Physical Properties of Sodium, Potassium, and Ammonium Lactate Solutions ALBERT A. DIETZ AND ED. F. DEGERING Purdue University, Lafayette, Ind.
Sodium and potassium lactate solutions have been used as substitutes for glycerol, but few data are recorded dealing with their properties. In this study some physical properties of sodium, potassium, and ammonium lactate solutions are reported. These salts were prepared from very pure acid obtained from the U. S. Bureau of Dairy Industry. Through the use of different concentrations of the salts, either singly or in combination, many desirable properties can be obtained. The density, index of refraction, viscosity, boiling and freezing points, and surface tension of sodium, potassium, and ammonium lactate solutions are reported. These properties were determined for concentrations ranging from 1 to 90 per cent.
H. H. SCHOPMEYER American Maize-Products Company, Roby, Ind.
ODIUM and potassium lactate solutions were used extensively by the Central Powers during 1914-18 in pharmaceuticals and for all purposes demanding a product with the physical properties of glycerol. The physical properties of sodium and potassium lactate solutions may be varied to an even greater extent than those of glycerol. As a hygroscopic agent sodium lactate compares well with glycerol and has been used successfully in the humidifying of tobacco. With the increased demand for glycerol in the present crisis, the alkali lactate solutions may once again play an important role by permitting the conservation of glycerol for national defense. The sodium, potassium, and ammonium lactates were first described by Engelhardt and Maddrell (6) in 1847. They found that the lactates formed sirupy fluids, from which the salts could not be crystallized. Between the time of this early investigation and the war of 1914-18, little work was done on these salts. With a shortage of glycerol, Seuberg and Reinfurth (6) became interested in the glycerol-like properties of the sodium and potassium lactate solutions. These solutions were used extensively by the Central Powers as glycerol Ersatz, and were marketed under the names of “Perglycerin” and “Perkaglycerin”, respectively. The most extensive physical data were recorded by Neuberg and Reinfurth (6). With the exception of a table giving the densities of potassium lactate solutions, their work dealt with the properties of sodium lactate. These authors gave no data on the purity of their solutions, nor did they include information concerning the methods used in determining the constants. Their values extend over wide ranges, which indicates that they did not intend them t o represent absolute values. Certain of their data are not recorded in the best units; e. g., the viscosity is given in Engler units, and many of the determinations were made beyond the range of accuracy of the instrument (2). In addition t o the above work, a few isolated properties of little significance have been recorded. Reyher (8) determined the densities and viscosities of four dilute sodium lactate solutions (0.125 to 1N ) . Schryver (9) reported the relative viscosity of a normal sodium lactate solution between 5.6’ and 58.5’ C., and found the molal freezing point lowering to be 3.940’ C. Ostwald (7) gave sufficient data so that the density of a single dilute solution of each (sodium, potassium, and ammonium lactates) can be calculated. With the possible increased demand for glycerol substitutes in the
S
present crisis, and with the possibility of developing new uses, a thorough study of the physical properties of the lactate solutions is appropriate.
Preparation of Solutions Inasmuch as it was desirable t o start with highly concentrated lactic acid, which was not commercially available, a very pure acid was obtained from the U. S. Bureau of Dairy Industry. This acid had been prepared by the method of Smith and Claborn (IO),and an analysis (by a modified Eder and Kutter procedure, 4) pave 60 per cent “directly titratable acid” and 102.0 per cent ‘ total acidity”, both expressed as lactic acid. The analysis and purity of similar samples of lactic acid are reported by Watson (22). It had the following physical properties: na# = 1.4361 and dzs = 1.2143. SODIUM AND POTASSIUM LACTATE SOLUTIONS. The concentrated solutions of these salts were prepared by the slow addition of saturated solutions of the corresponding hydroxides to the lactic acid. The reaction flasks were kept cool with an ice bath, as heat and a local excess of alkali caused discoloration. The resulting solutions were more dilute than was desired and so were concentrated to about 80 per cent in vacuo, with the bath temperature kept below 50’ C. The potassium lactate solution contained a small amount of a gelatinous precipitate at this point, which was removed by filtering through a Jena fritted glass filter. To ensure the absence of anhydrides, the final adjustments to the neutral point of phenolphthalein were made after the concentrated solutions had stood for one week, a procedure used by Dietzel and Rosenbaum ( 3 ) in the preparation of pure potassium lactate for conductivity work. The sodium or potassium content of the solutions was determined by decomposing them with sulfuric acid and weighing the corresponding sulfates. This procedure is satisfactory, as the alkalies used met the AMIIERICAN 1444
INDUSTRIAL AND ENGINEER IN G CHEMISTRY
November, 1941
1445
to three decimal places, and the results found in this investigation are of the same order, although no direot comparison can be made because of the difference in temperature. The results for the dilute solutions as given by Reyher (8) fall on the sodium lactate curve in Figure 1.
1.5-
14
*SODIUM LACTATE
Viscosity The viscosities of the solutions were determined with the aid of an Ostwald viscometer. According to the equation, R=
2Vd
x
1000 tQ
where V = ml. of liquid of density d and viscosity q millipoise flowing through a capillary of radius r mm. in 1 seconds FIGURE1. DENSITY OF AQUEOUSLACTATES
OF AQUEOUS LACTATES" TABLEI. DENSITY
Conon % byWa)ght 1 2 5 10 20 30 40 50 60 70 77.15 78.04 80 90 0
dodium Lactate d$6" d:' 1.0071 1.0042 1.0103 1.0074 1.0255 1.0225 1.0511 1.0480 1.1035 1.1002 1.1576 1.1542 1.2114 1.2078 1.2666 1.2629 1.3170 1.3131 1.3757 1.3717 1.4126 1.4085
... ... ...
For water, dZb
-
... ...
.*.
Potaasium Lactate
d:! 1.0048 1.0098 1.0247 1,0496 1.1017 1.1562 1.2138 1.2736 1.3346 1.3969
d:' 1.0018 1.0068 1.0217 1.0465 1,0985 1.1528 1.2102 1.2699 1.3307 1.3928
1 .'44e6
1."426
...
.**
... ...
Ammonium Lactate
G:' d:' 1,0025 0.9996 1.0049 1 * 0020 1,0092 1.0122 1,0218 1.0248 (1.0492) (1.0461) 1.0703 1.0734 (1.0986) (1.0954) 1.1174 1.1207 1.1394 1.1427 1.1596 1.1630
...
...
1 .'iizs 1.2004
1 .'i793 1.1969
the Reynolds number of the instrument was 206 for water. Since a Reynolds number as high as 500 is permissible, and since the Reynolds numbers of all solutions to be tested would be less than 206, the instrument was considered satisfactory. The time of flow of all solutions was determined at 25" C., frequently checking the time for water. The viscosities were calculated according to the equation: q
Adt
-B d
where A , B = constants for the viscometer mVlOOO B (calcd. from physical data) = 8 ~ 1 where nt = 1.1 V = vol. of liquid (8.7ml.) passing through capillary of length E cm. (10.1 cm.) Constant A was then calculated using water for the standard
0.99707.
4
I
I
*SODIUM
w 100
CHEMICAL SOCIETY specifications (1). The concentrated solutions were diluted t o the desired concentrations with triple distilled water. AMMONIUMLACTATE SOLUTIONS. The concentrated ammonium lactate solution was prepared by passing dry ammonia into lactic acid diluted with about 10 er cent water. The ammonia was passed in under reflux, until tEe theoreticai amount had been absorbed. At first an odor of ammonia persisted, but this disappeared after the solution had stood in a glass-stoppered bottle for one week. The ammonia content was determined by Kjeldahl.distillation, and the dilute solutions were prepared as in the previous cases. All solutions were stored in lass-stoppered Pyrex bottles, and the physical properties were 8etermined as rapidly as possible The stability of the lactates and their solutions was satisfactorily described by Engelhardt and Maddrell (6). The alkali lactates are stable below 150' C., but ammonium lactate cannot be heated without decomposition.
OPOTASSLUM &AMMONIUM
I
Density The densities of the solutions were determined with a pycnometer a t 25" C. Table I and Figure 1 give the densities in air. Neuberg and Reinfurth (6) gave the specific gravities of sodium and potassium lactate solutions a t 15" C.
LACTATE LACTATE
60
40
20
'0
0.1
0.3
0.2
MOL E
0.4
0.5
0.6
FRACTION
FIGURE 2. FLUIDITY OF AQUEOUSLACTATES AT
The 20 and 40 per cent ammonium lactate solutions had a t first been prepared too dilute, and it became necessary to remove the excess water on a steam plate. As a result of this heating, the properties of these two solutions do not fall in line with those of the other concentrations, but the values are included because the data were available and insufficient material was on hand to repeat their preparation. These values are accordingly recorded in parentheses in the tables but have some value in that they indicate the effect of heat on ammonium lactate solutions.
LACTATE
25'
c.
TABLE 11. VISCOSITY'AND FLUIDITY~ OF AQUEOUSLACTATES AT 25" C. Sodium Laotate Potssaium Lactate lOOOb 1000 Conon % by Werght 9" 9 v 1 1 9.29 107.7 9.12 109.7 2 9.60 104.2 9.34 107.0 5 10.60 94.39 9.99 100.2 10 11.28 88.63 12.40 80.65 20 14.90 67.11 20.38 49.06 21.05 47.50 30 36.38 27.49 40 32.89 30.41 72.91 13.72 54.92 18.21 179.79 5.562 50 1.816 113.20 550.63 60 8.834 70 3798.5 0.263 334.66 2.98fJ 80 90 0 For water, 7 8.94 millipoi(le8. a Fluidity reciprooal of poises.
-
-
... ...
... ...
-
... ...
... ...
Ammonium Laotate
loo0
1
9
9.29 107.6 9.48 105.6 98.32 10.17 11.73 85.22 (15.45) (64.82) 27.48 36.89 (31.50) (31.75) 54.10 18.48 9.898 101.03 4.430 225.73 1.334 749.8 5370.0 0.186
INDUSTRIAL AND ENGINEERING CHEMISTRY
1446
Table I1 gives viscosity in millipoises and fluidity in reciprocal poises. I n Figure 2 fluidity is plotted against mole fraction. The viscosity data cannot be compared to any of those already reported (6, 8 ) , Since Previous reports have not given sufficient information for the conversion of their values to poises.
TABLEIV. BOILINGPOINTSOOF AQUEOUS LACTATES AT 742.0 MM. PRESSURB
bc,""$&~
Index of Refraction The refractive indices of the solutions were determined with an Abbe refractometer, with water a t 25" C. circulating past the prisms. The results are recorded in Table I11 and Figure 3. The curves for the index of refraction have a slight curvature when plotted on a large scale. When weight per cent is plotted against index of refraction, the curves lie so close to one another that we could almost use the average value in determining the concentration of any of the solutions.
... ...
~
% CONCENTRATON By WEIGHT
bCyon%&a
Sodium Lactate 1 2 5 10 20 30 40 50 60 70 77.15 78.04 ... 80 90 a For water, n g 1.3329.
...
-...
AQUEOUS LACTATES AT
Potsssium Laotate
... ...
1.4417
I
20
Potassium Lactate
... ...
I 40
Ammonium Laotate 1.3340 1.3353 1,3397 1.3470 (1.3607) 1.3761 (1.3902) 1.4059 1.4208 1.4351
...
1.'4496 1.4630
Ammonium Laotstc 99.530 e. 199.93 (101.01) ini.91 (104.07) 105.49 107.9 111.9 117.8 132.3
99.68' C. 100.13 101.35 103.11 105.67 109.35 114.58 123.12
% CONCENTRATION BY
FIGURE 3. REFRACTIVE INDEXOF AQUEOUS LACTATES AT 25" C.
OF
Sodium Lactate
5 99.750 e. 10 100.11 20 101.43 30 103.31 40 105.53 50 108.73 60 112.88 70 119.43 80 90 For water, b. p. 99.330
0
TABLE111. INDEX OF REFRACTION^ 25' C.
Vol. 33, No. 11
b
I 60
I 80
I
WEIGHT
FIGURE4. BOILINGPOINTSOF AQUEOUS LACTATES AT 742 RIM. MERCURY PRESSURE
ing point was soon reached, and thus it is believed that the values are near the true boiling points. The decomposition was detected by the liberation of ammonia and not by discoloration. Table IV gives the boiling points of the solutions a t 742.0 mm. To obtain exact boiling point data for 760 mm., additional information would have to be available, but for practical purposes the boiling point a t 760 mm. could be obtained by adding 0.67" C. to each of the values. It is only a t the higher temperatures that an error would be introduced, and this error would probably be within that of the experiment. The results are plotted in Figure 4. The few values for the boiling point that are given by Neuberg and Reinfurth (6) are of the same order as those reported a t this time.
Freezing Points Boiling Point For the determination of the boiling point of the solutions, a n ebulliometer holding 6-7 ml. of solution was used. It was so constructed that the liquid could readily percolate over a well holding a n Anschiitz thermometer, calibrated by the National Bureau of Standards. The solutions were boiled until the maximum temperature was reached. The barometer was read frequently, but it did not change significantly from 742.0 nun. of mercury. The sodium and potassium salts gave no trouble, but the ammonium lactate solutions decomposed on boiling. This decomposition was greatest for the more concentrated solutions, owing to the higher temperatures. Therefore, the data for ammonium lactate are of value only as the boiling points of the decomposing solutions. Since such small amounts of solutions were required, the boil-
A quart thermos jar was used for the cooling bath. I n it a mixture of carbon tetrachloride and chloroform was cooled to about 10' C. below the expected freezing point. About 25 ml. of the solution, in a 35-mm. test tube, were cooled in the bath with continuous stirring. Before freezing, the solution was allowed to supercool slightly and the maximum temperature of the crystallizing mass was taken as the freezing point. Since only a slight degree of supercooling was allowed and since the temperature was read to only 0.1" C., no correction for the supercooling was necessary. Stem and thermometer corrections were made. Table V and Figure 5 show the freezing points of the solutions. Solutions more concentrated than those given in Table V could not be crystallized a t temperature higher than -70" C. but formed glassy solids. Fifty per cent sodium lactate could not be stirred a t -35" C. and became solid a t about -55" C.;
INDUSTRIAL AND ENGINEERING CHEMISTRY
November, 1941
TABLE V. FREEZING POINTS” Conon., ?& #
by Weight Sodium Lactate 5 - 2 . 2 0 c. -4.1 10 20 -9.7 -18.2 30 40 -32.6 50 60 a For water, f. p. O.Oo C.
... ...
-
OF
1447
AQUEOUS LACTATES
Potassium Lactate -1.6’ C. -3.7 -8.6 -16.1 -28.1 -51.0
...
Ammonium Laotate -1.90 c. -3.3 (-7.6) -14.8 (-21.1)
-5i:i
FIGURE 6. SURFACE TENSION OF AQUEOUS LACTATES AT 29’ C.
TABLE VI.
Conon., ?& by Weight Sodium Laotate 1 70.4 10 69.6 .., 20 30 68.6 40 64.8 50 45.4 60 56.7 70 60.7 80 90
FIGURE 5. FREEZING POINTS OF AQUEOUS LACTATES
a t -65’ C. it was even brittle. The same was true of 60 per cent potassium lactate, except that i t did not become solid until about -65’. These concentrated solutions would perhaps crystallize on long standing at very low temperatures, but it is doubtful if the exact crystallizing temperature could be detected. The values of the sodium lactate solutions reported by Neuberg and Reinfurth (6) are consistently higher than those reported here. On the weight per cent basis, sodium lactate would give the best results in antifreeze mixtures, but its solutions become viscous more rapidly than those of potassium and ammonium lactates, which is a disadvantage where high fluidity is desired.
Surface Tension The surface tension was determined with a du Nouy tensiometer. It was found exceedingly difficult to obtain reliable readings for the dilute solutions. During the first few moments the surface tension was comparatively low, and upon standing it became higher. With the concentrated solutions the readings were more uniform and it is felt that they are more reliable, but all values are subject to the errors of the instrument. The data are interesting in that the surface tension of ammonium lactate in the high concentrations is quite different from that of the sodium and potassium salts. The values for the ammonium lactate solutions above 30 per cent are of particular interest, for these are the concentrations that would be required for antifreeze solutions, and the low surface tensions would minimize the creeping tendency. It would be interesting to redetermine the surface tensions by the capillary rise method. The results are most readily seen in Figure 6.
... ...
a
29” c.
SURFACE TENSION4 O F AQUEOUSLACTATES AT (IN DYNES)
Potassium Lactate
Ammonium Laotate
...
(66*.1) 35.4
... ...
34.4 36.4 35.6 38.2 44.5
... ... ...
...
66.4 66.4 65.4 63.4
(36.8)
For water, surface tension = 71.4 dynes.
I
TABLE VII. CONCENTRATIONS UNITS
bCyonxglb8 1 2 6 10 20 30 40 50 60 70 77.15 78.04 80 90
Sodium Grams/ 100 ml. 1.0042 2.0146 6.1125 10.480 22.004 34.626 48.312 63.145 78.786 96.019 108.666
... ... ...
Lactate Mo!e fraotion 0.00162 0.00328 0.00839 0.01765 0.03864 0.06446 0.09680 0.13850 0.19429 0.27278 0.35182
... ...
Potassium Laotate Ammonium Lactate Grams/ MoJe Grams/ Mo!e 100 ml. fraotion 100 ml. fraotion 1.0018 0.00142 0.9996 0.00169 2.0040 0.00342 2.0136 0.00286 5.1085 0.00740 5.0460 0.00877 10.465 0.01638 10.218 0.01835 21.970 0.03395 20.922 0.04035 34.584 0.05682 32.109 0.06723 48.408 0.08568 63.495 0.12324 43.816 65.870 0.10083 0.14398 79.842 0.17413 68.364 0.20147 97.496 0.24698 81.172 0.28185 112.%1
... ...
0.33313
... ...
...
9i.344 107.721
...
o.ibi20 0.60220
Literature Cited
Concentration of Solutions
(1) Am. Chem. SOC.,“Specifications for Analytical Reagent Chemicals”, 1941. (2) Barnard, D. P.. in “Soience of Petroleum”, p. 1073, London, Oxford Univ. Press, 1938. (3) Dietzel, It., and Rosenbaum, E., 2.Elektrochem., 33, 19f3-200 (19271 (4) Eder, R and Kutter, F., Helu. Chim. Acta, 9,557-8(1920). (5) Engelhardt, H., and Maddrell, R., Ann., 63, 83-120 (1847). (8) Neuberg, C.,and Reinfurth, E., Ber., 53, 1783-91 (1920). (7) Ostwald, W., J . prakt. Chem., 18,328-71 (1878). (8) Reyher, R., 2. physik. Chem., 2, 744-67 (1888). (9) Sohryver, S.B.,PTOC. Roy. SOC.(London), 83B,95123 (1910). (10) Smith, L. T.,and Claborn, H. V., IND.ENG.CHEM.,News Ed., 17,641(1939). (11) Watson, P. D., IND. ENG.CHEM.,32, 399-401 (1940).
Since the solutions were prepared on the per cent by weight basis, most of the tables and graphs are made using per cent by weight to represent the concentrations. Table VI1 was prepared to represent other units (mole fraction, per cent by volume).
PBBJSENTED before the Division of Industrial and Engineering Chemistry at the lOlst Meeting of the American Chemical Society, St. Louis, Mo. Abstracted from a portion of a thesis submitted by A. A. Diet5 to the faoultj of Purdue University in partial fulfillment of the requirements for the degree of dootor of philosophy. The work waa sponsored by the American MaizeProducts Company.
