Hvdroxvethvlcellulose and Its-Uses U'. E. GLOOR, B. I€. MAHLMAN, AND R. D. ULLRICH Hercules Powder Company, Wilmington, Del.
A
newly introduced variety of alkali-soluble hydroxyethylcellulose is described, and its solubility, resistance to precipitation, and compatibility properties are tabulated. Data are presented on its physical characteristics. A description is given of the pattern of end uses suggested by the literature, in the fields of filament, sheet, textile and paper hishing, and ink. Recent work indicates the utility of the material in mineral flotation and in improvement of flocs obtained in water treatments.
a t room or elevated temperatures: and a water-soluble grade, degree of substitution about 1.4 or higher. The present production processes for making hydroxyethylcellulose are based on the reaction between alkali cellulose and ethylene oxide (23,68) or ethylene chlorohydrin (&). The over-all reaction, for the production of a material of D.S. 1.0, can be written as follows:
[CaH70z(OH)a]n Cellulose
A
LTHOUGH hydroxyethylcellulose has been described in the
technical literature for the past 30 years or more, few uses in commerce have developed. This article describes the properties of hydroxyethyl~ellulose,and summarizes some of the published literature on its uses. Some hitherto unpublished information on the use of hydroxyethylcellulose, developed in the laboratories of the Hercules Powder Company, is presented. While the organosoluble derivatives-cellulose nitrate, cellulose acetate, and ethylcellulose-have been of industrial importance since 1870, the water- and alkali-soluble derivatives have been broadly available in the United States only since 1935. These latter materials include sodium carboxymethylcellulose (commonly known as cellulose gum or CMC), methylcellulose, and both water-soluble and alkali-soluble forms of hydroxyethylcellulose. FUNDAMENlAL CONCEPTS
The root of all these products, cellulose, is a polymer composed of many anhydroglucose units, each unit bearing three hydroxyl groups. All commercial derivatives of cellulose are obtained by etherifying or esterifying these hydroxyl groups to a greater or lesser degree. The number of hydroxyl groups per glucose unit that have reacted is known as the degree of substitution (D.S.) of the material, and this, together with the average length of the cellulose molecules (degree of polymerization, D.P.) chiefly determines the properties of the cellulose derivative. Obviously, the uniformity of kubstitution also has a bearing on these properties. In general, the solubility characteristics of cellulose derivatives are closely related to the degree of Substitution and the nature of the substituent groups. For a given derivative of cellulose the degree of polymerization to a large extent determines its viscosity insolution. The common organosoluble derivatives ordinarily have degrees of substitution from 2.0 tu 3.0,while watersoluble materials have a degree of substitution above 0.4. Alkalisoluble materials on the other hand may have a degree of substitution as low as 0.1 to 0.2-i.e., only an average ef 0.1 or 0.2 hydroxyl group on each glucose unit is etherified. These produrts are substantially insoluble in pure water. HYDROXY ETHY LCELLULOSE
The literature discloses three general types of hydroxyethylcell u l o s e o n e of low substitution, degree of substitution about 0.05 to 0.15, dispersible in chilled caustic solutions; a second type, degree of substitution ranging from 0.2 to 0.9, soluble in caustic
+ CiHiO
(NaOH HzO)
[C~HIOZ(OH)Z(OC~H~OH) 1. Hydroxyethylcellulose
In this reaction, the function of the sodium hydroxide is to swell the cellulose fibers uniformly and to catalym the etherification. Among the many etherification processes used or proposed with cellulose, this is unique because no by-products are directly formed, although care must be taken in the choice of conditions of etherification so that an unduly large loss of the reagent does not occur through side reaction. The variety of hydroxyethylcellulose described in this article has a degree of substitution of 0.35 to 0.4, and is referred to as HEC. The material is a white fibrous solid, tasteless and odorless, with a density of 1.49 a t 25" C., when cast in film form. Ita refractive index, in this form, is 1.534 a t 25" C. when measured using artificial (tungsten) light. The solubility of HEC is described in Table I. Particularly worthy of note is the fact that the material is soluble in alkaline 40% urea solutions. The fact that the solubility of the material changes with the strength of the alkali is also illustrated by Figure 1. Because HEC gives clear and bright solutions in 701,caustic, and such solutions can be made a t a casting viscosity, they can be laid down as films and set or gelled by flooding with water or with neutralizing salt or acid solutions. A romparison of several surh precipitating media is shown in Table 11 Two viscosity grades of HEC are now available: one testing trom 500- to 800-cp. viscosity when measured a t 5% concentration (bone-dry basis) in 7% sodium hydroxide, the other showing 2000 to 3000 cp. under the same conditions. Viscosities are nieasured upon solutions at 25 C., using the Brookfield viscometer, Model LVF, and appropriate spindles and speeds. CASTING FILMS FROM HEC
The extrusion of varieties of hydroxyethylcellulose other than HEC into film by methods similar to those used in processing cellophane has been described by Schorger and Shoemaker (48). Suitable solutions of HEC may be laid down as wet films on various substrates by the familiar knife-coating, doctor-blade, or reverse-roll methods. These films can be gelled with precipitants, washed free of salts, stripped from the base, and dried. The washed film often shows such good adhesion to glass, commonly used as a casting surface, that the stripping of continuous films for testing is difficult. 2150
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Other possible methods of holubiliration involve the use of chromatea (by photoholubilization, the action of light causing a reaction between the chromium salt and the HEC), and contact of the material with tannins. Available data (66)indicate that the toxicity of water-soluble hydroxyethylcellulose is low. Because the conventional uses of cellulose derivatives have been largely concerned with those materials which are soluble in water or organic solvents, there had been little mention in the literature of the uses of alkali-soluble derivatives in commerce even aa late as 1943 (88). At first glance it would appear that cellulose ethers soluble only in alkali would fmd restricted use, but a survey of literature on the uses already suggested indicates real possibilities despite this apparent limitation. I n general, 4 to 10%aqueous solutions of strong alkalies are solvente, aa shown in Table I. The tetraalkyl- or tetraaryl-substituted ammonium b w s , Schweitzer's reagent, and sodium hydroxide-urea-zinc oxide mixtures ($2)have also been suggested. Use of strong urea aa a solvent would eliminate the caustic properties of the foregoing, and further utilization depends on the development of proper recovery methods.
10,000
lo00
100
10
7
TABLEI. SOLUBILITYOF HYDROXYETHYWE~LLULOSE (HEC)
However, the washed film can be dried on a water-repellent substrate such a$ polyethylene sheet to form clear, tough films. Physical properties of such unplaaticised film cast from HEC were determined in the laboratory.
An 8% solution of HEC in 7% sodium hydroxide was knifecast on polyethylene substrate, set by treatment With ammonium sulfate solution, washed salt-free m t h water, and dned at 70' C. before stripping. The film was condi.tioned 48 hours at 50% relative humidity and 77' F. before being tested at same conditions; the Scott IP4 tester was used. Film thickness Tensile strength Elongation at break Flexibility
2.1 mils 13 400 pounds per square inch 6 l a 0 dpuble folds, M.I.T. flex tester
The compatibility characteristics of HEC are shown in Table 111. It is compatible with the other water-soluble cellulose derivatives and with a few other unrelated materials. Because water washing to remove caustic can also remove water-soluble modifiers, the film-washing procedure for compatibility determinations was changed somewhat as indicated in the footnote to Table 111. Ethyl alcohol (95%) waa used aa a wash in cases where the modifying film former was soluble in both hot and cold water. The ethyl alcohol served mainly to remove sodium hydroxide from the surface of the films, but did not swell or penetrate them. For some purposes, such as paper coatings that contain pigments, the neutralized salts may be left in the coating and the washing eliminated. These films are insoluble in organic solvents such as ethyl alcohol, toluene, acetone, and butyl acetate. Insolubilization of hydroxyethylcellulose can also be accomplished in a number of other ways. A film containing approximately 20 to 30% glyoxal becomes water-resistant when cured at 105' C. for 1 or 2 hours (3). Water-soluble phenolic resins react with the HEC upon heating to make a film more insoluble. Urea and formaldehyde can be added to the HEC solution, and will ineolubilize the film when heated (6).
(D.8.0.35 to 0.4. 2% HEC shaken into solvent and examinedafter standing under conditions shown) Relative Degree of Solubility' 4 hours at room temperature Solvent 12 hours at 0' C. Water I I 8-H 8 8 8 8 8-H 8-H 0-G 0-H-G S-H-G 5H-G P8 P8 5H 8-H P8 8 P8 PBH P8 8-H
ethers-teated. a 8. Soluble. P8. Partly soluble. H. H85y. G. Gel. I. Inaoluble.
Examination of the early patents on production of hydroxyethylcellulose, such as those of Schorger and Lilienfeld, indicates that the control of substitution of the product was apparently a matter of proportioning reagents to alkali cellulose. As a result, the products were not too uniform from batch to batch. Modern analytical developments, such as the modified %isel analysis described by Morgan ($&, enable the producer to apply better checks on the process and the product, with the result that more uniform products are currently available.
TABLE11. BEHAVIOR OF HEC SOLUTIONS IN ALKALI UPON ADDITION OF PRECIPITANTS (D9 0 35 to 0.4. To 50 ml. of stock eolution of 7 % HEC in 577 NaOH solhtio& of salts show: were added slowly with stirring. Salt solut!ons weri all of 10% concentration in water. Amount that could be added before solution changed from a clear liquid to state shown is given) Reagent Volume A%d. M1. Change Noted A11 803, 15 Firm gel 50 Not precipitated Nab1 16-20 Firm gel NasPOd NarSOr 50 Slight gel, so!idified overnight Mg80r 5-7 Cloudy aolution 25 Milky gel Ha804 15 Firm gel CaClr 10 Firm gel
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dopes was suggested by Maxwell (84),who found that the dimen-
TABLE 111. COMPATIBILITY OF HEC WITH WATER-SOLVBLB sional stability of the regenerated cellulose sheet thus made was MODIFIERS
(D.S. 0.35 t o 0.4)
Material Starch Gelatin, 150 bloom Gum arabio Gum tragacanth Gum karaya British gum Dextnn Carboxymethylcellulose 70-L Method L Polyvinyl alcohol Zein Casein Sodium alginate
Compatibilities at Indicated Ratios of HEC to Other Ingredient 3:l 1:1 1:3 SI I I C C C I I I I I I I I I C C I
C
C
C
C I SI
I
I
C C I C
C C
I
C
C 1
I C I
After casting alkali solutions lilm with gelatin and zein were washed with cold water; Methocel films'with hot water; remainder with 96% ethyl alcohol to remove caustic, before drying and examining. Compatible with glycerol, glycols, sorbitols, and similar compounds used a8 softeners
USES OF ALKALI-SOLUBLE HYDROXYETHY LCELLULOSES
In the outline which follows, no attempt has been made to include a complete bibliography of the uses of hydroxyethylcellulose, but it does show the main patte'rn of end uses in which experimenters believed the material would be useful. Statements concerning possible uses of hydroxyethylcellulose are not intended as recommendations to use this material in the infringement of any patent. FORMED AS FILAMENTS, ETC. Much of the early patent literature on hydroxyethylcellulose was concerned with the use of alkali-soluble varieties in the preparation of filaments and rayon (26,28-80,33, 40, 41, 46, 47), staple fiber (29),artificial horsehair (29),and artificial straw (29,61). Trail1 (69)in discussing the advantages of glycol cellulose over viscose in rayon mentioned solution stability, absence of sulfide vapors, and freedom from need to age the spinning dopes or to desulfurize or bleach the product. He also indicated that the fibers had wet strength equal to that of viscose. Later workers reached other conclusions (233, 34, 48, 62). Although the material has not yet found wide use in rayon manufacture, the work of Maxwell (34)suggests interesting possibilities. By incorporating 2% of an alkali- or water-soluble hydroxyethylcellulose in viscose spinning solutions, filaments were obtained which were more sensitive than ordinary viscose rayon to direct dyes. A somewhat later development was the use of SHEETFORMS. the alkali-soluble cellulose ethers, among which hydroxyethylcellulose is always mentioned, for making cellophanelike film and foil (4, 27-80, 33, 40,46, 68), sheets or plates (28-30,33,46,63), shaped or molded articles (4, 28, $9, 41, 46), tubing (41, 61), sponge (63),bottle caps (49,69), bands (29,49,63),and insulating goods (46). The possibility of making bands of hydroxyethylcellulose containing 88% water, and wrapping them over bottle tops, packages, and rubber goods in the wet state, subsequently allowing them to shrink, was disclosed by Shoemaker (61). Thin foil of hydroxyethylcellulose was prepared by Schorger (48),who showed that it was possible to make this foil with better tensile strength than an equal elongation to commercial regenerated cellulose foil. He also stated that the change in area with variation in atmospheric humidity is less for films based on cellulose hydroxyalkyl ethers than for those based on cellophane. Shoemaker also showed the uf I f these ethers in bottle caps, stating that they are inherently n c flexible than cellophane made without plasticization. A drawback in the production of foils baaed upon hydroxyethylcellulose appears to be a slow formation speed-10 feet per minute-and need for excessive drying. Refrigeration to a temperature of not less than 8' F. has been suggested as a remedy for the latter obstacle. The addition of hydroxyethylcellulose to cellophane casting
improved, resulting in better adhesion of moistureproofing layers to the base sheet. Fundamental to the production of useful articles from alkalisoluble cellulose ethers is their coagulation in the desired form after shaping. The early reference of Lilienfeld (28) disclosed the fundamental operations. A solution of 100 parts of such hydroxyethylcellulose is made in 900 to 1200 parts of 5 to 8% caustic. I t is cast into a layer and coagulated by contact with 10% sulfuric acid, 25% acetic acid, 30% ammonium chloride, 20v0 tannin solution, or 40% formaldehyde. The solid film is washed salt-free and dried. Mo%tof the filament, film, permanent sizing, and coating processes reviewed embody these operations. Solution concentrations of the cellulose ether may vary from 1.0 to 10%; sodium hydroxide strength is usually in the range of 4.5 to 8%. Other plasticizers, colors, and emollients may be added. Shoemaker (49)added 1 to 2% of sodium carbonate to the 6 to 7% solutions of the ether in 7.5 to 8% sodium hydroxide, used for forming bottle cap blanks on solid molds, so that contact with the coagulant caused the cap blanks to liberate gas and to release from the mold surface. Coagulating solutions mentioned include the familiar sulfuric acid--sodium sulfate-glucose-zinc chloride combinations used in the manufacture of viscose (34, 60), ammonium sulfate, magnesium sulfate, sodium bisulfate, alum, or even sodium hydroxide, 24% or stronger ($4). USEINTEXTILE FINISHES AND SIZES. The literature on finishing textiles with alkali-soluble hydroxyethylcellulose is extensive; this use is among the earliest mentioned and is of some commercial importance today. During World War 11 large quantities of cotton netting were stabilized against dimensional change under tropical conditions by treatment with alkaline solutions of celhlose and its ethers, followed by coagulation and finishing. Specific uses in the treatment of textiles mentioned are: Coatings (23,28,29,33,46,46,60) Finishes and dressings ($,IO,16,l'Y, $3,94,d8-L30,33,66, 48,46, ,o\
40 I
Yarn sizes (10, 18, 16, 17,$8, 29, 38, 39, 46, 46) Book cloth coatings ($8, $9) Filling open weaves ($9,4l, 46,46) Adhesives (89,88,41,46,46,68) Tracing cloth ( 8 ) Making cloth transparent ($9) Filling the back of pile fabric ( 9 , l l ) Waterproofing fabrics (18) Fabric from unwoven fibers has been made by printing designs from corrugated rollers on paper webs (16, 60). Thickness and wet strength can be controlled to provide textures useful as wash cloths, towels, and napkins, which will not disintegrate when wet. Solutions for textile treatment are stabilized by incorporating alkylene oxides in the coating formula (60, 61). An interesting application of the swelling properties of fibers of these hydroxyethylcelluloses is their use in thread woven into sleeves. Used as hose, this structure swells when wet and carries water (20). Mixtures of solutions of hydroxyethylcellulose and various rubber latices have been described for use in backfilling pile fabric ( 9 ) , and, using chloroprene latex, for coating cloth to make it impermeable to air (67). The use of cuprammonium solvent instead of alkali solutions gives finished cotton goods which are said to be mildewand rot-resistant ($1). Dyeing of textiles with vat dyes is claimed by a process in which hydroxyethylcellulose fibers are dyed with dissolved dyestuffs and developers suitable for cotton raw stock. The dyed cellulose ether is dissolved in aqueous alkali, the textile is treated with this colored alkali solution, and the usual coagulation, washing, and drying steps are then carried out (7). The use of hydroxyethylcellulose in permanent textile sizes was described by Cohoe (12). He showed that the use of aqueous alkali solutions containing 3.5 to 5% of hydroxyethylcellulose im-
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
parts a linenlike “hand” to cotton, and that 6 to 8% solutions give greater stiffness. Ten properties are listed, in which impregnation of thread with the cellulose ether before weaving imparts superiority over untreated cotton. Among these are permanency to laundering, better release of soil when laundered, and lem discoloration on aging. Tabular data and graphs show better fiber durability upon laundering, and reduction of shrinkage, especially of fill threads, when the cellulose ether size is used. A more recent article describing present-day use of a hydroxyethylcellulose made especially for textile sizing (Ceglin) was presented by Cornwell, Milne, and Porter (14). Softened textiles, treated with these celluloee ethers, are commonly produced by passing them through a bath containing aqueous glycerol; other softeners suggested are diethanol formamide, etc. (63). Formulations for sizing acetate yarn are shown (32). USES IN PAPER COATINQ.As with textiles, there have been many attempts to apply hydroxyethylcellulose t o paper coating and modification. Lilienfeld’s “master patents” (88)broadly disclosed the use of such films aa “dressings insoluble in water for textiles, paper and the like”; such dressings are applied by padding or spreading alkaline solutions of hydroxyethylcellulose which may also contain softeners (soap, glycerol, and turkey red oil) and fillers such aa china clay or talc, vegetable oils, and starch. Reichel and Hindry ( 4 1 ) made similar disclosures. Other patents cover paper coating (6, B,49), beater additives to provide a toweling or calendered paper of better wet strength (6),transparent paper (% nonwoven I), fabric from bleach sulfite stock (60), and sausage casing (64). Recent developments (18) have aroused interest in these materials for producing machinefinished papers for printing. Light sensitizers have been incorporated in paper coated with this cellulose ether, for use in reproducing line drawings (63). USES AS PIQMENT BINDERS,INKS, ETC. In this field we find mention of the alkali solutions of hydroxyethylcellulpse as a thickener for textile printing (&?, $9,3.9,39),as fixing agents for pigments (MJ 99, 33), as binding agents (@?),as a coating for metal printing plates (&), and in making ink for marking blueprints (19). For textile printing, the use of mica, carbon black, zinr white, color lakes, and alkali-resistant dyes was suggested (98). MISCELLANEOUS USES. Aside from leather coating (98,41) and artificial leather (.99),these uses are fairly recent and indicate the stimulation of industrial thinking that is produced by the availability of a new material. Such uses include fillers for greases (@), addition to soap ‘as a filler (66) or before solidification to help the “set” (N), addition to hydraulic cement used in lining deep wells to retard its solidification at high pressures and temperatures (1, 31),and use in ceramics as a binder before sintering (37). Work in Hercules laboratories has indicated that these hydroxyethylcelluloses, added in fibrous form to slurries of ground minerals prior to flotation, will have the same action as starch, commonly used, with lesa than a tenth as much of the cellulose ether as starch required. Upon the basis of this work, it is indicated that similar benefits could be attained through the use of fibrous hydroxyethylcellulose in the water-grinding of pigments and of ores prior t o concentration and in the flocculation of water-treatment coagulants and sewage sludges. The insolubility of HEC in organic liquids suggests that it merits consideration for greaseproofing paper, paperboard, and textiles; its alkali solubility has not yet been exploited in thickening the alkaline fluids used in some storage batteries. The general references to the use of the material as a filler (41) suggests ita incorporation in light-colored urea or melamine plastics, or cast phenolic resins in which the hydroxyethyl groups should provide very reactive linkages. The excellent adhesion to glass of washed wet films and their property of sealing upon drying indicate that the product may be used in making complex decalcomanias, advertising displays, and closures.
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LITERATURE CITED (1) Anon., Office of Technical Services, U. S. Dept. Commerce, OTS Rept., PB 52025 (1947). (2) Bonnet, L., Teintex, 2,679-87 (1937). (3) Broderick, A. E., Brit. Patent 592,210 (Sept. 11, 1947). (4) Broderick, A. E., U. S. Patents 2,173,470, 2,173,471 (Sept. 19, 1939). (5) Ibid., 2,469,431 (May 10, 1949). (6) Brown Co., Brit. Patent 423,471 (Feb. 1, 1935). (7) Carroll, W. B., Jr., U. S. Patent 2,448,515 (Sept. 7, 1948). (8) Clark, J. A., Am. Dyesfuf Reptr., 29,549-50 (1940). (9) Clark, J. A., Can.Patent 425,220 (January 1945). (10) Clark, J. A., Teztile Mfg., 64, 252 (1938). (11) Clark, J. A., U. S. Patent 2,391,867 (Jan. 1, 1946). (12) Cohoe, W. P., Chemistry &Industry, 56,381-7 (1937). (13) Cornwell, R. T. K., U. 5. Patent 2,390,780 (Dec. 11, 194k). (14) Cornwell, R. T. K., Milne, D., and Porter, D. S., Am. Dyestuf Reptr., 35, 304 (1946). (15) Craik, J., and Davis, W., J . Soe. Dyers CoZoriste, 55, 597-606 (1939). (16) Curado, M., and Finalbargo, J., U. S. Patent 2,372,713 (April 3, 1945). (17) Dreyfus, H., Ibid., 2,056,892 (Sept. 29, 1936). (18) Erickeon, D. R., Paper Trade J., 128,243-4 (June 23, 1949). (19) Fisher, J. R., Jr., U. S. Patent 2,466,799 (April 12, 1949). (20) Goldthwait, C. q., Tmtile World,95,105,196 (1945). (21) Goldthwait, C. F., et al., U. S. Patent 2,417,869 (March 26, 1947). (22) Hagedorn, Max, et al., Ger. Patent 523,434 (1929). (23) Hubert, E., Ibid., 363,192 (1920). (24) Huey, H. I., and Russell, W. W., U. 9. Patent 2,378,360 (June 12,1945). (25) Kalle & Co. A.-G., Get. Patent 718,339 (1942). (26) Kargin, V. A,, and Ukhanova, 2. V., Tekh. ByuZZ. CUIV, 1959, No. 2,29-31; Khim. Referat. Zhur., 1940, No. 7,111. (27) Lanning, D. D., U. 8.Patent 2,467,436 (April 19, 1949). (28) Lilienfeld, L., Ibid., 1,722,927, 1,722,928 (July30, 1929). (29) Ibid., 2,266,919 (Dec. 9, 1941). (30) Liveaey, A. S., and Craik, J., Ibid., 2,406,174 (June 30, 1936). (31) Ludwig, N. C., Ibid., 2,427,683 (Sept. 23, 1947). (32) Mantell, C. L., Tmlik Reseurch J.,16,481-6 (1946). (33) Maxwell, R. W., U. 8.Patent 2,137,343 (Nov. 22, 1938). (34) Ibid., 2,162,460 (June 13, 1939). (35) Morgan, P. W., IND. ENQ.CHEM.,ANAL.ED., 18,500 (1946). (36) Mosher, H. H., Am. DyestuffReptr., 29,531,570 (1940). (37) N. V. Philips Gloelampfabrik,Brit. Patent 552,719 (1943). (38) Ott, E.. New York, Interscience Publishers, “Cellulose and Ita Derivatives,” p. 782,1943. (39) Oxley, H. F., etal., U. S. Patent 2,184,564 (Dec. 26, 1939). (40) Powers, D. H., Bock, L. H.. and Houk, M.. Ibid., 2,087,649 (July 20, 1937). (41) Reichel, F. H., and Hindry, W. F., Ibid., 2,172,109 (Sept. 6, 1939); Can. Patent 378,431. (42) Richter, G. A,, U. 8. Patents 2,045,411 (June 23, 1936); 2,054,299 (Sept. 15, 1936); 2,067,163 (Oct. 13, 1936). (43) Roehner, T. G., and Murray, G. W., Ibid., 2,441,720 (May 18, 1948). (44) Scherer, W., Ger. Patent 739,671 (1943). (45) Schorger, A. W., U. S. Patent 1,863,208 (June 14,1932). (46) Ibid., 1,914,172 (June 13, 1933); Brit. Patent 389,634 (March 14,1933). (47) Schorger, A. W.,U. S. Patents 1,941,276, 1,941,278 (Dec. 26, 1933). ENO.CHEM.,29, (48) Schorger, A. W., and Shoemaker, M. J., IND. 114 (1937). (49) Shoemaker,M. J., U. S. Patent 1,877,606 (Sept. 13, 1932). (50) I W . , 1,898,601 (Feb. 21,1933). (51) Ibid., 2,029,131 (Jan. 28,1936). (52) Shorygin, P. P., et aZ., J . Applied Chem. (U.S.S.R.), 9, 1634 (1936). (53) Slifkin, 6. C., U. S. Patent 2,474,700 (June 28,1949). (64) Smith, J. P., Ibid., 2,144,899, 2,144,900 (Jan. 24, 1939); Brit. Patents 475,534,478,538. (55) Smyth, H. F., Jr., et a?.,J. Am. Pharm. Assoc., Sci. Ed., 36,336-6 (1947). (56) Soc. Anon. Alliance EuropBenne, Belg. Patent 446,052 (1942). (57) Solov’ev, N. P., Russian Patent 65,199 (1945). (58) Thomas, E. B., and Oxley, H. F., U. 8.Patent 2,135,128 (Nov. 1, 1938). (59) Traill, D., J. SOC.Chem. Ind., 53,337T (1934). (60) Voss,J., Kalle & Co. A.-G., Ger. Patent 683,205 (1939). (61) Ibid., 725,658 (1942). (62) Wakelin, J., SilkandRayon, 12,868-74 (1938). (63) Woodhouse, J. C., U. S. Patent 2,170,845 (Aug. 29,1939). RECEIVED June 15, 1950.
