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Oxidimetric determination of triphenylphosphine
1594
Short communications
Talanta, 1969, Vol. 16, pp. 1594 to 1596. Persamon Press. Printed in Northern Ireland
Oxidimetric deter~ation
of ~ip~aylp~sp~ne
(Received 18 April 1969. Accepted 18 June 1969) (TPP) is widely used in co-ordination chemistry and extensive studies have been made with regard to its donor properties. However, there is a lack of suitable analytical methods for its rapid and accurate determination. Oxidation of TPP with ~me~ylsulphoxide to its oxide which is then ~avime~~ly dete~ined as its boron ~uo~de adduct,’ oxidation with concentrated sulphuric acid and potassium persulphate at 330” to phosphorus pentoxide which can be determined by conventional methods,* and a mercurimetric methods based on the formation of difficultly soluble crystals of (Ph,P), . HgCls have been proposed. All these methods are indirect, tedious and time-consuming, the second has to be carried out in the absence of moisture and the third is subiect to many interferences. Investigation of the behaviour of TPP towards various oxidants showed that iodine and &loran&e-T, i% acidic medium in the presence of organic solvents such as benzene and carbon te~ac~oride, readily oxidize TPP to phosphine oxide. These oxidations form the basis of a procedure for the rapid and accurate determination of TPP, TRIPHIWYLPHOSPHINE
EXPERIMENTAL Reagents Chlorumke-T, O-1N. Approximately O*lN aqueous chloramine-T solution was prepared and standardized iodometrically by the procedure of Bishop and Jennings.4 Iodine, @lN. Approximately @IN aqueous iodine solution was prepared and standardized with t~os~p~~ via dichromate. Triphe~y~h~sphine. B.D.H. “O.A.S.” grade was used in the experiments. Procedures Determination of optimum conditions. Rnown amounts of TPP were weighed into an iodineflask, and after adjustment of the reaction conditions, a known excess of iodine or chloramine-T solution was added. After being allowed to stand for various intervals of time at room temperature the amount of unwns~ed oxidant was determined with t~~ulphate. The extent of oxidation was determined from the ratio of the number of mmole of oxidant consumed under the reaction conditions to the number of mmole of TPP taken. Recommended method. To O-3-0-5 mmole of triphenylphosphine add 10 ml of benzene or carbon tetrachloride to dissolve it. Then add 5 ml of IM sulphuric acid and exactly 20 ml of &lN iodine or chloramine-T solution. Mix well for a minute and then determine the residual iodine or chloramine-T (in this case after the addition of acidified potassium iodide) with thiosulphate. The amount of ~phenylphosp~me (X) is given by the expression: ,=(v,
-
V&Z x 131.1 loo0 g
where VI is the volume (ml) of thiosulphate consumed in the blank experiment, V, is the volume (ml) of thiosulphate consumed by the excess of iodine or chloramine-T left after the oxidation of TPP, and 2 is the normality of the sodium thiosulphate solution. The values obtained are accurate to within @5 %. The method can be adapted for the determination of t~phenylpho~~ne in many of its metal complexes. A known amount of the complex containing about p2-07 mmole of TPP is accurately weighed and to this are added 10 ml of benzene or carbon tetrachloride, 20 ml of 10% potassium iodide and 20 ml of 1M sulphuric acid. Then 20 ml of @lN iodine solution are introduced and after the contents have been well mixed for a minute, the excess of iodine is determined witb thiosulphate. The amount of TPP present is then calculated as above, RESULTS
AND
DISCUSSION
A representative set of results obtained is given in TabIe I. It is seen that the oxidation of TPP with either chloramine-T or iodine is completed within a minute in acid medium when either benzene or carbon tetrachloride is added. The oxidation product appeared from the consumption of two equivalents of oxidant per mole of TPP to be triphenylphosphine oxide. This was confirmed from chemical and infrared examination of the product. In the absence of organic solvents, it was found
Short communications
1595
TABLEI.-OXIDATION OF TRIPHEN~PHOSPHINE(TPP) WITH IODINEAND CHUIMMINE-T
Aqueous medium A 0.2M HISOI
@2M HCI 0*2M CH,COOH (pH 2.65) B 0*2M H,SO*
TPP taken, mmole
Standing period, min
0.5496 05183 0.4347 0.3961 0.4946 05306 0.3432 0.4786 O-4636 O-4892 0.6782 0.5642 0.4038 0.5446 0.4848 * 0*4912*
2 5 15 30 2 5 30 2 5 30
Oxidant consumed, meq 1.094 l-036 0.865 O-788 O-989 1.056 0.683 O-959 0.926 0.978 1.352 1.128 0.804 1.085 0.486 0.493
5 15 30 2 10
Oxidant TPP 1.990 1.999 1.991 I.990 2*OcG l-990 1.991 2.004 1.998 l-999 I.994 1.999 l-990 1.992 1.002 lGO4
Amount of oxidant taken = l-681 meq of chloramine-T or 1.980 meq of iodine. Total volume = 100 ml. Organic solvent used = 10 ml of benzene or carbon tetrachloride. A: Oxidations carried out with chloramine-T. B: Oxidations carried out with iodine. * Oxidations carried out without the addition of organic solvent. that on the addition of excess of aqueous iodine solution to TPP, a brown solid appeared which presumably is a complex of the type (PHsP-I+)Ior (PH,P-IJ which impedes the rapid oxidation of TPP. Complex formation of TPP with halogens under suitable conditions has been reported.6~7 Oxidation of TPP with chloramine-T was also slow in absence of organic solvents. In Table II are recorded typical results obtained with some metal complexes. The agreement between the expected and experimental values is within &@5%. The method has of course to be
TABLEII.-DETERMINATION Compound (Ph,P . HgCl&
(PhaP),HgCla
(Ph,PCdCl,),
(Ph3P)&dCls
OF
TRIPHENnPHOSPHINE(TPP)
IN
METAL
COMPLEXES
Weight of complex taken, g
TPP expected, mmole
TPP found, mmole
0.2122 0.2091 O-1292 0.1687 0.1189 0.2692 0.2509 0.2089 0.2416 0.2586 0.2941 0.2018 0.2125 0.1986 0.2009 0.2341
0.397 0.391 0.242 O-316 0.299 0.677 0.630 0.525 0.542 0.580 O-660 0.453 @600 0.561 O-567 0.661
0.396 0.390 0.241 0.317 O-299 0.674 0.628 0.527 o-540 O-578 0.658 0.454 0.601 O-559 0.565 0.659
Amount of oxidant taken = 2015 meq of iodine. carbon tetrachloride.
Organic solvent used = 10 ml of benzene or
1596
Short communications
modified suitably for the determination oxidation states of metals.
of TPP in complexes
featuring
Department of Chemistry, Indian Institute of Technology Madras-36, India
stabilization
of unusual
V. R. S. RAO G. ARAVAMUDAN
Snmmary_--A method for the determination of triphenylphosphine based on its oxidation to phosphine oxide by iodine or chloramine-T in acid medium in presence of benzene or carbon tetrachloride is described. The oxidation is completed within 2 min and the analytical values are accurate to within O-5’%. The method is applicable to determination of triphenylphosphine in its metal complexes. Zusammenfassung-Ein Verfahren zur Bestimmung von Triphenylphosphin wird beschrieben, das auf seiner Oxidation zu Phosphinoxid in saurem Medium mit Jod oder Chloramin-T in Geeenwart von Benz01 oder Tetrachlorkohlenstoff beruht. Die Oxidatiocist in 2 min beendet und die analytischen Werte stimmen auf 0,5 %. Das Verfahren Itit sich auf die Bestimmung von Triphenylphosphin in seinen Metallkomplexen anwenden. R&r&-Gn decrit une methode pour le dosage de la triphenylphosphine basee sur son oxydation en oxyde de phosphine par l’iode ou la chloramine T en milieu acide en presence de benzene ou de tetrachlorure de carbone. L’oxydation est achevee en 2 mn et les valeurs analytiques sont precises a 0,5% p&s. La mtthode est applicable II la determination de la triphenylphosphine dans ses complexes metalliques. 1. 2. 3. 4. 5. 6. 7.
REFERENCES H. H. Szmant and 0. Cox, J. Org. Chem., 1966,31,1595. R. Poggi and A. Polverini, Atti. Accad. Lincei, 1926, 4, 315. J. H. Kolitowska, Roczniki Chem., 1928, 8, 568. E. Bishop and V. J. Jennings, Talanta, 1958, 1, 197. K. R. Bhaskar, S. N. Bhat, S. Singh and C. N. R. Rao, J. Znorg. Nucl. Chem., 1966,28,1915. M. F. Ali and G. S. Harris, Chem. Commun., 1966,819. A. D. Beveridge, G. S. Harris and F. Inglis, J. Chem. Sot., A, 1966,520.
Talanta. 1969, Vol. 16, pp. 1596 to 1601. Pereamon Press. Printed in Northern Ireland
Calorimetric determination of thorium with Methylthymol Blue (Received 9 June 1969. Accepted 23 June 1969) The formation METHYLTHYMOL BLUE (MTB) is one of the most useful indicators in complexometry. of intensely blue complexes has also been utilized for calorimetric determination of many metals such as zirconium,l-e hafnium,8 thorium,5~7~Bniobium,0-1Stitanium,11~18gallium,6~~4~~6aluminium,1~-~~ iron,llm10 mercury,20 some rare earths,al-*s magnesium,a’,a* and also for indirect determination of fluoridezs,so. The selectivity of these reactions is low, except for the reactions with zirconium and hafnium which proceed in strongly acidic medium (0.2-l.OM hydrochloric or perchloric acid) where the other elements do not form complexes with the indicator. Up to now, the reaction of thorium with MTB has been studied only in acidic medium, by Otomo,’ Tikhonov,6 and Vasilenko and Shanya .8 According to these authors a Th(MTB), complex is formed and has an absorption maximum at 570-595 nm. The molar absorptivity varies from 3.9 x lo* to 5.00 x lo3 l.mole-l.mm-l, depending on the PH. l4 No attempts were made to eliminate the interference of elements under the same conditions. During the systematic study of this thorium-MTB reaction, we have found that thorium forms a violet I:2 complex with MTB in slightly alkaline medium (pH 9-10) even in the presence of EDTA and DCTA; the absorption maximum is at 535 MI. Because EDTA masks almost all other elements against this reagent, we have studied this reaction thoroughly as a new and very sensitive method
Short communications
Talanta, 1969, Vol. 16, pp. 1594 to 1596. Persamon Press. Printed in Northern Ireland
Oxidimetric deter~ation
of ~ip~aylp~sp~ne
(Received 18 April 1969. Accepted 18 June 1969) (TPP) is widely used in co-ordination chemistry and extensive studies have been made with regard to its donor properties. However, there is a lack of suitable analytical methods for its rapid and accurate determination. Oxidation of TPP with ~me~ylsulphoxide to its oxide which is then ~avime~~ly dete~ined as its boron ~uo~de adduct,’ oxidation with concentrated sulphuric acid and potassium persulphate at 330” to phosphorus pentoxide which can be determined by conventional methods,* and a mercurimetric methods based on the formation of difficultly soluble crystals of (Ph,P), . HgCls have been proposed. All these methods are indirect, tedious and time-consuming, the second has to be carried out in the absence of moisture and the third is subiect to many interferences. Investigation of the behaviour of TPP towards various oxidants showed that iodine and &loran&e-T, i% acidic medium in the presence of organic solvents such as benzene and carbon te~ac~oride, readily oxidize TPP to phosphine oxide. These oxidations form the basis of a procedure for the rapid and accurate determination of TPP, TRIPHIWYLPHOSPHINE
EXPERIMENTAL Reagents Chlorumke-T, O-1N. Approximately O*lN aqueous chloramine-T solution was prepared and standardized iodometrically by the procedure of Bishop and Jennings.4 Iodine, @lN. Approximately @IN aqueous iodine solution was prepared and standardized with t~os~p~~ via dichromate. Triphe~y~h~sphine. B.D.H. “O.A.S.” grade was used in the experiments. Procedures Determination of optimum conditions. Rnown amounts of TPP were weighed into an iodineflask, and after adjustment of the reaction conditions, a known excess of iodine or chloramine-T solution was added. After being allowed to stand for various intervals of time at room temperature the amount of unwns~ed oxidant was determined with t~~ulphate. The extent of oxidation was determined from the ratio of the number of mmole of oxidant consumed under the reaction conditions to the number of mmole of TPP taken. Recommended method. To O-3-0-5 mmole of triphenylphosphine add 10 ml of benzene or carbon tetrachloride to dissolve it. Then add 5 ml of IM sulphuric acid and exactly 20 ml of &lN iodine or chloramine-T solution. Mix well for a minute and then determine the residual iodine or chloramine-T (in this case after the addition of acidified potassium iodide) with thiosulphate. The amount of ~phenylphosp~me (X) is given by the expression: ,=(v,
-
V&Z x 131.1 loo0 g
where VI is the volume (ml) of thiosulphate consumed in the blank experiment, V, is the volume (ml) of thiosulphate consumed by the excess of iodine or chloramine-T left after the oxidation of TPP, and 2 is the normality of the sodium thiosulphate solution. The values obtained are accurate to within @5 %. The method can be adapted for the determination of t~phenylpho~~ne in many of its metal complexes. A known amount of the complex containing about p2-07 mmole of TPP is accurately weighed and to this are added 10 ml of benzene or carbon tetrachloride, 20 ml of 10% potassium iodide and 20 ml of 1M sulphuric acid. Then 20 ml of @lN iodine solution are introduced and after the contents have been well mixed for a minute, the excess of iodine is determined witb thiosulphate. The amount of TPP present is then calculated as above, RESULTS
AND
DISCUSSION
A representative set of results obtained is given in TabIe I. It is seen that the oxidation of TPP with either chloramine-T or iodine is completed within a minute in acid medium when either benzene or carbon tetrachloride is added. The oxidation product appeared from the consumption of two equivalents of oxidant per mole of TPP to be triphenylphosphine oxide. This was confirmed from chemical and infrared examination of the product. In the absence of organic solvents, it was found
Short communications
1595
TABLEI.-OXIDATION OF TRIPHEN~PHOSPHINE(TPP) WITH IODINEAND CHUIMMINE-T
Aqueous medium A 0.2M HISOI
@2M HCI 0*2M CH,COOH (pH 2.65) B 0*2M H,SO*
TPP taken, mmole
Standing period, min
0.5496 05183 0.4347 0.3961 0.4946 05306 0.3432 0.4786 O-4636 O-4892 0.6782 0.5642 0.4038 0.5446 0.4848 * 0*4912*
2 5 15 30 2 5 30 2 5 30
Oxidant consumed, meq 1.094 l-036 0.865 O-788 O-989 1.056 0.683 O-959 0.926 0.978 1.352 1.128 0.804 1.085 0.486 0.493
5 15 30 2 10
Oxidant TPP 1.990 1.999 1.991 I.990 2*OcG l-990 1.991 2.004 1.998 l-999 I.994 1.999 l-990 1.992 1.002 lGO4
Amount of oxidant taken = l-681 meq of chloramine-T or 1.980 meq of iodine. Total volume = 100 ml. Organic solvent used = 10 ml of benzene or carbon tetrachloride. A: Oxidations carried out with chloramine-T. B: Oxidations carried out with iodine. * Oxidations carried out without the addition of organic solvent. that on the addition of excess of aqueous iodine solution to TPP, a brown solid appeared which presumably is a complex of the type (PHsP-I+)Ior (PH,P-IJ which impedes the rapid oxidation of TPP. Complex formation of TPP with halogens under suitable conditions has been reported.6~7 Oxidation of TPP with chloramine-T was also slow in absence of organic solvents. In Table II are recorded typical results obtained with some metal complexes. The agreement between the expected and experimental values is within &@5%. The method has of course to be
TABLEII.-DETERMINATION Compound (Ph,P . HgCl&
(PhaP),HgCla
(Ph,PCdCl,),
(Ph3P)&dCls
OF
TRIPHENnPHOSPHINE(TPP)
IN
METAL
COMPLEXES
Weight of complex taken, g
TPP expected, mmole
TPP found, mmole
0.2122 0.2091 O-1292 0.1687 0.1189 0.2692 0.2509 0.2089 0.2416 0.2586 0.2941 0.2018 0.2125 0.1986 0.2009 0.2341
0.397 0.391 0.242 O-316 0.299 0.677 0.630 0.525 0.542 0.580 O-660 0.453 @600 0.561 O-567 0.661
0.396 0.390 0.241 0.317 O-299 0.674 0.628 0.527 o-540 O-578 0.658 0.454 0.601 O-559 0.565 0.659
Amount of oxidant taken = 2015 meq of iodine. carbon tetrachloride.
Organic solvent used = 10 ml of benzene or
1596
Short communications
modified suitably for the determination oxidation states of metals.
of TPP in complexes
featuring
Department of Chemistry, Indian Institute of Technology Madras-36, India
stabilization
of unusual
V. R. S. RAO G. ARAVAMUDAN
Snmmary_--A method for the determination of triphenylphosphine based on its oxidation to phosphine oxide by iodine or chloramine-T in acid medium in presence of benzene or carbon tetrachloride is described. The oxidation is completed within 2 min and the analytical values are accurate to within O-5’%. The method is applicable to determination of triphenylphosphine in its metal complexes. Zusammenfassung-Ein Verfahren zur Bestimmung von Triphenylphosphin wird beschrieben, das auf seiner Oxidation zu Phosphinoxid in saurem Medium mit Jod oder Chloramin-T in Geeenwart von Benz01 oder Tetrachlorkohlenstoff beruht. Die Oxidatiocist in 2 min beendet und die analytischen Werte stimmen auf 0,5 %. Das Verfahren Itit sich auf die Bestimmung von Triphenylphosphin in seinen Metallkomplexen anwenden. R&r&-Gn decrit une methode pour le dosage de la triphenylphosphine basee sur son oxydation en oxyde de phosphine par l’iode ou la chloramine T en milieu acide en presence de benzene ou de tetrachlorure de carbone. L’oxydation est achevee en 2 mn et les valeurs analytiques sont precises a 0,5% p&s. La mtthode est applicable II la determination de la triphenylphosphine dans ses complexes metalliques. 1. 2. 3. 4. 5. 6. 7.
REFERENCES H. H. Szmant and 0. Cox, J. Org. Chem., 1966,31,1595. R. Poggi and A. Polverini, Atti. Accad. Lincei, 1926, 4, 315. J. H. Kolitowska, Roczniki Chem., 1928, 8, 568. E. Bishop and V. J. Jennings, Talanta, 1958, 1, 197. K. R. Bhaskar, S. N. Bhat, S. Singh and C. N. R. Rao, J. Znorg. Nucl. Chem., 1966,28,1915. M. F. Ali and G. S. Harris, Chem. Commun., 1966,819. A. D. Beveridge, G. S. Harris and F. Inglis, J. Chem. Sot., A, 1966,520.
Talanta. 1969, Vol. 16, pp. 1596 to 1601. Pereamon Press. Printed in Northern Ireland
Calorimetric determination of thorium with Methylthymol Blue (Received 9 June 1969. Accepted 23 June 1969) The formation METHYLTHYMOL BLUE (MTB) is one of the most useful indicators in complexometry. of intensely blue complexes has also been utilized for calorimetric determination of many metals such as zirconium,l-e hafnium,8 thorium,5~7~Bniobium,0-1Stitanium,11~18gallium,6~~4~~6aluminium,1~-~~ iron,llm10 mercury,20 some rare earths,al-*s magnesium,a’,a* and also for indirect determination of fluoridezs,so. The selectivity of these reactions is low, except for the reactions with zirconium and hafnium which proceed in strongly acidic medium (0.2-l.OM hydrochloric or perchloric acid) where the other elements do not form complexes with the indicator. Up to now, the reaction of thorium with MTB has been studied only in acidic medium, by Otomo,’ Tikhonov,6 and Vasilenko and Shanya .8 According to these authors a Th(MTB), complex is formed and has an absorption maximum at 570-595 nm. The molar absorptivity varies from 3.9 x lo* to 5.00 x lo3 l.mole-l.mm-l, depending on the PH. l4 No attempts were made to eliminate the interference of elements under the same conditions. During the systematic study of this thorium-MTB reaction, we have found that thorium forms a violet I:2 complex with MTB in slightly alkaline medium (pH 9-10) even in the presence of EDTA and DCTA; the absorption maximum is at 535 MI. Because EDTA masks almost all other elements against this reagent, we have studied this reaction thoroughly as a new and very sensitive method