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Chemistry. — "«- and p-thiophenic arid." By Prof. A. F. Holleman 

 and Dr. G. L. Voerman. 



(Communicated in the meeting of December 29, 1007). 



A very remarkable research on these acids was published in 1886 

 by V. Meter, who discovered the same. In the main it amounts to 

 this, that in addition to the theoretically possible monocarboxylic 

 acids of thiophen 



i :ico,u rrp S H 

 V V 



Mp. 126°.2 Mp. 138°.4 



a third isomer was obtained, called a-thiophenic acid m.p. 117.5 — 118°, 

 which, however, in its derivatives such as the amide, the phenylurea 

 derivative of the amide, the amidoxime and the thienone (C 4 H 8 S) 8 CO, 

 so completely resembled the corresponding derivatives of the «-acid 

 that they would have been declared identical, were it not that from 

 the a-derivates the a-acid m.p. 118° was regenerated, whilst the 

 «-derivates yielded the «-acid m.p. 126\ V. Meter expresses himself 

 as follows: "Die Vergleichung der <i- mid a-Saure ergab immer von 

 "Neuem das merkwürdige Resultat, dass die beiden Sauren wirklich 

 "in ihren Eigenschaften durchaus versehieden sind, und dass die Ver- 

 «schiedenheiten sich als constante, (lurch keinerlei Reinigung oder 

 "Umwandlungen zu entfernende Eigenschaften erwiesen; dass aber 

 "alle Derivate der beiden Sauren in ihren physikalischen Eigenschaften 

 "absolut zusammenfallen und für identisch (im gewöhnlichen Shine) 

 "erklart werden müssten, wenn sie nicht die Eigenschaft besassen, 

 "dass jedes aus der a-Saure dargestellte Derivat bei der Rückführung 

 "auch wieder «-Saure, jedes a-Derivat dagegen a-Saure lieferte." 



As the a-acid had also been obtained by oxidation of tar-thiotolene 

 which is a mixture of a- and ( ?-thiotolene [2 — 3 methylthiophen], 

 V. Meter suspected that this ./-acid might be after all a mixture of 

 a- and (J-acid, and he really succeeded, by oxidation of a mixture 

 of the two thiotolenes in definite proportion, or by slow crystallisa- 

 tion of a mixture of o.- and ,3-acid from cold water, in obtaining an 

 acid which agreed in every respect with the a-acid. This was no 

 doubt an important step forward, but the behaviour of such a 

 mixture and also of the derivatives obtained therefrom still remained 

 a very remarkable one. 



i) A. 236, 200; also V. Meyer, die Thiophengruppe p. 188—207. 



