LITERATURE CITED
ACKNOWLEDGMENT
The author wishes to acknowledge the contributions of other members of the Radiological Physics Division of Argonne Sational Laboratory, especially L. D. AIarinelli, who initiated the program and maintained an active interest in the work; Harriet Nelvton and Harry Moses, n-ho planned and directed the field tests; and Jack G. Dodd, Jr., ivho assisted in the dewlopment of the equipment and in the performance of the tests and analyzed most of the field samples. Tlif use of hydrogen n a s suggested by IT. H. Rodebush of the University of Illinoiq.
Birge, R. T., Phys. Rev. 40, 207-27 (1932). Moses, H., Fourth Atomic Energy Commission Air Cleaning Conference, Argonne Sational Laboratory, Sovember 1955, TID-7513, Pt. 1, pp. 177-85, Div. of Resctor Development, Washington, D. C., 1956.
Rice. C. K. (to General Electric co.), U. S. Patent 2,550,498 (April 24, 1951). Roberts, H. S., “Temperature, Its in lleasurement and ;ontrol Science and Industry, pp. 60410, Reinhold, Xex- \-irk, 1911. Schultz, H. 4 ., Argonne Sational Lab., Rept. on Biological, Medical and Biophysics Programs, ANL5518, 35-43 (1956).
Schultz, H. d., Dodd, J. G., Jr., AirgonneSational Lab., Division of Biological and Medical Research, quart. Rept. ANL-4948, 109-29 (1953). Sutton, 0. G., Quart. J . Roy. Jleteorol. SOC.73, 257-81 (1917). Ibid.,pp. 426-36. White, W. C., Pioc. I.R.E. 38, 852-8 (1950). Khite. R.C.. Hickev. J. J.. Elect r o n ; ~21, ~ 100-102 ilIarch’l948). RECEIVEDfor reviev October 23, 1956. Accepted June 20, 1957. Symposium on Air Pollution, Division of .halytical Chemistry, 130th Meeting, ACS, dtlnntic City, S . J., September 1956. K o r k performed under the auspices of the U. S. .Itomic Energy Commission.
Determination of Xanthate Sulfur in Viscose J. P. DUX and L. H. PHIFER Research and Development Division, American Viscose Corp., Marcus Hook, Pa.
b Existing methods for determining the concentration of cellulose xanthate in viscose are laborious and timeconsuming. The proposed method i s rapid (approximately 20 minutes per determination) and precise. The undiluted viscose is forced through a specially constructed ion exchange column under pressure in order to remove other sulfur-containing compounds, and the xanthate concentration determined by measuring the ultraviolet absorbance at 303 mp of a diluted sample of the eluent. Because the method depends on accurate knowledge of the molar extinction coefficient of the xanthate group, it i s not absolute but must be calibrated in terms of another procedure. The average value of 19 determinations of the molar extinction coefficient on viscoses of known xanthate concentrations as determined by the gravimetric sulfate method was 15,940, with a standard deviation of *2.8%. Comparison with the Samuelson-Giirtner procedure on five viscoses yielded an average extinction coefficient of 15,800 A270 (average deviation).
I
the Viscose process and in research on cellulose xanthate there has long been need for a rapid, accurate method of determining the concentration of cellulose xanthate in viscose. This concentration is variously expressed as per cent of xanthate sulfur, a term generally used in technical control; or as the y-value, which is the degree of substitution of the cellulose multiplied by a factor of 100 N TECHNCBL COiiTROL O f
1842
ANALYTICAL CHEMISTRY
and is a term frequently used in research on viscose solutions. The importance of this determination lies in the fact that it is a n index of the “age” of the viscose, as cellulose xanthate is unstable in aqueous solution and continually decomposes as the viscose “ripens.” All methods in the literature are timeconsuming and in some cases subject to obvious inaccuracies. Because viscose contains, in addition to cellulose xanthate, other sulfur-containing compounds such as trithiocarbonate ion, perthiocarbonate ion, and sulfide ion (usually considered together as the “by-product sulfur compounds”), most methods depend on separation of the cellulose xanthate from the viscose and subsequent determination of total sulfur in cellulose xanthate. This separation is usually effected by precipitation of sodium cellulose xanthate by neutral salt (1, 4). Other methods involve decomposition of the by-product compounds by acetic acid, which is assumed not to decompose the cellulose xanthate ( 3 ) . I n the Fink, Stahn, and Natthes method ( 2 ) , an insoluble nitrogencontaining derivative is formed, which is then analyzed for total nitrogen by Kjeldahl determination. This method is probably the most accurate, but involves working with a highly toxic reagent and is laborious. I n 1951 Samuelson and Gartner (5) published a novel method of separating cellulose xanthate from by-product compounds-passing a dilute solution of viscose through an anion exchanger. The by-product ions, being small and all divalent, are strongly adsorbed Tvhile the cellulose xanthate ions are too large to diffuse into the resin phase and are
easily ivashed through the ion exchange column. The method proposed here is a modification of the Samuelson-Gartner procedure, and much more rapid. It differs in the methods of ion exchange of the viscose and of estimating cellulose xanthate concentration. In the Samuelson-Gartner procedure a small (2- to 3-gram) sample of viscose is diluted, passed through a conventional ion exchange column, and quantitatively washed through the column. The cellulose xanthate concentration is estimated by iodine titration of the reaction product of the cellulose xanthate and sodium zincate. In the present procedure undiluted &cose is forced through a specially designed ion exchange column, a sample weighed and diluted, and the cellulose xanthate determined by measurement of the maximum ultraviolet absorbance of the solution in a Beckman spectrophotometer. The tedious dropm-ise ion exchange and quantitative washing steps are eliminated and the iodine titration is replaced by simple determination of ultraviolet absorbance. APPARATUS A N D REAGENTS
Because viscose is a highly T’lscous ’ liquid (30 to 100 poises), pressure must be used to force the viscose through the ion exchange bed. In initial experiments a hypodermic syringe mas used, but this proved difficult and somewhat hazardous because of the danger of breakage. Therefore the high pressure stainless steel ion exchange column pictured in Figure 1 was designed.
1
m
mination of cellulose content before and after ion exchange indicates that after the first 3 ml. of viscose have been eluted, the viscose is not further diluted, and the cellulose and xanthate contents of further fractions are essentially constant and equal to those of the original viscose. The rebin used was Amberlite IRA 400, although probably any strong base resin would be satisfactory. If other resins are used, care should be taken to obtain about the same bead size (20 to 50 mesh) as IRA 400. Smaller particles tend to pack too tightly and impede the flow of the viscose. The IRA 400 was equally efficient in the chloride or the hydroxide form, although the hydroxide form was used in the experiments reported.
Figure 1 . Stainless steel high pressure ion exchange column
The top and bottom of the column are detachable (screwon) for easy cleaning. A piece of stainless steel screening (60-mesh) is placed in the bottom piece t o prevent the resin beads from being forced through the column. The column is clamped to a ringstand 1%ith the bottom piece, including screening, scren-ed on. About 6 grams of moist resin n-hich hare been sucked dry on a Buchner funnel are poured in and tamped down as tightly as possible, by using a rubber stopper on the end of a glass rod. The tamping is necessary to avoid channeling of the viscose. Viscose is poured in the remainder of the column and the top piece screwed on. Air pressure of about 30 to 40 pounds forces the viscose through the resin. The first 3 or 4 ml. of viscose to come through the column are discarded because of dilution of the viscose by the water present in the resin bed. Deter-
0
"1 \
The by-product sulfur ions are very strongly adsorbed on the resin. It was impossible to elute these ions with sodium hydroxide solution, probably because they are all divalent. To regenerate the resin for further use it is necessary to dec0mpo.e the by-products with acid after thorough washing with distilled water to remove excess viscose. Unless a great many determinations are to be made, it is more economical to discard the resin after each run than to expend time and energy on regeneration. This ion exchange occurs completely beyond the pH limit claimed by the manufacturer (pH 10 for IRA 400). The concentration of sodium hydroxide in viscose varies from 5 to 10%. ABSORPTION SPECTRUM OF CELLULOSE XANTHATE
The cellulose xanthate in the ionexchanged viscose is determined by measuring the ultraviolet absorbance a t 303 mp. Figure 2 shows the absorption spectrum of cellulose xanthate in alkaline solution in the range 200 to 400 mp, where the intense peak a t 303 mp may be observed. The spectrum of the by-product ion, trithiocarbonate, is also reproduced in Figure 2 ; the interference of the two spectra is easily seen. For this reason the
-SODIUM CELLULOSE XANTHATE SODIUM TRITHIOCARBONATE SOLVENT O.IH NAOH
--_
I
removal of the by-product compounds is necessary. The peak indicated a t 225 mfi is unsatisfactory-for example, the absorbance of trithiocarbonate ion is higher here than a t 303 mp, and the degradation products of cellulose absorb in this region. Alkaline solutions of sodium cellulose xanthate are unstable and decompose to form by-products. This instability is increased by decreasing hydroxide ion concentration and increasing temperature, and it is therefore advisable to read the absorbance of the solution as soon as possible after ion exchange or to keep the solution cold during any waiting period. Figure 3 shows the per cent decrease in the absorbance a t 303 mp us. time for two temperatures (0' and 25' C.) and two sodium hydroxide concentrations (0.1 and 1.ON) PROCEDURE
Approximately 6 grams of resin are placed in a metal exchange column and packed tightly with a glass rod. Six t o 10 ml. of viscose are added and the top is screwed on. The air pressure (range 30 to 40 pounds) is turned on and 3 to 4 ml. of the viscose are collected and discarded to avoid dilution by the water present in the resin. One to 3 drops of the viscose are then collected in a weighed 50-ml. volumetric flask containing about 20 ml. of 0.1N sodium hydroxide. After again weighing to get the weight of viscose added, the flask is shaken thoroughly to dissolve the viscose. The solution is diluted to volume rrith O.lAr sodium hydroxide and chilled in an ice bath. If further dilution is to be made immediately, chilling is not necessary. Five milliliters of the solution are then diluted t o 250 ml. with 0.1N sodium hydroxide (cold, if the sample is not to be immediately read). The absorbance a t 303 mp is then determined with a Becliman DU spectrophotometer, using 0.LY sodium hydroxide as a reference. There should not be more than 1 hour between the sample collection and reading, even if the sample is maintained a t 0" C.
30pzj---f 0
20
9
---0'C
I
x 1.21
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Figure 2. Ultraviolet absorption spectra of sodium cellulose xanthate and sodium trithiocarbonate
Figure 3. Stability of sodium cellulose xanthate as a function of alkalinity and temperature VOL. 29, NO. 12, DECEMBER 1957
1843
DETERMINATION OF MOLAR EXTINCTION COEFFICIENT OF CELLULOSE XANTHATE
To calculate the per cent xanthate sulfur or ?-value of the viscose it is necessary to know t,he molar extinction coefficient of cellulose xanthate. It was necessary therefore to calibrate the procedure, using viscose of known cellulose xanthate concentration as determined by the gravimetric sulfate method, which has long been known to be reproducible and accurate, if laborious. The xanthate sulfur content is determined by difference from a determination of total sulfur and by-product sulfur in the viscose. I n the total sulfur determination a dilute sample of viscose is oxidized with a strong solution of sodium hypobromite and boiled with hydrochloric acid to remove excess bromine, and the sulfur is determined by precipitation as barium sulfate. The by-product sulfur compounds are determined by precipitating the cellulose xanthate from a dilute viscose solution with saturated sodium chloride, filtering to remove the cellulose xanthate, and determining the sulfur in the filtrate by oxidation with sodium hypobromite and precipitation as barium sulfate. The results of these experiments are shown in Table I.
A further check on the molar extinction coefficient was provided by determining the ultraviolet absorbance of solutions obtained by the SamuelsonGartner procedure (6). Two samples of the same viscose were ion-exchanged as in the original Samuelson-Gartner procedure. Cellulose xanthate was determined in one sample by the original Samuelson-Gartner method-iodine titration of the reaction product with sodium zincate-and the other sample was diluted with 0.1N sodium hydroxide and the ultraviolet absorption a t 303 mp determined (Table 11). All experiments were run on the same viscose as it aged. DISCUSSION OF RESULTS
The average value of 19 determinations of extinction coefficient listed in Table I is 15,940. The standard deviation is 450 or 12.8%. As each value is the result of a complete determination, including ion exchange, weighing, and dilution, this standard deviation is a measure of the reproducibility of the entire method. Confidence in this value of the extinction coefficient is increased by the results listed in Table 11, where the extinction coefficients were determined in an entirely different manner. The average of these five results, 15,800, agrees very well with the average value from Table I. Using the value 15,900 for the extinction coefficient, the following formulas may be used for calculating the per cent xanthate sulfur or ?-value of 1844
ANALYTICAL CHEMISTRY
the viscose when determined according to the above procedure. 70
by-product carbon disulfide are to be analyzed.
xanthate sulfur = 2.5 X 64 X 100 X absorbance at 303 mfi 15,900 X sample weight - 1.005 X absorbance at 303 mp sample weight absorbance at 330 mfi X 50 X 162 X 100 7-value = 15,900 X 20 X sample weight X % cell. in viscose
-
2.545 X absorbance at 303 mfi sample wt. X % cell. in viscose
where 162 is the molecular weight of the glucose monomer unit of cellulose. A certain error is introduced into the calculation, in that the per cent xanthate sulfur is calculated on the weight of a sample of ion-exchanged viscose, and not on the original viscose. I n other words, a given sample of viscose will weigh less when all its by-product sulfur ions have been replaced by an equivalent amount of hydroxide ions. However, if commercial viscoses are used-Le., without excessive by-product carbon disulfide-it can easily be calculated that the error introduced is less than 2%. A viscose containing 2% carbon disulfide as by-product compounds, which is an extreme limit for commercial viscoses, will weigh approximately 1.5% less after ion exchange. To a certain extent this error has been compensated by the calibration procedure, so that the actual error is less than 1.5%. As the over-all precision of the method is &2.8’%, the error introduced by this factor is negligible. However, this fact should be considered if solutions containing large quantities of
Table l.
Viscose Sample A
B
The procedure given has been designed as an optimum one to balance the requirements of speed and accuracy in the handling of a large number of samples. Precision might be slightly improved by weighing a larger sample than the 1 to 3 drops of viscose described in the procedure. However, in view of the inherent errors in the method (spectrophotometric measurements, instability of the xanthate, etc.), it is doubtful whether any real improvement would result. The 0.lN instead of 1.ON sodium hydroxide was chosen on the basis of economy in running a large number of viscoses on a routine basis, even though the xanthate is more stable in 1.ON sodium hydroxide, as shown in Figure 3. As experiments indicate that the extinction coefficient of cellulose xanthate is not a function of the alkaliniby of the solution, 1.ON sodium hydroxide may be used as diluent if desired. When 8% sodium hydroxide solution is passed through the column, the resulting solution has an absorbance of approximately 0.003. As in the de-
Determination of Molar Extinction Coefficient of Cellulose Xanthate by Comparison with Gravimetric Sulfate Procedure
% Xanthate Sulfur (BaS04 Method)
Ion Exchange, UV Method
Wt. of sample, g.
1.59 0.3503 1.62 0.3539 1.55 0.3565 1.62 0.3677 1.62 1.54 Av. 1.59 i 0.03 (av. dev.) 0.2931 1.05 1.06 0.2935 1.01 0.2964 0.98 0.2859 1 .. m 0.2775 . 1.03 0.2960 1.04 0.2990 0.2940 Av. 1.04 0.2898 f 0.02 (av. dev.) 0.2901
C
.4v.
1.57 0.1647 1.59 0.1607 1.55 0,1552 1.60 0.1711 1.56 0.1635 1 . 5 7 f 0.02 (av. dev.)
rlbsorbance
Molar extinction coef., E
at
303 mp 0.565 0.562 0.590 0 . 565
16,200 16 000 15,900 16,100 ~
Av. 0.310 0.315 0.300 0.290 0.299 0.318 0.295 0.305 0.302 0.305 0.255 0.241 0.239 0.264 0.263
16,000
16,300 16,500 15;600 15,600 16,600 16,500 15,200 16,000 16,000 16,200 Av. 16,000 15,700 15,200 15,600 15;600 16,300 Av. 15,700
scribed procedure a dilution of 2500 is made, the interference from material dissolved from the resin bed is insignificant. This procedure is not absolute, but must be calibrated in terms of another method. On the other hand, it is extremely rapid compared with existing methods. A determination can be made in 20 minutes, while the minimum time for the Samuelson-Gartner method is about 2 hours.
Table II. Determination of Molar Extinction Coefficient of Cellulose Xanthate by Comparison with SamuelsonGartner Method
Viscose Sample D Ripening Time, Days 0 1 2 3 4
ACKNOWLEDGMENT
?-Value by SamuelsonGartner Method 44.2 43.2 34.2 29.1 27.0
Molar Extinction Coefficient 15 ,200 15,900 15,800 16,400 15,500
*
The authors rrish to acknolvledge the assistance of John F. Crow, John P. Dismukes, David P. Sigley, and Ann JI7,
Av. l5iSoo 270 (av. dev.)
Knox in carrying out the experimental program reported. LITERATURE CITED
(1) Barthelemy, H. L., Williams, L., IND.ENQ. CHEM.,ANAL. ED. 17, 624 (1 945). ( 2 ) Fink, H., Stahn, R., Matthes, A., 2.angew. Chem. 47,602(1934). (3) Geiger, E., Helv. Chim. Acta 13, 286, 299- f 1930). \ - - - - ,
(4) Herrnans, P.H.,“Physics and Chemistry of Cellulose Fibers,” p. 340, Elsevier, Amsterdam, 1949. (5) Samuelson, O., Gartner, F., Acta Chem. Scand. 5, 59G (1951).
RECEIVEDfor review March 13, 1957. Accepted July 19, 1957. Division of Cellulose Chemistry, 131st Meeting, ACS, Miami, Fla., April 1957.
Determination of Mononitrothiophene and Dinitrothiophene in Nitrobenzene WLADlMlR LEIBMANN and J. T. WOODS Organic Chemicals Division, American Cyanamid Co., Bound Brook,
b Dinitrothiophene in nitrobenzene i s determined by colorimetric reaction with alcohol and sodium hydroxide. To measure total mono- and dinitrothiophene in nitrobenzene, the mononitrothiophene i s nitrated quantitatively to dinitrothiophene and the total dinitrothiophene in the nitrated sample obtained colorimetrically. Dinitrobenzene does not interfere. Trinitrobenzene, if present, will interfere with the colorimetric test. However, its presence in the sample either before or after nitration i s unlikely. The method has a precision, expressed as standard deviation, within about 2 370 (relative) over the range of 5 to 500 p.p.m. of nitrothiophene.
I
s o m uses of mononitrobenzene, minute amounts of mononitrothiophene and dinitrothiophene in nitrobenzene have a deleterious effect. The literature failed to disclose a quantitative method for the determination of either mono- or dinitrothiophene. Meyer and Stadler found that dinitrothiophene gives a violet color with alcohol containing a trace of sodium hydroxide (Sj. A method based on this color reaction had been used for some time in these laboratories for the detection of dinitrothiophene in nitrobenzene. This investigation showed that this colorimetric test could be used for quantitative determination of dinitrothiophene. Mononitrothiophene nitrates easily to dinitrothiophene. The N
N. J.
dinitrothiophene formed can be determined colorimetrically and mononitrothiophene calculated by difference from the amount of dinitrothiophene obtained before and after nitration of the sample. COLORIMETRIC DETERMINATION OF DINITROTHIOPHENE
Apparatus. The spectrophotometric measurements were made with a Model DU Beckman spectrophotometer. Properly calibrated 1-cm. Corex cells were used. Reagents. Ethyl alcohol, formula 3A. Sodium hydroxide, approximately 0 . W . Sodium sulfate, anhydrous C.P. reagent. Mononitrobenzene (nitrothiophenefree), made by nitration of thiophenefree benzene. 2-Nitrothiophene, Arapahoe Chemical Co., Catalog No. 103. Dinitrothiophene was prepared by nitration of 2-nitrothiophene. Approximately 20 grams of 2-nitrothiophene were nitrated in the cold with 150 ml. of white fuming 97% nitric acid. The dinitrothiophene was precipitated by the addition of ice, filtered, washed with ice water, and recrystallized from ethyl alcohol (Formula 3A). The material had a melting point of 52.2” C. and yielded the following analysis: per cent carbon, theory: 27.6, found: 27.6; per cent hydrogen, theory: 1.2, found: 1.4; per cent nitrogen, theory: 16.1, found: 16.4. I n agreement with the statements made by Hartough (W), Rinkes (4), and Steinkopf and Hopner ( 5 ) , it is reasonable t o assume that the material ob-
tained was a mixture of 2,4- and 2,5dinitrothiophene. As both are reported to give the same violet color Tyith alcohol and sodium hydroxide, the calibration curve \vas established with this mixture. Analysis of Sample. A 0.2-ml. portion of the sodium hydroxide reagent was added to a 5.0-nil. portion of the nitrobenzene sample in 5.0 ml. of ethyl alcohol. The solution was swirled for 15 seconds to allow the color to develop. The transmittancy of the resulting color was measured a t 540 mp against a reference solution of a second 5-ml. portion of the sample and 5 ml. of ethyl alcohol. The amount of dinitrothiophene vias read from a
Y
4
i
-1
5r
400
500
550
600
WAVE LENGTH, M r
Figure 1. Spectrophotometric curve of color obtained with dinitrothiophene VOL. 29, NO. 12, DECEMBER 1957
1845
