Monitoring the Polymorphic Transformation of Imidacloprid Using in Situ FBRM and PVM

摘要

The objective of this work was to study the polymorphic transformation of imidacloprid from form II to form I in ethanol by using in situ focused beam reflectance measurement (FBRM) and particle vision measurement (PVM). The solubility and metastable zone width of the two forms were measured, and the influences of temperature and amounts of added imidacloprid to the transformation were investigated. Higher temperature accelerates the transformation and improves the transformation efficiency. More substrates prolong the time of the transformation. The transformation was identified as a solution-mediated transformation. The single crystals of the two forms were obtained. The crystal structure of form I has not been reported before, Tautomerism exists between the two polymorphs of imidacloprid. Analysis of molecular structures and stacking modes shows that more hydrogen bonds exist in form I. It indicates that the change of the hydrogen bond interaction maybe the driving force of the transformation. In this study, the transformation process of imidacloprid from form II to form I in ethanol solvent was mainly discussed. The single crystals of the two forms were obtained, and their molecular structures and stacking modes were discussed. In order to obtain some critical information, in situ techniques of FBRM and PVM were used to determine the solubility of both the forms in ethanol and to monitor chord counts, chord length distribution, and morphology of the particles. The influences of temperature and amounts of added imidacloprid were studied systematically.