Accuracy. T h e purification procedure effectively removes all possible interferences. T h e accuracy depends upon the reliability of the composition estimates of the polymer standards ( +2y0 for t h e major isomers). However, the absolute accuracy is difficult to assess because of possible non linearities introduced by two structural effects. First, polychloroprenes are copolymers of cis- and trans-polychloroprene, while the standards are essentially homopolymers. Second, although the predominate mode of addition of monomers units is head-to-tail, 10 to 15y0 of the monomer units are inverted, producing head-to-head and tail-to-tail sequence isomers ( 2 ) . Since
the cis isomer does not exceed 20% in typical polychloroprenes, nonlinearities introduced by these additional types of structural isomerism should have at most a small effect on the analysis, but no independent method of verification exists. ACKNOWLEDGMENT
LITERATURE CITED
(1) Aufdermarsh, C. A., Jr., Pariser, R., J. Polymer Sci., in press. ( 2 ) Ferguson, R. C., J . Polymer Sca.,
in press.
( 3 ) Jones, J. W., E. I. du Pont de Xemours & Co., unpublished data, 1963. (4) Maynard, J. T., Mochel, UT.E., J . Polymer S a . 13, 251 (1958). ( 5 ) Sternberg, J. C., Stillo, H. S., Schwendeman, R. H., ANAL.CHEM.32, 84 (1960).
The author acknowledges the contributions of several persons to this work. Polymer samples were provided by C. A. Aufdermarsh, Jr., J. W. Crary, W. J. Keller, J. T. Maynard, and R. M. Tabibian. J. W. Jones wrote the computer program and B. E. McGrath processed the data.
RAYMOND C. FERGUSON Elastomer Chemicals Department Experimental Station E . I. du Pont de h'emours & Co. Wilmington, Del Presented in part at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., 1964.
Nonaqueous Titration of High Molecular Weight Nitrogen Compounds SIR: Xonaqueous titrimetry has become a valuable analytical technique and has been used to analyze a h-ide range of nitrogenous bases including amines ( I ) , pyrazines ( S ) , amides ( 8 ) , and amine oxides (9). Short chain quaternary ammonium halides such as tetra-n-butylammonium bromide have been successfully determined in acetic anhydride using perchloric acid in acetic acid as t'itrant (7) but no procedure is reported for directly titrating the high molecular weight ammonium halides and methyl sulfate salts now of general commercial interest. Several procedures are reported in which the high molecular weight ammonium compounds are converted to acetates and titrated in propionic acid with perchloric acid ( 5 ) or in glacial acetic acid with perchloric acid (6), but these do not permit differentiation between salts with various anions. This paper presents a quantitative method for the direct nonaqueous titration of high molecular weight quaternary ammonium halides and acetates (alkyltrimethyl, dialkyldimethyl, and benzylalkyldimethyl) and the salts of fatty tertiary amines. I3isulfate and methyl sulfate salts can be qualitatively identified but their titration is not quantitative. This procedure, which uses perchloric acid in dioxane as the titrant and acetic anhydride as solvent, also permits determination of mixtures of ammonium halide salts and tertiary amines or mixtures of tertiary and secondary amines in a single analysis. EXPERIMENTAL
Apparatus. h Coleman Companion p H meter and a 13rown recorder were uqed in the titrations. T h e titrant wa> introduced using a Sargent con-
s t a n t rate buret with a 10-ml. capacity. The electrodes were Beckman glass and calomel fiber electrodes in which t h e usual aqueous KCl solution was replaced with an acetic anhydride solution of the desired salt. All the electrodes were equilibrated in acetic anhydride at least 24 hours prior to use and were stored in the solvent when not in use. Reagents and Solutions. Lithium perchlorate, anhydrous salt, and perchloric acid, 70%, were obtained from G. Frederick Smith Chemical Co., Columbus, Ohio. T h e acetic anhydride a n d chloroform were' ACS Reagent Grade. T h e dioxane was purified b y refluxing with sodium metal and distilling. Perchloric acid in dioxane, 0.05N, was prepared by adding 4.5 nil. of perchloric acid to dioxane and diluting to one liter. The acid was standardized against standard 4-amino pyridine (G. Frederick Smith Chemical Co.) dissolved in acetic anhvdride. The tetrabutyl ammonium sulfate was prepared by the reaction of tetrabutyl ammonium hydroxide with sulfuric acid. The quaternary ammonium halides and the amines used are commercially available inaterials and were used as received after drying. The quaternary ammonium acetates were formed as described by I'ifer and Wollish ( 4 ) . The amine salts were prepared by reacting stoichiometric amounts of the dissolved amine with the appropriate acid. The amides were purified by recrystallization. Procedure. A sample of approuimately 3.5 X moles is weighed directly into a 100-nil. beaker or a 5-nil. aliquot is taken of a solution of 0.007 moles in 100 ml. of chloroform. T o the weighed sample, 5 ml. of chloroform are added t o effect solution. Acetic anhydride (30 ml.) is added and the sample is titrated with 0.05N perchloric acid in dioxane. The results
are plotted by the Brown recorder and the end point is ascertained by taking the point of inflection of the titration break. It is important to keep the level of dioxane in the final solution under 25%. DISCUSSION
The effects of titrant, solvent, and electrode pair for the titration of ammonium salts were determined by varying one parameter at' a time and analyzing a standard solution of dimethylditallowammonium chloride. The results were compared on the basis of the end point potential, half-neutralization potential, and the potential change at the titration break, measured as AI? End Point (AE,,). For this work, the half-neutralization potential ( H S P ) is the midpoint of t,itration and the AE,, is defined as the difference in millivolts between 90% and l l O ~ oof the sample titration. The titration data obtained under varying conditions are given in Table I. All the electrodes were similar in performance with the exception of the LiC104-KC1 combination which gave abnormal titration curves. This 1)henomenon was reproducible and occurred in the titration of both sample and solvent. Since both the LiC104 and KCl when used alone gave tyi)ical curves, as did a LiC104-LiC1 solution, it must be the particular LiC1O4-KC1 combination which caused the aliiiarent change in the potential. Similar interferences of potassium and sodium ions are reported ( 2 ) in nonaqueous titration of weak acids with tetrabutylammonium hydroxide and the effect iyas caused by the reaction of the liotas3ium ion with the glass electrode. In the present case, however, this is not a VOL. 36, NO. 1 1 , OCTOBER 1964
2205
~
~~
~
Table 1.
Table It.
Titration of Nitrogen Compounds Compound EP H S P AEep
Variations in Titration Conditions
Variation LiC104 in AcnO (0.1M) LiC104(O.1M) + KC1 (sat'd sol.) in AcoO LiCl in AcpO (sat'd sol.) KC1 in AcpO (sat'd sol.) LiC104 (0.1M) + LiCl (sat'd sol.)
Results EP H'VP AE,, Various calomel reference electrodesa -594 mv. -344 mv. 450 mv. - 581 - 662 - 725 - 630
Ammonium salts Dimethyl ditallow, C1Trimethyl dodecyl, ClDimethvl didode&l, C1Dimethyl benzyl alkyl, C1Dimethyl ditallow, BrDimethvl ditallow, AcDimethyl ditallow, Me-
. .
- 400 -412 - 463 - 384
469 388 332
Various solvents Acetic anhydride Acetic acid Dioxane
- 594 - 770 -400
- 344 - 730 - 270
450 30 142
Various titrants HC104 in dioxane HC104 in acetic acid HC10, in acetic anhydride 0
- 594 - 700 -552
- 344 - 440 - 395
so4so4- 2
450 284 195
( Tetrabutyl)2-
Amines Dimethyl dodecyl Dimethyl tallow Methyl ditallow Didecyl Ditallow Octyl Methyl ditallow-HC1 Methyl dicoconut-HC1 Methyl ditallow-HOAc Dimethyl tallow-HOAc (Methyl ditallow)z-HzSO4
Glass electrode used as indicating electrode.
satisfactory explanation because the KCl electrode performed in a normal manner. It is believed that the reverse response of the LiCIOa-KC1 electrode arises from deposition of KClOa in the fiber of the electrode. These data in Table I also show that limited solubility of salts (KC1 and LiC1) in acetic anhydride does not necessarily limit their usefulness as electrolytes. This is in contrast to the work of Wimer (8)who reported that LiCl could not be used as an electrolyte solution. Both the LiCl and KCl electrolyte performed as well as electrolytes having a greater solubility in acetic anhydride. Acetic anhydride is the preferable solvent to use because it gives the largest AEcp. Of the titrants examined, the HClO, in dioxane was the preferred one. The HClOh in acetic anhydride titrant, which was prepared by mixing 70y0 perchloric acid with acetic anhydride, became deep red in color upon standing overnight'. It was less than half its theoretical normality, indicating a definite interaction between the two compounds. The conditions determined as optimum for titrating quaternary nitrogen compounds are similar to Wimer's for amides and include perchloric acid in dioxane, acetic anhydride solvent, and an electrode pair of glass-calomel containing LiCIOk. The influence of appreciable amounts of dioxane upon the system, introduced either from the titrant or as part of a dioxane-acetic anhydride mixed solvent! was studied. When the concentration of dioxane was 25% or less by volume a t the end of the titrat'ion, satisfactory curves were obtained. However, when the dioxane level rose higher than 25%, a double break was noted near the end point indicating some interference from the dioxane. 2206
ANALYTICAL CHEMISTRY
The mechanism of this reaction is not known. Approximately ten quaternary ammonium salts and ten amine salts were examined and compared with amines and amides analyzed under the same conditions. Typical examples are shown in Table 11. The quaternary results indicate that the chain length or substitution on the nitrogen atom does not affect the potentials measured; the slight variation in end point potential is insignificant because of the large AE.,. However, the anion portion of the molecule does alter the AEep as well as the EP and HIVP, as was expected. The amine salts are comparable in titration to the quaternaries. Primary and secondary amines are acetylated to amides in the acetic anhydride solvent and titrated in the same end point potential range as amide samples. As with the quaternaries, the alkyl chain length of the
-600
-350
450
-563
-305
447
-584
-326
479
-605
-347
437
-668
-437
369
- 468
- 247 484
- 700
- 589
- 240 - 670
- 80 330a - 580 1255
-413 -413 -463 - 775 - 705 - 775
- 106 -113 - 138 - 638 - 600 - 656
694 562 175 200 150
-681
-419
375
- 676
-431
369
- 456
- 244 444
- 481 - 275 - 350 - 760
SEC A M I N E H
QUATERNARY AND AMINE
ME SO^ AND HS04
H SEC
AMINE HCL I
QUATERNARY 8 R H
AMINE
HCL
U
QUATERNARY C L H
ACETATE
H
QUATERNARY ACETATE H
TERT
SULFATE
AMINE
H QUATERNARY S U L F A T E
1
I I
-100
-200
I
-300
-400
I
-500
I
-600
I
I
-700
-800
MILLIVOLTS
Figure 1 .
- 190 255" - 615 1505
amines does not affect the end point potential. Sulfate salts gave two distinct breaks in this system indicating that both the sulfate and bisulfate ions are being
H
AMINE
450
5
PRIM. AMINE
AMINE
...
Amide Dodecanamide - 806 - 694 138 N-(2-hydroxyethyl) dodec- 819 - 706 100 anamide Titration not quantitative.
AMIDE
TERT
1165
Half-neutralization point ranges
titrated. The titration is essentially quantitative but precision was poor; values ranged from 98 to 107% of theory for the total titration. The results approached a 1 : l ratio for the two species. Methyl sulfate and bisulfate salts gave similar H S P and E P but the results were not quantitative with values ranging from 45 to 85y0of theory. The titration of the high molecular weight nitrogen compounds except for the sulfates is quantitative and the standard deviation calculated from replicate analyses of the ditallowdimethylammonium chloride is 1.47% a t the l00Y0 level. The half-neutralization potential ranges of the nitrogen compounds examined are shown in Figure 1. The data graphically show those compounds whose H S P are sufficiently separated to allow differential titration in mixtures, such as tertiary amines and quaternary ammonium chlorides or tertiary and secondary amines. The information in Figure 1 together with the AEeP given in Table I1 shows that the workable range of the HC104 in dioxane titrant with the acetic anhydride solvent is -50 to -800 mv. As would he espected, the A K e p value for each compound is dependent upon the H S P and becomes smaller as the N T P apl~roaches -800 mv. The reproducibility of the H S P was determined from replicate analysis of the
Table 111.
Titration of Mixtures
Mg.
Compounds Compounds Ditallow methyl amine and Ditallow amine Uitallow dimethyl amm. chloride and Ilitallow dimethyl arnni. bromide Ditallow methyl amine and Ditallow dimethyl amm. chloride
EP
HSP
A E e p Expected Found
-313
-114 -656 -295 -450
325 150 50 325 221 290
- 725
-375 - 710 -232 -595
ditallowdimethylamnionium chloride. The standard deviation is 15.4 my. Three samples of mixed nitrogen compounds were titrated and the results are given in Table 111. Good agreement was obtained between the expected and experimental reault,s. The halfneutralization potential of each component is approximately the same as when titrated alone but the end point potential of the coxiiiiouiici titrated first changed api)ro?iimately 100 to 200 mv. as would be expected. The diffwences in H S P and AE,,, for the two compounds titrated in the first arid third mixture are ideal for analyzing such samples. Since the sampler titrated were comniercial samples, the observed differences were expected. In the second mixture, the small millivolt differences between H S P and
ca.-100
-385
56 1 46 4 82 61 97
82
57.8 45 2 83 8 64 5 99 5 83 5
the lower A E c p make the end points less sharp but the result\ show that the method is quantitative and it is possible to perform differential titrations of mixtures of quaternaries. LITERATURE CITED
(1) Fritz, J. S., Fulda, 11. O., ANAL. CHEX 25, 1837 (1953). ( 2 ) Harlow, G. A , , Ibid., 34, 148 (1962). (3) Murray, R. W.,Iteilley, C. S.,lbicl., D. 313R. ( 4 ) Pifer, C. W., Wollish, E. IT., Ibi-d., 24, 300~ fl9.52).~ ~ , ( 5 ) Iiiddirk, J. A , . Ibid., 32, 178R (1960). ( 6 ) Ibid., p. 1771t. ( 7 ) Streuli, C. A.,Ibid., 30, 997 (1958). (8) \\:?mer, D. C., Ibid., p. 77. ( 9 ) Vi imer, I>. C., Ibid., 34,873 (1962).
MARYE L L E N P Z X H O F F J . H. BENEDICT Ivorydale Technical Center Procter & Gamble Co. Cincinnati, Ohio
Thin Layer Chromatographic Separation of Orthophosphate and Pyrophosphate SIR: Recently the application of chromatographic techniques to difof phosphate mixtures has been made. 1 %use ~ of paper chromatography, \Yestman and Scott (8) have determined members of the family of chain phosphates as high as the dodeca1)hosphate and a number of ring phos1)hates. Two-dimensional chromatography as described by KarlKroupa ( i t ) , can be wed to distinguish clearly betlveen the family of ring and the family of chain phosphates. Paper chroniatogralihy has also been successful in the se1)aration of the various phosphate esters of both orthophosphate and condensed phosphates. Hanes and Isherwood ( 2 ) develolied this method te for seliaration of the ~ ~ h o s p h a esters. Recently. Ohaehi and Iran Wazer (?) have reported the separation of long chain phosphates by paper chromatogral)hy. Hettler (3) compiled a refercnce list including all the work until I958 on the chromatographic separation of phosl)hates. S o method for the separation of
phosphate mixtures by thin layer chromatography was found in the literature. Therefore, a method was developed for the thin layer chromatographic separation of phosphates. This method was evaluated by using phosl)horus-32tagged c o m p u n d s and autoradiograms of the chromatogram. Examination of the autoradiogram was made to decide when adequate separation of the compounds had been achieved. The film used for the autoradiograms was Kodak Royal Medical x-ray film. Time of exposure is dependent on the level of activity on the chromatogram, but in general, the film was exiiosed for 24 to 48 hours. Ph o s 1) h or u s - 32 -1 a be 1e d p y r o p h o sphate was prepared using an adaptation of the procedures given by Lowenstein (6) and Campbell and Kilpatrick ( 1 ) . Cellulose powder (13rinkmann Instruments;, Inc.) was a satisfactory adsorbent for thin layer separation of orthophosphate and pyrophosphate using the solvent system suggested by Kolloff ( S ) . Silica gel G and aluminum
Solvent tront
OO
0 +
+
Orthophosphate
Pyrophosphate
oriqin
Figure 1 . Autoradiogram of orthophosphate and pyrophosphate Chromatogram development time, 1 hour; exposure time for x-ray film, 2 4 hours; temperature, 2 3 ' C.; autoradiogram, 2 0 0 mm. by 50 mm.; solvent front, 1 3 5 mm. from origin; origin, 1 0 mm. from bottom of chromatogram; R j values, 0 . 8 3 (ortho) and 0 . 6 1 (pyro).
VOL. 3 6 ,
NO. 1 1 ,
OCTOBER 1964
2207,
