CONTENTS XXI 



VI. Carotenoids and Related Compoutrds {continued) - • 



(d) Effect of "Isomerization of cis Compounds on Spectral 



Characteristics ............-....;...; 649 



g. Structural Configuration of Stereoisomers. .. ."%.... 649 



(5) Adsorption Phenomena (Chromatography). . 652 



■'-•r . a.- AppHcations af the Chromatographic Technic 653 



■ '" b. Theoretical Basis for Chromatography 654 



c. Practical Considerations in Chromatography 655 



d. Use of Chromatographj' in the Study of Carotenoids 659 



7. Methods for the Preparation of Carotenoids 661 



8 . Related Compounds 661 



(1 ) Phytofluene 661 



a. Occurrence 661 



VII. Distribution, Properties, and Chemistry of the Vitamins A 667 



1 . Introduction and Historical Development 667 



2 . Occurrence of the Vitamins A 675 



(1) Vitamin A in Fishes 675 



(2) Vitamin A in Animals Other Than Fishes 677 



(3) Distribution of Vitamins Ai and Aq 678 



(4) Vitamin- A-Like Compounds in the Retina 680 



(5) Vitamin A in Mammalian Tissues Other Than the Retina 684 



(6) Vitamin A and Carotene in Milk 685 



(7) Vitamin A in Egg Yolk 687 



(8) Vitamin A in the Free and the Esterified Form 687 



3 . Structure of the Vitamins A 690 



(1) Vitamin A (A,) 690 



(2) Vitamin As 692 



(3) Stereoisomeric Forms of Vitamin Ai 696 



4. Occurrence and Structure of Compounds Related to Vitamin A 701 



(1) Vitamin A Aldehyde 701 



(2) Vitamin A Acid 704 



(3) Vitamin A Ethers and Homologues 705 



a. Vitamin A Methyl Ether 707 



b. Homovitamin A and 5-Deh\-drohomovitamin A Ethers 707 



(4) Vitamin A Epoxide 709 



(5) Kitol 710 



5. SjTithesis of Vitamin A and Related Compounds 713 



( 1 ) Introduction 713 



(2) Kuhn-Morris Synthesis 715 



(3) Milas Syntheses 716 



a. Milas "A" Method 717 



b. Milas "B" Method and Isler Procedure 717 



(4) Oroshnik Synthesis 718 



(5) Synthesis of Arens and van Dorp 718 



a. Synthesis 1 718 



b. Synthesis 2 719 



(,6) Synthesis of Karrer, Jucker and Schick 719 



(7) Synthesis of Vitamin A from Dimethylaminovitamin A 720 



(8) Synthesis of Vitamin A Acid by the Milas Method 721 



