Polycrystalline growth in precipitation of an aromatic amine derivative and l-glutamic acid

Abstract

The effect of initial supersaturation and temperature on the particle morphology of l-glutamic acid and an aromatic amine derivative has been compared in batch experiments by pH-shift precipitation in water at temperatures of 5–80 °C. At higher initial supersaturation ratios both systems give rise to polycrystalline particles, which have been identified to grow by a spherulitic growth mechanism. On the other hand, single crystals can be obtained at low values for the initial supersaturation. The aqueous aromatic amine system yields plate-like crystals, whereas the β-polymorph of l-glutamic acid crystallizes as needle-like particles at low initial supersaturation. While the monocrystalline plate-like particles are precipitated directly from solution in case of the aromatic amine, monocrystalline needles of β- l-glutamic acid could only be crystallized by transforming the initially precipitated metastable α-polymorph. The onset of polycrystalline growth can be observed at intermediate initial supersaturation in crystallization of both the aromatic amine and β- l-glutamic acid. The aromatic amine derivative shows switching from monocrystalline plate-like crystals at a constant initial supersaturation value, whereas β- l-glutamic acid displays a transition from needles to spherulites, at a supersaturation level that becomes lower as the temperature increases. This switch in growth mechanism could not be found for the α-polymorph of l-glutamic acid. The spherulite morphology becomes more compact at higher initial supersaturation ratios.