Protoporphyrin (IX) and its dimethyl ester were obtained in homogeneous polycrystals of high purity, in a good yield, from hemin by the modification of Ramsey's method. Purity and physicochemical properties of these crystals were confirmed by ultraviolet, infrared, and NMR spectra, differential thermal analysis, and X-ray power diffraction analysis. The dimethyl ester had hitherto been reported as melting at 223∼230°but differential thermal analysis showed that a part of the molecular structure and crystal form underwent change accompanied by heat evolution and, therefore, this temperature was found to be the decomposition point. There was also an endothermic phenomenon at 180°, with transition of the crystal phase.
