9 OXIDATIVE DEGRADATION 47 



8. OXIDATION WITH PERMANGANATE AND OZONE 



The introduction of oxidative degradation with potassium permanganate 

 was of decisive importance for the elucidation of the structure of the caro- 

 tenoids. By this means it was possible for the first time to obtain large fragments 

 (dicarboxylic acids, etc.) which gave a clue to the constitution of these pigments. 

 Details of these oxidations will be given in the description of individual 

 carotenoids (cf. p. 132). The reader is also referred to the original hterature^^. 

 The results of degradative oxidation are so reliable that it is possible to draw 

 conclusions regarding the structure of a carotenoid from the absence of certain 

 degradation products (cf. xanthophyll, p. 201). 



Thus, potassium permanganate degradation of an unsubstituted j8-ionone 

 ring yields dimethylmalonic acid, a : a-dimethylsuccinic acid and a : a-dimethyl- 

 glutaric acid. The same degradation products are formed from an a-ionone ring. 



Degradation by means of ozone is also an important method for elucidating 

 the constitution of carotenoids. By this means, it is possible for instance, to 

 show that the end groups of lycopene are zsopropylidene groups^^. Similarly, 

 an fsopropylidene group can be shown to be present in y-carotene. Furthermore, 

 by the controlled ozonisation of j3-carotene and /S-ionone, Pummerer, Rebmann 

 and Reindel^^ succeeded in isolating large degradation fragments identical 

 with those obtained from permanganate oxidations. 



An observation which was of considerable importance in the elucidation of 

 the constitution of carotenoids was made by Karrer and co-workers^*. They 

 showed that, in addition to the degradation products obtained by means of 

 permanganate, the ozonisation of /3-carotene gives rise to geronicacid (a:a-di- 

 methyl-S-acetylvaleric acid), while a-carotene yields geronic as well as iso- 

 geronic acid (y:y-dimethyl-S-acetyl valeric acid) 2^. 



9. partial degradation of carotenoids with permanganate 



AND chromic acid 



Another important contribution to the elucidation of the constitution of 

 carotenoids was the introduction of step-wise degradation with alkaline 

 permanganate (Karrer and co-workers)^® and of partial oxidation with 

 chromic acid (KuHN and Brockmann^'^). Both methods allow the isolation of 

 large degradation fragments from the structure of which it is possible to draw 

 conclusions regarding the constitution of the parent pigments. Thus Karrer 

 and co-workers^® succeeded in preparing j3-apo-2-carotenal, ^-apo-3-carotenal 

 and /3-apo-4-carotenal by the stepwise degradation of jS-carotene (cf. p. 144). 

 KuHN and Brockmann obtained various ketonic products, e.g. jS-carotenone 

 and semi-j3-carotenone by the mild chromic acid oxidation of /S-carotene, 

 References p. §1—32. 



