k2) Cheng, K. L., ANAL.CHEM.28, 1738
(1?56). (3) Eeigl, F., West, P. W., Ibzd., 19, 351 (1947). (4) Hoste, J., Anal. Chim. Acta 2, 402 11948). ( 5 i Hosie, J., Gillis, J., Ibid., 12, 158 (1955). (6) Parker, C. A . , Harvey, L. G., Analyst 86, 54 (1961).
(7) Strenge, K., Arch. Gewerbepathol. Gewerbehyg. 16, 588 (1958). (8) Suzuki, Y., Nishiyama, K., Matsuka, Y., Shikoku Iaaku Zasshi 11, 77 (1957). (9) Reisz, H.,- "Microanalysis by the Ring Oven Technique," Pergamon Press. ., London. 1961. ~. . (lo, keisz, H., Ibid., p. 74. (11) West, P. W., Llacer, A. J., Cimerman, Ch., Mikrochimica Acta 6 , 1165 (1962).
RECEIVEDfor review May 22, 1964. Accepted July 1, 1964. One of the authors (Ch. Cimerman) was on a sabbatical leave from the Technion Israel Institute of Technology, Haifa. Both authors wish to acknowledge the support of the Division of Air Pollution of the U. S. Public Health Service under Research Grant APOOl17.
Determination of Diethyl Sulfate, Ethyl Hydrogen Sulfate, and Sulfuric Acid in Mixtures D. K. BANERJEE, M. J. FULLER, and H. Y. CHEN' Research Division, U. S. Industrial Chemicals Co., Cincinnati, Ohio
A method for the determination of diethyl sulfate, ethyl hydrogen sulfate, and sulfuric acid in mixtures is described, Ethyl hydrogen sulfate and sulfuric acid are determined by nonaqueous titration with tetrabutylammonium hydroxide using pyridine as a solvent, Diethyl sulfate is determined by hydrolysis at 130" C. and titration of the sulfuric acid formed with aqueous base. Evidence of an unusual reaction between neutral diethyl sulfate and pyridine leading to the formation of a titratable complex was also obtained. Precision and recovery data for synthetic mixtures and production samples of ethylene absorbate are presented.
S
is produced by the hydrolysis of ethylene absqrbate which is a nearly anhydrous mixture of diethyl sulfate, ethyl hydrogen sulfate, and sulfuric acid containing some tars and polymers. Sumerous method.; for the analysis of mixtures of (C2Hs)?SOcC2H5HS04and H2S0, have been described ( 1 . 6 , 8 ) and critically revieu ed by Harris and Himmelblau ( 5 ) . They concluded that most of these methods are complex, indirect, and not suitable for clearcut reproducible quantitative work. Since a rapid control procedure for these three components in ethylene absorbate ~ o u l d be very useful for material balance calculations, a new approach u h g rapid titration in aqueous and nonaqueous media was investigated. Titration of a mixture of the three components in pyridine with tetrabut>-lammoniumhydroxide gave a curve with three inflection points. The H2S04 and C2H5HS04content of samples was PKTHETIC ALCOHOL
Present address, Research Department, Goodyear Tire and Rubber Co., Akron, Ohio. 1
2016
ANALYTICAL CHEMISTRY
determined from the first two inflection points of this curve. The third inflection point was caused by an unusual reaction between neutral (C2Hj)2SOI and pyridine leading to the formation of a titratable complex. The nature of this reaction was clarified by infrared and nuclear magnetic resonance spectrometry. However, this reaction which is relatively slow could not be used for quantitative determination of the diethyl sulfate. The latter was determined by hyd'rolysis of the mixture a t 120" to 130' C. and titration of the sulfuric acid formed with aqueous base. Satisfactory precision and recoveries were obtained using these methods for synthetic mixtures and production samples of ethylene absorbate. EXPERIMENTAL
Apparatus. A constant-rate buret of 10-ml. capacity and a delivery rate of 1 ml. per minute (E. H. Sargent & Co., Model C ) was used with a Beckman Model 76 p H meter for the nonaqueous titrations with 0 . 1 s tetrabutylammonium hydqoxide. The barrel of the constant-rate buret was sealed with a special baffle-type Teflon seal to prevent attack by the reactive titrant. Other types of seals were not suitable for use with the tit,rant. The titration curves were automatically recorded with a Sargent SR recorder used a t 5 millivolts full scale and a chart speed of 2 inches per minute. A Beckman general purpose glass electrode and a sleeve t,ype calomel electrode modified to contain methanol saturated with KCl were used as the electrode pair. The reservoir containing the titrant was connected to the two way stopcock on the constantrat,e buret through an all glass line. The titrant was protected from moisture and carbon dioxide with a mixture of Drierite and Ascarite. The buret tip and 100-ml. titration vessel were protected from air with a nitrogen blanket and the solutions were stirred with a Teflon covered magnetic stirring bar.
Reagents. Practical grade Eastman diethyl sulfate was purified using the method described by Harris and Himmelblau ( 5 ) . Synthetic mixtures containing 30.82 (I), 62.04 (11) and 82.82% (111) by weight of diethyl sulfate were prepared by mixing the purified material and 98% sulfuric acid. The samples were purged uith nitrogen, stoppered, and heated a t 70" C. for tF\o hours. * h o t h e r synthetic mixture (IV) had the same composition as I1 but was not heated. The mixtures were then allowed to stand for a month a t about 25" C. before samples were withdraxn periodically for analysis. The 0.1S tetrabutylammonium hydroxide (TBAH) titrant in benzenemethanol was prepared as described by Cundiff and Markunas (3, 4) and standardized against J. T. Baker reagent grade benzoic acid dried a t 103" C. for 1 hour. The pyridine used as solvent was purified by allowing it to stand overnight over sodium hydroxide followed by flash distillation. A 5% heads cut was discarded and the remainder collected. The distilled pyridine was satisfactory if equal breaks aere obtained in the titration of sulfuric acid with TRAH using the purified pyridine as solvent for the acid. Procedure for H2SOa and C2H5HSO4. From a tared Grethen weighing bottle containing the sample, add 75 to 100 mg. of sample to 40 ml. of purified pyridine in a 100-ml. beaker. Titrate the solution immediately under a nitrogen blanket keeping the tip of the buret just above the surface of the liquid in the beaker. Stop the flow of titrant \$hen a curve with three inflection points has been recorded. Calculate the H2SOa and C?HsHSO, content of the sample as follons: Per cent H2S04
=
B X S X 20
Per cent CzHsHSOa= ( A - B ) X A' X E 10 x c
Table I. Reaction of the System HzS04-C2H5HS04-(C~H5)zS04 with MIBK
Contact time before titration, minutes 0
12 30
H2SO4,
% 12.51 13.89 27.12
CzHs-
(CJL)z-
% 38.53 36.41 19.94
40.07
HSO4,
so4, %
...
...
I
6
0 3
a
7
ML. 0.1N TBAH
Figure 1.
Titration curve of synthetic mixture II (see Table IV)
A = ml. of titrant consumed to the first inflection point B = ml. of titrant consumed between the first and second inflection points c = Sample wt. in grams for nonaqueous titrat,iion D = Equivalent wt. of H2S04 = mol. wt. 2 E = Equivalent wt,. of CzHsHS04 = mol. wt. N = Normality of tetrabutylammonium hydroxide Procedure for (C2EI5j2SO4. Transfer a 1- t o 1.5-gram sample of absorba t e to a 15-ml. round bottom flask containing 3 ml. of water. Xttach a reflux condenser and reflux the sample until a single phase is formed. Stop the flow of water in the condenser and insert a thermometer through the condenser into the liquid in the flask. Boil t,he sample until the temperature reaches 120" to 130" C. Start the water flow t,hrough t'he condenser and continue refluxing the sample for an additional 15 minutes. Transfer the sample to a 250-ml. Erlenmeyer flask and titrate the solution with standardized 0.5N aqueous sodium hydroxide using phenclphthalein as indicator. Calculate the (CnH5j2S04 content of the sample as follows: Per cent (C2H&SO4 =
F
[
x
hiNaOA
G
F
=
G
=
H
=
- 2~. (.-Ix
NTBAH)
mina as a n excellent differentiating solvent through a wide range of acid strengths and u5ed it for the titration of sulfuric acid. Later, Cundiff and Markunas (4) stated that purified methyl isobutyl ketone reacted with strong acid solutes, the extent of reaction being a function of contact time. As shown in Table I, M I B K could not be used as a solvent for the titration of mixtures of H2S04, C2H5HS04 and (CzH5)2S04 because of an apparent timedenendent side reaction with this solvent. The values shown for zero time are averages of five determinations. With increase in the time of contact to 30 minutes! there was a drastic change in the ratio of H2S04 and C2H5HS04 found. This could he ascribed to a shift in equilibrium caused by reaction of
these strong acids with the MIBK. The total milliequivalents of H2S04 and C2H5HS04remained constant although the ratio changed. Because of these difficulties pyridine was used throughout as the solvent for the titration of the absorbate mixtures since it did not react with HnS04or C2H5HS04. Titration Curves. Titration curves obtained with 0.l.V T13AH using a synthetic mixture of (CZH5),SO, and and a typical plant sample are shown in Figures 1 and 2. The first inflection point is partially caused by the first hydrogen of the sulfuric acid present. Ethyl hydrogen sulfate prepared by the method of Nazarova and Tsukervanik ( 7 ) gave a curve with an inflection point in the same region as the first equivalent of HzS04. I n view of this, the volume of titrant consumed to the first inflection point is caused by the first hydrogen of H2S04 1)lus the hvdrocen of the CIH,HSOd. The - " second inflection point results from the weaker hydrogen of the H2S04. The appearance of the third inflection point, was dependent on the elapsed time between solution of the sample in pyridine and the actual titration. Temperature was also a factor as no I
< >
g
110 C SaOH used for
Xilliliters of aqueous titration Sample wt. in grams for aqueous titration Equivalent weight of (CzH5)&304 = mol. wt. 2 RESULTS AND DISCUSSION
Solvents. n r u s s a n d Wyld ( 2 ) recommended methyl isobutyl ketone (JIII3K) purified with activated alu-
Figure 2.
Titration curve of typical plant sample VOL. 36, NO. 10, SEPTEMBER 1964
2017
Table II. Effect of Time on Reaction between (CZH&S04 and Pyridine
Diethyl sulfate found, Method Complete hydrolysis to H2SO4 Bromoform extraction Pyridine reaction, immediate titration Pyridine reaction, 1-hr. standing Pyridine reaction, 2-hr. standing Pyridine reaction, 3-hr. standing
loot 1
5
4
3
ML. O.IN TBAH
Figure 3. Titration curve of the complex formed by the reaction of pyridine and (CzHdSOd
third inflection point was obtained on titration of a solution cooled in an ice bath. As discussed below, the third inflection point results from a titratable complex formed by the reaction of pyridine and (C2H5)2SO4. h titration curve of this complex obtained with T B A H is shown in Figure 3. Reaction between Pyridine and Diethyl Sulfate. The first evidence of a reaction between (CzH&SO4 and pyridine was obtained by infrared spectrometry. The spectrum of a cold mixture of diethyl sulfate and pyridine was obtained immediately after mixing and after six hours standing. The sample analyzed after six hours showed a definite increase in absorption at 8 microns and a decrease in the intensity cf the characteristic bands for diethyl sulfate. This was evidence for a slow reaction between pyridine and (C2Hs)2SO4 since neither of these compounds shows absorption a t 8 microns. The nature of this unusual reaction was clarified by high resolution nuclear magnetic resonance spectrometry. The proton magnetic resonance spectra of (C2Hs),SOaand a sample of ethylene absorbate showed that the ethyl groups were in (C2H5),S04 and C&HSO, magnetically equivalent. However, as shonn in Figure 4, the proton magnetic resonance spectrum of an excess of
(3
27.80 26.88 10.28
24,23 25.55 26.28
diethyl sulfate in pyridine varied with time. Immediately after mixing, the spectrum was merely a composite of the spectra of (C2H&S04 and pyridine. With increase in reaction time, there was an increase in the intensity of peak groups 1 and 3 because of the appearance of a reaction product. At the same time, peak groups 4 and 5 which are characteristic of pyridine
7
10
101
C
7
b Figure 4. Proton magnetic resonance spectra of excess diethyl sulfate in pyridine A. B. C.
201 8
Immediately after mixing
20 minutes after mix:ng 16 hours after mixing ANALYTICAL CHEMISTRY
90
8.0
7.0
6.0
P. EM. F
5.0
40
30
20
M M TETRAMETHYLSILANE
1.0
0
disappeared. The appearance and increase in intensity of new ethyl peak groups 6,S, 9, and 11 also pointed to the formation of a reaction product. With a solution equimolar in pyridine and (CzHs)2SOathe reaction was comlilete in about an hour. Xo further changes were noted on the addition of either pyridine or (C2HSj2SO4. The above exlierimental results can best be explained in terms of the following reaction between pyridine and (C2H&)Z804.
C2HsSO4-,(peak groups 11, 8j, C2&)2SO1 (peak groups 7 ! IO),
0
Table 111.
Conditions Recovery, 70 Recommended hydrolysis 97 34 t o HZSO4 10-minute reflux 95 56, 96 21,
N
\
CJ&+ (peak groups 9, 6). Peak groups 1 and 3 were caused by the ring protons . The peak assignments were
0
in
15-minute reflux 20-minute reflux, final temp. 103" C.
s
is shown in Table 11. The results shown were obtained by titration of the niixture I1 with TBAH. Recoveries of (C2Hs),S04increased with the time of contact with pyridine and leveled off after three hours. The recovery after 3-hours contact was almost equal to the (C2Hs)&304 value obtained by the bromoform extraction method of Harris and Himmelblau (6) but somewhat lower than that
(\ \
C2Hs+
The three nonequivalent ethyl peak groups observed would correspond to
Table IV.
97 27,97 90, 97 10, 9 i 84 9.5 80 97 43, 96 00, 97 85,97 20, 97 29
\
CzHs+ made on the basis of the shielding effect of t,he free electric charge. The molecule formed in t,he postulated reaction
\
Hydrolysis of (CzHs)2SO4and TBAH Titration
CZH5 apparently reacted with the tetrabutylammonium hydroxide to produce the third inflection point in Figures 1 and 2. The time dependence of the reaction
Precision and Recovery Data for Synthetic Mixtures and Production Samples
Synthetic I
%
C;HSOH calcd. Total recovery Total SO4 recovered Total 804 calculated
53.65 35.00 7 16 2 36
53.94 35.21 6.24 2 36
55,09 35,42 6.88 2.34
54.38 33.93 6.96 2.37
55,49 33.65 7.12 2.53
Average with 9570 confidence limits
Average % So4
5 4 . 5 1 i 0.95 34.64 i 0.99 6.87 i 0 . 4 5 2.39 0,097 0.93 99.34
53,39 26.38 4.28
*
84.05 84.21
Synthetic I1 19 60 48 10 27 95 1 03
19 45 49 37 28 30 1 11
19.92 48.10 28,95 1.08
19.03 48,62 28.76 1.06
19.92 28,35 1.18
Total recovery
Total SO1 recovered Total SO4 calculated
19.58 i 0.45 48.54 i 0.96 28.46 =t0.49 1.09 i 0.07 1.83 99.50
19.18 36,97 17.73
73.88 73.60
Synthetic I11 HISO4 C2HsHSO4 (C2Hs)ySOa HzO CyHsOH calcd. Total recovery Total YO4 recovered Total SO4 calculated
8 25 64 0
HySO4 CnHsHdOa
19 48 47 54
19 23 46 95
HIS04 GHHjHS04 (C,H,),SOa H,O Total recovery
11 66 39 99 43 50 0 54
11 58 40 50 43 44 0 49
H,SO,
11 11
11 05
42 17 43 34 0 36
40 39 43 02 0 32
80
8 15
34 02 64
24 57 63 38 0 58
8.27 24.73 64.28 0.63
8.06 25.69 63.43 0.58
8.29 24.91 63.09 0.55
8.31 25.05 63.64 0.60 1.33 98.93
f 0.36 i 0.57 f 0.61 i 0.03
8.14 19.08 39,65
66.87 66.54
Synthetic I V 19 47 46 73
19 32 46 85
19.37 i 0.19 47.02 f 0.56
Production absorbate 4/22/64
Cy HjHSO4 (C?Hj)uS04
HyO Total recovery
10 41 43 0
84 94 06 51
11 37 40 64 43 91 0 42
11 41 41 31 43 83 0 55
11.37 f 0 . 4 0 40.88 i 0.94 43.55 i 0 . 4 2 0.50 i 0 . 0 3 96.30
11 14 40 67
10.99 41.41 43.43 0 47 96.77
Production absorbate 4/25/64 10 42 43 0
59 81 67 51
11 07 40 94 43 67 0 47
0 49
i 0.37 i 0.76 i 0.49 f 0.08
VOL. 36, NO. 10, SEPTEMBER 1964
2019
obt,ained by complete hydrolysis to sulfuric acid. An att,empt was made to reduce the time required for the quant'itative reaction of the (C2Hj)zSOa and pyridine by heating 75-mg. samples of pure (C2H&S04 and pyridine a t about 100" C. for varying periods of time before titration. For a heating t'ime of 10 minutes the recoveries varied from 99.0 to 100.57,. Increase of the time of heating to 15 minutes resulted in recoveries of 100.7 to 101.77,. However, when mixture I1 was heated before t,itration the recovery of (C2H&S04 was low and the end point was no longer clearly defined. The most' reasonable explanation for this is a shift in the equilibrium in t'he mixture produced by the heating, Although recoveries of (C2H&S04were good when the samples were allowed t'o stand in contact with pyridine for 2 to 3 hours, this procedure cannot be recommended as a practical method of analysis for control work because of the time involved. I n addition the method would not be al)l)licable to (C2H&S04 concentrations below 77, as the third inflection point is completely obscured below this level. Hydrolysis of Diethyl Sulfate. Two methods for the hydrolysis of (C2H6)2SO, were investigated. The amounts of H2SOaand C2H6HSOain a mixture can be distinguished by nonaqueous titration with TI3XH. Hence, complete hydrolysis to H2SOais not required mit'h the nonaqueous method. The one condition that is necessary is the complete conversion of all the (C2H5)2SO4 present. I n preliminary work, 75mg. samples of purified (C2H&S04 were mixed with 1.5 ml. of wat'er and refluxed for times varying between 10 and 20 minutes before titration with TBAH. The recoveries obtained are shown in Table 111. The result's com-
2020
ANALYTICAL CHEMISTRY
pared favorably with the complete hydrolybis to H2S04. However, when this method was applied to mixture 11, the results for (CsH5)&O4were lo^ when compared to the complete hydrolysis to H2SOa and an aqueous titration. I n one instance, the amount of (C2H5)2SO, found wa5 24.37% as compared to 27.80% by the recommended procedure. Precision and Recovery. The results obtained uqing the recommended procedures with synthetic mixtures and 2 production samples are shown in Table IT'. Water was determined by a Karl Fischer method using pyridine as a solvent instead of methanol to avoid any possibility of reaction of the samples with alcohol to produce water. The ethyl alcohol values were calculated by the method suggested by Harris and Himmelblau ( 5 ) where any increase in acidity after the samples are allowed to stand is caused by the formation of alcohol by hydrolysis. Considering the complexity of the mixture, the precision of the results for each component was satisfactory. For mixtures I, 11, and 111 the total recoveries were all above 99% although mixture I11 gave a somewhat lower total recovery than I and I1 for some unknown reason. Diethyl sulfate was also determined for mixtures I , 11, and I11 by the bromoform method of Harris and Himmelblau ( 5 ) . The values of 5.09, 26.88, and 62.0197,, respectively, for the 3 samples compared favorably with the values obtained by hydrolysis. The bromoform method was not applicable to the production samples because of the formation of a precipitate of unknown composition during the extraction. The recoveries as sulfate were very close to the total sulfate calculated from the composition of the synthetic mixtures. For the production
samples, the precision for each component compared favorably with that obtained for the synthetic mixtures. This was in spite of the fact that the plant samples contained carbon and low molecular weight polymers which tend to settle out, thus making sampling more difficult. No sulfate recoveries could be calculated for the plant samples since their initial composition was not known. The total recoveries with these samples were of the order of 96%. This is not surprising, since carbon and low molecular weight polymers could very well account for the remaining 4% of material. In view of the satisfactory results obtained, H2S04, C2H6HS04,and (C2HJ2SO, in mixtures can be determined simply and rapidly by the recommended procedures. S o special skill is required in the application of the titration procedures for control purposes. The determination of H2S04and C2HsHS04 by titration with TBAH is rapid and most of the time required in the analysis is for the complete hydrolysis of (C2&)2-
so,.
LITERATURE CITED
(1) Breslow, D. S., Hough, R. S., Fairdough, J. T., J . Am. Chem. SOC.7 6 ,
5361 (1964). (2) Bruss, D. B., W'yld, G. E. A., AXAL. CHEM.29, 232 (1987). (3) Cundiff, R. H., Markunas, P. C., Ibid., 30, 1450 (1958). (4) Ibid., 34, 584 (1962). (5) Harris, H. G., Himmelblau, D. M., Ibid., 33, 1764 (1961). (6) Hellin, iMcj Jungers, J. C., Bull. SOC. Chim. 1956, 386. ( 7 ) Nazarova, Z. S . , Tsukervanik, I. P., J . Gen. Chem. ( U S S R ) 18, 430 (1958). (8) Plant, S. G. P., Sidgwick, K. V., J . SOC.Chem. Ind. 40, 14T (1921). RECEIVEDfor review July 5, 1962. Resubmitkd June 11, 1964. Accepted June 29, 1964.
