ORGANIC cHEMISTRY - II

BSCM302

Experiment 7

Aim of the Experiment

To Prepare 5-Nitro salicylic acid from Salicylic acid

Principle

Nitration on salicylic acid occurs byplacing a nitro group on the armatic ring system via an electrophilic aromatic substitution reaction.Here calcium nitrate is used as the nitrating agent in presence of acetic acid.Two groups -CO2H and OH in salicylic aacid 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 favoured since the -CO2H 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 effects.We can also use anhydrous nitric acid or concentrated nitric acid and concentrated sulphuric acid as nitrating reagent.

Reaction:

1. Generation of electrofile

Ca(NO₃)₂+ 2CH₃COOH -----> 2CH₃COO^-NO₂⁺+ Ca(OH)₂

2. Attack on benzene ring by acetyl nitrate

Materials required

Chemicals:

Salicylic acid - 2 g

Acetic acid- 10 ml

Calcium nitarte tetrahydrate - 3 g

Apparatus:

Conical flask , Funnel , Beaker,Filter paper

Procedure

3 g of calcium nitrate tetrahydrate is dissolved in 10 ml of acetic acid within a 100 ml conical flask by gently heating on a water bath.2 g of salicylic acid is added and the reaction mixture is heated on a boiling water bath (below 80 degree) for few minutes.A dark red solution is formed.Then the dark red coloured reaction mixture is poured into a 100 ml beaker Containing 20 ml ice cold water.

Aturbid dark red coloured solution forms which is kept in a refrigerator and after4-5 hours yellow crystals of 4-Nitro salicylic acid separates out.The crude product is filtered at the suction pump,washed with cold water and dried.Yellow precipitate of 4-Nitro salicylic acid is obtained with yield of 1.32 g m.p.234 ⁰C

Exp-7 5-nitro_salicylic_acid_mp4

Observation:

Amount of Salicylic acid taken = g

Amount of 5-Nitro salicylic acid formed = g

Mol.formula of =C7H6O3

Mol.formula of = C7H5NO5

Mol.wt.of Salicylic acid = 138 g/mol

Mol.wt. Of 5-Nitro salicylic acid =198 g/mol

Calculations:

138 g of Salicylic acid gives 198 g of 5-Nitro salicylic acid

Therefore,2 g of Salicylic acid would give __________?(x) g of 5-Nitro salicylic acid X = 198 x 2 /138 = g

Experimental yield= g

^{%Yield =}x 100 %

Result & Conclusion

i) Yield of 5-Nitro salicylic acid = %

ii) Melting point of 5-Nitro salicylic acid = ⁰C. (Reported value =234°C)

Reference Material:

Green synthesis

Questions:

Give list of m-directing group.

Give list of o and p directing group.

Developed by

Dr. Parin Kanaiya,

Assistant Professor, Chemistry

parin.kanaiya@gsfcuniversity.ac.in

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