Grignard reagents reaction with cadmium chloride

Grignard reagents derived from aryl bromides are readily prepared and may be converted into organocadmium compounds by treatment with cadmium chloride (cf. Section 5.8.4, p. 616). Reaction of an organocadmium with a carboxylic acid chloride constitutes a convenient synthesis of aryl alkyl ketones. 

X-5 The reaction of a cadmium Grignard reagent (R2Cd) with an acid chloride. This reaction requires the formation or a cadmium Grignard which can be formed as shown below... 

The use of organocadmium compounds, RjCd, lies in the fact that they react only with acid chlorides and no other carbonyl compounds. Thus, acid chlorides can be converted to ketones with no risk of further reaction. Organocadmium compounds are prepared (Equation 15.3) by reaction of cadmium chloride with a Grignard reagent, and the reactions only work well when R is aryl or primary alkyl. An example is provided in Figure 15.45. 

These materials, generally prepared from the corresponding Grignard reagents by the addition of cadmium chloride, provide a milder reagent system than the Grignard that allows selectivity in reaction with phosphorus trichloride (Equation 4.21).34-43-63... 

Many organocadmium compounds are known but few have been of commercial importance. Wanklyn first isolated diethyl cadmium in 1856. The properties of this and other dialkylcadmiums are listed in Table 4. In general, these materials are prepared by reaction of an anhydrous cadmium halide with a Grignard or alkyUithium reagent followed by distillation of the volatile material in an inert atmosphere or in vacuo. Only the liquid dimethyl compound is reasonably stable and then only when stored in a sealed tube. Dimethylcadmium is mildly pyrophoric in air and produces dense clouds of white, then brown, cadmium oxide smoke, which is highly toxic if breathed (45). When dropped into water, the liquid sinks in large droplets that decompose with a series of small explosive jerks and pops. For this reason, and particularly because of the low thermal stability, most dialkylcadmium materials are prepared and used in situ without separation, eg, in the conversion of acid chlorides to speciality ketones (qv) ... 

Many dialkyl and diaryl cadmium compounds have found use as polymerization catalysts. For example, the diethyl compound catalyzes polymerization of vinyl chloride, vinyl acetate, and methyl methacrylate (45), and when mixed with TiCl can be used to produce polyethylene and crystalline polypropylene for filaments, textiles, glues, and coatings (45). With >50% TiCl diethyl cadmium polymerizes dienes. Diethyl cadmium maybe used as an intermediate ethylating agent in the production of tetraethyllead. The diaryl compounds such as diphenylcadmium [2674-04-6]> (C H Cd, (mp 174°C) are also polymerization catalysts. These compounds are also prepared using Grignard or arylUthium reagents in tetrahydrofiiran (THF) solvent but may be prepared by direct metal substitution reactions such as ... 

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