Problem 195 - A Complete Resource Book in Chemistry for JEE Main

Question

Number of ethylene glycol molecules that condense with conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) to form dioxane.

Step-by-Step Solution

Answer

Two ethylene glycol molecules condense to form one dioxane molecule.

Step 1: Identify the chemical reaction

Dioxane is formed by the condensation of ethylene glycol in the presence of concentrated sulfuric acid. The reaction involves the removal of water molecules.

Step 2: Understand the formula for ethylene glycol

Ethylene glycol is a diol with the chemical formula \( ext{C}_2 ext{H}_6 ext{O}_2\). It consists of two hydroxyl (OH) groups.

Step 3: Determine the structure of dioxane

Dioxane is a cyclic ether with the chemical formula \( ext{C}_4 ext{H}_8 ext{O}_2\), formed by joining two ethylene glycol molecules and eliminating water (H2O).

Step 4: Relate the condensation process

In the condensation of ethylene glycol to form dioxane, two molecules of ethylene glycol combine, resulting in a structure that includes a six-membered ring with two ether oxygens. This reaction involves the loss of two water molecules (one from each hydroxyl group pair).

Step 5: Calculate the number of ethylene glycol molecules

Since each dioxane molecule is formed from two ethylene glycol molecules, \( ext{C}_2 ext{H}_6 ext{O}_2\), precisely two molecules of ethylene glycol are needed to form one molecule of dioxane.

Key Concepts

Condensation Reaction

A condensation reaction in organic chemistry is a type of chemical process where two molecules combine to form a single molecule, usually accompanied by the loss of a small molecule such as water. This reaction is essential in various synthetic pathways, leading to the formation of complex molecules. In the specific case of ethylene glycol's condensation to dioxane, two molecules of ethylene glycol come together. Upon combination, they eliminate two water molecules, forming a six-membered ring structure known as dioxane. This type of reaction is useful in creating cyclic ethers and other polymerizations, thereby playing a pivotal role in chemical synthesis and industrial applications.

Condensation reactions can occur under different conditions, including the presence of acids or bases. For ethylene glycol to effectively condense into dioxane, an acid catalyst such as concentrated sulfuric acid is typically used. The acid facilitates the dehydration of ethylene glycol and helps stabilize the resulting cyclic ether structure.

Ethylene Glycol

Ethylene glycol is a simple diol, meaning it has two hydroxyl (OH) groups attached to its carbon atoms. Its chemical formula, \( ext{C}_2 ext{H}_6 ext{O}_2\), reflects this structure. This makes ethylene glycol both a versatile solvent and an important building block in organic chemistry. It is widely used in antifreeze formulations due to its low freezing point but also serves an essential role in chemical reactions, especially in forming polymers and cyclic compounds.

In the reaction forming dioxane, each ethylene glycol molecule contributes two carbon atoms and its hydroxyl groups. These groups participate in the condensation process, resulting in the elimination of water. This reaction underscores the reactivity of the hydroxyl groups and showcases how simple molecules can be transformed into more complex structures through carefully controlled reactions.

Dioxane Formation

Dioxane formation is an intriguing example of how small organic molecules like ethylene glycol can combine into more complex cyclic structures through condensation reactions. The result, dioxane, is a clear liquid and is a six-membered heterocyclic ether containing two oxygen atoms. Following the condensation process, these oxygens form part of the ring structure, bridging the carbon atoms contributed by ethylene glycol, and giving dioxane its characteristic shape.

Dioxane is formed under acidic conditions where concentrated sulfuric acid acts as a catalyst, guiding and facilitating the reaction. The two water molecules are eliminated to allow the remaining atoms to form the stable ring structure of dioxane. This formation is crucial in the synthesis of various organic compounds and demonstrates the potential of cyclic ethers in both industrial and research settings. Such reactions highlight the elegance of organic synthesis, transforming small and simple molecules into complex ones with varied applications.