Coupling Viedma ripening with racemic crystal transformations

mechanism of deracemization

Christos Xiouras, Joop H. Ter Horst, Tom Van Gerven, Georgios D. Stefanidis

Research output: Contribution to journalArticle

12 Citations (Scopus)
14 Downloads (Pure)

Abstract

It has been recently observed that coupling Viedma ripening with a seeded in situ metastable racemic crystal to conglomerate transformation leads to accelerated and complete deracemization: crystal transformation-enhanced deracemization. By means of a simple kinetic model, we show that the mechanistic pathway of this new process depends profoundly on the interplay between the crystal transformation and racemization processes, which in turn influence the nucleation process of the counter enantiomer. If the nucleation of the counter enantiomer is suppressed (e.g., by sufficiently fast racemization, low amount of racemic compound or gradual feed, low relative solubility between racemic compound and conglomerate), deracemization proceeds via a second order asymmetric transformation (SOAT) and is limited primarily by the dissolution rate of the racemic crystals and the growth rate of the preferred enantiomer crystals. Breakage and agglomeration accelerate the process, but contrary to conventional Viedma ripening, they are not essential ingredients to explain the observed enantiomeric enrichment. If the nucleation process of the counter enantiomer is not sufficiently suppressed, deracemization is initially controlled by the dissolution rate of the racemic crystals, but Viedma ripening is subsequently required to convert the conglomerate crystals of the counter enantiomer formed by nucleation, resulting in slower deracemization kinetics. In both cases, the combined process leads to faster deracemization kinetics compared to conventional Viedma ripening, while it autocorrects for the main disadvantage of SOAT, i.e., the accidental nucleation of the counter enantiomer. In addition, crystal transformation-enhanced deracemization extends the range of applicability of solid-state deracemization processes to compounds that form metastable racemic crystals.

Original languageEnglish
Pages (from-to)4965-4976
Number of pages12
JournalCrystal Growth and Design
Volume17
Issue number9
Early online date24 Jul 2017
DOIs
Publication statusPublished - 6 Sep 2017

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Enantiomers
enantiomers
Crystals
Nucleation
counters
crystals
nucleation
Kinetics
Dissolution
dissolving
kinetics
Crystallization
agglomeration
ingredients
Agglomeration
Solubility
solubility
solid state

Keywords

  • viedma ripening
  • deracemization
  • crystal transformation
  • racemic compound

Cite this

Xiouras, Christos ; Ter Horst, Joop H. ; Van Gerven, Tom ; Stefanidis, Georgios D. / Coupling Viedma ripening with racemic crystal transformations : mechanism of deracemization. In: Crystal Growth and Design. 2017 ; Vol. 17, No. 9. pp. 4965-4976.
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Coupling Viedma ripening with racemic crystal transformations : mechanism of deracemization. / Xiouras, Christos; Ter Horst, Joop H.; Van Gerven, Tom; Stefanidis, Georgios D.

In: Crystal Growth and Design, Vol. 17, No. 9, 06.09.2017, p. 4965-4976.

Research output: Contribution to journalArticle

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T1 - Coupling Viedma ripening with racemic crystal transformations

T2 - mechanism of deracemization

AU - Xiouras, Christos

AU - Ter Horst, Joop H.

AU - Van Gerven, Tom

AU - Stefanidis, Georgios D.

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N2 - It has been recently observed that coupling Viedma ripening with a seeded in situ metastable racemic crystal to conglomerate transformation leads to accelerated and complete deracemization: crystal transformation-enhanced deracemization. By means of a simple kinetic model, we show that the mechanistic pathway of this new process depends profoundly on the interplay between the crystal transformation and racemization processes, which in turn influence the nucleation process of the counter enantiomer. If the nucleation of the counter enantiomer is suppressed (e.g., by sufficiently fast racemization, low amount of racemic compound or gradual feed, low relative solubility between racemic compound and conglomerate), deracemization proceeds via a second order asymmetric transformation (SOAT) and is limited primarily by the dissolution rate of the racemic crystals and the growth rate of the preferred enantiomer crystals. Breakage and agglomeration accelerate the process, but contrary to conventional Viedma ripening, they are not essential ingredients to explain the observed enantiomeric enrichment. If the nucleation process of the counter enantiomer is not sufficiently suppressed, deracemization is initially controlled by the dissolution rate of the racemic crystals, but Viedma ripening is subsequently required to convert the conglomerate crystals of the counter enantiomer formed by nucleation, resulting in slower deracemization kinetics. In both cases, the combined process leads to faster deracemization kinetics compared to conventional Viedma ripening, while it autocorrects for the main disadvantage of SOAT, i.e., the accidental nucleation of the counter enantiomer. In addition, crystal transformation-enhanced deracemization extends the range of applicability of solid-state deracemization processes to compounds that form metastable racemic crystals.

AB - It has been recently observed that coupling Viedma ripening with a seeded in situ metastable racemic crystal to conglomerate transformation leads to accelerated and complete deracemization: crystal transformation-enhanced deracemization. By means of a simple kinetic model, we show that the mechanistic pathway of this new process depends profoundly on the interplay between the crystal transformation and racemization processes, which in turn influence the nucleation process of the counter enantiomer. If the nucleation of the counter enantiomer is suppressed (e.g., by sufficiently fast racemization, low amount of racemic compound or gradual feed, low relative solubility between racemic compound and conglomerate), deracemization proceeds via a second order asymmetric transformation (SOAT) and is limited primarily by the dissolution rate of the racemic crystals and the growth rate of the preferred enantiomer crystals. Breakage and agglomeration accelerate the process, but contrary to conventional Viedma ripening, they are not essential ingredients to explain the observed enantiomeric enrichment. If the nucleation process of the counter enantiomer is not sufficiently suppressed, deracemization is initially controlled by the dissolution rate of the racemic crystals, but Viedma ripening is subsequently required to convert the conglomerate crystals of the counter enantiomer formed by nucleation, resulting in slower deracemization kinetics. In both cases, the combined process leads to faster deracemization kinetics compared to conventional Viedma ripening, while it autocorrects for the main disadvantage of SOAT, i.e., the accidental nucleation of the counter enantiomer. In addition, crystal transformation-enhanced deracemization extends the range of applicability of solid-state deracemization processes to compounds that form metastable racemic crystals.

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