132 CAROTENOID HYDROCARBONS OF KNOWN CONSTITUTION X 



Karrer and Helfenstein'^^ quantitatively estimated the acetic acid 

 formed by the permanganate oxidation of carotene and thus estabhshed the 

 presence of 4 groupings of the type 



=CH-C=CH- 



CH, 



It was therefore concluded that the two /?-ionone rings are joined by a 

 chain of 4 isoprene residues. Furthermore, according to Kuhn and Ehmann^" 

 and Kuhn and L'Orsa^^, the results of chromic acid oxidation indicated the 

 presence of 2 groupings of the type 



— CH2-C=C 



I 

 CH3 



These results led Karrer, Helfenstein, Wehrli and Wettstein^^ and 

 Karrer and Morf^^ to propose the now accepted formula for jS-carotene. The 

 structure of j3-carotene was confirmed by the later investigations of Pummerer, 

 Rebmann and Reindel^*, Strain^^ and Kuhn and Winterstein^^. The latter 

 authors showed that thermal decomposition of the pigment gives rise to 

 2 :6-dimethylnaphthalene. 



