Copper(I) Chloride-Sulfur Dioxide


[7758-89-6]  · ClCu  · Copper(I) Chloride-Sulfur Dioxide  · (MW 99.00) (SO2)

[7446-09-5]  · O2S  · Copper(I) Chloride-Sulfur Dioxide  · (MW 64.06)

(reagent for the preparation of arenesulfonyl chlorides from arenediazonium ions1)

Physical Data: see entries for Copper(I) Chloride and Sulfur Dioxide.

Form Supplied in: individual reagents commercially available; mixture is normally prepared in glacial acetic acid.

Preparative Methods: for a reaction of typical scale, glacial acetic acid (600 mL) is placed in a 4000 mL beaker and stirred magnetically. Sulfur dioxide is delivered from a cylinder through a bubbler tube with a fritted glass end immersed beneath the surface of the acetic acid. Introduction is continued for 15-30 min until saturation is evidenced by the fact that most of the SO2 bubbles reach the surface of the acetic acid. Copper(I) chloride (15 g) is added to the solution, and the introduction of sulfur dioxide is continued until the yellow-green suspension becomes blue-green and most of the solids dissolve (20-30 min). The mixture is placed in an ice bath until use.

Handling, Storage, and Precautions: mixtures of copper(I) chloride and sulfur dioxide should be prepared immediately before use. The saturated SO2 solution is noxious and must be prepared and used in a fume hood. Sulfur dioxide is intensely irritating to the eyes and respiratory tract.

Arenesulfonyl Chlorides.

A mixture of copper(I) chloride and sulfur dioxide is very effective in converting arenediazonium ions to arenesulfonyl chlorides (eq 1).1 The diazonium solution is added slowly to the cooled copper(I) chloride-sulfur dioxide mixture and a normally vigorous evolution of nitrogen occurs with formation of the sulfonyl chloride. The original literature2 recommends copper(II) chloride as the copper source which is reduced in situ to copper(I) chloride, the active catalyst. More recently, it has been found that the use of copper(I) chloride in the above procedure is superior in reproducibly providing active catalytic mixtures.1,3

A wide variety of aromatic amines can be converted to aromatic sulfonyl chlorides via their diazonium salts by this method. Some examples are collected in Table 1. In addition, a group of fluorinated arenesulfonyl chlorides have been prepared by the same method.4 In general, aromatic amines with electron-withdrawing substituents give the best results. For aromatic amines with electron-donating substituents, yields can be improved by the addition of magnesium chloride, which serves to raise the chloride concentration.2 This method for the preparation of arenesulfonyl chlorides is simple and straightforward compared to alternate methods such as aromatic substitution by Chlorosulfonic Acid or oxidation of aromatic thiols with Chlorine water.

1. Hoffman, R. V. OS 1981, 60, 121; OSC 1990, 7, 508.
2. Meerwein, H.; Dittmar, G.; Göllner, R.; Hafner, K.; Mensch, F.; Steinfort, O. CB 1957, 90, 841.
3. Yale, H. L.; Sowinski, F. JOC 1960, 25, 1824.
4. Gerig, J. T.; Roe, D. C. JACS 1974, 96, 233.

Robert V. Hoffman

New Mexico State University, Las Cruces, NM, USA

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