Question

Glucose reacts with acetic anhydride to form (A) Mono acetate (B) Tetra acetate (C) Penta acetate (D) Hexa acetate

Short answer

The product of the reaction between glucose and acetic anhydride is (C) Penta acetate. As glucose has five hydroxyl groups, each group can participate in acetylation to form esters with acetic anhydride.

Step-by-step solution

1. Analyze glucose structure

Glucose is a hexose sugar, having a six-carbon chain with one aldehyde group and five hydroxyl groups in its linear form, and pyranose ring structure in its cyclic form. The cyclic form is more stable and prevalent in nature. Each of the hydroxyl groups can potentially react with acetic anhydride.

2. Analyze the reaction of glucose with acetic anhydride

Acetic anhydride (CH3-C(=O)-O-C(=O)-CH3) reacts with hydroxyl groups to form ester (acetate) derivatives. This reaction is known as acetylation. Since glucose has five hydroxyl groups, each of these can participate in acetylation, depending on the reaction conditions.

3. Determine the number of acetate groups formed in the product

In this reaction, we need to consider each option (A to D) to determine the correct product. If acetic anhydride reacts with one hydroxyl group, it will form a monoacetate compound (option A). If all five hydroxyl groups react with acetic anhydride, it will form a pentaacetate compound (option C). It is essential to note that tetraacetate (option B) and hexaacetate (option D) products cannot form during this reaction, as there are no intermediate functional groups between mono-, tri-, and pentaacetate.

4. Identify the correct product

Considering the possible reaction products and the given options, the correct answer is (C) Penta acetate, where all five hydroxyl groups in glucose have reacted with acetic anhydride to form esters.

Key concepts

Glucose Structure

Glucose is a fundamental sugar in biology, known as a hexose sugar because it contains six carbon atoms. Among these carbon atoms, glucose features a chain of carbons with an aldehyde group at one end and hydroxyl groups attached to the remaining carbons. This gives it the formula C\(_6\)H\(_{12}\)O\(_6\).
In its linear form, glucose can transform into a cyclic structure known as a pyranose ring. The cyclic form is more stable and occurs prevalently in nature.

• Glucose exists in two forms: linear and cyclic (pyranose).
• The cyclic form is typically more stable.
• Features an aldehyde group and multiple hydroxyl groups.

Understanding glucose's structure is key to appreciating its reactivity, especially when reacting with other chemicals like acetic anhydride.

Acetylation Reaction

Acetylation is a critical chemical reaction where an acetyl group is introduced into a compound. In the specific instance of glucose reacting with acetic anhydride, acetylation occurs as acetic anhydride interacts with the hydroxyl (OH) groups present in glucose.

During the acetylation of glucose:

• Acetic anhydride reacts with hydroxyl groups to form ester linkages, resulting in acetate derivatives.
• This reaction is instrumental in transforming glucose into different useful derivatives, often making it more reactive or changing its physical properties.
• The reaction typically requires an acidic or basic catalyst to proceed efficiently.

Understanding acetylation allows us to predict the outcomes when glucose interacts with acetic anhydride, as in the formation of pentaacetate.

Hydroxyl Groups in Glucose

The hydroxyl groups in glucose are key to its reactivity and functionality. In glucose, there are five hydroxyl groups which are involved in forming hydrogen bonds and maintaining its solubility in water.

The role of these groups includes:

• Facilitating chemical reactions such as acetylation, as they can react with reagents like acetic anhydride.
• Contributing to the structural integrity of glucose by enabling the transformation from its straight chain to cyclic form through intramolecular bonding.
• Influencing the sweetness and energy content of glucose due to their capacity to engage in biochemical reactions.

In acetylation, each hydroxyl group in glucose can potentially react with acetic anhydride to form an ester linkage, culminating in a molecule such as pentaacetate when all five groups participate.