With solvent mixtures containing alcohols (Table I), Rf values d e c m with increase in the molecular weight of the alcohol added (4, 8). No movement of the ions occurred with pentanolchloroform mixtures. Butanol and %propanol aided in the slight movement of cobalt and iron only (Table I). Solvent mixtures 14 and 16 containing ketones gave better movement for the cations. Acetone mixtures gave a reasonable Rf value for iron(II1) only. However, the presence of %butanone aided in the migration of all four cations. With this solvent, cobalt and nickel gave greater Rf values than iron and copper, because the nitrates of cobalt and nickel form complexes with 2butanone (8). The presence of hydrochloric acid modified the migration tendencies of the ions in each case (Table I), and helped to give constant and reproducible R, values. When hydrochloric acid was used, iron had an Rf value of 1.0 in all cases. The Rf values decreased in the following sequence when acid-containing solvents were employed : Fe > Cu > Co > Mi. (Chloroformmethanol and chloroform-acetone systems were exceptions.)
The addition of phenol to an organic solvent enhanced the polarity and acidity simultaneously. Hence, Rf values for the cations increased in its presence. Addition of acetic acid modified the Rf values still more. However, increasing the percentage of phenol to 10% had no useful effect. Separations with ternary or polynary mixtures were better than those with binary combinations. The solvents containing hydrochloric acid were generally more successful and gave h e r separations (see Figure 1). Separations with mixtures containing alcohols and acids were successful (Figure 1,A to D), although separations with ketone-containing mixtures were better (Figure 1,E and F). Linstead, Burstall, and Wells (6) have shown that solvents containing low molecular weight ketones, water, and acid are satisfactory for iron, cobalt, nickel, and manganese separations. Results of our separations are in agreement with those of Linstead et $. (6). However, our studies with solvents containing aliphatic alcohols and hydrochloric acid were successful, contrary to previous findings (6). Solvents 22 and 24 gave a good separation (Figures 2 and 3), while solvent 23
gave nearly quantitative separation for the ions under study (Figure 4). Time required for separations is much more than shown in Table I for R, studies of single cations. This is partly due to the interfering effect of cations on the movement of each other and partly due to other adjustments x a d e t o ensure good separations. LITERATURE CITED
(1)Harasawa, S.H., J . Chem. SOC.Japan, Pure Chem. Sed. 72, 107, 236, 423 (1951). (2)Lacourt, A., Sommereyns, H. G., DeGeyndt, E., Jacquet, O., Mikrochic 36, 117 (1951). (3) Lacourt, A., Sommereyns, G., Jac uet, o., Wantier, G., B ~ U .h e . d i m . France 1951, 873. (4) Laekowski, D. E.,McCrone, W. C., ANAL.CHEM. 23, 1579 (1951). (5) Lederer, M., A d . Chim. Acta 4, 629 (1950); 5, 185 (1951). (6) Linstead, R. P., Burstall, F. H., Wells, R. A., J . Chem. SOC.1950, 516. (7) Pollard, F. H.,Elbeith, M., McOmie, J. F. W . , Discussions Faraday SOC.7 , 183 (1949). ( 8 ) Pollard, F. H., McOmie, J. F. W., “Chromatographic Methods of Inorganic Analysis,” Butterworths, London, 1953. RECEIVED for review December 18, 1961. Accepted June 27, 1962.
Spectrophotometric Determination of Hydroperoxide in Diethyl Ether WINTHROP C. WOLFE Building Research Division, National Bureau of Standards, Washington 25, D. C. ,An improved acidic titanium reagent for determining hydroperoxide is described. The reagent is used to determine hydrogen peroxide, terf-butyl hydroperoxide, 1 -ethoxyethyl hydroperoxide, and the unknown peroxide resulting from the oxidation of diethyl ether on storage or on exposure to 1 -Ethoxyethyl ultraviolet radiation. hydroperoxide has been postulated as a product of the oxidation of diethyl ether in air. Samples of diethyl ether, which had been oxidized in storage or by exposure to ultraviolet radiation, are analyzed by the acidic titanium method, using the improved reagent, and by an iodometric method, and the results are compared. Residues from the evaporation of oxidized ether are analyzed in an attempt to identify the oxidation products.
R
Ecent publications (7, 10) show a renewed interest in the acidic titanium method (6, 9) for hydrogen peroxide and various organic and 1328
ANALYTICAL CHEMISTRY
inorganic hydroperoxides which can be converted to hydrogen peroxide. Unlike iodometric methods (2, 6, 8, 12), often used for hydrogen peroxide and hydroperoxides, the acidic titanium method is not affected by air or oxidbing agents and does not require titration. The titanium method is extremely sensitive and uncertainties due to blank determination can be eliminated by using an optical spectrometer or filter photometer, with the reagent as the blank. With the development of pure, colorless titanium tetrachloride and a technique for preparing stable sdutions in water or in aqueous hydrochloric acid solution ( I ) , acidic titanium reagent can be prepared from any desired concentration of acid and of titanium. This is impossible by means of the methods used to prepare acidic titanium sulfate solution. EXPERIMENTAL
Preparation of Acidic Titanium Tetrachloride Reagent. A 10-ml. portion of 6 N hydrochloric acid and
a 10-ml. portion of water-white titanium tetrachloride (1) were cooled separately in beakers surrounded with crushed ice. The chilled titanium tetrachloride was added dropwise to the chilled acid solution. (Foaming may occur if the acid solution is added to the titanium tetrachloride.) The mixture was allowed to stand at ice temperature until the yellow solid dissolved and was then diluted to 1 liter with 6N hydrochloric acid. Solutions prepared in this way contain about 4 mg. of Ti per ml. and are stable; the titanium tetrachloride did not hydrolyze when the reagent was allowed to stand at room temperature for 18 months. However, solutions prepared in the same manner from titanium tetrachloride and distilled water or less concentrated hydrochloric acid solutions became turbid on standing at room temperature-i.e., a solution prepared from 20 ml. of titanium tetrachloride and 2 liters of 1N hydrochloric acid formed a white precipitate of TiOz on standing at room temperature for one month. Analysis of Aqueous Hydrogen Peroxide Solutions. Aliquots of aqueous hydrogen peroxide solutions were
diluted to known volumes in volumetric flasks with acidic titanium tetrachloride reagent. Measurements of the yelow color were made with a Beckman Model B optical spectrometer a t the wavelength of maximum absorbance or with a filter photometer (Fisher Scientific Co. Electrophotometer), using a blue filter. The wavelength a t maximum absorbance, as measured with a Cary Model 12 recording spectrophotometer, was 415 mp for the titaniumperoxide complex formed from T i c & and H20z in dilute hydrochloric acid and 410 mp for the titanium-peroxide complex formed from titanyl sulfate and H2O2 in dilute sulfuric acid. Previous values for the wavelength a t maximum absorbance for the titanyl sulfate-peroxide complex are 400 mp (9), 407 mp (7), 410 mp (6), and 420 mp (IO). Because titanium solutions absorb slightly a t the wavelengths used, all measurements were made with matched cells of the same shape and diameter, using titanium tetrachloride solutions as the blanks. To determine peroxide content from instrumental reading, it was necessary to calibrate the instrument and cells with hydrogen peroxide solutions of known concentration. With the optical spectrometer or filter photometer used, titanium analysis of a large number of solutions, previously standardized with permanganate (5), showed that the relationship of peroxide concentration to absorbance or scale reading was linear, following Beer's law, a t concentrations of from 1 to 30 pg. of peroxide as H202 per ml. of solution. The same relationship was observed and identical calibration curves were obtained with the same instruments and cells in the titanium analysis of an additional number of aqueous hydrogen peroxide solutions, previously standardized by the iodometric method (5). Analysis of tert-Butyl Hydroperoxide and 1-Ethoxyethyl Hydroperoxide [CH&HrO-CH(OOH)CHa]. Previous investigators have reported that tert-butyl hydroperoxide and organic peroxides do not form complexes with titanyl ion (7). It was found that commercial samples of di-tert-butyl peroxide, lauroyl peroxide, and benzoyl peroxide did not react with acidic titanium tetrachloride reagent. However, commercial tert-butyl hydroperoxide (from Lucidol Division, Wallace & Tiernan, Inc., 1740 Military Rd., Buffalo 5, N. Y.) reacted slowly with acidic titanium tetrachloride reagent to give a yellow color. The sample of tert-butyl hydroperoxide was analyzed by two different iodometric methods and by a modified titanium method and the results by all three methods agreed within experimental error. In t,he iodometric method of Kokatnur and Jelling (4), as adapted by Siggia (II), 0.2 to 0.3 gram of tert-butyl hydroperoxide was weighed into a 250ml. iodine flask and dissolved in 50 ml. of absolute ethanol. Saturated K I solution (2 ml.) and 2 ml. of glacial acetic acid were added and the flask was stoppered with a glass stopper wet with absolute ethanol. The solution
was heated almost to boiling and heating continued just below the boiling point for 5 minutes. The solution was titrated while hot with standardized 0.1N sodium thiosulfate solution without starch indicator. In the iodometric method adapted from the directions by Eggersgluss (g), 0.2 to 0.3 gram of tert-butyl hydroperoxide was weighed into a 250-ml. iodine flask. T o this were added 40 ml. of 2N hydrochloric acid and 1 gram of solid potassium iodide. The mixture was allowed to stand for 30 minutes and titrated with standardized 0.1N sodium thiosulfate solution, using starch indicator. A blank determination was performed in the same manner, omitting the peroxide, and the titer subtracted from that of the sample. In the modified titanium method, approximately 0.2 gram of tert-butyl hydroperoxide was weighed into a 100ml. beaker and rinsed into a 500-ml. volumetric flask with acidic titanium tetrachloride reagent, mixed thoroughly, and allowed to stand for 30 minutes. The quantity of hydroperoxide was calculated from the measurement with an optical spectrometer or filter photometer. A sample of l-ethoxyethyl hydroperoxide, prepared by the method of Milas, Peeler, and Mageli (6) (Found: &, 1.4067; lit., 1.4091) was assayed by the Eggersgluss iodometric method and by the modified titanium method. The results of six determinations by each method agreed within experimental error. The acidic titanium method does not distinguish between H202 and organic hydroperoxide in a mixture (7). Probably the organic hydroperoxide hydrolyzes to form H202 and the yellow color observed is due to the complex between titanyl ion and Ht02. This was confirmed by experiments with the Eggersgluss iodometric method and the modified titanium method, in which both tert-butyl hydroperoxide and 1ethoxyethyl hydroperoxide were allowed to stand in contact with the acidic solutions for approximately 5 minutes instead of 30 minutes. In each case, the results were approximately 30 to 40% lower and were changing too rapidly to obtain accurate data. Determination of Peroxide in Diethyl Ether. Peroxide in oxidized ether or solutions of hydrogen peroxide or l-ethoxyethyl hydroperoxide in ether were analyzed as follows. A known volume of ether, usually 50 ml., was transferred to a 250-ml. separatory funnel, 5 ml. of acidic titanium tetrachloride reagent was added, and the mixture shaken vigorously. The phases were allowed to separate and the lower aqueous layer was drawn off. If the aqueous layer was colorless or if the yellow color was barely visible, both layers were discarded and another extraction was performed on a larger volume of ether to have a measurable color intensity in the extract. If the aqueous phase was deep y d o w or orange, the extraction was repeated on the already extracted ether layer with additional 5-ml. portions of extracting
solution until the last extract was colorless. In the latter case, the extracta were combined and diluted to a suitable volume with more acidic titanium tetrachloride reagent. The yellow color of the combined extracts was measured with an optical spectrometer or filter photometer as with aqueous hydrogen peroxide solutions. A series of recovery experiments was performed to test the efficiency of extraction of hydroperoxide from diethyl ether by acidic titanium tetrachloride reagent. Weighed amounts of peroxide, analyzed iodometrically, were added to 100-ml. portions of anhydrous, peroxide-free ether. The resulting solutions of peroxide in ether were then analyzed by extracting with acidic titanium tetrachloride reagent with subsequent measurement as already described. The results are shown in Table I.
Table 1. Extraction of Hydroperoxide from Diethyl Ether with Titanium Tetrachloride Solution
Hydrogen peroxide Amount Amount added, mg. extracted, mg. (iodometric method) (titanium method) 0.0s
0.08
1-Ethoxyethyl hydroperoxide Amount Amount added, mg. extracted, mg. (iodometricmethod) (titanium method) 0.33 0.28 0.61 0.56 0.90 0.84 1.16 1.12 1.43 1.39 2.85 2.79 5.63 5.58 8.22 8.36
The titanium and iodometric methods were compared on a number of samples of ether which had developed peroxide on storage or on irradiation with ultraviolet light in the presence of oxygen. The iodometric method used was that of Wheeler (12) as modified by Ricciuti, Coleman, and Willits (8). The values are recorded in Table 11.
Analysis of Residues from the Evaporation of Oxidized Ether. Values in Table I11 were obtained with samples of ether which had developed peroxide on storage or on irradiation with ultraviolet light in the presence of oxygen. These ether samples were evaporated a t 25" to 30" C. in a closed system in a stream of nitrogen. The evaporated ether was collected in traps surrounded by solid carbon dioxide. After most of the ether had been removed in this manner, the sample was evaporated to an oily residue a t the same temperature, using a water asVOL 34, NO. 10, SEPTEMBER 1962
* 1329
Table II. Comparison of the Titanium and lodometric Methods for Determining Peroxide in Diethyl Ether
Amount of peroxide as mg. of HzOz per ml. of ether Colorimetric Wheeler titanium method iodometric method 5.2 0.2 0.2 1.3 1.4 0.1 0.7 3.3“ 8.1” T.Ta
1 .60 1.1
4.5 0.2 0.2 1.1 1.2 0.1 0 6
3 .os
7.1“ 6.5“ 1.5” 0.9
Irradiated with ultraviolet lamp in the presence of oxygen to accelerate eroxide formation. The other samples ad developed peroxide from storage under various conditions.
K
pirator. The residue, in each case, vas completely miscible with water m d with ether. The residues were weighed accurately, diluted with water, and analyzed by the titanium method. The ether n-hich had evaporated and was collected in the cold traps was also analyzed by the same method, but no correction was made in the table. Most of the peroxide was recovered in the residue, although there was always some lose in the evaporated ether. RESULTS AND DISCUSSION
AIost previous investigators are of the opinion that organic peroxides and hydroperovides do not form yellow complesea with titanyl ion (2, 7). Eggersgluss 12) hydrolyzed organic h\droperovideG with hydrochloric acid a t room temperature and analyzed the hydrogen pero\-ide liberated iodo-
metrically. Pobiner (7) degraded organic hydroperoxides with sulfuric acid at elevated temperatures and determined the hydrogen peroxide by using titanyl sulfate. I n the present investigation, hydrogen peroxide was liberated from tert-butyl hydroperoxide and l-ethoxyethyl hydroperoxide on standing at room temperature with hydrochloric acid. Satterfield and Bonne11 (10) indicated the possibility of titanium complexing with certain organic hydroperoxides and pointed out that the organic titanium-peroxide complex may have a slightly greater absorptivity than the complex of titanium with hydrogen peroxide. However, Pobiner ( 7 ) showed that the low absorptivity of the complex developed between tert-butyl hydroperoxide and titanyl sulfate was due t o incomplete degradation of the organic hydroperoxide to H202. This is confirmed by analyses of tert-butyl hydroperoxide and 1-ethoxyethyl hydroperoxide reported in the present paper, in which acid hydrolysis for 30 minutes was necessary. The composition of solutions of TiC14 in water or aqueous hydrochloric acid solution and the nature of the yellow complex formed from aqueous solutions of TiC14 and H202 are unknown. However, it has been reported that HzOzand TiC14 combine in equimolar proportions and that the formula for the yellow complex formed between titanyl sulfate and Hz02can be written < i[.[
(S04),]-*H2 (3).
It seems
likely that the yellow complex formed by the reaction between TiCl4 and Hz02 in aqueous hydrochloric acid solu-
r
,O
tionhas the formula Ti l ( 0
1
1-2 Cla H2.
1
As shown in Table I, both hydrogen peroxide and l-ethoxyethyl hydroperoxide were recovered quantitatively from diethyl ether solutions by extraction with acidic titanium tetrachloride reagent. According to Table 11, satisfactory agreement was obtained in the analysis of various unknown ether samples by the iodometric and titanium methods. In Table 111, the weight of the residues compares fairly well with the amount of peroxide found in the residue by analysis, if the peroxide is calculated on the basis of the molecular weight of 1-ethoxyethyl hydroperoxide rather than using the molecular weight of hydrogen peroxide. This tends to confirm the previous supposition that 1-ethoxyethyl hydroperoxide is one of the products of the autoxidation of diethyl ether (6). ACKNOWLEDGMENT
The author acknowledges the assistance of Dr. May X. Inscoe of the Physical Chemistry Division, h’ational Bureau of Standards, in measuring the wavelength a t maximum absorbance for the titanium-peroxide complex. LITERATURE CITED
(1) C]labaugh, W. S., Leslie, R. T., GilChrist, R., J . Res. Kat. Bur. Std. 55, No. 5, 261, RP 2628 (November 1955). (2) Eggeisgluss, W., “Organische Peroxyde, Monograph No. 61 for Angew. Chem. and Chem. Inq.-Tech., pp. 15-18,
Verlag Chemie, Weinheim/Bergstrasse,
1951. (3) Gmelins “Handbuch der anorgan-
ischen Chemie,” 8th ed., Titanium, System N o . 41, pp. 268-71, 308, 322-3. Verlag Chemie, 1951. (4) Kokatnur, V. R., Jelling, M., J. Am.
Chem. SOC.63, 1432 (1941). (5) Kolthoff, I. M., Sandell, E. B., “Text-
book of Quantitative Inorganic Analysis,” 3rd ed., pp. 574, 600, 705-7, Macmillan, Xen York, 1962. (6) Milas, N. A , , Peeler, R. L., Jr., Mageli, 0. L., J . Am. Chem. SOC.76,
2322 (1954). (7) Pobiner, H., ANAL.CHEM.33, 1423 Table 111.
Hydroperoxide Content of Diethyl Ether and Residue from Evaporation
Weight of residue. mg.“
Hydroperoxide content of ether sample-before evaporation, mg.b Calculated as Calculated rn HzOz C4HIo0a
HydroDeroxide content of - residue, mg.C Calculated as Calculated as HzOz C4HioOa
36.0 16 50 12 37 43.2 23 66 15 47 6T.0 60 187 27 84 503.4 197 615 160 499 a Weight of residue obtained from the evaporation of 100 ml. of ether. Hydroperoxide determined by the titanium method and based on 100 ml. of ether. Calculated as H ~ 0 2and also as l-ethoxyethyl hydroperoxide, C4H1003. Values represent mg. of hydroperoxide in residue from the evaporation of 100 ml. of
ether. Kot corrected for hydroperoxide lost on evaporation.
i1961 - -)., I--
(8) Ricciuti, C., Coleman, J. E., Willits, C. O., Zbid., 27, 405 (1955). (9) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” pp. 420-3. Interscience. New York. 1944. (10) Satterfield, C. N., Bonnell, A. H., ANAL.CHEM.27, 1174 (1955). ( 1 1 ) Siggia, S., “Quantitative Organic
Analysis via Functional Groups,” 2nd ed., pp. 148-9, Wiley, New York,
1954. (12) Wheeler. D. H..’ Oil and 9; 89 (April 1932).
RECEIVED April 5, 1962. Accepted June 4, 1962.
1330
ANALYTICAL CHEMISTRY
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