This paper is part of the Special Issue on the 21th Conference of the IAPS.
Photoisomerization of Alfa Calcidol by a Sensitized Quantum Chain Reaction†
Article first published online: 30 DEC 2011
© 2011 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2011 The American Society of Photobiology
Photochemistry and Photobiology
Volume 88, Issue 4, pages 769–773, July/August 2012
How to Cite
Estruch, G. A. and Aramendía, P. F. (2012), Photoisomerization of Alfa Calcidol by a Sensitized Quantum Chain Reaction. Photochemistry and Photobiology, 88: 769–773. doi: 10.1111/j.1751-1097.2011.01054.x
- Issue published online: 9 JUL 2012
- Article first published online: 30 DEC 2011
- Accepted manuscript online: 30 NOV 2011 09:55AM EST
- Received 1 October 2011, accepted 22 November 2011
The production of vitamin D3 is a pharmaceutically relevant process, producing high added-value products. Precursors are extracts from vegetal origin but bearing mainly an E geometry in the 5,6 double bond. The synthesis of vitamin D3 (5-E-α-calcidol) with the correct Z stereochemistry in the 5,6 double bond from the E isomer using anthracene and triethylamine (TEA) as the sensitizer system was studied from the kinetic and mechanistic point of view. The sensitized isomerization of E-calcidol by irradiation of anthracene takes place only in deoxygenated solution and yields the Z isomer in ca 5% yield in the photostationary state. When TEA is added to the system, the E–Z reaction is not inhibited by oxygen any more, the quantum yield of photoisomerization to the Z isomer grows linearly with the concentration of E-calcidol, while conversions higher than 95% to the Z isomer are reached in the photostationary state and E–Z quantum yields as high as 45 at [E-calcidol] = 25 mm are reached. If TEA is replaced by 1,4-diazabicyclo[2.2.2]octane, the reaction rate drops to one-third at the same amine concentration. The observations can be explained by a quantum chain reaction mechanism. The high conversion achieved eliminates the need of isomer separation.