( «515 ) 



Notwithstanding till this, nobody, since this elaborate research of 

 V. Meyer, has been engaged (luring- the last 20 years in the study 

 of these acids, although it mighl have been expected from the deve- 

 lopment of the phase-rule that the latter might possibly give us a 

 closer insight into the phenomena described above. 



The probable cause of all this is that these acids are not readily 

 accessible, and that those engaged in researches connected with the 

 phase-rule have not ventured to prepare the same. When Dr. Voerman, 

 at my request, undertook the closer study of these acids we had, first 

 of all, to find a better process for the preparation of these substances. 



In the case of the «-acid we have indeed succeeded in a very 

 satisfactory manner. We have also worked out another and improved 

 method for the preparation of the /3-acid ; but it is still unsatisfactory 

 owing to the small yield. Therefore, we have been obliged to restrict 

 ourselves, provisionally, to the study of the acids themselves; the 

 derivatives will be taken in hand when more material has been 

 obtained. 



Preparation of a-thiophenic acid. By V. Meyer and his pupils, this 

 acid was best obtained by oxidation of propiothienon C 4 H 3 S.COC a H 5 , 

 because the oxidation of the much more readily accessible acetothienon 

 C 4 H 3 S.COCH 3 yielded a mixture of «-thiophenic acid and thienyi- 

 glyoxylic acid, which it was rather troublesome to separate. We have 

 succeeded in converting acetothienon almost quantitatively into «- 

 thiophenic acid, being guided by the following considerations. If 

 we oxidise a methyl ketone, experience has taught that the methyl 

 group very readily changes to carboxyl thus forming a glyoxylie 

 acid: R.CO.CH 3 ->R.CO.C0 2 H. If, however, we attempt to go further 

 and obtain the corresponding carboxylic acid : R.CO.C0 2 H— >R.C0 2 H 

 a difficulty is experienced and the oxidising mixture then also attacks 

 the group R so that the yield of the carboxylic acid becomes 

 generally unsatisfactory. Now some time ago, I found a method for 

 converting acids R.CO.C0 2 H quantitatively into R.C0 2 H; this is 

 rendered possible by the application of hydrogen peroxide which 

 causes a ready resolution according to the scheme : 



R HO OH H = RC00H + C ° 2 + H *° 



This method has led to the desired result in this case. The 



oxidation of acetothienon is, therefore, done in two stages, first the 



formation of thienylglyoxylic acid which is subsequently oxidised to 



-thiophenic acid. The practical application of these processes was 



as follows : 



35* 



