Esters general preparation

The most widely used method for the preparation of carboxylic acids is ester hydrolysis. The esters are generally prepared by heterocyclization (cf. Chapter II), the most useful and versatile of which is the Hantzsch s synthesis, that is the condensation of an halogenated a- or /3 keto ester with a thioamide (1-20). For example ethyl 4-thiazole carboxylate (3) was prepared by Jones et al. from ethyl a-bromoacetoacetate (1) and thioformamide (2) (1). Hydrolysis of the ester with potassium hydroxide gave the corresponding acid (4) after acidification (Scheme 1). 

As previously mentioned the esters of thiazolecarboxylic acids are generally prepared by the Hantzsch s synthesis (17, 20),... 

CP esters are generally prepared as the ammonium salt [9038-38-4] by the reaction of cellulose with phosphoric acid and urea at elevated temperatures (130—150°C). The effects of temperature and urea/H PO /cellulose composition on product analysis have been investigated (33). One of the first commercially feasible dameproofing procedures for cotton fabric, the Ban-Flame process (34,35), was based on this chemistry. It consists of mixing cellulose with a mixture of 50% urea, 18% H PO, and 32% water. It is then pressed to remove excess solution, heated to 150—175°C for 5—30 minutes, and thoroughly washed (36). 

Generally, monochloroacetic acid [79-11-8] (MCA) is added to the reaction slurry containing sufficient excess sodium hydroxide to neutralize the MCA and effect its reaction. The use of esters of MCA has also been reported (52). Common reaction diluents are isopropyl alcohol, /-butyl alcohol, or ethyl alcohol (53,54). Dimethoxyethane has also been reported to be effective (55). The product is isolated and washed with aqueous alcohol or acetone to remove by-product salts. Unpurified cmde grades are generally prepared in the absence of diluents (56—59). 

General Preparation of Esters, 227 General Cleavage of Esters, 229... 

The section on general preparation of esters should also be consulted. 

Ester eliminations are normally one of two types, base catalyzed or pyrolytic. The usual choice for base catalyzed j5-elimination is a sulfonate ester, generally the tosylate or mesylate. The traditional conditions for elimination are treatment with refluxing collidine or other pyridine base, and rearrangement may occur. Alternative conditions include treatment with variously prepared aluminas, amide-metal halide-carbonate combinations, and recently, the use of DMSO either alone or in the presence of potassium -butoxide. 

General Preparations of Esters General Cleavage of Esters Transesterification Enzymatically Cleavable Esters Heptyl, 381... 

One of the most general preparative routes to allyl- and 2-butenylboranes involves the reaction of an allylic organometallic species and an electrophilic borylating reagent. Various esters of allylboronic acid have been prepared in this way2,4-5. 

This section covers the preparation and reactions of quinoxalinecarboxylic esters, generally the most convenient derivatives of quinoxalinecarboxylic acids. 

Alkynenitriles, RC=CC=N, are generally prepared by dehydration of acid amides. RC=CC(=0)NH2, with phosphorous pentoxide. For HC=CC=N and NsCChCChN [130] this is the only available method it requires the previous synthesis of the carboxylic esters and their conversion into the acid amides. In principle it should be possible to prepare these useful... 

The acid moiety generally determines the odor of esters derived from aromatic or araliphatic acids. Unless stated otherwise, the esters are prepared from the corresponding acids or acid derivatives and alcohols by the customary methods. 

Oxetanones can be generally prepared by displacement processes on various /3-substituted carboxylic acids or by halolactonization of /3,y-unsaturated acids. A very general and reliable method consists of treatment of a /8-hydroxy acid with benzenesulfonyl chloride and pyridine at 0°C (equation 91). The yields of /3-lactones are usually in excess of 80% (79JOC356, 74JOC1322). An alternative method involves cyclization of the benzenethiol ester of a /3-hydroxy carboxylic acid by means of mercury(II) methanesulfonate in acetonitrile (equation 92). The yields were excellent in the two cases reported (76JA7874). 

Synthesis Epoxy resins consisting ofglycidyl ether, ester and amines are generally prepared by the condensation reaction between diol, dibasic acid or amine and epichlorohydrin in the presence of sodium hydroxide with the elimination of hydrochloric acid. The commercially available epoxy resins are, however, made by the reaction of epichlorohydrin and bisphenol-A. Cashew nut shell liquid (CNSL)-based novolac epoxy resins have also been reported [342]. 

Preparation of a Boc-Protected a-Amino Aldehyde via Reduction of the Corresponding Phenyl Ester General Procedure 12 1... 

Recovery of naturally occurring esters is accomplished by steam distillation, extraction, pressing, or by a combination of these processes. Synthetic esters are generally prepared by reaction of an alcohol with an organic acid in the presence of a catalyst such as sulfuric acid, p tolucitcsullonic acid, or mcthancsulfonic acid. 

Preparation. The general preparation of u-hydroxy acids is by the hydrolysis of an a-halo acid or by Ihe acid hydrolysis of the cyanohydrins of an aldehyde or a ketone. 0-Hydroxy acids may be made by catalytic reduction of 0-keut esters followed by hydrolysis. 0-Hydroxy acids can also he prepared by ihe ReformaCsky reaction y-Hydroxy acids are seldom obtained in the free slate because of ihe case wilh which they form... 

Oxadiazoles have often attracted the attention of medicinal chemists as stable bioiso-steres of metabolically labile esters. 1,3,4-Oxadiazoles are generally prepared by cyclodehydration of 1,2-diacylhydrazines or their equivalents. Symmetrical 2,5-disubstituted examples were able to be rapidly prepared in a one-pot condensation-cyclodehydration of benzoic acids (2 equiv) with hydrazine dihydrochloride, in the presence of... 

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