Problem 12 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Glucose on prolonged heating with HI gives : (a) \(n\)-Hexane (b) 1 - Hexene (c) Hexanoic acid (d) 6-iodohexanal

Step-by-Step Solution

Answer

(a) n-Hexane

Step 1: Understanding the Reaction

To determine the product when glucose is heated with hydroiodic acid (HI), we need to analyze the reaction. Glucose is a carbohydrate (a polyhydroxylated aldehyde) with a specific structure that can be reduced to an open-chain alkane.

Step 2: Identifying the Reduction Process

When glucose is subjected to prolonged heating with HI, it undergoes reduction. HI is a strong reducing agent, which means it adds hydrogen atoms to the glucose, effectively reducing it and removing oxygen atoms as water, leading to the formation of an alkane.

Step 3: Conversion to Alkane

The reduction of glucose by HI converts it into an alkane through deoxygenation. Given that glucose has six carbon atoms, the reduction process results in the formation of n-hexane, a six-carbon alkane without any functional groups.

Step 4: Conclusion

The end product of the reaction of glucose with prolonged heating in the presence of HI is n-hexane. This is because all functional groups are removed and only the carbon chain backbone remains as the alkane.

Key Concepts

Hydroiodic Acid Reaction

Hydroiodic acid (HI) plays a significant role as a reducing agent in organic reactions. When used with glucose, HI donates hydrogen molecules which interact with the carbohydrate structure. This reaction leads to the loss of oxygen atoms from the glucose, an essential aspect of the reduction process. The strong reducing capacity of HI makes it effective in breaking down complex carbohydrate molecules, such as glucose, into simpler compounds.

• HI donates hydrogen, assisting in the reduction.
• Reduction involves the removal of oxygen atoms as water.
• This results in a simpler, less complex compound.

This reaction typically occurs under prolonged heating, allowing the reduction process enough time to fully convert glucose. For educational purposes, understanding the nature and strength of HI in its reactions with carbohydrates can illustrate the versatility of hydrohalogenation reactions in organic chemistry.

Carbohydrate Deoxygenation

Carbohydrate deoxygenation is a process where oxygen atoms are removed from carbohydrate molecules, such as glucose. In this chemical reaction, hydroiodic acid removes the oxygen, leading to a more saturated compound. Deoxygenation changes the original polyhydroxylated structure of glucose, which involves several hydroxyl (OH) groups, into a more simplified structure devoid of these oxygen-containing groups.

• Deoxygenation removes oxygen atoms from glucose.
• Transformed glucose becomes a linear hydrocarbon chain.
• This change simplifies the structure into an alkane.

This conversion is significant in organic chemistry, particularly in the synthesis of hydrocarbons from naturally occurring sugars. The process showcases the transformation of a carbohydrate molecule into an alkane by strategically removing functional groups, emphasizing the chemical versatility in transforming complex molecules into simpler ones.

Formation of Alkanes

The formation of alkanes from glucose through deoxygenation via hydroiodic acid is a fascinating transformation. After removing all the oxygen atoms from glucose, only a simple carbon backbone remains. This results in the creation of n-hexane, which is a six-carbon alkane. Alkanes are saturated hydrocarbons, meaning they contain only single bonds between carbon atoms and are fully hydrogenated.

• Alkanes are fully saturated hydrocarbons.
• The process involves converting a complex carbohydrate into a simple hydrocarbon.
• N-hexane is the end product in this case.

This transformation highlights the fundamental process of reducing carbohydrates to form simpler hydrocarbon structures. It also demonstrates the utility of redox chemistry in altering complex organic molecules into basic but essential hydrocarbon forms, which are foundational in various industrial applications.