Protic Acid Immobilized on Solid Support as an Extremely Efficient Recyclable Catalyst System for a Direct and Atom Economical Esterification of Carboxylic Acids with Alcohols

Abstract

A convenient and clean procedure of esterification is reported by direct condensation of equimolar amounts of carboxylic acids with alcohols catalyzed by an easy to prepare catalyst system of perchloric acid immobilized on silica gel (HClO(4)-SiO(2)). The direct condensation of aryl, heteroaryl, styryl, aryl alkyl, alkyl, cycloalkyl, and long-chain aliphatic carboxylic acids with primary/secondary alkyl/cycloalkyl, allyl, propargyl, and long-chain aliphatic alcohols has been achieved to afford the corresponding esters in excellent yields. Chiral alcohol and N-t-Boc protected chiral amino acid also resulted in ester formation with the representative carboxylic acid or alcohol without competitive N-t-Boc deprotection and detrimental effect on the optical purity of the product demonstrating the mildness and chemoselectivity of the procedure. The esters of long-chain (>C(10)) acids and alcohols are obtained in high yields. The catalyst is recovered and recycled without significant loss of activity. The industrial application of the esterification process is demonstrated by the synthesis of prodrugs of ibuprofen and a few commercial flavoring agents. Other protic acids such as H(2)SO(4), HBr, TfOH, HBF(4), and TFA that were adsorbed on silica gel were less effective compared to HClO(4)-SiO(2) following the order HClO(4)-SiO(2) >> H(2)SO(4)-SiO(2) > HBr-SiO(2) > TfOH-SiO(2) >> HBF(4)-SiO(2) approximately TFA-SiO(2). When HClO(4) was immobilized on other solid supports the catalytic efficiency followed the order HClO(4)-SiO(2) > HClO(4)-K10 > HClO(4)-Al(2)O(3) (neutral) > HClO(4)-Al(2)O(3) (acidic) > HClO(4)-Al(2)O(3) (basic).

Biomass valorization derivatives: Clean esterification of 2-furoic acid using tungstophosphoric acid/zirconia composites as recyclable catalyst

“…Traditional methods for the synthesis of 2-furoate esters include the Fischer esterification reaction for the condensation of the corresponding alcohols with 2-furoic acid using acid catalysts such as sulfuric acid [12,13], toluene-4-sulfonic acid [14], thionyl chloride [15], chloro-trimethyl-silane [16], potassium carbonate [17], chloridic acid [18], silica gel-immobilized perchloric acid [19], among others. Other methods include: oxidative esterification of furfural using manganese (IV) oxide as catalyst [20], reaction between 2-furoic acid with alkyl iodide using IRA 904 in acetonitrile as catalyst [21], reaction between 2-furoylchloride and alcohols [22] and transesterification of methyl or ethyl 2-furoate using a long-chain alcohol catalyzed by 4 A molecular sieves [23].…”

Use of Crude Glycerol from Biodiesel Producers and Fatty Materials to Prepare Allyl Esters

“…Moreover, they were higher the ones described by Biermann et al [23] using calendula oil or tung oil and allyl alcohol as starting material. Similar yields were only reached when allyl fatty esters were prepared by esterification of free carboxyllic acid and allyl alcohol using HClO 4 -SiO 2 as catalyst [24], or from metal carboxylates and allyl halydes, not a friendly reagent [25].…”

Facile and eco-friendly synthesis of bis(tetrahydrobenzofuran-2-yl)alkane derivatives catalyzed by H2S04.SiO2 under solvent-free conditions

“…23 H 2 SO 4 •SiO 2 has already been used in cylcoadditions, 24 Beckmann rearrangements, 25 glycosylations, 26 condensations 27 and esterifications. 28 During our on-going efforts to develop convenient approaches to tetrahydrobenzofuran derivatives as H + /K + -ATPase inhibitors, 29 we discovered that H 2 SO 4 •SiO 2 was a high-efficient and recyclable catalyst for preparing the bis(2-tetrahydrobenzofuranyl)alkanes in a synthetically practical procedure (solvent-free, stoichiometric ratios and short reaction times) with widely functional group compatibility.…”