In-water Dehydration Reaction of an Aromatic Diol on an Inorganic Surface

The effect of a synthetic saponite surface on the in-water dehydration reaction of diol was examined using 4-formyl-1-methylquinolinium salt (MQu(+)) as a substrate. The equilibrium between aldehyde (MQu(+)-Aldehyde) and diol (MQu(+)-Diol) was affected by the surrounding environment. The equilibrium behavior was observed by H-1 nuclear magnetic resonance (NMR) and UV-vis absorption measurements. Although MQu(+) was completely in the form of MQu(+)-Diol in water, the equilibrium almost shifted to the MQu(+)-Aldehyde side when MQu(+) was adsorbed on the saponite surface in water. In addition, the MQu(+)-Aldehyde ratio depended on the negative charge density of saponite. The factors that determine MQu(+)-Aldehyde: MQu(+)-Diol ratio were discussed from the thermodynamic analysis of the system. These data indicate that the electrostatic interaction between the charged saponite surface and MQu(+) stabilized the aldehyde side enthalpically and destabilized it entropically. The major reason for these results is considered to be the difference in adsorption stabilization between MQu(+)-Aldehyde and MQu(+)-Diol on saponite surfaces.

Automated summary

The study investigated the effect of a synthetic saponite surface on the in-water dehydration reaction of diol using MQu(+) as a substrate. The data suggest that the negative charge density of saponite surface affects the equilibrium between MQu(+)-Aldehyde and MQu(+)-Diol in water. The electrostatic interaction between charged saponite surface and MQu(+) plays a significant role in stabilizing aldehyde side enthalpically and destabilizing it entropically.