THE GRIGNAED REAGENT ON 0-PHTHALIC ESTERS. 6 



As first pointed out by H. G. Bethmann,*^ certain properties 



of succinic acid correspond to the following space formula, with 



its two carboxyl groups in the ^m?is-position, and the ease, with 



COOH which succinic esters react with four molecules 



of the Grignard reagent and produce glycols, 



V — —p^ can be readily explained by adopting the 



\ / same formula, the two carboxyl groups in 



/ ,-'-''' '"'---, \ the trans-Y>osiiioB. having no space influence 



^ ^- — I — y -^ upon the course of the reaction. But, in 



\ / the case of o-phthalic acid, only one ester 



COOH group enters into reaction with two molecules 



of the Grignard reagent, as already pointed out, and phthalide 



is formed as the intermediate product. This must be considered 



as due to steric hinderance, or, in other words, to the effect of 



the as-position of the two carboxyl groups in o-phthalic acid. 



On the other hand, F. Ullmann and C. Schaepfer"^ obtained 



(C0H5), C.<^.C(CÄ), 

 tetraphenyl-29-xylylene glycol | | by the 



OH OH 



action of phenyl magnesium bromide upon terephthalic acid 

 dimethyl ester, the reaction being, evidently, quite analogous to 

 that which occurs in the case of succinic esters. It, thus, 

 appears very probable that the two carboxyl groups in tere- 

 phthalic acid are in the /ra^s-position. 



These considerations enable us to discuss a little more fully 

 than hitherto the different space formulae of benzene proposed 

 from time to time. The following may be regarded as their 

 representatives : 



1) Zeitschr. f. physik. Chem., (1890), 5, ^09. 



2) Ber., (1904), 37, 200rf. 



