Unexpected crystallization and X-ray crystal structure of racemic 1-phenyl-2-(4-pyridyl)ethanol intermediate

Abstract

We have isolated, by crystallization, the intermediate, 1-phenyl-2-(4-pyridyl)ethanol, from the condensation reaction of 4-methylpyridine with benzaldehyde in which the aim was to obtain the model compound 4-styrylpyridine in absence of a condensing agent. Single crystal X-ray analysis shows the formation of an intermolecular hydrogen bond O–H···N between the nitrogen atom of a pyridine group and the oxygen atom of the OH of the neighboring molecule, which helps to stabilize the crystal structure. Crystal structure determination clearly revealed that the solid is chiral and racemic, as expected. The title compound crystallizes in an orthorhombic system with a space group Pna2₁ with two pairs of R and S enantiomers in each crystal cell (a = 15.591(1) Å, b = 12.691(1) Å, and c = 5.589(1) Å). Spectroscopic NMR data gave evidence that the isolated compound is actually the alcohol just before the dehydration process that yields the double bond of the 4-styrylpyridine.