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Determination of thiourea and some of its organic derivatives with sodium vanadate, hexacyanoferrate(III), Cerium(IV) sulphate, manganese(III) and manganese(IV)
Tulunr,~. Vol. 26. pp. 1049 to 1051 0 Pergamon Press Lid 1979. Printed in Great Britain
DETERMINATION OF THIOUREA AND SOME OF ITS ORGANIC DERIVATIVES WITH SODIUM VANADATE, HEXACYANOFERRATE(III), CERIUM(IV) SULPHATE, MANGANESE(II1) AND MANGANESE(IV) N. KRISHNAMURTHY,G. UPENDRA PRASADand K. RAMARAO Department of Chemistry. Andhra University, Waltair-530003. India (Received 10 January 1978. Revised 14 April 1979. Accepted 5 May 1979)
Summary-The determination of thiourea and some of its organic derivatives with sodium vanadate, hexacyanoferrate(III), cerium(IV) sulphate, manganese(II1) and manganese(IV) is described. A mixture of iodate and iodide is used as catalyst. Ferroin. N-phenylanthranilic acid and p-ethoxychrysoidine can be used as indicators.
Thiourea possesses several industrial, medicinal and analytical applications, and consequently its determination has received considerable attention. The
various methods used are based on its tendency to react with metals either to undergo desulphurization or complex formation, or on its quantitative oxidation to different products by various oxidants in acidic and alkaline media. They were reviewed by Gupta’ and Singh and Verma.2 The other methods were recently well documented by Cyganski3 The present work describes the determination of thiourea and some organic derivatives oiz., N-phenyl thiourea, N,N’-diethyl thiourea and N,N’-diphenyl thiourea with sodium vanadate, hexacyanoferrate(III), cerium (IV) sulphate, manganese(II1) and manganese(IV) by simple and direct titrimetric methods in presence of a mixture of iodate and iodide (as catalyst), with ferroin, N-phenylanthranilic acid or p-ethoxychrysoidine as indicator. EXPERIMENTAL Reagents
Thiourea and NJ’-diethyl thiourea: 0.1M solutions were prepared in distilled water and standardized.2*4 N-Phenyl thiourea and N,iV’-diphenyl thiourea: 0.1M solutions were prepared in 50% v/v sulphuric acid and standardized with potassium iodate’ Solutions (0.1M of cerium(IV) sulphate,4 potassium hexacyanoferrate(III).6 sodium vanadam* and manganese(III)6*7 and a 0.05M sohition of manaanese(IV)* were .nrenared . and standardized. Catalyst solution was prepared by mixing 20 ml of 0.1M potassium iodide and 4 ml of 0.1M potassium iodate and diluting to 250 ml. Ferroin (O.O25M), 0.1% N-phenylanthranilic acid and 0.1% p-ethoxychrysoidine solutions were prepared in distilled water.4 All other reagents used were of analytical reagent grade. Procedure
Enough IOM sulphuric acid is added to the sample to
give 6M acid concentration after titration with sodium vanadate, hexacyanoferrate(II1) or cerium(IV) sulphate, or 4M after titration with manganese(II1) or manganese(N). in a total volume of 100 ml. Then 5 ml of catalyst mixture are added, followed by dilution with distilled water so that the total volume at the equivalence point will be lOOmI. The solution is then titrated with the standardized oxidant, with 0.05 ml of ferroin or 0.2 ml of N-phenylanthranilic acid or p-ethoxychrysoidine solution as indicator.
RESULTSAND
DKXXJSSION
The difficulties encountered in the determination of thiourea and its organic derivatives with cerium(IV) sulphate, potassium hexacyanoferrate(II1) and manganese.(III) are widely discussed.1*2 Sodium vanadate and manganese(IV) have not previously been used for the direct determination of thiourea or its organic derivatives. We have now used all five titrants for the purpose, in sulphuric acid medium with a mixture of iodate and iodide as catalyst. The acid and the catalyst concentration ranges for a total volume of lOOm1 are given in Table 1. At concentrations of acid and catalyst below those given in the table, the reaction with sodium vanadate. or hexacyanoferrate(III) is slow, and with the other oxidants the reaction proceeds beyond the disulphide stage. At acid concentrations above those proposed, the reaction with cerium(IV) sulphate is slow, and with the other oxidants the reaction proceeds beyond the disulphide stage because the reaction between the catalyst and the reductant is slow. Larger volumes of the catalyst have no adverse effect, but small volumes are always preferable because the brown colour of larger amounts of iodine masks the colour change of the indicator. In the titration with hexacyanoferrate(II1) a white precipitate is formed at sulphuric acid concentrations above 4M, and increases as the titration progresses.
1049
1050
SHORT
COMMUNlCATlONS
Table 1. Conditions for the determination
of thiourea and some of its organic derivatives 0.1 N solns.
Species titrated
Titrant
Thiourea
N-Phenyl thiourea
N,N’-Diethyl thiourea
N,N’-Diphenyl thiourea
.
Catalyst, ml
Sodium vanadate Hexacyanoferrate(II1) Cerium(IV) sulphate Manganese(II1) Manganese(IV)
S-8 5-8 4-8 3-6 24
1.O-6.0 0.6-5.0 0.2-6.0 2.0-6.0 4.G6.0
5-8 4-8 -
1.04.0 0.24.0 -
Sodium vanadate Hexacyanoferrate(II1) Cerium(IV) sulphate Manganese(II1) Manganese(IV)
58 51 5-8 3-5 3-5
1.0-6.0 2.0-5.0 0.6-6.0 5.cL6.0 5.o-6.0
5-8 5-8 -
1.C%O 0.660
Sodium vanadate Hexacyanoferrate(II1) Cerium(IV) sulphate Manganese(III)
5-8 5-8 5-8 3-6
2.0-6.0 2.5-5.0 4.G6.0
5-8 5-8 5-8 -
l&4.0 1.0-4.0 2.ti.o
Sodium vanadate Hexacyanoferrate(II1) Cerium(IV) sulphate
67 6-7 6-8
0.5-5.0 2.c5.0 2.5-5.0
5-I 5-8 5-8
0.5-3.0 1.54.0 lG4.0
It is ferrocyanic acid, as pointed out by Bates et a1.,9 and confirmed by qualitative tests. The iodine produced by the acid and the catalyst mixture first oxidizes the thiourea or its derivatives to the disulphide, itself being reduced to iodide and re-oxidized by the titrant. At the end-point, when all the iodide has been converted into iodine, the first excess of titrant reacts with the indicator. With ferroin as indicator, its normal colour deepens and there is a brownish red precipitate just before the equivalence point. This is possibly due to the formation of the Fe(phen):+ -21; complex, as pointed out by Gopala Rao et ~1.” The colour change from brownish red precipitate to pale blue is sharp and the precipitate disappears. The colour change is from pink to yellow with p-ethoxychrysoidine and from yellow to violet with N-phenylanthranilic acid. Ferroin and p-ethoxychrysoidine can be added at the beginning but N-phenylanthranilic acid acid should preferably be added near the equivalence point, when the colour of iodine starts to appear, since the indicator is partially destroyed if added at the beginning.
Table 2. Determkation Substance determined Thiourea N-Phenyl thiourea N,N’-Diethyl thiourea N,N’-Diphenyl thiourea
0.01N solns. Acid, M Catalyst, ml
Acid, M
Sodium vanadate 37-150 (0.2) 70-280 (0.2) 65-264 (0.2) 41-416 (0.2)
l&5.0
-
With hexacyanoferrate(III), only ferroin is satisfactory as indicator. The indicator correction is negligible. The ranges of determination and coefficients of variation are given in Table 2. Quantitative results are not obtained in the titration of N,N’-diphenylthiourea with manganese(II1) and of NJ‘-diethylthiourea and of N,N’-diphenylthiourea with manganese(IV). High values are obtained when more than 0.6 mmole of thiourea or its derivatives is titrated with manganese(II1) or manganese(IV). The titrations can also be done with O.OlN solutions. Accurate results are obtained with sodium vanadate, hexacyanoferrate(II1) and cerium(IV) sulphate, but low results are obtained with manganese (III) and manganese(IV). The acid and catalyst concentrations are given in Table 1. The indicator correo tion is found to be 0.2ml with O.OlN oxidant solutions. The maximum relative error with respect to methods used for standardization ranged from 0.35 to 0.85%. hexaSastry I1 has reported that the conditional
of thiourea and some of its organic derivatives
Range of the substance determined, mg HexacyanoCerium(IV) Manganese ferrate(II1) sulphate (III) 37-150 (0.2) 7G280 (0.2) 65-264 (0.2) 41-416 (0.2)
37-l 50 (0.2) 70-280 (0.2) 65-264 (0.2) 4’1416 (0.2)
15-37 (0.3) 28-70 (0.3) 26%6 (0.4)
The values given in parentheses represent the maximum coefficient of variation (4 determinations).
Manganese (IV) 15-37 (0.3) 28-70 (0.3)
SHORT COMMUNlCATlONS
cyanoferrate(III)/(II) potential increases from 0.675 V in 0.48M sulphuric acid to 1.357 V in the 6.65U acid. Hence at the acidity used, hexacyanoferrate(II1) can oxidize ferroin. Acknowledgements--Two of us (G.U.P. and K.R.R.) desire to express their gratitude to the authorities of Andhra University, Waltair, for the award of Junior Research Fellowships (U.G.C.). REFERENCES I. P. C. Gupta, Z. Anal. Gem., 1963, l%, 412. 2. B. Singh and B. C. Verma, J. Sci. Ind. Rex, 1965, 2.4, 536.
TAL. 26/l I-E
1051
3. A. Cyganski, Talanta, 1978, 25, 52. 4. I. M. Kolthoff, R. Ijelcher~ _V. A. Stenger and G. Matsyama, Textbook of Volumetric Analysis, Vol. III, pp. 128,236,237,387,634. Interseience, New York, 1957. 5. B. Singh and B. C. Verma, Z. Anal. Gem., 1963, 194, 112. 6. A. Berka, J. Vulterin and J. Zyka, Newer Redox Tin-ants, p. 11. Pergamon, London, 1965. 7. C. 0. Ingamells, Talonta, 1959, 2, 171. 8. S. K. Mandal and B. R. Sanf ibid., 1976, 23, 485. 9. J. C. Bates, K. M. Davies and G. Stedman, J. Chem Sot. (Dalton), 1974, 246. 10. G. G. Rao. M. Gandikota and S. G. Viswanath. And Chim. Act& 1976, 87, 511. 11. G. S. Sastry, Ph.D. Thesis, Andhra University, 1965.
DETERMINATION OF THIOUREA AND SOME OF ITS ORGANIC DERIVATIVES WITH SODIUM VANADATE, HEXACYANOFERRATE(III), CERIUM(IV) SULPHATE, MANGANESE(II1) AND MANGANESE(IV) N. KRISHNAMURTHY,G. UPENDRA PRASADand K. RAMARAO Department of Chemistry. Andhra University, Waltair-530003. India (Received 10 January 1978. Revised 14 April 1979. Accepted 5 May 1979)
Summary-The determination of thiourea and some of its organic derivatives with sodium vanadate, hexacyanoferrate(III), cerium(IV) sulphate, manganese(II1) and manganese(IV) is described. A mixture of iodate and iodide is used as catalyst. Ferroin. N-phenylanthranilic acid and p-ethoxychrysoidine can be used as indicators.
Thiourea possesses several industrial, medicinal and analytical applications, and consequently its determination has received considerable attention. The
various methods used are based on its tendency to react with metals either to undergo desulphurization or complex formation, or on its quantitative oxidation to different products by various oxidants in acidic and alkaline media. They were reviewed by Gupta’ and Singh and Verma.2 The other methods were recently well documented by Cyganski3 The present work describes the determination of thiourea and some organic derivatives oiz., N-phenyl thiourea, N,N’-diethyl thiourea and N,N’-diphenyl thiourea with sodium vanadate, hexacyanoferrate(III), cerium (IV) sulphate, manganese(II1) and manganese(IV) by simple and direct titrimetric methods in presence of a mixture of iodate and iodide (as catalyst), with ferroin, N-phenylanthranilic acid or p-ethoxychrysoidine as indicator. EXPERIMENTAL Reagents
Thiourea and NJ’-diethyl thiourea: 0.1M solutions were prepared in distilled water and standardized.2*4 N-Phenyl thiourea and N,iV’-diphenyl thiourea: 0.1M solutions were prepared in 50% v/v sulphuric acid and standardized with potassium iodate’ Solutions (0.1M of cerium(IV) sulphate,4 potassium hexacyanoferrate(III).6 sodium vanadam* and manganese(III)6*7 and a 0.05M sohition of manaanese(IV)* were .nrenared . and standardized. Catalyst solution was prepared by mixing 20 ml of 0.1M potassium iodide and 4 ml of 0.1M potassium iodate and diluting to 250 ml. Ferroin (O.O25M), 0.1% N-phenylanthranilic acid and 0.1% p-ethoxychrysoidine solutions were prepared in distilled water.4 All other reagents used were of analytical reagent grade. Procedure
Enough IOM sulphuric acid is added to the sample to
give 6M acid concentration after titration with sodium vanadate, hexacyanoferrate(II1) or cerium(IV) sulphate, or 4M after titration with manganese(II1) or manganese(N). in a total volume of 100 ml. Then 5 ml of catalyst mixture are added, followed by dilution with distilled water so that the total volume at the equivalence point will be lOOmI. The solution is then titrated with the standardized oxidant, with 0.05 ml of ferroin or 0.2 ml of N-phenylanthranilic acid or p-ethoxychrysoidine solution as indicator.
RESULTSAND
DKXXJSSION
The difficulties encountered in the determination of thiourea and its organic derivatives with cerium(IV) sulphate, potassium hexacyanoferrate(II1) and manganese.(III) are widely discussed.1*2 Sodium vanadate and manganese(IV) have not previously been used for the direct determination of thiourea or its organic derivatives. We have now used all five titrants for the purpose, in sulphuric acid medium with a mixture of iodate and iodide as catalyst. The acid and the catalyst concentration ranges for a total volume of lOOm1 are given in Table 1. At concentrations of acid and catalyst below those given in the table, the reaction with sodium vanadate. or hexacyanoferrate(III) is slow, and with the other oxidants the reaction proceeds beyond the disulphide stage. At acid concentrations above those proposed, the reaction with cerium(IV) sulphate is slow, and with the other oxidants the reaction proceeds beyond the disulphide stage because the reaction between the catalyst and the reductant is slow. Larger volumes of the catalyst have no adverse effect, but small volumes are always preferable because the brown colour of larger amounts of iodine masks the colour change of the indicator. In the titration with hexacyanoferrate(II1) a white precipitate is formed at sulphuric acid concentrations above 4M, and increases as the titration progresses.
1049
1050
SHORT
COMMUNlCATlONS
Table 1. Conditions for the determination
of thiourea and some of its organic derivatives 0.1 N solns.
Species titrated
Titrant
Thiourea
N-Phenyl thiourea
N,N’-Diethyl thiourea
N,N’-Diphenyl thiourea
.
Catalyst, ml
Sodium vanadate Hexacyanoferrate(II1) Cerium(IV) sulphate Manganese(II1) Manganese(IV)
S-8 5-8 4-8 3-6 24
1.O-6.0 0.6-5.0 0.2-6.0 2.0-6.0 4.G6.0
5-8 4-8 -
1.04.0 0.24.0 -
Sodium vanadate Hexacyanoferrate(II1) Cerium(IV) sulphate Manganese(II1) Manganese(IV)
58 51 5-8 3-5 3-5
1.0-6.0 2.0-5.0 0.6-6.0 5.cL6.0 5.o-6.0
5-8 5-8 -
1.C%O 0.660
Sodium vanadate Hexacyanoferrate(II1) Cerium(IV) sulphate Manganese(III)
5-8 5-8 5-8 3-6
2.0-6.0 2.5-5.0 4.G6.0
5-8 5-8 5-8 -
l&4.0 1.0-4.0 2.ti.o
Sodium vanadate Hexacyanoferrate(II1) Cerium(IV) sulphate
67 6-7 6-8
0.5-5.0 2.c5.0 2.5-5.0
5-I 5-8 5-8
0.5-3.0 1.54.0 lG4.0
It is ferrocyanic acid, as pointed out by Bates et a1.,9 and confirmed by qualitative tests. The iodine produced by the acid and the catalyst mixture first oxidizes the thiourea or its derivatives to the disulphide, itself being reduced to iodide and re-oxidized by the titrant. At the end-point, when all the iodide has been converted into iodine, the first excess of titrant reacts with the indicator. With ferroin as indicator, its normal colour deepens and there is a brownish red precipitate just before the equivalence point. This is possibly due to the formation of the Fe(phen):+ -21; complex, as pointed out by Gopala Rao et ~1.” The colour change from brownish red precipitate to pale blue is sharp and the precipitate disappears. The colour change is from pink to yellow with p-ethoxychrysoidine and from yellow to violet with N-phenylanthranilic acid. Ferroin and p-ethoxychrysoidine can be added at the beginning but N-phenylanthranilic acid acid should preferably be added near the equivalence point, when the colour of iodine starts to appear, since the indicator is partially destroyed if added at the beginning.
Table 2. Determkation Substance determined Thiourea N-Phenyl thiourea N,N’-Diethyl thiourea N,N’-Diphenyl thiourea
0.01N solns. Acid, M Catalyst, ml
Acid, M
Sodium vanadate 37-150 (0.2) 70-280 (0.2) 65-264 (0.2) 41-416 (0.2)
l&5.0
-
With hexacyanoferrate(III), only ferroin is satisfactory as indicator. The indicator correction is negligible. The ranges of determination and coefficients of variation are given in Table 2. Quantitative results are not obtained in the titration of N,N’-diphenylthiourea with manganese(II1) and of NJ‘-diethylthiourea and of N,N’-diphenylthiourea with manganese(IV). High values are obtained when more than 0.6 mmole of thiourea or its derivatives is titrated with manganese(II1) or manganese(IV). The titrations can also be done with O.OlN solutions. Accurate results are obtained with sodium vanadate, hexacyanoferrate(II1) and cerium(IV) sulphate, but low results are obtained with manganese (III) and manganese(IV). The acid and catalyst concentrations are given in Table 1. The indicator correo tion is found to be 0.2ml with O.OlN oxidant solutions. The maximum relative error with respect to methods used for standardization ranged from 0.35 to 0.85%. hexaSastry I1 has reported that the conditional
of thiourea and some of its organic derivatives
Range of the substance determined, mg HexacyanoCerium(IV) Manganese ferrate(II1) sulphate (III) 37-150 (0.2) 7G280 (0.2) 65-264 (0.2) 41-416 (0.2)
37-l 50 (0.2) 70-280 (0.2) 65-264 (0.2) 4’1416 (0.2)
15-37 (0.3) 28-70 (0.3) 26%6 (0.4)
The values given in parentheses represent the maximum coefficient of variation (4 determinations).
Manganese (IV) 15-37 (0.3) 28-70 (0.3)
SHORT COMMUNlCATlONS
cyanoferrate(III)/(II) potential increases from 0.675 V in 0.48M sulphuric acid to 1.357 V in the 6.65U acid. Hence at the acidity used, hexacyanoferrate(II1) can oxidize ferroin. Acknowledgements--Two of us (G.U.P. and K.R.R.) desire to express their gratitude to the authorities of Andhra University, Waltair, for the award of Junior Research Fellowships (U.G.C.). REFERENCES I. P. C. Gupta, Z. Anal. Gem., 1963, l%, 412. 2. B. Singh and B. C. Verma, J. Sci. Ind. Rex, 1965, 2.4, 536.
TAL. 26/l I-E
1051
3. A. Cyganski, Talanta, 1978, 25, 52. 4. I. M. Kolthoff, R. Ijelcher~ _V. A. Stenger and G. Matsyama, Textbook of Volumetric Analysis, Vol. III, pp. 128,236,237,387,634. Interseience, New York, 1957. 5. B. Singh and B. C. Verma, Z. Anal. Gem., 1963, 194, 112. 6. A. Berka, J. Vulterin and J. Zyka, Newer Redox Tin-ants, p. 11. Pergamon, London, 1965. 7. C. 0. Ingamells, Talonta, 1959, 2, 171. 8. S. K. Mandal and B. R. Sanf ibid., 1976, 23, 485. 9. J. C. Bates, K. M. Davies and G. Stedman, J. Chem Sot. (Dalton), 1974, 246. 10. G. G. Rao. M. Gandikota and S. G. Viswanath. And Chim. Act& 1976, 87, 511. 11. G. S. Sastry, Ph.D. Thesis, Andhra University, 1965.