The production of nicotineamide during the thermal desorption of 3-cyanopyridine (3CYP) from Ni2+- and Al3+- exchanged bentonite. A TG-MS, variable temperature DRIFTS and XRD study

Abstract

Samples of air-dried and heated Ni²⁺- and Al³⁺-exchanged bentonite (SWy-2) have been exposed to 3-cyanopyridine (3CYP) vapour for six days. The resulting intercalates were studied using variable temperature XRD, DRIFTS, thermogravimetry (TG) and TG-MS. The amount of water co-adsorbed with 3CYP did not influence the initial 13.2 Å spacing of the Al³⁺-complex but the d-spacing of the heated Ni²⁺-sample was ca. 5 Å less that the 21.5 Å spacing of its air-dried counterpart. This difference in layer spacings suggests that 3CYP adopts an arrangement in which the plane of the aromatic ring is parallel with the aluminosilicate layer in the Al³⁺-clay whereas in the Ni²⁺-form the plane of the ring is perpendicular to the clay surface. TG-MS confirmed that 3CYP and water were the major species desorbed from all samples and that the contraction in the d-spacing upon heating the Ni²⁺-3CYP complex arose from loss of these species. The appearance of a band near 1680 cm⁻¹ in the VT-DRIFTS spectra at temperatures above 150 °C indicated the formation of amide(s). Correlation with TG-MS data confirmed the transformation of small quantities of 3CYP to nicotinamide. Some 3CYP was protonated in the Al³⁺-samples.