Important reactions of benzoic acid MCQs With Answer

Important reactions of benzoic acid MCQs With Answer — This concise introduction covers essential benzoic acid reactions tailored for B.Pharm students. Learn key concepts like electrophilic aromatic substitution (nitration, sulfonation), formation of benzoyl chloride, esterification, reduction to benzyl alcohol, decarboxylation, Kolbe electrolysis, and oxidative transformations (KMnO4 oxidation of alkylbenzenes). Emphasis on reaction conditions, reagents, regiochemistry, mechanisms, and pharmaceutical relevance helps strengthen organic chemistry foundations. Useful keywords: benzoic acid reactions, esterification, acid chloride, nitration of benzoic acid, decarboxylation, Kolbe electrolysis, reduction, B.Pharm exam prep. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which directing effect does the carboxylic acid (-COOH) group exhibit in electrophilic aromatic substitution on the benzene ring?

• Ortho-directing
• Para-directing
• Meta-directing
• Non-directing

Correct Answer: Meta-directing

Q2. The nitration of benzoic acid primarily yields which major product under standard conditions?

• o-Nitrobenzoic acid
• m-Nitrobenzoic acid
• p-Nitrobenzoic acid
• Dinitrobenzoic acid

Correct Answer: m-Nitrobenzoic acid

Q3. Which reagent converts benzoic acid to benzoyl chloride efficiently?

• Lithium aluminum hydride (LiAlH4)
• Thionyl chloride (SOCl2)
• Sodium borohydride (NaBH4)
• Hydrogen peroxide (H2O2)

Correct Answer: Thionyl chloride (SOCl2)

Q4. Fischer esterification of benzoic acid with methanol in presence of acid catalyst gives:

• Benzyl methyl ether
• Methyl benzoate
• Benzyl alcohol
• Benzoic anhydride

Correct Answer: Methyl benzoate

Q5. Which oxidizing agent oxidizes toluene to benzoic acid under laboratory conditions?

• Pd/C hydrogenation
• KMnO4 (hot, alkaline)
• LiAlH4
• Nitric oxide (NO)

Correct Answer: KMnO4 (hot, alkaline)

Q6. Treatment of benzoic acid with diazomethane (CH2N2) yields:

• Benzyl chloride
• Methyl benzoate
• Benzoic anhydride
• Benzoic acid methyl radical

Correct Answer: Methyl benzoate

Q7. Decarboxylation of benzoic acid using soda lime (NaOH + CaO) gives:

• Benzene
• Toluene
• Phenol
• Biphenyl

Correct Answer: Benzene

Q8. Which reagent reduces benzoic acid to benzyl alcohol effectively?

• Sodium borohydride (NaBH4)
• Lithium aluminum hydride (LiAlH4)
• PCC (pyridinium chlorochromate)
• KMnO4

Correct Answer: Lithium aluminum hydride (LiAlH4)

Q9. Benzoic acid reacts with sodium hydroxide to form which product?

• Benzyl alcohol
• Sodium benzoate
• Benzene sulfonate
• Benzoic anhydride

Correct Answer: Sodium benzoate

Q10. What is the approximate pKa of benzoic acid (indicating acidity)?

• pKa ≈ 2.0
• pKa ≈ 4.2
• pKa ≈ 7.0
• pKa ≈ 10.5

Correct Answer: pKa ≈ 4.2

Q11. Which reaction demonstrates benzoic acid’s ability to form an acid chloride intermediate for further acylation reactions?

• Reaction with PCl5 to form benzoyl chloride
• Oxidation with KMnO4
• Hydrogenation over Pd/C
• Reaction with Grignard reagent to form tertiary alcohol

Correct Answer: Reaction with PCl5 to form benzoyl chloride

Q12. In the presence of concentrated sulfuric acid, benzoic acid undergoes sulfonation at which position predominantly?

• Ortho position
• Meta position
• Para position
• No substitution occurs

Correct Answer: Meta position

Q13. Formation of benzoic anhydride from benzoic acid typically requires which type of reagent or condition?

• Dehydrating agent like SOCl2 or P2O5
• Strong reducing agent
• Electrophilic halogenation
• Peroxide initiation

Correct Answer: Dehydrating agent like SOCl2 or P2O5

Q14. Which method is commonly used to synthesize benzoic acid from benzene derivatives industrially or in lab?

• Nitration then reduction
• Oxidation of alkylbenzenes (e.g., toluene) with strong oxidants
• Hydrogenation of benzaldehyde
• Friedel-Crafts alkylation

Correct Answer: Oxidation of alkylbenzenes (e.g., toluene) with strong oxidants

Q15. Kolbe electrolysis of sodium benzoate mainly produces which hydrocarbon?

• Biphenyl
• Benzene
• Toluene
• Benzyne

Correct Answer: Benzene

Q16. Which reagent will convert benzoic acid into its methyl ester under mild, high-yield conditions without strong acid?

• Diazomethane (CH2N2)
• NaBH4 in methanol
• PCC in methanol
• Acetic anhydride

Correct Answer: Diazomethane (CH2N2)

Q17. When benzoic acid is treated with concentrated nitric acid and sulfuric acid, nitration occurs. Which intermediate controls regioselectivity?

• Benzoate anion
• Carboxyl protonated form stabilizing ortho
• Sigma-complex where -COOH is meta-directing
• Benzoyl radical

Correct Answer: Sigma-complex where -COOH is meta-directing

Q18. Which of the following best describes benzoic acid’s solubility behavior in water?

• Highly soluble at room temperature
• Poorly soluble in cold water but solubility increases with temperature
• Completely insoluble in all temperatures
• Soluble only in organic solvents, not water

Correct Answer: Poorly soluble in cold water but solubility increases with temperature

Q19. Reaction of benzoic acid with SOCl2 produces benzoyl chloride. What is a common subsequent reaction of benzoyl chloride?

• Nucleophilic acyl substitution to form esters or amides
• Electrophilic aromatic substitution on benzene ring
• Oxidative cleavage to phenol
• Radical polymerization

Correct Answer: Nucleophilic acyl substitution to form esters or amides

Q20. Which reagent would selectively reduce the carboxylic acid group of benzoic acid to benzaldehyde (one-step selective reduction)?

• PCC
• DIBAL-H at low temperature (from benzoyl derivative)
• LiAlH4 directly
• KMnO4

Correct Answer: DIBAL-H at low temperature (from benzoyl derivative)

Q21. Which of the following reactions is not typically observed with benzoic acid?

• Formation of amide on reaction with amines (using coupling agents)
• Friedel-Crafts alkylation directly on benzoic acid
• Conversion to benzoyl chloride
• Esterification to give alkyl benzoates

Correct Answer: Friedel-Crafts alkylation directly on benzoic acid

Q22. Benzoic acid can be converted into benzyl alcohol by which two-step sequence?

• Reduction to benzaldehyde then hydrogenation to benzyl alcohol
• Formation of acid chloride then reduction with LiAlH4
• Direct catalytic hydrogenation
• Nitration then reduction

Correct Answer: Formation of acid chloride then reduction with LiAlH4

Q23. Which chemical reagent is commonly used to activate benzoic acid for amide bond formation in peptide coupling?

• Thionyl chloride (SOCl2) alone
• Dicyclohexylcarbodiimide (DCC) or EDC with HOBt
• KMnO4
• NaBH4

Correct Answer: Dicyclohexylcarbodiimide (DCC) or EDC with HOBt

Q24. Which of the following reactions demonstrates decarboxylative cross-coupling involving benzoic acid derivatives in modern organic synthesis?

• Fischer esterification
• Transition-metal-catalyzed decarboxylative arylation
• Saponification only
• Kolbe electrolysis exclusively

Correct Answer: Transition-metal-catalyzed decarboxylative arylation

Q25. In the presence of strong bases, benzoic acid is deprotonated to form which species that is more water soluble?

• Benzyl cation
• Benzoate anion
• Benzoyl radical
• Benzoic ester

Correct Answer: Benzoate anion

Q26. Which halogenation of benzoic acid under electrophilic conditions is most favored (regioselectively)?

• Ortho-bromination
• Meta-bromination
• Para-chlorination
• Benzylic bromination

Correct Answer: Meta-bromination

Q27. Which reactive intermediate is formed when benzoic acid is treated with PCl5?

• Benzyl chloride
• Benzoyl chloride
• Benzene sulfonyl chloride
• Benzoic radical cation

Correct Answer: Benzoyl chloride

Q28. Benzoic acid undergoes decarboxylation most readily when which condition is applied?

• Heating with soda lime (NaOH/CaO)
• Cooling to −78°C
• Neutral aqueous solution
• Photochemical irradiation only

Correct Answer: Heating with soda lime (NaOH/CaO)

Q29. Which statement about benzoic acid’s reactivity in Friedel-Crafts acylation is correct?

• Benzoic acid readily undergoes Friedel-Crafts acylation without modification
• The -COOH group poisons Lewis acid catalysts, preventing direct Friedel-Crafts
• Benzoic acid is a strong activator for Friedel-Crafts reactions
• Benzoic acid is converted to benzyl chloride first to enable Friedel-Crafts

Correct Answer: The -COOH group poisons Lewis acid catalysts, preventing direct Friedel-Crafts

Q30. Which of the following is a common pharmaceutical application of benzoic acid derivatives?

• As antiviral nucleosides
• As preservatives and antimicrobial agents (e.g., sodium benzoate)
• As opioid analgesics
• As anesthetic gases

Correct Answer: As preservatives and antimicrobial agents (e.g., sodium benzoate)

Q31. The conversion of benzoic acid to benzoyl peroxide typically involves which key reagent?

• Hydrochloric acid
• Hydrogen peroxide (H2O2) and base
• LiAlH4
• Grignard reagent

Correct Answer: Hydrogen peroxide (H2O2) and base

Q32. When benzoic acid is heated with phenol in presence of acid catalyst, the product formed is:

• Benzyl phenyl ether
• Phenyl benzoate (an ester)
• Biphenyl
• Benzaldehyde

Correct Answer: Phenyl benzoate (an ester)

Q33. Which spectroscopic change indicates conversion of benzoic acid to benzyl alcohol?

• Disappearance of carbonyl (C=O) stretch around 1700 cm−1 in IR
• Appearance of strong C=O peak at 1700 cm−1
• Shift of aromatic peaks only
• New nitrile peak

Correct Answer: Disappearance of carbonyl (C=O) stretch around 1700 cm−1 in IR

Q34. Which reagent would convert benzoic acid to benzaldehyde in a single, mild transformation (practical synthetic route)?

• Partial reduction of benzoyl chloride with Rosenmund reduction (H2/Pd-BaSO4)
• NaBH4 reduction directly
• Oxidation with KMnO4
• Photochemical decarboxylation

Correct Answer: Partial reduction of benzoyl chloride with Rosenmund reduction (H2/Pd-BaSO4)

Q35. Which process is useful to protect the carboxyl group of benzoic acid during multi-step synthesis?

• Formation of methyl ester (esterification)
• Oxidation to benzoic anhydride
• Formation of benzoyl peroxide
• Direct nitration

Correct Answer: Formation of methyl ester (esterification)

Q36. Which reagent sequence converts benzoic acid into benzyl chloride (via reduction then chlorination)?

• LiAlH4 to benzyl alcohol, then SOCl2 to benzyl chloride
• SOCl2 directly to benzyl chloride
• KMnO4 oxidation then HCl
• PCC then NaCl

Correct Answer: LiAlH4 to benzyl alcohol, then SOCl2 to benzyl chloride

Q37. What product results from the esterification of benzoic acid with ethanol under acidic conditions?

• Ethyl benzoate
• Benzyl ethyl ether
• Benzoic acid ethylidene acetal
• Ethyl benzyl ketone

Correct Answer: Ethyl benzoate

Q38. Which statement best explains why benzoic acid is a weaker acid than acetic acid? (Note: this is a trick — check reasoning.)

• Benzoic acid is stronger due to resonance with the aromatic ring
• Benzoic acid is weaker because the aromatic ring donates electron density via resonance
• Benzoic acid is similar in acidity; actually benzoic acid is slightly stronger than acetic acid due to resonance stabilization of the benzoate anion
• Benzoic acid is non-acidic

Correct Answer: Benzoic acid is similar in acidity; actually benzoic acid is slightly stronger than acetic acid due to resonance stabilization of the benzoate anion

Q39. Which reagent is commonly used to selectively convert benzoic acid to benzoyl imidazole (active ester) for peptide coupling?

• Carbonyldiimidazole (CDI)
• LiAlH4
• KMnO4
• Thionyl chloride only

Correct Answer: Carbonyldiimidazole (CDI)

Q40. Reaction of benzoic acid with phenylmagnesium bromide (a Grignard reagent) typically yields after workup:

• Benzoic acid unchanged
• Tertiary alcohol after addition to benzoyl chloride equivalent (requires prior activation)
• Methyl benzoate directly
• Benzene via protonation

Correct Answer: Tertiary alcohol after addition to benzoyl chloride equivalent (requires prior activation)

Q41. Which reaction converts benzoic acid into benzoyl cyanide or related nitrile derivatives useful in synthesis?

• Direct treatment with HCN
• Conversion to acid chloride, then reaction with NaCN
• Oxidation with KMnO4
• Hydrogenation

Correct Answer: Conversion to acid chloride, then reaction with NaCN

Q42. Which of the following conditions favors formation of ortho-substituted product during substitution on benzoic acid despite its meta-directing nature?

• Use of bulky electrophile only
• Use of intramolecular directing groups or steric control under special conditions
• Strongly basic aqueous conditions
• Absence of electrophile

Correct Answer: Use of intramolecular directing groups or steric control under special conditions

Q43. Which transformation is an example of nucleophilic acyl substitution of benzoic acid derivatives?

• Conversion of benzoyl chloride to benzamide by ammonia
• Nitration of benzoic acid to nitrobenzoic acid
• Hydrogenation of benzene ring
• Kolbe electrolysis to benzene

Correct Answer: Conversion of benzoyl chloride to benzamide by ammonia

Q44. Which reagent is used for the decarboxylative formation of biaryl compounds from benzoic acid derivatives in modern cross-coupling?

• Cu or Pd-catalyzed decarboxylative coupling
• H2SO4 only
• LiAlH4
• NaBH4

Correct Answer: Cu or Pd-catalyzed decarboxylative coupling

Q45. Which transformation converts benzoic acid to benzamide under laboratory conditions?

• Direct heating with ammonia (often via activation to acid chloride or using coupling agents)
• Treatment with H2/Pd
• Oxidation with KMnO4
• Photochemical rearrangement

Correct Answer: Direct heating with ammonia (often via activation to acid chloride or using coupling agents)

Q46. Which reagent would you choose to form benzoyl ester under neutral to basic conditions without strong acid?

• DCC coupling of benzoic acid with alcohol
• Concentrated H2SO4 with alcohol
• PCC oxidation
• Photolysis

Correct Answer: DCC coupling of benzoic acid with alcohol

Q47. Which of the following best describes the mechanism of esterification of benzoic acid by methanol in presence of acid?

• Nucleophilic aromatic substitution
• Nucleophilic acyl substitution via protonation of carbonyl followed by nucleophilic attack
• Free radical addition across the ring
• Electrophilic aromatic substitution

Correct Answer: Nucleophilic acyl substitution via protonation of carbonyl followed by nucleophilic attack

Q48. Which product is expected when benzoic acid is chlorinated under radical conditions targeting benzylic position?

• Benzoyl chloride
• Benzyl chloride (from benzylic C–H substitution)
• Chlorobenzene (aromatic substitution)
• Benzoic anhydride

Correct Answer: Benzyl chloride (from benzylic C–H substitution)

Q49. Which method would you use to prepare sodium benzoate as a preservative from benzoic acid?

• Neutralization with sodium hydroxide (NaOH)
• Oxidation with KMnO4
• Reduction with LiAlH4
• Reaction with thionyl chloride

Correct Answer: Neutralization with sodium hydroxide (NaOH)

Q50. Which reagent combination is suitable to convert benzoic acid into benzylamine (via reduction then amination)?

• LiAlH4 to benzyl alcohol, then SN2 with ammonia
• Reduction to benzaldehyde then reductive amination with ammonia and NaBH3CN
• Direct amide formation followed by Hofmann degradation only
• Oxidation then nitration

Correct Answer: Reduction to benzaldehyde then reductive amination with ammonia and NaBH3CN

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