Synthesis and Characterization of Benzoin: Yield Analysis, IR Spectroscopy, and Green Chemistry Principles

Benzoin, a white crystalline compound, is commonly used in organic synthesis. This laboratory report focuses on the synthesis of benzoin through a condensation reaction and subsequent analysis of the product. The reaction involves the condensation of two molecules of benzaldehyde to form benzoin, catalyzed by cyanide ions. The overall reaction can be represented as:
2C6​H5​CHOCN−​(C6​H5​CHO)2​

Experimental Procedure:

1. Materials and Apparatus:
   • Benzaldehyde
   • Sodium cyanide (NaCN)
   • Ethanol
   • Distillation setup
   • Reflux apparatus
   • Separatory funnel
   • Ice bath
   • Analytical balance
2. Synthesis of Benzoin:
   • 10 mL of benzaldehyde was mixed with 10 mL of ethanol in a round-bottom flask.
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   • To this mixture, a catalytic amount of sodium cyanide (0.5 g) was added.
   • The reaction mixture was refluxed for 2 hours.
   • The reaction progress was monitored by TLC (Thin Layer Chromatography).
   • After completion, the reaction mixture was cooled and the product was extracted using a separatory funnel with water.
3. Purification of Benzoin:
   • The crude benzoin obtained was purified through recrystallization using ethanol as the solvent.
   • The purified product was then dried and weighed to determine the yield.
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Results:

1. Calculation of Theoretical Yield:
   • The molar mass of benzaldehyde is 106.12 g/mol.
   • The theoretical yield of benzoin can be calculated using the stoichiometry of the reaction and the molar masses of reactants and product.
     Theoretical Yield= 2 moles of limiting reactant×molar mass of benzoin ​
   • Actual Yield and Percent Yield:
     • The actual yield of benzoin obtained from the experiment was measured by weighing the purified product.
     • The percent yield was calculated using the formula: Percent Yield=( Theoretical Yield Actual Yield ​ )×100

3. Characterization of Benzoin:
   • The synthesized benzoin was characterized by IR spectroscopy to confirm the presence of functional groups.
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Discussion:

1. Reaction Mechanism:
   • The condensation reaction involves the attack of cyanide ion on benzaldehyde, leading to the formation of an intermediate.
   • The intermediate undergoes intramolecular rearrangement to produce benzoin.
2. Yield Analysis:
   • Discrepancies in the yield may arise due to side reactions, incomplete reactions, or losses during the purification process.
   • Any impurities in the starting materials can also affect the yield.
3. IR Spectroscopy:
   • The IR spectrum of benzoin was analyzed to identify characteristic peaks, such as the carbonyl group and aromatic C-H stretches.

In conclusion, the synthesis of benzoin was successfully achieved through the condensation reaction of benzaldehyde with sodium cyanide. The experimental yield was determined, and the product was characterized using IR spectroscopy. The laboratory provided valuable insights into organic synthesis techniques, yield calculations, and characterization methods.
Questions:

1. Benzoin contains functional groups, namely a hydroxy ketone and an alcohol.
2. Infrared spectroscopy is employed to confirm the presence of an alcohol functional group in the product, typically observed in the range of 3600 to 3200 cm-1. While this signal on the IR spectrum suggests a successful reaction, additional confirmation through NMR can provide further evidence of benzoin production.
3. NMR analysis is effective in revealing structural differences between reactants and products, such as the presence of aromatic hydrogens and an alcohol functional group. Benzoin is anticipated to exhibit peaks around 7-8 ppm with an integration number of ten, distinguishing it from the starting material.
4. Thiamine served as the catalyst, facilitating the condensation of benzoin.
5. Hazardous chemicals utilized in the experiment included nitric acid and sodium hydroxide. Nitric acid is highly corrosive, capable of causing skin and eye burns, while sodium hydroxide, also corrosive, can lead to burning sensations, blurred vision, and shock.
6. This experiment adhered to green principles as it achieved a 100% atom economy, minimizing toxic waste by using thiamine as the catalyst instead of alternative options.
7. The experiment followed several Principles of Green Chemistry, including Atom Economy, Prevention, Less Hazardous Chemical Syntheses, Catalysts, and Inherently Safer Chemistry for Accident Prevention.

Data:
Table 1

Table 2