284 HISTORY OF CHEMISTRY. [LECTURE XIV. 



in coal tar. Ethyl and propyl pyridines are already known, 

 however. 01 On oxidation, these bases behave exactly like the 

 alkyl derivatives of benzene ; that is to say, every side-chain, 

 by sufficiently energetic oxidation, yields a CO. 2 H group ; so 

 that, in this case also, conclusions may be drawn as to the 

 number of side-chains in the base oxidised, from the basicity 

 of the acid produced. 



The isomerisms amongst the derivatives of pyridine are far 

 more complicated than in those of benzene, since the hydrogen 

 atoms are not similarly related to the pyridine nucleus and 

 three different mono-substitution products must exist, as was 

 probably first pointed out by Weidel. ' 2 This conclusion is like- 

 wise confirmed by experiment, as three mono-carbonic acids, 03 

 three methyl-pyridines 4 and three ethyl-pyridines 5 are known. 

 Determinations of the positions of the substituting atoms or 

 groups in the pyridine series have been accomplished with 

 tolerable certainty by Skraup. 66 



As additional supports for the pyridine formula, there may 

 also be adduced the synthesis of pyridine by Ramsay 7 (which 

 is upon the same lines as the famous synthesis of benzene from 

 acetylene by Berthelot 6S ) as well as the synthesis of pyridine 

 derivatives. 09 Finally the conversion of pyridine derivatives 

 into benzene derivatives 70 is of importance in this connection. 



The formula for quinoline is also based upon numerous 

 syntheses, of which that by Konigs 71 may be mentioned here as 

 the first. This was followed by that of Baeyer 7 - and then by 



61 Williams, Jahresbericht 1855, 549; 1864, 437; Cahours and Etard, 

 Comptes Rendus. 92, 1079; Ladenburg, Berichte. 16, 2059 ; 17, 772 and 

 1 121 ; 18, 1587 ; Hofmann, ibid. 17, 825. 62 Ibid. 12, 2012. Ki Huber, 

 Annalen. 141, 271 ; Berichte. 3, 849 ; Weidel, ibid. 12, 1989 ; Skraup, ibid. 

 12, 2331. w Weidel, ibid. 12, 1989; Behrmann and Hofmann, ibid. 



17, 2681. ^ Wischnegradsky, ibid. 12, 1480; Ladenburg, ibid. 16, 



2059. 6(! Skraup and Cobenzl, Monatshefte. 4, 450 ; compare also 

 Ladenburg, Berichte. 18, 2967. 67 Ibid. 10, 736. tis Ann. Chim. [4] 

 9, 469. 0!) Hantzsch, Annalen. 215, I ; Pechmann and Welsh, Ber- 

 ichte. 17, 2384 ; Behrmann and Hofmann, ibid; 17, 2681. 7() Ladenburg, 

 ibid. 16, 2059. n Ibid. 12, 453. ~' 2 Ibid. 12, 460. 



