II. CIIKMISTUY AND IN'DUSTUIAL I'KKP AUATIOX 



19 



witli dilute (0.1 N) chromic acid, OjO-dih^'droxy /3-caroteiie is formed. With 

 a larger amomit of chromic acid, one of the trimethylcyclohexenyl rings is 

 opened to form semi-/i-carotenonc (XXVI) Avhich can lose water easily to 

 giveanhydro-/3-carotenone (XXVI I ).Karrer and his associates oxidized care- 

 fully |S-carotene with potassium permanganate and destroyed one of the 

 trimethylcyclohexenyl rings without affecting the other ring or the coii- 



TABLE VI 

 l?i:i,ATivi: PoTKXciKs OK Stereoisomeric Provitaahn a Carotenoids in the Rat 



(Zechmeister) 



" Ex Pyracantha. 



^ Et pro-7-carotene by iodine catalysis. 



jugated system. Thus, they produced 2-apocarotenal (XXVIII) which was 

 reduced with aluminum isopropoxide to 2-apocaroteno]. Using the same 

 method but different amounts of potassium pemianganate, the same work- 

 ers oxidized j8-carotene at the fourth double bond and obtained 4-apocaro- 

 tenal (XXIX), which was also reduced to 4-apocarotenol. All these products 

 were found to be biologically active. Table VII lists these provitamins A 

 together with some of their physical properties. 



It has also been known for some time''^ that both a- and /3-carotenes add 

 iodine to fomi the corresponding diiodides, which are biologically active. 



In certain cases biologically inactive carotenoids have been converted to 



