THERMOGRAVIMETRIC STUDY OF THE DESORPTION OF CYCLOHEXYLAMINE AND PYRIDINE FROM AN ACID-TREATED WYOMING BENTONITE

Four 15 g samples of an unsedimented Wyoming bentonite were treated with 200 cm3 of 0.025, 0.050, 0.100 and 0.250 mol dm-3 H2SO4 for 1 h at room temperature (samples I-IV, respectively). Three further 15 g samples were treated with 200 cm3 of 50% (v/v) H2SO4 for 1 h at 20-degrees-C (sample V), and 1 and 2 h under reflux (samples VI and VII, respectively). X-ray fluorescence and diffraction studies revealed that only samples VI and VII suffered any substantial structural attack. The resulting acidity of the clays, determined by cyclohexylamine desorption, indicated that sample V contained the largest number of protons at 0.59 mmol H+ (g clay)-1. Sample V was also the most efficient catalyst for the dehydration and etherification of hexan-1-ol, giving a combined product yield of 17.0% after 2 h reflux in neat reactant. The parent bentonite and samples I and II showed no discernible catalytic activity despite measured acidities of 0.1, 0.24 and 0.34 mmol H+ (g clay)-1. In contrast samples III and IV gave combined product yields of 4.5 and 11.0%, respectively, which correlated well with the measured acidities of 0.38 and 0.48 mmol H+ (g clay)-1. Samples VI and VII, prepared by reflux in acid, contained 0.3 and 0.1 mmol H+ (g clay)-1, respectively, and gave combined product yields of 13.0 and 6.0%.