626 SCIENCE PROGRESS 



predominate, but these would be brought into equilibrium by 

 the presence of a small amount of the intermediate alcohol, 



C(CHs), rC(CHs),OH "I C(CH 3 ) = CH.. 



» <£ I ^ I 



CH.C(CH 3 ) 3 LCH 2 .C(CH 3 ) 3 J CH,.C(CH 3 ) 3 



Isodibutylene Isomeric define 



The complete equilibrium between the four compounds could 

 therefore be reduced by varying the conditions to either of two 

 simple cases of reversible isomeric change. 



Isomeric Change without a Catalyst. — It was one ot the striking 

 merits of Butlerow's observations that they not only established 

 the existence of reversible isomeric changes, but also revealed 

 the mechanism by which these changes were brought about. 

 In the absence of the acid, or on diluting it with water, the 

 hydration of the olefine and the dehydration of the alcohol were 

 alike suspended. Under these conditions, therefore, dynamic 

 equilibrium between isomers was no longer possible, and the 

 isomerides became as stable as, for instance, ethyl alcohol, 

 CH 3 . CH 2 . OH, and methyl ether, CH 3 . O . CH 3 . As Butlerow 

 expressed it, a special reagent — sulphuric acid — was necessary 

 to bring about in the tertiary alcohols the " condition of equili- 

 brium, depending on incessant isomeric change" which he had 

 studied so successfully in the derivatives of isodibutylene. 



But is such a special agent always necessary in order to 

 establish a reversible isomeric change ? In Butlerow's opinion 

 this was not so, and his discussion of this alternative type of 

 change forms one of the most important features of his paper. 

 Recent work has rendered it doubtful whether such cases 

 actually exist ; but a large number of instances are known in 

 which a condition of equilibrium is established in presence of 

 traces of alkaline and saline impurity so minute that it is a 

 matter of the utmost difficulty to get rid of them, and unless 

 extraordinary precautions are taken the state of affairs postulated 

 by Butlerow is substantially realised — at least, to the extent 

 that isomeric change proceeds without the conscious addition of 

 a catalytic agent. The conclusions which he drew in reference 

 to compounds which behaved in this way may be described 

 most clearly by a direct paraphrase : 



" In such cases, all attempts to establish a definite chemical 

 structure for the substance would be useless, since molecules of 

 the two or more isomeric varieties would always be present. It 



