applicable. The lower normality titrants were advantageous when only a small amount of the deriva t I\' .e 14.2,s available. As isomerism does not affect the neutralization equivalent, this procedure appears more reliable than iiirlting point data as a means of identification. The phenj-lhydrazone, p-nitrophenylhydrazone. and phenylosazone derivstives as \yell as 2,4dinitrophenylhydrazine rrere titratable by this procedure. I n addition, 5,5 - dimethyl - 1.3cyclohexanedione (Dimedon), a specific reagent for aldehydes, as well as derivatives of dimedon TTere titratable. No differentiation between dimedon and aldehyde derivatives was possible.
ACKNOWLEDGMENT
The authors express their appreciation to James D. Frederickson for providing the 2,4-dinitrophenylhydrazones and the melting point data, as well as valuable advice in the course of this investigation. LITERATURE CITED
(1) Bruse, D. B., Kvld, G. E. A , , X 4 . 4 ~ . CHEM.29, 232 (1957). ( 2 ) Buyske, D. -2 Owen, L. H., Wilder, P., Hobbs, M. E., Ibid., 28, 910 (1956). (3) Cundiff, R. H., Markunas, P. C., Ibid., 28, 792 (1956). (4;Ibid., 30, 1450 (1958). i:5) Deal, V. Z., \T7yld, G. E.il., I b i d . , 27, 47 (1955). ~
(61 Fritz, J. S., Moye, A . J., Richard, 11.J., Ibid., 29, 1685 (1957). ( i )Fritz, J. S., Yamamura, S. S., Ibid., 29, 1079 (1957). (8) Harlow, G. A,, Xoble, C. 11.. TTgId, G. E. A,, Ibid., 28, 787 (1956). ('3) Lynn, W. S., Steele, L. A., Staple, E., Ibzd., 28, 132 (1956). (10) Nakayama, S . , Japan Analyst 5 , 4.59 (1956). (11) Pifer, C. W.,\.T'ollish,E. G., Schmall, 1L3A \ . ~ L . CHEK 25, 310 (1953). (1'2) Pifer, C. W., Kollish. E. G., Schmall, 11..J . Am. Pharm. Assoc., Sci. Ed 42, 509 (1953). (13) Pippen, E. L., Eyring, E. J., Xonaka, 11.,AXAL.CHEM.29, 1305 (1957). RECEIT-ED for review January 3, 1958. .lrcepted May 9, 1958.
Titration of Acids in Nonaqueous Solutions with Tetrabutylammonium Hydroxide Reaction of Solvents with Strong Acids ROBERT H. CUNDIFF and PETER C. MARKUNAS R. J. Reynolds Tobacco Co., Winston-Solem, N. C.
b A number of solvents commonly employed for acid determinations in nonaqueous media react in varying degrees with strong acids. Acetone, isopropyl alcohol, methyl isobutyl ketone, dimethylformamide, acetonitrile, and pyridine were investigated; only pyridine was completely satisfactory for the analysis of mixtures Containing strong acids.
D
further work with the tetr:iliutylammonium hydroxide titrant (Z), errors similar t,o those 011tained with the nonexchanged b a w \yere obtnined occasionally with t,he anion exchanged titrant. Fritz and Yanianiura (3) substantiated that tlie new source of error result'ed frmn the reaction of strong acids with the solvent used. They found that tlir major limitation of acetone as a solvent for differentiating titrations of acid inistures was its react'ion with strong acids. A study was made of the behavior of strong acids with a number of d v e n t s comnionly employed in the nonaqueous titrations. The solvents used were acetone. isopropyl alcohol, methyl isobutyl ket,one (4-methyl 2-pentanone dimethylformamide, acetonitrile. and pyridine. Of these solvents, only pyridine was completely satisfactory for use n.itli strong acids. All the other solvents reacted in varying amounts. The error caused by reaction of a11 iadividiial acid with a solvent 1 ~ iiclr 3 ~ CRISG
sufficiently large in most instances to preclude the use of a n y one solvent. Hoxever, in differentiating titrations ~ l f acid niivtures containing a strong acid, a marked effect on the accuracy of analysis was observed. Observations similar t o those of Fritz and Yamamura, but unreported, may have dissuaded others from using thi; procedure for differentiating titrationc of strong acids. The purpose of thiq ktudy is to report the magnitude of the error caused by this reaction and to shon t h a t exact quantitative data \.an be obtained if proper experiniental conditions are employed. EXPERIMENTAL
N o a t of the reagents are described in
t h e following article ( 2 ) . Acetone, ace-
tonitrile, isopropyl alcohol, and dimethylformamide (DMF) were all of commercial grade; methyl isobutyl ketone ,MIBK) was purified as described bv Rruss and Wyld (1). The same titrimetric procedure was used as in the following work ( 2 ) . If the acid sample contained appreciable I\ ater, the methyl isobutyl ketone solutions n ere not homogeneous. Homogeneity was maintained in these samples b y addition of acetone. The solvent-solute interaction may tle illustrated by comparing results c h a i n e d in the respective solvents I\ lien determining sulfuric acid, hydrochloric acid, and a mixture of these 1\30 acids (Tables I , 11, and 111).
Figure 1 shows the potentiometric curves obtained in the titration of sulfuric acid in acetonitrile, dimethylfornianiide, pyridine, isopropyl alcohol, acetone, and methyl isobutyl ketone, respectively. Table I lists the results obtained on titration of 10% sulfuric acid in each of the above soh-ent's. Resuks in pyridine solution Tvere excellent. Results in the other solvents, if calculated for total acidity: \\-ere not too far from theoretical. However, there was considerable variance on the basis of the volume of titrant for the individual equivalents. This was particularly noticeable in the titrations in dimeth?-lforinaniide. Three inflections \\-ere present in the potentioimtric curve, as indicated in Figure 1; tlie additional inflection resulted from the hydrolysis of diniethylforiiiamide to formic acid. Although formic acid may be determined in this titration, only two equivalence points, the first and third, were used for t,he calculations in Table I. The longer the sulfuric acid remained in contact with diinetli~-lformaiiiide, tlie greater the amount of formic acid formed and t,he greater the difference in volume for the tn.o equivalents of sulfuric acid. The c u r w in Figure 1 for the titrat,ioii of sulfuric acid ivas obtained from a sample which \!-as held in diniethylfornianiide for 15 minutes prior to titration to emphasize blie solvent-solute reaction. If sulfuric acid VOL. 30, NO. 9, SEPTEMBER 1958
1447
were titrated immediately, only two inflections were observed in the potentiometric curve, although the two equivalents still titrated unequally. Dimethylformamide was not investigated further as a solvent, for such a reaction rendered it unusable in titrations involving strong acids. Two inflections were obtained in the potentiometric curve when hydrochloric acid was titrated in each of the solvents with the exception of pyridine. The first inflection was due to hydrochloric acid, and the second inflection was due in part to the residual acid in the solvent itself and in part to products of the reaction of the acid with the solvent. Figure 2, Fyhich shows the potentiometric curve for hydrochloric acid in acetonitrile, is typical of the curves for hydrochloric acid when titrated in acetone, isopropyl alcohol, and methyl isobutyl ketone. The curve for hydrochloric acid when titrated in pyridine is included for comparison. Table I1 gives the results obtained when titrating 10% hydrochloric acid in pyridine, acetone, isopropyl alcohol, acetonitrile, and methyl isobutyl ketone. The results in pyridine solution were both precise and accurate. The results based on volume of titrant to the ,second end point were satisfactory in the other solutions, but if hydrochloric acid were determined in an acid mixture, completely erroneous results would be predicted. The volume of titrant required for neutralization of hydrochloric acid dropped markedly the longer the hydrochloric acid remained in contact with methyl isobutyl ketone. I n addition to this effect, none of the titrations of strong acids in methyl isobutyl ketone
Table 1.
Solvent Acetone
Curves shifted and broken for clarity 1. Acetonitrile 2. Dirnethylformamide 3. Pyridine 4. Isopropyl alcohol 5. Acetone 6. Methyl isobutyl ketone
Figure 1. Titration of sulfuric acid with 0.1 N tetrabutylammonium hydroxide in various solvents
were too suitable, primarily because of poor potential readings. Hence, this solvent was not evaluated further. The effect of solvent-solute reactions would be expected to be much more pronounced in a differentiating titration of acid mixtures containing one or more strong acids. This was borne out when mixtures of sulfuric and hydrochloric acids were titrated. The potentiometric curve for the
Determination of Sulfuric Acid with 0.1 N Tetrabutylammonium Hydroxide
Added, Found,
Recovery,
Mg.0
Mg.
14.71 33.24 40.83 18.50 26.06 34.05 14.69 21.66 29.17 50.98 25.49 40.78 16.00 25.00 40.00 21.94 29.41 37.34
%
Found, Mg.b
Recovery,
%
Found, Mg." 14.60 33.04 40.59 18.33 25.88 23.76 14.60 21.50 28.96 52.77 25.32 40.95 16.18 25.58 39.67 21.94 29.37 37.34
14.39 97.9 14.80 100.6 32.77 98.6 33.28 100.1 40.25 98.6 40.93 100.2 100.5 18.59 97.6 Isopropyl 18.06 99.5 26.03 98.7 alcohol 25.72 33.89 99.5 98.7 33.60 100.7 14.80 98.0 Acetoni14.39 100.5 21.76 98.1 trile 21.24 100.1 98.3 29.20 28.68 DMF 47.49 93.2 57.94 113.6 21.75 85.3 28.89 113.4 33.82 82.9 48.08 117.9 MIBK 15.72 98.3 16.64 104.0 25.01 97.7 26.14 102.1 39.10 97.8 40.23 100.6 Pyridine 21.94 100.0 21.98 100.0 29.30 99.6 29.41 100 0 37.38 100.1 37.25 99.8 Based on volume of titrant to first end point. * Based on difference in volumes between final and first end point. c Based on total volume of titrant. 5
~~
1448
ANALYTICAL CHEMISTRY
Recovery,
%
99.3 99.4 99.4 99.0 99.3 99.2 99.4 99.3 99.3 103.4 99.3 100.4 101.1 99.9 99.2 100.0 99.9 100.0
titration of the sulfuric-hydrochloric acid mixture contained two inflections, the first end point representing the volume of titrant for the hydrochloric acid and one-half the sulfuric acid, the second end point representing the volume of titrant for the remainder of the sulfuric acid. Figure 3 illustrates the titrations of the acid mixture in pyridine and acetone solutions. Table I11 lists the results obtained when titrating mixtures of sulfuric acid and hydrochloric acid in pyridine, isopropyl alcohol, acetone, and acetonitrile. The results in pyridine were in good agreement: The results in the other three solvents demonstrate the inaccuracies caused by a small amount of solvent-solute interaction. DISCUSSION
The longer the strong acid solutes remained in contact with the solvent, the greater the solvent-solute reaction, with correspondingly larger errors being realized in the titration. This time effect was most pronounced in dimethylformamide solutions, to a lesser extent in methyl isobutyl ketone and acetonitrile solutions, and only to a small degree in acetone and isopropyl alcohol solutions. There was no interference in pyridine solutions, regardless of how long the solute remained in contact with pyridine prior to titration.
Table 11.
Determination of Hydrochloric Acid with 0.1 N Tetrabutylammonium Hydroxide
Solvent Acetone IsoDroDvl . * " alcohol Acetonitrile MIBK Pyridine
Added, Mg. 8.44 14.20 21.46 11.06 16.70 22.24
Found,
Recovery,
Found,
Mg.0
%
Mg.b
%
8.20 14.09 21.30 10.93 16.59 22.13
97.2 99.2 99.3 98.8 99 3 99 5
8.35 14.24 21.49 11.12 16 82 22 40
98.9 100.3 100.3 100.5 100 7 100 7
16.51 21.86 27.90 12.25 25.43 26.46
16.10 21.34 27.03 11.77 24.60 25.9
97.5 97.6 96.9 96.1 96.7 98.0
16.36 21.67 27.45 12.15 25.17 26.39
99.1 99.1 98.4 99.2 99.0 99.7
17.05 22.59 28.09
17.05 22.59 28.13
100.0 100.0 100.1
...
...
*..
...
Recovery,
... ...
Based on volume of titrant to first end point.
1
10.5 M L . 1
I
Figure 2. Titration of hydrochloric acid with 0.1 N tetrabutylammonium hydroxide in two solvents 1.
Curves shifted for clarity Pyridine 2. Acetonitrile
* Based on volume of titrant to second end point. Table 111.
Solvent Isopropyl alcohol Acetone Acetonitrile Pyridine
Figure 3. Titration of sulfuric-hydrochloric acid mixture with 0.1N tetrabutylammonium hydroxide in two solvents 1.
Curves shifted for clarity Pyridine 2. Acetone
Determination of Acid Mixtures with 0.1 N Tetrabutylammonium Hydroxide
Hydrochloric Acid Added, Found, Recovery, mg. mg. % 8.35 8.23 98.7 11.30 11.12 98.4 5.93 5.73 96.7 8.57 8.31 97.0 12.31 11.96 97.2 6.79 6.57 96.7 8.25 7.78 94.3 11.57 11.24 97.1 16.73 16.10 96.2 5.31 5.31 100.0 11.08 11.05 99.7 5.64 5.62 99.6
Pyridine has an unpleasant odor, titrations must be performed in an inert atmosphere, and it has much more of a leveling effect in the titration of strong acids than do the other solvents investigated. I n spite of these limitations, most inflections are sufficiently sharp to permit accurate determinations, and the absence of side reactions makes it the most suitable solvent for use in determinations of acid mixtures containing one or more strong acids. No effects noted with strong acids were observed in the titration of weak and very weak acids. I n the absence of strong acids, any of the solvents
Sulfuric Acid Added, Recovered, Recovery, mg. mg. % 10.82 11.33 104.7 7.55 7.76 102.8 14.85 15.01 101.1 10.72 10.83 101.o 7.48 7.66 102.4 14.51 14.60 100.6 9.41 9.60 102.0 10.49 10.62 101.2 14.98 15.42 102.9 7.06 7.08 100.3 6.90 6.89 99.9 16.08 16.03 99.7
investigated may be used with complete confidence in the results. ACKNOWLEDGMENT
The authors express their appreciation to Eleanor G. Rollins and Tony J. Miller, who performed several of the determinations, and to A. J. Sensabaugh for preparation of the figures. LITERATURE CITED
(1) Bruss, D. B., Wyld, G. E. A,, ANAL. CHEW29, 232 (1957). (2) Cundiff, R. H., Markunas, P. C., Ibad., 30, 1450 (1958). (3) Fritz, J. S., Ynmamura, S. S., Ibid., 29, 1079 (1957). RECEIVEDfor review January 18, 1958. Accepted May 9,1958.
VOL. 30, NO. 9, SEPTEMBER 1 9 5 8
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