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)
