Spectroscopic and Thermoanalytical Characterization of (+)-Fenfluramine Hydrochloride

Abstract

We have analyzed the vibrational, structural, and thermal properties of a pure enantiomer of fenfluramine. At room temperature the samples, as-received or ground, are in the α-phase, in which hydrogen bonds are formed among adjacent molecules. Evidence of these H bonds is no longer found in samples which have been annealed above a critical temperature. Grain size, sample treatment, or defects influence the temperature range where the H bonds break down; this phenomenon is accompanied by thermal effects such as endothermic peaks or anomalies of heat capacity, and followed by a slow structural rearrangement into a γ-phase. No evidence of hydrogen bonds is found in the water recrystallized fenfluramine, which maintains up to the melting temperature a crystallographic form (β-form) distinct from both α- and γ-phases. It is suggested that “folded” and “extended” fenfluramine molecules are characteristic of the α- and β-phase, respectively.