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The curious case of acetaldehyde phenylhydrazone: resolution of a 120 year old puzzle where forms with vastly different melting points have the same structure

The curious case of acetaldehyde phenylhydrazone: resolution of a 120 year old puzzle where forms with vastly different melting points have the same structure
The curious case of acetaldehyde phenylhydrazone: resolution of a 120 year old puzzle where forms with vastly different melting points have the same structure
The solid forms of acetaldehyde phenylhydrazone were investigated in detail over a century ago, with curious results: it was reported that a low melting form could be transformed into a high melting form by trace alkali, and the reverse process could be brought about with trace acid. Our reinvestigation of this puzzle with modern instrumentation has shown that all samples, although exhibiting sharp melting points varying from 56 to 101 °C, have identical IR and solid-state NMR spectra and identical crystal structures. NMR studies of the melts provided the key to the understanding of this strange behavior: differently melting samples did so because they initially melted to liquids with different proportions of the Z and E isomers, although given enough time they all tended to the same equilibrium proportion. The leading role of the isomerization rate in the melt was confirmed in cyclic differential scanning calorimetry experiments and accompanying simulations. In the case of polymorphism, different structures melt to the same liquid. In the present case, the same structure melts to different liquids.
1528-7483
Bernades, Carlos
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Carravetta, Marina
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Coles, Simon J.
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Van Eck, Ernst R.H.
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Meekes, Hugo
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Minas da Piedade, Manuel E.
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Pitak, Mateusz
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Podmore, Mike
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de Ruiter, Tobian A.H.
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Söğütoğlu, Leyla-Cann
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Steendam, René R. E.
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Threlfall, Terry L.
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Bernades, Carlos
df09b393-afd2-404c-8cd0-a0953d416087
Carravetta, Marina
1b12fa96-4a6a-4689-ab3b-ccc68f1d7691
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Van Eck, Ernst R.H.
f93e2578-161d-4db9-9ceb-a38c1311e6a8
Meekes, Hugo
2efde48e-73b4-4762-9a8c-329fb85cb4ac
Minas da Piedade, Manuel E.
f60abdbf-9c03-417f-aebc-1549411df03f
Pitak, Mateusz
eeb6a00f-2291-4376-830f-d30dfd607ed1
Podmore, Mike
6ef23c67-15c5-48a3-b6cb-e96eddce72ce
de Ruiter, Tobian A.H.
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Söğütoğlu, Leyla-Cann
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Steendam, René R. E.
c6beaa43-04a3-47b9-a766-3bb6be768975
Threlfall, Terry L.
6c670746-9730-49fc-9381-e45ae4807450

Bernades, Carlos, Carravetta, Marina, Coles, Simon J., Van Eck, Ernst R.H., Meekes, Hugo, Minas da Piedade, Manuel E., Pitak, Mateusz, Podmore, Mike, de Ruiter, Tobian A.H., Söğütoğlu, Leyla-Cann, Steendam, René R. E. and Threlfall, Terry L. (2019) The curious case of acetaldehyde phenylhydrazone: resolution of a 120 year old puzzle where forms with vastly different melting points have the same structure. Crystal Growth & Design. (doi:10.1021/acs.cgd.8b01459).

Record type: Article

Abstract

The solid forms of acetaldehyde phenylhydrazone were investigated in detail over a century ago, with curious results: it was reported that a low melting form could be transformed into a high melting form by trace alkali, and the reverse process could be brought about with trace acid. Our reinvestigation of this puzzle with modern instrumentation has shown that all samples, although exhibiting sharp melting points varying from 56 to 101 °C, have identical IR and solid-state NMR spectra and identical crystal structures. NMR studies of the melts provided the key to the understanding of this strange behavior: differently melting samples did so because they initially melted to liquids with different proportions of the Z and E isomers, although given enough time they all tended to the same equilibrium proportion. The leading role of the isomerization rate in the melt was confirmed in cyclic differential scanning calorimetry experiments and accompanying simulations. In the case of polymorphism, different structures melt to the same liquid. In the present case, the same structure melts to different liquids.

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e-pub ahead of print date: 7 January 2019

Identifiers

Local EPrints ID: 427779
URI: https://eprints.soton.ac.uk/id/eprint/427779
ISSN: 1528-7483
PURE UUID: 37127594-baee-47b1-a56b-9528f34a2cb6
ORCID for Marina Carravetta: ORCID iD orcid.org/0000-0002-6296-2104
ORCID for Simon J. Coles: ORCID iD orcid.org/0000-0001-8414-9272
ORCID for Mateusz Pitak: ORCID iD orcid.org/0000-0002-3680-7100

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Date deposited: 29 Jan 2019 17:30
Last modified: 30 Jan 2019 01:36

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Contributors

Author: Carlos Bernades
Author: Simon J. Coles ORCID iD
Author: Ernst R.H. Van Eck
Author: Hugo Meekes
Author: Manuel E. Minas da Piedade
Author: Mateusz Pitak ORCID iD
Author: Mike Podmore
Author: Tobian A.H. de Ruiter
Author: Leyla-Cann Söğütoğlu
Author: René R. E. Steendam
Author: Terry L. Threlfall

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