XXll CONTENTS 



VII. Distribution, Properties, and Chemistry of the Vitamins A (continued) 



(9) Synthesis of Vitamin A Acid Ethyl Ester by the Method of 



Schwarzkopf and Collaborators 721 



(10) Synthesis of Vitamin A Ethers 722 



a. Milas Synthesis from Glycol Methyl Ether 722 



b. Milas Synthesis from 5-Dehydrovitamin A Methyl Ether. . . 723 



(11) Other Syntheses of Vitamin A 724 



(12) Syntheses of Homologues of Vitamin A Ethers 724 



6 . Properties of Vitamins A and Related Compounds 726 



( 1 ) General Physical Properties 726 



(2) Distillation 727 



(3) Absorption Spectra 728 



(4) Reaction with Antimony Trichloride (Carr-Price Test) 732 



(5) Related Compounds Formed by Action of Acids on Vitamin A. 733 



a. Anhydrovitamin A 733 



(a) Structure of Anhydrovitamin A 734 



(b) Properties of Anhydrovitamin A 735 



(c) Distribution of Anhydrovitamin A 736 



(d) Vitamin A Activity of Anhydrovitamin A 736 



b. Rehydrovitamin A 736 



c. Isoanhydrovitamin A 738 



d. Subvitamin A 738 



VIII. Distribution, Properties, and Chemistry of the Provitamins D and 



V itamins D 739 



A. Introduction 739 



B. Provitamins D 744 



1 . Occurrence of the Provitamins D 745 



( 1 ) Ergosterol 745 



(2) 7-Dehydrocholesterol 746 



2 . Properties of the Provitamins D 748 



3. Structure of the Provitamins D 749 



(1) Ergosterol (Provitamin D;) 750 



(2) 7-Dehydrocholesterol (Provitamin D3) 754 



(3) 22-Dihydroergosterol (Provitamin D4) 755 



(4) Other Provitamins D 755 



4 . Synthesis of the Provitamins D 756 



( 1 ) 7-Dehydrocholesterol 756 



(2) 22-Dihydroergosterol 756 



(3) 7-Dehydrositosterol 757 



(4) Other Provitamins D 757 



C. Conversion of the Provitamins D to the Vitamins D 758 



1 . Introduction 758 



2 . Processes of Activation 759 



3 . Chemistry of the Activation Products 762 



( 1 ) Lumisterols 764 



(2) Tachysterols 765 



a. DihydrotachysteroU - ' 767 



(3) Vitamins D . . . ' ^ 768 



(4) Toxisterols 768 



(5) Suprasterols I and II 769 



