Preparation of Ergocalciferol and Cholecalciferol

Preparation of Ergocalciferol (Vitamin D₂)

Ergocalciferol, also known as Vitamin D₂, is synthesized from ergosterol, a compound found in fungi and yeast. The preparation involves the following steps:

1. Source of Ergosterol: Ergosterol is extracted from fungi (such as yeast) and used as the precursor for ergocalciferol.

2. UV Irradiation: Ergosterol is subjected to ultraviolet (UV) irradiation, specifically UV-B light (290–315 nm). This step converts ergosterol into previtamin D₂.

   Reaction:

   $$\text{Ergosterol}\stackrel{\text{UV-B}}{\to }{\text{Previtamin D}}_2$$

3. Thermal Isomerization: Previtamin D₂ undergoes a spontaneous thermal isomerization (at room temperature), resulting in the formation of ergocalciferol.

   Reaction:

   $${\text{Previtamin D}}_2\stackrel{\text{Heat}}{\to }{\text{Ergocalciferol (Vitamin D}}_2\text{)}$$

Preparation of Cholecalciferol (Vitamin D₃)

Cholecalciferol (Vitamin D₃) is synthesized from 7-dehydrocholesterol, which is present in the skin of animals, including humans. The process involves the following steps:

1. Source of 7-Dehydrocholesterol: 7-Dehydrocholesterol is a precursor found in the skin.

2. UV Irradiation: When exposed to sunlight, specifically UV-B light (290–315 nm), 7-dehydrocholesterol is converted into previtamin D₃.

   Reaction:

   $$\text{7-Dehydrocholesterol}\stackrel{\text{UV-B}}{\to }{\text{Previtamin D}}_3$$

3. Thermal Isomerization: Previtamin D₃ undergoes a thermal isomerization process to form cholecalciferol (Vitamin D₃).

   Reaction:

   $${\text{Previtamin D}}_3\stackrel{\text{Heat}}{\to }{\text{Cholecalciferol (Vitamin D}}_3\text{)}$$

Summary of Reactions:

Ergocalciferol (Vitamin D₂) Preparation:

1. Ergosterol → UV-B → Previtamin D₂
2. Previtamin D₂ → Heat → Ergocalciferol (Vitamin D₂)

Cholecalciferol (Vitamin D₃) Preparation:

1. 7-Dehydrocholesterol → UV-B → Previtamin D₃
2. Previtamin D₃ → Heat → Cholecalciferol (Vitamin D₃)

Both processes depend heavily on UV-B light exposure followed by a thermal isomerization to form the active Vitamin D compounds.