730 REPORT — 1893. 



lu tlie course of this investigation I have already made a detailed study of the 

 di- methyl, di-ethyl, di-cetyl, and di-benzyl derivatives of ethyl butanetetracarboxyl- 

 ate, formed by the action of alcohol radicals on its di-sodium compound. 



These derivatives on hydrolysis yield tetracarboxylic adds, which possess some 

 veiy remarkable properties, which have not been, so far as I know, observed in the 

 case of any other organic acids. These acids, although they contain four carboxyl 

 groups, do not in all cases behave as tetrabasic acids. On determining their basi- 

 city by titration with standard solution of potassium hydrate, some of them react 

 as di-basic acids. Notably is this the case with di-benzyl butanetetracarboxylic 

 acid, the result being the same whether phenol phthalein or litmus be used as the 

 indicator. In this connection it is to be noted that on forming the silver or calcium 

 salts of di-benzyl butanetetracarboxylic acid, they were found to have the formuliB 

 CjHjoOgAg, and CjoHjoOgCa + SH^O respectively. On the other hand, di-methyl 

 and di-ethyl butanetetracarboxylic acid on titration with potassium hydrate give 

 different results according as phenol phthalein or litmus is used as an indicator. 

 They behave as tetrabasic acids when phenol phthalein is employed. If, how- 

 ever, one or two drops of litmus solution be added to the solution of these acids in 

 potassium hydrate, which, as shown by phenol phthalein, had been neutraUsed by 

 hydrochloric acid, a distinctly blue colouration is produced. On adding more 

 hydrochloric acid the blue colouration changes gradually to a red tint, and the 

 solution appears to become neutral to litmus, only when sufficient hydrochloric 

 acid is added to neutralise one half of the potassium hydrate, which was equivalent, 

 as shown by phenol phthalein, to the tetracarboxylic acid present. The silver 

 salts of di-methyl and di-ethyl butanetetracarboxylic acid, unlike that of di-benzyl 

 butanetetracarboxylic acid, are tetrabasic. 



The di-substitiited butanetetracarboxylic acids we have obtained, when heated 

 to 200°, all lose two molecules of carbonic anhydride, yielding di-substituted adipic 

 acids. The study of these acids appeared to be especially interesting in view of 

 the recent work on the di-substituted succinic, and glutaric, and pimelic acids. In 

 accordance with Van 't Hoff's theory, the di-substituted succinic and glutaric acids 

 are found in two modifications. The substituted pimelic acids, on the other hand, 

 have only been found in one modification. 



Considerable interest is therefore attached to the question of isomerism in the 

 substituted adipic acids. We have found that the di-substituted adipic acids, 

 obtained from substituted butanetetracarboxyUc acids, invariably exist in two 

 modifications, which are readily capable of separation by crystallisation from 

 benzene or toluene. 



The difference between the melting points of the two modifications is usually 

 60-80°. For example, two modifications of di-benzyl adipic acid were isolated, 

 one crystallising in diamond-shaped crystals, which melted at 211-3°, the other 

 crystallising in six-sided prisms melting at 152°. Of these derivatives of adipic 

 acid the di-methyl alone have been previously obtained. They were prepared by 

 Zelinsky, by the hydrolysis of ethyl dicyandimethyl adipate.' 



Experiments on succinic acid have shown that the more alkyl groups there are 

 introduced, the more readily can an anhydride formation take place, and it was 

 thought that this would also be the case in the adipic series. Now, the anhydride 

 of adipic acid has been formed, yet on attempting to form anhydrides by heating 

 the substituted adipic acids in sealed tubes with acetyl chloride, in no case could 

 any evidence of an anhydride formation be obtained. On the other hand, whether 

 the higher melting or lower melting modification was employed, a partial conversion 

 into the other modification was eflected. This result is remarkable, and cannot at 

 present be understood. 



The author has also formed ethyl dibromohutanetetracarboxylate, by the 

 action of bromine on a solution of ethyl butanetetracarboxylate in chloroform. 

 It crystallises in magnificent prisms, which melt at 82-3°. The author is engaged 

 in the investigation of this substance, and expects interesting results from the 

 etudy of its derivatives and its use in synthetical chemistry. 



' Ber., 24, ii. 997 



