Lead I by the Dithizone Method

Theory In solution, dithizone (diphenylthiocarbazone) exhibits tautomerism as shown below  

The enol-ioxm of Dithizone (I) behaves as monoprotic acid having a dissociation constant pKa = 4.7 upto a pH range of about 12 obviously, the acid proton is inherited due to the thiol moiety in (I). In reality, two kinds of metal dithizonates are invariably formed, namely  

They are of greater analytical value because of their high stability and greater solubility in organic solvents. 

The poor stability and miserable solubility in organic solvents render these products of insignificant analytical importance. 

however, pertinent to mention here that dithizone is an extremely sensitive reagent and, therefore, helps in the determination of lead either from a neutral or faintly alkaline medium to the extent of a few micrograms. 

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