Question

Describe simple chemical tests that would serve to dis tinguish between: (a) propionic acid and methyl acetate (b) n-butyryl chloride and n-butyl chloride (c) \(\mathrm{p}\) -nitrobenzamide and ethyl \(\mathrm{p}\) -nitrobenzoate (d) glyceryl tristearate and glyceryl trioleate (e) benzonitrile and nitrobenzene (f) acetic anhydride and \(\mathrm{n}\) -butyl alcohol (g) glyceryl monopalmitate and glyceryl tripalmitate (h) ammonium benzoate and benzamide (i) \(\mathrm{p}\) -bromobenzoic acid and benzoyl bromide Tell exactly what you would do and see.

Short answer

To distinguish between the given compound pairs, perform simple chemical tests involving solubility, reactions, or color changes. Some examples include: (a) For propionic acid and methyl acetate, add sodium bicarbonate (NaHCO3) and observe effervescence due to CO2 release by propionic acid. (b) For n-butyryl chloride and n-butyl chloride, add silver nitrate (AgNO3) and observe the formation of white precipitate of silver chloride (AgCl) by n-butyryl chloride. (c) For p-nitrobenzamide and ethyl p-nitrobenzoate, test solubility in water. (d) For glyceryl tristearate and glyceryl trioleate, add iodine (I2) solution and observe color disappearance in case of glyceryl trioleate. (e) For benzonitrile and nitrobenzene, add concentrated hydrochloric acid (HCl) and heat the mixtures; benzonitrile will form a white precipitate of benzoic acid. (f) For acetic anhydride and n-butyl alcohol, add 2,4-dinitrophenylhydrazine (2,4-DNP) and observe yellow or orange precipitate in case of acetic anhydride. (g) For glyceryl monopalmitate and glyceryl tripalmitate, dissolve in ethanol (EtOH), add iodine solution, and observe color disappearance in case of glyceryl tripalmitate. (h) For ammonium benzoate and benzamide, heat both compounds separately and detect ammonia fumes in case of ammonium benzoate. (i) For p-bromobenzoic acid and benzoyl bromide, add water and observe hydrolysis in case of benzoyl bromide, forming a white precipitate of benzoic acid.

Step-by-step solution

(a) Propionic Acid and Methyl Acetate

To distinguish between propionic acid and methyl acetate, we can perform a simple chemical test: 1. Add a few drops of sodium bicarbonate (NaHCO3) solution to separate samples of both compounds. The propionic acid, being a carboxylic acid, will react with the sodium bicarbonate to form carbon dioxide (CO2) gas, which can be observed as effervescence. On the other hand, methyl acetate, an ester, will not show any reaction.

(b) n-Butyryl Chloride and n-Butyl Chloride

These compounds can be differentiated using the following test: 1. Add a few drops of silver nitrate (AgNO3) solution to separate samples of both compounds. n-Butyryl chloride, an acyl chloride, will react with silver nitrate to form a precipitate of silver chloride (AgCl), which is a white insoluble compound. However, n-butyl chloride, being an alkyl chloride, will not react with silver nitrate and no precipitate will be observed.

(c) p-Nitrobenzamide and Ethyl p-Nitrobenzoate

The chemical test to differentiate these compounds is as follows: 1. Dissolve both compounds separately in water. While p-nitrobenzamide is soluble in water, ethyl p-nitrobenzoate is not, as it is an ester compound. Thus, the solubility behavior will help in distinguishing them.

(d) Glyceryl Tristearate and Glyceryl Trioleate

To distinguish between these two compounds, perform a iodine test: 1. Mix both compounds with a few drops of iodine (I2) solution. Glyceryl tristearate will not react with iodine due to its saturated structure, and no color change will be observed. On the other hand, glyceryl trioleate contains double bonds and will react with iodine, leading to the disappearance of iodine's brown color. This change will indicate the presence of glyceryl trioleate.

(e) Benzonitrile and Nitrobenzene

The simple test to differentiate these two is: 1. Add a few drops of concentrated hydrochloric acid (HCl) to both compounds and slowly heat the mixtures. Benzonitrile will hydrolyze in the acid solution to form benzoic acid, which on further heating with more HCl solution will give off a white precipitate of benzoic acid. Nitrobenzene, however, will not react with hydrochloric acid and no precipitate will form.

(f) Acetic Anhydride and n-Butyl Alcohol

These compounds can be differentiated using the following test: 1. Add a small quantity of 2,4-dinitrophenylhydrazine (2,4-DNP) to separate samples of both compounds. Acetic anhydride will react with 2,4-DNP to form a yellow or orange precipitate, while n-butyl alcohol will not show any reaction and no precipitate will form.

(g) Glyceryl Monopalmitate and Glyceryl Tripalmitate

The chemical test to differentiate these compounds is as follows: 1. Dissolve both compounds separately in ethanol (EtOH), and then add a few drops of iodine solution. Glyceryl monopalmitate does not contain a C=C double bond and, therefore, will not react with iodine, whereas glyceryl tripalmitate will react with the iodine, causing color of the iodine to disappear.

(h) Ammonium Benzoate and Benzamide

To distinguish between these compounds, perform the following test: 1. Heat both compounds separately. Ammonium benzoate will give off ammonia fumes, which can be detected by a pungent smell. Benzamide, however, will not show such a behavior when heated.

(i) p-Bromobenzoic acid and Benzoyl Bromide

The simple test to differentiate these two is: 1. Slowly add a few drops of water to both compounds. The p-bromobenzoic acid will not react with water, while benzoyl bromide will instantaneously hydrolyze in the presence of water to form a white precipitate of benzoic acid and release hydrogen bromide gas.

Key concepts

Propionic Acid

When trying to distinguish between propionic acid and methyl acetate, a simple yet effective chemical test can be employed using sodium bicarbonate. This test takes advantage of the acid-base reaction in which carboxylic acids react with sodium bicarbonate to produce carbon dioxide gas.

Here's how you can perform this test:

• Add a few drops of sodium bicarbonate (NaHCO₃) solution to a small sample of the compound.
• Observe the solution for effervescence, which indicates the production of carbon dioxide.

If effervescence is observed, the compound is propionic acid. This is because the acid reacts with the bicarbonate to release CO₂ as a gas. Propionic acid, being a carboxylic acid, will undergo this reaction, while methyl acetate, being an ester, will not and thus show no effervescence.

This test is a straightforward way to identify the presence of carboxylic acids in organic molecules.

Methyl Acetate

Methyl acetate is a simple ester which can be identified by its lack of reaction with sodium bicarbonate compared to carboxylic acids like propionic acid. In chemical testing, methyl acetate's lack of reaction is primarily used to differentiate it from carboxylic acids because it does not produce carbon dioxide gas when treated with sodium bicarbonate.

Key characteristics of methyl acetate include:

• It does not effervesce when reacted with sodium bicarbonate.
• It is a clear, volatile liquid with a fruity odor.
• It has a relatively low boiling point.

Utilizing these properties allows chemists to differentiate methyl acetate from similar compounds that might otherwise be mistaken for it. Thus, knowing methyl acetate's reactivity—or lack thereof—can be instrumental in proper identification.

Acyl and Alkyl Chloride Differentiation

Differentiating between acyl and alkyl chlorides, like n-butyryl chloride and n-butyl chloride, involves a test using silver nitrate (AgNO₃). This test can reveal the presence of certain functional groups based on the reactions they undergo.

Here is how the test works:

• Add a few drops of silver nitrate solution to a sample of the compound.
• Observe the solution for the formation of a white precipitate.

Acyl chlorides, such as n-butyryl chloride, will react with silver nitrate to form a white precipitate of silver chloride (AgCl). On the other hand, alkyl chlorides like n-butyl chloride will not form a precipitate in this reaction.

This simple precipitation test provides a clear distinction between these classes of chlorides, aiding in the identification of acyl chloride groups in organic compounds.

Ester Solubility

Solubility tests in different solvents can help identify specific organic compounds like esters. For compound differentiation, understanding the solubility behavior can be very crucial. Esters often exhibit distinct solubility patterns compared to other functional groups.

Consider the example of differentiating p-nitrobenzamide and ethyl p-nitrobenzoate:

• Test the solubility by adding each compound to water.
• Observe whether the compound dissolves.

In this scenario, p-nitrobenzamide will dissolve in water due to its polar amide group, whereas ethyl p-nitrobenzoate is insoluble due to its ester linkage, which is less polar.

This distinction makes solubility testing a practical method for determining the presence and identity of ester groups within unknown samples.

Iodine Test for Unsaturation

The iodine test is a useful method for detecting unsaturation in lipids or related compounds. It exploits the ability of iodine to react with double bonds present in unsaturated compounds. Saturated compounds, like fats, do not react with iodine in this way.

Follow these steps for the iodine test:

• Add a few drops of iodine solution to the compound.
• Note any change in color.

For example, when testing glyceryl tristearate and glyceryl trioleate, glyceryl trioleate will react with iodine, causing the brown color of iodine to fade. This occurs because glyceryl trioleate contains double bonds. Conversely, glyceryl tristearate, which is saturated, will not alter the color because it doesn't have these reactive double bonds.

Thus, the iodine test is a quick and effective method to determine the presence of unsaturation in compounds.