Benzoic esterification with

FIGURE 19.7 The mechanism of acid-catalyzed esterification of benzoic acid with methanol. 

Both for reaction in and IV the order with respect to catalyst is 0.5. The activation enthalpies are 96.6 3.4 and 97.6 3.4 kJ mol-1 respectively when Ti(OBu)4 is used as the catalyst. This is not too far from the activation enthalpies200 for the Sn(II)-cata-lyzed esterification of B with isophthalic acid (85.1 4.9) and with 2-hydroxyethyl hydrogen isophthalate (85.8 4.2). It is also close to the Ti(OBu)4-catalyzed esterification of benzoic acid with B (85.8 2.5)49. This is probably due to the formation of analogous intermediate complexes and similar catalytic mechanisms. On the other hand, the activation entropies of reactions III and IV are less negative than those of the reaction of benzoic or isophthalic acid with B. This probably corresponds to a stronger desolvation when the intermediary complex is formed and could be due to the presence of the sodium sulfonate group. 

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 rate enhancement for the esterification of benzoic acid with methanol was close to 100, when compared with the classical heating under reflux. On the other hand, the rate enhancement for the esterification with n-pentanol, using the same power level (560 W) was only 1.3. The approximate reaction temperature was almost the same for the two alcohols (134 °C and 137 °C respectively). It should be noted, however, that the rate enhancement for the esterification in pentanol increased to 6 times when a higher power level (630 W) was used, the reaction temperature being higher (162 °C). 

Using this information, it was possible to optimize the reaction conditions to achieve a particularly high rate enhancement. The rate enhancement of the esterification of benzoic acid with 1-propanol (Scheme 4.1) was increased from 18 to 60 times when the volume was increased from 10 mL to 20 mL at 560 W and increased further to 180 times by increasing the power level to 630 W. 

A Study of the Esterification of Benzoic Acid with Methyl Alcohol Using... 

Combined crown ether and quaternary salt catalysis of the esterification of benzoic acid with phenacyl bromide... 

The hyperbranched polyesteramides described above can also easily be functionalized by esterification with various mono carboxylic acids like acetic acid, benzoic acid, 2-ethylhexanoic acid, stearic acid, (un)satuxated fatty acids, or (meth)acrylic acid. With the exception of the latter mentioned acids, which give highly temperature sensitive products, the synthesis of these functionalized hyperbranched polyesteramides can be performed in two different ways ... 

This does not occur in the case of catalyst and reactants here described. With Bronsted-type catalysis, the reaction between the benzoyl cation, Ph-C" =0, and the hydroxy group in phenol is quicker than the electrophilic substitution in the ring. This hypothesis has been also confirmed by running the reaction between anisole and benzoic acid in this case the prevailing products were (4-methoxy)phenylmethanone (the product of para-C-benzoylation) and methylbenzoate (obtained by esterification between anisole and benzoic acid, with the co-production of phenol), with minor amounts of phenylbenzoate, phenol, 2-methylphenol and 4-methylphenol. Therefore, when the 0 atom is not available for the esterification due to the presence of the substituent, the direct C-acylation becomes the more favored reaction. 

Ardizzone et al. used the esterification of benzoic acid with methanol to test the catalytic performance of different SZ catalysts. " Water had to be continuously removed from the reaction medium to shift the reaction equilibrium to product formation and to avoid catalyst deactivation by sulfate leaching. According to these authors, catalysts with a higher density of acid sites with KdL values in the range —14.2 to -5.6 performed better. Acid sites with pKa. of... 

An optimised enzymatic synthesis of methyl benzoate in an organic medium was reported by Leszczak and Tran-Minh [43]. Methyl benzoate is part of the aroma of some exotic fruits and berries. The ester has been produced by direct esterification of benzoic acid with methanol in hexane/toluene catalysed by lipase from Candida rugosa. 

The effect of group (a) (non-polar solvents) was examined in the esterification of benzoic acid with 1-butanol over a Dowex-W X2 catalyst [454]. The solvent affected both the Helfferich distribution coefficients and the esterification rates. Dielectric constants, corresponding to the composition of the pore liquid, were estimated and the kinetic data related to the polar properties of the medium within the catalyst. In Fig. 18 are plotted specific rate coefficients versus the reciprocal value of dielectric constant of the pore liquid. The slope of the correlation is positive as for... 

Substituents in the ortho position, almost without exception, reduce the reactivity of benzoic acid derivatives a significant rate increase is a prima facie case for intramolecular catalysis (see p. 201). This effect is associated in the case of the esterification of or/fio-substited benzoic acids with a somewhat lower enthalpy of activation, and a greater decrease in the entropy of activation. The first factor may be due to a secondary steric effect145, whereby the energy of the initial state is raised because the carboxyl group is twisted out of the plane of the ring, to reduce non-bonded interaction with the or/fio-substituent (see p. 178), and delocalization energy is lost. The lower entropy term is presumably accounted for by the bulk effect of the substituent. 

Plazl, I., Esterification of benzoic acid with ethanol by conventional and microwave heating in stirred tank reactor, Acta Chim. Slovenica, 1994, 41,437. 

Asymmetric esterification of benzoic acid with racemic (l-bromoethyl)benzene was performed with chiral cyclic guanidines as stoechiometric bases4 the ester was obtained with ee below 15%. The chiral guanidines 6 were obtained from a chiral diamine of C2 symmetry which was tranformed first to urea and then to several guanidines through an intermediate chloroformamidinium chloride (Figure 4). 

Several reaction were examined the dehydrobromination of bromoalkanes, the esterification of benzoic acid with 1-bromobutane and the macrolactonisation of [Pg.138]

Esterifications of benzoic acids with ethanol, N HCl ref. 14, p. 189. Reaction of benzoic acids with cyclohexanol, acid catalyst ref. 16. Reaction of benzoyl chlorides with ethanol ref. 14, p. 189. Reaction of anilines with formic acid ref. 14, p. 190. 

Ethylparaben is prepared by the esterification of p-hydroxy-benzoic acid with ethanol (95%). 

This mechanism (A = acid catalyzed, AC = acyl transfer, 1 = unimolecular) is observed in the esterification of 2,4,6-trisubstituted benzoic acids with R groups of moderate -i-M effect e.g. methyl). The Aac2 mechanism is blocked by the steric interference of the ortho substituents. Therefore, the acylium cation (17) is generated with anhydrous sulfuric acid and then treated with the alcohol (equation 2). R groups with strong -i-M effects, like methoxy, are not tolerable, as the aromatic nucleus undergoes sulfo-nation under the conditions. A variation of the AacI mechanism for aliphatic acids is achieved by using... 

The esterification of benzoic acid with methyl alcohol containing O18 gave, as a by-product, water containing only O10 6... 

The reaction catalysed by 16 was an esterification with benzoic anhydride and the best kinetic resolution obtained (s = 67) with benzylic alcohol 19 was at - 40 °C. A value of 67 is very good for a kinetic resolution. However, exceptional results were obtained using phosphine 18. This catalyst is effective with a variety of alcohols and conditions. The best result was obtained with 20, AC2O and, crucially, catalyst which had been recrystallised to >99.9% ee. In this instance s = 390 ... 

Large-scale production of cocaine (both licit and illicit) essentially involves extraction of the total bases, which are then totally hydrolyzed so that all three ester alkaloids, cocaine, cinnamoyl cocaine, and the truxillines, are converted to ecgonine. The ecgonine is then methylated, followed by esterification with benzoic acid to cocaine. All of the ecgonine in the leaves is converted to the desired product in this way, which is a more efficient process than attempting to extract and separate out only the actual cocaine content from the plant. 

Hydroxy-ffj-aminobenzoic acid is obtained by the nitration and reduction of -Hydroxy benzoic acid, which on esterification with methanol yields orthocaine. 

Problem 15.23. Write the equation for esterification of benzoic acid with propanol. 

Problem 15.63. Thioalcohols behave like alcohols in reacting with carboxylic acids to form esters. Write the equation for esterification of benzoic acid with propanethiol. 

As outlined in Scheme 6, isovanillin (35) was converted to aryl iodide 36 via MOM-protection, protection of the aldehyde, and subsequent iodination. Hydrolysis of the acetal and Wittig olefination delivered phenol 37 after exposure of the intermediate aldehyde to methanolic hydrochloric acid. Epoxide 41, the coupling partner of phenol 37 in the key Tsuji-Trost-reaction, was synthesized from benzoic acid following a procedure developed by Fukuyama for the synthesis of strychnine [62]. Birch reduction of benzoic acid with subsequent isomerization of one double bond into conjugation was followed by esterification and bromohydrin formation (40). The ester was reduced and the bromohydrin was treated with base to provide the epoxide. Silylation concluded the preparation of epoxide 41, the coupling partner for iodide 37, and both fragments were reacted in the presence of palladium to attain iodide 38. 

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