Crystal structure determination and thermal behavior upon melting of p-synephrine

• The refinement of the crystal structure is achieved from X-ray powder diffraction.
• P-Synephrine is revealed to be a racemic compound.
• Degradation during melting can be bypassed using high DSC scan rates.
• The temperature and enthalpy of melting are then proposed for this compound.

The crystal structure of p-synephrine was solved from a high-resolution X-ray powder diffraction pattern optimized by energy-minimization calculations using the Dreiding force field. The title compound crystallizes in a monoclinic system (space group P21/c, Z = 4, with a = 8.8504(11) Å, b = 12.1166(15) Å, c = 9.7820(11) Å, β = 122.551(2)°, V = 884.21(19) Å3 and d = 1.256 g cm−3). Since p-synephrine degrades upon melting, its melting data were determined from DSC experiments carried out as a function of the heating rate. This method allowed determining a melting temperature and enthalpy equal to 199.8 ± 1.3 °C and 57 ± 3 kJ mol−1, respectively.

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