Acid Catalysed Hydrolysis of Ester
The acid-catalyzed hydrolysis of ester is a chemical reaction in which an ester molecule reacts with water in the presence of an acid catalyst to produce a carboxylic acid and an alcohol. The acid catalyst helps to facilitate the reaction by donating a proton to the ester molecule, making it more susceptible to nucleophilic attack by water. This process is commonly used in organic synthesis and industrial processes.
3 Key excerpts on "Acid Catalysed Hydrolysis of Ester"
eBook - ePubApplied Biocatalysis
Volume 1
- Harvey W. Blanch, Douglas S. Clark, Harvey W. Blanch, Douglas S. Clark(Authors)
- 2021(Publication Date)
- CRC Press(Publisher)
...These enzymes are, for the most part, mechanistically well understood, highly stable, cofactor independent, and commercially available. These are attributes that make them well suited for commercial applications both in aqueous solutions and in organic media. They also carry out hydrolysis, a reaction with limited commercial appeal. In organic media, however, these enzymes catalyze a variety of reactions including esterification, transesterification, thiotransesterification, interesterification (acyl exchange), lactone synthesis, aminolysis, and oximolysis [ 3, 41 ]. All these reactions are possible only in low water environments. Because hydrolytic enzymes are mechanistically similar, specific hydrolases will not be grouped into separate classifications; rather, general categories of organic synthesis will be examined. Ester Synthesis: General Lipases, both as free enzyme powders and in whole cells, have been used to catalyze esterifications in nearly anhydrous solvents. Bell and coworkers performed lipase-catalyzed fatty acid acylations by suspending cells of Rhizopus arrhizus in octanol containing palmitic or oleic acid [ 116 ]. Yields of the octyl esters in excess of 70% were obtained both in batch and continuous systems [ 117 ]. The lipase remained active in the solvents for a month with no loss in operational stability. Similar synthetic reactions have generated much interest in the production of geranyl butyrate [ 118 ], menthyl acetate [ 119 ], waxes and emulsifiers [ 120, 121 ], and stereo- and regioselective preparative acylations for intermediates in chemical synthesis [ 4, 122, 123 ]. In some cases, conventional esterification has given way to transesterification, whereby a good leaving group on the acyl donor is used and high yields of ester synthesis can be obtained [ 41 ]. Lipase catalysis has been extended to supercritical fluids...
eBook - ePubGreen Vegetable Oil Processing
Revsied First Edition
- Walter E. Farr, Andrew Proctor, Walter E. Farr, Andrew Proctor(Authors)
- 2013(Publication Date)
- Academic Press and AOCS Press(Publisher)
...The 3-D structures are determined by roughly 20 different naturally-occurring amino acids linked together in a chain-like fashion forming a macromolecule. These macromolecules fold into 3-D structures (Copeland, 2000). The individual amino acid’s side chain enables the chemical reactivities that produce the enzyme’s ability to distinguish, orientate, and bind the substrate to the active site. Once the substance has been engaged with the active site of the enzyme, the chemical reaction takes place followed by the release of the chemical products. The International Union of Biochemistry and Molecular Biology has developed a nomenclature for naming enzymes, Enzyme Commission Number (EC number). Each enzyme is given a four-sequence number to classify it based on the chemical reaction it catalyzes. EC 3—Hydrolases are enzymes that breakdown molecules using water. The chemical equation is as follows: A – B + H 2 O → A – OH + B – H EC 3.1—Hydrolases that react on ester bonds. EC 3.1.1—Hydrolases that react on the ester bond located on the carboxylic acid. Lipases (EC 3.1.1.3) are enzymes that in the presence of water cleave the fatty acids present on triacylglycerols. Lipases use an amino acid catalytic triad serine-histidine-aspartic acid/glycine (Ser-His-Asp/Glu) for ester bond hydrolysis (Brumlik, et al., 1996 ; Shu et al., 2007). In this triad, histidine acts as a general base forming a hydrogen bond with a catalytic serine residue which then allows the formation of the first tetrahedral transition state. At low pH conditions, i.e., pH 3 and lower, histidine will be protonated. If histidine is already protonated, the hydrogen bond formation with catalytic serine residue will not occur, and reaction will not proceed, thereby reducing or eliminating enzymatic activity (Kerovuo, 2008). Most enzyme reactions are reversible, but the reaction conditions typically must be dramatically changed for a reverse reaction to occur...
eBook - ePubBiodiesel Science and Technology
From Soil to Oil
- Jan C.J. Bart, N Palmeri, Stefano Cavallaro(Authors)
- 2010(Publication Date)
- Woodhead Publishing(Publisher)
...Acid-catalysed production of biodiesel can economically compete with base-catalysed processes using virgin oils, especially when the former uses low-cost feedstocks [ 16, 17 ]. The accepted chemical mechanism for homogeneous acid-catalysed transesterification (Fig. 8.4) consists of: (i) protonation of the TG carbonyl group by the acid catalyst (key interaction); (ii) nucleophilic attack by an alcohol molecule on the protonated carbonyl (electrophilic species); (iii) solvent-assisted proton migration; (iv) cleavage of the intermediate hemiacetal species; (v) formation of a protonated alkyl monoester and diglyceride DG; and (vi) proton transfer to regenerate the acid catalyst [ 38 ]. The sequence is repeated twice to yield three alkyl monoesters and glycerol. Comparison of Figs 8.2 and 8.4 thus shows that acid catalysis is characterised by formation of a more electrophilic species and base catalysis by that of a stronger nucleophile. This crucial distinction is responsible for the observed differences in activity. The acid strength requirements of an organic reaction are strongly influenced by the presence of electron donor or withdrawing substituents on the functional group undergoing chemical transformation. 8.4 Mechanism of acid-catalysed transesterification of triglycerides. Fewer studies have dealt with acid-catalysed transesterification of lipid feedstocks than base-catalysed synthesis of biodiesel. In homogeneous acid transesterification of SBO with BuOH three reaction regimes were observed, as for base-catalysed reactions [ 12 ]. Transesterification followed pseudo-first-order kinetics. Acid-catalysed transesterification kinetics of SBO [ 12 ] and waste frying oil [ 106 ] have been reported. The rate of acid-catalysed methanolysis of pure FA (from saponified SBO or crude rice bran oil (CRBO)) is faster (99% conversion in 1 h at 338 K) than methanolysis of 60% FFA containing CRBO (> 90% conversion in 6 h) or CRBO + 5% H 2 O (2% after 3 h) [ 107 ]...
