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Determination of thiourea and its organic derivatives with iodine trichloride
SHORT
Talenta, Vol. 24, pp. 515-516. Pergamon Press, 1977. Pnnted
515
COMMUNICATIONS
m Great Bntain.
DETERMINATION OF THIOUREA AND ITS ORGANIC DERIVATIVES WITH IODINE TRICHLORIDE KIUSHNA
K. !&WA, M. I’.
S~~~D~Y
Department of Chemistry, Government Science College, Jabalpur 482001, India and
SAMEER BOSE Department of Chemistry, University of Jabalpur, Jabalpur 482001, India
(Recerved 11 June 1976. Revised 1 February 1977. Accepted 11 February 1977)
Summary-Thiourea and its organic derivatives and thiosemicarbazide are determined in water, methanol or glacial acetic acid medium by reaction with an excess of iodine trichloride in the presence of mercuric chloride. The reaction is complete in 15 min. The excess of iodine trichloride is evaluated by adding potassium iodide and titrating the liberated iodine with thiosulphate. A variety of organic thioureas can be determined with an average accuracy and precision of 0.2%.
A number of oxidimetric methods have been published for the determination of thiourea and its organic derivatives. The most widely used procedure for thiourea involves oxidation with hypoiodite.’ The reaction is essentially complete in about 4 min and a longer reaction time of up to 30 min has no effect. Bromine in acid medium can also be used for thiourea.’ Gupta3 determined N-phenyl-, N,N’methylphenyl-, N,N-ethylphenyland N,N’-diphenylthrourea with bromate-bromide mixture in acid medium, and the first three of these with iodine in presence of sodium bicarbonate. In both cases the main reaction involves removal of sulphur from the thiourea to give the corresponding urea and sulphate. The iodimetric determination is limited to water-soluble thioureas. In bromimetric determination, the aryl group undergoes nuclear bromination and thus the total consumption of bromine varies with the sample. Unfortunately, even under the optimum conditions, the consumption of bromine differs from
Table 1. Determination
the theoretical and, therefore, an empirical correction has to be made. Tiwari and Pande4 titrated thiourea and its ally1 and phenyl derivatives with N-bromosuccinimide, the reaction products being thought to be the corresponding urea and elemental sulphur. Organic derivatives of thiourea are not particularly soluble in water, and this imposes a limit on the concentration range that can be analysed in aqueous medium. Verma and Bose5 titrated N-ph~yl~ioureas in glacial acetic acid with lead tetra-acetate. This procedure is not applicable to diphenyl and alkyl thioureas. A cerimetric titration in acetonitrile proposed by Verma and Kumar’ is applio able only to thiourea and its N-substituted alkyl derivatives. Phenyl iodosoacetate has also been applied in 4& 80% acetic acid to determine N-aryl and alkyl thioureas7 Hydrochloric acid solutions of iodine monochloride and iodine trichloride have been used extensively as analytical
of thioureas with iodine trichloride Purity, % Deviation, % Present method*
Thiourea Thiosemicarbazide N-Allylthiourea N-Methylthiourea N-Butylthiourea N-Phenylthiourea N-o-Tolylthiourea N-pAnisylthiourea N-m-Chlorophenylthiourea N-Phenyl-N’-methylthiourea N,N’-Diphenylthiourea sag-bias-Toiyl)t~ourea sy~-bi~Tolyl~hiourea 2-Methylthiouracil * Average of 8 determinations
98.2 99.5 97.6 99.1 96.4 98.9 98.6 97.8 99.6 96.8 99.8 99.3 98.4 99,o
Comparison method 98.0 99.3 97.4 99.2 96.1 99.3 98.2 97.6 99.4 97.2 99.5 99.0 98.1 98.7
Av.
Max
0.1 0.1
0.1 0.1
0.1 0.1
0.2 0.1 0.1 0.3 0.3 0.4 0.3 0.4 0.3 0.5 0.4 0.6
8:: 0.2 0.2 0.2 0.3 0.1 0.2 0.3 0.4
516
SHORT
COMMUNICATIONS
reagents. Kagan and co-workers*-” worked out volumetric determinations for many organic substances with these reagents, based on substitution, addition or oxidation reactions. In oxidations, they noted that both reagents react similarly. Thiourea is oxidized to its disulphide on titrating with iodine monochloride.’ A similar method is described for alkyl and aryl derivatives of thiourea.i3 These reagents have also been used for titrating mercap tans in presence of starch and iodide.14 A rapid and precise procedure is described in the present communi~tion for determination of thiourea and its alkyl and aryl derivatives with iodine trichloride. The samples are dissolved in water, methanol or glacial acetic acid and treated with an excess of iodine trichloride in the presence of a sufficient amount of mercuric ions. After completion of the reaction the excess of oxidant is evaluated iodimetritally. EXPERIMENTAL
Reagents Iodine trichlaride solution, O.lN. A simple method of preparation was u~ed,~ based on the reaction KI + 2KIOs + 12HCl+ 3ICls + 6H20. For 1 litre of 0.1N iodine trichloride, dissolve 3.57 g of potassium iodate in 100 ml of hot water. After cooling add 1.38 g of potassium iodide, 41.7 ml of concentrated hydrochloric acid and dilute to 1 htre. Standardize iodimetrically. Thioureas. As a check independent methods were used to determine the purity of samples. Thiourea’ and thiosemicarbazide” were determined by hypoiodite oxidation, alkylthioureas by non-aqueous cerimetric titration,6 phenylthioureas by bromine oxidation3 and Pb(TV) titration.’ Diphenylthiourea was determined by non-aqueous alkalimetric titrationI and other diarylthioureas and 2-methylthiouracil by total sulphur analysis by the volumetric Carius method.” The methanol and glacial acetic acid were reagent grade solvents. Procedure
loride and not iodide. This view is supported by the observation that on addition of excess of iodine trichloride to a suspension of mercuric iodide in water a clear solution results. In view of all this, the reaction of iodine trichloride with tbioureas in presence of mercury(H) can be written as follows: RNH . CS . NHR’ + 41Clj -I- 5H,O -+ RNH . CO. NEW + H2S0, + 4IClf 8HCl The reaction of thiosemicarbazide is ~NH, ’ cs . NHNH, i- 101cls + 8~~0 +2HCN + 2N, + 2H2S0., t 1OICl + 20HCl Similar products were proposed by Suchomelova and Zykar8 for the reaction of thiosemicarbazide with lead tetra-acetate. Semicarbazide reacts with iodine trichloride in the presence of mercury(H) according to the equation NH2. CO 1NHNH* + ICls -+HCN + Nz + ICI + 2HCl The reaction is quantitative and complete in 5 min with about 50% excess of oxidant added. In the absence of mercury(II), molecular iodine is liberated and if this is to be titrated extra care is needed to prevent the escape of iodine. Furthermore, the reaction becomes slow and a period of about 40 min is required for complete oxidation in the presence of about 200% excess of oxidant. The consumption of iodine trichlo~de is, however, the same as that in the presence of mercur~I1~ Iodine bichloride is a powerful oxidant and reacts with several compounds, Hydrazine, ascorbic acid, thiophene, hydrogen sulphide and mercaptans interfere seriously. Compounds that can be tolerated even when present in large amounts include glucose, alanine, formic acid, urea, glutaric acid, butylamine, diethylamine and carbon disulphide. Acknowledgement-Thanks are due to University Grants Commission, New Delhi, for financial assistance to K.K.V. REFERENCES 1.
Take a sample solution in water, methanol or glacial acetic acid, containing 0.02-0.1 meq of -NHCSNH- group, in a 200-ml flask with a ground-glass stopper. Add 10 ml of a saturated aqueous solution of mercuric chloride followed by about 100% excess of iodine trichloride solution, with swirling. Allow the flask to stand for 15 min. When 2-methylthi&racil is being determined, immerse the flask for 5 min in a water-bath heated to 60” and then cool. Add 20% aqueous solution of potassium iodide until the first formed brick-red precipitate of mercuric iodide dissolves, then 5 ml more. Titrate the liberated iodine with 0.04M thiosulphate delivered from a lo-ml burette, with starch as indicator. Run a blank determination.
RF.SULTS AND
DISCUSSION
The method yielded results accurate and precise to about 0.2% for a variety of thioureas. It is found that the amount of excess of oxidant has a marked effect on the reaction velocity. With 200% excess of the reagent the reaction is complete in about 5 min. Mercuric chloride is added to the reaction mixture, ostensibly to complex the iodide ions formed by reduction of iodine trichloride, but no mercuric iodide is apparently precipitated, presumably because the reduction product from the titrant is iodine monoch-
S. Skramovsky, Cusopis ~eskoslou. ~ek~a~tva,
1941,
21, 1.
2. L. Rosenthaler. Pharm. Actn Helv.. 1955, 3% 332. 3. P. C. Gupta, Analyst, 1963, 88. 896. 4. R. D. Tiwari and U. C. Pande. ibid.:1969. 94. 813. 5. K. K. Verma and S. Bose, J. Indian dhem. sot., 1973, 50.499. 6. B. C. Verma and S. Kumar, Talanta, 1973, 20, 916. 7. K. K. Verma, Z. Anal. Chem., 1975, 275. 287. 8. Y. A. Fialkov and F. E. Kagan, Ukrain. Khim. Zh., 1952, 18. 55.
9. A. I. Gengrinovich,
F. E. Kagan and Y. A. Fialkov,
Tr. Komis. po Analit Khim., Akad. Nauk SSSR, Otdel. Khim. Nauk, 1954, 5. 237. 10. F. E. Kagan, Ukrain. Khim. Zh., 1956, 22, 94. 11. F. E. Kagan and C. I. Shakh, ibid., 1957, 23, 537. 12. J. Cihalii and J. RtiiEka, Chem. Listy, 1955, 49, 1176. 13. B. Singh, B. C. Verma and M. S. Saran, J. Indian Chem. Sot., 1962,,39. 211. 14. A. Srivastava and S. Bose, ibid., 1974, 51. 736. 15. N. D. Cheronis and T. S. Ma, Oraanic Functional Group Analysis, p. 541. Interscience, New York, 1964. 16. J. S. Fritz, Anal. Chem., 1952, 24, 674. 17. A. Steyermark, Quantitatioe Organic Micro-analysis. p.
276. Academic Press, New York, 1961. 18. L. Suchomelova and J. Zyka, J. Electroanal. Chem., 1963, 5. 57.
Talenta, Vol. 24, pp. 515-516. Pergamon Press, 1977. Pnnted
515
COMMUNICATIONS
m Great Bntain.
DETERMINATION OF THIOUREA AND ITS ORGANIC DERIVATIVES WITH IODINE TRICHLORIDE KIUSHNA
K. !&WA, M. I’.
S~~~D~Y
Department of Chemistry, Government Science College, Jabalpur 482001, India and
SAMEER BOSE Department of Chemistry, University of Jabalpur, Jabalpur 482001, India
(Recerved 11 June 1976. Revised 1 February 1977. Accepted 11 February 1977)
Summary-Thiourea and its organic derivatives and thiosemicarbazide are determined in water, methanol or glacial acetic acid medium by reaction with an excess of iodine trichloride in the presence of mercuric chloride. The reaction is complete in 15 min. The excess of iodine trichloride is evaluated by adding potassium iodide and titrating the liberated iodine with thiosulphate. A variety of organic thioureas can be determined with an average accuracy and precision of 0.2%.
A number of oxidimetric methods have been published for the determination of thiourea and its organic derivatives. The most widely used procedure for thiourea involves oxidation with hypoiodite.’ The reaction is essentially complete in about 4 min and a longer reaction time of up to 30 min has no effect. Bromine in acid medium can also be used for thiourea.’ Gupta3 determined N-phenyl-, N,N’methylphenyl-, N,N-ethylphenyland N,N’-diphenylthrourea with bromate-bromide mixture in acid medium, and the first three of these with iodine in presence of sodium bicarbonate. In both cases the main reaction involves removal of sulphur from the thiourea to give the corresponding urea and sulphate. The iodimetric determination is limited to water-soluble thioureas. In bromimetric determination, the aryl group undergoes nuclear bromination and thus the total consumption of bromine varies with the sample. Unfortunately, even under the optimum conditions, the consumption of bromine differs from
Table 1. Determination
the theoretical and, therefore, an empirical correction has to be made. Tiwari and Pande4 titrated thiourea and its ally1 and phenyl derivatives with N-bromosuccinimide, the reaction products being thought to be the corresponding urea and elemental sulphur. Organic derivatives of thiourea are not particularly soluble in water, and this imposes a limit on the concentration range that can be analysed in aqueous medium. Verma and Bose5 titrated N-ph~yl~ioureas in glacial acetic acid with lead tetra-acetate. This procedure is not applicable to diphenyl and alkyl thioureas. A cerimetric titration in acetonitrile proposed by Verma and Kumar’ is applio able only to thiourea and its N-substituted alkyl derivatives. Phenyl iodosoacetate has also been applied in 4& 80% acetic acid to determine N-aryl and alkyl thioureas7 Hydrochloric acid solutions of iodine monochloride and iodine trichloride have been used extensively as analytical
of thioureas with iodine trichloride Purity, % Deviation, % Present method*
Thiourea Thiosemicarbazide N-Allylthiourea N-Methylthiourea N-Butylthiourea N-Phenylthiourea N-o-Tolylthiourea N-pAnisylthiourea N-m-Chlorophenylthiourea N-Phenyl-N’-methylthiourea N,N’-Diphenylthiourea sag-bias-Toiyl)t~ourea sy~-bi~Tolyl~hiourea 2-Methylthiouracil * Average of 8 determinations
98.2 99.5 97.6 99.1 96.4 98.9 98.6 97.8 99.6 96.8 99.8 99.3 98.4 99,o
Comparison method 98.0 99.3 97.4 99.2 96.1 99.3 98.2 97.6 99.4 97.2 99.5 99.0 98.1 98.7
Av.
Max
0.1 0.1
0.1 0.1
0.1 0.1
0.2 0.1 0.1 0.3 0.3 0.4 0.3 0.4 0.3 0.5 0.4 0.6
8:: 0.2 0.2 0.2 0.3 0.1 0.2 0.3 0.4
516
SHORT
COMMUNICATIONS
reagents. Kagan and co-workers*-” worked out volumetric determinations for many organic substances with these reagents, based on substitution, addition or oxidation reactions. In oxidations, they noted that both reagents react similarly. Thiourea is oxidized to its disulphide on titrating with iodine monochloride.’ A similar method is described for alkyl and aryl derivatives of thiourea.i3 These reagents have also been used for titrating mercap tans in presence of starch and iodide.14 A rapid and precise procedure is described in the present communi~tion for determination of thiourea and its alkyl and aryl derivatives with iodine trichloride. The samples are dissolved in water, methanol or glacial acetic acid and treated with an excess of iodine trichloride in the presence of a sufficient amount of mercuric ions. After completion of the reaction the excess of oxidant is evaluated iodimetritally. EXPERIMENTAL
Reagents Iodine trichlaride solution, O.lN. A simple method of preparation was u~ed,~ based on the reaction KI + 2KIOs + 12HCl+ 3ICls + 6H20. For 1 litre of 0.1N iodine trichloride, dissolve 3.57 g of potassium iodate in 100 ml of hot water. After cooling add 1.38 g of potassium iodide, 41.7 ml of concentrated hydrochloric acid and dilute to 1 htre. Standardize iodimetrically. Thioureas. As a check independent methods were used to determine the purity of samples. Thiourea’ and thiosemicarbazide” were determined by hypoiodite oxidation, alkylthioureas by non-aqueous cerimetric titration,6 phenylthioureas by bromine oxidation3 and Pb(TV) titration.’ Diphenylthiourea was determined by non-aqueous alkalimetric titrationI and other diarylthioureas and 2-methylthiouracil by total sulphur analysis by the volumetric Carius method.” The methanol and glacial acetic acid were reagent grade solvents. Procedure
loride and not iodide. This view is supported by the observation that on addition of excess of iodine trichloride to a suspension of mercuric iodide in water a clear solution results. In view of all this, the reaction of iodine trichloride with tbioureas in presence of mercury(H) can be written as follows: RNH . CS . NHR’ + 41Clj -I- 5H,O -+ RNH . CO. NEW + H2S0, + 4IClf 8HCl The reaction of thiosemicarbazide is ~NH, ’ cs . NHNH, i- 101cls + 8~~0 +2HCN + 2N, + 2H2S0., t 1OICl + 20HCl Similar products were proposed by Suchomelova and Zykar8 for the reaction of thiosemicarbazide with lead tetra-acetate. Semicarbazide reacts with iodine trichloride in the presence of mercury(H) according to the equation NH2. CO 1NHNH* + ICls -+HCN + Nz + ICI + 2HCl The reaction is quantitative and complete in 5 min with about 50% excess of oxidant added. In the absence of mercury(II), molecular iodine is liberated and if this is to be titrated extra care is needed to prevent the escape of iodine. Furthermore, the reaction becomes slow and a period of about 40 min is required for complete oxidation in the presence of about 200% excess of oxidant. The consumption of iodine trichlo~de is, however, the same as that in the presence of mercur~I1~ Iodine bichloride is a powerful oxidant and reacts with several compounds, Hydrazine, ascorbic acid, thiophene, hydrogen sulphide and mercaptans interfere seriously. Compounds that can be tolerated even when present in large amounts include glucose, alanine, formic acid, urea, glutaric acid, butylamine, diethylamine and carbon disulphide. Acknowledgement-Thanks are due to University Grants Commission, New Delhi, for financial assistance to K.K.V. REFERENCES 1.
Take a sample solution in water, methanol or glacial acetic acid, containing 0.02-0.1 meq of -NHCSNH- group, in a 200-ml flask with a ground-glass stopper. Add 10 ml of a saturated aqueous solution of mercuric chloride followed by about 100% excess of iodine trichloride solution, with swirling. Allow the flask to stand for 15 min. When 2-methylthi&racil is being determined, immerse the flask for 5 min in a water-bath heated to 60” and then cool. Add 20% aqueous solution of potassium iodide until the first formed brick-red precipitate of mercuric iodide dissolves, then 5 ml more. Titrate the liberated iodine with 0.04M thiosulphate delivered from a lo-ml burette, with starch as indicator. Run a blank determination.
RF.SULTS AND
DISCUSSION
The method yielded results accurate and precise to about 0.2% for a variety of thioureas. It is found that the amount of excess of oxidant has a marked effect on the reaction velocity. With 200% excess of the reagent the reaction is complete in about 5 min. Mercuric chloride is added to the reaction mixture, ostensibly to complex the iodide ions formed by reduction of iodine trichloride, but no mercuric iodide is apparently precipitated, presumably because the reduction product from the titrant is iodine monoch-
S. Skramovsky, Cusopis ~eskoslou. ~ek~a~tva,
1941,
21, 1.
2. L. Rosenthaler. Pharm. Actn Helv.. 1955, 3% 332. 3. P. C. Gupta, Analyst, 1963, 88. 896. 4. R. D. Tiwari and U. C. Pande. ibid.:1969. 94. 813. 5. K. K. Verma and S. Bose, J. Indian dhem. sot., 1973, 50.499. 6. B. C. Verma and S. Kumar, Talanta, 1973, 20, 916. 7. K. K. Verma, Z. Anal. Chem., 1975, 275. 287. 8. Y. A. Fialkov and F. E. Kagan, Ukrain. Khim. Zh., 1952, 18. 55.
9. A. I. Gengrinovich,
F. E. Kagan and Y. A. Fialkov,
Tr. Komis. po Analit Khim., Akad. Nauk SSSR, Otdel. Khim. Nauk, 1954, 5. 237. 10. F. E. Kagan, Ukrain. Khim. Zh., 1956, 22, 94. 11. F. E. Kagan and C. I. Shakh, ibid., 1957, 23, 537. 12. J. Cihalii and J. RtiiEka, Chem. Listy, 1955, 49, 1176. 13. B. Singh, B. C. Verma and M. S. Saran, J. Indian Chem. Sot., 1962,,39. 211. 14. A. Srivastava and S. Bose, ibid., 1974, 51. 736. 15. N. D. Cheronis and T. S. Ma, Oraanic Functional Group Analysis, p. 541. Interscience, New York, 1964. 16. J. S. Fritz, Anal. Chem., 1952, 24, 674. 17. A. Steyermark, Quantitatioe Organic Micro-analysis. p.
276. Academic Press, New York, 1961. 18. L. Suchomelova and J. Zyka, J. Electroanal. Chem., 1963, 5. 57.