Problem 85 - A Complete Resource Book in Chemistry for JEE Main

Question

The pesticide DDT slowly changes to (a) p, p-dichlorodiphenyldichloroethene (b) p, p'-dichlorodiphenyldichloroethane (c) p, p'-dichlorodiphenylethene (d) \(\mathrm{CCl}_{3}-\mathrm{CHO}\) and chlorobenzene

Step-by-Step Solution

Answer

DDT degrades into both (a) p, p'-dichlorodiphenyldichloroethene and (b) p, p'-dichlorodiphenyldichloroethane.

Step 1: Understand DDT Degradation

DDT stands for Dichloro-Diphenyl-Trichloroethane. It is known to degrade into several products due to environmental processes or biological metabolism. Understanding this will help us determine into which form DDT usually degrades.

Step 2: Identify Common DDT Degradation Products

The common breakdown products of DDT are DDE (Dichlorodiphenyldichloroethene) and DDD (Dichlorodiphenyldichloroethane). These compounds are known to form through the dechlorination process over time when DDT is exposed to the environment.

Step 3: Match Options With Products

Compare the given options with the known degradation products. Option (a) is p, p'-Dichlorodiphenyldichloroethene, matching DDE. Option (b) is p, p'-Dichlorodiphenyldichloroethane, matching DDD. Option (c) is a non-chlorinated version of DDE, which is not common. Option (d) does not fit the common degradation knowledge of DDT.

Step 4: Choose the Correct Degradation Product

Based on the known information about DDT degradation, it primarily degrades to either DDE or DDD. Therefore, the correct answers align with Options (a) and (b).

Key Concepts

DDE (Dichlorodiphenyldichloroethene)

DDE, or Dichlorodiphenyldichloroethene, is a significant byproduct of DDT degradation. This compound is formed when DDT loses hydrogen chloride (HCl).
DDE is more persistent in the environment than its parent compound DDT. This means it can remain in the soil and water for extended periods, sometimes several decades. Here are some key points about DDE:

• Persistence: DDE is renowned for its long-term stability, making it a commonly found pollutant in many ecosystems.
• Biomagnification: It accumulates in the fatty tissues of organisms, leading to increased concentrations higher up the food chain.
• Biological Impact: It is toxic to wildlife, particularly birds, as it thins eggshells, leading to reduced reproductive success.

Understanding DDE helps gauge the environmental impact of historical DDT use. It serves as a marker for the environmental persistence and impact of chlorinated organic compounds.

DDD (Dichlorodiphenyldichloroethane)

Another major degradation product of DDT is DDD, or Dichlorodiphenyldichloroethane. This compound forms when DDT undergoes reductive dechlorination, which is a chemical reaction involving the replacement of chlorine atoms with hydrogen. Some important aspects of DDD include:

• Formation Process: DDD forms under anaerobic conditions, which are environments lacking oxygen. It typically occurs in waterlogged soils or sediments.
• Environmental Behavior: Similar to DDE, DDD is persistent in the environment. It can also bioaccumulate, impacting organisms in similar ways.
• Toxicological Effects: DDD is toxic but generally regarded as less harmful than DDT itself. However, it still poses risks to the health of wildlife and, potentially, humans.

Both DDD and DDE highlight the resilience of chlorinated compounds and their long-term impact on the environment.

Environmental chemistry

Environmental chemistry explores the chemical interactions in the natural world, focusing on pollutants like DDT and its degradation products, DDE and DDD. DDT originally gained popularity for its effectiveness as a pesticide, but environmental awareness brought attention to its long-lasting negative effects. Key ideas in the field include:

• Pollutant Behavior: Environmental chemistry helps understand how substances like DDT behave over time, examining how they degrade or persist.
• Impact Assessment: It assesses the ecological and health impacts of chemical compounds that move through air, water, and soil.
• Remediation Strategies: Understanding chemical properties and interactions aids in developing methods to reduce or eliminate environmental contaminants.

By studying the environmental chemistry of DDT, scientists develop insights into managing and mitigating the effects of similar persistent organic pollutants.