STABILITY OF STEREO-ISOMERS 139 



H 3 CCCO 



is known only as anhydride, 



C 



>0 

 H 3 CCCO 



and the anhydride is not attacked by water. 



Such hindrance to reaction, due to replacement of 

 hydrogen, which is equivalent to an acceleration of re- 

 action in the presence of hydrogen, was found by Victor 

 Meyer l in the region of esterification, in the most striking 

 manner. 



First, it appears that if in benzoic acid the two hydrogen 

 atoms nearest the carboxyl group are replaced, esterifi- 

 cation almost fails even in excess of methyl alcohol saturated 

 with hydrochloric acid. Representing the position of the 

 carboxyl group by i, the following numbers were obtained : 



2.4 C 6 H 3 Br 2 COOH .... 95 % ester, 



2.6 C 6 H 3 Br 2 COOH . . . . o 



3.4.5 C G H 2 Br 3 COOH .... 96 



2.4.6 C c H 2 Br 3 COOH .... 4 



It appeared next that the mass of the radicle placed in 

 the ortho-position is of influence, and that especially heavy 

 ones (Cl = 35-5, NO 2 = 46, Br 3 80, I = 127) prevent 

 esterification even at the boiling point, whilst others 

 (CHo = 15, OH = 17, F = 19) do so only at atmospheric 

 temperature. This is quite in agreement with Menschut- 

 kin's discovery with regard to the initial velocity of esteri- 

 fication of different acids since, e, g. the following are the 

 values for methyl derivatives of acetic acid : 



H 3 CCOOH 46 



H 3 CCH 2 COOH 41 



(H 3 C),CHCOOH 29 



(H 3 C)~CCOOH 8 



whilst similar results regarding the alcohols were given 

 on p. 132. 



1 Zeitschr.f. Pliys. CJtem. 21. 149. 



