Alcohols esterification reactions

The esterification reaction in making ester oils is commonly carried out with a catalyst at about 210°C while removing excess water as it forms (32). Excess acid or alcohol is then stripped off, and unreacted acid is neutrali2ed with calcium carbonate or calcium hydroxide before final vacuum drying (qv) and filtration (qv). 

Similarly, another important esterification reaction of isopropyl alcohol iavolves the production of tetraisopropyl titanate [546-68-9], a commercial polymeri2ation catalyst, from titanium tetrachloride [7550-45-0] and isopropyl alcohol. 

Completion of Esterification. Because the esterification of an alcohol and an organic acid involves a reversible equiUbrium, these reactions usually do not go to completion. Conversions approaching 100% can often be achieved by removing one of the products formed, either the ester or the water, provided the esterification reaction is equiUbrium limited and not rate limited. A variety of distillation methods can be appHed to afford ester and water product removal from the esterification reaction (see Distillation). Other methods such as reactive extraction and reverse osmosis can be used to remove the esterification products to maximize the reaction conversion (38). In general, esterifications are divided into three broad classes, depending on the volatility of the esters ... 

Use of Azeotropes to Remove Water. With the aliphatic alcohols and esters of medium volatility, a variety of azeotropes is encountered on distillation (see Distillation, azeotropic and extractive). Removal of these azeotropes from the esterification reaction mixture drives the equihbrium in favor of the ester product (39). 

Process Applications The production of esters from alcohols and carboxylic acids illustrates many of the principles of reactive distillation as applied to equilibrium-limited systems. The equilibrium constants for esterification reactions are usually relatively close to unity. Large excesses of alcohols must be used to obtain acceptable yields with large recycles. In a reactive-distiUation scheme, the reac-... 

Esters can also be synthesized by an acid-catalyzed nucleophilic acyl substitution reaction of a carboxylic acid with an alcohol, a process called the Fischer esterification reaction. Unfortunately, the need to use an excess of a liquid alcohol as solvent effectively limits the method to the synthesis of methyl, ethyl, propyl, and butyl esters. 

Acid-catalyzed ester hydrolysis can occur by more than one mechanism, depending on the structure of the ester. The usual pathway, however, is just the reverse of a Fischer esterification reaction (Section 21.3). The ester is first activated toward nucleophilic attack by protonation of the carboxyl oxygen atom, and nucleophilic addition of water then occurs. Transfer of a proton and elimination of alcohol yields the carboxylic acid (Figure 21.8). Because this hydrolysis reaction is the reverse of a Fischer esterification reaction, Figure 21.8 is the reverse of Figure 21.4. 

Fischer esterification reaction (Section 21.3) The acid-catalyzed nucleophilic acyl substitution reaction of a carboxylic acid with an alcohol to yield an ester. 

Highly concentrated ether carboxylic acids with a low degree of ethoxylation even at room temperature can give an esterification reaction with the non-converted nonionic, especially with the fatty alcohol, to several percentage points. The result may be that a too low value is found for the ether carboxylate content. This mistake in analysis can be avoided by saponification of the formed ester [238]. Two hundred to 300 mg matter and ca 100 mg NaOH were weighed in a 50-ml Erlenmeyer glass, heated with 20 ml ethanol under reflux, and after cooling supplied with water to 100 ml. Afterward a two-phase titration was carried out. 

Tanaka and Kakiuchi (6) proposed catalyst activation via a hydrogen donor such as an alcohol as a refinement to the mechanism discussed by Fischer (7) for anhydride cured epoxies in the presence of a tertiary amine. The basic catalyst eliminates esterification reactions (8). Shechter and Wynstra ( ) further observed that at reaction conditions BDMA does not produce a homopolymerization of oxiranes. 

Under certain conditions, the trifluoroacetic acid catalyzed reduction of ketones can result in reductive esterification to form the trifluoroacetate of the alcohol. These reactions are usually accompanied by the formation of side products, which can include the alcohol, alkenes resulting from dehydration, ethers, and methylene compounds from over-reduction.68,70,207,208,313,386 These mixtures may be converted into alcohol products if hydrolysis is employed as part of the reaction workup. An example is the reduction of cyclohexanone to cyclohexanol in 74% yield when treated with a two-fold excess of both trifluoroacetic acid and triethylsilane for 24 hours at 55° and followed by hydrolytic workup (Eq. 205).203... 

We can calculate an enthalpy of reaction with bond enthalpies by assuming the reaction consists of two steps first, bonds break, and then different bonds form. This approach can be simplified further if we consider the reaction consists only of reactive fragments, and the products form from these fragments. The majority of the molecule can remain completely unchanged, e.g. we only need to consider the hydroxyl of the alcohol and the carboxyl of the acid during a simple esterification reaction. 

Catalytic sol-gel lipase immobilizates were rapidly commercialized (by Fluka) after their invention in 1995 because of their remarkably stable activity in esterification reactions (and also in the kinetic resolution of chiral alcohols and amines) along with unique stability (residual activity of 70% even after 20 reaction cycles is common). The original procedure for the encapsulation produced by the fluoride-catalysed hydrolysis of mixtures of RSi(OCH3)3 and Si(OCH3)4 has been improved... 

Esterification reactions are acid catalyzed [18-21], and an overall reaction order of 3 (2 with respect to acid and 1 with respect to alcohol) is generally accepted [9], Thus, the acid behaves both as reactant and as catalyst. It can be assumed that the concentration of acid groups, cacid, is the sum of the concentrations of carboxylic end groups (tTPA) and carboxylic groups of the free acid (TPA). 

Esterification Reactions. Possibly the simplest reaction on poly(vinyl alcohol) would be the acetylation to regenerate the poly(vinyl acetate), Equation 2. While this reaction occurs readily, with acetic anhydride in pyridine solution, the result-... 

There are several chemical reactions that can be used as an alternative to achieve covalent functionalization of CNTs. Two of them are amidation and/or esterification reactions. Both reactions take advantage of the carboxylic groups sitting on the side-walls and tips of CNTs. In particular, they are converted to acyl chloride groups (-C0-C1) via a reaction with thionyl (SO) or oxalyl chloride before adding an alcohol or an amine. This procedure is very versatile and allows the functionalization of CNTs with different entities such as biomolecules [154-156], polymers [157], and organic compounds [158,159] among others. 

The reaction of a carboxylic acid with an alcohol to form an ester is called an esterification reaction. An esterification reaction is one type of condensation reaction. In a similar type of condensation reaction, an amide can be formed from a carboxylic acid and an amine, but this process is slightly longer and will not be discussed here. 

Esterification. Another reaction which can be used in the determination of surface silanol groups is their esterification with alcohols. This reaction has also found industrial application. The formation of surface esters by the action of alcohols on silica is covered in a patent to Her (226). The reaction products, called estersils, are hydrophobic. 

Figure 1 Structural formula of HA and the ethyl (Hyaff7), docecyl (Hyaff73) and benzyl (Hyaffl 1) esters. The esterification reaction was carried out starting from a quaternary ammonium salt of HA and the ethyl, dodecyl and benzyl alcohols, respectively, in a suitable aprotic solvent.

Furthermore, the apphcabihty in a Mitsunobu esterification reaction and a Diels-Alder reaction was proven (Scheme 10.13). The polymer-bound benzyl alcohol (70) was reacted with 4-acetamidophenol in the presence of the Mitsunobu reagent to give phenyl ether (71) in quantitative yield. It was released from the polymeric support in high yield. 

The failure to fit the data over the complete conversion range from 0 to 100% to a third-order plot has sometimes been ascribed to failure of the assumption of equal functional group reactivity, but this is an invalid conclusion. The nonlinearities are not inherent characteristics of the polymerization reaction. Similar nonlinearities have been observed for nonpolymerization esterification reactions such as esterifications of lauryl alcohol with lauric or adipic acid and diethylene glycol with caproic acid [Flory, 1939 Fradet and Marechal, 1982b]. 

Lipases are enzymes that catalyze the in vivo hydrolysis of lipids such as triacylglycerols. Lipases are not used in biological systems for ester synthesis, presumably because the large amounts of water present preclude ester formation due to the law of mass action which favors hydrolysis. A different pathway (using the coenzyme A thioester of a carboxylic acid and the enzyme synthase [Blei and Odian, 2000]) is present in biological systems for ester formation. However, lipases do catalyze the in vitro esterification reaction and have been used to synthesize polyesters. The reaction between alcohols and carboxylic acids occurs in organic solvents where the absence of water favors esterification. However, water is a by-product and must be removed efficiently to maximize conversions and molecular weights. 

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