A student prepares ethyl benzoate by the reaction of benzoic acid with ethanol using a sulfuric acid catalyst. The following compounds are found in the crude reaction mixture: ethyl benzoate (major component), benzoic acid, ethanol, and sulfuric acid. Using a handbook, obtain the solubility properties in water for each of these compounds. Indicate how you would remove benzoic acid, ethanol, and sulfuric acid from ethyl benzoate. At some point in the purification, you should also use an aqueous sodium bicarbonate solution.
Don't we just add aq. NaHCO3 to the mixture and then a water layer and an ether layer forms. The ether layer will only contain ethyl benzoate? I'm not sure if this right, it seems too easy, any suggestions will be helpful.
A flow chart showing the separation would be great.
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Mix the mixture with water
The solubility properties of the compounds in water are as follows:
1. Ethyl benzoate: It is slightly soluble in water and mainly soluble in organic solvents such as ether.
2. Benzoic acid: It is moderately soluble in water.
3. Ethanol: It is completely miscible with water, meaning it forms a homogeneous solution in any proportion.
4. Sulfuric acid: It is highly soluble in water.
To separate the compounds and purify ethyl benzoate, the following steps can be followed:
Step 1: Add aqueous sodium bicarbonate (NaHCO3) to the crude reaction mixture. This will react with unreacted benzoic acid present in the mixture, converting it into its sodium salt (sodium benzoate). Sodium benzoate is water-soluble and can be separated.
Step 2: After adding NaHCO3, a fizzing or effervescence may be observed due to the release of carbon dioxide gas. Stir the mixture gently until the fizzing stops.
Step 3: Allow the mixture to separate into two layers: an aqueous layer and an organic layer.
Step 4: Drain off the aqueous (lower) layer containing the sodium benzoate into a separate container. This will remove the benzoic acid from the mixture.
Step 5: Transfer the organic (upper) layer, which mainly contains ethyl benzoate, into a separate container. This can be done by carefully decanting or using a separatory funnel.
Step 6: To remove any remaining sulfuric acid, wash the organic layer with water. Add a small amount of water to the organic layer, shake gently, and then allow the mixture to separate into two layers.
Step 7: Drain off the aqueous layer to remove any water-soluble impurities.
Step 8: Repeat Step 6 and Step 7 for thorough washing.
Step 9: After the final wash, separate the purified ethyl benzoate from the organic layer. This can be done by removing the solvent (e.g., ether) using methods like evaporation or distillation, depending on the boiling point of the solvent.
The final product will be purified ethyl benzoate.
Here is a flowchart summarizing the steps involved in the separation process:
1. Crude reaction mixture
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2. Add aq. NaHCO3
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3. Formation of two layers: aqueous and organic
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4. Drain off aqueous layer (removing benzoic acid)
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5. Transfer organic layer (containing ethyl benzoate) to a separate container
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6. Wash organic layer with water to remove sulfuric acid
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7. Drain off aqueous layer
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8. Repeat steps 6 and 7
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9. Separate purified ethyl benzoate from the organic layer
Remember to ensure safety precautions and handle the chemicals according to proper laboratory procedures.
To obtain the solubility properties in water for each of the compounds involved, you can refer to a chemical handbook or database. Here are the general solubility properties for the compounds mentioned:
1. Ethyl benzoate: Ethyl benzoate is insoluble in water but soluble in organic solvents like ether or dichloromethane.
2. Benzoic acid: Benzoic acid is sparingly soluble in water but highly soluble in organic solvents.
3. Ethanol: Ethanol is miscible with water, meaning it is completely soluble.
4. Sulfuric acid: Sulfuric acid is highly soluble in water and forms an aqueous solution.
Now, let's proceed to the purification process:
1. Add aqueous sodium bicarbonate (NaHCO3) to the crude reaction mixture. This step is to neutralize the remaining sulfuric acid. The reaction between sodium bicarbonate and sulfuric acid produces water, carbon dioxide, and sodium sulfate. The water-soluble sodium sulfate can be discarded, while carbon dioxide will bubble out of the mixture.
2. After the sodium bicarbonate neutralization step, you will have two layers: an aqueous layer (containing sodium bicarbonate, water, and any water-soluble impurities) and an organic layer (containing ethyl benzoate and any organic solvents).
3. Separate the two layers by carefully draining off the aqueous layer from the bottom. You can use a separatory funnel or a separation funnel for this purpose. The organic layer will now be isolated.
4. To remove any remaining water-soluble impurities from the organic layer, you may wash it with water. Introduce a small amount of water into the organic layer, shake gently, and then drain off the water. Repeat this washing step several times, if necessary.
5. After washing, you will have the purified ethyl benzoate in the organic layer. You can further concentrate or dry the organic layer using an appropriate technique (e.g., rotary evaporation).
Remember that this is a simplified explanation, and actual purification techniques may vary depending on the specific lab setup and the requirement of the experiment. It is always best to consult a practical laboratory procedure or your instructor's guidelines for a detailed and accurate purification process.