46 Proceedings of the Royal Irish Academy. 



The above boiling points are nncorrected. In the case of amyl- 

 pyrrol, since the quantity of liquid was small, and the thermometer by 

 no means all that could be desired, the correction to be applied -would 

 in all probability amount to five or six degrees, which would bring its 

 boiling point into still closer conformity with KopjD's law. 



On the other hand, the ethyl-pyrrol obtained by the action of 

 ethyl iodide on potassium-pyrrol is stated by Lubawin, its discoverer, 

 to boil between 155° and 175° C. From tlae description given of it, 

 the compound was manifestly in an impure state ; but if obtained free 

 from foreign matter it would, no doubt, be found to have the boiling 

 point 133+19x2-l7l°C. It is, in short, a true homologue of 

 pyrrol. The isomerism of these two ethyl-derivatives may be ex- 

 plained by the following constitutional schemes : 



Pyrrol. Ethyl-ppTol (Luba'win). Ethyl-pjorol. 



(C,H,) = X H(C,H3 (C3H5) ) = NH (C,H,) = N (C^H,). 



"We may, I think, reject as disproved the surmise of Kottnitz, 

 that in Lubawin' s ethyl-pyrrol the ethyl is united to the nitrogen. 



If these formulae are correct, it should be possible to substitute in 

 the compound C^HiJ^ (C0H5), by Lubawiu's process, an ethyl group 

 for one of the nuclear atoms of hydrogen, and so to ari'ive at the base 

 ■C4H3 (C2H5) NCoHg. I have, in fact, observed that potassium acts on 

 ethyl-pyrrol, evolving hydrogen : but the action is extremely slow, 

 whereas pyrrol is violently attacked by the metal. The slight 

 action in the former case may, possibly, be due to the presence of im- 

 purities. On this point I cannot at present speak with certainty, the 

 quantity of liquid in my possession not permitting of a satisfactory 

 solution of it. 



In planning methods for obtaining derivatives of pyrrol, it must be 

 borne in mind that the two ethyl compounds just mentioned by no 

 means represent all the different modes of substitution of which the 

 pyrrol molecule is theoretically susceptible. If we apply here the 

 beautiful ideas of Kekule on the isomerism of benzol derivatives, it 

 will be evident, pre-supposing the correctness of Baeyer's formula, 

 that the introduction into the molecule of any given radicle might 

 give rise to three isomeric bodies, accordingly as it displaced what 

 we may call the imidic hydrogen, or one of either of the pairs of 

 hydrogen atoms adjacent to, and remote fi'om, the nitrogen. Here we 

 have indicated the existence of a large number of derivatives, some of 

 which may yet prove of therapeutic importance. From experiments 

 on which I am at present engaged, in conjunction with my friend Dr. 

 Lapper, it is evident that the toxic properties of pp-rol, which are 

 powerful, are modified in an interesting manner by the substitution of 

 alcoholic groups for its imidic hydrogen. So far our results afford a 

 striking parallel to the interesting observations of Crum-Brown on the 

 physiological action of strychnia and aconitia, and their derivatives. 

 Our experiments shall form the subject of a future communication. 



