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 Ni 21 -and Al 31 -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 A ˚spacing of the Al 31 -complex but the d-spacing of the heated Ni 21 -sample was ca. 5 A less that the 21.5 A ˚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 Al 31 -clay whereas in the Ni 21 -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 Ni 21 -3CYP complex arose from loss of these species. The appearance of a band near 1680 cm À1 in the VT-DRIFTS spectra at temperatures above 150 1C 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 Al 31 -samples.