Grignard Reaction Lab

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This experiment was performed in order to prepare the Grignard reagent from aryl or alkyl halides and demonstrate the principles of organometallic chemistry. The Grignard reagent was prepared via a radical mechanism. The Grignard reagent was then used to prepare a carboxylic acid from carbon dioxide, demonstrating its ability to create carbon-carbon bonds by acting as a strong nucleophile. As the R group of the Grignard reagent was unknown, molecular weight and melting point were then used to identify the resulting carboxylic acid. The molecular weight was determined using titration techniques and the melting point was measured using a Mel-Temp Apparatus.

Data and Results In the formation of the Grignard reaction, the solution turned cloudy
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The Grignard reagent is an organometallic compound as it includes a carbon atom bound to magnesium and a halide, usually bromine. Grignard reagents must be prepared in an aprotic solvent, such as diethyl ether or THF, because the MgBr, is a strong nucleophile and thus a strong base. There must also not be any water in the solution for the same reason. As such, the solvent must be anhydrous, the glassware must be totally dry and the humidity should be minimized. There are several other side reactions that need to be considered when preparing a Grignard reagent other than reactions with the solvent. The first is the reaction between the Grignard reagent and oxygen dissolved in the solution, which produces peroxides. The second is the reaction between the Grignard reagent and the carbon dioxide dissolved in the solution, which produces carboxylates. However, these were not of major importance in this procedure because there is only a very minimal amount of these two gases dissolved in the ether used as the solvent. In order to completely prevent the occurrence of these two side reactions, the procedure muse be performed in the absence of air, which was too expensive and complicated for this experiment. The third side reaction is the reaction between the Grignard reagent and the original halide. As the Grignard reagent is a strong nucleophile, it will react with the original halide. This cannot be prevented but can be minimized by keeping the concentration of magnesium very high and the concentration of the halide low. This works because the formation of the reagent is the favored

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