Analysis of Synthetic Anionic Detergent Compositions RALPH HOUSE and J. L. DARRAGH California Research Corp., Richmond, Calif.
I n the manufacture of synthetic anionic detergents, it is desirable to obtain accurate control analyses of the product w-ith a minimum expenditure of effort and time. The main ingredients of interest are active (sodium alkyl sulfates or alkylbenzenesulfonates), sodium sulfate and, occasionally, low molecular weight sulfonate additives such as benzene-H, toluene-& and xylenesulfonates. In addition, color of the product is quite important from the standpoint of quality control. Epton’s quaternary titration procedure was quite satisfactory for determining active ingredient when modified to obtain greater accuracy. Further improvement is obtained by use of a more convenient standardization procedure and a more stable quaternary ammonium halide solution. The volumetric procedure of Ogg, Willits, and Cooper for inorganic sulfate is shown to be applicable to these detergent compositions upon appropriate modification. Low molecular weight aromatic sulfonate additives are readily separated from the main active ingredient by extraction with aqueous hydrochloric acid from ethyl ether and estimated by ultraviolet analysis of the neutralized aqueous layer. Tristimulus colorimetry is utilized as a rapid, objective method of measuring color of these products. For solution colors the amount of color is expressed on a linear scale in terms of equivalent color bodies, permitting direct linear comparison of samples and more quantitative analysis of the causes of color formation. This combination of methods provides a comprehensive scheme for convenient control analysis of the main ingredients in wholesale synthetic anionic detergent compositions.
Epton’s procedure is based on the greater chloroform solubility of the organic sulfate or sulfonate salt of a long chain cationic ion (cetyl pyridinium ion) compared to that of the corresponding salt of the methylene blue ion. Upon shaking an acidified, twophase (chloroform and water) system containing methylene blue and an anionic surfactant, the blue color concentrates almost exclusivrly in the chloroform layer. The addition of excess cetyl pyridinium bromide (CPRr) to this mixture shifts the color almost completely into the aqueous layer as illustrated by the following equation:
+
+
R-Ar-S03MB CP+ (CHCI3-Blue) (HzOColorless)
R-Xr-SO&P MB+ (CHC1,- (H,O-Blue) Colorless)
Epton’s improvement over previous colorimetric methods (17) consisted of establishing the experimental condition which gave a etoichionietric end point eaqy to detect and reproduce-namely, the point a t which the color is distributed equally between the chloroform and water phases. Modifications applied by the authors to make Epton’s procedure more accurate and more easily used consisted of the following: 1. Use of a 100-ml. stoppered graduate which permits a more accurate comparison of color in the two phases. 2. Sriewing the sample by a combination of about equal amounts of reflected and transmitted light which permits easier detection of the end point.
A
LTHOUGH a multitude of anionic surfactant types have been synthesized and tested during the past two decades, only tTvo types have achieved major commercial importancenamely alkyl sulfates and alkylhenzenesulfonates. The commercial success of these t n o types has placed considerable emphasis on the development of accurate, reproducible analytical procedures. Analysis of surfactant products is conveniently divided into four main sections: active ingredient, inorganic or “builder” components, water, and color. This paper is primarily concerned with the first and last sections, although inorganic sulfate is given special mention because of its almost universal presence in products containing either of these two surfactant types. ACTIVE INGREDIENTS
The majority of the methods described in the literature for analyzing alkvlbenzenesulfonates and alkyl sulfates are based on the observation that large cationic molecules react stoichiometrically with these anionic compounds to yield products soluble in chloroform or carbon tetrachloride but insoluble in water (6, 13, 20, 23, 68, SO, 38, 42, 45, 4 7 ) . Other methods which are described involve the following principles: change in color of dye with changing surfactant concentration (25, 4 6 ) , turbidimetric measurements upon addition of a cationic surfactant (26); and iodometric titration of phenols produced by caustic fusion of alkyl aryl sulfonates ( 6 2 ) . Of the methods proposed to date that of Epton (1%)appears to be the most accurate, flexible, and reproducible when modified as discussed.
I
I
U .
0
4 8 TITER, MILLILITERS
1P
16
Figure 1. Correction Curves for Quaternary Ammonium Ion Titration Detergent D-40
3. Cetyl pyridinium bromide (CPRr) may be advantageously replaced by a deoiled commercial long chain quaternary ammonium compound such as ,4TM-50, an alkylbenzyl trimrthylammonium chloride with an alkyl chain averaging 12 carbons (Oronite Chemical Co., San Francisco, Calif.). The chief advantage gained from substituting ATM-50 for cetyl pyridinium bromide lies in the fact that cetyl pyridinium bromide tends t o crystallize olit of solution a t room temperature even a t concentrations of 0.001 to O.O05M, while the deoiled commercial product is completely miscible with water and is thus a more reliable standard. 4. Standardization of cetyl pyridinium bromide solutions with potassium dichromate ( 1 2 ) offers the advantage of a direct primary standard, but, in practice, it was more convenient to standardize directly using sulfonic acids ( S ) , prepared directly either from pure alkyl aryl sulfonates or from commercial products such as Detergent D-40 (Oronite Chemical Co., San Francisco, Calif.). I n either case, the weighed acid is first titrated with standard caustic, and then an appropriate aliquot titrated with the quaternary solution, a direct comparison being obtained between the standard caustic and the quaternary solution. This procedure is equally effective for standardizing commercial 1492
1493
V O L U M E 2 6 , NO. 9, S E P T E M B E R 1 9 5 4 Table I.
Comparison of Methods for Obtaining Active Content, %
(Commercial sodium alkylbeneenesulfonate) .Ilcohol" p-Toluidine HydroCPBr Titration Extraction chloride 36.0 ... 36 4 , 3 6 6 29.2 ... 29.0 25.6 25 7 ... T h e alcohol extract was deoiled by extracting iyith isopentane. Sample
a
quaternaries, which may not react in a completely stoichiometric manner, as do pure quaternaries, such as cetyl pyridinium bromide. Also as Epton showed ( l a ) ,if the concentration of CPBr is lower than 0.005Jf (as may sometimes be desirable), the reaction with the anionic surfactant is no longer quantit'atively stoichiometric, and dichromate standardization becomes invalid; whereas, use of the derived acid of the surfactant in question yields a valid standardization regardless of the concentration of the quat,ernary solution. 5. Accuracy of Epton's method depends on obtaining a titer very close to 10 ml. which requires a preliminary titration to determine the exact aliquot necessary and dispensing the sample from a buret. Weatherburn ( 4 6 ) attempted to overcome this difficulty by assuming a linear relationship between error and size of aliquot such that two or more results obtained with different size aliquots permitted the correction to be made. Because the most accurate end point is obtained in the range of 5- to 15ml. titer, it is considered more desirable when running large numbers of titrations on the same type of anionic surfactant to establish the correction factor for titer variations from 5 to 15 ml. Examples of the types of variation observed are shown in Figure 1. .4 correction curve must be determined experimentally for a given concentration and type of quaternary, and a given type of anionic surfactant to obtain the greatest accuracy. At low concentrations of quaternary (0.OOlJf) the ratio of methylene blue indicator to quaternary is sufficiently high to cause this correction factor to increase quit,e rapidly for t,iters of less than 10 ml.
Two other methods commonly employed to estimate active contents of detergent products" are ext,raction nit,h ethyl alcohol, and the p-toluidine hydrochloride-carbon tetrachloride extraction method of IIarron and Schifferli (30). These procedures give results comparable with the quaternary titration method, but the alcohol extraction is nonspecific, and both procedures are more time-consuming than the quaternary titration method. A comparison of results obt'ained using the three procedures on an alkyl aryl sulfonate is shown in Table I. Equivalent weights used in the cetyl pyridinium bromide and p-toluidine procedures were obtained on t,he purified acids prepared as described in Section 4. .4s pointed out by Ept'on ( l a ) and Jones (ZO), the reaction of these anionic surfactants and the rationic molecules becomes less quantitative as the chain length decreases. This effect is shown in a more quantitative manner by the data in Table 11. hlkylbenzenesulfonates with alkyl chains of ten or more carbons are seen to yield stoichiometric results, but, when the chain length is reduced to six carbons, a 6% error is introduced, increasing to about 30% error for butylbenzenesulfonate. The end point is still reasonablj- sharp for hesylbenzenesulfonate, but is somewhat broad in the case of butylbenzene sulfate and almost impossible to determine in t'he case of benxenesulfonate and ethylbenzenesulfonate. K i t h dialkylbenzenesulfonates the approach t'o stoichiometric results is considerably poorer and depends on other factors besides chain length (31). PREPARATION O F P U R I F I E D S U L F O N I C ACIDS
A 1- to 1.5-gram sample of a sodium alkyl aryl sulfonate plus about an equal weight of sodium sulfate is dissolved in about 50
ml. of water, and transferred to a 250-ml. separatory funnel. Three extractions are then carried out with 50-ml. portions of ethyl ether to remove any oil which may be present. The aqueous solution is then acidified with 25 ml. of 6a\r hydrochloric acid and extracted twice with 50-ml. portions of ethyl ether. The combined ether layers are then washed with three 15-ml.
portions of 3 5 hydrochloric acid to assure complete removal of sodium ions, and the combined aqueous washes are then extracted once more with 50 ml. of ether. The combined ether extracts of the acidified solutions are transferred t,o a tared, 250-ml. beaker which is placed directly on a 120' to 140" C. steam plate to evaporate the ether, After removal of the ether, the beaker is left on the steam plate until constant weight is reached (15 minutes) to obtain complete removal of water and hydrochloric acid (Sulfonic acids are hygroscopic and rapidly absorb water from the atmosphere at room temperature.) and is then titrated with standard caustic using phenolphthalein indicator. The pure alkyl aryl sulfonate, 1-decylbenzene sodium sulfonate gave an equivalent weight about t,wenty-one units higher than that calculated from the chemical formula of the acid (319 compared to 298). Within the experimental error of the method these results imply that one a-ater of hydration is associated with the sulfonic acids a t temperature of heating (about 120" to 140" C.). On the other hand, a sample of commercial dodecylbenzene sulfonate derived from polypropylene benzene apparently yields anhydrous sulfonic acid under the test condit'ions. This is indicated by agreement (&hin experimental error) between equivalent weights obtained by this procedure and by quaternary titration of a sample of the sodium salt which had been thoroughly dried by vacuum dessication at 10" C. The quaternary solution had been standardized against the purified acid.
Table 11.
1 2
3 4 .5
6 7 8
9
Comparison of Calculated AI olecular Weights
(Obtained by CPBr titration and the sulfated ash method o n purlfieda sodium salts) Calculated CPBr Soluiion from Chenii- Standardized Sulfated Sample cal Formula with KzCrgOr Ash ... 346 346 Oronite alkane sulfonateb 500-600° F. alkane boiling range Sodium dodecylbenzene348 348 346 sulfonate Sodium decylbenzene320 322 326 sulfonate Sodium hexylbenzene264 281 264 sulfonate Sodium-n-butylbenzene236 299-304 236 sulfonate Sodium ethylbenzene208 1120 c sulfonate Sodium benzenesulfonate 180 3090C ... Sodium sulfonate from ... 397 394 high boiling fraction of polypropylene benzene (600-720° F.) Sodium sulfonate from low ... 320 272 boiling fraction of polypropylene benzene (335-500' F.)
a These sulfonates obtained by careful deoiling and desalting of neutralized products made by mild sulfonation of corresponding alkylbenzenes. Alkylbenzenes used in 2, 3, and 4 prepared b y alkylation of benzene with corresponding n-1-olefins. T h e n-butylbenzene and ethylbenzene obtained from Eastman Kodak Co. J. T . Baker's C . P . benzene was used in sample 7. b Current Oronite alkane boils over a narrower range. C T o obtain usable end points these samples were titrated along with known amounts of higher molecular weight sulfonates. Values are corrected for added high molecular weight of sulfonates.
T I T R A T I O Y PROCEDURE ( 1 2 )
After weighing the surfactant sample and diluting to volume, an aliquot containing about 15 mg. of surfactant is pipetted into a 100-ml. stoppered graduate and 15 ml. of chloroform added along Kith 25 ml. of methylene blue indicator solution (0.003% methylene blue chloride, 1.2% sulfuric acid, and 5.0% sodium sulfate). About 5 ml. of 0.005M quaternary solution is added, and the mixture is shaken vigorously for 2 to 3 minutes. The quaternary is then added in increments (with vigorous shaking after each increment) until visual observation shows that the end point is reached, as defined by equivalent amounts of blue color in the two phases. Verification of the end point is obtained by addition of two to three drops of quaternary solution which should cause the aqueous layer to be noticeably bluer than the chloroform layer. The end point is most readily detected if the sample is viewed by about half reflected and half transmitted light, but more important, the samples should always be viewed under the same lighting conditions that are used in the standardization of the quaternary solution.
1494
ANALYTICAL CHEMISTRY
Table 111.
Results of Separation of High and Low Molecular Weight Sulfonates
Weight Ratio, ~ l k~~~l ~ l suifonate-Benzenesulfonate 9 9 . 0 / 1 .o 95.6/4.4
Sodium Benaenesulfonate. Mg. Calculated Found 0.0332 0,0297 0.0144 0.0137
DETERMINING ALKYL ARYL SULFONATES AND ALKYL SULFATES IN PRESENCE OF EACH OTHER
Because this titration method does not distinguish between alkyl sulfates and alkyl aryl sulfonates (and it is sometimes desirable to analyze mixtures of the two) some other analytical procedure is necessary in order to determine the above types selectively. The ease with which alkyl sulfates hydrolyze in dilute acid solutions presents a convenient method for estimating this constituent selectively in the presence of alkyl aryl sulfonates. The procedwe involves preparing a solution of the sample containing alkyl sulfate plus alkyl aryl sulfonate a t a concentration about five times that of the titrating quaternary ammonium solution. P.0
sulfonates used as commercial detergents, the reverse is true. Therefore, a multiple extraction of the sample between ethyl ether and a 3 to 4N hydrochloric acid solution yields the low molecular weight sulfonates quantitatively in the aqueous phase and the detergent-type sulfonates in the ether phase. The aqueous phase may then be neutralized and inspected in the ultraviolet region of the spectrum to determine the amount and type of additive. The accuracy of the analysis depends upon the complexity of the added sulfonates. Simple, one-component systems, such as benzene or toluenesulfonate, are determined quite accurately; whereas, a multicomponent system, such as that obtained from sulfonation of mived isomeric xylenes, is more difficult. A comparison of ultraviolet traces obtained on pure benzenesulfonate, and the aqueous extracts (neutralized aqueous layer af ter ether-hydrochloric acid extraction) from detergent sulfonate with and without added benzenesulfonate is shown in Figure 2. The peslrs a t 262 and/or 269 mp are used to calculate the amount of benzenesulfonate in the aqueous solution. Peak heights are determined by measuring the height above background absorption. For example, a t the 262-mp peak, background is determined by drawing a straight line between the valleys a t 260 and 267 mp. The procedure for separating the high and low molecular weight sulfonates is essentially the same as that described for purifying the sulfonic acids, with the following modifications: 1. The sample size is chosen t o yield approximately 0.05% of low molecular weight sulfonate in the final combined aqueous phase after dilution t o volume. 2. The deoiling Rtep is not necessary. 3. The water layer is neutralized and heated to remove ether, and, if necessary, filtered t o yield a clear solution before inspecting in the ultraviolet region of the spectrum.
cZ 1.0 2
88 d:
Results obtained by this procedure on samples of alkyl aryl sulfonate containing known amounts of benzenesulfonate are shown in Table 111. 0.5
I
/’
INORGANIC SULFATE BY VOLUMETRIC TITRATION
I \
/’
\
P40
P60 WAVE LENGTH, Mu
280
Figure 2. Ultraviolet Spectra of Aqueous Sodium Benzenesulfonate Solutions Sodium benzene sulfonate (0.05%) Alkane sulfonate/benzene sulfonate (95.6 to 4.4 weight ratio) 3. Alkane sulfonate 1. 2,
One portion is diluted five times and 10 ml. of portion is titrated with the quaternary solution to determine the total alkyl sulfate plus alkyl aryl sulfonate. Then a 50-ml. aliquot of the original solution is refluxed with 50 ml. of approvimately 0.5A\r sulfuric acid overnight on a steam plate t o destroy the alkyl sulfate. After appropriate dilution an aliquot of this solution is titrated with the quaternary yielding a value for the alkyl aryl sulfonate concentration, the difference between these two titrations representing the alkyl sulfate. LOW MOLECULAR WEIGHT SULFONATE ADDITIVES
Low molecular weight sulfonates are sometimes added to the higher molecular weight detergent-type sulfonates t o obtain changes in the various physical properties. These materials may or may not appear in the titration procedure, and in many cases it is desirable to know the type and amount of low molecular weight sulfonate which is present. A procedure developed for accomplishing this depends on the fact that alkylbenzenesulfonates with the alkyl group containing four or less carbons are considerably more soluble in aqueous acid medium than in wet, acidified ethyl ether; whereas, for the higher molecular weight
Both alkyl sulfate and alkyl aryl sulfonate products normally contain appreciable quantities of sodium sulfate. The usual gravimetric procedurc for determining sulfate is rather lengthy, and a quick, accurate procedure is desirable. especially for control work where large numbers of samples may have to be analyzed. Many volumetric procedures for sulfate determination have been reported from time t o time ( 2 , 10, 1.6, 15, 27, 29, SS, 55, S9, 41, 45’). The procedures involving titration with barium chloride solution, using tetrahydroxyquinone or potassium rhodizonate as indicators, and electrometric methods, involving lead salts as the titrating agent, appear to be most promising. A modification of the procedure of Ogg, Willits, and Cooper ( 3 5 ) was quite useful in this respect. Using potassium rhodizonate as the indicator, the average operator is able to obtain results with an accuracy of about 1% after a few practice runs to become familiar with the method. Commercial alkyl aryl sulfonates and alkyl sulfates were found not to interfere u p to a weight ratio of surfactant-to-sodium sulfate of 80 t o 20; interference was noted a t higher ratios mainly as a reduction in the sharpness of the end point. Lower molecular Xq-eight sulfonates, such as benzenesulfonate, can apparently be tolerated a t higher ratios as seen in Table IV. I n addition, the interfering effcct of sulfonate is decreased by using a smaller sample size, although this also decreases the over-all accuracy. This method cannot be used in built detergents containing phosphates due t o the variable interfering effect of phosphates. I n this titration where all other variables were held constant, the results varied somewhat with titer size. This difficulty was overcome by plotting the experimentally determined variation in the form of a correction curve, Figure 3. A 5-ml. titer yields a factor of 1.00 because the barium chloride solution was standard-
1495
V O L U M E 26, NO. 9, S E P T E M B E R 1 9 5 4
more of barium chloride and noting that the solution is redder than the filter ( 5 5 ) . The end point is more easily detected if all light directed upward from the box is masked off except for that passing through the filter and the solution.
1.09
0.94
WATER AND OIL (LO
K
Q Y
4
0.86
0.78 2
0
ML.
4
6
8
10
OF 0.19 M O L A R B A CLz SOLUTION
Figure 3. Effect of Barium Chloride Titer Volume on Accuracy of Sulfate Determination
ized against 10 ml. of a sulfate solution of just twice the molarity of the barium chloride. For analyzing sulfonate products containing only small amounts (0.2 to loyo)of sulfate, the sulfonate may first be removed by extracting the acidified hydrochloric acid sample with ethyl ether, boiling off most of the hydrochloric acid, neutralizing, and then titrating. A more rapid, but slightly less accurate, procedure requires addition of a known amount of sulfate to the solution to be titrated so as to give a sulfonate-sulfate ratio (less than 80 to 20) which will yield a good end point, and then subtract the calculated titer for the added sulfate from that actually obtained on the mixture. Corrected titers (Figure 3 ) are used in all of this work to obtain the high& accuracy.
Table IV.
Type of Sulfonate Oronite alkane sulfonate
Benzenesulfonate 0
b
Water content is usually determined by azeotropic distillation ( 4 ) , but several other procedures are also applicable (11). Oil content is normally estimated by extraction with petroleum ether or isopentane from a 70% ethyl alcohol solution followed by weighing the residue after evaporation of the solvent on a steam bath or weathering off at room temperature.
Effect of Sulfonate on the Titration for Sulfate Total XapSOd, RIg
5.68 14.34 14.38 14.48 14.57 1 4 .G6 5.91 14.00 14.17 14.72
Artiial .__._I. Calculated CorrPcted U a SulX a Sulfo- Titer 0 019-I4 Titer fonate, nate-NaBOa, BaClr, 0 019M 3Ig Wt Ratio .IT I BaCh, M I 2.10 2 n9 Si1 0/100 5.30 5.28 76/24 45.2 5.31 5.32 57 4 80/20 5.35 5,45a 86 86/14 5.38 5, 89/11 115 5.6b 5.42 91/9 144 2.18 2.18 92/8 72.2 Sil 0/100 5,zo 5.19 30 701’30 5.26 5.25 120 89/11 5.47 5.45
Somewhat anemic (pinkish, indefinite) end,points, fair reproducibility. Very poor end point and poor reproducibility.
Results obtained by the hydrochloric acid-ether extraction procedure on known mixtures of sulfate and sulfonate are shown in Table V. PROCEDURE FOR INORGANIC SULFATE
Special Equipment (35). -4 polished glass color filter with 377, spectral transmission a t 550 & 2 mp and an opal glass stand lighted from below so the filter and the solution can be compared by transmitted light (Eastman Kodak Co.). Procedure. After dissolving the weighed sample and diluting to volume, an aliquot is taken containing 10 to 15 mg. of sulfate (calculated as sodium sulfate) and transferred to a 150-ml. beaker. Fifteen milliliters of 957c ethyl alcohol are added along with two drops of universal indicator and the pH is adjusted to 6.5 to 7.5 by dropwise addition of 0.05N hydrochloric acid and/or sodium hydroxide a8 necessary. One-half ml. of indicator solution (4.0 mg. potassium rhodizonate per ml. of water must be prepared fresh each day and kept in an ice bath while in use) is added and the standard barium chloride solution (0.02M) added rapidly until a red-orange color comparable to that of the filter appears. As the first reddish color fades, barium chloride is added slowly with constant swirling of the beaker until the color in the beaker again assumes the same red-orange hue as that of the filter. The exact end point is reached when the two colors are found t o match 60 seconds after the last dropwise addition of barium chloride; then, confirmation is obtained by adding 1 t o 2 drops
Table V.
Titration of Sodium Sulfate after Extraction of Oronite Alkane Sulfonate with Ether
h-a Sulfonate Calculated Titer Actual Titer Na?SO4. S a Sulfonate, X a Sulfate, Wt. 0.019.1.1 BaC12, 0.019M hlg. G. Ratio hI1. BaClz, MI. 4.45 4.40 300 0.2 40/60 4.40 60/40 4.45 300 0.45 4.44 85/15 4 45 300 1.7 99/1 4.45 4.55 300 29.7
BUILDERS
Khile the analytical procedures mentioned are all that are needed in most cases for analyzing production samples of anionic surfactants, several other ingredients may be present in retail products, chief among which are the polyphosphates. A breakdown of the various phosphates present can be obtained by the procedure of Quimby ( 3 6 ) , Bell ( 7 ) , Jones (ZI), and others ( S T ) , and satisfactory procedures for other ingredients are described in the literature--e.g., silicates (SZ), carbonates (24, @), and borates (8). For cases where other types of surfactants and additives-e.g., foam additives-may be present the analyses required will depend largely on the results of preliminary qualitative tests. However, attempts to establish generalized schemes for analysis of complex surfactant products have been published by various authors ( 1 , 6, 13, 18, 44, 48). COLOR
iinother important property of surfactant products is their color, usually contributed by the active ingredient. Measurement of this property is carried out by many different procedures; most of which possess the inherent disadvantage that they depend on the ability of individual operators to compare the color with some set of standards and accurately decide on the nearest match. Day-to-day and operator-to-operator variability can become rather large under these circumstances. Fortunately, instruments (Photovolt Lumetron, Model 402E, Photovolt Corp., New York, and Hunter multipurpose reflectometer, Henry A. Gardner Laboratories, Bethesda, Rld.) are available for rapid, easy measurement of both surface and solution color of products in the internationally defined I.C.I. tristimulus system (16, 19). Advantages of this system are several with Some of the more important being: 1. Rapid measurement with excellent reproducibility independent of the operator’s color vision. 2 . Designation of the color in a n internationally accepted system which is applicable to both transmitted and reflected color. 3. The results may readily be converted to a system of three independent variables corresponding to the subjective color characteristics of brightness, hue (red, yellow, blue, etc.), and amount, thus permitting ready visualization of comparative colors directly from the data. In practice, the sample is measured by obtaining the per cent transmission or reflectance of a standard light source impinging on the sample after passage through a tristimulus filter, three different filters (amber, blue, and green) being used to define the color. Trilinear coordinates in the I.C.I. system are calculated
1496
ANALYTICAL CHEMISTRY
from the three measured transmission or reflectance values ( A ,
B, and G ) by the following equations: =
x+
X Y +Z'Y =
x+
Y Y +Z'Z =
Table VI. Z
x $- Y + z
X = 0.8A 4-O.18B Y = G 2 = 1.18B
+ +
Because z y z = 1, two independent variables are obtained from the trilinear coordinates, the third variable being Y = G which is a measure of brightness or luminosity. By means of the charts in Hardy's "Handbook of Colorimetry" ( 1 6 ) x and y can be converted to the more readily understood polar coordinates of dominant wave length and purity, corresponding roughly to the psychical quantities of hue and amount. For a given colored compound the dominant mave length will remain fairly constant, and purity will increase a ith increasing concentration of the compound. Curves showing the experimental relationship between concentration of color bodies and per cent purity for solution color are plotted in Figure 4 for a detergent sample and for a pure compound, potassium dichromate. Although the shapes of the two curves are not exactly the same, they are coincident from 0 to 40 or 50% purity.
The approximate linearity of the curves in Figure 4 from 0 to 20y0 purity and the almost identical shape of the curves for extremely different color bodies in this region suggests the utility of defining an equivalent color body (ECB) for solution color measurement, and a standard cell length of 0.1 mm. For maximum accuracy the solution to bp measured should be adjusted in concentration t o give a purity value in the range 5 to 20%) the measured value then being linearly transformed to the hypothetical standard conditions of a 0. I-mm. cell and product concentration of 100%. Defining one equivalent color body as equaling one one-hundredth of a purity unit yields a convenient scale for designating colors covering a wide range (10,000 equivalent color bodies corresponding to a pure spectral color for a liquid viewed through O.l-mm. thickness), with a linear relationship existing beta een equivalent color body value and amount of color in the sample from zero to about 2000 t o 3000 equivalent color bodies. One equivalent color body corresponds to a 1.016 X 10-7M solution of potassium dichromate in a 0 I-mm. cell. 1 PO
80
40
0
PO 40 60 TRISTIMULUS % SATURATION
Sample 1 2.0 1.016 X 10-1
Detergent active, % KzCrz07, mole/li t er Tristimulus solution color (50.0-mm. cell), 70purity Equivalent (ECB)
color
bodies
E C B (for a 0.1-mm. cell)
10.0
2.0 20.32 X 10-0 84.0
1000
8400
1000 500
- = 2.00
Sample 2 0 la
1.016 X 10-6
10.0
1000
loo0 = 2.00 500
E C B (for 0.1-mm. cell and 2,00(100)2 , 0 0 (100) = 2ooo 100% active) (2.0) (0.1) a Sample diluted t o obtain color on the linear portion of the curve (Figure
-
4),
> cK,
80
0 3 .
ee
LINEAR COLOR SYSTEMS
0
Hypothetical Conversion of Linear Color System
80
Figure 4. Relationship between Concentration and Color Saturation D e t e r g e n t and dichromate solutions
0
4
8
12
16
PO
LOVIBOND YELLOW
Figure 5.
Relationship between Tristimulus and Lovibond Colors
solution of active is suggested as the standard concentration in place of 100% active. The experimental relationship between tristimulus color measurements and the Lovibond system as obtained by direct tristimulus measurements on some of the Lovibond reference filters of direct interest for surfactant products is qhown in Figure 5 . Other tristimulus measurements of Lovibond slides were reported by Bronell (9). The same experimental correlation can readily be obtained for others such as the Saybolt and Gardner systems. For example, an oil giving a +30 Saybolt color nould measure 0.24 equivalent color body and for - 16 Saybolt the corresponding value would be 9.0 equivalent color bodies. I n the prewnt discussion color measurements involve samples with yellow and yelloworange colors, but the same principles should apply for other colors sueh as blue, green, and red, although these are not presently involved in surfactant products. For comparison of samples which differ considerably in hue (dominant wave length), purity values are not quantitatively comparable and if this type of comparison is desirable, data such as that reported by Sewhall, Kickerson, and Judd (54)should be utilized to allow for the fact that pure spectral colors-e.g., red and yellow-do not appear to the average observer t o possess the same amount of color, red usually being thought considerably stronger than yellow. PROCEDURE FOR TRISTIMULUS SOLUTION COLOR
Conversion t o the linear system is illustrated in Table VI by the following hypothetical example in which a colorless detergent active is contaminated by potassium dichromate. The measured per cent puritieP a t the same active concentration and cell length fail to denote the correct ratio of color bodies in the two samples, but, \Then converted to the linear system, the resulting color values are a direct measure of the concentration of equivalent color bodies. For molar relationships a 1.0M
Special Equipment. Photovolt Lumetron hlodel 402E and matched precision absorption cells, 50 mm. in length. hleasurement of liquid or solution color with this instrument (a split beam, two photocell type) involves use of matched absorption cells for a colorless standard [Carbon tetrachloride, C.P. (J. T. Baker), has proved to be a very satisfactory standard, but colorless ethyl alcohol or rrater are also quite satisfactory. Also clear solutions should be used for turbid solutions cause light scattering, which increases as the wave length increases. ] and the sample.
V O L U M E 2 6 , NO. 9, S E P T E M B E R 1 9 5 4 The incandescent light source is operated a t full voltage to obtain the closest approximation to I.C.I. Illuminant C. Each of the three tristimulus filters of the instrument is adjusted to read 100% transmittance for the standard liquid followed by measurement of the per cent transmittance obtained upon replacing the standard with the sample. Ordinarily, no difficulty is encounteied in obtaining results reproducible to 0.2 unit on the scale ranging from 0 to 100 units. ACKNOW LEDGV ENT
The authors wish to acknowledge the contributions made during the course of this work by many members of the California Research Corp. staff, especially 11. T. Sigh for assistance in evaluating the procedure for inorganic sulfate; R. D. Clark for the ultraviolet spectral analysis associated with the procedure for low molecular weight sulfonates; and A. C. Ettling for preparation of some of the alkyl aryl sulfonates used in the investigation. LITERATURE CITED (1) (2) (3) (4) (5) (6)
(7) (8) (9) (10) (11)
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RECEIVEDfor review March 2 2 . 1954. Accepted July 17, 1954. Presented before the Dirision of Industrial and Engineering Chemistry, Symposium on Synthetic Detergents, a t t h e 125th Meeting of t h e AMERICAN CHEMICAL SOCIETY,Kansas City, K a n . , RIarch 1954. Other paper8 from t h e symposium were published in Industrial & Engineerina Chemistry, September 1954.
New Molecular Addition Compounds of 2,4,7=Trinitrofluorenone DONALD E. LASKOWSKI and WALTER C. MCCRONE Armour Research Foundation, Illinois Institute of Technology, Chicago,
The iniestigation was undertaken to determine the types of benzene derivatives capable of forming molecular addition compounds with 2,4,7-trinitrofluorenonein the microscopic mixed fusion technique. From the large number of compounds tested, it can be concluded that those substituent groups known to release electrons to the benzene ring either by an inductive mechanism, or by a resonance mechanism generally lead to 2,4,7-trinitrofluorenone addition compound formation. Conversely, those substituent groups know-n to withdraw electrons from the benzene ring do not allow addition compound formation to occur. In polysubstitution, positional isomerism does not appear to influence addition compound forming tendencies to any great extent except that in certain instances of para disubstitution (hydroquinone,p-aminophenol, and p-diphenylbenzene) addition compound formation does not occur while other positional isomers of these compounds do form addition compounds. This work should be useful in qualitative organic analysis involving microscopic techniques.
I
111.
T WAS reported recently (3) that 2,4,7-trinitrofluorenone (TKF) is able to form molecular addition compounds with
certain benzene derivatives as well as with polynuclear aromatic compounds. Since this fact is of extreme importance in the use of the microscopic mised fusion method of analysis ( S ) , it was decided to survey a large number of compounds to determine the extent of this reaction. As a result of this investigation, it was hoped to be able to formulate rules for predicting the possibility of formation of molecular addition compounds between 2,4,7-trinitrofluorenone and benzene derivatives. EQUIPMENT AND REAGENTS
A polarizing microscope fitted with a 16-mm. objective and a 1OX eyepiece was used in these experiments to detect addition compound formation. A Kofler hotbar, such as that supplied by W. J. Hacker and Co., Inc., New York. K.Y., was used to prepare the mixed fusions. The 2.4,7-trinitrofluorenone was supplied by Dajac Laboratories, Division of hlonomer Polymer, Inc., Leominster, Mass. It used without further purification. No special attempt was made to purify the chemicals used in these experiments; for the most part, they were Eastman Kodak
