The Grignard Reaction - Synthesis of 1,2-Diphenyl-1,2-Propanediol Via a Diastereoselective Reaction
Objective:
The purpose of this experiment was to prepare the Grignard reagent methylmagnesium iodide and react it with benzoin to form the 3o alcohol 1,2-diphenyl-1,2-propanediol, through an addition reaction pathway.
Introduction: Grignard reagents are alkyl or aryl-magnesium halides that act as the nucleophile in Grignard reactions, where ketones are reacted with the reagent, then treated with acid to produce an alcohol. In the case of this experiment, methylmagnesium iodide was created from methyl iodide and magnesium metal. It acted as the Grignard Reagent in Part B upon which it was reacted with benzoin to create 1,2-diphenyl-1,2-propanediol. A racemic mixture of benzoin was used, and such theoretically both diasteriomers of the diol could have be formed. However the methylmagnesium iodide is diasterioselective as it generally prefers to attack one particular face of the benzoin molecule. By comparing the obtained melting points and comparing them to literature value, the diastereomer formed in the isolated purifeed product can be determined
Reaction Equation:
Fig 1: Reaction equation for the formation of the Grignard Reagent
Table 1: Reagent Properties and Amounts used Chemical | Structure | Formula | Mass or Volume Required (g or mL) | M.W. (g/mol) | Density (g/cm3) | # Moles | m.p./b.p. (°C) | Actual Mass (g) | Methyl Iodide | | CH3I | 24 mL | 141.94 | 2.28 | 0.3855 | 42.5 | 52.72 g (24 mL) | Magnesium Metal | | Mg(s) | 0.58g | 24.31 | N/A | 0.0239* | 648 | 0.58g | Methyl-magnesium iodide | | CH3MgI | 3.97g† | 166.24 | ~1.26 | 0.0239† | N/A | 3.97g†(~3mL) |
* Limiting Reagant
† Theoretical yield, assumes 100% recovery =nCH3MgI = nLimiting reagent = nMg
=0.0239 mols
=3.97g
Fig. 2: Reaction equation for the Grignard Reaction
Table2: Reagent Properties and Amounts Used Chemical | Structure | Formula | Mass or Volume Required (g or mL) | M.W. (g/mol) | Density (g/cm3) | # Moles | m.p./b.p. (°C) | Actual Mass (g) |
The purpose of this experiment was to prepare the Grignard reagent methylmagnesium iodide and react it with benzoin to form the 3o alcohol 1,2-diphenyl-1,2-propanediol, through an addition reaction pathway.
Introduction: Grignard reagents are alkyl or aryl-magnesium halides that act as the nucleophile in Grignard reactions, where ketones are reacted with the reagent, then treated with acid to produce an alcohol. In the case of this experiment, methylmagnesium iodide was created from methyl iodide and magnesium metal. It acted as the Grignard Reagent in Part B upon which it was reacted with benzoin to create 1,2-diphenyl-1,2-propanediol. A racemic mixture of benzoin was used, and such theoretically both diasteriomers of the diol could have be formed. However the methylmagnesium iodide is diasterioselective as it generally prefers to attack one particular face of the benzoin molecule. By comparing the obtained melting points and comparing them to literature value, the diastereomer formed in the isolated purifeed product can be determined
Reaction Equation:
Fig 1: Reaction equation for the formation of the Grignard Reagent
Table 1: Reagent Properties and Amounts used Chemical | Structure | Formula | Mass or Volume Required (g or mL) | M.W. (g/mol) | Density (g/cm3) | # Moles | m.p./b.p. (°C) | Actual Mass (g) | Methyl Iodide | | CH3I | 24 mL | 141.94 | 2.28 | 0.3855 | 42.5 | 52.72 g (24 mL) | Magnesium Metal | | Mg(s) | 0.58g | 24.31 | N/A | 0.0239* | 648 | 0.58g | Methyl-magnesium iodide | | CH3MgI | 3.97g† | 166.24 | ~1.26 | 0.0239† | N/A | 3.97g†(~3mL) |
* Limiting Reagant
† Theoretical yield, assumes 100% recovery =nCH3MgI = nLimiting reagent = nMg
=0.0239 mols
=3.97g
Fig. 2: Reaction equation for the Grignard Reaction
Table2: Reagent Properties and Amounts Used Chemical | Structure | Formula | Mass or Volume Required (g or mL) | M.W. (g/mol) | Density (g/cm3) | # Moles | m.p./b.p. (°C) | Actual Mass (g) |