Oxidation processes: liquid-phase oxidations and oxidizing agents MCQs With Answer

Introduction

This quiz collection on Oxidation processes: liquid-phase oxidations and oxidizing agents is designed for M.Pharm students preparing for MPC 204T Pharmaceutical Process Chemistry. It focuses on reagent selection, mechanisms, catalytic systems, selectivity, mass-transfer issues and safe, green practices in liquid-phase oxidation. The questions probe both theoretical understanding and practical decision-making encountered in pharmaceutical synthesis — from classical chromium reagents to modern TEMPO and aerobic catalytic methods. Use these MCQs to reinforce concepts, identify weak areas, and practice the reasoning required for exam questions and real-world process development.

Q1. Which oxidizing agent is commonly used with TEMPO for selective oxidation of primary alcohols to aldehydes under mild aqueous conditions?

• PCC (pyridinium chlorochromate)
• Hydrogen peroxide (H2O2)
• Bleach (sodium hypochlorite, NaOCl)
• Potassium permanganate (KMnO4)

Correct Answer: Bleach (sodium hypochlorite, NaOCl)

Q2. Which oxidant is often considered “green” because its reduction product is water and it generates minimal hazardous byproducts?

• Molecular oxygen (O2)
• Hydrogen peroxide (H2O2)
• Chromium(VI) reagents (e.g., CrO3)
• Potassium permanganate (KMnO4)

Correct Answer: Hydrogen peroxide (H2O2)

Q3. Which reagent is most commonly used as a peracid for Baeyer–Villiger oxidation of ketones to esters in organic synthesis?

• Pyridinium chlorochromate (PCC)
• meta-Chloroperbenzoic acid (mCPBA)
• Potassium permanganate (KMnO4)
• Jones reagent (CrO3/H2SO4)

Correct Answer: meta-Chloroperbenzoic acid (mCPBA)

Q4. Swern oxidation converts alcohols to carbonyls using activated dimethyl sulfoxide. Which activating reagent is typically used to form the active DMSO species?

• Pyridinium chlorochromate (PCC)
• DMSO activated with oxalyl chloride (COCl)2
• Dess–Martin periodinane (DMP)
• Jones reagent (CrO3/H2SO4)

Correct Answer: DMSO activated with oxalyl chloride (COCl)2

Q5. Which reagent is a classical strong oxidant used to convert primary alcohols directly to carboxylic acids under aqueous acidic conditions?

• PCC (pyridinium chlorochromate)
• Jones reagent (CrO3 in aqueous H2SO4/acetone)
• TEMPO/NaOCl catalytic system
• Dess–Martin periodinane (DMP)

Correct Answer: Jones reagent (CrO3 in aqueous H2SO4/acetone)

Q6. Which class of oxidants is especially hazardous due to shock sensitivity and potential for explosive decomposition in organic solvents?

• Concentrated hydrogen peroxide (H2O2)
• Potassium permanganate (KMnO4)
• Organic peracids and peroxides (e.g., mCPBA, t‑BuOOH)
• Sodium hypochlorite (NaOCl)

Correct Answer: Organic peracids and peroxides (e.g., mCPBA, t‑BuOOH)

Q7. In liquid‑phase aerobic oxidations catalyzed by transition metals, what is the primary role of molecular oxygen?

• Solvent for the reaction
• Terminal oxidant (electron acceptor) to reoxidize the catalyst
• Ligand for the metal catalyst
• Radical initiator only without being consumed

Correct Answer: Terminal oxidant (electron acceptor) to reoxidize the catalyst

Q8. Which oxidizing reagent is preferred for mild, chemoselective oxidation of sensitive secondary alcohols to ketones without overoxidation?

• Jones reagent (CrO3/H2SO4)
• PCC (pyridinium chlorochromate)
• Dess–Martin periodinane (DMP)
• Potassium permanganate (KMnO4)

Correct Answer: Dess–Martin periodinane (DMP)

Q9. The Baeyer–Villiger oxidation proceeds through which mechanistic intermediate/type of rearrangement?

• Radical chain propagation
• Pericyclic concerted insertion without intermediate
• Criegee intermediate: nucleophilic addition of peracid followed by rearrangement
• Nucleophilic acyl substitution at the α‑carbon

Correct Answer: Criegee intermediate: nucleophilic addition of peracid followed by rearrangement

Q10. Phase‑transfer catalysts are often used in liquid‑phase oxidations to facilitate transfer of which species into the organic phase?

• Anionic oxidants (e.g., hypochlorite, permanganate)
• Neutral gaseous oxygen molecules
• Metal nanoparticles
• Light (photons) for photochemical oxidations

Correct Answer: Anionic oxidants (e.g., hypochlorite, permanganate)

Q11. Which oxidizing reagent selectively oxidizes primary alcohols to aldehydes under anhydrous conditions and minimizes overoxidation to acids?

• PCC (pyridinium chlorochromate)
• Jones reagent (CrO3/H2SO4)
• Potassium permanganate (KMnO4)
• Hydrogen peroxide (H2O2)

Correct Answer: PCC (pyridinium chlorochromate)

Q12. In liquid‑phase aerobic oxidations, what is a common engineering limitation that affects reaction rate and selectivity?

• Insufficient gas–liquid mass transfer of oxygen from the gas phase into the liquid
• Poor thermal conductivity of the catalyst particles
• Excessive light scattering in the reactor
• Lack of stirring affecting solid–solid contact

Correct Answer: Insufficient gas–liquid mass transfer of oxygen from the gas phase into the liquid

Q13. TEMPO‑mediated oxidations operate by which formal mechanistic pathway for alcohol oxidation?

• Hydride transfer to a nitro radical anion
• Nitroxyl radical/oxoammonium redox cycle (nitroxyl radical-mediated oxidation)
• Concerted pericyclic hydrogen transfer
• Single‑electron transfer to form carbon radicals as the only step

Correct Answer: Nitroxyl radical/oxoammonium redox cycle (nitroxyl radical-mediated oxidation)

Q14. Which reagent is widely used for allylic oxidation of alkenes to form allylic alcohols or carbonyls?

• SeO2 (selenium dioxide)
• PCC (pyridinium chlorochromate)
• Dess–Martin periodinane (DMP)
• mCPBA (meta‑chloroperbenzoic acid)

Correct Answer: SeO2 (selenium dioxide)

Q15. What is the principal drawback of using chromium(VI) oxidants (e.g., Jones, PCC) in pharmaceutical process chemistry?

• They are insufficiently reactive for most alcohol oxidations
• Significant toxicity and environmental disposal concerns from chromium waste
• They cannot oxidize secondary alcohols
• They require photochemical activation

Correct Answer: Significant toxicity and environmental disposal concerns from chromium waste

Q16. Which oxidant is commonly used in the Sharpless asymmetric epoxidation protocol?

• Hydrogen peroxide (H2O2)
• tert‑Butyl hydroperoxide (t‑BuOOH, TBHP)
• PCC (pyridinium chlorochromate)
• SeO2 (selenium dioxide)

Correct Answer: tert‑Butyl hydroperoxide (t‑BuOOH, TBHP)

Q17. What is a key practical advantage of Dess–Martin periodinane (DMP) compared to chromium(VI) reagents?

• Generates stoichiometric chromium waste instead of iodine waste
• Operates under mild, neutral to slightly acidic conditions with high chemoselectivity
• Requires high temperatures and strong acid for activation
• Is insoluble in common organic solvents and thus heterogeneous

Correct Answer: Operates under mild, neutral to slightly acidic conditions with high chemoselectivity

Q18. Which reagent is especially useful for oxidative cleavage of vicinal diols to give carbonyl compounds (aldehydes/ketones)?

• Periodic acid (HIO4)
• Potassium permanganate (KMnO4) under neutral conditions
• PCC (pyridinium chlorochromate)
• Dess–Martin periodinane (DMP)

Correct Answer: Periodic acid (HIO4)

Q19. When a primary alcohol is exposed to excess strong oxidant in aqueous conditions, what is the typical final oxidation product?

• Aldehyde
• Carboxylic acid
• Ketone
• Ester

Correct Answer: Carboxylic acid

Q20. For selective oxidation of a primary alcohol in the presence of a secondary alcohol, which modern catalytic method is commonly preferred?

• Jones reagent (CrO3/H2SO4)
• TEMPO‑catalyzed oxidation with NaOCl (Anelli–Montanari type conditions)
• Potassium permanganate (KMnO4)
• mCPBA (meta‑chloroperbenzoic acid)

Correct Answer: TEMPO‑catalyzed oxidation with NaOCl (Anelli–Montanari type conditions)

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