Catalysis: heterogeneous vs homogeneous and applications in drug synthesis MCQs With Answer

Catalysis: heterogeneous vs homogeneous and applications in drug synthesis MCQs With Answer

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Catalysis: heterogeneous vs homogeneous and applications in drug synthesis MCQs With Answer is a focused quiz set designed for M.Pharm students studying Advanced Organic Chemistry II. These questions explore core concepts of homogeneous and heterogeneous catalysis, their mechanistic differences, kinetics parameters like TON/TOF, catalyst deactivation and regeneration, ligand effects, and practical implications in API manufacture. Emphasis is placed on real-world drug synthesis examples, green chemistry considerations, immobilized chiral catalysts, and scale-up issues such as metal leaching, selectivity and catalyst recovery. This resource challenges students to connect fundamental catalysis principles with pharmaceutically relevant transformations and process decisions encountered in industry and research.

Q1. Which statement best distinguishes homogeneous catalysis from heterogeneous catalysis?

  • The catalyst and reactants are in the same phase in heterogeneous catalysis.
  • Homogeneous catalysts are always metal complexes while heterogeneous are always enzymes.
  • Homogeneous catalysis involves catalysts molecularly dispersed in the reaction medium, whereas heterogeneous catalysis involves a catalyst in a different phase (usually solid) than the reactants.
  • Heterogeneous catalytic reactions cannot be selective.

Correct Answer: Homogeneous catalysis involves catalysts molecularly dispersed in the reaction medium, whereas heterogeneous catalysis involves a catalyst in a different phase (usually solid) than the reactants.

Q2. Which parameter specifically measures the number of substrate molecules converted per active catalytic site before deactivation?

  • Turnover frequency (TOF)
  • Turnover number (TON)
  • Activation energy
  • Catalyst loading

Correct Answer: Turnover number (TON)

Q3. In an industrial hydrogenation of an active pharmaceutical ingredient (API), which heterogeneous catalyst is most commonly used for selective hydrogenation of C=C bonds?

  • Pd/C (palladium on carbon)
  • AlCl3
  • Grubbs catalyst
  • Jacobsen’s catalyst

Correct Answer: Pd/C (palladium on carbon)

Q4. Which of the following is a typical advantage of heterogeneous catalysts over homogeneous catalysts in pharmaceutical process chemistry?

  • Higher molecular-level tunability of active site ligands
  • Easier catalyst recovery and recycling due to phase separation
  • Always higher intrinsic activity per metal atom
  • Inherently better enantioselectivity

Correct Answer: Easier catalyst recovery and recycling due to phase separation

Q5. Which phenomenon describes the loss of catalytic activity in heterogeneous catalysts due to strong adsorption of impurities such as sulfur or phosphorus?

  • Leaching
  • Poisoning
  • Promoter effect
  • Ligand dissociation

Correct Answer: Poisoning

Q6. In palladium-catalyzed Suzuki–Miyaura cross-coupling used in API synthesis, what is a common issue when using heterogeneous Pd/C that must be monitored for regulatory compliance?

  • Insufficient acidity
  • Residual palladium leaching into final product
  • Excessive polymerization
  • Loss of stereochemistry

Correct Answer: Residual palladium leaching into final product

Q7. Which analytical technique is most useful for detecting and quantifying metal leaching from heterogeneous catalysts into solution at trace levels?

  • Infrared spectroscopy (IR)
  • Inductively coupled plasma mass spectrometry (ICP-MS)
  • Nuclear magnetic resonance (NMR)
  • Ultraviolet-visible spectroscopy (UV-Vis)

Correct Answer: Inductively coupled plasma mass spectrometry (ICP-MS)

Q8. Why are immobilized chiral ligands or supported chiral catalysts important for pharmaceutical asymmetric synthesis?

  • They remove the need for chiral resolution completely in every case.
  • They combine the enantioselectivity of homogeneous catalysts with easier recovery and reuse like heterogeneous systems.
  • They guarantee zero metal contamination.
  • They always provide faster reaction rates than homogeneous catalysts.

Correct Answer: They combine the enantioselectivity of homogeneous catalysts with easier recovery and reuse like heterogeneous systems.

Q9. Which of the following statements about turnover frequency (TOF) is TRUE?

  • TOF is the total number of substrate molecules converted by the entire catalyst batch during its lifetime.
  • TOF is expressed as conversions per unit time per active site and indicates intrinsic catalyst activity.
  • TOF decreases linearly with temperature for all catalysts.
  • TOF and TON are equivalent terms and can be used interchangeably.

Correct Answer: TOF is expressed as conversions per unit time per active site and indicates intrinsic catalyst activity.

Q10. Which catalytic approach was adopted to replace a homogeneous expensive rhodium-catalyzed asymmetric hydrogenation in a scalable API process to reduce cost and metal contamination risk?

  • Use of a supported heterogeneous Pd/C with no enantioselectivity
  • Immobilized chiral rhodium on a solid support to enable recovery
  • Switch to stoichiometric chiral auxiliaries only
  • Elimination of hydrogenation step entirely without alternative

Correct Answer: Immobilized chiral rhodium on a solid support to enable recovery

Q11. Which type of solid acid catalyst is commonly used in pharmaceutically relevant reactions such as esterification and resin-based catalysis for scale-up?

  • Amberlyst (sulfonic acid resin)
  • Grubbs catalyst
  • Karstedt’s catalyst
  • Hantzsch ester

Correct Answer: Amberlyst (sulfonic acid resin)

Q12. Which mechanistic step is NOT typically associated with homogeneous organometallic catalytic cycles used in cross-couplings?

  • Oxidative addition
  • Transmetalation
  • Reductive elimination
  • Heterogeneous adsorption-desorption equilibrium on a solid surface

Correct Answer: Heterogeneous adsorption-desorption equilibrium on a solid surface

Q13. Which strategy is effective to minimize palladium contamination when using homogeneous Pd catalysts in API synthesis?

  • Increase reaction temperature indefinitely
  • Use scavenger resins or metal-scavenging agents and optimize ligand/catalyst amount
  • Omit any work-up and directly crystallize API
  • Always use base-free conditions

Correct Answer: Use scavenger resins or metal-scavenging agents and optimize ligand/catalyst amount

Q14. In heterogeneous nanoparticle catalysis, what effect does decreasing particle size to the nanometer range typically have?

  • Decreases surface area-to-volume ratio
  • Increases the fraction of surface atoms and often increases catalytic activity per metal atom
  • Prevents any metal leaching
  • Automatically imparts enantioselectivity

Correct Answer: Increases the fraction of surface atoms and often increases catalytic activity per metal atom

Q15. Which of the following is a common advantage of homogeneous catalysts in fine chemical synthesis compared with heterogeneous catalysts?

  • Better ease of catalyst separation
  • Higher tolerance to heterogeneous poisons
  • Greater ability to fine-tune electronic and steric properties via ligand design, enabling higher chemo- and enantioselectivity
  • Unlimited recyclability without any loss of activity

Correct Answer: Greater ability to fine-tune electronic and steric properties via ligand design, enabling higher chemo- and enantioselectivity

Q16. Which catalytic process uses a solid porous aluminosilicate with shape-selective properties and is relevant for selective transformations in drug intermediates?

  • Zeolite-catalyzed reactions
  • Photoredox homogeneous catalysis
  • Biocatalysis by free enzymes only
  • Phase-transfer catalysis in homogeneous solvent

Correct Answer: Zeolite-catalyzed reactions

Q17. Which approach best reduces the environmental footprint of catalytic steps in API manufacturing (aligning with green chemistry)?

  • Use stoichiometric heavy-metal reagents instead of catalysts
  • Shift to catalytic, high-atom-economy reactions, minimize solvent use and enable catalyst recycling
  • Increase excess reagents to drive conversions
  • Always carry out reactions at very high solvent volumes

Correct Answer: Shift to catalytic, high-atom-economy reactions, minimize solvent use and enable catalyst recycling

Q18. Which type of catalysis is typically associated with reactions occurring at active sites on solid surfaces and involving adsorption, surface reaction and desorption steps?

  • Homogeneous organocatalysis
  • Enzymatic catalysis
  • Heterogeneous catalysis
  • Phase-transfer catalysis

Correct Answer: Heterogeneous catalysis

Q19. In palladium-catalyzed hydrogenation using Pd/C, which operational parameter is most likely to influence selectivity between hydrogenation of nitro group versus C=C bond?

  • Pressure of hydrogen and choice of solvent and catalyst loading
  • Color of the reactor
  • Amount of inert air in the headspace
  • Ambient noise level

Correct Answer: Pressure of hydrogen and choice of solvent and catalyst loading

Q20. Which catalytic innovation has enabled continuous, safer and scalable processing for many drug syntheses by combining heterogeneous catalysts with flow reactors?

  • Batch high-pressure autoclaves exclusively
  • Packed-bed flow reactors with immobilized catalysts to allow continuous operation and facile heat/mass transfer
  • Use of purely stoichiometric reagents without catalyst
  • Open-air random stirring of slurry catalysts only

Correct Answer: Packed-bed flow reactors with immobilized catalysts to allow continuous operation and facile heat/mass transfer

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