36 



before the limil of soliihilily of llie free diol is readied. It can be 

 obtained pure by sucking off and washing with alcoiiol of 96 7o- J' is 

 a compound tiiat was discovered already before by Bokskken and Van 

 GtFFEN') but which was not isolated and more closely examined tiieii. 



The aqueous solution of this potassium salt has an alkaline reaction, 

 and the potassium can be determined (iiiantilalivelj by titration with 

 methyl orange, which proves anew that the corresponding complex 

 boric acid is an exceedingly weak acid. Besides this coin pound 

 C,H,,0,BK, a dipotassium compound C,H,,Ü,BK was obtained from 

 very strong potassium hydroxide. 



Under the same circumstances crystalline compounds can also 

 be obtained from cis-1.2 liydridene diol, cis 1.2 cyclopentane 

 diol, and cis-1.2 and cis 2.3 tetrahydroiiaphtalene diols. These 

 compounds consist of potassium salts of either of the two types 

 or of both, some of which could, howe\ei', not yet be obtained pure 

 and free from potassium hydroxide being sometimes (o.a. in the case 

 of liydridene diol) too easily soluble, both in water and in alcohol, 

 so that they cannot be washed with one of these solvents. 



It is remarkable that in the di-potassium compound of cis-cyclo- 

 liexane diol boric acid both potassium atoms can be titrated with 

 nielhyl orange and MCI, but that in the corresponding compound of 

 cis-cyclo |ieiitaiie diol only one of the two potassium atoms can 

 thus be titrated. We reserve a further discussion of this point till 

 some future occasion. 



We may point out here that these compounds supply us with a 

 method to separate isomer cis- and trans- cyclic J. 2 diols from 

 each other, the latter not giving such compounds. For in many cases 

 the beautiful method of separation with the aid of acetone compounds 

 found by Van Loon') is attended with important drawbacks, as has 

 appeared from another investigation (to which I hope to refer 

 later on. ') 



The fact that the formation of these cyclic and only exceedingly 

 weakly acid compounds seems to be a general property of the 1.2 

 and 1.3 diols, leads to the conclusion that the more strongly acid 

 boro-complexes, which arise in appreciable quantities only in poly 



1) Recueil 39, 183 (1920). 



«) These Proc. Vol. XXlll p. 60 (1920), and proefschrift Delft p. 59; of 

 BöESEKEN and Derx, Recueil 40, 519. 



') The new method of separation has already been sucessfully applied by 

 Mr. Maan to the methyl 1. cyclohexane l.SJ diols. The cis-diol was obtained in a 

 much purer state than by the acetone method, as the action of acids is now 

 fully eliminated. 



