Question

Which of the following comes out in the aqueous layer of the first extraction with \(3 \mathrm{M} \mathrm{HCl}\) ? A. 9-fluorenone B. ethyl 4-aminobenzoate C. Benzoic acid D. diethyl ether

Short answer

B. Ethyl 4-aminobenzoate

Step-by-step solution

Understanding Aqueous Extraction with Acid

In an extraction using an acidic solution such as 3 M HCl, the goal is to determine which compound will become protonated and thus more soluble in the aqueous (water) layer.

Analyzing 9-fluorenone

9-fluorenone is a ketone and does not have a basic nitrogen or carboxyl group that could be protonated easily with HCl. It will remain in the organic layer.

Analyzing Ethyl 4-aminobenzoate

Ethyl 4-aminobenzoate contains an amino group, which is basic and can be protonated by HCl. The protonated form will be more soluble in the aqueous layer.

Analyzing Benzoic Acid

Benzoic acid has a carboxylic acid group, which can be deprotonated by a base, making it more likely to remain in the aqueous layer if extracted with a base. In acidic conditions, it remains in the organic layer.

Analyzing Diethyl Ether

Diethyl ether is an ether and is not affected by HCl. It will remain in the organic layer.

Conclusion

Based on the analysis, ethyl 4-aminobenzoate will be protonated and thus become more soluble in the aqueous layer in the presence of 3 M HCl.

Key concepts

Aqueous Layer

In organic chemistry, an aqueous layer refers to the water-based component of a mixture that contains other substances. When you perform an extraction, you often deal with two immiscible layers: an organic layer and an aqueous layer. The aqueous layer is the one where polar substances, often salts and other water-soluble compounds, are found.
During an extraction, compounds are separated based on their relative solubilities in water (the aqueous layer) and an organic solvent (the organic layer). Knowing which layer a compound will move into helps in isolating or purifying substances.
For instance, when you add 3 M HCl during extraction, it can protonate certain compounds, making them more soluble in water, thus moving them into the aqueous layer. In our exercise, the specific focus is to discern which of the given compounds will enter the aqueous layer upon protonation, with the answer being ethyl 4-aminobenzoate due to its basic amino group.

Protonation

Protonation is the process in which a proton (H⁺) is added to a molecule, effectively converting it into a positively charged ion. This process is particularly relevant during extractions involving acid solutions.
Consider the compound ethyl 4-aminobenzoate from our exercise. This compound has an amino group that is basic. When it interacts with 3 M HCl, the acidic environment donates a proton to the amino group, resulting in a protonated form that is more water-soluble.
The general effect of protonation is to make the compound more polar and hence more soluble in the aqueous layer. Protonation changes the solubility dynamics considerably, as seen with ethyl 4-aminobenzoate moving from the organic layer to the aqueous layer due to its protonated form.

Solubility

Solubility refers to the ability of a substance to dissolve in a particular solvent. In the context of our exercise, this means understanding how compounds dissolve in either the organic layer or the aqueous layer.
Several factors affect solubility, including polarity, molecular size, and the presence of functional groups that can interact with the solvent. For example, in acidic extraction with 3 M HCl, the solubility of a compound can be altered by protonation. Ethyl 4-aminobenzoate, which contains a basic amino group, becomes protonated and hence more soluble in the aqueous phase.
Understanding the solubility changes can help predict which layer a substance will move into during extraction. This knowledge is crucial for successfully isolating compounds in organic chemistry.