"Preparation of Schiff’s Base from benzaldehyde"

 

Preparation of Schiff’s Base from benzaldehyde

Theory:

Schiff bases are a class of compounds that contain a carbon-nitrogen double bond with an imine functional group (R-N=CR'). They are typically synthesized by condensation reactions between a primary amine and an aldehyde or ketone. Schiff bases find applications in coordination chemistry, organic synthesis, metal ion detection, biological activities, dye chemistry, optoelectronic devices, corrosion inhibition, and chelation. They are versatile compounds with uses ranging from catalysis and drug development to sensing and materials science. In this case, we will be synthesizing a Schiff base by reacting aniline (primary amine) with benzaldehyde (aldehyde) in the presence of ethanol as a solvent.

Chemicals Required:

1. Aniline (C₆H₅NH₂)
2. Ethanol (C₂H₅OH)
3. Benzaldehyde (C₆H₅CHO)

Apparatus Required:

1. Round-bottom flask
2. Magnetic stirrer
3. Ice bath
4. Heating source (e.g., hot plate)
5. Filtration setup (filter funnel, filter paper)
6. Weighing balance
7. Glassware (beakers, measuring cylinders)

Chemical reaction:

Mechanism:

Procedure:

1. Measure 2 mL of aniline (C₆H₅NH₂) using a measuring cylinder and transfer it to a round-bottom flask.
2. Add 20 mL of ethanol (C₂H₅OH) to the round-bottom flask containing aniline. Stir the mixture until the aniline is completely dissolved.
3. In a separate container, measure 3.5 mL of benzaldehyde (C₆H₅CHO).
4. Place the round-bottom flask with the aniline-ethanol solution on a magnetic stirrer.
5. Add the benzaldehyde dropwise to the aniline-ethanol solution while stirring continuously. The reaction mixture should turn yellow as the Schiff base is formed.
6. After the addition is complete, continue stirring the reaction mixture at room temperature for 10 minutes to ensure complete reaction.
7. Remove the round-bottom flask from the heating source and allow it to cool to room temperature.
8. Set up a filtration setup with a filter funnel and filter paper. Transfer the reaction mixture to a separating funnel. Extract the Schiff base precipitate from it.
9. Dry the filtered Schiff base by placing it in an oven at a suitable temperature (e.g., 60°C) or by placing it in a desiccator until a constant weight is achieved.
10. Weigh the dried Schiff base to calculate the yield and determine its purity.

Observations:

Colour	pale yellow to dark brown
Crystal shape	can be diverse, including needle-like crystals, plate-like crystals, or irregular-shaped crystals
Melting point	2200C
Boiling Point	2480C

 

Calculations:

To calculate the theoretical yield, we need to determine the limiting reagent. The reactants are aniline and benzaldehyde. We will calculate the moles of each reactant and compare them to find the limiting reagent.

Molar mass of aniline (C₆H₅NH₂)= 93.13 g/mol

Molar mass of benzaldehyde (C₆H₅CHO): 106.12 g/mol

Moles of aniline = (volume in mL x density) / molar mass Moles of aniline = (2 mL x 1.021 g/mL) / 93.13 g/mol = 0.0219 mol

Moles of benzaldehyde = (volume in mL x density) / molar mass

Moles of benzaldehyde = (3.5 mL x 1.044 g/mL) / 106.12 g/mol = 0.0345 mol

Now, let's compare the moles of each reactant:

Moles of aniline= 0.0219 mol

Moles of benzaldehyde= 0.0345 mol

From the comparison, we can see that aniline is the limiting reagent because it has fewer moles than benzaldehyde. Therefore, we will use the moles of aniline to calculate the theoretical yield.

The reaction between aniline and benzaldehyde produces 1 mole of the Schiff base.

Molar mass of C₆H₅-CH=N-C₆H₅ = (Molar mass of C₆H₅) + (Molar mass of CH) + (Molar mass of N) + (Molar mass of C₆H₅)) = (12.01 g/mol x 6) + (1.01 g/mol) + (14.01 g/mol) + (12.01 g/mol x 6)

Molar mass of Schiff base = 152.19 g/mol

Theoretical yield = Moles of limiting reagent x molar mass of the Schiff base

Theoretical yield = 0.0219 mol x 152.19 g/mol

Theoretical yield = 3.34 g

Actual yield = 2.8 grams

Theoretical yield = 3.34 grams

Now we can calculate the percentage yield:

Percentage yield = (Actual yield / Theoretical yield) x 100

Percentage yield = (2.8 g / 3.34 g) x 100

Percentage yield = 83.83%

Therefore, the calculated percentage yield of the Schiff base would be approximately 83.83%.