH was 7. Secondly, the role of vinyl esters and alcohols in lipase-catalyzed ester synthesis in ionic liquids was investigated. When the number of carbon atoms of the vinyl ester was increased, the optimum activity was found for six carbon atoms. The influence of the alkyl chain length of the alcohol was tested, the optimal length being four carbon atoms. The rate of catalyzed ester synthesis of esters was found to be closely dependent on the solvent medium, being higher in [omim +][PF 6 −].

Kinetic study of heterogeneous catalytic hydrogenation of cyclohexene to cyclohexane in ionic liquid–alcohols mixtures

Abstract Heterogeneous catalytic hydrogenation of cyclohexene, catalyzed by Pt/Al2O3, was carried out in solutions of 2-hydroxyethylammonium formate (a room temperature ionic liquid, RTIL) mixed with methanol, ethanol and propan-2-ol at 25 °C. The rate constants of the reaction in ionic liquid alcohol mixtures were higher than alcohol alone. First-order rate constant of the reaction in the RTIL relative to propan-2-ol is approximately 28. Furthermore, the rate constant of the reaction increases with the mole fraction of the ionic liquid. Single-parameter correlations of log k vs. normalized polarity parameter ( E T N ), hydrogen-bond acceptor basicity (β) and hydrogen-bond donor acidity (α) do not give acceptable results in the solutions. In addition, log k does not show an acceptable dual-parameter correlation with π* (dipolarity/polarizibility, one of the Kamlet–Taft parameters for solvent that shows the dipolarity of the solvent) and α, π* and β and E T N and β. However single-parameter correlation of log k vs. π* gives reasonable results. The increase of the reaction rate with π* is attributed to the non-polar nature of the reactants.

Enzymatic production of isoamyl acetate in an ionic liquid–alcohol biphasic system

A systematic investigation and optimization on the conditions for the biphasic enzymatic production of isoamyl acetate in ionic liquid solvents is reported. As a catalyst, immobilized Candida antarctica lipase B was used. As the best imidazolium type ionic liquid, [bmim]PF 6 was selected and other reaction conditions such as initial water content, acetic acid to isoamyl alcohol substrate ratio, [bmim]PF 6 to isoamyl alcohol solvent ratio, enzyme amount and temperature were optimized. The recyclability of the applied IL per se and together with enzyme were also studied and found to be reusable in 7 and 10 cycles, respectively. With the adjusted optimum conditions high isoamyl acetate yields (near 100%) were achieved.

Palladium‐Catalyzed Heck Arylations of Allyl Alcohols in Ionic Liquids: Remarkable Base Effect on the Selectivity.

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The electrochemistry of TEMPO-mediated oxidation of alcohols in ionic liquid

The detailed electrochemistry of TEMPO-mediated oxidation of alcohols to carbonyl compounds in ionic liquid medium is presented. It is shown that TEMPO diffusion currents are suppressed in IL medium, relative to acetonitrile solvent, due to the high viscosity of the IL medium; however, the presence of substrate and base reagent significantly reduces IL viscosity, improving performances significantly. Cyclic voltametry shows that the kinetics of the reaction between electrooxidized TEMPO and the alcohol are similar in both media. It was also observed that in the case where the oxidation product is non-enolizable, electrolyses (diaphragm cell) with catalytic quantities of TEMPO, and in the presence of base (2,6-lutidine), results in close to 100% Faradaic and 100% chemical efficiencies. In contrast, prolonged electrolysis of alcohols yielding enolizable products results in catalyst deactivation due to the irreversible reaction between the active form of the catalyst and the product, which ultimately leads to low product yields and catalyst loss. Under these circumstances, reasonable Faradaic and chemical selectivities can only be obtained with partial electrolyses (to ≤1F/mol).

A Simple, Efficient and Recyclable Copper(II) Acetylacetonate Catalytic System for Oxidation of sec-Alcohols in Ionic Liquid

A selective oxidation of secondary alcohols to the corresponding ketones in room temperature ionic liquid was achieved by using copper acetylacetonate/tert-butylhydroperoxide system. The catalytic system can be recycled and reused for five runs without any significant loss of catalytic activity and products are obtained in excellent yield.

Aerobic, catalytic oxidation of alcohols in ionic liquids

An efficient and simple catalytic system based on RuCl3 dissolved in ionic liquids has been developed for the oxidation of alcohols into aldehydes and ketones under mild conditions. A new fluorinated ionic liquid, 1-n-butyl-3-methylimidazolium pentadecafluorooctanoate, was synthesized and demonstrated better performance that the other ionic liquids employed. Moreover this catalytic system utilizes molecular oxygen as an oxidizing agent, producing water as the only by-product.

Arylation of Allylic Alcohols in Ionic Liquids Catalyzed by a Pd‐Benzothiazole Carbene Complex.

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Arylation of Allylic Alcohols in Ionic Liquids Catalysed by a Pd‐Benzothiazole Carbene Complex

AbstractThe reaction of aryl bromides with allylic alcohols catalysed by a Pd‐benzothiazole carbene complex, in tetrabutylammonium bromide as solvent, leads principally to β‐arylated carbonyl compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)