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The primary objective of this experiment was to explore the reduction of benzoin to 1,2-diphenylethane-1,2-diol utilizing sodium borohydride as the reducing agent.
Additionally, the experiment aimed to assess the efficacy of this reduction process by employing thin-layer chromatography (TLC) as a characterization technique. Through this experiment, we sought to gain insights into the feasibility and practicality of utilizing sodium borohydride for the reduction of benzoin, a key organic transformation in synthetic chemistry.
The reaction involved the reduction of benzoin to 1,2-diphenylethane-1,2-diol using sodium borohydride as the reducing agent.
The central chemical transformation in this experiment entails the reduction of benzoin () to 1,2-diphenylethane-1,2-diol () employing sodium borohydride () as the reducing agent. The reaction mechanism can be represented as follows:
In this process, benzoin undergoes reduction by sodium borohydride in the presence of water to yield 1,2-diphenylethane-1,2-diol along with sodium metaborate () and hydrogen gas (). The reducing agent, sodium borohydride, serves as the source of hydride ions (), which are transferred to the carbonyl carbon of benzoin, resulting in the formation of a hydroxyl group and the corresponding alcohol product. This reduction reaction proceeds under mild conditions, offering high selectivity and yield, making it a versatile tool in organic synthesis.
The experimental procedure commenced by meticulously measuring 0.520 grams of benzoin () and dispensing it into a 25 mL Erlenmeyer flask. To facilitate the dissolution of benzoin, 4 milliliters of ethanol () were added to the flask.
Ethanol served as the solvent to aid in the dissolution of the solid benzoin crystals, ensuring a homogeneous mixture.
Next, the Erlenmeyer flask containing the benzoin-ethanol mixture was gently heated on a sand bath or a hot plate. The gentle heating process aimed to promote the dissolution of the benzoin crystals, ensuring that all solid particles were completely solubilized in the ethanol solvent. The swirling motion facilitated uniform heating and mixing, ensuring that benzoin dissolved completely, leading to the formation of a clear solution.
Subsequently, sodium borohydride () was added gradually to the benzoin-ethanol solution over a period of 5 minutes. The addition of sodium borohydride as a reducing agent initiated the reduction reaction, wherein the hydride ions () provided by sodium borohydride facilitated the reduction of the carbonyl group in benzoin to yield 1,2-diphenylethane-1,2-diol (). The gradual addition of sodium borohydride helped control the reaction rate and minimize side reactions.
Following the addition of sodium borohydride, the reaction mixture was swirled for an additional 20 minutes. This prolonged stirring period allowed for thorough mixing and ensured the completion of the reduction reaction. During this time, the reaction mixture gradually transitioned from a yellow hue to a clear appearance, indicating the progress of the reduction process.
After the completion of the reaction, the mixture-containing flask was carefully transferred to an ice bath to quench the reaction and promote the precipitation of the product. To the cooled mixture, 5 milliliters of distilled water () were added, followed by the addition of 0.3 milliliters of 6M hydrochloric acid (). The addition of hydrochloric acid served to acidify the reaction mixture, facilitating the protonation of any remaining borohydride ions and aiding in the formation of the desired product.
To further isolate the product, an additional 2.5 milliliters of distilled water were added to the reaction mixture, promoting the precipitation of the product as a white solid. The precipitate, consisting of the desired 1,2-diphenylethane-1,2-diol product along with any impurities, was separated from the reaction mixture through vacuum filtration. Following filtration, the solid product was washed with 10 drops of ice-cold water to remove any residual impurities and unreacted reagents.
Once washed, the solid product was transferred to a drying apparatus and subjected to vacuum drying for a duration of 15 minutes. Vacuum drying facilitated the removal of residual solvent and moisture, ensuring the isolation of a dry and pure product. Finally, the resulting solid, still retaining some moisture, was weighed and its melting point was determined, providing valuable insights into the purity and identity of the synthesized product.
While direct characterization techniques were not employed in this experiment, the identity of the product was inferred based on the reaction conditions and anticipated outcomes. The synthesized product was presumed to be 1,2-diphenylethane-1,2-diol (), also known as benzoin diol or hydrobenzoin. This assumption was substantiated by the nature of the reduction reaction undergone by benzoin () in the presence of sodium borohydride ().
The stoichiometry of the reaction indicates the addition of two equivalents of sodium borohydride and two equivalents of water, leading to the formation of one equivalent of 1,2-diphenylethane-1,2-diol. This theoretical reaction pathway supports the assumption that the product obtained from the reduction of benzoin is indeed 1,2-diphenylethane-1,2-diol.
Furthermore, the physical properties of the synthesized product, such as its white color and solid state, were consistent with the expected characteristics of 1,2-diphenylethane-1,2-diol. Additionally, the melting point range of the product fell within the anticipated range for 1,2-diphenylethane-1,2-diol, further supporting its identity.
While direct characterization techniques, such as spectroscopic analysis or elemental analysis, were not employed to confirm the identity of the product, the combination of reaction principles, observed physical properties, and expected outcomes provided compelling evidence for the synthesis of 1,2-diphenylethane-1,2-diol in this experiment. Further characterization techniques could be employed in future studies to validate the identity and purity of the synthesized product.
The yield of the experiment was determined, showing a mass of 0.546 g for the crude product and 0.295 g for the recrystallized product. The melting points were recorded as 131-135°C for the crude product and 137-138°C for the recrystallized product.
TLC was performed to characterize the product. Two TLC plates were used, and three separate solutions were prepared for each plate. The Rf values were calculated based on the observed spots.
The experimental results indicated successful reduction of benzoin to 1,2-diphenylethane-1,2-diol, as evidenced by the TLC analysis. The slight discrepancy in the mass of the crude product compared to the starting material was attributed to the presence of excess water, which was later removed through recrystallization.
The TLC analysis revealed differences in Rf values between the starting material and the final product, supporting the hypothesis that the product obtained was indeed 1,2-diphenylethane-1,2-diol. The relatively impure nature of the crude product was reflected in its melting point range and TLC profile.
In conclusion, the experimental procedure aimed at reducing benzoin to 1,2-diphenylethane-1,2-diol using sodium borohydride as the reducing agent was successfully executed. The synthesis pathway involved the addition of hydride ions to the carbonyl group of benzoin, leading to the formation of 1,2-diphenylethane-1,2-diol. This transformation was inferred based on the reaction scheme and anticipated outcomes, as well as the observed physical properties of the synthesized product.
The effectiveness of the reduction reaction was further validated through thin-layer chromatography (TLC), which revealed chemical differences between the starting material (benzoin) and the final product. The distinct Rf values obtained for the two compounds provided evidence of successful conversion, with the final product exhibiting a lower Rf value indicative of enhanced interaction with the TLC plate.
While the experimental yield of the reaction was determined to be 56%, indicating moderate efficiency under the given conditions, the synthesis of 1,2-diphenylethane-1,2-diol was achieved with a reasonable degree of success. The discrepancy between the theoretical and actual yields may be attributed to various factors, including incomplete reaction conversion, side reactions, or experimental errors. Further optimization of reaction conditions and purification techniques could potentially improve the yield and purity of the synthesized product.
Overall, the successful reduction of benzoin to 1,2-diphenylethane-1,2-diol represents a significant achievement in organic synthesis, demonstrating the applicability of sodium borohydride as a versatile reducing agent and the importance of characterization techniques in confirming chemical transformations. Further investigations into reaction kinetics, mechanistic pathways, and alternative reducing agents could contribute to the advancement of synthetic methodologies in organic chemistry.
Analysis of Benzoin Reduction via Sodium Borohydride. (2024, Feb 27). Retrieved from https://studymoose.com/document/analysis-of-benzoin-reduction-via-sodium-borohydride
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