Predict the solubility of ethyl 4-aminobenzoate in water, 1.0 M NaOH (aq), and 1.0 M HCl (aq). Explain your prediction thoroughly for full credit. If a chemical equation is necessary, draw it on a paper and insert a picture here. HzN- O-CH2CH3 Ethyl 4-aminobenzoate
The Correct Answer and Explanation is:
Ethyl 4-aminobenzoate, also known as ethyl 4-aminobenzoate, is a weakly basic compound. Its solubility in different solvents—water, NaOH, and HCl—depends on the nature of its functional groups and their interactions with the solvents. Here’s how the solubility is predicted in each case:
- In Water:
Ethyl 4-aminobenzoate has an amine group (-NH2) attached to a benzene ring, which is relatively hydrophobic due to the nonpolar nature of the aromatic ring. However, the amine group itself is polar and can form hydrogen bonds with water molecules. The ester group (-O-CH2CH3) is also somewhat polar but less so than the amine group. While the compound is somewhat polar, the overall hydrophobicity of the benzene ring and ester group may reduce its solubility in water compared to more polar molecules. Therefore, the solubility of ethyl 4-aminobenzoate in water is expected to be moderate to low. - In 1.0 M NaOH (aq):
In a basic environment, the amine group (-NH2) can accept a proton, converting into its conjugate base form, an amide (NH2 → NH3⁺). This deprotonation reaction increases the water solubility of the compound. The conjugate base is more polar and interacts well with the water in the NaOH solution. Therefore, ethyl 4-aminobenzoate is likely to be much more soluble in 1.0 M NaOH than in pure water because the amine group becomes protonated and the molecule as a whole becomes more hydrophilic. The reaction is as follows: HzN- O-CH2CH3+OH−→HzN- O-CH2CH3−\text{HzN- O-CH}_2\text{CH}_3 + \text{OH}^- \rightarrow \text{HzN- O-CH}_2\text{CH}_3^-HzN- O-CH2CH3+OH−→HzN- O-CH2CH3− - In 1.0 M HCl (aq):
In an acidic environment like 1.0 M HCl, the amine group (-NH2) can become protonated to form an ammonium ion (-NH3⁺), which is highly polar and hydrophilic. This protonation will increase the solubility of ethyl 4-aminobenzoate in HCl. The ester group remains unaffected by the acid. As a result, the solubility of ethyl 4-aminobenzoate in 1.0 M HCl is expected to be moderate to high because the molecule’s amine group is protonated and thus more soluble in water. The reaction is as follows: HzN- O-CH2CH3+H+→HzN+ O-CH2CH3\text{HzN- O-CH}_2\text{CH}_3 + \text{H}^+ \rightarrow \text{HzN}^+\text{ O-CH}_2\text{CH}_3HzN- O-CH2CH3+H+→HzN+ O-CH2CH3
Summary of Predictions:
- Water: Moderate to low solubility due to the hydrophobic nature of the benzene ring and ester group.
- 1.0 M NaOH: High solubility due to the formation of a conjugate base (amide), making the compound more hydrophilic.
- 1.0 M HCl: Moderate to high solubility due to protonation of the amine group, which enhances solubility.
