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

Mostafa Baghbanzadeh ^A and C. Oliver Kappe ^A ^B

+ Author Affiliations

- Author Affiliations

^A Christian Doppler Laboratory for Microwave Chemistry (CDLMC) and Institute of Chemistry, Karl-Franzens-University Graz, Heinrichstrasse 28, A-8010 Graz, Austria.

^B Corresponding author. Email: oliver.kappe@uni-graz.at

Australian Journal of Chemistry 62(3) 244-249 https://doi.org/10.1071/CH08450
Submitted: 21 October 2008 Accepted: 18 December 2008 Published: 20 March 2009

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.

Acknowledgement

M.B. thanks Shahid Beheshti University and the Ministry of Science, Research and Technology of Iran for a scholarship. We gratefully acknowledge Professor Minoo Dabiri for facilitating M.B.’s leave.

References

[1] (a) For recent books, see: Microwaves in Organic Synthesis, 2nd edn (Ed. A. Loupy) 2006 (Wiley-VCH: Weinheim).
       (b) C. O. Kappe, A. Stadler, Microwaves in Organic and Medicinal Chemistry 2005 (Wiley-VCH: Weinheim).
       (c) Microwave-Assisted Organic Synthesis (Eds P. Lidström, J. P. Tierney) 2005 (Blackwell: Oxford).
       (d) C. O. Kappe, D. Dallinger, S. S. Murphree, Practical Microwave Synthesis for Organic Chemists – Strategies, Instruments, Protocols 2009 (Wiley-VCH: Weinheim).

[2] (a) For general recent review articles, see: Kappe C. O., Angew. Chem. Int. Ed. 2004, 43, 6250. doi:10.1002/ANIE.200400655
       (b) A. De La Hoz, A. Díaz-Ortiz, A. Moreno, Chem. Soc. Rev. 2005, 34, 164.
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