To perform the assay of Benzyl penicillin.

 Experiment

Aim:

 To perform the assay of Benzyl penicillin.

 Structure:

Molecular Formula: 

C16H12N2045

Mol. Wt.:

 356.4 g/mol

Category: 

Antibacterial.

Theory: 

(Iodimetric assay)

Benzyl penicillin does not react with iodine in neutral aqueous medium. In alkaline

medium, the alkaline penicillin is decomposed giving penicilloic acid which can be oxidized by known excess standard iodine and the excess unused is back titrated against standard sodium thiosulfate using starch as an indicator.

Procedure:

• Reconstitute one vial of benzylpenicillin with water, transfer the solution into 200 ml measuring flask, wash the bottle three times with water, transfer the washing into

the measuring flask and complete to the mark with water.

• Transfer 5.0 ml into glass stoppered conical flask, add 5.0 ml 1.0 M NaOH and stand for 30 minutes over a boiling water bath.Cool, and then add 7.0 ml 1.0 M HCl followed by 25.0 ml 0.02 M iodine.

•Allow to stand for 15 minutes then titrate the excess iodine against 0.02 M sodium

thiosulfate (Na2S2O3) using starch as an indicator (starch is added when solution

colour becomes straw yellow).

Results and calculations:

4 Moles iodine = 1 mole benzylpenicillin iodine = 1/4 Benzylpenicillin.

1ml M iodine =Molecular Wt. of benzylpenicillin Molar ratio x Molarity

                   1000       

 = 1 mole of iodine = 2 mole Na2S204

Use: 

It is used as antibacterial drug.

Reference:

Dr. Abhishek Tiwari, Dr. Rajeev Kumar " A practical book of medicinal chemistry" Nirali Prakashan Pune 2019 pp 72-73

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