Green Bromination of Trans-Stilbene: An Exploration of Eco-Friendly Chemistry

Abstract

This study embarked on a journey to brominate trans-stilbene through an eco-conscious methodology, significantly reducing the reliance on hazardous chemicals in favor of greener alternatives. The synthesized product was subjected to rigorous testing to ascertain its configuration, focusing on identifying it as either Syn or Anti isomer.

Introduction

The chemical reaction involving the addition of bromine across the double bond of trans-stilbene to yield 1,2-dibromo-1,2-diphenylethene presents a fascinating study in stereochemistry. This process can lead to the creation of two chiral centers, paving the way for the formation of four potential stereoisomers.

Given the achiral nature of the reactants, this experiment does not control the absolute stereochemistry of the resulting product. However, it is possible to determine the relative stereochemistry, specifically whether the bromine atoms are added in a Syn (on the same side) or Anti (on opposite sides) fashion. This distinction is crucial due to the significant difference in melting points between the diastereomers, which can be used as a key identifier of the resultant compound.

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Traditionally, bromination reactions have been conducted using elemental bromine in hazardous solvents such as dichloromethane or tetrachloride. These materials pose significant risks due to their toxicity and environmental impact. In response, this experiment adopts a greener approach by generating molecular bromine in situ through the oxidation of sodium bromide with a bleach solution in an acidic medium. Ethanol serves as a safer solvent alternative, aligning with the principles of green chemistry to minimize environmental harm.

Experimental Procedure

Safety Measures and Preparations

To ensure safety, appropriate personal protective equipment including lab coats, goggles, and gloves were utilized throughout the experiment.

The reactants and the resulting products are known to be corrosive and irritating; hence, all manipulations were conducted in a fume hood. Special caution was taken to avoid the use of acetone near the reaction setup to prevent any adverse reactions with bromine.

Reagent Table

Methodology

A water bath was prepared and stabilized at approximately 60°C. A mixture of trans-stilbene, sodium bromide, ethanol, glacial acetic acid, and a magnetic stirrer was combined in a 50 ml round-bottom flask, which was then attached to a water-cooled reflux condenser. The flask was submerged in the water bath and the mixture was stirred until most of the solid had dissolved. Subsequently, a solution of household bleach was added dropwise over a few minutes while continuing the stirring and heating, leading to the formation of a cloudy white suspension.

Upon cooling to room temperature, the pH of the mixture was adjusted to neutral using a sodium bicarbonate solution if necessary. The product was then crystallized in an ice bath, collected by vacuum filtration, and dried with air. The mass, theoretical yield, and percent yield of the product were determined. Finally, the product's melting point and infrared (IR) spectrum were analyzed to characterize the compound.

Results and Analysis

Observations and Yield

The initial appearance of trans-stilbene as a white crystalline solid transformed upon the addition of bleach, indicating the progress of the reaction. The final product was a white solid, and its mass was accurately quantified. The melting point of the product was observed to be between 235.7°C and 241.2°C, indicative of a specific diastereomer.

Theoretical Yield and Percent Yield

The theoretical yield was calculated based on stoichiometry, and the actual yield was determined to be 28.9% of the theoretical value. This discrepancy can be attributed to various factors such as incomplete reaction, product loss during handling, or the purification process.

Mass of Weigh Vessel: 1.829g
Mass of Product and Weigh vessel: 2.055g
Mass of Product: 0.226g
Melting Point: 235.7ᵒC - 241.2ᵒC
Theoretical Yield: 0.783g
Percent Yield: 28.9%

Discussion

The melting point analysis is a crucial tool in identifying the nature of the synthesized compound. The observed melting point range closely aligns with that of the Anti-1,2-dibromo-1,2-diphenylethane diastereomer, suggesting the successful synthesis of this specific configuration. This conclusion is further supported by IR spectroscopy, which provides insight into the molecular structure through the identification of functional groups. The IR spectrum of the product showcased characteristic peaks that corroborated the presence of bromine atoms attached to the ethane backbone, affirming the bromination of trans-stilbene.

Conclusion

In conclusion, this experiment successfully synthesized Anti-1,2-dibromo-1,2-diphenylethane from trans-stilbene using an environmentally friendly approach. The distinct melting point and IR spectroscopic data confirmed the Anti configuration of the product. This study not only demonstrates the feasibility of greener alternatives in chemical syntheses but also contributes to the understanding of stereochemical outcomes in bromination reactions. Through this work, we underscore the importance of adopting sustainable practices in the laboratory, aligning with broader environmental objectives while advancing chemical knowledge.