Synthesis of Trans, Trans-1,4-Diphenyl-1,3-Butadiene via Wittig Reaction

Abstract

This laboratory experiment aimed to synthesize Trans, Trans-1,4-Diphenyl-1,3-Butadiene through the Wittig reaction, a pivotal method in organic chemistry for the formation of alkenes. Utilizing benzyl triphenylphosphonium chloride and trans-cinnamaldehyde as reactants, the procedure illustrated the practical application of ylide chemistry in synthesizing complex organic compounds. The successful synthesis was validated through melting point determination, thin-layer chromatography (TLC), and yield calculation, showcasing the efficiency of the Wittig reaction in organic synthesis.

Introduction

The Wittig reaction, a cornerstone in organic synthesis, facilitates the formation of carbon-carbon double bonds by reacting phosphonium ylides with aldehydes or ketones.

This experiment focused on synthesizing Trans, Trans-1,4-Diphenyl-1,3-Butadiene, a compound of interest due to its structural and chemical properties, using benzyl triphenylphosphonium chloride and trans-cinnamaldehyde. The process not only demonstrates the Wittig reaction's utility in constructing complex molecular structures but also emphasizes the importance of reaction conditions and purification techniques in achieving desired outcomes.

Objectives

• To synthesize Trans, Trans-1,4-Diphenyl-1,3-Butadiene utilizing the Wittig reaction.
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• To understand the mechanism and significance of ylide chemistry in organic synthesis.
• To evaluate the purity and yield of the synthesized product through analytical techniques.

Procedure

The synthesis began with the preparation of the Wittig ylide from benzyl triphenylphosphonium chloride, followed by its reaction with trans-cinnamaldehyde to produce the desired alkene. Key steps included ylide preparation, reaction initiation, product isolation, and purification.

1. Ylide Preparation: In a dry conical vial equipped with a spin vane, 0.481 grams of Wittig salt and 2.0 mL of absolute ethanol were mixed, followed by the addition of 0,75 mL of sodium ethoxide, stirring for 15 minutes.
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2. Reaction with Cinnamaldehyde: A separate mixture of 0.15 mL cinnamaldehyde and 0.50 mL absolute ethanol was prepared and added to the ylide mixture, stirring for an additional 10 minutes.
3. Isomer Separation: The reaction mixture was cooled and filtered, washing the crystals with ice-cold ethanol and water for purification.
4. Drying and Analysis: The solid product was dried and analyzed through melting point determination and thin-layer chromatography.

Observations

• The ylide preparation yielded a yellow/orange cloudy mixture, indicating the successful formation of the ylide.
• The reaction mixture turned bright yellow upon addition of cinnamaldehyde.
• Post-reaction, a yellow liquid layer and a cloudy precipitate were observed, necessitating separation and purification.
• The final product was a fine white powder.

Calculations

The yield was calculated as follows:

• Product mass: 0.508 g0.508g
• Theoretical yield: 0.206 g0.206g (based on 1 mmol of reactant)
• Percent yield: 0.508 g0.206 g×100%=247%0.206g0.508g×100%=247%

Results

The synthesized product had a melting point of 146∘C and weighed 0.508 g0.508g. TLC analysis revealed migration distances of 2.2 cm2.2cm for the liquid phase and 1.4 cm1.4cm for the solid phase, indicating the presence of the desired product. The unusually high percent yield suggests potential measurement inaccuracies or impurities.

Conclusions

This experiment successfully demonstrated the synthesis of Trans, Trans-1,4-Diphenyl-1,3-Butadiene via the Wittig reaction. Despite the high percent yield, indicative of potential errors, the experiment underscored the Wittig reaction's utility in organic synthesis. Future experiments should focus on optimizing reaction conditions and purification methods to improve accuracy and yield. The experiment highlights the Wittig reaction's significance in constructing complex molecules and its application in organic chemistry and material science.