Tdanta. 1968. Vol. IS. pp. 741 to 746. Peqamon Press. Printed in Northmu Irdand

DETERMINATION OF HYDROGEN PEROXIDE BY XENON TRIOXIDE OXIDATION

ROBERT H. KRUEGER*, JOHN P. W AIUUNE@ and BRUNO JASELZIS Department of Chemistry, Loyola University, Chicago, Illinois 60626, U.S.A.

(Received 15 December 1967. Accepted 14 March 1968)

Summary_-Aqueous xenon trioxide solution has been used as the oxidizing agent in three precise methods of analysis for hydrogen peroxide. A catalytic method, which utilizes hydrogen peroxide to initiate the reaction between t-butanol and xenon trioxide, is described for determining amounts of hydrogen peroxide as low as 0.9 yg or 36 parts per milliard (ppM). A direct spectrophotometric titration was found to have a lower limit of about 50 ,ug or 20 ppM. An indirect titrimetric method was also used to determine hydrogen peroxide in amounts as low as 50 ,ug with a relative standard deviation of 4% which decreased to 1% for amounts over 200 ,ug.

XENON trioxide has previously been proposed for the determination of primary and secondary alcohols1 and certain organic acids. e Aqueous solutions of xenon trioxide

(“xenic acid’) are strong oxidizing agents. Appelman and Malm3 have estimated

the redox potential of the Xe(VI)-Xe(0) couple to be about +1*8 V in acidic and +@9 V in basic solution. It will oxidize ammonia to nitrogen, hydrogen peroxide to oxygen, chloride to chlorine and manganese(I1) to permanganate. Xenic acid also reacts readily with vie-diols to yield carbon dioxide and xenon.4

Aqueous solutions of hydrogen peroxide in acid media are usually determined by titration with potassium permanganate5 or cerium(IV),6 or iodometrically’ with ammonium molybdate as catalyst. Recently the direct titration of hydrogen peroxide in alkaline bromide media has been accomplished with sodium hypoch1orite.s

Aqueous xenon trioxide solution may also be used to determine hydrogen perox- ide. A catalytic method, a direct spectrophotometric titration, and an indirect titra- tion method are described for determining amounts of hydrogen peroxide as low as 36 parts per milliard (ppM).

Apparatus

EXPERIMENTAL

The change in absorbance of xenon trioxide at 200 rncc was measured with a Cary Model 14 spectrophotometer. Matched quartz cells of l-cm optical path were used. A Reckman Expanded Scale pH Meter equipped with a saturated calomel and glass electrode was used for all pH measure- ments.

Reagents

Xenon trioxide standard solution was prepared by the hydrolysis of xenon hexatluoride. Since the hydrolysis by-product, hydrofluoric acid, did not interfere in the reaction, no attempt was made

* Present address: Borg-Warner Corporation, Des Plaines, Illinois. t Present address: Central Michigan University, Mt. Pleasant, Michigan.

741

742 ROBERT H. KRUGER, JOHN P. WARRINER and BRUNO JASELSKIS

to remove it from the standard solution. Reagent grade chemicals were used without further puriflca- tion. tButano1 was purified by distillation. The hydrogen peroxide was standardized against sodium iodide, ammonium molybdate being used to catalyse the reaction. Standard sodium thio- sulphate was used for the titration of the tri-iodide resulting from this oxidation. This solution was also used to titrate the iodine from the oxidation of iodide by the xenon trioxide. A 5-ml semi-micro burette was used for all titrations.

Procedure The catalytic method employed a solution of hydrogen peroxide, t-butanol and phosphate buffer

in one beaker; xenon trioxide was added to a second beaker. Hydrogen peroxide catalysed the reac- tion between t-butanol and xenon trioxide. Equal amounts of potassium dihydrogen phosphate and potassium monohydrogen phosphate (8 x lo-*M) were added to buffer the solution to pH 7. The hydrogen peroxide concentration was varied from 1 x lO+‘M to 5 x 1O-6M; the initial xenon tri- oxide and t-butanol cpncentrations were held constant at 2.7 x 1O-4M, and 1 x 10-&M respectively. The volume of solution in each beaker was either 10 or 15 ml, so that on mixing, the total volume was exactly 25 ml. The reaction was initiated by quickly mixing the two solutions and a portion of the mixed solution was at once transferred to a l-cm quartz cell. The reference cell contained the same concentration of phosphate buffer solution. The cells were placed in the Cary 14 spectrophotometer and the change in absorbance of xenon trioxide at 200 rnp was recorded as a function of time. Hydro- gen peroxide and i-butanol do not absorb at these low concentrations.

The spectrophotometric titration method was based on the fact that both hydrogen peroxide and xenon trioxide absorb at 200 mp. For this determination 2.5 ml of a solution of 8.15 x lo-‘M hydrogen peroxide in @08M perchloric acid was placed in a l-cm quartz cell. The reference cell contained the same concentration of perchloric acid. The absorbance of the peroxide was measured at 200 m,u. Then on addition of 509.d increments of 2.7 x 1O-sit4 XeO, the absorbance decreased to reach a minimum near the equivalence point. Each reading was taken after allowing 30 set for com- plete reaction. With excess of xenon trioxide added the absorbance increased. The intersection of two straight lines drawn through these points was the equivalence point.

For the titrimetric determination, solutions were prepared by transferring aliquots of standard hydrogen peroxide, buffer, and excess of xenon trioxide into 50-ml Erlemneyer flasks. These solu- tions were diluted to 22 ml with triply distilled water. Preliminary experiments at room temperature were run to determine the minim&& time for complete oxidatioA of-hydrogen peroxide. After the reaction was complete, the solution was acidified with perchloric acid, sodium iodide was added, and the liberated tri-iodide titrated with standard thiosulphate solution. The amount of xenon trioxide consumed was equal to the difference between a blank run (no hydrogen peroxide) and the run with hydrogen peroxide. A plot of xenon trioxide consumed vs. hydrogen peroxide taken was made to determine the amount of hydrogen peroxide in an unknown solution. Regression analysis was used to find the intercept and slope of the resulting linear plot.

RESULTS AND DISCUSSION

Catalytic determination

Aqueous xenon trioxide will not oxidize dilute solutions of t-butanol. However, the reaction can be initiated by the addition of hydrogen peroxide as catalyst. The time of initiation of the reaction (r) depends on the concentration of hydrogen peroxide as is shown in Fig. 1. This fact can be utilized for determining amounts of hydrogen peroxide as low as 0.9 lug or 36 parts per milliard. A log-log plot of hydrogen peroxide vs. 7 or of hydrogen peroxide against the time needed to halve the initial absorbance of xenon trioxide at 200 rnp gives a straight line as shown in Fig. 2. The concentration of hydrogen peroxide can be read directly from the log-log plot, giving the results as shown in Table I. The relative precision decreased from about &3 % at the higher concentration to about f 15 ‘A at the lower concentrations.

This method is very sensitive to trace impurities in the solution. The halide ions (Cl-, Br-, I-) interfere in the determination by increasing the initiation time but do not reduce the precision of the method. Metal ions such as copper(I1) and

Determination of hydrogen peroxide by xenon trioxide oxidation 143

1 I I I I I I I

2 4 6 0 IO 12 14 TIME, MIN

FIG. l.-Effect of hydrogen peroxide concentration on reaction time.

IO-

8-

b-

z r 4-

g

2-

to'/2 Initial Value

1 I I I I I I I I 20 3040 60 80 100 200 300 400 bO0

H202. PARTS PER MiLLlARD

FIG. 2.-Determination of hydrogen peroxide by change in reaction time.

From initiation time From half-life

Time, min Taken ppM* Found ppM Time, min Taken, ppM Found, ppM

1.7 360 350 2.3 360 345 3.0 180 175 3.6 180 185 44 108 112 5.0 108 112

105 36 34 11.1 36 34 _

l ppM = parts per milliard = parts per(American) billion = parts per lo*.

iron(II1) increase the rate of reaction. Trace amounts of organic compounds which are easily oxidized by aqueous xenon trioxide also interfere in the determination. Phosphate, perchlorate, sulphate, fluoride and nitrate ions at low concentration have little effect on the catalytic determination. For precise results, the unknown solution should be run the same day under conditions identical to those used in obtaining values for known solutions.

744 ROBERT H. KRUEGER, JOHN P. WARRINER and BRUNO JASEISKIS

I I I I I I I 1 I I I

0.1 0.2 03 w 0.5 XENON TRIOXIDE. ml

FIG. 3.Spectrophotometric titration of hydrogen peroxide by xenon trioxide.

Spectrophotometric titration

The spectrophotometric titration was carried out by measuring the change in absorbance at 200 rnp as xenon trioxide was added to hydrogen peroxide. The results of this determination are given in Fig. 3. This method is good for determining hydrogen peroxide to a lower limit of about 50 ,ug or 20 ppm, as shown in Fig. 3 where 2.04 pmole of hydrogen peroxide were taken and 2.12 ,umole were found; the error found was within &4 % which decreased to &2 % for amounts higher than 120 ,ug. Higher amounts of hydrogen peroxide give a better titration curve. Titrations run at pH higher than 1 are not as precise because the reaction is slower. Interfering ions in this determination were similar to those found in the catalytic method described above.

Titrimetric determination

The results of the titrimetric determination of hydrogen peroxide with xenon trioxide at pH 1 are summarized in Table II. Similar results were found at pH 10. The rate of the reaction is pH-dependent. At pH 10 the reaction was complete in less than 1 min, while at pH 1 the reaction required about 5 min. In general, the larger the excess of xenon trioxide, the faster the reaction.

A plot of the amount of xenon trioxide consumed against the amount of hydrogen peroxide taken gives a straight line which on extrapolation has intercept c and slope m. The values for these constants are given in the footnote to Table II. The theoretical intercept c should be zero, and the slope m should be equivalent to the stoichiometric ratio of xenon trioxide to hydrogen peroxide (1: 3) for a complete oxidation of hydro- gen peroxide to oxygen. The small observed deviations from the theoretical value may be caused by trace impurities in the water and by short-lived species of xenon in oxidation states lower than xenon(VI),1° such as XeO, or XeO, which can react with water to produce small amounts of hydrogen peroxide.

The titrimetric method may be used to determine hydrogen peroxide in amounts as low as 50 ,ug, with relative standard deviation 4 %, which decreases to 1% for am- ounts over 200 pg. Sulphate, nitrate, phosphate and fluoride ions do not interfere.

Determination of hydrogen Peroxide by xenon trioxide oxidation 145

T~~~~I1.-Tmuramu CDElZRMINATIONOPHYDROGRN PEROXIDE BY OXIDA’ITON WITH WNON TRIOXIDE

Xenon trioxide consumed, Hydrogen Peroxide, pole pmole Taken Found+

1.72 2.57 2.57 264 5.14 5.12 3.59 7.71 1.75 540 12.85 12.75

lO*l 25.70 25.76 1472 38.55 38.52

* Calculated from the equation y = c + mx by least squares treatment of data where y is .uumole of xenon tri- oxide consumed and x is pmole of hydrogen peroxide taken. Values for c, m, and m’ (the theoretical slope for hydrogen Peroxide completely oxidized to oxygen) are respectively 0.787, 0.362, and 0.333.

Easily oxidized compounds such as alcohols, aldehydes, ketones, and organic acids as well as halides (I-, Br, Cl-) interfere in the determination of hydrogen per- oxide. However, this interference is dependent on the amount of contaminant present and can sometimes be overcome. As an example, the addition of chloride in an amount twelve times the concentration of hydrogen peroxide increased the time of reaction to 15 min. Higher concentration of chloride further increases the time for reaction. A plot of xenon trioxide used vs. hydrogen peroxide taken gave a straight line passing through the origin with a slope of O-336 as compared to the theoretical 0.333. This appears to indicate a more stoichiometric reaction than without choride and may mean that xenon trioxide oxidized the chloride to chlorine or a higher oxidation state, which in turn oxidized hydrogen peroxide to oxygen.

It was found that acetic acid did not interfere if an equivalent amount of chloride was added or if the acid strength was increased to 3M perchloric acid. The total reaction time was 60 min for chloride additions and 15 min for the determinations run in 3M perchloric acid.

It was not possible to determine hydrogen peroxide in the presence of organic peracids, for xenon trioxide would not oxidize the peracid but the peracid interfered in the iodometric determination of excess of xenon trioxide.

A direct titration of hydrogen peroxide with xenon trioxide was attempted, with Bromocresol Purple as a redox indicator. The titration was carried out in alkaline bromide media over the pH range 8-10, with sodium carbonate or sodium borate used as a buffer. The results were erratic and not reproducible. It appeared that the indicator was destructively oxidized by xenon trioxide. A more stable redox indicator may offer a better chance for this method.

Acknowledgement-This work was supported in part by the National Science Foundation (NSF-GT- 5045).

Zusannnenfassung-WUrige Xenontrioxidlosung wurde als Oxi- dationsmittel bei drei genauen Methoden xur Bestimmung von Wasserstoffperoxid verwendet. Eine katalytische Methode wird beschrieben, die Wasserstoffperoxid xur Einleitung der Reaktion

746 ROBERT H. KRUEGER, JOHN P. WARRINER and BRUNO JASELSKIS

zwischen t-Butanol und Xenontrioxid verwendet und Wasserstoff- peroxid-Mengen bis 0,9 ,~g oder 36 ppb zu bestimmen gestattet. Eine direkte spektrophotometrische Methode hatte eine untere Grenze von etwa 50 ,~g oder 20 ppm. AuDerdem wurde eine indirekte titrimetrische Methode verwendet, um Wasserstoffperoxid in Mengen von 50,~g mit einer relativen Standardabweichung von 4% zu bestimmen, die bei Mengen tiber 200 ,ug auf 1% abnimmt.

R&xnnLGn a utilisd une solution aqueuse de trioxyde xenon comme agent oxydant dans trois m&odes preCises d’analyse de l’eau oxygen& On d&it une m&ode catalytique, qui utilise l’eau oxyg&e pour amorcer la reaction entre le t-butanol et le trioxyde de xenon, pour determiner des quamites d’eau oxygen& aussi petes que 0,9 pg ou 36 parties par milliard @PM). On a trouve u’un titrage spectrophoto- metrique direct a une limite inferieure de 5 1 yg ou p.p.m. On a aussi utilise une methode titrimetrique indirecte pour doser l’eau oxygen&s en quantites aussi faibles que 50 ,og avec un &art type relatif de 4 %, qui s’abaisse a 1% pour des quantitls sup&ieures a200 ,ug.

REFERENCES

1. B. Jaselskis and J. P. Warriner, Anal. Chem., 1966,38,563. 2. B. Jaselskis and R. H. Krueger, Talanta, 1966, 13,945. 3. E. H. Appehnan and J. G. Malm, J. Am. Chem. Sot., 1964,86,2141. 4. B. Jaselskis and S. Vas, ibid., 1964, 86,2078. 5. G. E. Huckaba and F. G. Keyes, ibid., 1948,70,1640. 6. E. C. Hurdis and H. Romeyn, Anal. Chem., 1954,26,320. 7. G. Charlot and D. Bexier, Quantitutiue Inorganic Analysis, p. 522. Wiley, New York, 1957. 8. W. H. McCurdy and H. F. Bell, Talantu, 1966,13,925. 9. F. Dudley, G. Gard, and G. Cady, Znorg. Chem., 1963,2,228.

10. E. H. Appelman and J. G. Malm, J. Am. Chem. Sot. 1964,86,2297.