Final answer:
Sodium carbonate is used in caffeine extraction from tea leaves because it increases caffeine's nucleophilicity for easier solvent extraction. Supercritical CO₂ extraction is a separate method used for decaffeinating coffee beans, which is highly effective and preserves flavor and aroma while posing fewer health risks compared to traditional organic solvents.
Step-by-step explanation:
Sodium carbonate is used in the process of extracting caffeine from tea leaves primarily for its alkaline properties. It aids in deprotonating the phenolic groups in caffeine, which increases the molecule's nucleophilicity, allowing it to react more readily with a solvent for extraction. This process is different from supercritical carbon dioxide extraction which is a more recent, effective, and environmentally friendly method used for decaffeinating coffee beans. In this method, supercritical CO₂, which acts both as a gas and a liquid due to its unique state beyond its critical temperature and pressure, penetrates into the beans like a gas and dissolves the caffeine like a liquid. Unlike traditional organic solvents, supercritical CO₂ does not have the same health concerns and leaves the flavor and aroma profiles intact while removing 97-99% of caffeine.