Understanding Grignard Reagent Formation and Triphenylmethanol Synthesis

What are the reactions and procedures involved in the synthesis of Grignard reagent and triphenylmethanol?

Reactions and Procedures:

Reaction: Magnesium turnings react with bromobenzene to form a Grignard reagent.

Mg + C6H5Br → C6H5MgBr

Procedure: Grind 1.06 g of magnesium turnings and add them to a dried 250 mL round-bottom flask along with a few crystals of iodine. Dissolve 6.4 grams of bromobenzene in 20 mL of anhydrous ethyl ether and add this mixture to the addition funnel. Add 6-8 mL of the bromobenzene solution to the magnesium turnings. If no reaction occurs, place a beaker of 45°C water under the flask. Continue adding the remainder of the bromobenzene solution while maintaining reflux using a warm water bath.

Reaction: The Grignard reagent reacts with benzophenone to form triphenylmethanol.

C6H5MgBr + (C6H5)2CO → (C6H5)3COH

Procedure: Dissolve 7.2 grams of benzophenone in 25 mL of dry ethyl ether and add this solution to the Grignard reagent. Maintain a gentle boil by adding the solution slowly. Once the addition is complete, continue refluxing for 15 minutes using a water bath. Finally, cool the mixture to room temperature.

Details of the Synthesis:

The given experiment involves the synthesis of a Grignard reagent followed by the formation of triphenylmethanol. In Part A, the Grignard reagent is formed by the reaction of magnesium turnings with bromobenzene. This reaction takes place in an ethereal solution under reflux conditions to ensure efficient conversion. The reagent is essential in organic synthesis due to its nucleophilic properties.

Part B focuses on the reaction between the Grignard reagent and benzophenone to produce triphenylmethanol. Benzophenone acts as the carbonyl compound, and the resulting alcohol product undergoes further reactions in organic chemistry.

Expected Signals in the IR Spectrum:

Based on the structure of triphenylmethanol, certain signals are expected to be observed in the IR spectrum as follows:

- A broad signal around 3300-3500 cm^-1, indicating the presence of O-H stretch of the alcohol group.

- A strong, sharp signal around 1600-1650 cm^-1, indicating the presence of C=O stretch in the carbonyl group of benzophenone.

The key signal that confirms the formation of triphenylmethanol is the broad peak in the region of 3300-3500 cm^-1, corresponding to the O-H stretch. This signal is crucial in identifying the successful synthesis of the desired product.