Problem 35 - A Complete Resource Book in Chemistry for JEE Main

Question

Which will not give formaldehyde on heating or upon distillation? (a) paraldehyde (b) trioxane (c) formalin (d) paraformalehyde

Step-by-Step Solution

Answer

Paraldehyde will not give formaldehyde on heating or distillation.

Step 1: Identify the Chemical Structures

First, let's identify what each of the compounds in the question is composed of:\(\text{a) Paraldehyde}\) is a cyclic trimer of acetaldehyde. \( \text{b) Trioxane}\) is a cyclic trimer of formaldehyde. \(\text{c) Formalin}\) is an aqueous solution of formaldehyde. \(\text{d) Paraformaldehyde}\) is a polymer of formaldehyde.

Step 2: Determine the Heating Effects on Each Compound

When heated, \(\text{Paraldehyde}\) will not decompose into formaldehyde since it is not derived from it. \(\text{Trioxane}\) breaks down into formaldehyde upon heating. \(\text{Formalin}\) will release formaldehyde when heated. \(\text{Paraformaldehyde}\) also decomposes into formaldehyde when heated.

Step 3: Identify the Compound Not Producing Formaldehyde

Based on step 2, among the given compounds, \(\text{Paraldehyde}\) does not produce formaldehyde when heated or distilled as it is not related to formaldehyde initially.

Key Concepts

Paraldehyde

Paraldehyde is an interesting compound made up of three acetaldehyde molecules forming a cyclic structure. Unlike many similar chemical compounds, paraldehyde is not connected to formaldehyde directly. This distinction plays a crucial role when it comes to heating because paraldehyde does not break down into formaldehyde when subjected to heat.

Paraldehyde is often used in medicinal applications due to its sedative and hypnotic properties. It has historically played a role in treating conditions like insomnia and as an anticonvulsant. In a laboratory context, paraldehyde is known for its distinct chemical behavior.

**Key Points About Paraldehyde:**

• Derived from acetaldehyde.
• Does not decompose into formaldehyde when heated.
• Has medical applications as a sedative.

Trioxane

Trioxane is a cyclic compound made from three formaldehyde units tightly joined to form a ring structure. One of its key characteristics is its ability to decompose into formaldehyde when heated.

This decomposition is particularly interesting because it allows trioxane to serve as a formaldehyde source in various chemical reactions. In practical uses, trioxane can often be found in household and industrial applications where a controlled release of formaldehyde is required.

**Key Points About Trioxane:**

• Made from formaldehyde units.
• Decomposes into formaldehyde upon heating.
• Used as a source of formaldehyde in chemical reactions.

Formalin

Formalin is a widely recognized term in both industrial and academic settings. It is essentially a solution of formaldehyde dissolved in water, typically containing around 37% formaldehyde, balanced with methanol to stabilize the solution.

Upon heating, formalin releases formaldehyde gas, a property leveraged in various industrial processes and biological preservation techniques, such as preserving biological specimens in labs or mortuaries. The challenge with handling formalin is primarily due to its pungent odor and potential health hazards.

**Key Points About Formalin:**

• Solution of formaldehyde and water.
• Releases formaldehyde gas when heated.
• Commonly used for preservation purposes.

Paraformaldehyde

Paraformaldehyde is essentially a polymerized form of formaldehyde. In its simplest form, it appears as a white, powdery solid. When subjected to heat, paraformaldehyde readily depolymerizes to release formaldehyde gas. This characteristic makes it an important reagent in laboratories, particularly when gaseous formaldehyde is required without liquid carriers.

Used in a variety of settings, paraformaldehyde is favored in cases where slow and controlled release of formaldehyde is necessary, such as in certain agricultural applications or as a disinfectant.

**Key Points About Paraformaldehyde:**

• Polymer of formaldehyde.
• Breaks down to formaldehyde when heated.
• Used in labs for formaldehyde gas generation.