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 and bubbled and then turned to a darker brown color. The mass of the product was measured to be 0.588g. The melting point of the product was between 119C and 121C. 9.1 mL of NaOH were used to reach the endpoint of the titration, when the phenolphthalein indicator changed from clear to pink. As the NaOH solution had a molarity of 0.91M, 9.1 mL of the solution was equivalent to 0.91 mmol of NaOH. The reaction runs with a one to one ratio meaning that there was also 0.91 mmol of the unknown acid. Since 116 mg of the unknown acid were used in the titration, this gives a molecular weight of the acid of 127.47 grams/mole. This molecular weight is near to the molecular weight of benzoic acid, at 122 grams/mole, but is also near to the molecular weights of 2-methylbenzoic acid and 3-methylbenzoic acid, at 136 grams/mole. However, with the melting point information, the unknown acid was identified as benzoic acid, which has a melting point of 122C that is extremely close to the measured melting point of 119C-121C. This molecular weight is near to the molecular weight of benzoic acid, at 122 grams/mole, but is also near to the molecular weights of 2-methylbenzoic acid and 3-methylbenzoic acid, at 136 grams/mole. However, with the melting point information, the unknown acid was identified as benzoic acid, which has a melting point of 122C that is extremely close to the measured melting point of 119C-121C. Discussion and Conclusion Organometallic chemistry involves the bonding of carbon atoms with metal atoms. …show more content…
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 reaction. The Grignard reagent is formed via the combination of an alkyl halide with magnesium metal. The magnesium metal attacks the halide creating a radical alkyl product and a radical magnesium atom in association with the halide. The two radicals then combine to form R-MgX. Due to the difference in electronegativity between the carbon and the magnesium atom that are bound together, there is strong polarization and the carbon atom possesses a partial negative charge. This negative charge turns the carbon
Data and Results In the formation of the Grignard reaction, the solution turned cloudy and bubbled and then turned to a darker brown color. The mass of the product was measured to be 0.588g. The melting point of the product was between 119C and 121C. 9.1 mL of NaOH were used to reach the endpoint of the titration, when the phenolphthalein indicator changed from clear to pink. As the NaOH solution had a molarity of 0.91M, 9.1 mL of the solution was equivalent to 0.91 mmol of NaOH. The reaction runs with a one to one ratio meaning that there was also 0.91 mmol of the unknown acid. Since 116 mg of the unknown acid were used in the titration, this gives a molecular weight of the acid of 127.47 grams/mole. This molecular weight is near to the molecular weight of benzoic acid, at 122 grams/mole, but is also near to the molecular weights of 2-methylbenzoic acid and 3-methylbenzoic acid, at 136 grams/mole. However, with the melting point information, the unknown acid was identified as benzoic acid, which has a melting point of 122C that is extremely close to the measured melting point of 119C-121C. This molecular weight is near to the molecular weight of benzoic acid, at 122 grams/mole, but is also near to the molecular weights of 2-methylbenzoic acid and 3-methylbenzoic acid, at 136 grams/mole. However, with the melting point information, the unknown acid was identified as benzoic acid, which has a melting point of 122C that is extremely close to the measured melting point of 119C-121C. Discussion and Conclusion Organometallic chemistry involves the bonding of carbon atoms with metal atoms. …show more content…
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 reaction. The Grignard reagent is formed via the combination of an alkyl halide with magnesium metal. The magnesium metal attacks the halide creating a radical alkyl product and a radical magnesium atom in association with the halide. The two radicals then combine to form R-MgX. Due to the difference in electronegativity between the carbon and the magnesium atom that are bound together, there is strong polarization and the carbon atom possesses a partial negative charge. This negative charge turns the carbon