Abstract: A process for preparing a vitamin D derivative including providing an ultraviolet irradiation apparatus for photochemical reactions, which has an ultraviolet radiation-emitting lamp, an optical system which receives light from the ultraviolet radiation-emitting lamp and emits ultraviolet rays having a specific wavelength, and a quartz rod which receives the ultraviolet rays having the specific wavelength from the optical system and emits the ultraviolet rays, irradiating a solution of a provitamin D derivative with the ultraviolet rays emitted from the quartz rod to cause a photochemical reaction to the provitamin D derivative solution, thereby forming a previtamin D derivative, and subjecting the previtamin D derivative to a thermal isomerization reaction to prepare the vitamin D derivative.

Abstract: Disclosed herein are an ultraviolet irradiation apparatus for photochemical reactions which can irradiate the photo-reactive solution with ultraviolet rays having a specific wavelength suitable for the intended photochemical reaction at a high efficiency, and a process by which a provitamin D derivative can be converted into a provitamin D derivative at a high efficiency by means of a photochemical reaction by one-step process of light irradiation, thereby preparing a vitamin D derivative at a high efficiency.