Preparation of Methyl 3-Nitrobenzoate (OCR A Level Chemistry A): Revision Note

PAG 6.3: Preparation of methyl 3-nitrobenzoate

• The equation for the reaction is:

C₆H₅COOCH₃    +    HNO₃  → C₆H₄(NO₂)COOCH₃  + H₂O 

Method

• Add 2.0 g of methyl benzoate to a small conical flask

• Place the flask in an ice-water bath

• Slowly add 4.0 cm³ of concentrated sulfuric acid

• In a separate test tube, prepare the nitrating mixture by combining:

  • 1.5 cm³ concentrated nitric acid

  • 1.5 cm³ concentrated sulfuric acid

• Cool the nitrating mixture in the ice bath

• Insert a thermometer into the conical flask and keep the temperature below 6 ^oC

• Slowly add the nitrating mixture to the flask over about 15 minutes, keeping the temperature low throughout

• After addition, allow the mixture to stand at room temperature for 15 minutes

• Pour the contents of the flask over crushed ice

  • This will cause the product to solidify

• Allow the ice to melt, then recover the solid by Buchner filtration

The nitration of methyl benzoate using an ice bath

Recrystallisation & melting point

• Recrystallisation is carried out in a water-ethanol mixture

• The crystals are recovered and dried

• The melting point of 3-nitromethylbenzoate is 78 ^oC

Key hazards

• The concentrated sulfuric and nitric acid are very corrosive and oxidising so safety glasses and gloves should be worn

• Methyl benzoate is moderately harmful

• Ethanol is flammable so recrystallisation should be done with a hot plate not a naked flame

Practical skills reminder

• This practical develops essential skills in the preparation and purification of a solid organic product, including:

  • Maintaining strict temperature control during reaction using an ice bath

  • Preparing and safely handling a nitrating mixture (HNO₃/H₂SO₄)

  • Isolating the solid product using Buchner filtration

  • Recrystallising the product using a mixed solvent system

  • Using melting point analysis to assess identity and purity