Antimony Pentachloride

Biographical Sketches

Paulo Glória studied Applied Chemistry - Organic Chemistry at FCT/UNL in Lisbon, Portugal from 1996 to 2001. In 2000, he joined the research group of Prof. Ramon Estévez Cabanas at the University of Santiago de Compostela (Spain), as Erasmus student. In 2001, he received a research grant from Fundation of FCT/UNL and joined the research group of Prof. S. Prabhakar and Prof. A. Lobo under the project ‘Synthetic Methods for N-Heterocyclic ­Systems based on Sigmatropic Rearrangements.’ He is currently working towards his PhD, with a doctoral fellowship from Fundação para a Ciência e a Tecnologia (FCT, Lisbon, Portugal).

Introduction

Inorganic compounds are well-known in organic synthesis due to their many applications. One of these compounds is antimony pentachloride (SbCl₅), which has a trigonal bipyramidal configuration in the gaseous state. [1] Examination of the Raman spectra [2] [3] points to retention of the trigonal bipyramidal configuration in both the liquid and the solid state. This reagent has several applications and can be used as a Lewis acid, as a chlorination agent for olefins and aromatic compounds, and as a Diels-Alder catalyst.

Abstracts

(A) Chlorination of aromatic compounds by antimony pentachloride [4] has received relatively little attention, except as a route to polychlorinated compounds. An investigation of the ­reaction of SbCl5 with halobenzenes and toluene indicated that chlorination proceeds by electrophilic substitution, involving an attacking species of low activity. This was evidenced by the almost exclusive ortho/para orientation. [5]
(B) Tetrasulfur tetranitride (S4N4) reacts in inert solvents with a wide variety of Lewis acids to give isolable adducts. [6] The interest in exploiting the potential synthetic utility of the adduct S4N4·SbCl5 led to a preliminary result in which treatment of a-bromomethyl ketones 1 with the adduct in toluene at reflux gave the corresponding chloro compounds 3 in good to excellent yields, regardless of the bulkiness of the groups at the a¢-position of ­ketones 1. [7]
(C) Improved regioselectivity in catalyzed Diels-Alder cycloadditions between non-symmetrical benzoquinones and mono-substituted butadienes can be achieved with SbCl5. [8]
(D) SbCl5 in sub-stoichiometric quantity, in moist acetonitrile, is an efficient and mild system for the deprotection of TBS derivatives of amines, phenols, primary alcohols and aryl carboxylic ­acids. Yields for this deprotection are good to excellent. High ­selectivity for OTBS cleavage is noted in the presence of a ketal group. [9]

References

• 1 Roualt M. Ann. Phys.  1940,  14:  78 
• 2 Moureau H. Magat M. Wetroff G. Proc. Indian Acad. Sci.  1938,  7:  361 
• 3 Jensen KA. Z. Anorg. Chem.  1943,  250:  264 
• 4 Muller H. J. Chem. Soc.  1862,  41 
• 5 Kovacrc P. Sparks AK. J. Am. Chem. Soc.  1960,  82:  5740 
• 6 Alange GG. Banister AJ. J. lnorg. Nucl. Chem.  1978,  40:  203 
• 7 Kim KJ. Kim K. Tetrahedron Lett.  1997,  38:  4227 
• 8 Tishler M. Fieser LF. Wendler NL. J. Am. Chem. Soc.  1940,  62:  2866 
• 9 Glória PMC. Prabhakar S. Lobo AM. Gomes MJS. Tetrahedron Lett.  2003,  44:  8819