N-α-Pyridyl-N'-Benzoyl Thiourea as a Chelating Agent for the Determination of Rhodium

Chemical Laboratories, Presidency College, Calcutta-700 012 Manuscript received 4 November 1976, accepted 18 June 1977 N-\( \alpha\)-pyridyl-N'-benzoyl thiourea is a useful chelating agent for the gravimetric as well as spectrophotometric determination of rhodium(III). The metal chelate is precipitated In the pH range of 3.5 to 5.5 and can be weighed as Rh(C13H10N3OS)3. Rhodium(III) is determined gravimetrically with the thio-ligand In presence of palladium(II), platinum(IV), iridium(IV), osmium(VI), ruthenium(III) and commonly associated base metals by the use of masking agents or controlling the acidity of the solution. The light brown chelate formed by rhodium with N-\( \alpha\)-pyridyl-N'-benzoyl thiourea can be extracted quantitatively with chloroform in the pH range 5.24-6.3 in presence of ethanol. The extract obeys Beer's law at 360 nm over the concentration ranging from 0.69 \(\mu\)g Rh ml-1 to 6.9\(\mu\)g Rh ml-1.The colour of the extract is stable for 24 hours. It is possible to determine microgram quantities of rhodiun(III) spectrophotometrically using N-\( \alpha\)-pyridyl-N'-benzoyl thiourea as a colour forming reagent in presence of most of base metals and all other platinm metals. The sensitivity of the colour reaction and the molar absorptivity of the complex are 0.0102\(\mu\)g Rh cm-2 and 9.54x 103 1.mole-1 cm-1 respectively. Gyanide ion, however, Interferes with the spectrophotometry of the metal