Can Molecular Sieves be Used as Water Scavengers in Microwave Chemistry?

Abstract

The use of sealed-vessel microwave-assisted organic synthesis in combination with 4 Å molecular sieves as water scavengers is investigated. Two classical model transformations, namely acetal formation and imine formation, are evaluated under both conventional heating and microwave dielectric heating. The results obtained in these studies indicate that molecular sieves cannot be used effectively as water scavengers in microwave-assisted transformations owing to the fact that these zeolites are generally most effective in adsorbing water at room temperature. For both acetal and imine formation, performing these reversible reactions at a higher temperature in the presence of molecular sieves leads to significantly reduced conversions compared with experiments at room temperature.