1196
J. W. JORDAN, B. J. HOOK, AND C. Y. FINLAYSON
ORGANOPHILIC BENTONITES. I1 ORQANICLIQUIDGELS J. w.JORDAN,’ B. J. HOOK,’ AND C. M. FINLAYSON’ Mellon Institute, Pittsburgh, Pennsylvania Received November 88,1949 INTRODUCTION
The striking behavior of certain organic ammonium complexes of montmorillonite in various organic liquids has already been described in previous publications (6, 7). This work was a continuation of research by Hauser (3), who discovered that hydrophilic clays may be converted to the organophilic condition by reaction with appropriate organic ammonium salts. A bentonite originally exhibiting high swelling in water will, after base-exchange reaction with certain organic ammonium salts, show a decided aversion to water and a remarkable tendency to swell in various organic liquids. In fact, the treated clay will swell to a much greater extent in some organic systems than will its untreated counterpart in water. In further study of such clay complexes the liquid-binding capacity of these materials has been evaluated from the standpoint of gel formation, and important factors in the production of gels have been investigated. MATERIALS AND METHODS
As in the previous work, bentonite from the National Lead Company property at Clay Spur, Wyoming, was used. Aside from a relatively small proportion of accessory nonclay material, this product was essentially pure montmorillonite according to thermal* and x-ray ana lyse^.^ A base-exchange determination4 was made by the ammonium acetate method (2) on a sample of clay obtained after thorough sedimentation of nonclay impurities from an aqueous 2 per cent dispersion. A cation-exchange value of 94 milliequiv. per 100 g. of clay was reported on a sample containing 6.4 per cent of adsorbed moisture. This computes to approximately 100 milliequiv. per 100 g. of dry clay mineral. The ammonium compounds were distilled-grade materials obtained from commercial sources, viz., Sharples Chemicals, Inc., for short-chain amines, Armour and Company for higher aliphatie amines, and Onyx Oil and Chemical Company and Armour and Company for quaternary ammonium salts. The reaction products were generally prepared by adding dilute (5 per cent) aqueous amine acetate or ammonium halide solutions or dispersions to the super1 Holder of Fellowship on Lead sustained by the National Lead Company a t the Mellon Institute, Pittsburgh, Pennsylvania. 2 The thermal analysis was performed through the courtesy of R. E. Grim of the Illinois Geological Survey. 3 The x-ray diffraction analysis of the sample was carried out by L. E . Alexander of the Department of Chemical Physics of the Mellon Institute. 4 The base-exchange determination was made through the courtesy of F. J. Williams of the National Lead Company Research Laboratoriea in Brooklyn, New York.
ORGANOPHILIC BENTOSITES. I1
1197
natant liquid resulting from allowing a 3.25 per cent aqueous bentonite slurry
to sediment for 1 hr. Where larger quantities of product were required than could be made conveniently in laboratory equipment, pilot-scale preparation was resxted to. In these cases a 3.25 per cent bentonite slurry was pumped through a No. 6 Sharples supercentrifuge to remove the nonclay minerals. After analysis for solids content the effluent was then used for subsequent reaction with amine acetates or quaternary ammonium halides. Reaction of amine salt with clay was accompanied by thorough flocculation. Filtration of the flocculent precipitates was easy in most cases. After washing, the filter cakes were dried at about 85"C., and pulverized. In the first paper of the series (6) the ability of the reacted clay to imbibe organic liquids was evaluated by allowing a weighed sample to swell to an equilibrium gel volume in contact with an appreciable excess of liquid. In the present study the clay complex was placed in contact with organic liquid in such proportion as to be generally in excess of the amount required for complete immobilization of the liquid. For this purpose 20 per cent of dry solid on the basis of total mixture was sufficient to provide stiff gels in most cases. A comparative measure of gel strengths was afforded by a determination of the depth of penetration into the gels by a standard A.S.T.M. grease cone. Penetrations were measured by means of a precision-type penetrometer, using the procedure specified for unworked greases (A.S.T.M. Designation: D217-44T). Thixotropy customarily necessitated a short waiting period after filling the sample can and before releasing the penetrometer cone, but this period never exceeded 15 min. The achievement of equilibrium conditions in these gels consisted for the most part in stirring the bentonite complex into the liquid with a laboratory mixer and following up with a spatula. Where the mobility of the liquid and the adsorption energy of clay complex for liquid were low, passage through a three-roll paint mill was occasionally obligatory, as in the preparation of gels with linseed and petroleum oils. Reproducibility of results was on the order of i 3 scale divisions (tenths of a millimeter) for a reading of 200 for repeated readings on one gel, or approximately 1 4 in 200 for two gels of the same composition. RESULTS AND DISCUSSION
Primary normal aliphatic ammonium bentonites were prepared at 100 milliequiv. of amine per 100 g. of clay with amines of chain length from four to eighteen carbon atoms in steps of two. Gelling tests were made in polar liquids, such as alcohols and ketones, and in nonpolar liquids such as benzene and mineral spirits, as well as in nitrobenzene, which combines highly polar with highly organic characteristics. Since gelation was poor in the first two types and excellent in the third, it was concluded that a mixture of a polar and a nonpolar type should be chosen for optimum solvation. Such a mixture was afforded by a combination of methanol and toluene, neither one of which was as effective by itself. The gelling abilities of these homologous complexes were determined in various mixtures of toluene with methanol, and the optimum gel strengths plotted (figure 1) as a function of amine chain length. The butyl- and hexyl-ammonium
1198
J. W. JORDAN, B. J. HOOK, AND C.
M. FINLAYSON
complexes a t 20 per cent solids gave, at best, only muddy soups which were beyond the practical limits of measurement by the penetrometer. Essentially maximum gelation was first achieved in the series with the dodecyl complex, and increases in amine chain length up to eighteen carbon atoms showed little further influence upon gel structure. In appearance the best gels (four in number) were smooth homogeneous olive-brown systems, translucent in bulk and in thin section. Concurrent with the general increase in gelling ability of the foregoing series with increase in size of the amine molecule was a decrease in the amount of methanol required for maximum gelation. This is depicted graphically in figure 2, where the percentage of methanol in the optimum toluene-methanol mixture is related to the chain length of the amine. On the adsorption of organic molecules
URBDN ATOMS IN AMINE CWlN
FIQ.2 FIQ. 1 FIQ.1. Optimum gel strengths of primary aliphatic ammonium bentonites in toluenemethanol mixturea (20 per cent solids). FIO.2. Per cent methanol required for optimum gelation of primary aliphatic ammonium bentonites in toluenemethanol mixtures (20 per cent solida).
by montmorillonite (Hendricks (4), Bradley (l), and MacEwan (8-10)) an attempt has been made to correlate the amount of methanol necessary for optimum gel strength with the area of clay surface remaining uncoated by amine molecules. Such a correlation is obviously not tenable for the entire series, as evidenced by the character of the curve in figure 2. However, another important factor here is the initial spacing of the montmorillonite flakes with respect to one another. An x-ray diffraction study of this same homologous group of complexes (6) has indicated that in the dry state the clay flakes are oriented t o a large extent in parallel positions, with a space of only 4 b. separating them in the case of amines having ten or fewer carbon atoms. This space, which represents the effective van der Waals thickness of a hydrocarbon chain, is more or less completely occupied by the amine chains. With twelve or more carbon atoms the area covered by the amine chains is sufficiently great so that adjacent parallel oriented clay platelets are unable to approach one another more closely than a
1199
ORGANOPHILIC BENTONITES. I1
w.,
distance of 8 or the thickness of two hydrocarbon chains. Because of this spatial characteristic and of the gross difference in order of gelation of those complexes having amines of fewer than twelve carbon atoms (figure l), only the CITGI~group will be considered. Bradley (1) and MacEwan (10) postulate hydrogen bonding between methanol and montmorillonite, giving rise to ad.sorptive forces of higher magnitude than the van der Waals forces operating to adsorb nonpolar liquids. Hence, the methanol in a toluene-methanol mixture should be preferentially adsorbed, to the extent of the capacity of the clay complex. This capacity has been approximated, in terms of available uncoated surface area, from a computation of the total surface area of the clay (0.8 X loz3A? per gram of montmorillonite) and of the area coated by the amine molecules. and is presented in table 1. TABLE 1 Ssatial re2ations for homologous alkylammonium bentonites W B O N ATOM
IN AMINE W I N
LAYEPS O? *KINE BETWEEN FLAKES
APKA AVAILABLE PEP WETEANOL
UNCOATED APE* OF CLAY
YOLECULP
A .a
per cent
0 6 8 10 12 14 16 18
100 66 58
51 43 36 28 21
9.6 X 8.3 X 7.1 X 5.9 x 4.8 X 3.7 x 2.6 X
loza
lo2' lo*' 10'8 loz8 1023 loz*
35 20 6.1 4.0 3.0 2.6 2.0
5.3 x ,3.0 x 0.93 X 0.61 X 0.45 X 0.40 X 0.30 X
102'
1.8 2.8 7.6 9.7 10.7 9.2 8.7
1023 10" lopa loz' loz8 loza
Pauling (11) lists the effective diameter of the methyl group as 4 A. Assuming that the methanol molecules are adsorbed onto the uncoated surfaces of the clay through the mechanism of hydrogen bonding (CH8-O-H
I
I
+
O s i or
H-O-CH-H + O S i as MacEwan suggests) and that close packing is maintained, the minimum area covered by one molecule would be on the order area calculated as being of 12 A? This is not far out of line with the 9-11 available for each methanol molecule, especially when it is considered that the figure for total area did not take into account the edges of the flakes, which would appreciably increase the available area. Since the agreement appears to be more than coincidental, confirmation seems to be at hand for the earlier proposal that solvation in binary liquid mixtures involves the formation of an adsorption complex between the uncoated portion of the clay and the more polar member of the liquid mixture, followed by solvation of the adsorption complex in the less polar remnant. It is probable that in the amine complexes below CIZthe forces of attraction between flakes, acting through only half the distance, are of considerably higher magnitude. Therefore, it is not unlikely
1209
J. W. JORDAN, B. J. HOOK, AND C. M. BINLAYSON
that the disproportionately larger quantities of methanol are required to exert a sort of mass action effect in crowding between flakes and forcing them apart, making the organophilic surfaces more readily available to the less highly adsorbable hydrocarbon molecules. In consideration of the finding that an amine of more than ten carbon atoms is required for maximum gel strength in this type of system, further work was confined to organic ammonium compounds above this critical limit. Gel strengths for dodecyl-, hexadecyl-, and octadecylammonium bentonites were determined in mixtures of toluene with various normal primary aliphatic alcohols up to and including decyl. Figure 3 shows a family of curves relating penetration for gels of 20 per cent octadecylammonium bentonite as a function of the percentage 40(
36C
i
-
I
320 2-
P I-
PQ 28C
Li 2 a w
+?’. ...
24C
z 0
U
n Methanol c--4-
:F
20c
160
Ethanol
~-Isopropanol -d-
-.A-
C--D
IO
,
,
,
20
30
40
- n-Butonol n-Hexanol ,
,
,
,
50
60
70
80
PER CENT ALCOHOL I N MIXTURE
90
FIG.3. Gel strength of octadecylammonium bentonite in toluene-alcohol mixtures (20 per cent solids). of six different alcohols in alcohol-toluene mixtures. A few salient features may be readily observed in this graph. All of the curves consist of two distinct sections: a very steep slope a t low alcohol concentrations, rapidly approaching a gel strength maximum, and a more gradual slope of opposite sign extending from the gel maximum. The steep slopes are interpreted as representing practically complete adsorption of the alcohols from the mixtures. This adsorption renders the clay surface more completely coated with organic matter and consequently more organophilic. At the point of complete coverage the adsorption complex is more compatible with the toluene and solvates in it more readily and to a greater extent. The second portion of the curve is probably indicative of the dilution effect of the excess of alcohol upon the solvating capacity of the toluene. It would not seem logical for methanol to have much in common with the eighteen-carbon-atom chains covering most
1201
ORGANOPHILIC BENTOSITES. I1
of the clay surface; consequently the deleterious dilution effect does actually diminish as the character of the alcohol approaches that of the amine hydrocarbon tail. In order t o avoid repetition of data, it will suffice to state here that the corresponding curves for the CM and CIZcomplexes are essentially similar.
FIG.4. Relationship between size of alcohol and amount required for optimum gelation of aliphatic ammonium bentonites in toluene-alcohol mixtures.
'1
2
4 5 6 7 8 CARSON CHAIN LENGTH OF ALCOHOL
3
9
IO
FIG.5 . Alcohol requirements for optimum gelation of aliphatic ammonium bentonites in tbluene-alcohol mixtures.
With all three complexes the gel strength maxima occur at low percentages of alcohol, these maxima occurring at progressively higher concentrations of
alcohol with increasing molecular size of the alcohol (figures 4 and 5). The linearity of these curves suggests a simple relationship between amount of alcohol required and molecular weight. This relationship is brought out in table 2, where mole fractions of alcohols a t gel maxima are related to the uncoated areas of the three amine-bentonite complexes. These mole fractions are moderately constant
1202
J. W. JORDAN, B. J . HOOK, AND C. 311. FINLAYSOS
Ethyl. . . . . . . . . . . . . . . . . . . . . . . . . Propyl. ........................ Butyl. ......................... Hexyl. . . . . . . . . . . . . . . . . . . . . . . . . . Decyl.. . . . . . . . . . . . . . . . . . . . . . . . . Average. .......................
-
0.086 0.092 0.097 0.091 0.087 0.091
Number of alcohol molecules. . . 0.51 X lo2* Uncoated area of clay.. . . . . . . . . 43 per cent Uncoated area of clay., . . . . . . . . 6.9 X 10" A.2 Available area per molecule. . . . 11.6 A.x
1
I
0.056 o'058 0.053 0.057 0.060 0.058
1
0.044
1
0.32 X 1028 28 per cent 3.7 X 10"
0.048
0.045
A.p
0.037 0.037 0.045 0.24 X lo*$ 21 per cent 2 . 6 X 10" La 10.8
11.6
A.B
URBON CWIN LENGTH OF ALCOHOL
Fro. 6. Gel strengths of aliphatic ammonium bentonites in optimum toluene-alcohol mixtures.
sticking out at an appreciable angle to the clay surface; and that one particular grouping in common to all of them is involved in the adsorption phenomenon. On the basis of this evidence, it is hypothesized that the adsorption of alcohols takes place through hydrogen bonding between the -OH groups of the alcohols and the -0 group on the silicate surface, Le., R-0-H
I + 0-Si.
1203
OKChSOPHILIC BESTOHITES. I1
With all three complexes gel strength maxima decrease in magnitude with increasing molecular size of alcohol. This is brought out in figure 6 , which indicates gel strength as a function of carbon chain length of the alcohols in the toluene-alcohol mixtures. MacEwan (10) states that the energy of adsorption of clay for alcohols decreases with increasing molecular size of aliphatic alcohols. This was corroborated by the necessity for milling the octadecylammonium bentonite system in mixtures of toluene with alcohols higher than propyl, in order t o attain stable equilibrium values. It is believed that this decrease in adsorption energy is related to the decrease in gel strengths occasioned by the use of the higher alcohols.
I
5
I
10 IS PER CENT METHANOL
I
I
20
25
F I ~7.. Gel strengtb of octadecylammonium bentonites of various amine:clay ratios in toluene-methanol mixtures (20 per cent solids). faINE:cLAY RATIO
For a given amine the ratio of amine to clay is an important factor in the gelling ability of the complex. Octadecylammonium bentonites were prepared by the addition of various ratios of amine acetate to centrifuged clay disperaiom from 50 to 200 milliequiv. of amine per 100 g. of clay in 25 milliequiv. steps. Although the retention of amine was not complete, it was substantial, even above the cation-exchange capacity of the clay. Figure 7 depicts the gelling ability of the various complexes (noted in terms of milliequivalents of amine added per 100 g. of clay) as a function of concentration of methanol in various toluenemethanol mixtures. Optimum gels were obtained in the region of chemical equivalence of amine cation to clay anion (figure 8). Gel maxima for the various complexes decreased in regular manner as the amine:clay ratio diverged from this point, representing an amine:clay ratio of approximately 90 milliequiv. per
1204
J. TV. JORDAN, B. J. HOOK, AND C. M. FINLAYSON
100 g. This substantiates the hypothesis, based on swelling data, that below the region of chemical equivalence the ionic nature of the complex together with its scantier roating of hydrocarbon material renders it relatively incompatible with the solvating medium. Beyond the region of stoichiometric proportions it is presumable that the adsorptive forces of the clay become progressively more saturated by excess adsorbed amine and consequently less capable of promoting solvation by the liquid medium. A further observation from figure 7 is that, although the actual maximum gel strengths vary according to two intersecting curves of opposite slope (figure 8 ) , the amount of methanol required for gel strength maxima varies as a continuous function of the ratio of amine to clay (figure 9). This falls in line with data presented in figure 2; i.e., as the surface area of the clay flakes becomes
{:I\ Y z
E3
75 100 125 150 175 MlLLlEQUlVlLENTS 4MlNE PER I O O G R A M S O F C L 4 I
‘50
FIG.8
FIG.9
FIG.8. Gel strengths of octadecylttmmonium bentonites in optimum toluene-methanol mixtures (20 per cent solids). FIG.9. Relationship between amine:clay ratio and amount of methanol required for optimum gelation of octadecylammonium bentonites in toluene-methanol mixtures.
more completely coated by amine molecules, less area remains for adsorption of methanol. The fact that the methanol requirement is not eliminated in this range of high amine content is interpreted as indicating an adsorptive rompetition between amine and methanol for the 20 per cent of space remaining over and above that preempted by the amine attached through ion-exchange reartion. DebyeScherrer x-ray photographs were made of the above octadecylammonium bentonite complexes and of related complexes covering several intermediate ratios of amine:clay. The basal plane spacings of samples, d(001), have been plotted in figure 10 against ratio of amine:clay as determined by Kjeldahl nitrogen analysis. On this same graph are plotted auxiliary data, e.g., per cent of basal plane area coated by amine, and separation of the platelets in Angstrom units. The precision of the method is believed sufficient to warrant th,e discrete changes in the slope of the curve. The lowest horizontal section, a t 4 A. separa-
1205
ORGANOPHILIC BESTONITES. I1
tion, apparently represents the situation in which less than half the surface area of the clay is coated by amine molecules lying flat with the planes of the zigzag chains parallel to the surfaces of the flakes. In the region of 50 per ce2t coverage, it is obviously necessary that the flakes separate by another 4 A. distance in order to make room for a double layer of amine chains between adjacent platelets. Addition of further amine beyond the quantity necessary for complete coverage of the flakes instigates a crowding situation; in order to accommodate the crowd the amine chains must rise up on edge. The effective width of a zigzag hydrocarbon chain is computed from Pauling’s (11) data as 4.9 A. Actually, a spacing of 10.4 1.was observed between flakes for the situation involving two layers of chains oriented edgewise on the clay surfaces. This orien20 J
I
COVERED BY AM I NE 40 60 I
I
80
100
I
I
(28
FIG.10. Effect of increasing ratio of octadecylamine to bentonite upon basal plane spacings.
tation should theoretically provide space for about 25 per cent more molecules, a prediction which agrees reasonably well with observation. Further crowding must gradually force the amine mo1e:ules up on end, accounting for the next jump to a fla,ke separation of 23-24 A. This is in satisfactory proximity to the figure of 25 A. computed for the length of the octadecylamine molecules. The continuous halo no doubt indicates flakes in all stages of separation, with the average increasing toward the highest amin$:clay ratio, as evidenced by the disappearance of the distinct band at the 10 A. level for th,e final sample. Sedletski1 and Yusupova (12) have found d(001) values up to 28 A. for montmorillonite clays occurring in petroliferous areas. This high spacing they attribute to adsorption of organic components from the petroleum oils in a somewhat analogous manner. It is the opinion of the authors that the reasonable coincidence between ob-
1206
J . M-. JORDAN, B. J. HOOK, A N D C. M. PINLAYSOX
served and calculated data in the foregoing paragraphs would tend to refute the postulate of Johnson (5) that the exchange capacity of montmorillonite is directly related to the broken edge bonds of the clay mineral flakes. Assuming the validity of this latter picture of the base-exchange reaction, it would be difficult to interpret the spatial relationships which have been fitted together here. QUATERNARY AMMONIUM COMPLEXES
Complexes in which the bentonite is completely clad by reaction to stoichiometric proportions with larger organic ammonium salts give general confirmation to the story which has been built up. For example, dimethyldihexadecylammonium bentonite, in which the organic portion is in 40 per cent excess of the amount necessary to provide complete monomolecular coverage of tho clay min-
6
"
MOO-
-
c
8
-
>
-0001 P E R CENT SOLIOS
0
2
4 6 8 1 ROTATIONAL RATE, R P M
0
FIQ.12 FXQ. 11 FIG.11. Viscosity of refined linseed oil containing dimethyllauryloetylammonium bentonite, aa observed Kith a Brookfield viscosimeter. FIQ.12. Dimethyldioctadeoylammonium bentonite in petroleum oil
era1 surfaces, will gel in toluene alone. Addition of methanol serves merely to reduce the gel strength. This suggests that the previously propounded proposition is essentially valid, i.e., that the clay complex should he entirely coated by organic matter attached through ion-exchange reaction for maximum compatibility with a nonpolar solvating organic liquid such as toluene. MacEwan (10) states that aromatic hydrocarbons are adsorbed by montmorillonite, whereas completely saturated aliphatic hydrocarbons are not. This correlates well with the spontaneous gelation of the above complex in toluene and with the much lesser gelation in mineral spirits. Apparently, residual attractive forces must remain operative between the clay and the molecules of the surrounding medium. These forces, together with a solvent effect of the liquid upon the hydrocarbon coating of the clay, are believed responsible for the dispersion and gelation which take place. In a nonpolar aliphatic liquid of low mobility and poor solvent action-light
ORQANOPHILIC BENTONITES. I1
1207
white mineral oilkexternally applied mechanical energy in lieu of the energy of the system is sufficient to disperse dimethyldihexadecylammonium bentonite to produce a smooth homogeneous light-colored translucent gel (penetration 165 a t 20 per cent solids). In the same liquid octadecylammonium bentonite provides only a muddy opaque slurry of low viscosity. However, the addition of 5 per cent of a polar liquid, such as butyl acetate, acetone, or butanol, converts the slurry to a stiff translucent gel with a penetration of 120. Figure 11 illustrates the effect of dimethyldodecylhexadecylammonium bentonite upon the viscosity of refined linseed oil. Thixotropy of these dispersions was evident a t all four concentrations in that, at all four spindle speeds of the Brookfield viscosimeter, the apparent viscosities decreased rather rapidly u-ith rotation of the spindle, finally leveling off a t the recorded equilibrium values. A qualitative measure of the degree of thixotropy characteristic of the stiff gels is brought out in figure 12, which s h ~ w sthe effect of mechanical agitation upon the cone penetration of a 20 per cent gel of dimethyldioctadecylammonium bentonite in a petroleum lubricating oil. The agitation in this case consisted of sixty complete strokes at one per second in a standard grease worker immediately prior to determination of penetration. This effect is quite apparent in the case of thin gels of octadecylammonium bentonite in mixtures of toluene with various polar liquids. SUMMARY
Various aliphatic ammonium bentonite complexes were made by cation-exchange reaction and gels of these materials prepared in several organic liquids and liquid mixtures. Using a grease cone penetrometer to measure gel strength, typical highly swelling liquids comprising mixtures of a nonpolar hydrocarbon (toluene) and polar aliphatic compounds (alcohols) were studied as regards factors involved in gelation. Gel strength as a criterion of liquid-binding capacity was found to be generally comparable to the swelling test used in previous work. Approximately 50 per cent coverage of the clay flakes by organic matter attached through ion-exchange reaction appeared essential for good gelation. Optimum gelation occurred in the range of complete ion-exchange reaction of clay with the organic ammonium salt. Confirmation of earlier theories as to the mechanism of solvation was afforded. Complexes characterized by complete coating of the clay flakes xere gelled in single nonpolar liquid systems, and the thixotropy of such gels was illustrated. The authors wish to express their indebtedness to E. A . Hauser and R . E. Grim for helpful suggestions and to members of the Brooklyn and Baroid Sales Division Laboratories of the National Lead Company for their cooperation, To E. W. Tillotson, Assistant' Director of the\Mellon.Institute, is extended apprcciation for his friendly counsel. REFEREKCES (1) (2)
BRADLEY, W . F.: J. Am. Chem. SOC.87, 975-81 (19.15). Gn.4HAM,
R. P., A N D SULLIVAN, J. D . : J. Am. Ceram. SOC.21, liW2 (1938)
1208
R. C. PLUMB, A. E. MARTELL, AND F. C. BERSWORTH
HAUSER, E. A . : Private communication. HENDRICKS, S.B.: J. Phys. Chem. 46, 65-81 (1941). JOHNSON, A. L.: J . Am. Ceram. SOC.32, 210-14 (1949). JORDAN, J. W . : J. Phys. & Colloid Chem. 63, 294-306 (1949). JORDAN, J. W.: Mineralog. Mag. 28, 598-605 (1949). (8)MACEWAN, D. 32.2.C.: Nature 164, 577-8 (1944). D. M. C.: Nature 167, 159 (1946). (9) MACEWAX, (10) MACEWAN, D. M. C.: Trans. Faraday SOC.44, 349-67 (1948). (11) PACTLING, L.: The N a t u r e of the Chemical Bond. Cornell University Press, Ithaca, Xew York (1948). (12) SEDLETSKIi, I . D., AND YUSUPOVA, S. M.:Compt. rend. acad. sci. U.R.S.S. 46, 27-30 (1945). (3) (4) (5) (6) (7)
SPECTROPHOTOMETRIC DETERMIXATION OF DISPLACEMENT SERIES OF METAL COMPLEXES OF THE SODIUM SALTS OF ETHYLENEDIAMINETETRCETIC ACID’ ROBERT C. PLUMB,2 ARTHUR E. MARTELL,
AND
F. C. BERSWORTHa
Department of Chemistry, Clark Universzty, Worcester, Massachusetts Recetved November 14, 1949
Ethylenediaminetetraacetic acid is a white crystalline amino acid with four replaceable protons. The di-, tri-, and tetrasodium salts of this acid react with metal ions such as lead, zinc, cadmium, chromium, cobalt, nickel, copper, and the alkaline earth metals to form stable complexes which resist the action of most of the agents which precipitate these metals. Discussion of this complexforming action has appeared in various papers (1, 2). The order of stability of these various metal complexes in buffered solutions is the subject of this paper. Of the alkaline earth metals, only calcium has been included in this displacement series, since calcium, barium, strontium, and magnesium have already been thoroughly investigated by Schwarzenbach (2). EXPERIMENTAL
Purification of ethylenediaminetetraacetic acid: The pure acid was obtained by acidifying the tetrasodium salt to a pH of 1.2, collecting the precipitate, washing it with hot water, and recrystallizing it from hot water. Standard solutions of the sodium salt were prepared from weighed quantities of the acid dissolved in carbonate-free sodium hydroxide solution. Preparation of 0.1000 A4 metal salt solutions: Solutions of calcium, cadmium, 1 Read by Dr. John J. Singer, of the Bersnorth Chemical Company, at the 1949 Fall Meeting of the American Oil Chemists’ Society, which was held in Chicago, Illinois. z At present a graduate student in the Department of Chemistry, Brown University, Providence, Rhode Island 3 Address. Bersworth Chemical Company, Framingham, Massachusetts.
