REACTION OF A MONOLAYER WITH SUBPHASE - DEHYDRATION OF A SECONDARY ALCOHOL OVER SULFURIC-ACID

The kinetics of the acid-catalyzed dehydration of 1-phenyl-l-hexadecanol to (Z)-l-phenyl-l-hexadecene have been studied on aqueous sulfuric acid-air interface for expanded (π <0.1 mN m-1) and compressed (π = 25 mN m-1, kept constant) monolayers. Below a threshold area/molecule region, the initial rate of the reaction is lower than above it, but as the reaction proceeds, affording more area/ molecule, the rate increases till a stage is reached where the effect of the reverse reaction (itself sensitive to the state of expansion) begins to outweigh this, resulting in the novel effect of the reversal in the net direction of the reaction during its course. For compressed film at constant surface pressure, contrived zero-order kinetics are followed, and the reaction is dramatically slower than for the expanded state. But the surface compression while decreasing the rate at the same time increases the yield of the reaction. This has been explained in terms of the product molecules being removed from contact with the subphase at high surface pressures. © 1990, American Chemical Society. All rights reserved.