4-(Dimethylamino)pyridinium Chlorosulfite Chloride

[86128-91-8]  · C7H10Cl2N2OS  · 4-(Dimethylamino)pyridinium Chlorosulfite Chloride  · (MW 241.16)

(synthesis of esters and amides from carboxylic acids; dehydration of aldoximes; synthesis of chlorosilanes)

Physical Data: mp 155-157 °C.

Solubility: sol CH2Cl2.

Preparative Methods: generated by reaction of 4-Dimethylaminopyridine with Thionyl Chloride in CH2Cl2 at -20 °C and isolated as a solid. The reagent is most commonly prepared and used in situ.1

Purification: need not be isolated; no methods have been described for its purification.

Handling, Storage, and Precautions: must be assumed to be moisture sensitive; precautions should be taken in accordance with those advised for both DMAP and SOCl2.

Carboxyl Activation: Synthesis of Esters and Amides from Carboxylic Acids.

4-(Dimethylamino)pyridinium chlorosulfite chloride is more reactive than either Thionyl Chloride or thionyl chloride/pyridine for carboxyl activation. Aliphatic and aromatic, as well as amino acids (in racemic form), undergo activation (via the acyl halide) and subsequent esterification by reaction with an alcohol at -20 °C (eq 1).1 The esterification step requires the addition of a second equivalent of DMAP and this method has been applied to a range of functionalized carboxylic acids.

High yields of esters are obtained from both acid-sensitive (cyanoacetic acid) and base-sensitive carboxylic acids (3-phenylpropionic acid and trichloroacetic acid) and, in these latter cases, use of 4-(dimethylamino)pyridinium chlorosulfite chloride is much more effective than use of thionyl chloride alone. The esterification process has been claimed to be independent of the steric environment of the carboxyl function, though this reagent may be of more limited value with heavily substituted benzoic acids.2

Carboxyl activation, in the presence of a primary amine, leads to the corresponding amide in excellent yield (eq 2).3 In both the esterification and amidation processes and the oxime dehydration reaction discussed below, recovery of DMAP is straightforward.

Dehydration of Aldoximes.

A range of alkyl, aryl, and heteroaryl aldoximes undergo smooth dehydration with 4-(dimethylamino)pyridinium chlorosulfite chloride at -10 to +10 °C to give the corresponding nitriles in 70-100% yield (eq 3).4

Synthesis of Chlorosilanes.

t-Butyldiphenylsilanol has been converted to the corresponding chlorosilane in quantitative yield using 4-(dimethylamino)pyridinium chlorosulfite chloride (eq 4).5 The use of oxalyl chloride/DMAP (see Oxalyl Chloride) is also highly effective for this transformation, but a number of other reagents (concentrated HCl; MeCOCl; SOCl2; o-phenylene cyclohexylphosphorochlorimidate/SO2Cl2) either fail completely or give inferior yields of product.

1. Arrieta, A.; García, T.; Palomo, C. SC 1982, 12, 1139.
2. Jütten, P.; Dornhagen, J.; Scharf, H.-D. T 1987, 43, 4133.
3. Descours, D.; Festal, D.; Leger, J.-M.; Carpy, A. HCA 1991, 74, 1757.
4. Arrieta, A.; Palomo, C. S 1983, 472.
5. Mullen, D. G.; Barany, G. JOC 1988, 53, 5240.

Timothy Gallagher

University of Bristol, UK

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