Objective: To prepare 5-Nitro salicylic acid from salicylic acid

Apparatus/Glassware Required: Conical flask, beaker, volumetric flask, measuring cylinder, water bath, suction pump and Buchner funnel

Chemicals Required: Salicylic acid, Acetic acid and Calcium nitrate tetrahydrate

Principle: Nitration on salicylic acid occurs by placing a nitro group on the aromatic ring system via an electrophilic aromatic substitution reaction. Here calcium nitrate is used as the nitrating agent in presence of acetic acid. Two groups –COOH and –OH in salicylic acid complement each other since they both direct the entering nitro group to the 5^th position. The 5^th position and the 3^rd position are both electronically favored since the –COOH group is meta-directing and the –OH group is ortho-para directing. The nitro group is attached at the 5^th position, and not at the 3^rd position, due to steric effect.

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Procedure:

1. Dissolve 6 g of calcium nitrate in 20 mL of acetic acid within a 250 mL conical flask and gently heat on a water bath.
2. To the above mixture add 4 g of salicylic acid and heat on a boiling water bath (below 80^oC) for few minutes.
3. A dark red solution is formed. Then the reaction mixture is pour into a 250 mL beaker containing 20 mL ice cold water.
4. The above solution is keep refrigerator and after 4-5 hours yellow crystals of 4-nitrosalicylic acid separates out.
5. The crude product is filtered at the suction pump, washed with cold water and dried.

Uses: Mainly used as Synthetic intermediate

Note: Clear yellow-beige to orange-brow; insoluble in water; M.P. 228° C

Precautions: The concentrated acids are corrosive. Gloves should be worn when transferring these reagents.