Gas-phase Meerwein–Ponndorf–Verley reaction: correlation of the 3665 cm−1 IR band with the cis-alcohol selectivity

The two Lewis acid sites assumed to catalyze the Meerwein–Ponndorf–Verley (MPV) reaction are identified by IR bands at 3782 and 3660–3680 cm−1. Different combinations of heat-treatment protocols were used and the results indicated that the final temperature, ramp rate, and gas environment make a difference in the relative intensities of the 3782 and 3665 cm−1 bands. Combining different heat-treatment procedures, samples were produced where the 3782 and 3665 cm−1 band intensities moved in opposite directions (i.e., one increasing and the other decreasing). The MPV reduction of 4-tert-butylcyclohexanone with 2-propanol in the gas phase was studied at 100 °C in a nitrogen atmosphere. The increasing trend of the relative intensity of the 3665 cm−1 band showed a correlation in favor of the formation of cis-4-tert-butylcyclohexanol (cis-4-TBCHL). This suggests that the species associated with the 3665 cm−1 band are likely responsible for cis-4-TBCHL selectivity.