Authors:
A. SchmidtUniversity of Innsbruck Institute of Pharmacy, Ph. Technology Innrain 52 6020 Innsbruck Austria Innrain 52 6020 Innsbruck Austria

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V. NiederwangerUniversity of Innsbruck Institute of Pharmacy, Ph. Technology Innrain 52 6020 Innsbruck Austria Innrain 52 6020 Innsbruck Austria

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U. GriesserUniversity of Innsbruck Institute of Pharmacy, Ph. Technology Innrain 52 6020 Innsbruck Austria Innrain 52 6020 Innsbruck Austria

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Abstract  

Two polymorphic forms, a dioxane solvate and the amorphous form of the local anaesthetic drug prilocaine hydrochloride (N-(2-methylphenyl)-2-propylamino monohydrochloride, PRCHC) were characterized by thermal analysis (hot stage microscopy, differential scanning calorimetry, thermogravimetry), vibrational spectroscopy (FTIR, FT-Raman-spectroscopy), powder X-ray diffractometry and water vapor sorption analysis. The formation and thermodynamic stability of the different solid phases is described and presented in a flow chart and an energy temperature diagram, respectively. Mod. I (m.p. 169C) is the thermodynamically stable form at room temperature and present in commercial products. This form crystallizes from all tested solvents except 1,4-dioxane which gives a solvate with half a mole of 1,4-dioxane per mole PRCHC. Mod. II occurs only on desolvation of the dioxane solvate and shows a lower melting point (165.5C) than mod. I and a lower heat of fusion. Thus, according to the heat of fusion rule, mod. II is the thermodynamically less stable form in the entire temperature range (monotropism) but kinetically stable for at least a year. Freeze-drying of an aqueous solution leads to the amorphous form. On heating and in moist air amorphous PRCHC exclusively crystallizes to the stable mod. I. PRCHC exemplifies that certain metastable polymorphic forms are only accessible via a specific solvate, but not via any other crystallization path. Since no crystallization from 1,4-dioxane was performed in earlier solid-state studies of this compound, PRCHC was to this date rated as monomorphic.

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Journal of Thermal Analysis and Calorimetry
Language English
Size A4
Year of
Foundation
1969
Volumes
per Year
1
Issues
per Year
24
Founder Akadémiai Kiadó
Founder's
Address
H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
Publisher Akadémiai Kiadó
Springer Nature Switzerland AG
Publisher's
Address
H-1117 Budapest, Hungary 1516 Budapest, PO Box 245.
CH-6330 Cham, Switzerland Gewerbestrasse 11.
Responsible
Publisher
Chief Executive Officer, Akadémiai Kiadó
ISSN 1388-6150 (Print)
ISSN 1588-2926 (Online)

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Geopolymers

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Author:
J. Davidovits