Question

Identify the binary mixture(s) that can be separated into individual compounds, by differential extraction, as shown in the given scheme. (A) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\) and \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) (B) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) and \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{OH}\) (C) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\) (D) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{OH}\) and \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{COOH}\)

Short answer

The binary mixture that can be separated by differential extraction is (A) \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{OH}\) and \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{COOH}\).

Step-by-step solution

Understand Differential Extraction

Differential extraction separates compounds based on their differential solubility in two immiscible solvents, often water and an organic solvent. Acidic or basic functional groups present in a compound can be exploited to make the compound ionizable and hence soluble in water under appropriate conditions.

Analyze Compounds in Option (A)

\(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{OH}\) (phenol) can be made ionizable by treating it with a strong base like NaOH to form phenoxide which is water-soluble. \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{COOH}\) (benzoic acid) will remain in the organic layer until pH is raised sufficiently to deprotonate the carboxylic acid and make it water-soluble. Hence, these compounds can be separated by differential extraction.

Analyze Compounds in Option (B)

Both \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{COOH}\) (benzoic acid) and \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{CH}_{2}\mathrm{OH}\) (benzyl alcohol) can be made ionizable; however, benzyl alcohol lacks acidic or basic functional groups to render it ionizable to an extent for differential extraction.

Analyze Compounds in Option (C)

\(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{CH}_{2}\mathrm{OH}\) (benzyl alcohol) is not significantly ionizable whereas \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{OH}\) (phenol) can be ionized with base to make it water-soluble. Therefore, differential extraction is not an option here.

Analyze Compounds in Option (D)

Both compounds in this option possess acidic groups, but \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{CH}_{2}\mathrm{COOH}\) (phenylacetic acid) will require higher pH to deprotonate compared to \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{CH}_{2}\mathrm{OH}\) (benzyl alcohol), which doesn't readily ionize due to a lack of acidic groups. They cannot be separated by differential extraction.

Determine the Suitable Binary Mixture

From the analysis, the only binary mixture that can be separated by differential extraction is the one with compounds that can be selectively ionized, which is option (A).

Key concepts

Solubility in Immiscible Solvents

Understanding the principles of solubility in immiscible solvents is fundamental when we discuss differential extraction. This method is a cornerstone in chemistry, particularly in the context of separating components in a mixture. Solubility refers to a compound's ability to dissolve in a solvent. Immiscible solvents are liquids that do not mix with each other, forming distinct layers, like oil and water.

In differential extraction, we exploit the different solubility characteristics of compounds when exposed to two immiscible solvents. Typically, one of these solvents is water, which is polar, and the other is an organic solvent, which is non-polar or less polar. A common example of an organic solvent is diethyl ether.

Compounds that are more polar will have a greater affinity for the polar solvent (water), while non-polar compounds prefer the organic layer. Changing conditions such as pH can shift the solubility of a compound, making it more soluble in the polar or non-polar phase, thus allowing for their separation.

Ionizable Compounds

An ionizable compound is a species that can release or accept a proton (H⁺), thus converting into an ion in the presence of a polar solvent, usually under specific pH conditions. Ionization is a critical aspect in the process of differential extraction because the ionized form of a compound is often more water-soluble than its non-ionized counterpart.

Take acids and bases, for instance. They are classic examples of ionizable compounds. When we add a strong base to an acidic compound, it tends to donate a proton and transform into its ionized form, which is generally more soluble in water. Similarly, a compound with a basic functional group can accept a proton in the presence of a strong acid and become ionized, enhancing its water solubility.

This attribute is what makes certain compounds suitable for separation through differential extraction. By adjusting the pH of the aqueous layer, we can selectively ionize one compound over another, leading to their separation as they distribute between the aqueous and organic phases.

Separation of Compounds

The separation of compounds using differential extraction leverages the concept of selective solubility and ionization. During this process, a mixture is introduced to two immiscible solvents. We aim to dissolve each compound into a different solvent, facilitating separation.

Here's how the process often unfolds: when the mixture is shaken with the solvent pair, each component of the mixture associates with the solvent with which it has greater solubility. If a component can be made ionizable through pH manipulation or another means, it will preferentially move into the aqueous phase if that component becomes charged.

The trick is to alter the solution's pH level to a point where only one of the compounds ionizes and transfers to the aqueous layer. This process can repeatedly be adjusted and performed until the compounds are entirely separated. By carefully understanding the chemical nature of the compounds in question, scientists can plan and execute an effective differential extraction protocol.