Reactions of Esters A Preview

Butyl acetate (contributes to characteristic pear odor) 

Among the chemicals used by insects to communicate with one another, esters occur 

Ethyl cinnamate (one of the constituents of the sex pheromone of the male oriental fruit moth) 

Notice that (/ )-(Z)-5-tetradecen-4-olide is a cyciic ester. Recaii from Section 18.15 that cyciic esters are caiied lactones and that the suffix -olide is characteristic of iUPAC names for iactones. 

Esters of glycerol, called glycerol triesters, triacylglycerols, or triglycerides, are abundant natural products. The most important group of glycerol triesters includes those in which each acyl group is unbranched and has 14 or more carbon atoms. Structurally related phosphatidylcholine is a component of cell membranes (Section 24.4). 

From acid anhydrides (Sections 15.8 and 19.5) Acyl transfer from an acid anhydride to an alcohol is a standard method for the preparation of esters. The reaction is subject to catalysis by either acids (H2SO4) or bases (pyridine). 

Esters can participate in hydrogen bonds with substances that contain hydroxyl groups (water, alcohols, carboxylic acids). This confers some measure of water solubility on low-molecular-weight esters methyl acetate, for example, dissolves in water to the extent of 33 g/100 mL. Water solubility decreases as the carbon content of the ester increases. Fats and oils, the glycerol esters of long-chain carboxylic acids, are practically insoluble in water. 

Chapter 19 Carboxylic Acid Derivatives Nucleophilic Acyl Substitution 

TABLE 19.4 Conversion of Esters to Other Carboxylic Acid Derivatives 

Reaction with ammonia and amines (Section 19.11)) Esters react with ammonia and amines to form amides. Methyl and ethyl esters are the most reactive. 

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The structure and nomenclature of sulfonate esters (see 113, 114, or 115) are described in Chapter 20 (Section 20.11.2). It is also true that sulfonate esters are good leaving groups in the substitution reactions described in this chapter (see Section 11.2.4). Sulfonate esters are prepared by the reaction of sulfonic acids with alcohols—much the way that carboxylic acid esters are prepared from carboxylic acids and alcohols (described in Chapter 20, Section 20.11.2). More commonly, sulfonate esters are prepared by the reaction of a sulfonyl chloride (see 112) with an alcohol. This reaction is also described in Chapter 20. This section presents only a simple preview of that chemistry, with the goal of showing that it is easy to convert alcohols into sulfonate esters, which are then useful as leaving groups in substitution reactions. The formal mechanism of these reactions will be discussed in Chapter 20. 

Dicarboxyiic Acids 747 Carbonic Acid 748 Sources of Carboxyiic Acids 749 Synthesis of Carboxyiic Acids by the Carboxyiation of Grignard Reagents Synthesis of Carboxyiic Acids by the Preparation and Hydroiysis of Nitriies Reactions of Carboxyiic Acids A Review and a Preview 753 Mechanism of Acid-Cataiyzed Esterification 754 intramoiecuiar Ester Formation Lactones 757... 

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