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Esters are chemical compounds derived from an inorganic acid or organic acid in which at least one -OH (hydroxyl) group is replaced by an -O-alkyl (alkoxy) group.
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- Carboxylic acids react with alcohols to form esters, as long as a mineral acid catalyst is present. This reaction is only slightly exothermic, and its equilibrium may be shifted in either direction by the choice of reaction conditions. The reverse of ester formation is ester hydrolysis. The mechanism of esterifi cation is acid-catalyzed addition of alcohol to the carbonyl group followed by acid-catalyzed dehydration. Intramolecular ester formation results in lactones, favored only when five- or six-membered rings are produced.
- K. Peter C. Vollhardt, Neil E. Schore (2011) Organic chemistry : structure and function 6th ed. Ch. 19 : Carboxylic Acids
- α,β-Unsaturated aldehydes are converted directly to carboxylate esters by MnO2 and NaCN in an alcohol solvent. Sodium cyanide catalyzes the oxidation by forming a cyanohydrin that is susceptible to MnO2 oxidation. Methanolysis of the acyl cyanide intermediate in the example below gives the methyl ester in excellent yield.
The oxidation of allylic alcohols directly to methyl carboxylates has been reported using MnO2 and sodium cyanide in methanol.
Aldehydes dissolved in alcohols react with 1 to 2 equivalents of aqueous NaOCl or Oxone (a potassium triple-salt that contains potassium peroxymonosulfate, KHSO5) to furnish the corresponding esters.
- George S. Zweifel and Michael H. Nantz, Modern Organic Synthesis (2006), Ch. 4 : Functional Group Transformations: Oxidation and Reduction