Question

Statement 1 o-hydroxy benzene sulphonic acid on heating to \(373 \mathrm{~K}\) changes to \(\mathrm{p}\) -hydroxy benzene sulphonic acid and Statement 2 Sulphonation of phenol is a reversible process.

Short answer

Answer: Yes, both statements are true. The sulphonation of phenol is a reversible process that involves the reaction of phenol with sulfuric acid in the presence of heat (373 K), resulting in the formation of ortho- and para-sulphophenol. Heating o-hydroxy benzene sulphonic acid shifts the equilibrium towards the formation of p-hydroxy benzene sulphonic acid, which is the major product in this reaction.

Step-by-step solution

Identify the reactants and products

In this step, we need to identify the starting compounds and the products in the given statements. o-hydroxy benzene sulphonic acid, which is commonly known as ortho-sulphophenol, will change to p-hydroxy benzene sulphonic acid, commonly known as para-sulphophenol, upon heating. The given statements suggest that sulphonation of phenol is a reversible process, which means this reaction can occur in both the forward and reverse directions.

Write the balanced chemical equation

First, we need to write the balanced chemical equation for the sulphonation of phenol: C6H5OH (Phenol) + H2SO4 (Sulfuric Acid) \(\overset{373 K}{\longleftrightarrow}\) C6H4(OH)SO3H (ortho-sulphophenol) + H2O (Water) Notice that we used a double arrow (↔) to represent the reversible reaction, where the reaction is occurring in both the forward and reverse directions.

Describe the sulphonation process

Sulphonation of phenol is a reversible process that takes place in the presence of sulfuric acid. In this reaction, the -OH group present at the ortho position of the phenol reacts with the H2SO4, and results in the formation of the -SO3H group at either the ortho or para position. Heating the o-hydroxy benzene sulphonic acid to 373 K shifts the equilibrium towards the formation of p-hydroxy benzene sulphonic acid, which is the major product in the reaction. #Conclusion# Both statements are true. o-hydroxy benzene sulphonic acid (ortho-sulphophenol) changes to p-hydroxy benzene sulphonic acid (para-sulphophenol) on heating to 373 K, and sulphonation of phenol is a reversible process that involves sulfuric acid and phenol reacting to form ortho- and para-sulphophenol.

Key concepts

Ortho-Sulphophenol

Sulphonation is a common chemical reaction involving the introduction of a sulphonic acid group into an organic molecule. In the case of phenol, when it reacts with sulfuric acid, one of the products formed is ortho-sulphophenol. This compound has a sulphonic acid group (-SO₃H) directly attached to the carbon atom next to the one bearing the hydroxyl group (-OH) on the benzene ring.

Ortho-sulphophenol is synthesized due to the ortho-directing effect of the -OH group, which means the incoming -SO₃H group prefers to attach at the position adjacent to the -OH group. This positional preference impacts not only the physical properties but also the reactivity of the compound in further chemical reactions.

Para-Sulphophenol

Parallel to its ortho counterpart, para-sulphophenol is another product of the sulphonation of phenol. In para-sulphophenol, the sulphonic acid group is attached to the carbon atom directly opposite the carbon with the hydroxyl group on the aromatic ring. This occurs primarily due to the influence of the sulphuric acid and the controlled temperature during the reaction.

The para position is often favored in less crowded environments or at higher temperatures, leading to a higher proportion of para-sulphophenol being produced. This positional isomerism between ortho and para variants reflects in the distinct melting points, solubilities, and other physical characteristics pertinent to their respective molecular structures.

Reversible Reaction

Understanding reversible reactions is essential in the context of phenol sulphonation. A reversible reaction is a chemical process that can go forwards and backwards under certain conditions. In the reaction between phenol and sulfuric acid, we obtain a mixture of ortho-sulphophenol and para-sulphophenol, which can revert back to the original reactants.

This reversibility indicates that the products can decompose back into phenol and sulfuric acid. The ability of a system to reach a state of dynamic equilibrium, where the rate of the forward reaction equals the rate of the reverse reaction, is a fundamental understanding for students tackling such chemistry concepts.

Chemical Equilibrium

When discussing reversible reactions, the concept of chemical equilibrium becomes crucial. Chemical equilibrium is the point in a reversible reaction at which the rates of the forward and reverse reactions are equal, resulting in no net change in the concentration of reactants and products over time.

As observed in the sulphonation of phenol, heating the reactants or changing the concentrations can shift the equilibrium, favoring either the production of ortho-sulphophenol and para-sulphophenol or regenerating the original reactants. An understanding of Le Chatelier's principle can help predict how changes in reaction conditions will affect the position of equilibrium and the concentrations of substances present at equilibrium.