Picric acid is obtained by treating phenol first with concentrated sulfuric acid, converting it to phenol-2,4-disulphonic acid, and then with concentrated nitric acid to yield 2,4,6-trinitrophenol. The modern method is preferred for improved yield in the preparation of picric acid.
How is picric acid (2,4,6-trinitrophenol) typically prepared from phenol, and why is the modern method involving concentrated sulfuric acid utilized for better yield?
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Picric acid (2,4,6-trinitrophenol) is prepared from phenol by nitration, where phenol reacts with a mixture of concentrated nitric acid and sulfuric acid. The sulfuric acid serves as a dehydrating agent and provides a medium for the nitration reaction. The modern method involving concentrated sulfuric acid is favored for better yield because sulfuric acid helps maintain a more anhydrous environment, reducing side reactions and enhancing the efficiency of nitration. Additionally, concentrated sulfuric acid aids in the formation of the nitronium ion, a key intermediate in the nitration process, leading to improved selectivity and higher yields of picric acid.