October. 1925
INDUSTRIAL AND ENGINEERING CHEMISTRY
1043
The Ripening of Viscose' By George de Wyss THEVISCOSE CO., MARCUSH O O K ,
PA.
ROSS and Bevan2 first advanced the theory that a
of the reaction between carbon disulfide and the excess chemical change takes place during the ripening of sodium hydroxide-chiefly, sodium thiocarbonate, sodium viscose. Their method of analysis, in which they carbonate, and sodium sulfide. If viscose is decomposed separated by-product sulfur from xanthate sulfur by the use by a mineral acid, the following main reactions take place: of a salt solution, showed a constant decrease of xanthate cellulose xanthate is hydrolyzed with the formation of resulfur, which led them to conclude that the cellulose xanthate, generated cellulose and dithiocarbonic acid, which latter more correctly termed the cellulose ester of dithiocarbonic being unstable decomposes into carbon disulfide and water: acid, loses dithiocarbonic acid groups during the ripening, ROCS2Na H2S04 = ROH NaHSOI HKO& HzCOSz = HzO Cs1 (1) the original CJ31005 xanthate resulting first in a xanthate Sodium thiocarbonate reacts with the acid to form the with 12 carbon atoms to one dithiocarbonic acid group, then sodium salt, carbon disulfide in one with 18, one with 24 carbon atoms, and finally and hydrogen sulfide: in regenerated cellulose. The generally accepted conclusion that a chemical Na&& 4- HgS04 = NaaSOI By different ways of analCSa HnS (2) change takes place during the ripening of viscose has ysis Ost, Westhoff, and recently been put in doubt by Leuchs and by Herzog. On treatment with minGessner3 and Wolffenstein Investigation of Leuchs's method of analysis showed eral acid, thiocarbonates and Oser4 came to the same it to be erroneous. By a modification of it the true therefore produce carbon conclusion. On the other amount of xanthate sulfur in viscose can be determined. disuE.de just as well as does hand, Leuchss published exThis new method of analysis has been tried out on the cellulose xanthate, and periments which led him to potassium ethylxanthate and on mixtures of potassium the proportion xanthate a different view of the subethylxanthate and sodium thiocarbonate. Several vissulfur to C&oOb can by ject. He decomposed viscoses, analyzed when fresh and during the ripening, no means be ascertained by cose with sulfuric acid and showed a distinct decrease in the amount of xanthate simply decomposing the visdetermined the amounts of sulfur, the proportion of sulfur to cellulose falling more cose with a mineral acid carbon disulfide and hydrothan 50 per cent during 160 hours. and determining t h e gen sulfide liberated. -4samount of carbon disulfide suming that all the carliberated. bon disulfide set free has Furthermore, if cellulose xanthate decomposes according its origin in the decomposition of cellulose xanthate, and that all the by-product sulfur is liberated as hydrogen sul- to the theory of Cross and Bevan, carbon disulfide is refide and sulfur, from the fact that he obtained practically generated, which would react with the sodium hydroxide constant values for the proportion CS2:C$-IloOs,he concludes to form thiocarbonate: that no chemical change takes place during the ripening of 3C& 6NaOH = NapCOs 2NazCS3 3H10 (3) viscose. From this equation, together with Equation 2, it can be In a recent publication Herzog and Hege16 came to conseen that a t least two-thirds of the carbon disulfide eventually clusions similar to those of Leuchs. They likewise studied the ripening of viscose by determining the amount of carbon split off from the cellulose xanthate during the ripening would disulfide and hydrogen sulfide resulting from the decomposi- reappear as carbon disulfide upon acidification with a mineral tion of viscose by an acid, and observed only a slight increase acid. The ratio CS2: CJ3,005 as determined by Leuchs of hydrogen sulfide and a slight decrease of carbon disulfide would then show only a slight decrease, though a chemical change in the cellulose xanthate molecule were actually during the ripening. involved. Theoretical About twenty years ago Cross and Bevan' found that cellulose xanthate remains unattacked if treated with a As the ripening of viscose is important in its technical use, it was sought to clear away the difference of opinion weak acid such as acetic or lactic acid, whereas thiocarbonatea that exists as to the chemical changes involved. Reflection are unstable in the presence of these acids. It seemed led to the conviction that Leuchs is wrong in his conclusion possible that this property of viscose might be used to modify that only cellulose xanthate can produce carbon disulfide Leuchs's procedure so as to distinguish between xanthate when viscose is decomposed by a mineral acid, and that carbon disulfide and thiocarbonate carbon disulfide. If a therefore the ratio carbon disulfide so evolved to cellu- dilute solution of viscose is acidified with acetic acid, its lose will indicate how many dithiocarbonic acid groups color gradually changes from a deep yellow to a very light are combined with the cellulose molecule. Viscose is a yellow. This change in color indicates the disappearance solution of cellulose xanthate, in which we find, besides the of the thiocarbonate. At this moment all the carbon dicellulose compound, sodium hydroxide and the products sulfide and practically all the hydrogen sulfide set free by the action of the acetic acid can be removed by extracting 1 Presented before the Division of Cellulose Chemistry a t the 69th the viscose solution with ether. Treated with mineral acid Meeting of the American Chemical Society, Baltimore, Md., April 6 t o 10, the purified viscose solution still produces carbon disulfide, 1925. 9 B n . , 84, 1513 (1901). which can have no other origin than cellulose xanthate. By * A n n . , sea, 340 (1911). its determination, therefore, the true amount of xanthate 4 Kunstseide, 7, 28 (1925). sulfur can be ascertained. 6 Chcm. Ztg., 47, SO1 (1923).
C
+
++
+
+
+
8
Kolloid-2.. 86, 196 (1924).
U.S. Patent 717,356 (1902).
+
+
+
INDUSTRIAL AND ENGINEERING CHEMISTRY
1044
Vol. 17, No. 10
Table I Curve I (Figures 1 and 3) 7.97% Cellulose
Age Hours 0 39.5 88 117 136
%S 2.67 1.68 1.38 1.25 1.13
-.OS%
S:CsHtoOs
Salt ye NaCl
1.69 1.06 0.88 0.79 0.72
30.0 16.2 11.2 8.6
6.6
Age Hours 0 16.5 22.5 41
88.5
115.5
Cellulose
%S
S:CsHioO,
Salt YoNaCl
Age Hours
7.49% Cellulose
%S
Salt
S: CSIIIOOS % NaCl
2.31 1.79 1.66 1.51 1.17 1.05
Method of Analysis
One hundred cubic centimeters of a dilute viscose solution containing about 1 per cent cellulose were pipetted into a 250-cc. separatory funnel, acidified with 10 per cent acetic acid, and lightly shaken until the deep yellow color due to the thiocarbonate had disappeared. It was found important to add enough acetic acid to obtain an acid reaction towards litmus. Once the solution had become practically colorless it was thoroughly shaken with 100 cc. of ether. After settling, the aqueous solution was drawn off into a second separatory funnel and again extracted with ether. The aqueous layer was drawn off into a 200-cc. flask, the two lots of ether washed with 25-cc. of water, and the wash water added to the original solution. The flask was then connected through a ground-glass joint with an ascendant condenser and a drop funnel. Attached to the upper end of the condenser was a U-tube filled with pumice stone that had been saturated with a concentrated copper sulfate solution and dried a t 120' C. This tube was connected with two U-tubes half filled with a 5 per cent alcoholic potassium hydroxide solution, the last tube being connected with a suction line. Ten to fifteen cubic centimeters of sulfuric acid (1:5) were added through the drop funnel, and a slow current of air was drawn through the apparatus.
I n order to prevent any decomposition of potassium xanthate due to the heat evolved during the neutralization of the alkali, the temperature was kept down by addition of a few pieces of ice to the xanthate solution. After standing for 5 minutes the cold solution was filtered through a Gooch crucible, and the precipitate of copper xanthate washed with water. The precipitate was then decomposed on the filter by 10 cc. of concentrated nitric acid, the filter washed with hot water, and the aqueous cupric nitrate solution evaporated to dryness. The dry residue was taken up with a small amount of hot water, neutralized with sodium carbonate, and slightly acidified with acetic acid. After addition of 1 to 2 grams of potassium iodide, the copper was titrated with 0.1 N sodium thiosulfate solution, l cc. thiosulfate being equivalent to 0.006357 gram copper or 0.01283 gram sulfur. Potassium Ethylxanthate
Before this method was applied to viscose it was tried out on potassium ethylxanthate, the sulfur content of which was exactly known. By adding a solution of sodium dithiocarbonate to the ethylxanthate solution the effectiveness of the acetic acid and ether treatment could be determined. As a control the potassium ethylxanthate was first analyzed by straight precipitation as copper salt in acid solution. The results were as follows:
17
15
Theory for CaHsOSoK Straight precipitation
14
Treatment with acetic acid and ether
113
91
10 cc. NaoCSs solution added
12
20 cc. NaoCSa solution added 10 cc. NapCSa solution added, no
'?I1
acetic acid and ether treatment
:XI
Sulfur Per cent
0.5025 0.5816 0.4986 0.5040 0.6053 0.5229
15.69 18.09 15.46 15.89 15.76 16.39
39.95 40.08 39.91 39.79 40.43 40.04 40.25
0.4986
30.49
78.47
These figures show that the carbon disulfide resulting from the thiocarbonate can be eliminated quantitatively by the treatment with acetic acid and ether, and that the xanthate carbon disulfide set free by the mineral acid can be caught quantitatively in the alcoholic potassium hydroxide solution.
08
a7 06 05 O4
Thio. cc.
Substance Gram
16
1 0
2 0 30 40 50 6 0 70 Bo 90 103 110 I20 130 140 150 Ibo 170 190 1%
700
Hoiias
F i g u r e 1-Change
In X a n t h a t e Sulfur w i t h Age
At the end of a half hour the content of the flask was heated to the boiling point and kept a t this temperature for one hour, in order to expel all the carbon disulfide set free during the decomposition of the cellulose xanthate by the sulfuric acid. The carbon disulfide was drawn through the tube filled with pumice stone, where traces of hydrogen sulfide still present reacted with the copper sulfate, and into the alcoholic potassium hydroxide solution. There it formed potassium ethylxanthate. By means of a water bath the pumice stone tube was kept a t 75" C. in order to prevent loss of carbon disulfide through adsorption. The alcoholic potassium ethylxanthate solution was transferred from the two U-tubes into a 600-cc. beaker, neutralized with 10 per cent acetic acid, and after addition of an excess of 5 cc. of acid the xanthate was quantitatively precipitated as copper xanthate by addition of an excess of a 10 per cent copper sulfate solution.
-7.8%
Age Hours 0 20 43 48 90.5 116.5 140.5 165 216
T a b l e I1 Curve XI (Fipures 1 and 3) Cellulose~-----7.67~ CelluloseSalt Salt % Age % 470 S S:C8HloOs NaCl Hours % S S:CsHloOs NaCl 1.68 1.56 1.37 1.36
1.1s
1.08 1.03 0.95 0.81
1.09 1.01 0.89 0.88 0.77 0.70 0.67 0.62 0.53
10.4 8.6 8.2 5.7 4.2 3.4 2.5 0.6
2 24 29 BO 95.5 119 144 149 191.5 197
1.54 1.37 1.32 1.27 1.13 1.06 0.98 0.97 0.85 0.81
1.03 0.91 0.88 0.85 0.75 0.71 0.65 0.65 0.57 0.54
10.0 9.2 7.6 4.6 3.8 2.8 2.7 1.3 1.0
Viscose
When different viscoses were analyzed during their ripening a t 18" C., fairly concordant results were obtained with viscoses made under practically the same conditions. (Tables I, 11, and 111) The three curves in Figure 1, representing the averages of two or three different viscoses, show a de-
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1925
cided decrease in the ratio S: C&oO& Curve I represents viscoses made with an excess of carbon disulfide in order to get as near as possible to the ratio S: C6Hla05 equal to 2 : l . The two other curves were obtained with viscoses made with less than the theoretical amounts of carbon disulfide. Curve I shows that more than 50 per cent of the total decrease occurs within the first third of the time of observation, and a similar tendency is observed in the other curves. It is apparent, then, that the initial rate of decomposition is faster, probably involving the change of the Ce stage to the Clz stage. I n Table IV and Figure 2 are shown results where total carbon disulfide S, xanthate S, and sulfide S were
1045
Salt Numbers
The state of ripening was also determined by a method similar to the one published first by Hottenroth,8namely, the determination of the concentration of a salt solution necessary to start coagulation of a viscose solution. The average salt number curves (Figure 3) for the same viscoses have practically the same shape as the curves for the ratio S: CSHIOOS. The quick drop a t the beginning of ripening is perhaps more marked than in the case of sulfur (Figure 1). Two samples of viscose were kept a t a temperature of 10' C., and it was found that the drop in the values of the ratio S: C&100~,as well as that of the salt numbers, took
110
u",
mIo 0 0 0 O
io
20
30
40
50
60
70
BC
90
100 110
1m
1?1o 140 150 160
170
IN 190
zoo
I I I I I T o
IO
2 0 30 40 50
t)ouns Figure 2-Change
i I I ! ! I I 1 In
70 e~ 90 m I W wo 130 140 150 yIOUR5
Figure 3-Change
i n Xanthate and By-product Sulfur with Age
all determined for the same viscose during ripening. By decomposing the dilute viscose solution with mineral acid without first treating it with acetic acid and ether, the total amount of carbon disulfide S was determined. This represented the sum of xanthate S plus the amount of thiocarbonate S set free as carbon disulfide according to Equation 3. By deducting the amount of xanthate S from the amount obtained for total carbon disulfide S, the value of this thiocarbonate S was obtained. The amount of sulfide S was also determined by adding 25 cc. of the dilute viscose solution to an excess of 0.1 N potassium iodide-iodate solution, which had previously been acidified with sulfuric acid, and titrating the excess iodine with 0.1 N sodium thiosulfate solution. This sulfide S represented the sulfur present as sulfide plus the amount of thiocarbonate S set free as hydrogen sulfide (Equation 3). Thereby five curves were obtained. The values for total S obtained by adding those for total carbon disulfide S and sulfide S remain practically constant. The curve for total c a h o n disulfide S shows a small drop, whereas the one for sulfide S shows a slight rise, which is in accordance with the results published by Leuchs and by Herzog and Hegel, though they were misled in their interpretation. The values for xanthate S, however, again show a decided drop, those for thiocarbonate-carbon disulfide S increasing correspondingly.
SO
w tw lea m
n*r
i n Salt Number with Age
about four times as long as for viscoses kept a t 18" C. This is in accordance with the known fact that increase in temperature hastens the ripening, whereas decrease in temperature retards it. Table IV Viscose Conlaining 8.05 Per cent Cellulose (Figure 2 ) PER CENT s S :CFHInor----- 7 ThioThiocarcarbonbonXan- ate Total Xan- ate Total Hours Sulfide thate CSz CSz Total Sulfide thate CSz Cs2 Total 0.47 1 . 4 0 0.57 1 97 2.44 0.30 0.88 0.36 1 24 1 53 0 67.5 0.64 1.02 0 . 5 4 1:86 2.50 0.40 0.64 0.53 1.17 1:57 0.68 0.96 0.86 1.82 2.50 0.43 0.54 0.60 1.14 1.57 115 0.70 0.71 1.09 1.80 2.50 0.44 0.45 0.68 1.13 1.57 169
Conclusions
By the use of Leuchs's method, so modified as to eliminate obvious sources of error, it is demonstrated that the ripening of viscose is attended by chemical changes in the cellulose xanthate molecule, thus substantiating the original conclusions of Cross and Bevan. The change in the ease of coagulation of the viscose also apparently parallels these chemical changes. 8
Chem. Zlg., 39, 119 (1915).
Table I11 Curve I I I (Figures 1 and 3 ) 7.68% Cellulose
Age
Hours 0 16.5 64 68.5 89 112.5 136
%S 1.33 1.16 0.93 0.91 0.82 0.76 0.71
S : CsHloOs 0.88
0.76 0.61 0.60 0.54 0.50 0.47
7.37, Cellulose
7 37, Cellulose
I---
Salt
% NaCl 5.2 3.8 1.8 1.6 1.2 0.6 0.3
Age
Hours 0 22 65.5 88.5 112.5 161
%S 1.25 1 08 0.56 0.78 0.70 0.59
S : CsHloOs 0 57
0.75 0.60 0.54 0.49
0.41
Salt
% NaCl 7.0 5.2 2.5 1.8
0.3
Age Hours 0 19 115.5 162.5
%S 1.31 1.05 0.70 0.61
Salt
S : CSHIOOS % NaCl
0.91 0.75 0.49 0.42
7.5 5.2 0.6 0.2
