Saint-Gilles

Since the pioneering work of Berthelot and Pean de Saint-Gilles in 1862, it has been well known that solvents strongly influence both reaction rates and the posi-... 

Kinetic Considerations. Extensive kinetie and mechanistic studies have been made on the esterification of carboxylic acids since Berthclot and Saint-Gilles first studied the esterification of acetic acid. A number of mechanisms for acid- and base-catalyzed esterification have been proposed. One possible mechanism for the bimolecular acid-catalyzed ester hydrolysis and esterification is shown below. 

This was first demonstrated in 1862 by Berthclot and Saint-Gilles. who found that when equivalent quantities of ethyl alcohol and acetic acid were allowed to react, the esterification stopped when two-thirds of the acid had reacted. Similarly, when equal molar proportions of ethyl acetate and water were heated together, hydrolysis of the ester slopped when about one-third of the ester was hydrolyzed. By varying the molar ratios of alcohol to acid, yields of ester ft(V were obtained hy displacement of the equilibrium. The results of these tests were in accordance with the mass action law- shown. K = letter- lwuter f acid uU-ohrd]. However, in many eases the equilibrium constant is affected by the proportion of reactants. The temperature as well as the presence of salts may also affect the value or the equilibrium constant. 

M. Berthelot and L. Pean de Saint-Gilles, Chim. Phys. 68, 225 (1863). 

M. Berthelot and P. Saint-Gilles,Mffff. Chim. Phys. 65, 385 (1862). 

Berthelot and Saint-Gilles (Ann. Chim.Phys. 1863, 68, 225) made up mixtures of ethyl alcohol and acetic acid in various proportions, heated them to 160 °C - 200 C until equilibrium was attained, chilled them and analysed them to determine the extent of esterification. Numerous experiments were made with equivalent amounts of alcohol and acid. It was found that almost exactly two-thirds of the reactant molecules were converted to ester and this ratio was not detectably affected by the temperature. The results of further experiments are given in table 1, where % denotes number of moles of alcohol to 1 of add, ng denotes number of moles of add to 1 of alcohol, denotes fraction of add esterified and fraction of alcohol esterified. 

It must be regarded as a fortunate accident that this equilibrium is so insensitive to temperature. The heat of reaction for esterification is only H = 2 kcal mole (Kharasch, Bur. Stand. J. Res. 1929, 2, 359). It follows from this that between 160 C and 200 °C the equilibrium quotient K should change by only about 20% most of this will be in the small factor 1 — x and the percentage change in x will in most cases be much less. Berthelot and Saint-Gilles concluded wrongly that the equilibrium is independent of temperature. 

These experiments are mainly of historical interest because they were used by van t Hoff (Ber. dtsch. chem. Ges. 1877, 10, 669) to test the recently formulated law of chemical equilibrium. The above anal3 sis is essentially equivalent to van t Hoff s. Guldberg and Waage (Forhandl. Vid. Selsk. Christiania, 1864, 35, 42) by contrast expressed the experimental measurements of Berthelot and Saint-Gilles by the purely empirical relation... 

Jean-Louis Peyraud UMR INRA-ENSAR Production du lait 35590 Saint-Gilles, France... 

The reaction studied was the quatemarization of triethylamine by ethyl iodide at 100 °C [N. Menschutkin, Z. Phys. Chem., 6, 41 (1890)]. Menschutkin s first discussion on solvent effects dealt with the reactions between acetic anhydride and alcohols [Z. Pl s. Chem., 1,611 (1887)]. The catalytic role of solvents was already recognized in 1862 by Berthelot and Pean de Saint Gilles in their Recherches sur les Aflinit6s [see, e. g., H. G. Grimm, H. Ruf, and Wolff, Z. Phys. Chem., B13,301 (1931)]. 

Ann. Chim.y 1862, Ixv, 385 1862, Ixvi, 5, no 1863, Ixviii, 225 see also Berthelot and Saint-Martin, z6., 1872, xxvi, 433 Swarts, Bull. Soc. Chim. Belg., 1928, xxxvii, LIX. L6on P an de Saint-Gilles (Paris 4 January 1832-22 March 1863), a wealthy man who had a private laboratory PoggendorfT, (i), hi, loio. 

Berthelot and Saint-Gilles found that rise of temperature greatly increases the reaction velocity but pressure has little influence. It was suggested that the temperature dependence was exponential. The equilibrium state was almost independent of temperature. Dilution with an indifferent solvent reduced the velocity and this was inversely proportional to the volume (which is correct). Experiments with many organic acids and alcohols showed that the equilibrium position is practically the same, varying only from 61 to 72 per cent conversion, with equivalent amounts. The effect of mass was clearly demonstrated by experiments with n equivalents of ethyl alcohol to i of acetic acid, when the conversion in equilibrium was as follows (one of 13 cases investigated) ... 

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