Esterification s. Carboxylic acids

Esterification s. Carboxylic acid esters from carboxylic acids, Redoxesterification Esters, active s. Carboxylic acid esters, active Etherates s. Alane etherates Ethers (s. a. Alkoxy...,... 

Ester enolates 27, 843 suppl. 29 Esterification s. Carboxylic acid esters from carboxylic acids... 

In this definition ko is the rate constant for CH3COOR and k is the constant for RCOOR thus = 0 for R = CH3. Table 7-11 lists some values. Taft s Es steric constants are in some instances based on averages of several different reactions, so MacPhee et al. have defined a steric constant Es by Eq. (7-52) for a single reaction, namely, the acid-catalyzed esterification of carboxylic acids in methanol at 40°C. Es values are also given in Table 7-11. Additional Es and Es values are available. 

Shieh, W. and Dell, S. and Repic, 0. (2002). Large scale microwave-accelerated esterification of carboxylic acids with dimethyl carbonate. Tetrahedron Letters, 43, 5607-5609. 

Price and Hammett s rule has found confirmation in the reaction of benzaldehyde with acetone and ethyl methyl ketone (Gettler and Hammett, 1943), in the acid-catalyzed hydration of olefins (Taft, 1956a), in the hydrolysis of esters catalyzed by ion-exchange resins (Samelson and Hammett, 1956), in acid-catalyzed deoxymercuration (Kreevoy et al., 1962), and in the esterification of carboxylic acids in methanol (Smith, 1939). Taft (1956b) has noted that the rule seems to require the following modifications. The entropy-bearing substituent... 

Shieh, W.-C. Dell, S. Repic, O. Nucleophilic catalysis with DBU for the esterification of carboxylic acids with dimethyl carbonate. J. Org. Chem. 2002, 67, 2188-2191. 

Table V summarizes several reactions that have been demonstrated on a laboratory scale 1 know of no industrialized chemical process using Nafion as a superacid catalyst. Although many of the reactions were carried out with stirring a mixture of reactants and Nafion-H, several alkylation, disproportionation, rearrangement, and esterification reactions were performed by means of the flow-reaction method in the liquid or gas phase. For instance, in the esterification of carboxylic acids with alcohols, when a mixture of the acid and alcohol was allowed to flow over a Nafion-H catalyst at 95-125°C with a contact time 5 s, high yields, usually S90%, of the corresponding ester were obtained (82). It had been found that no reactivation of the catalyst was needed because the catalytic activity of the Nafion remained unchanged for prolonged periods of operation.

The Dubois steric constant E s is a revised Taft steric constant defined using the acid-catalyzed esterification of carboxylic acids (at 40 °C) as reference reaction [MacPhee, Panaye et al, 1978a, 1978b]. 

A differently anchored Mukaiyama reagent is the N-methylpyridinium iodide salt 57 [71], which has been obtained by reaction of the Merrifield resin with N-Boc-aminocaproic acid in the presence of cesium carbonate to give the supported ester 55 (Scheme 7.19). Further Boc-deprotection and reaction with 6-chloronicoti-noyl chloride in the presence of Hxinig s base furnished the anchored 2-chloro-pyridine 56, which was transformed into the final N-methylpyridinium salt 57 after N-methylation in neat methyl iodide. This supported reagent has been used in the rapid microwave-assisted esterification of carboxylic acids and alcohols in the presence of triethylamine as base, with dichloromethane as solvent at 80 °C, the products being obtained in high purity after simple resin filtration [72],... 

H. Kita, S. Sasaki, K. Tanaka, K. Okamoto and M. Yamamoto, Esterification of carboxylic acid with ethanol accompanied by pervaporation, Chem. Lett., 1988, 2025. 

STEGLICH HASSNER Dirad esterification Direct room temperature esterification of carboxylic acids with alcohols, Including ten alcohols with the help of dfcydohexytcartxxSimide (DCC) and S-dtekylamnopyridlne catalysts 3. 

Alkylative esterification of carboxylic acids with alkyl halides are effected by action with TMG (1) [65]. An ester is given by the TMG (1) mediated reaction of y-hydroxy-a,p-unsaturated carboxylic acid with methyl iodide without lactone formation after isomerization [65a]. Barton s base effectively works in the alkylation of sterically hindered carboxylic acid [3]. Ethanolysis of the acetate of tertiary alcohol occurred easily in 86% yield in the presence of BTMG (2) [66] (Scheme 4.24). 

Chakraborti, A.K., Singh, B., Chankeshwara, S.V., Patel, A.R. 2009. Protic acid immobilized on solid support as an extremely efficient recyclable catalyst system for a direct and atom economical esterification of carboxylic acids with alcohols. Journal of Organic Chemistry 74 5967-5974. 

The mechanism for acid-catalyzed esterification of carboxylic acids is completely reversible, but is driven to the right (toward the ester product) but application of Le Chatelier s principle and removal of water (also see Chapter 18, Section 18.6.3). Another application of Le Chatelier s principle uses a large excess of the alcohol (butanol for the formation of 70) to shift the equilibrium toward the ester by increasing the probability that it will react with alcohol rather than with water. Note that if ester 70 is treated with an acid catalyst and water rather than butanol, the mechanism shown will convert the ester back to the acid. In other words, if water replaces butanol, the mechanism from 70 to 21 is that for acid-catalyzed hydrolysis of an ester to a carboxylic acid (Section 20.2). 

Esterification of carboxylic acid 7 followed by ring closure metathesis (RCM) of h/s-olefin 16 to unsaturated azathilone 2 (Scheme 16.5) [26-28]. 

Polymeric amines can be proton acceptors, acyl transfer agents, or ligands for metal ions. The 2- and 4-isomers of poly(vinylpyridine) (11) and (12) and the weakly basic ion exchange resins, p-dimethylaminomethylated PS (2) and poly(2-dimethylaminoethyl acrylate), are commercial. The ion exchange resins are catalysts for aldol condensations, Knoevenagel condensations, Perkin reactions, cyanohydrin formation and redistributions of chlorosilanes. " The poly(vinylpyridine)s have been used in stoichiometric amounts for preparation of esters from acid chlorides and alcohols, and for preparation of trimethylsilyl ethers and trimethylsilylamines from chlorotrimethylsilane and alcohols or amines. Polymer-suppored DBU (l,8-diazabicyclo[5.4.0]undec-7-ene) (52) in stoichiometric amounts promotes dehydrohalogenation of alkyl bromides and esterification of carboxylic acids with alkyl halides. The protonated tertiary amine resins are converted to free base form by treatment with aqueous sodium hydroxide. 

Since the imidazolide method proceeds almost quantitatively, it has been used for the synthesis of isotopically labeled esters (see also Section 3.2), and it is always useful for the esterification of sensitive carboxylic acids, alcohols, and phenols under mild conditions. This advantage has been utilized in biochemistry for the study of transacylating enzymes. A number of enzymatic transacylations (e.g., those catalyzed by oc-chymo-trypsin) have been shown to proceed in two steps an acyl group is first transferred from the substrate to the enzyme to form an acyl enzyme, which is then deacylated in a second step. In this context it has been shown[21] that oc-chymotrypsin is rapidly and quantitatively acylated by Af-fraw.s-cinnamoylimidazole to give /ra/w-cinnamoyl-a-chymotrypsin, which can be isolated in preparative quantities and retains its enzymatic activity (see also Chapter 6). 

S Kim, JL Lee, YC Kim. A simple and mild esterification method for carboxylic acids using the mixed carboxylic-carbonic anhydrides. J Org Chem 50, 560, 1985. 

This method is called the Fischer esterification. It s a condensation reaction where the loss of a water molecule accompanies the joining of the alcohol portion to the acid portion. The acid gives up the OH and the alcohol gives up the H to make the water molecule. All steps in the mechanism are reversible (that is, it establishes an equilibrium), so removing the ester as soon as it forms is helpful. Removal of the ester is normally easy since esters typically have lower boiling points than alcohols and carboxylic acids. Figure 12-20 illustrates the mechanism for the acid-catalyzed formation of an ester by the reaction of an alcohol with a Ccirboxylic acid. 

Various combinations of reactant(s) and process conditions are potentially available to synthesize polyesters [Fakirov, 2002 Goodman, 1988], Polyesters can be produced by direct esterification of a diacid with a diol (Eq. 2-120) or self-condensation of a hydroxy carboxylic acid (Eq. 2-119). Since polyesterification, like many step polymerizations, is an equilibrium reaction, water must be continuously removed to achieve high conversions and high molecular weights. Control of the reaction temperature is important to minimize side reactions such as dehydration of the diol to form diethylene glycol... 

There are several examples of dehydrations of chemicals derived by renewable resources by use of heteregeneous catalytic approaches in the literature. These can be categorized into three types of reactions (a) reactions in which one (or more) molecule(s) of water is eliminated from a single substrate molecule, (b) reactions in which one (or more) molecule(s) of water is generated as the result of an esterification reaction between an alcohol and a carboxylic acid or carboxylic acid derivative and (c) reactions in which one (or more) molecule(s) of water is generated due to an etherification reaction between two alcohol functionalities. 

Schreiber and co-workers (436) prepared a library calculated to contain 2.18 million polycyclic compounds through the 1,3-dipolar cycloaddition of a number of nitrones with alkenes supported on TentaGel S NH2 resin (Scheme 1.83). (—)-Shikimic acid was converted into the polymer bound epoxycyclohexenol carboxylic acid 376 (or its enantiomer), coupled to the resin via a photolabile linker developed by Geysen and co-workers (437) to allow release of the products from the resin in the presence of live cells by ultraviolet (UV)-irradiation. A range of iodoaromatic nitrones (377) was then reacted with the ot,p-unsaturation of the polymer-bound amide in the presence of an organotin catalyst, using the tandem esterification/ dipolar cycloaddition methodology developed by Tamura et al. (84,85) Simultaneous cyclization by PyBrop-mediated condensation of the acid with the alcohol... 

The synthetic approach used in this work is shown in Scheme 9. Two known solution pathways were used to convert shikimic acid to an epoxide intermediate. In fact, both the (-)35 and the (+)36 enantiomers were formed. After minor synthetic transformations, these epoxides were linked to Ten-tagel S aminomethyl resin with an o-nitrophenyl-derived photocleavable linker 7437 via amide bond formation to give intermediate 75. The first point of variation was added via various iodo-benzyl nitrone carboxylic acids 76 via 1,3-dipolar addition/esterification reactions. Highly constrained resin-bound tetracyclic hydrooxazoles 77 were thereby produced. 

With the aid of BOP [benzotriazol-l-yl-oxytris(dimethylamino) phosphonium hexafluorophosphate, Castro s reagent]20 in the presence of DMAP it is possible to transform the free carboxylic acid 33 into activated intermediate 34 in preparation for subsequent esterification with 14 Other methods for esterification include application of DCC and the procedures introduced by Yamaguchi and Mukaijama (see Chapters 5, 6, and 9). 

The catalytic action of ChE s is, however, not limited to ester hydrolysis. Thus, these enzymes catalyze also the reverse reaction, i.e., esterification of acids with choline (14). They promote transesterification 15) and the condensation of hydroxylamine with acids 14) or esters 15). Anhydrides of carboxylic acids are also substrates of ChE s 16, 17) and can undergo all the reactions, mentioned with esters, i.e., hydrolysis, esterification, and hydroxamation. 

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