Synthesis and Characterization of 4-Bromobenzophenone via Friedel-Crafts Acylation

Introduction

Friedel-Crafts acylation serves as a pivotal reaction in organic chemistry, facilitating the incorporation of acyl groups into aromatic rings. This reaction, pivotal for synthesizing aryl ketones, involves the reaction of an aromatic compound with an acyl halide in the presence of a Lewis acid catalyst, typically AlCl3. Despite its limitations, including potential carbocation rearrangement, this methodology remains a cornerstone for aromatic compound synthesis due to its simplicity and effectiveness.

Benzophenone and its derivatives, such as 4-bromobenzophenone, stand as fundamental components in organic synthesis, acting as precursors in various chemical processes.

The synthesis of 4-bromobenzophenone through the Friedel-Crafts acylation of bromobenzene with benzoyl chloride underlines the practical application of this reaction, showcasing the electrophilic substitution mechanism facilitated by the acylium ion.

Materials and Methods

Equipment and Instruments

• Steam bath
• Rotary evaporator
• Infrared (IR) spectroscopy equipment

Chemicals

• Bromobenzene (2.0 mL, 3.0 g, 19 mmol)
• Benzoyl chloride (3.3 mL, 4.0 g, 30 mmol)
• Anhydrous aluminium chloride (4.0 g, 30 mmol)
• Sodium hydroxide (10% solution)
• Diethyl ether
• Light petroleum (boiling range 60-80°C)
• pH indicator paper

Procedure

The synthesis began by mixing bromobenzene and benzoyl chloride in a 50 mL Erlenmeyer flask, followed by the gradual addition of anhydrous aluminium chloride.

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The mixture was agitated and heated in a boiling water bath for 20 minutes. After cooling, the mixture was quenched with ice and neutralized with 10% NaOH solution to dissolve any residual acids and aluminium salts. The organic phase was extracted with ether, dried, and concentrated using a rotary evaporator. Finally, the product was purified by recrystallization from light petroleum, yielding a colorless solid of 4-bromobenzophenone.

Results and Analysis

Observations and Analytical Data

The reaction's completion was indicated by the formation of a white precipitate upon addition of NaOH solution. The reagents' masses and the final product's mass and melting point are detailed in accompanying tables, with the product showing a melting point range of 83-85°C, aligning closely with literature values.

Table 1. The mass of reagents used in the experiment

Table 2. Mass and melting point of 4-bromophenone

Table 3. IR spectrum of 4-bromobenzophenone

The IR spectrum confirmed the presence of aromatic C=C stretching and C=O stretching of the ketone group, with expected wavenumbers. However, the anticipated C-Br stretch was not observed, likely due to experimental limitations or the purity of the sample.

NMR spectroscopy further validated the structure of 4-bromobenzophenone, with chemical shifts corresponding to the expected hydrogen environments within the molecule.

Table 4. NMR spectrum of 4-Bromobenzophenone