DL-Methionine
Melting Point and Thermal Stability of DL-Methionine
Melting characteristics: DL-methionine has aclear and fixed melting pointof281–283 °C(decomposition). During heating, the crystals melt into a transparent liquid, and then decompose with the release of a small amount of methyl mercaptan (CH3SH) gas (with a characteristic pungent odor) when the temperature exceeds the melting point. It is worth noting that the melting point of DL-methionine is higher than that of L-methionine (280 °C) and D-methionine (279 °C), which is due to the denser crystal lattice formed by the racemic mixture of two enantiomers, resulting in stronger intermolecular forces.
Thermal stability: DL-methionine has good thermal stability at temperatures below 100 °C. It will not decompose when heated at 80 °C for a short time (e.g., during drying), which meets the requirements of industrial processing such as granulation and tableting. However, prolonged heating above 200 °C will cause the cleavage of the C-S bond in the side chain, producing volatile sulfur-containing compounds and reducing the purity of the product.
Storage stability: DL-methionine should be stored in a sealed, cool, and dry warehouse. It is stable when isolated from moisture and high temperature, with a shelf life of more than 2 years. However, it will undergo slow oxidation when exposed to humid air and oxygen for a long time, with the sulfur atom in the side chain being oxidized to a sulfoxide group, forming DL-methionine sulfoxide, which reduces its biological activity.
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