STUDIES ON THE ISOMERIZATION OF VITAMIN D AND RELATED COMPOUNDS WITH ACIDIC REAGENTS:II. MECHANISM OF THE ISOMERIZATION OF VITAMIN D2 AND ITS ISOMERS WITH BORON TRIFLUORIDE

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Kinetic experiments on the isomerization of vitamin D2, pre-D2, 5, 6-trans-D2 and T2 with BF3 were investigated by using the determination method as reported previously (1). The related components in the reaction mixtures were confirmed to be one of the starting compounds, iso-D2 and iso-T2 in all cases by applying the qualitative method using both TLC and GLC. Then, the components were individually determined by the proposed method according to lapse reaction times. The con-version rates of all the starting compounds followed apparent first-order kinetics and the rate constants of vitamin D2, pre-D2, 5, 6-trans-D2 and T2 were 0.277, 0.462, 0.693 and 0.330, respectively. When the yields of iso-D2 and iso-T2 to the concentrations of converted starting compounds were calculated on the basis of the corresponding reaction times, the initial rates of yields of iso-D2 and iso-T2 at zero conversions of the starting compounds were respectively 100 and 0% in all cases. The results induced the conclusions in all cases that iso-D2 was originated as the first reaction product directly from the starting compounds while iso-T2 was the second reaction product originated via iso-D2. The conclusions are summarized as follows: Vitamin D2, pre-D2, 5, 6-trans-D2 or T2 →BF3 iso-D2 →BF3 iso-T2 The reaction mechanism was discussed from the conclusions (Fig. 4).
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