Grignard Reaction Lab Report

Introduction In a Grignard reaction, a Grignard reagent (R–MgX) adds to the carbonyl group in an aldehyde or ketone to form an alcohol (Figure 1). The reaction of a Grignard reagent with formaldehyde can be to synthesize a primary alcohol, with any other aldehyde can be used to synthesize a secondary alcohol, while the reaction with ketone is useful in the synthesis of a tertiary alcohol. Figure 1. General reaction mechanism of a Grignard Reaction The preparation of the Grignard reagent involves the adding of an alkyl halide to a suspension of magnesium metal in an anhydrous ether solvent through a radical mechanism. Side reactions include the slow reaction of the Grignard reagent with oxygen and carbon dioxide in the air, the reaction
Mechanism for coupling reactions In this experiment, a Grignard reagent was prepared and reacted with benzophenone to synthesize triphenylmethanol, a tertiary alcohol (Figure 4). The Grignard reagent was prepared with dry magnesium turnings, bromobenzene and anhydrous ether. To isolate the alcohol, dilute acid was used to convert the magnesium salt to free alcohol and the mixture was washed with water and sodium chloride to remove remaining magnesium salt and water. Anhydrous sodium sulfate was used to dry the organic layer and all solvent was removed through rotary evaporation. To purify the product, the crude product was washed with hexane and recrystallized from hot 2-propanol.
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2) 3) Figure 4. Reaction mechanism for the preparation of Grignard reagent and the Grignard synthesis of triphenylmethanol Infrared (IR) spectroscopy, which measures the vibrations of atoms interacting with infrared light, can be used to determine the functional groups present in a molecule. We measured the melting range and used the IR analysis to determine the identity of the product.
Methods
The methods followed in this lab report were identical to those found in the Pomona College Organic Chemistry 110A Laboratory Manual with no