Propylparaben: Physical Characteristics

The chapter discusses the physical characteristics of propylparaben. Propylparaben occurs as odorless, tasteless, colorless crystals, or a white crystalline powder. Nomenclature, formulae, and elemental analysis of propylparaben are given. The reported dissociation constant (pKa) of propylparaben is 8.4 at 22°C. Partition coefficients for propylparaben in vegetable oils and water are given. Propylparaben has been reported to be very slightly soluble in water, but freely soluble in alcohol and ether. The solubilities of propylparaben in various solvents, and the solubilities of propylparaben in water at 25°C as a single component and in mixtures with other parabens are discussed. Crystals of propylparaben are translucent and colorless, belonging to the monoclinic system. Photomicrographs of crystalline propylparaben, obtained using optical microscopy are described. The chapter presents the crystallographic properties of propylparaben. The melting point of propylparaben is reported to be 95–99°C. The mass spectrum of propylparaben was recorded using a JEOL JMS-DX-303 spectrometer, operated in the electron impact mode. Propylparaben is known to be stable in contact with air, but the bulk substance should still be stored in a cool, dry place in a well-closed container. Propylparaben, along with its metabolites, was found in blood and urine after its oral and intravenous administration.