28 SCIENCE PROGRESS 



H 



\/ N 



CH CH C /\ 



/ \ /% / \ II I 



HC CH HC CH HC CH \^ 



II I II I /H II II I 



HC CH HC C/ HC CH ^\ 



\^ \/\ \/ I 11 



N N N \/ 



/\ I I N 



C.H.CO CgH^CO C,H,CO 



(i) (ii) (iii) (iv) 



When solutions of this compound are shaken with air or 

 treated with halogens they are decolorised, 4 : 4'-dipyridyl 

 (iv) and benzoic acid being the principal products. 



Dimroth and Heene {Ber., 1921, 54, 2934) by reducing a 

 mixture of pyridine and acetic anhydride with zinc dust have 

 obtained i : i''-diacetyltetrahydro-4 : 4'-dipyridyl : 



/CH : CH\ /CH : CH. 



AcN( ;CH . CH( ;nac 



\CH : CH/ \CH : CH^ 



which is dissociated on gentle warming in glacial acetic acid, 

 giving an intensely blue solution. This is decoloured by air or 

 by iodine, the products in the former case being mainly 4 : 4'- 

 dipyridyl with some pyridine, and in the latter the reverse. 

 The explanation suggested for this change is similar to that 

 proposed by Weitz, Roth and Nelken, namely, that the radical 

 reacts in two forms, (v) and (vi) : 



/CH:CHv /H Ac\ ^CH — CH^, 



AcN( ;C( )Nf Vh 



\CH : CH^ \ / \CH = CH^ 



(v) (vi) 



/CH : CH. /^^ '■ ^^\ 



AcN; /CH . O . O . CH NAc 



\CH:CH/ \cH:CH^ 



(vii) 



Reacting the first form a peroxide (vii) is formed which through 

 the intermediate formation of a compound (viii) loses acetic 

 acid, the two radicals uniting to give 4 : 4'-dipyridyl (iv) : 



/CH : CH. /OH Ac. XH : CH^ 

 Ac^( ;C( )N^ )CH 



\CH : CH/ \ HO/ ^CH : CH^ 

 (viii) (ix) 



