Patent ID: 6902654

Claim:
A process for preparing a vitamin D derivative, comprising: providing a reaction container configured to contain a solution of a provitamin D derivative and an ultraviolet irradiation apparatus configured to irradiate the solution of the provitamin D derivative in the reaction container with an ultraviolet irradiation, the ultraviolet irradiation apparatus comprising an ultraviolet radiation-emitting lamp, an optical system positioned to be struck by light from the ultraviolet radiation-emitting lamp and configure to emit ultraviolet rays having a specific wavelength, a quartz rod positioned to be struck by the ultraviolet rays from the optical system, and a projection lens positioned to be struck by and to irradiate the solution of the provitamin D derivative in the reaction container with the ultraviolet rays through the quartz rod, the projection lens being configured to control a spot size of the ultraviolet rays having the specific wavelength; irradiating the solution of the provitamin D derivative with the ultraviolet rays emitted from the projection lens of the ultraviolet irradiation apparatus to cause a photochemical reaction of the provitamin D derivative and form a previtaniin D derivative; and subjecting the previtamin D derivative to a thermal isomerization reaction to prepare the vitamin D derivative.