Esterification esters

FIGURE 21-38 Synthesis of cholesteryl esters. Esterification converts cholesterol to an even more hydrophobic form for storage and transport. 

Medium Boiling Esters. Esterification of ethyl and propyl alcohols, ethylene glycol, and glycerol with various acids, e.g.. chloro- or bromoaceiic. or pyruvic, by the use of a third component such as benzene, toluene, hexane, cyclohexane, or carbon tetrachloride to remove the water produced is quite common. 

Medium Boiling Esters. Esterification of ethyl and propyl alcohols, ethylene glycol, and glycerol with various acids, eg, chloro- or bromoacetic, or pyruvic, by the use of a third component such as benzene, toluene, hexane, cyclohexane, or carbon tetrachloride to remove the water produced is quite common. Benzene has been used as a co-solvent in the preparation of methyl pyruvate from pyruvic acid (101). The preparation of ethyl lactate is described as an example of the general procedure (102). A mixture of 1 mol 80% lactic acid and 2.3 mol 95% ethyl alcohol is added to a volume of benzene equal to half that of the alcohol (ca 43 mL), and the resulting mixture is refluxed for several hours. When distilled, the overhead condensate separates into layers. The lower layer is extracted to recover the benzene and alcohol, and the water is discarded. The upper layer is returned to the column for reflux. After all the water is removed from the reaction mixture, the excess of alcohol and benzene is removed by distillation, and the ester is fractionated to isolate the pure ester. 

This is the general mechanism for acid catalyzed oxygen isotope exchange of carboxylic acids and esters, esterification, ester hydrolysis, and amide hydrolysis (see Vol. 10). 

Figure 12 Enantiomer separation of a-Iipoic methyl ester (esterification with diazomethane) and determination of enantiomeric purity of R enantiomer 40-m Pyrex glass capillary with 3-ac-2,6-pe p CD at 180°C.

Figure 13 Enantiomer separation of analgesic drug ibuprofen as methyl ester (esterification with diazometh-ane). 25-m Pyrex glass capillary with per-pentyl-p-CD and per-methyl-p-Cd (1 1, w/w) at 140 C,...

An ester is a chain composed primarily of carbon and hydrogen atoms. This chain is typically attached to the parent steroid hormone at the 17th carbon position (beta orientation), although some compounds do carry esters at position 3 (for the purposes of this article it is not crucial to understand the exact position of the ester). Esterification of an injectable... 

Lipases and esterases comprise a versatile group of enzymes that catalyze the hydrolysis of esters, esterifications and transesterifications via an acyl enzyme intermediate (Chapter 11). Various other nucleophiles can attack this acyl enzyme complex in addition to water. 

V, N -Dicyclohexylcarbodiimide. DCC Nitroacetic esters. Esterification conventional methods, but it can be p serves to anchor nitroacetyl groups to h> 4-O-Alkyltetronic acids.- Preparau acids under mild conditions relies on the e... 

Vinyl esters. Esterification followed by oxidation (in situ thermolysis) generates the target esters. 

Ester hydrolysis Hydrolytic decarboxylation of /3-keto esters Esterification... 

The thiol esters of CoA are required for the enzyme reactions 3 to 6 of Fig. 6 to proceed. The free acids are inert as substrates. The reactions can be induced with the free acids if CoA and ATP are added to the incubations with crude enzyme preparations, although the reaction rates are much lower than with the CoA thiol esters. Esterification with CoA is presumably catalyzed by acetyl thiokinase. 

There are several naturally occurring androgens and probably thousands of synthetic androgens. Some of the more commonly used synthetic androgens are esters. Esterification of steroids bearing a hydroxyl group at the 17-position has been demonstrated to improve duration of biolo-... 

G. Celluloseester R esters cellulosiques Reaction of - cellulose with inorganic or organic acids yields cellulose esters (->esterification) ... 

L. is used in - soaps, - metallic soaps, in- alkyd resins and in synthesis of lauric esters (- esterification). 

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