- Email: [email protected]
The determination of thiourea
MICROCHEMICAL
JOURNAL
VOL.
The Determination
JOSEPH
F. ALICIKO,
IV,
PAGES
551-553
(1960)
of Thiourea
Squibb Institute for Medical Brunswick, New Jersey
Research, New
Iodimetric, argent)imetric, and oxidimebric methods have been used for the determination of thiourea,’ a compound which has had for years, some medical use. A simple and rapid titration with perchloric acid in glacial acetic acid can be used as the basis for a new met,hod for determining t,his compound. In the conventional method for the titration of bases, urea is too weak a base to be titrated. Recently,2 however, it has been shown that under certain conditions and the employment of acetic anhydride a quantitative response may be obtained. Gutterson and Ma3 discuss the behavior of urea in various solvents. The addition of mercuric acetate to urea in glacial acetic acid has no effect on the consumption of perchloric acid. However, by the use of mercuric acetat’e in the titration of thiourea, quantitative result’s are obtained.
Reagents Perchloric Acid Xolution. The preparation of O.lN solution has often been described.4-7 The O.OlN solution was prepared by simple dilution with glacial acetic acid. Mercuric Acetate. The mercuric acetate reagent used consisted of 30 g. of mercuric acetate dissolved in 1000 ml. of glacial acetic acid. Glacial Acetic Acid. Reagent grade glacial acetic acid was used. Indicator. Crystal Violet, 0.1% in glacial acetic acid, may be used, but 0.1% Quinaldine Red in glacial acetic acid gives a sharper endpoint. 551
552
J. F. ALICINO
Procedure A portion (3-5 mg.) of sample is dissolved in 5 ml. of glacial acetic acid, with warming, if necessary, to facilitate solution; 1 ml. of mercuric acetate solution, together with one drop of indicator is added. In the case when Crystal Violet is used, the endpoint is reached when the purple color changes to green; in the case of Quinaldine Red, the solution turns from pink to colorless. A blank is run on the same quantities of solvent, indicator, and mercuric acetate and should be less than 0.1 ml. of O.OlN HClOd (1 ml. of O.OlN HClO, is equivalent to 0.761 mg. of thiourea). Typical results are shown in Tables I and II. TABLE Microtitration
Sample w.
wt.,
I of Thiourea
Vol. of O.OlN HClO+ ml.
3.805 4.946 6.706 4.697
Thiourea, %
5.00 6.47 8.84 6.17
TABLE Macrotitration
100.0 99.6 100.3 99.9
II of Thiourea
Vol. Sa,mple mg. 49.40 94.90 41.85 33.94
wt.,
O.lN
of HC104, ml.
Thiourea, %
6.49 12.46 5.50 4.45
100.0 99.9 100.0 99.8
Discussion A useful application of the nonaqueous method of titrating thiourea was suggested in determining the composition of certain t,hiourea adducts of certain hydrocarbons. In a study8 with squalene and isooctane the number of moles of thiourea was determined by direct titration. By this technique it was established that as many as 12 MICROCHEMICAL
JOURNAL,
VOL.
IV,
ISSUE
1
DETERMINATION
OF
THIOUREA
553
moles of thiourea could combine with the hydrocarbon. These findings were substantiated by carbon, hydrogen, and sulfur analyses as well as other evidence. In an attempt to extend the scope of this method, some experiments with thiouracil were conducted. The results with thiouracil revealed the fact that this substance could also be titrated, but that the endpoint was reached at a slower rate. The difficulty was resolved by adding a known excess of perchloric acid and backtitrating with pot.assium acid phthalate after 10 min. The results calculated as neut’ralization equivalent are shown in Table III. TABLE III Thiouracil Calc.
Found
128.1
122 124 125 124
Conclusion Thiourea in the presence of mercuric acetate can be titrated with perchloric acid in glacial acetic acid. This procedure can be applied to thiouracil and may also be useful in dealing with other similar compounds containing sulfur.
References 1. Dal Nogare, S., in Organic Bnalysis, Vol. 1, Interscience, New York, 1953, Chap. 8. 2. Streuli, C. A., Anal. Chem., 30, 997 (1958). 3. Gutterson, I)., and T. S. Ma, Mikrochim. Acta, 1960, 1. 4. Markunas, P. C., and J. A. Riddick, Anal. Chem., 23, 337 (1951). 5. Fritz, J. S., Acid Base Titrations in Non-Aqueous Solvents, G. Frederick Smith Chemical Co., Columbus, Ohio, 1952. 6. Pifer, C. W., E. G. Wollish, and M. Schmall, J. Am. Pharm. Assoc., Sci. Ed., 42, 509 (1953). 7. Fritz, J. S., and G. P. Hammond, Quantitative Organic Analysis, Wiley, New York, 1957, Chap. 3. 8. Eidenoff, M. L., private communication.
Received May
1, 1960
JOURNAL
VOL.
The Determination
JOSEPH
F. ALICIKO,
IV,
PAGES
551-553
(1960)
of Thiourea
Squibb Institute for Medical Brunswick, New Jersey
Research, New
Iodimetric, argent)imetric, and oxidimebric methods have been used for the determination of thiourea,’ a compound which has had for years, some medical use. A simple and rapid titration with perchloric acid in glacial acetic acid can be used as the basis for a new met,hod for determining t,his compound. In the conventional method for the titration of bases, urea is too weak a base to be titrated. Recently,2 however, it has been shown that under certain conditions and the employment of acetic anhydride a quantitative response may be obtained. Gutterson and Ma3 discuss the behavior of urea in various solvents. The addition of mercuric acetate to urea in glacial acetic acid has no effect on the consumption of perchloric acid. However, by the use of mercuric acetat’e in the titration of thiourea, quantitative result’s are obtained.
Reagents Perchloric Acid Xolution. The preparation of O.lN solution has often been described.4-7 The O.OlN solution was prepared by simple dilution with glacial acetic acid. Mercuric Acetate. The mercuric acetate reagent used consisted of 30 g. of mercuric acetate dissolved in 1000 ml. of glacial acetic acid. Glacial Acetic Acid. Reagent grade glacial acetic acid was used. Indicator. Crystal Violet, 0.1% in glacial acetic acid, may be used, but 0.1% Quinaldine Red in glacial acetic acid gives a sharper endpoint. 551
552
J. F. ALICINO
Procedure A portion (3-5 mg.) of sample is dissolved in 5 ml. of glacial acetic acid, with warming, if necessary, to facilitate solution; 1 ml. of mercuric acetate solution, together with one drop of indicator is added. In the case when Crystal Violet is used, the endpoint is reached when the purple color changes to green; in the case of Quinaldine Red, the solution turns from pink to colorless. A blank is run on the same quantities of solvent, indicator, and mercuric acetate and should be less than 0.1 ml. of O.OlN HClOd (1 ml. of O.OlN HClO, is equivalent to 0.761 mg. of thiourea). Typical results are shown in Tables I and II. TABLE Microtitration
Sample w.
wt.,
I of Thiourea
Vol. of O.OlN HClO+ ml.
3.805 4.946 6.706 4.697
Thiourea, %
5.00 6.47 8.84 6.17
TABLE Macrotitration
100.0 99.6 100.3 99.9
II of Thiourea
Vol. Sa,mple mg. 49.40 94.90 41.85 33.94
wt.,
O.lN
of HC104, ml.
Thiourea, %
6.49 12.46 5.50 4.45
100.0 99.9 100.0 99.8
Discussion A useful application of the nonaqueous method of titrating thiourea was suggested in determining the composition of certain t,hiourea adducts of certain hydrocarbons. In a study8 with squalene and isooctane the number of moles of thiourea was determined by direct titration. By this technique it was established that as many as 12 MICROCHEMICAL
JOURNAL,
VOL.
IV,
ISSUE
1
DETERMINATION
OF
THIOUREA
553
moles of thiourea could combine with the hydrocarbon. These findings were substantiated by carbon, hydrogen, and sulfur analyses as well as other evidence. In an attempt to extend the scope of this method, some experiments with thiouracil were conducted. The results with thiouracil revealed the fact that this substance could also be titrated, but that the endpoint was reached at a slower rate. The difficulty was resolved by adding a known excess of perchloric acid and backtitrating with pot.assium acid phthalate after 10 min. The results calculated as neut’ralization equivalent are shown in Table III. TABLE III Thiouracil Calc.
Found
128.1
122 124 125 124
Conclusion Thiourea in the presence of mercuric acetate can be titrated with perchloric acid in glacial acetic acid. This procedure can be applied to thiouracil and may also be useful in dealing with other similar compounds containing sulfur.
References 1. Dal Nogare, S., in Organic Bnalysis, Vol. 1, Interscience, New York, 1953, Chap. 8. 2. Streuli, C. A., Anal. Chem., 30, 997 (1958). 3. Gutterson, I)., and T. S. Ma, Mikrochim. Acta, 1960, 1. 4. Markunas, P. C., and J. A. Riddick, Anal. Chem., 23, 337 (1951). 5. Fritz, J. S., Acid Base Titrations in Non-Aqueous Solvents, G. Frederick Smith Chemical Co., Columbus, Ohio, 1952. 6. Pifer, C. W., E. G. Wollish, and M. Schmall, J. Am. Pharm. Assoc., Sci. Ed., 42, 509 (1953). 7. Fritz, J. S., and G. P. Hammond, Quantitative Organic Analysis, Wiley, New York, 1957, Chap. 3. 8. Eidenoff, M. L., private communication.
Received May
1, 1960