Reactant Grignard

Several aEylation reactions are known, frequently using an organometaEic derivative of the compound being aEylated, or a strongly electropositive metal in conjunction with the reactants. Grignard reactions are in this group. 

The intermediates may be produced from silicon tetrachloride by interaction with the appropriate Grignard reagent, the composition of the product depending upon the proportions of the reactants ... 

Intramolecular Grignard Reactions. Some chemists use the reactivity of a substituent in the Gtignard reagent to generate the desired product. For example, a one-step spiroaimelation reaction has been developed by taking advantage of a dihaUde or a cyano-haUde reactant (92—94). 

In liquid-solid processes reaction takes place between a liquid reactant and an insoluble or sparingly soluble solid which must be finely divided to speed up the process. Another measure to accelerate the process is to use an aqueous solution of a phase-transfer agent (typically a quaternary ammonium salt). The solid can also be a catalyst for reactions between liquid components, e.g. in acylations, carried out both conventionally in the presence of metal chlorides (mostly AICI3) or catalysed by zeolites and Grignard reactions. 

The proposed catalytic cycle is in accordance with the results of the kinetic studies. The dependence of the reaction rate on the substrate and Grignard reagent indicates that both reactants are involved in the rate-limiting step. This step is preceded by fast equihbria between complexes, for example, a substrate-bound cr-complex and jr-complex and substrate-unbound complex A. 

Another example is the reaction of indoles with nitrosoarenes in the presence of acids. The redox potentials of the reactants cannot justify an outer-sphere ET process, thus the formation of the phenylaminoxyl detected for the reaction carried out in the ESR cavity, could be more likely justified by an inner-sphere ET mechanism95. In fact the reaction of quinoline N-oxide with primary alkyl Grignards for which an outer-sphere mechanism was earlier proposed, takes place through classical nucleophilic addition96. 

The Grignard reaction is often one of the first reactions encountered for the preparation of organometallic compounds. As such it provides a method for the conversion of an alkyl bromide to an alkane. From the example shown below it is seen that the overall oxidation level change from the organic reactants to the products is from 0 to —2, so a reduction has occurred. Magnesium is the reductant and is itself oxidized from 0 to +2 oxidation state. The actual reduction takes place in the first step of the process in which the C-Br bond is converted to a C-Mg-Br bond. The reaction with water is merely a hydrolysis that does not change the oxidation state of carbon. 

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