Sweetening of petroleum fractions – Doctor's treatment In the traditional Doctor's treatment process for removing mercaptans (sweetening), the key reagent in the solution is:

Introduction / Context:
Mercaptans (R–SH) in petroleum streams cause odor and corrosion. The Doctor's treatment is a classic sweetening process used historically to convert mercaptans to disulfides, reducing odor and improving product quality.

Given Data / Assumptions:

• Treatment applied to lighter petroleum fractions.
• Alkaline solution is used along with a lead compound and elemental sulfur.
• Objective is oxidation of mercaptans to disulfides.

Concept / Approach:
Doctor's solution consists of sodium plumbite (Na2PbO2) in sodium hydroxide. In the presence of sulfur, mercaptans are converted to disulfides (RSSR), which are less odorous and remain in the oil phase. Sodium plumbite acts as a catalyst/oxidant species in the alkaline environment.

Step-by-Step Solution:

Verification / Alternative check:
Refining texts list Doctor's solution as Na2PbO2/NaOH; modern processes use alternative catalysts to avoid lead, but the classical answer remains sodium plumbite.

Why Other Options Are Wrong:

• Sodium hydroxide: Present as solvent/base but not the distinctive Doctor reagent.
• Cupric chloride / potassium isobutyrate: Not used in the Doctor process; other sweetening or extraction schemes exist.

Common Pitfalls:
Confusing Doctor's treatment with Merox (mercaptan oxidation using cobalt/molybdenum catalysts); the key reagent in the classical Doctor method is sodium plumbite.

Final Answer:
sodium plumbite