Lewis Acidity of Alkali Metal Salts

Relative Lewis acidities of metal salts have been measured with several methods. Fukuzumi and coworkers have developed an excellent method using fluorescence spectra of 10-methylacridone (AcrCO)-metal salt complexes (6). The fluorescence energy (hvf) decreases with increasing the Lewis acidity of metal salts, and the 

Acid Catalysis in Modem Organic Synthesis. Edited by H. Yamamoto and K. Ishihara Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31724-0 

In these results, LiCl04 and NaCl04 show 0.53 and 0.34eV of AE, respectively. These results indicate that alkali metals have mild Lewis acidity compared to general Lewis acids. 

Also surprisingly, LiCl04 functions even in protic solvent [2]. With these useful and interesting natures of LiCl04, it has become a most popular alkali metal Lewis acid. 

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