JNTU B.Pharmacy III GREEN CHEMISTRY Previous Question Paper (February-2022 - R17)

The history of green chemistry emerged in the 1990s as a paradigm shift to address the environmental impact of chemical processes. It was formally established by the United States Environmental Protection Agency (EPA) through the Pollution Prevention Act of 1990, which prioritized source reduction over waste treatment. Paul Anastas and John Warner later codified the field in their seminal 1998 book, Green Chemistry: Theory and Practice, which introduced the Twelve Principles of Green Chemistry. These principles serve as a roadmap for designing safer chemicals, reducing hazardous byproducts, utilizing renewable feedstocks, and improving energy efficiency. Over the decades, the field has evolved from a niche academic concept into a global industrial standard, driven by the need for sustainable manufacturing, regulatory pressures like REACH, and the economic benefits of atom economy.

The ultrasonic approach, or sonochemistry, utilizes high-frequency sound waves (typically 20 kHz to 10 MHz) to induce chemical reactions through a phenomenon known as acoustic cavitation. When ultrasonic waves pass through a liquid, they create alternating high-pressure and low-pressure cycles. During the low-pressure cycle, microscopic bubbles form and grow; during the high-pressure cycle, these bubbles collapse violently.

This collapse generates localized 'hot spots' with extreme conditions, including temperatures reaching 5,000 K and pressures up to 1,000 atm, alongside high-speed liquid jets. These conditions facilitate green chemistry by:

• Increasing reaction rates significantly, often allowing reactions to proceed at room temperature.
• Reducing the need for toxic catalysts or solvents by enhancing mass transfer.
• Improving yields and selectivity by providing localized energy that avoids side reactions.
• Enabling the synthesis of nanomaterials and the degradation of organic pollutants in wastewater treatment.