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Determination of orthoesters by hydrolysis and Karl Fischer titrimetry
531
Short communications
0.4 and 25 mg. With higher amounts of mercury, the intermediate straight line gradually became parallel to the volume axis, consequently leading to erroneous results. The above phenomenon can be explained by the stepwise complex formation of mercury with the ligand. Evidently, at the lower ligand concentration a 1: 1 complex is formed, and this changes to a 1: 2 complex when the reagent is in excess. Some results are tabulated in Table I. Research and Control Laboratory Durgapur Steel Plant, Durgapur-3 West Bengal, India
BJMAL C. BERA MADAN M. CHAKRABARTTY
Inorganic Chemistry Department Jadavpur University Calcutta-32, India
SASWATI P. BAG
Department of Chemistry University of Utah, Salt Lake City Utah, U.S.A.
KANAI L. MALLIK
Summary-Amperometric titration of mercury (in the range of 0.4 to 3.5 mg) has been carried out with 2-mercaptobenzoxazole with a stationary electrode in stirred solution in a sodium acetate-acetic acid medium. Zusammenfassung_Quecksilber (0,4-3,5 mg) wurde mit einer ruhenden Elektrode in geriihrter Natriumacetat-Essigs&ue-Losung mit 2-Mercaptobenzoxazol amperometrisch titriert. R&sum6-On a r&alise le dosage amp&om&rique du mercure (de 0,4 a 3,5 mg) au moyen de 2-mercaptobenzoxazole avec une electrode stationnaire dans une solution sous agitation, en milieu acetate de sodium-acide ac&ique. REFERENCES 1 K. L. Mallik, Chem. Znd. (London), 1965, 724. a B. C. Bera and M. M. Chakrabartty, J. Indian Chem. Sot., in press. a Idem, Anal. Chim. Acta, in press. d A. I. Vogel, A Text Rook of Quantitative Inorganic Analysis, 3rd Ed. London, 1961.
Longmans,
Green 8~ Co.,
Determination of orthoesters by hydrolysis and Karl Fischer titrimetry (Received 10 September 1965. Accepted 22 October 1965) A simple, rapid analytical method for orthoesters was needed. To meet this need, a titrimetric method based on the acid hydrolysis of orthoesters was developed. Orthoesters can be quantitatively hydrolysed to carboxylic esters by shaking with water:’
R-C(OR’)s
0 II + H,O + R-C-OR’
+ 2R’OH.
The reaction is catalysed by acid.as8 The method we have developed involves adding an orthoester sample to a standard solution of water in trichloroacetic acid-methyl alcohol. After a timed reaction period, umeacted water is determined by Karl Frscher titration. This method is an altematrve to the aquametric procedure described by Smith et aZ.’which involves water formation by reaction with a boron trifluoride-acetic acid reagent. Our method is faster and requires no heating.
532
Short communications EXPERIMENTAL
Reagents and apparatus All of the orthoesters and the trichloroacetic acid used in this work were obtained from the J. T. Baker Chemical Company. Karl Fischer stahlised reagent was obtained from Fisher Scientific Company. A water solution was prepared by pipetting 10.0 ml of distilled water into a one 1. volumetric flask and diluting to volume with dry methyl alcohol. A trichloroacetlc acid solution was prepared by weighing 125 g of reagent-grade trichloroacetic acid into a 500-ml volumetric flask, and dissolvmg and diluting to volume with dry methyl alcohol. All flasks were dried at 110” for 30 min before use. Procedure Pipette 10.0 ml of trichloroacetic acid-methyl alcohol solution and 2@0 ml of water-methyl alcohol solution into a 125~ml glass stoppered Erlenmeyer flask. Add l-l.5 g of the orthoester sample, stopper the flask and allow the solution to stand 45 min with occasional swirling. Titrate the solution with Karl Fischer reagent. Also, titrate a reagent blank which has also stood for 45 min. Calculate the percentage of orthoester as follows: “/ = (V, - V,)(f)(M) 0 180.2(n)(W) where:
and
V, = V, = f = M = n = W =
volume of Karl Fischer reagent required to titrate blank (ml), volume of Karl Fischer reagent required to titrate sample (ml), Karl Fischer reagent standardlsation factor (mg of H,O/ml of reagent), molecular weight of orthoester, orthoester groups per molecule, weight of sample used (g).
RESULTS AND DISCUSSION This procedure was used in the analysis of four commercially available orthoesters. shown in Table I. TABLE L-ASSAY
The results are
OF ORTHOESTERS
Orthoester, Compound Triethyl orthoacetate, practical grade Triethyl orthopropionate, practical grade Trimethyl orthoformate, reagent grade Triethyl orthoformate, reagent grade
wt. % 95.2 94.8 98.8 99.2
The trichloroacetic acid-methyl alcohol reagent undergoes a slow esterification, producing a very small amount of water in the system. It is, therefore, important that blanks and samples stand the same length of time before titration. If this is done, no significant error is introduced. Because carboxylic esters are most likely impurnies in orthoesters, several were checked for interferences. No interference was found. Acknowledgement-The authors wish to thank Mr. I. Saleh and Mr. D. A. Danald for making many of the determinations used in this work. Research Division W. R. GRACE & Company Clarksville, Maryland, 21029, U.S.A.
DONALD J. CLANCY DAVID E. KRAMM
Summary-The acid hydrolysis of orthoesters has been made the basis of a titrimetric method. The method involves reaction of an orthoester with a known excess of water in a trichloroacetic acid-methyl alcohol system, followed by determination of unreacted water by Karl Fischer titration. Zusammenfassung--Die saure Hydrolyse von Orthoestern wurde zu einer titrimetrischen Bestimmungsmethode verwertet. Man hiI% den
Short communications Orthoestermiteinembekannten WasseriiberschuD in einemTrichloressigsaure-Methanol-System reagieren und bestimmt das nicht umgesetzte Wasser durch Karl Fischer-Titration. R&um?--L’hydrolyse acide des orthoesters a Bte prise pour base dune methode titrimetrique. La mtthode comprend la reaction d’un orthoester avec un exc& connu d’eau dans un systeme acide trichlorac& tique-methanol, suivie du dosage de l’eau qui n’a pas reagi par titrage selon Karl Fischer. REFERENCES 1 V. * H. 8 C. 4 D.
Migrdichian, Organic Synthesis, Vol. l., p. 332. Reinhold, New York, 1957. Kwart and M. B. Price, J. Am. Chem. Sot., 1960,82,5123. R. Noller in W. B. Saunders, Chemistry of Organic Compounds, 2nd ed., p. 175, 1957. M. Smith, J. Mitchell, Jr. and W. Hawkins, J. Am. Chem. Sot., 1944, 66, 715.
533
Short communications
0.4 and 25 mg. With higher amounts of mercury, the intermediate straight line gradually became parallel to the volume axis, consequently leading to erroneous results. The above phenomenon can be explained by the stepwise complex formation of mercury with the ligand. Evidently, at the lower ligand concentration a 1: 1 complex is formed, and this changes to a 1: 2 complex when the reagent is in excess. Some results are tabulated in Table I. Research and Control Laboratory Durgapur Steel Plant, Durgapur-3 West Bengal, India
BJMAL C. BERA MADAN M. CHAKRABARTTY
Inorganic Chemistry Department Jadavpur University Calcutta-32, India
SASWATI P. BAG
Department of Chemistry University of Utah, Salt Lake City Utah, U.S.A.
KANAI L. MALLIK
Summary-Amperometric titration of mercury (in the range of 0.4 to 3.5 mg) has been carried out with 2-mercaptobenzoxazole with a stationary electrode in stirred solution in a sodium acetate-acetic acid medium. Zusammenfassung_Quecksilber (0,4-3,5 mg) wurde mit einer ruhenden Elektrode in geriihrter Natriumacetat-Essigs&ue-Losung mit 2-Mercaptobenzoxazol amperometrisch titriert. R&sum6-On a r&alise le dosage amp&om&rique du mercure (de 0,4 a 3,5 mg) au moyen de 2-mercaptobenzoxazole avec une electrode stationnaire dans une solution sous agitation, en milieu acetate de sodium-acide ac&ique. REFERENCES 1 K. L. Mallik, Chem. Znd. (London), 1965, 724. a B. C. Bera and M. M. Chakrabartty, J. Indian Chem. Sot., in press. a Idem, Anal. Chim. Acta, in press. d A. I. Vogel, A Text Rook of Quantitative Inorganic Analysis, 3rd Ed. London, 1961.
Longmans,
Green 8~ Co.,
Determination of orthoesters by hydrolysis and Karl Fischer titrimetry (Received 10 September 1965. Accepted 22 October 1965) A simple, rapid analytical method for orthoesters was needed. To meet this need, a titrimetric method based on the acid hydrolysis of orthoesters was developed. Orthoesters can be quantitatively hydrolysed to carboxylic esters by shaking with water:’
R-C(OR’)s
0 II + H,O + R-C-OR’
+ 2R’OH.
The reaction is catalysed by acid.as8 The method we have developed involves adding an orthoester sample to a standard solution of water in trichloroacetic acid-methyl alcohol. After a timed reaction period, umeacted water is determined by Karl Frscher titration. This method is an altematrve to the aquametric procedure described by Smith et aZ.’which involves water formation by reaction with a boron trifluoride-acetic acid reagent. Our method is faster and requires no heating.
532
Short communications EXPERIMENTAL
Reagents and apparatus All of the orthoesters and the trichloroacetic acid used in this work were obtained from the J. T. Baker Chemical Company. Karl Fischer stahlised reagent was obtained from Fisher Scientific Company. A water solution was prepared by pipetting 10.0 ml of distilled water into a one 1. volumetric flask and diluting to volume with dry methyl alcohol. A trichloroacetlc acid solution was prepared by weighing 125 g of reagent-grade trichloroacetic acid into a 500-ml volumetric flask, and dissolvmg and diluting to volume with dry methyl alcohol. All flasks were dried at 110” for 30 min before use. Procedure Pipette 10.0 ml of trichloroacetic acid-methyl alcohol solution and 2@0 ml of water-methyl alcohol solution into a 125~ml glass stoppered Erlenmeyer flask. Add l-l.5 g of the orthoester sample, stopper the flask and allow the solution to stand 45 min with occasional swirling. Titrate the solution with Karl Fischer reagent. Also, titrate a reagent blank which has also stood for 45 min. Calculate the percentage of orthoester as follows: “/ = (V, - V,)(f)(M) 0 180.2(n)(W) where:
and
V, = V, = f = M = n = W =
volume of Karl Fischer reagent required to titrate blank (ml), volume of Karl Fischer reagent required to titrate sample (ml), Karl Fischer reagent standardlsation factor (mg of H,O/ml of reagent), molecular weight of orthoester, orthoester groups per molecule, weight of sample used (g).
RESULTS AND DISCUSSION This procedure was used in the analysis of four commercially available orthoesters. shown in Table I. TABLE L-ASSAY
The results are
OF ORTHOESTERS
Orthoester, Compound Triethyl orthoacetate, practical grade Triethyl orthopropionate, practical grade Trimethyl orthoformate, reagent grade Triethyl orthoformate, reagent grade
wt. % 95.2 94.8 98.8 99.2
The trichloroacetic acid-methyl alcohol reagent undergoes a slow esterification, producing a very small amount of water in the system. It is, therefore, important that blanks and samples stand the same length of time before titration. If this is done, no significant error is introduced. Because carboxylic esters are most likely impurnies in orthoesters, several were checked for interferences. No interference was found. Acknowledgement-The authors wish to thank Mr. I. Saleh and Mr. D. A. Danald for making many of the determinations used in this work. Research Division W. R. GRACE & Company Clarksville, Maryland, 21029, U.S.A.
DONALD J. CLANCY DAVID E. KRAMM
Summary-The acid hydrolysis of orthoesters has been made the basis of a titrimetric method. The method involves reaction of an orthoester with a known excess of water in a trichloroacetic acid-methyl alcohol system, followed by determination of unreacted water by Karl Fischer titration. Zusammenfassung--Die saure Hydrolyse von Orthoestern wurde zu einer titrimetrischen Bestimmungsmethode verwertet. Man hiI% den
Short communications Orthoestermiteinembekannten WasseriiberschuD in einemTrichloressigsaure-Methanol-System reagieren und bestimmt das nicht umgesetzte Wasser durch Karl Fischer-Titration. R&um?--L’hydrolyse acide des orthoesters a Bte prise pour base dune methode titrimetrique. La mtthode comprend la reaction d’un orthoester avec un exc& connu d’eau dans un systeme acide trichlorac& tique-methanol, suivie du dosage de l’eau qui n’a pas reagi par titrage selon Karl Fischer. REFERENCES 1 V. * H. 8 C. 4 D.
Migrdichian, Organic Synthesis, Vol. l., p. 332. Reinhold, New York, 1957. Kwart and M. B. Price, J. Am. Chem. Sot., 1960,82,5123. R. Noller in W. B. Saunders, Chemistry of Organic Compounds, 2nd ed., p. 175, 1957. M. Smith, J. Mitchell, Jr. and W. Hawkins, J. Am. Chem. Sot., 1944, 66, 715.
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