The melting point for pure caffeine, specifically in its anhydrous form, is typically between 227 to 228 °C (441 to 442 °F; 500 to 501 K).
Understanding Caffeine's Melting Points
Pure caffeine can exist in different forms, which influences its physical properties, including its melting point. The term "pure caffeine" commonly refers to its anhydrous state, meaning it does not contain water molecules within its crystal structure. However, caffeine can also form a monohydrate, which has a slightly different melting range.
- Anhydrous Caffeine: This is the most common form of pure caffeine, characterized by the absence of water molecules in its crystalline lattice.
- Caffeine Monohydrate: This form contains one water molecule associated with each caffeine molecule, leading to distinct physical properties, including a different melting point.
Understanding these distinctions is important for applications ranging from pharmaceutical formulation to quality control in food and beverage industries.
Detailed Melting Point Information
Here is a summary of the melting points for both forms of pure caffeine:
| Caffeine Form | Melting Point (Celsius) | Melting Point (Fahrenheit) | Melting Point (Kelvin) |
|---|---|---|---|
| Anhydrous | 227 to 228 °C | 441 to 442 °F | 500 to 501 K |
| Monohydrate | 234 to 235 °C | 453 to 455 °F | 507 to 508 K |
For more detailed physical and chemical properties of caffeine, you can refer to comprehensive data pages.
Other Key Properties of Pure Caffeine
Beyond its melting point, anhydrous pure caffeine exhibits several other notable characteristics:
- Appearance: It typically appears as odorless, white needles or a fine powder.
- Density: In its solid state, pure caffeine has a density of approximately 1.23 g/cm³.
- Boiling Point/Sublimation: Instead of reaching a typical boiling point where it transitions from liquid to gas, caffeine undergoes sublimation at 178 °C (352 °F; 451 K). Sublimation is a direct phase transition from solid to gas without passing through an intermediate liquid phase.
These properties are fundamental for the identification, purification, and various industrial applications of caffeine.
