Nucleation, growth, and pseudo-polymorphic behavior of citric acid as monitored in situ by attenuated total reflection Fourier transform infrared spectroscopy

Citation
H. Groen et Kj. Roberts, Nucleation, growth, and pseudo-polymorphic behavior of citric acid as monitored in situ by attenuated total reflection Fourier transform infrared spectroscopy, J PHYS CH B, 105(43), 2001, pp. 10723-10730
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY B
ISSN journal
1520-6106 → ACNP
Volume
105
Issue
43
Year of publication
2001
Pages
10723 - 10730
Database
ISI
SICI code
1520-6106(20011101)105:43<10723:NGAPBO>2.0.ZU;2-J
Abstract
The crystallization, dissolution, and associated pseudo-polymorphic behavio r of citric acid crystals from aqueous solution is investigated using tempe rature-programmed and isothermal batch experiments. Quantitative attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy is u sed to measure in situ the solution concentration and hence the reactant su persaturation over a wide range of solution undercoolings within the metast able zone. Detailed mapping out of the solubility-supersolubility diagram r eveals poor nucleation behavior as characterized by a very wide metastable zone width (typical value, 55 degreesC for a cooling rate of 0.05 K/min). S imultaneous ATR FTIR and optical turbidometric measurements are used to cro ss-correlate the supersaturation driving force to the nucleation behavior a s followed prior to and during crystallization within the metastable zone. Both temperature-programmed and isothermal measurements reveal behavior con sistent with spontaneous liquid-phase separation within the highly supersat urated mother liquor prior to crystallization, the occurrence of which is k nown as oiling-out, a phenomenon poorly understood in industrial crystalliz ation reactions. Parallel examination of the phase of the product crystals, using in situ and ex situ powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC), reveals the formation of the anhydrous form of citric acid via temperature-programmed experiments and the monohydrate phas e being crystallized via isothermal experiments. These results, which corre late with the solubility-supersolubility phase diagram, are rationalized in terms of the respective crystal chemistry of the anhydrate and monohydrate structures of citric acid, which is consistent with a solvent-mediated pha se transformation mechanism effecting the change from the anhydrate to the monohydrate form.