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Synlett 2005(8): 1342-1343  
DOI: 10.1055/s-2005-868479
SPOTLIGHT
© Georg Thieme Verlag Stuttgart · New York

Sulfamic Acid: A Very Useful Catalyst

Bo Wang*
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of ­Sciences, Lanzhou 730000, P. R. China
Fax: +86(931)8277088; e-Mail: mzlwb1978@hotmail.com;
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Publikationsdatum:
21. April 2005 (online)

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Introduction

Sulfamic Acid (NH2SO3H, SA) is a dry, nonvolatile, non-hygroscopic, odorless, uncorrodible crystalline solid with outstanding physical stability. It has been determined that SA is comprised not of the aminosulfonic acid form, but rather of +H3N-SO3 - zwitterionic units by both X-ray and neutron diffraction techniques. [1] It dissolves moderately in water, and can be highly ionized to form strongly acidic solutions. Sulfamic acid is immiscible with commonly used non-polar organic solvents, such as toluene and THF. It is commercially available and is inexpensive. Recently, SA emerged as a promising solid-acid catalyst for acid-catalyzed reactions, such as functional group protections and deprotections, [2-4] and the synthesis of isoamyl acetate [5] and polymeric ethers. [6] Moreover, some important organic transformations, including Beckmann rearrangement, [7] ­inter- and intramolecular imino Diels-Alder reactions, [8] and Pechmann [9] and Biginelli condensations, [10] [11] have also been performed successfully in the presence of sulfamic acid.

SA should be especially useful for applications in which a highly ionized nonvolatile acid is desired, or where ­precipitation of insoluble salts must be avoided. [12] It is widely used as a calibrating reagent in titrations, [13] a ­cleaning agent in industry, and an enzyme inhibitor in biochemistry. [14]