filling are difficult but possible in remote slave-manipulated determinations. Several G.A.B. interference filters that cover the required spectral range are used with this instrument (4). Separate holders which fit into a slot in the photometer sensing unit are provided for each filter. These housings protect the filters and allow the filter to be changed readily by the master slave manipulators. The width of the spectral band isolated by each filter is 12 to 14 mp a t the half-peak position, about 50% of the incident light of the band isolated is passed, and each filter has a colored backing filter as an integral part.
The light detector is a Densichron probe unit (IT. AI. Welch hlfg. Co.). It consists of a phototube and a magnetic modulation system. For most work with this photometer a blue probe having maximum response a t 400 mp is used. A Welch Densichron amplifier unit is installed outside the cell. It has proved very stable. OPERATIONAL PROCEDURE
A detailed operating procedure has been written for these photometers (6). Calibration curves and analyses are made in a conventional manner,
except that the determination is carried out remotely. LITERATURE CITED
(1) Frederick, E. J., .Vuc/eonics 12, 36
(1954).
(2) Lamb, C. E., Oak Ridge Sational
Laboratory, Oak Ridge, Tenn., private communication. AUK 1. 1957. (3) Oak Ridge ’ Sa3onal Laboratory, Oak Ridge, Tenn., ORNL-LR-Dwg. NO. 13584; ORNL-LR-Dw~. - NO. 13584, Parts 1-3. (4) Photovolt Corp., New York, N. Y., Bull, 180, “G.A.B. Interference Filters.” (5) Wagner, E. B., “Filter Photometer, ORNL Model Q-1734,” ORNL Master Analytical Manual, Method Nos. 1 003090,9 003090.
Determination of Combining Weight of Sulfonates C. M. Gardner, C. H. Hale, E. A. Setzkorn, and W. C. Woelfel, Development and Research Department, Continental Oil Co., Ponca City, Okla.
average combining weights of T comniercially available sulfonates are important because they are related HE
to the useful properties of the products. They are also needed in the calculation of active content from rapid titration data. The standard method for determining the combining weight of a sulfonic acid or sulfonate is to convert a weighed portion of the purified sulfonate (as its sodium salt) into sodium sulfate by a sulfated ash procedure ( 1 ) . This takes considerable time and requires careful correction for the presence of sodium carbonate, as combining weight is determined on the amount of sodium present. Another procedure is to run a p toluidine titration on a weighed portion of the purified sodium sulfonate (4). This is fairly satisfactory for the sulfonates of higher molecular weight, but fractionation may occur in the case of sulfonates of molecular weight lower than that of dodecylbenzene sulfonate. The reaction involved is not stoichiometric, as the alkali equivalent per gram of sample varies 11-ith the concentration of p-toluidine hydrochloride in the reagent. The sulfur content of a sulfonate can be used as a basis for calculating combining weight, but determination of sulfur by the classical gravimetric barium sulfate procedure would be too time-consuming. Recently, ASTAI Committee D-2 published a rapid combustion method for sulfur in petroleum products ( 8 ) . The sample is burned in a stream of oxygen by a high frequency furnace a t a temperature high enough to decompose practically any compound of sulfur and to liberate the sulfur as its oxides. Under the operating conditions employed, 93 to 95% of the sulfur evolved is absorbed as sulfur dioxide and titrated iodometri1712
ANALYTICAL CHEMISTRY
cally. The proportion of total sulfur liberated as sulfur dioxide appears to be constant for any given furnace operated under standardized conditions; this proportion is determined by ignition of potassium alum as a standard and is expressed as the “furnace constant.” Combustion and titration of a sample and calculation of its sulfur content from titer and furnace constant require only about 15 minutes. PREPARATION OF PURIFIED SULFONATE
of water and titrate with 0.1S acid. using phenolphthalein as indicator, Use hydrochloric acid if the combining weight is to be based on the sulfur content of the sulfonate; use sulfuric acid when the sulfated ash procedure for combining weight is to follow (1). At the phenolphthalein end point the sodium carbonate will be half neutralized. Add a volume of standard acid equal to the titration value, to neutralize the carbonate completely. Evaporate the solution to dryness on a steam bath, then finally dry in a vacuum oven for 3 hours at 100” C., cool in a desiccator, and weigh. Calculate the percentage of sodium chloride or sodium sulfate in the purified sample.
The sample of sulfonate must first be purified. Sodium sulfonate may contain unsulfonated hydrocarbon, sulfones, sodium sulfate from neutralization of excess sulfonating acid, water of solution and neutralization, plus other impurities. These are removed by a purification procedure, similar to the ASTM method ( I ) .
T o purify a barium or calcium sulfonate, it is first necessary to convert it to the sodium salt, so that the oil can be extracted from the sample. The procedure used is essentially that of Brooks, Peters, and Lykken ( 3 ) .
Dissolve 2 to 3 grams of the sample in 100 ml. of 1 to 1 isopropyl alcoholwater solution. Transfer to a 500-ml. separatory funnel, using 50 ml. of 1 to 1 isopropyl alcohol-water solution to aid in the transfer. Extract with 50 ml. of hexane, and repeat the extraction n i t h two 25-ml. portions of hexane. Draw the aqueous alcoholic solution containing the sulfonate into a 250-ml. glass-stoppered graduated cylinder. Combine the hexane extracts and wash n i t h 25 ml. of 1 to 1 isopropyl alcoholwater solution, adding the washing to the cylinder. Place the cylinder in a water bath a t 60” to 70’ C. for 20 minutes. Remove and add small portions of solid sodium carbonate to the solution in order to saturate and cause the separation of an alcoholic layer. Allow the two-phase system to stand a t least 2 hours. By means of a pipet transfer approximately 50 ml. of the alcoholic solution of sulfonate to a 150-ml. beaker and evaporate to about 10 ml. Add 15 nil.
Transfer 3 to 5 grams of the sulfonate to a 250-ml. beaker and add 50 ml. of chloroform to dissolve the sample. Add 50 nil. of 1 to 1 hydrochloric acid and mix the two phases, stirring with a glass rod while warming for 5 to 10 minutes on a steam bath. Transfer the solution to a 500-ml. separatory funnel, using 25 ml. of chloroform, 10 ml. of kvater, and 100 ml. of acetone to aid in the transfer. Shake the mixture vigor ously and, after the phase separation, draw off the lower chloroform-acetone phase into a 150-ml. beaker. Make two more extractions, each with 25 ml. of chloroform. Combine the three extracts and evaporate to dryness on a steam bath. The residue consists of sulfonic acid plus oil. Wash this residue into a separatory funnel, using a total of 75 ml. of isopropyl alcohol in making the transfer. Add 75 ml. of water and neutralize the sample with 25% sodium hydroxide. Proceed with the purification, extracting the oil with hexane as described for sodium sulfonate.
~~~
~
~
DETERMINATION OF COMBINING WEIGHT
Table I.
Thoroughly mix the dried and purified sulfonate by means of a spatula. Csing a 75- to 80-mg. sample. determine sulfur in accordance with the proposed ASTM procedure, using the induction-type furnace ( 2 ) . Titrate with 0.03119K potassium iodate solution (1 nil. = 0.5 mg. of sulfur). Calculate the combining weight of the sulfonate b y means of the following equation:
Sample Toluenesulfonic acid
Combining- weight -
Sodium alkylbenzene sulfonates h
=
32( 100 - Z i C 1 from Sa2C03)
6 in purified sulfonate
Table I s h o n i typical results on sulfonatci of n id(>lyvarying combining neight. Esperience in running several hundred samples has qhown that combining neightb on two samples of separately purified material nil1 usually differ by not mort’ than 1% of the average value. DISCUSSION
One purification step is the separation of sulfonate into an alcoholic phase by addition of solid sodium carbonate to the alcohol-water solution. K h e n the sodium carbonate content of the solution reaches a certain point, two liquid phases are formed. If the system is allowed to d a n d a t least 2 hours for complete separation, thr. sodium carbonate content of the alcoholic phase will be sinall and u-ill rarely exceed 1% of the purified sulfonate recovered on evaporation to dryness. The conibining weight based on sulfur determination i i subject to less error due to sodium carhonatr in the sulfonate than is the sulfated ash method. Table I1 s h o w the errors that would be made in a product having a combining reight of 350, if 1% of sodium carbonate in the sulfonate were ignored. Salts of carboxylic acids are sometimes present in petroleum sulfonates, but the amount rarely exceeds 1%. If carboxylates art’ known to be present.
Combining Weight of Sulfonates
Theory
Sodium 2,4-dimethylbenzenesulfonic acid
Combining M7eight Sulfated Induction ash p-Toluidine furnace method method method 176 174
172
...
208
C
D
F
Sodium petroleum sulfonate Sodium dodecylbenzene sulfonate Oleum sulfonated Sulfan sulfonated
352 359 356 355 572
Barium dinonylnaphthalene sulfonate
Sodium carbonate impurity in recovered RS03Xa = 1% Sulfated Induction Ash Furnace Method Method Kithout lja2C03 332 6 353 9 correction With Na2C03 correction 350 0 350 0 Correction 17 4 3.9
a portion of the sulfonic acid-oil residue may be titrated potentiometrically for
I
.
509 509 517 522 496 511 503 499 303 309
B
Table 11. Combining Weight Calculations with Respect to Sodium Carbonate Corrections Combining weight of RS03Na = 350
.
393 39 1 440 441 351 358 349 348
211 210
510 503 522 523 513 515 503 505 304 306 379 383 445 446 355 355 349 354 574
strong and Lveak acids ( 3 ) . This is simpler and probably more accurate than the ASTM method ( I ) , LITERATURE CITED
(1) Am. Sac. Testing Materials, “Stand-
ards on Petroleum Products and Lubricants,” Designation D 855-56 ( S o vember 1956).
(2) Ibid., p. 944. (3) Brooks, F., Peters, E. D., Lykken, L., ISD. ESG. CHEIM.,AKAL.ED., 18, 544 I1 9-46). \ - - - - I -
( 4 ) Marron, T. U., Schifferli, J., Ibid., 18, 49 (1946).
THIRDOklahoma Tetrasectional hZeeting ACS, Bartlesville, Okla., RIarch 1957.
Circulation-Type Apparatus for Spectrophotometric Titrations Thomas R. Sweet and James Zehner, McPherson Chemical Laboratory, The Ohio State University, Columbus 10, Ohio
photometric titrations, Fricker (2) suggested a n apparatus used with the Hilger Spekker absorptiometer. Lee, Edgerton, and Kelley (3) used a centrifugal pump in the spectrophotometric titration of radioactive samples. H o ~ ~ e v ethere r, was a need for a simple circulation-type apparatus that could easily be used lvith the Beckniaii DU spectrophotometer. FOR
APPARATUS
The cell is constructed from a con-
ventional I-cm. quartz cell by joining 6-mm. glass tubing a t the top and bottom, as shou-n in Figure 1. The cell is held in place by an ordinary cell holder, modified by the removal of a 9-mm. section from the center of one of the partitions. This makes room for the side tube and does not interfere with the ordinary use of the holder. A reference cell may be inserted in one of the other compartments to correct for any drift in the adjustments of the instrument or to observe the absorbance a t more than one wave length during a titration.
A special cover for the cell compartment was designed to allow the cell to move freely in the compartment and yet shield i t from all stray light. 4 diagram of the cover is shown in Figure 2. The sections in the diagram are fastened rigidly together except for the 19 x 1170 mm. strip in the section second from the top. This strip is allowed to slide freely with the cell. The cover is painted black and the tubes of the cell are covered with black tape. A wire is extended through the cover and hooked t o the handle of the cell holder, so that the whole assembly may be VOL. 30, NO. 10, OCTOBER 1958
1713
