Preparation and Properties of ellulose Phosphates a
.J. DAVID REID AND LAURENCE W. _VIAZZENO, JR. Southern Regional Research Laboratory, New Orleans, La. In preparation of samples by the urea-phosphoric acid method of phosphorylation. Degradation is very slight in these products. Incorporation of cellulose phosphates into a successful flameproofing formula reduces the afterglow, but too large an amount is required to achieve complete extinction of the afterglow-. Data are included giving the effect of change of time, temperature, and molar ratio on the phosphorylation of cellulose, hydroxyethylcellulose, ethylcellulose, and cellulose acetate.
Various methods of phosphorylating cellulosic matcrials have been investigated. A method using phosphorus oxychloride and pyridine as the phosphorylating agent has been adopted and a number of cellulosic products containing phosphorus and chlorine have been prepared and analyzed. Cloth phosphorylated by the above process is substantially flame- and glowproof but suffers so great a loss in tensile strength that it is impractical for the production of garments. Much of this degradation is avoided
T"F
work described in this paper was done as the result of military interest in the flameproofing of cotton cloth and a t the request of the Office of the Quartermaster General. The term "flameproofed cloth" is generally understood to mean a fabric which will not transmit flame across its surface after the igniting source has been removed. It is almost impossible to prevent charring of cellulosic material when i t is directly exposed to flame, but the presence of various materials, notably acid donors, will prevent further burning after the cloth is taken from the flame. One method of treatment consists of partial esterification of the cotton to t,he phosphate and the formation of the Ammonium salt. Although such esterification generally degrades cotton and causes a great loss in tensile strength, some methods have been developed which avoid much of this degradation 14, 20'). Information on the phosphorylation of cellulose is rather meager. It is curious that so few of the hundreds of articles concerned with the various esters of cellulose deal with cellulose phosphate. Perhaps revarch along these lines has been dismuraged by the fact that both phosphoric acid and cellulose, hecause of their trifunctional nature, have the possibility of iormirig many and mixed cross-linked polymers with consequent Insolubility. As late as 1933, Champetier ( 3 ) described the formation of a product containing one phosphoric group per thiee glucose residues in cellulose but this could not have been a true ester as it decomposed rapidla in aater. Tanner claimed (19) that cellulose phosphates were made by the action of phosphoric acid. in the presence of acid catalyst, but the composition, names, and iormulas he reported for his products seem unreasonable-in fact, repetition of his experiments in the present work did not lead to the products he described. Phosphorylation of cellulose with a large excess of a phosphoric dcid-phosphorus oxychloride mixture yielded water-soluble or highly degraded products which also were not in accord with patent claims (9) regarding the action of these reagents. Similarly, the reaction of relatively smaller amounts of phosphorus oxychloride on soda rellulose reported t o yield a u ater dispersible product ( 1 , 7 ) could not be repeated. the difference probablv being in the degree of degradation. h successful method of phosphorylation utiliaing pyridine as an itid t o esterification is reported by Malm and Waring (16). Their work was satisfactorily duplicated on purified linters and cuprammonium rayon. Thomas and Kosolapoff (20) also phosphorylated with phosphorus oxychloride and pyridine but treated further with gaseous ammonia to produce an ammonia salt or an amide of cellulose phosphate possessing desirable flame- and
glowproof qualities;. In repetition of this work, on cotton sewing thread, the strength loss was found to be only 9.5%. The preparation of a similar flameproof cellulosic material, b> the use of a urea-phosphoric acid mixt'ure, is described by Coppick and Hall (4)and is the basis of a t least one industrial application I t was on the basis of this development that the present, work was requested by t,he Quartermaster General. Cellulose is treated, in a single operation, with a mixture of urea and phosphoric acid and cured a t an elevated temperature fop one-half to one hour By varying the temperature and curing time the amount of phosphorus introduced can be controlled. A similar process using guanidine in place of urea has been patented recently (12). Other reagents have been employed successfully for the phosphorylation of esters and ethers of cellulose, among which are phosphorus trichloride and monophenyl phosphate (8), phosphorus pentoxide ( 1J ) , and chlorides of part,ially esterified polybasic acids (91). Xathansohn ( I O ) advocat,es the use of phosphorus oxychloride in acetone to increase the polymerizat'ion of cellulose acetate by cross linkage, while Nalm and Fordycc ( I S ) have claimed the converse by using a monochlorodiaryl phosphate, thus prevent,ing cross linkage and producing a soluble product. The principal method of phosphorylation which t,be aut'hore have adopted involves the treatment of cellulose or a, cellulosic material with phosphorus oxychloride (1 to 6 moles of POCla per OH) in pyridine a t 25" to 30" C, or a t 120" C. for I to 3 hours. In some cases the product is given a final wash with ammonium hydroxide to produce the ammonium salt of the phosphate residue. With cellulose in the form of cloth the authors were able to obt,ain a flame-resistant fabric containing 3.547, phosphorus, hut the tensile strength was reduced to approximately 50% of the original. It was found, as shown in Table I, that Rams resistance in cloth, measured by the standard test (j),can be achieved with as little as 1.2% phosphorus content, corresponding to an average substitution of 1 group per 15 to 20 glucose residues. This effect is much more difKcult to achieve with lighter weight cloth, even with higher phosphorus content, a,nd the loss of strength is correspondingly greater. While the presence of the ammonium radical in the phosphate on the cloth gives a flamcproof material, replacement of it with sodium by using dilute sodium hydroxide, alkaline soaps, or 57, sodium chloride solution destroys the flame resistance completely. This is reasonable, since ammonium phosphate is an excellent flameproofing agent while sodium phosphate is not. Reversion to the ammoniuni salt, is easily accomplished by tre:ttmcnt, of the cloth with a solu-
2828
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1949
TABLE I. FLAMEPROOFING OF COTTON CLOTH Sample No.
Loss in Reaction Tensile Time, Strength, FlameMin. % proofnessa 0 1 5 2 15
Analyses
N, % 0.02 0.28 26 3 3 24 0.44 40.87 4 5 37 1.45 5 10 53 0 Flameproofness measured by suspending swatch of fabric vertically over Bunsen burner and exposing it to a 1.50-inch luminous flame for 12 seconds. 1, Control sample wash treatment only. 6 Samples 2 t o 5'weighing approximately 2.7 grams were treated with a phos horylation mixture of 8 moles of pyridine to 1 mole of phosphorus oxycgloride at approximately 120° C . Ratio of POCls to OH is approximately 13.5 to 1. lb
+
P, %
0 09 0 85 1 18 2.32 3.54
C1, % 0 18 0 43 0 98 0 82 0 63
tion of ammonium chloride followed by rinsing with distilled water, thereby restoring the original flameproofness. The ion exchange property has been studied in a separate investigat>ion (11).
Since, under the conditions employed in these experiments, the high phosphorus content is accompanied by severe degradation, i t seemed that such insoluble ammonium cellulose phosphates might be utilized as additive insoluble glowproofing agents with an appropriate flameproofing formula. With this in mind the formula developed by Campbell and Sands ( d ) , of this laboratory, was tried. This method embodies the application of antimony oxide and chlorinated paraffins in an oil-in-water or waterin-oil emulsion which contains a urea-formaldehyde resin monomer to affix them permanently t o the cloth. The fabric thus produced cannot be ignited but has a characteristic afterglow of 3 to 4 minutes' duration in the charred area. Although it was possible to make the cloth glowproof by addition of a cellulose phosphate containing 7.1 % phosphorus, the material could not be used successfully with the formula because the phosphate caked on the surface of the fabric. Even when ground to a powder to pass a 325-mesh screen, the particle size of the phosphate was too large to penetrate the cloth. Microscopical examination of the antimony oxide used in the formula showed that, although it was stated to be 325-mesh, the particles were 1 to 4 microns in diameter with an average size of 2.25 microns. As no equipment was available to subdivide further the particles of cellulose phosphate, investigations along this line were abandoned. As may be seen from Table I, as much as 3.54% phosphorus can be introduced into the cellulose of cotton cloth in 10 minutes. A series of experiments was then conducted to determine the effect of change of molar ratio, time, and temperature on the product with the object of preparing a more highly substituted material which would not be so degraded as to be water soluble. For ease of manipulation, these experiments were performed on cotton linters, instead of cloth, as well as on hydroxyethylcellulose, cellulose acetate, and ethylcellulose. Short-time reaction rates can only be run efficiently on material such as cloth which can be filtered quickly. Since the materials used were finely divided, only longer-time determinations were made, with results m described in Table 11. The reaction of cellulose and a commercia1 sample of hydroxyethylcellulose, both of which are insoluble in pyridine, was very slow at room temperature, approximately 0.15 and 0.52% phosphorus being added, respectively, after 24 hours, Even after 864 hours the cellulose contained only 1.10% phosphorus, while the phosphorus content of the hydroxyethylcellulose had risen to 8.87%. When the temperature was raised to 120' C., approximately 9 t o 10% phosphorus could be added in 3 hours, which value corresponds t o approximately 1 atom of phosphorus per 1.5 glucose anhydride units assuming no other substituents had been introduced. Variations in molar ratio of phosphorus oxychloride to the cellulosic hydroxyls and the time of reaction, within the limits indicated, had comparatively little effect on the degree of phosphorylation.
2829
In contrast to the above-mentioned insoluble reactants, ethylcellulose and cellulose acetate, both of which are soluble in pyridine, reacted very well at room temperature, yielding productp containing 3.4 and 5.02% phosphorus, respectively. This represents 42 and 65% of the theoretical substitution possible assuming no loss of the substituent groups. When the reaction was carried out a t 120" C. the products contained less phosphorus than those obtained a t the lower temperature. Further analysis of the various phosphorylated products showed the presence of combined chlorine, in many cases approximately equal to the phosphorus content. A small amount of nitrogen, not shown in the table, was also detected, but this was found to be due t o pyridine which was tenaciously retained by the acidic groups present in the material. The pyridine was not removed by washing with dilute acetic acid but almost all could be removed by treatment of the material first with dilute alkali, followed by thorough washing, then treatment with dilute hydrochloric acid to replace the sodium ions. When the resulting free acid was treated with ammonium hydroxide, approximately 1 ammonium group per phosphate was introduced. Products of more complete substitution of ammonium ion were not stable, ammonia being liberated by boiling water as might be expected of a diammonium phosphate. An attempt was made to phosphorylate cellulose in a neutral solvent with the object of determining whether pyridine wat necessary. Dioxane was selected for this determination because Popov (17) claims that acetylation using acetyl chloride proceeds more readily in this medium than in pyridine and it war thought that these reactions might be analogous. The degree of phosphorylation, using only dioxane and phosphorus oxychloride, was negligible. Addition of small amounts of pyridine to the dioxane did not effect phosphorylation until its concentration reached approximately 20%. At this concentration the product contained approximately 3% phosphorus. A sample
TABLE11. PHOSPHORYLATION OF CELLULOSEAND DERIVATIVES WITH PHOSPHORUS OXYCHLORIDE IN PYRIDINE Run No.
Molar Temperature, Ratio a C. P0Ch:dH
Time, Hr.
Analysis of Product -P, %
CL %
Cotton Linters 1 2 3= 4 5 6 7 80 9"
25-30 25-30 25-30 120 120 120 120 120 120
1.10 0.15 0.29 9.03 8.60 8.30 6.74 8.50 9.10
0.40 0.29 0.11 4.50 8.80 9.50 6.30 8.20 11.50
0.41 8.87 0.52 7.52 9.25 8.90 8.71 10.35
0.60 3.89 0.25 4.02 9.40 11.08 7.14 9.38
3.67 3.93 3.40 4.37 3.60 1.24 1.07 1.20 1.11 1.41
0.69 0.88 1.17 2.69 2.24 2.92 3.26 2.48
Hydroxyethylcellulose 10 11 12 13 14 16 17
25-30 25-30 25-30 120 120 120 120 120
18 19 20 21 22 23 24 25 26 27
25-30 25-30 25-30 25-30 60 120 120 120 120 120
28 29 30 31 32 33
25-30 25-30 25-30 25-30 120 120
15
Ethylcellulose 1 2 4 6 2
2 4 4 4 6
24 24 2 24 3 3 1 6 24 3
Cellulose Acetate 1 2 2 4 4 4 4
4.68 0.20 5.02 0.67 1.71 4.89 4.41 1.99 4.31 2.77 2.42 3.86 insufficient pyridine to neutralize acid 2 2 48 1 24
a Runs were in acid medium-i.e formed in reaction. In all other cas& sufficient pyridine was added to neutralize the acid formed; the molar ratio of POCla to pyridine ranged from 1/6 to 1/8.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
phosphorylated in undiluted pyridine, under the same conditions of time and temperature, gave a product with 7.9% phosphorus content. PHOSPHORYLATION OF CELLULOSE
By Phosphoric Acid. An attempt was made to phosphorylate purified, low viscosity cotton linters by a slight modification of a patented method ( I O ) . Ten grams of purified, low viscosity cotton linters were placed in 150 grams of 96% phosphoric acid containing 0.4 gram of concentrated sulfuric acid. After 18 hours' standing a t room temperature, 0.5 gram of sulfuric acid in 50 grams of 96% phosphoric acid was added and the mixture allowed to stand for 30 hours longer. On pouring into water, filtering, washing, and drying, 9.5 grams of material were recovered which contained no phosphorus. A similar method described by Tanner (19) was also tried. Fourteen grams of purified, low viscosity, cotton 1intn.s werp treated for 2 minutes a t 5 " C. with a mixture of 78 grams of 100% sulfuric acid, 52 grams of 85% phosphoric acid, and 2.6 grams of glacial acetic acid The swollen mass was then placed in 1800 ml. of cold water and centrifuged. After thorough washing the phosphorus content was negligible. By Phosphorus Oxychloride. A small amount of phosphorylation was obtained using a method similar to that patented by Hagedorn and Guehring ( 7 ) with soda cellulose. Twentv grams of low viscosity,, purified linters were mercerized with 40% sodium hydroxide in an ice bath for 4 hours. The mass, p r e w d to a weight of 60 grams and shredded, was slowly added to 18.8 ml. (32 grams) of phosphorus oxychloride in 180 ml. of anhvdrous benzene. Although the mixture was continuously cooled in an ice bath, it boiled during the addition of the last t w o thirds of thc soda cellulose. It was then allowed t o qtand €or 16 hours a t room temperature, filtered, washed with ethyl alcohol and ether, and dried. The product was not dispersible in water. The phosphorus analysis was 3.06%. By Phosphoric Acid and Phosphorus Oxychloride. The combination of these two reagents, as described in the patent literature (9), gave very degraded products. Several variations were tried. Ten grams of purified, low viscosity linters were treated with a solution of 200 grams of 96% phosphoric arid and 200 grams of phosphorus oxychloride for 2 days a t room temperature. The supernatant liquid was decanted and ethyl alcohol added to the residue. It became hot and the product dissolved After neutralization of the solution with barium carbonate, the soluble barium cellulose phosphate was extracted from the precipitate with distilled water. The product was recovered by the addition of 5 volumes of ethyl alcohol t o the aqueous extract. The solution was filtered and the product dried. The analysis gave 5.2% phosphorus and 51.8% barium. In accordance with the second example of this patent a duplicate sample as described in the preceding paragraph was allowed t o stand 5 days a t room temperature. The supernatant liquid was decanted and the remaining gummy mass dropped into ethyl alcohol, with cooling. The product was insoluble in alcohol but swelled in it. After washing with water it was dried a t 65" C. in vacuum. The phosphorus analysis was 18.92%. Another variation was tried comprising 10 grams of low viscosity, purified linters which were treated with a solution consisting of 200 ml. of 96% phosphoric acid, 200 ml. of phosphorus oxychloride, and 5 ml. of concentrated sulfuric acid for 24 hours a t 1 5 O t o 18" C. The product was washed thoroughly with ethyl alcohol. It was very hvgroscopic and was decomposed on CLOTH. By Phosphorus Oxychloride and Pyridine. COTTOW Oven-dried samples of khaki-dyed herringbone twill, 8.5 ounces per yard (the type extensively used by the Army for work clothing), 15 X 6 cm., were immersed in a boiling mixture of 60 ml. of phosphorus oxychloride and 42 ml. of pyridine for various lengths of time (Table I). The samples were washed successively with pyridine and water after removal and were treated for 20 minutes with 10% ammonium hydroxide. They were thoroughly washed with distilled water, dried a t 60" C., and analyzed. Phosphorus was determined essentially by the method of Gerritz ( 6 ) ; chlorine by combustion in a Parr bomb followed by volumetric titration; and nitrogen by the usual Xjeldahl method except that longer digestion (3 hours) and distillation times were necessary since a small part of the nitrogen was present as pyridine (18). The cloth so produced was both flameproof (burning only a limited area beyond that directly exposed to flame) and glowproof. Washing with alkali or 5yo sodium chloride, to simulate sea water, replaced the ammonium with sodium thereby destroying the flame resistance. Subsequent treatment with 10% ammonium chloride, however, followed by washing with distilled water, restored these qualities.
Vol. 41, No. 12
PURIFIED COTTON-LINTER CELLCLOSE.The following preparation is typical for the phosphorylation of cellulose in the presence of pyridine. One hundred grams of dry, purified, low viscosity linters,.milled to 80 mesh, were mixed into 1 liter of anhydrous pyridine, and 170 ml. (285 grams) of phosphorus oxychloride added. The mixture was mechanically stirred and refluxed for 3 hours, filtered, and the brown product washed 3 times with a small amount of fresh pvridine. The material was then hydrolyzed with crushed ice. (A vigorous reaction occurred a t this point if the reaction product was not washed with fresh pyridine before the addition of ice.) After filtration and thorough washing with distilled water the product was treated 4 times with 1% sodium hydroxide with complete washing with distilled water after each treatment. This was follo~vedby 4 treatments with 5% hydrochloric acid, again with thorough washing after each treatment (negative chloride test on filtrate). The samples were dried in vacuum a t 60" C. The analysis yielded 8.48% phosphorus, 1.45% nitrogen, and 9.96% chlorine. CELLULOSEDERIVATIVES. The following preparation is , t,ypical for the phosphorylation of pyridine-soluble crllulost~ derivatives such as cellulose acetate and ethylcellulose. Ten grams of ethylcellulose (approximately 2.25 ethyl groups per glucose unit) were dissolved in 90 ml. of dry, cold pyridine and 13.6 ml. (22.8 grams) of phosphorus oxychloride were added with rapid stirring. The mixture gelled almost immediately and was allowed to stand a t room temperature for 2 hours, after which it was stirred with water. The product was well broken up and washed until free of the odor of pyridine, treated 1 hour with 5% acetic acid, washed until neutral, and dried at 105" C. The analysis yielded 3.40% phosphorus, 0.69% chlorine, and 2.34% nitrogen. Pyridine-insoluble derivatives of cellulose, such as hydroxyethylcellulose, were phosphorylated in the same manner as the cotton-linter cellulose as described above. By Phosphorus Oxychloride and Dioxane. Int,o each of three flasks Rere placed 10 grams of dry, purified, low viscosity linters, ground to 80 mesh, 110 ml. of anhydrous dioxane, arid 17 ml. (28.5 grams) of phosphorus oxychloride, Zero, I , and 5 ml. of anhydrous pyridine were added to different flasks and the mixt'ures were refluxed for 3 hours. The products were poured onto crushed ice, filtered, washed free of the odor of dioxane and pyridine with distilled water, and dried a t 60" C. S o phosphorus was detected on analysis of these samples. To the same quantities of linters, dioxane, and phosphorus oxychloride as mentioned in the preceding paragraph were added 25 ml. anhydrous pyridine. The mixt'ure was refluxed for 3 hours, poured onto ice, filtered, and thoroughly washed. The solid product was treated four times with 1yo sodium hydroxide, with thorough washing after each treatment, then four times with 5% hydrochloric acid, again with thorough washing after each treatment. The final product was dried a t 60" C. Analysis yielded 2.8% phosphorus. By Urea Phosphate. In order to obtain comparative samples of cellulose phosphate, the method, essentially as described by Coppick (4),was used. One hundred grams of high-viscosity linters were soaked in a solution consisting of 138 grams of phosphoric acid (85%), 240 grams of water, and 216 grams of urea. It was pressed t o a weight of 497 grams, shredded, and dried for one-half hour a t 100" C. The temperature was then raised to 150' C. for one-half hour after which t'he sample was mashed thoroughly with distilled water, dried in vacuum a t 60" C., and ground to 20 mesh in a Wiley mill. The ground sample was treated twice with 1% aqueous hydrochloric acid, followed by thorough washing with distilled water after each treatment. No ammonia was liberated on treatment of the final product with sodium hydroxide nor was there any residual chlorine present on shaking it with water or sodium hydroxide and testing the acidified filtrate with silver nit,rate. The product was dried in vacuum a t 30" C. for 4 days. The analysis yielded 3.93% phosphorus, 0.23% nitrogen, and 0.10% chlorine. SUMMARY
Various methods of phosphorylating cellulosic materials have been investigated. A method using phosphorus oxychloride and pyridine as the phosphorylating agent has been adopted and a number of cellulosic products containing phosphorus and chlorine has been prepared and analyzed. Cloth phosphorylated by the above process is substantially flame- and glowproof but suffers so great a loss in tensile strength that it is impractical for the production of garments. An attempt has been made to incorporate cellulose phosphate as a glowproofing agent into an otherwise successful flameproofing formula,
December 1949
INDUSTRIAL AND ENGINEERING
2831
ACKNOWLEDGMENT
(7) Hagedorn, M., and Guehring, E., U. S. Patent 1,846,524 (1932);
The authors are indebted t o W. A. Pons, Mrs. V. 0. Cirino, and Miss E. R. McCall of the analytical section of this laboratory for the analytical data, to Miss I. V. deGruy for the microscopical data, and to Edmund M. Buras, Jr., of the Cotkon Chemical Finishing Division for his interest and suggestions.
(8) Hagedorn, M., Reichert, 0.. and Guehring, E., U. 5. Patent
LITERATURE CITED
Burgess, Ledward & Co., Ltd., and Harrison, W., Brit. Patent 192,173 (1923).
Campbell, K. S., and Sands, J. E., Teztile W o r l d , 96, 118 (1946). Champetier, G., Compt. rend., 196, 930 (1933); Ann. Chim., 20, 5-96 (1933). d
CHEMISTRY
Coppiok, S., and Hall, W. P., in “Flameproofing Textile Fabrics,” by R. W. Little, A.C.S. Monograph 104, pp. 179 ff., New York, Reinhold Publishing Corp., 1947. (5) Federal Specification CCC-D-746 (1943) ; Jefferson Quartermaster DeDot. Saeoification 242 for Fire-, Water-, and Weather-R&istant Duck (1942). (6) Gerritz, H. W., J . Assoc. Oj%. Agr. Chemists, 2 3 , 3 2 1 (1940).
Brit. Patent 279,796 (1928).
2,002.81 1 (1936). (9) I. G. Farbenindustrie, Ger. Patent 547,812 (1932). (10) Ibid., 556,590 (1932). (11) Jurgens, J. F., Reid, J. D., and Guthrie, J. D., Testile Research J., 18, 42-44 (1948). (12) Leicester, J., and Wright, C. M., Brit. Patent 587,366 (1947). (13) Malm, C . J., and Fordyce, C. R., U.S. Patent 2,008,986 (1935). (14) Malm, C. J., and Waring, C. E . , I b i d . , 1,962,827 (1934). (15) Ibid., 1,962,828 (1934). (16) Nathansohn, Ibid., 1,891,829 (1932). (17) Popov, P. V., Compt. rend. acad. sci. U.R.S.S., 4 6 , 3 2 5 (1945). ENG.CHEM.,ANAL.ED., (18) Shirley, R. L., and Becker, W. W., IND. 17, 437-8 (1945). (19) Tanner, W. L., U. S. Patent 1,896,725 (1933). (20) Thomas, G. A., and Kosolapoff, G., Ibid., 2,401,440 (1946). (21) Weihe, A,, Ibid., 2,003,408 (1935). RECEIVED October 4, 1948. Presented before the Division of Sugar Chemistry and Technology and the Division of Cellulose Chemistry a t the 114th CHEMICAL SOCIETY? Portland, Ore. Meeting of the AMERICAN
Composition of Two Types of Cellulose Phosphates J. DAVID REID, LAURENCE W. MAZZENO, JR., AND EDMUND M. BURAS, JR. Southern Regional Research Laboratory, New Orleans, La. T h i s paper describes further experiments conducted in an effort to elucidate the structure of phosphates of cellulose prepared by the commercial urea phosphate method of preparing flameproofed cloth and by the pyridine-phosphorus oxychloride method. By electrometric titration it is shown that the combined phosphorus in cellulose phosphate prepared by the treatment of cellulose with urea phosphate is probably entirely in the form of a monosubstituted phosphate ester. There is no evidence of the formation of other, more highly substituted products. The structure of cellulose phosphate prepared by the treatment of cellulose with phosphorus oxychloridepyridine mixture is similar, except that, in a typical sample, approximately 23% of the phosphorus can be accounted for as a disubstituted phosphate ester. The chlorine also present in this product is probably attached directly to the carbons of the glucose units. A small amount of nitrogen is found in typical samples, presumably due to pyridine.
.x
A
DDTTIONAL experiments conducted in an effort to elucidate the structure of the phosphates of cellulose and certain cellulose derivatives are described herein. The typical procedures for preparation of phosphorylated cellulosic materials by various methods, referred to below, were described in the preceding paper (12). Although the tensile strength of moderately phosphorylated cotton cloth is greatly reduced, the general appearance and feel are changed very little. The cloth will char while in a flame but will not continue to burn when the flame is removed, and afterglow is confined to the charred area. Samples of cloth containing 5% phosphorus were found t o dye brilliantly with methylene blue, very lightly with Celliton blue, and to be relatively little affected by direct cotton dyee, such as Solantine Blue, and wool dyes, such as Kiton Red. When cellulose is more highly phosphorylated, say above 6% phosphorus, the fibers are degraded to a light brown powder.
The degree of degradation cannot be determined by viscometric methods since the product is practically insoluble in water and cuprammonium solutions. This is also true of phosphorylated hydroxye thylcellulose. It was found preferable to dry phosphorylated cellulosic materials in vacuum at 60” C. or below, since many samples undergo further degradation a t higher temperatures. This was particularly true with phosphorylated cellulose acetate which released acetic acid on standing at room temperature, probably because of autocatalyzed hydrolysis. If the combined phosphorus in a cellulose phosphate is not triply bound, the substance should behave as a mono- or dibasic acid. Nuessle (10)has recently proposed the dibasic structure for cellulose phosphate prepared by the urea phosphate method. H e points out that urea is too weak a base t o form a stable compound with the combined phosphoric acid as postulated by Coppick and Hall (5). While not ruling out the possibility of amido forms being produced, he prefers the dibasic acid structure. In order to investigate the structures of such cellulose phosphates the authors have applied an electrotitrimetric procedure t o their compounds and found a marked difference between the cellulose phosphate prepared by the urea phosphate method and that prepared by the pyridine-phosphorus oxychloride method. Discussion of the results of these findings is presented below under suitable headings. PREPARATION OF CELLULOSE PHOSPHATE
PREPARED BY UREA PHOSPHATE. The titration of a sampIe of cellulose phosphate prepared by the urea phosphate treatment (11) resembles that of a relatively insoluble dibasic acid or acid salt, as shown in Figure 1. The p H was determined by the glass electrode using a continuous reading amplifier (4). Relative conductance was determined by a 1000-cycle alternating current resistance-balanced bridge using bright platinum elmtrodes. Both properties were observed during the course of a single titration with each alkali in a cell similar t o that described by Buras and Reid (3). Successive duplicate determinatims on
