I S D C S T R I A L A S D ENGINEERING C H E M I S T R Y
December, 1926
Acknowledgment
1257
flavors to baking tests, and to the Exchange Lemon Products
Cellulose Xanthate’ By G. W. Blanco Dci PONTRAYONCo., BUFFALO, N. Y.
HE ever increasing popular approral and versatile uses of rayon here and abroad make it a timely subject for discussion. Approximately 160 million pounds of rayon are produced annually, 90 per cent of which is made by the viscose process. Viscose has commanded the attention of numerous investigators for the last quarter of a century and there is today a healthful amount of research contribution2 and patents bearing on miscellaneous phases of this important cellulose derivative. The field is one of complicated chemistry, and it is the purpose now to call attention to some of the salient points in the preparation and properties of cellulose xanthate without necessarily expanding on or adding to our present knowledge of the reactions involved.
T
GENERAL-It seems desirable first to review briefly some of the properties of carbon disulfide, comparing them with those exhibited by carbon dioxide. With caustic the former produces thiocarbonates, which in the presence of water decompose into sodium carbonate and hydrogen sulfide. Thiocarbonic acids are related to carbonic acid as indicated below:
c=o
\OH Carbonic /OH C=S \OH Sulfocarbonic
,/OH C==O ‘\SH Thiocarbonic
/SH
c-0
\SH Dithiocarbonic
/SH C-S \SH Trit.hiocarbonic
/OH
c=;s
\.SH Sulfothiocarbonic
These acids are very unstable. Trithiocarbonic acid decomposes into hydrogen sulfide and carbon disulfide. It may be precipitated by hydrochloric acid as a reddish brown, oily liquid from solutions of its alkali salts, which are the products of interaction between carbon disulfide and alkali ~ u l f i d e s . ~Secondary esters are formed by the action of alkyl halides (iodide) on the sodium s a l t - e . g., /SNa
c==s
\SNa
+
I\ C*HsI,CzHj
+
/SCzHt
- c=s
\SCsHi
A similar reaction starting with sodium ethyl xanthate proves the position of sodium in the xanthate ent’ity. Yanthogenic or sulfothiocarbonic acid represents the parent substance from which xanthates and their derivatives may be prepared. Ethyl xanthic acid, or the ester of dithiocarboxglic acid, is a heavy liquid insoluble in water and decomposing into alcohol and carbon disulfide a t 25’ C. It is both an ester Presented before the Midwest Regional Meeting a n d the Meeting of the Division of Cellulose Chemistry of the American Chemical Society. Madison, Wis., M a y 27 t o 29, 1926. * Margosches, “Die Viskose,” 1906. 3 Richter, “Organic Chemistry,” 3rd ed.. p 433.
+
+
The thiocarbonic acids resemble carbamic acid and its derivatives in general constitution, as will be brought out later.
?:/
/NHz
/OH c=o
Preparation of Xanthates
/OH
and an acid4 and may be prepared by shaking sodium alcoholate with carbon disulfide and treating the mixture with sulfuric acid, thus: /OGH6 CS2 C2H50Na = C=S \SNa /OCzHs /OC& C=S HzSOl = C=S NaHSOa \SNa ‘SH
c=o
C/ O4H
Carbamic acid
Sulfocarbamic, Dithiocarbamic thiocarbamic, or acid xanthogenamic acid /OCzHa /OCZH~
/NHz
c=o
c-0
\NH,
c=s
\NH,
Urea
Urethane
METALLIC XANTHATES-The /OR formula C--C
\SH
\NHz
\SH Thiocarbamic acid
\NH%
Thiourethane
xanthates having the general
were first discovered by Zeise in 1824. They
\SMe
are generally prepared by shaking an alcoholate with carbon disulfide, e. g., /OCzHs C& KOH CsH60H = C=S +H20
+
+
\SK
Potassium ethyl xanthate consists of yellow silky needles. Sodium ethyl xanthate is prepared in a similar manner. CELLULOSE XANTHATE-The first patent on CellUlOSe xanthate was taken out by Cross, Bevan, and Beadle in 1892.5 Cellulose treated with 15 per cent sodium hydroxide liquor and then pressed was treated with carbon disulfide to the extent of 30 to 40 per cent of the material used, in a closed vessel for 3 to 4 hours. The raw xanthate solution was subsequently purified by organic acids, sulfur dioxide, or salt solution. Cellulose xanthate is prepared by treating suitably cellulose material with the required amount or excess of caustic solution of given concentration at definite temperature for a specified length of time and afterwards removing the excess caustic. The alkali cellulose formed is disintegrated and allowed to mature for determined periods a t a constant temperature. It is then treated with carbon disulfide in a closed vessel observing predetermined optimum conditions. 4 Heuser, West, and Esselen. “Textbook of Cellulose Chemistry,” 1924, p. 64. 6 British Patent 8700 (18921
1258
Vol. 18, No. 12
INDUSTRIAL A N D ENGINEERING CHEMISTRY
/OCaH5 /@CzHs OCzHj /OCzHs The progress of the reaction may be followed approximately 2 c = s + c u s o 4 = c=s c 4 *2 c = s by the brown color imparted to the mass by the by-products \ SNa ‘8 s/ kcu generated. The xanthate formed is then dissolved in water \cu/ Cupric cuprous or weak caustic soda solution yielding a viscose solution similar to corn sirup in appearance. Solutions of salts of heavy metals precipitate metallic xanI n general, the action of caustic solutions on cellulose is thates and regenerate cellulose. prcportional to the strength of the solution. With 16 per (2) Action of alkyl iodides on the salts to form esters. cent solution (C6H&)?NaOH is obtained while concentra~ tions of 35 per cent or over give (C&005)2 z N ~ O H .Glad/OR /OR C=S IClHb = C=S NaI stone and Karrer7 claim the existence of (C6H1001)2NaOH regardless of the strength of caustic solution, while the ex\SNa \SCzH5 periments of Rassow and Wadwitas point to the formation of (C6HloOr)NaOH. I n the case of cottong the amount of These are liquids possessing a n odor of garlic and insoluble NaOH taken up increases until a specific gravity of 1.2 is in water. Ammonia decomposes them into mercaptans and reached; between 1.2 and 1.47 specific gravity is approxi- esters of sulfocarbamic acid-i. e., thiourethanes. (3) Action of halogenated fatty acids.I3 mately 12.28 per cent. With potassium hydroxide solution of specific gravity between 1.35 and 1.48 cotton takes up /OR /OR approximately 17.28 per cent KOH, indicating (C6H100.)2C=S ClCHzCOOH = C=S 4- NaCl KOH. Alcoholic caustic solutions prevent the swelling of \SNa \SCH~COOH cellulose, a property necessary in forming more than 1 celluEthyl xanthic acetic acid lose-NaOH combination. An increase of temperature de/x creases the rate and degree of conversion while lower tem(4) The residue C=S is of stronger acid function than peratures accelerate them. \S Cross and Bevanlo note further that during mercerization there is first acidification or opening up of the cellulose mole- the monocarboxylic acids of the fatty series. The latter, cule, the latter showing a superior acid formation in its therefore, do not decompose this group. (5) Action of iodine. reactions with bases. This change of chemical function is not attended ,by a change in weight and is not a consequence /OR /ORRO . of the fixation or withdrawal of groups reacting with caustic. iC=S 12 = d=s 2~a1 With regard to the formation of cellulose xanthate, Heuser” \SNa \s-s/ \C=S /OCeH904 proposes the formula C--C as representing the main Purification \SNa Cellulose xanthate or its solution may be purified by means product of the reaction, while Ost12 holds a different conof water, heat, dialysis, acids, excess alkali, alum, sodium /OCeHsOt.ONa ception, thus: C=S in which a second OH group carbonate, carbon dioxide, sulfur dioxide, acid sodium sulfite, etc. Some of these methods may be represented by the fol\SNa lowing equations: reacts. Cross and Bevanlo explain that in the reaction /OCaHsOaNaOH /OCBHSOIHZO
+
+
+
+
+ Hz0
c-s
+H,O
+
\SNa
/OCSHQO~HZO 2 c a 2Hz0 = PCsHnOa \SNa
+
one NaOH molecule is in direct combination with the cellulose. From the formation of mono- and di-benzoate derivatives of alkali cellulose they conclude that as a maximum proportion two hydroxyl groups in the cg units interact with caustic soda. This would indicate that the other OH groups are prevented from ester formation. When carbon disulfide reacts with alkali cellulose there is developed a certain amount of heat and approximately onequarter of a n atmosphere of pressure. The extent of ester formation and decomposition depends largely on the reaction temperature. Excess of caustic results in too many byproducts. I n the presence of air the initial xanthate is reverted, while the remainder of the cellulose is converted to xanthate. Characteristic Reactions
(I) Reaction with cupric salts to give a brown precipitate. The conversion of the precipitate to the cuprous form causes it to turn yellow immediately. Beltzer and Persoz, “Les Matieres Cellulosiques.” 1911, p. 47. Cellulosechemie, 2, 126 (1921); Helvetica Chim. Acta, 4, 811 (1921). 8 J . prakf. Chem., 106, 266 (1923). 9 J . SOC.Dyers Colourists, 41, 53 (1925). 10 Researches 190S1905, 1918, p. 93. 1 1 Die Kunslseide, January, 1925. 12 A n n . , 881, 3812 (1911); Z . angew. Chem., 26, 89 (1913). 0
9
3CSz
+ 6 NaOH
= NazCOa
+ NaOH (water)
= C===S \Sxa
+
NazCS3
+
HzS
+
COz (heat)
+ 21TazCSa + 3Hz0 (excess caustic)
Cellulose Xantho Fatty Acid and Derivatives14
These compounds may be prepared by the action of a fatty acid or its salt upon cellulose xanthate or cellulose xanthic acid. The cellulose xantho fatty acid formed may be then subjected to the action of ammonia in solid form or in a suspension with alcohol a t normal temperature. These new ammonia derivatives of cellulose xanthate are practically insoluble in water but soluble in aqueous alkalies. According to their mode of formation and chemical behavior, they may be classified as thiourethanes or esters of thiocarbamic acid. The following equations explain their reactions: /OCaHi003 /OCsHlOO3 +NaCl C=S CI.CH%CH0 \SNa \ONa \SCHzCOONa Xantho acetate Xanthate /OCsHioO; /OCaHioOs CHz(SH).COONa H.HNCsHs = C=S C==S ‘\NHCBH: Sodlum thioglycollate \SCHzCOONa Cellulose xantho anilide
+
+
+
1)
J . g r a k t . Chem., 71. Pt. 2, 264.
14
Lilieufeld, British Patents 231,800; 231,802 (1925).
INDUSTRIAL AND ENGI,YEERING CHEMISTRY
December, 1926
Ripening of Viscose
A freshly prepared solution of cellulose xanthate appears to have characteristics somewhat similar to those of a true solution. Upon standing it undergoes certain changes gradually assuming properties of a colloidal solution. This transition, which may be accelerated by increased temperatures or exposure to air, has been termed “ripening.” Ripening may be accelerated by addition of certain salts which will react with sodium h y d r 0 ~ i d e . l ~Upon prolonged standing the cellulose hydrate separates out spontaneously 3 r d contracts gradually according to the concentration of cellulose in viscose. Freshly prepared xanthates are sc1uL)le in strong alcohol and in salt solutions, but become insoluble upon standing. The solubility seems to be influenced by the composition and proportion of the by-products. l o E’ur.thermore, decomposition of the xanthate is materially iiifluenced by the conditions attending its preparation. There seems to be no evidence supporting the separation and re-aggregation of CGor larger units during ripening. Various theories have been advanced to interpret and explain such changes.’G Some of the reactions during ripening may be represented as f ~ l l o w s . ’ ~ /OCeHsOn /O(CeHoOa)zOH 4C=S 2H1.0 = 2 C d SNa \S?*Ta /O(CsHsOa)zOH /O(CsHoOa)r(OH)s 2c=s HzO = C=S \SNa \SNa
/OH
+ 2c=3
‘
+
C d g H = NaOH
+
2CS2 4NaOH = NazCOs 3Hz0 = NazCOs NazCSs
+
18
17
Coagulation of Viscose
Technically, viscose is coagulated in a bath consisting chiefly of sulfuric acid and sodium sulfate. Numerous reactions, some of uncertain character, take place with the subsequent regeneration of cellulose or probably cellulose hydrate. The following equations represent regeneration in its simplest form: /OC6HeO4 C=S HzS04 = NaHSOa -I- CSz CsHloOr \SNa Monocellulose /O(CsHsOa)r(OH)r HzS04 NaHSO4 CSz 4CeH1oOr C=S \SNa Regenerated Tetracellulose cellulose
+ c=:;
(b)
\sNa (C)
+ NazCSs 4- HzS + Hz0 + 3HzS
+
+
+
-
+
+
When coagulated in masses viscose effloresces with the formation of minute crystals which reduce the transparency of the mass.lg Sodium silicate is ordinarily added to prevent this. Technical Application
(d)
(e)
I n (a) the monocellulose xanthate is not precipitated by alcohol or sodium chloride. However, the solubility diminishes rapidly, the dicellulose derivative being insoluble in these reagents. ,4ccording to (a) and ( b ) the xanthate 15
units rrgrow” by taking up of water. During hydration the ratio E a : S remains the same and the cellulose increases. For instance, after 24 hours the ratio of S a : S: cellulose is 1 . 2 : 2 ;after seyeral days, 1:2:4.18
\SNa /OH
+ CSz
\SNa
(a)
1259
Massot, Z. angew Chem., 26, 261 (1913). Herzog, KoZloid.Z., 35, 193-S(1924). Die Kunstserde, August, 1925, p. 169.
Viscose may be used in the manufacture of rayon, cellophane, viscose caps, viscoid, artificial wool, horsehair, and straw; Vistra, sizing material for paper, dyeing, printing, and finishing of cellulose textiles. It must be understood that some of these uses have not yet been developed commercially. The many uses of rayon are generally known. Cellophane, which is essentially a resistant transparent film, is extensively used as a wrapper for candy and bakery goods, in novelties and millinery. Viscose caps are being made on a large scale, while artificial wool and Vistra are rapidly making a place for themselves in textile circles. 18 19
Heuser, Zoc. c i t . , p 68 Waite, U. S. Patent 689,337 (1901).
The Viscosity of Cuprammonium Solutions of Cotton Cellulose’” By F. C. Hahn and H. Bradshaw E. I.
DU
PONTDE NEWOURS & Co., HENRYCLAY,WILMINGTON, DEL.
NUMBER of valuable papers have been published on this subject in recent years, and the method as a control method is now under investigation by a standardization committee of the Division of Cellulose Chemistry. I n the writers’ opinion the most important paptrs are those of Joyner,3 Farrow and Neale,4 and SmalL5 Even with the precautions for the exclusion of air prescribed by Joyner, the writers did not find the method satisfactory for testing cotton that has been only slightly degraded by the purification process. They, therefore, about two years ago, undertook to investigate the applicability of the method to this type of cotton, using extreme
A
Presented before the Midwest Regional Meeting and a t the Meeting of the Division of Cellulose Chemistry of the American Chemical Society, Madison, Wis., May 27 to 29. 1926. Contribution No. 3 from the d u Pout Experimental Station. 8 J. Chem. SOC.(London), 121, 1511 (1922). 4 J. Terlrle Inst. 16, “157 (1924). 8 THISJOURNAL, 17, 515 (1925). f
precautions to exclude air. Soon after the work was started, the paper by Farrow and Neale came to their attention, and they also had the benefit of Small’s results prior to the publication of his paper. They found it particularly advantageous to use the mercury displacement method of removing air, and to use a glass ball in the viscometer because of its better visibility in the dark blue solution. Both of these ideas were obtained from Small. It was considered very important, however, to replace the air with an inert gas, preferably purified nitrogen. When a vacuum is maintained in the tube it is very difficult to prevent inward leakage of air, and a very little oxygen is extremely harmful. The cuprammonium solution was the same as that used by Small, containing 3 per cent copper and 16.5 per cent ammonia, together with 1 per cent sucrose. The high copper concentration is important because it facilitates the dissolving of high-viscosity cotton. For more easily soluble cottons, also, it permits d‘issolving a larger quantity. Using the
