Esterification of Aliphatic Acids

Chlorosulfonic acid, as well as catalysing the a-halogenation of aliphatic acids, also functions as an acidic dehydration catalyst which can be valuable in the esterification of carboxylic acids. 

chlorosulfonic acid catalyses the esterification of acetonedicarboxylic acid 136 by ethanol yielding the diethyl ester 137 (Equation 55).  

The reaction was examined under various conditions and was optimized to yield diethyl acetonedicarboxylate 137 (93% purity) in 72% yield. 

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Table 7-12. Kinetics of Acid-Catalyzed Esterification of Aliphatic Acids...

Gu YL, Shi F, Deng YQ (2004) Esterification of aliphatic acids with olefin promoted by Brpnsted acidic ionic liquids. J Mol Catal A Chem 212 71-75... 

Direct, acid catalyzed esterification of acryhc acid is the main route for the manufacture of higher alkyl esters. The most important higher alkyl acrylate is 2-ethyIhexyi acrylate prepared from the available 0x0 alcohol 2-ethyl-1-hexanol (see Alcohols, higher aliphatic). The most common catalysts are sulfuric or toluenesulfonic acid and sulfonic acid functional cation-exchange resins. Solvents are used as entraining agents for the removal of water of reaction. The product is washed with base to remove unreacted acryhc acid and catalyst and then purified by distillation. The esters are obtained in 80—90% yield and in exceUent purity. 

A very interesting steric effect is shown by the data in Table 7-12 on the rate of acid-catalyzed esterification of aliphatic carboxylic acids. The dissociation constants of these acids are all of the order 1(T, the small variations presumably being caused by minor differences in polar effects. The variations in esterification rates for these acids are quite large, however, so that polar effects are not responsible. Steric effects are, therefore, implicated indeed, this argument and these data were used to obtain the Es steric constants. Newman has drawn attention to the conformational role of the acyl group in limiting access to the carboxyl carbon. He represents maximum steric hindrance to attack as arising from a coiled conformation, shown for M-butyric acid in 5. 

Habid and Malek49 who studied the activity of metal derivatives in the catalyzed esterification of aromatic carboxylic acids with aliphatic glycols found a reaction order of 0.5 relative to the catalyst for Ti(OBu)4, tin(II) oxalate and lead(II) oxide. As we have already mentioned in connection with other examples, it appears that the activation enthalpies of the esterifications carried out in the presence of Ti, Sn and Pb derivatives are very close to those reported by Hartman et al.207,208 for the acid-catalyzed esterification of benzoic and substituted benzoic acids with cyclohexanol. These enthalpies also approach those reported by Matsuzaki and Mitani268 for the esterification of benzoic acids with 1,2-ethanediol in the absence of a catalyst. On the other hand, when activation entropies are considered, a difference exists between the esterification of benzoic acid with 1,2-ethanediol catalyzed by Ti, Sn and Pb derivatives and the non-catalyzed reaction268. Thus, activation enthalpies are nearly the same for metal ion-catalyzed and non-catalyzed reactions whereas the activation entropy of the metal ion-catalyzed reaction is much lower than that of the non-catalyzed reaction. 

The pressure generated in a reaction vessel, and hence the rate enhancement, depends on a number of factors including the MW power level, the volatility of the solvent, the dielectric loss of the reaction mixture, the size of the vessel and the volume of the reaction mixture [7, 20]. Gedye et al. [20] found that, in the esterification of benzoic acid with a series of aliphatic alcohols (Scheme 4.1) in closed Teflon vessels, the most dramatic rate enhancements were observed with methanol (the most volatile solvent). 

The reference intermolecular reaction for the aliphatic compounds is the formation of ethyl acetate from ethanol and acetic acid measured under the same conditions (20% ethanol-water, ionic strength 0.4 M) by Storm and Koshland (1972a). The esterification of benzoic acid in methanol at 25° is 290 times slower than that of acetic acid (Kirby, 1972), so this factor is used to correct the EM s, calculated otherwise in the same way, for the hydroxybenzoic acids. For the phenolic acids see notes m and n b Rate constants are in units of dm3 mol-1 s-1 c Storm and Koshland, 1972a d Storm and Koshland, 1972b Bunnett and Hauser, 1965... 

Extraction of free fatty acids from naturally occurring glycerides removal of HCl from chlorinated organic compounds recovery of aliphatic acids HE and HCl from aqueous solutions nitration of phenol solvent extraction in mineral processing interfacial polycondensation and esterification manufacture of organo-phosphate pesticides. 

Other important metabolites of O-glucuronidation are acylglucuronides. They are formed by esterification of carboxylic acids with glucuronic acid. Many therapeutic agents such as arylacetic acids (diclofenac, diflunisal), aliphatic acids (valproic acid) and arylpropionic acids (ketoprofen, naproxen) are metabolized as acylglucuronides (Fig. 31.37). 

BE3 -OEt2 easy-to-handle and convenient source of BF3 Lewis acid catalyst promotes epoxide cleavage and rearrangement, control of stereoselectivity BF3 MeOH esterification of aliphatic and aromatic acids cleavage of trityl ethers)... 

Figure /. Esterification of carboxylic acid (I) and amide groups (2) of proteins by an aliphatic alcohol...

Poly(butylene succinate) belongs to the poly(alkylene dicarboxylate) family that can be obtained by polycondensation of a,o>-diols such as ethylene glycol and 1,4-butanediol, with aliphatic dicarboxylic acids, such as succinic and adipic acid. PBS is commonly prepared via esterification of succinic acid and BDO or transesterification of dimethyl succinate and BDO to oligomers followed by a subsequent polycondensation reaction, removing excess BDO. Catalysts include SnCh [81], p-toluenesulfonic acid [82], tetrabutyltitanate [83] and lanthanide triflates [84]. To produce PBS with sufficiently high molar mass often chain-extenders are used. Examples are the use of diisocyanates [83,85-87], bisoxazoline [88] and biscaprolactamates [89]. 

The silica gel may adsorb the esters of the short-chain fatty acids. For the esterification of those acids, a chloroform solution of the Cj—C aliphatic acids (50/rl) is treated with an equal volume of a freshly prepared 1% solution of 2,2,2-trichloroethanol in chloroform, together with 150 /A of heptafluorobutyric anhydride (HFBA) in a closed tube at room temperature for 30 minutes. Excess trichloroethanol is removed by reaction with 50 1 of a 25% solution of palmitic acid in chloroform, added subsequently and left to react at room temperature for 15 minutes. (The trichloroethyl palmitate p>eak comes off the GC column long after the shorter-chain fatty acid ester peaks). Further purification is achieved by shaking with 100 /il of chloroform and 100 1 of 0.1 M HCl the aqueous layer is discarded, and the organic layer is washed with 100 fi of 0.1 M NaOH and evaporated to dryness. The residue is dissolved in 100 fil of diethyl ether for analysis by GC with electron capture detection [46]. 

Melt polycondensation is the most used procedure for the preparation of polyesters such as PBSu or PESu from butylene or ethylene diols and dicar-boxyllc acids. Poly(propylene alkylanedicarboxylate) polyesters can be also prepared by the two-stage melt polycondensation method (esterification and polycondensation) using proper amounts of aliphatic acids and 1,3-PD in a glass batch reactor using a procedure described in detail in Ref. [9]. The esterification reaction progress is monitored by measuring the amount of water produced as a by-product and removed by distillation. Other reaction conditions are included in Scheme 4.4. 

The chemistry and technological principles of methacrylic acid esterification with aliphatic alcohols is fairly well known. However, the reports dealing with the kinetics studies of esterification of methacrylic acid with n-propanol and isopropanol have not been found. 

The reaction kinetics of levulinic acid with aliphatic alcohols is not sufficiently known. In general only Bart et al. [1] gave kinetic information concerning the esterification of levulinic acid with n-butyl alcohol in a presence of sulphuric acid as a catalyst. Their experiments were concerned with a reversible process, and kinetic equations obtained by them correspond to a second order reaction. 

Rosset et al. (2013) reported biodiesel production by esterification of oleic acid with aliphatic alcohols using immobilized Candida antarctica lipase, showing high yields of biodiesel (above 90%) in less than 24 h with ethanol, n-propanol and n-butanol whereas with methanol, the enzyme was inactive after ten ( cles of reaction. In another report, Yin et al. (2013) studied an efficient bifimctional catalyst lipase/organophosphonic acid-functionalized silica (SG-T-P-LS) for biodiesel synthesis by esterification of oleic acid with ethanol. In this system, the process had a conversion ratio reaching 89.94 0.42% under the conditions that the ethanol/acid molar ratio was 1.05 1 and the SG-T-P-LS to free fatty acid weight ratio was 14.9 wt.% at 28.6 C (Yin et al., 2013). 

Rosset, IG Cavalheiro, MCHT Assaf, EM Porto, ALM. Enzymatic esterification of oleic acid with aliphatic alcohols for the biodiesel production by Candida antarctica lipase. Catalysis Letters, 2013, v. 143 (9), 863-872. 

There are various reports in the literature concerning kinetic studies of the Upase-catalyzed hydrolysis or synthesis of esters in microemulsions [8,9,49,83,84]. A simple MichaeUs-Menten kinetic model was proposed for the hydrolysis of triglycerides [85,86], while the esterifications of aliphatic alcohols with fatty acids follow a ping-pong bi-bi mechanism [87]. According to this mechanism the lipase reacts with the fatty acid to form a noncovalent enzyme-fatty acid complex, which is then transformed to an acyl-enzyme intermediate, while water, the first product, is released this is followed by a nucleophile attack (by the alcoholic substrate) to form another binary complex that finally yields the ester and the free enzyme. The kinetic parameters and determined in these studies represent apparent... 

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