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

• The equation for the reaction is:

C₆H₅COOCH₃    +    HNO₃  → C₆H₄(NO₂)COOCH₃  + H₂O 

Key steps in the procedure

• 2.0 g of methyl benzoate is added to a small conical flask
• The flask is immersed into an ice-water bath and 4.0 cm³ of concentrated sulfuric acid is slowly added
• A mixture of 1.5 cm³ of concentrated nitric acid and 1.5 cm³ concentrated sulfuric acid is made in a separate test tube and immersed in the ice bath - this is the nitrating mixture
• A thermometer is placed in the conical flask: the temperature must be kept below 6 ^oC
• The nitrating mixture is very slowly added to the flask over about 15 minutes ensuring the temperature remains low
• After the addition the mixture is allowed to remain at room temperature for around 15mins
• The contents of the flask are then poured over crushed ice where the product solidifies
• The ice is allowed to melt and the product is recovered 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