Pvridinium Salts of Cellulose Acetate-Chloroacetate C. J. MALM, J. W. MENCH, R. F. WILLIAMS, JR., AND G. D. HIATT Eastman Kodak Company, Rochester, N . Y .
W
T h e preparation of cellulose acetate-chloroacetates by a 3. Heterogeneous reacATER-SOLUBLE cellulose derivavariety of procedures is described, and properties and ~ ) i~~~~~ tives have been prepared methods of analysis are given. The reaction of these for the chloroacetic anhvin which varying amounts products with tertiary amines, such as pyridine, goes subdride but which will nbt of quaternary ammonium stantially to completion, yielding quaternary ammonium dissolve either the cellulose salts. A large number of these are water-soluble but halide groups serve as the ~~,$$~dorP~~&~"tfl h y d r o p h y l i c centers. hydrolyze readily in aqueous solution to regenerate procedure eliminates the These are obtained by recellulose acetate and liberate N-carboxymethylpyridinium necessity of precipitating the mixed ester, since the chloride. The pyridinium salt of a cellulose acetate-pacting a cellulose derivative material may be filtered out chloropropionateis also described. This is more stable to containing an active halogen of t h e reaction mixture. atom, such as a cellulose hydrolysis than the a-betaine compounds. Frequently, nonuniform products are obtained, so acetate-chloroacetate, with it was not used extensively. tertiary amines such as pyriB. Esterification of partially substituted cellulose acetates dine. Since completion of this work this same principle has been applied to the water-solubilization of sulfanilamide derivatives with chloroacetic acid : (16). When chloroacetic acid rather than anh dride is used, chloroOther well known, water-soluble derivatives of cellulose owe acetyl is introduced both by direct esteriLation and by partial their solubility characteristics to such groupings as hydroxyl, replacement of acetyl. The reaction rate is slower than when anhydride is used, and the amount of degradation is greater. sulfate, or carboxylate salts. Examples of the fist include the partially substituted cellulose ethers ( 1 )and esters (6); the second C. Hydrolysis of cellulose acetates in aqueous chloroacetic class is represented by cellulose sulfate and its salts (3, 8, 9); acid (24): and the third by salts of derivatives containing free carboxylic In this method, a portion of the acetyl is removed by hydrolysis acid groups, such as the acid phthalates and succinates (IQ), and is replaced in part by chloroacetyl. Since the hydrolysis the carboxymethyl ethers ( I " ) , or celluronic acid (86), obtained rate is greater than that of re-esterification, the resulting product from the nitrogen dioxide oxidation of cellulose. contains more unesterified hydroxyls than the starting material. A series of patents (11-14) describes the reaction of cellulose D. HydroIysis of cellulose acetate-chloroacetates: chloroacetate and acetate-chloroacetates with a wide variety of tertiary amines. These, however, do not characterize either the This procedure enables one to decrease the degree of substitution of the mixed esters prepared by methods A and B. starting materials or final products by analytical data, merely claiming a n increased affinity for acid dyes. More recently, METHODA-1. Four hundred grams of a cellulose acetate Olpin et al. ( 2 2 ) described the preparation of t\ cellulose acetatecontaining 31.1% of acetyl (1.68 groups per anhydroglucose unit) chloroacetate, containing 0.2 to 0.3 chloroacetyl and 2.1 to 2.3 were dissolved in a mixture of 1500 ml. of 1,4-dioxane and 800 acetyl groups per anhydroglucose unit, and its reaction with grams of chloroacetic anhydride, and the solution was heated pyridine t o yield an acetone-soluble compound having increased on a steam bath for 22 hours. After cooling and diluting with affinity for acid dyes. The previous work, thus, appears to have acetone, the reaction mixture was precipitated into distilled water. centered about the preparation of materials suitable for textile After thorough washing, the product was oven-dried at 70" C. utilization without study of the range of compositions of the METHODA-2. Fifty grams of a cellulose acetate containing mixed ester yielding water-soluble products. 31.1% of acetyl were dissolved in 100 grams of melted chloro-
o:zi
CELLULOSE ACETATE-CHLOROACETATES
Preparation and Properties.
Although a number of patents
( 4 , 5 , 17, 2.3) describe the preparation of acetate-chloroacetates, little or no data are available regarding the compositions of the resulting products. Since this work was completed, Izard a.nd Morgan (18) have described several methods of preparation of the mixed esters by some of the procedures used in this work. The mixed esters described in this paper cover a wide range of c6mposition and were prepared by means of four general procedures: A. Esterification of partially substituted cellulose acetates with chloroacetic anhydride: 1. Homogeneous reaction conditions, em loying a solvent for the anhydride; this method introduces chroroacetyl rapidly, the degree of esterification being controlled by the reaction time and temperature; only moderate degradation of the cellulose occurs. 2. Homogeneous reaction conditions, employing no solvent other than the chloroacetic anhydride; this method is similar in action t o the first, but causes somewhat greater degradation.
acetic anhydride, and the solution was heated on a steam bath for 24 hours. Isolation was accomplished as in A-1. METHODA-3. Thirty-five grams of a cellulose acetate containing 31.1% of acetyl were heated on a steam bath for 4 hours in a mixture of 70 grams of chloroacetic anhydride in 350 ml. of xylene. The product was filtered off, washed free of excess anhydride with xylene, and then with methanol. METHODB. Fifty grams of a cellulose acetate containing 31.1y0 of acetyl were dissolved in 450 grams of melted chloroacetic acid, and the solution was heated on a steam bath for 28 hours. Isolation was as described in A-1. METHODC. One hundred grams of cellulose acetate containing 40.5y0 of acetyl (2.53 groups per anhydroglucose unit) were dissolved in 1000 grams of 75% aqueous chloroacetic acid. The hydrolysis was catalyzed with 1.2 g r a m of concentrated sulfuric acid and was allowed to oroceed a t 40" C. for 8 days. Methanol was used as a precipitant for the product. D* One hundred grams Of acetatechloroacetate containing 30.2% of chloroacetyl and 22.2% of 1547
1
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INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I. PREPARATIOS OF CELLULOSE ACETATE-CHLOROACETATE
Method A-1
A-2 A-3 B C
D
Starting hlaterial ___ Acetyl Chloroacetyl Groups/ Groups/ anhydroanhydroglucose glucose % unit % unit 31.1 1.68 .. .. 31.1 1.68 .. .. 33 11 .. 11 1 . 6 8 . . .. .. 1.68 .. 40.5 2.53 22.2 1.70 30:2 1130
---
Product Acetyl Chloroacetyl Groups/ Groups/ anhydroanhydroglucose glucose yo unit % unit 28.0 1.93 18.3 0.70 27.8 2.0 28.8 1.0 2 7.3 1 0.61 21.4 1 .. 8 40 4 21 36 .. 65 0.88 11.9 0.75 10.7 0.30 8.9 0.38 24.3 0.73
acetyl (substantially a triester containing 1.3 chloroacetj I and 1.7 acetyl groups per anhydroglucosc unit) byere dissolved in a mixture of 810 grams of chloroacetic acid and 145 grams of water. The catalyst consisted of 1 gram of concentrated sulfuric acid and hydrolysis proceeded for 4 days a t 30" C. Isolation of the product was accomplished as in C. Analysis. The sum of acetyl and chloroacetyl was determined by the saponification in solution procedure ($1). The chloroacetyl group was removed intact by this method, as indicated by the absence of chloride ion in the saponification solution, whereas the modified Eberstadt method ( I O ) split off a small amounh of chlorine. Separate analysis of chlorine gave the amount of chloroacetyl. A method was developed for the complete removal of the chlorine by saponification; this gave results comparable in precision and accuracy t o standard methods: Samples of cellulose acetatechloroacetate (0.5- t o 1-gram) were suspended in 50 ml. of 1 t o 2 sodium hydroxide in unstoppered Erlenmeyer flasks, and the mixtures were allowed to evaporate to dryness on a steam plate overnight. (When the esters were not readily wetted by the solution, a small amount of methanol was added.) Fifty milliliters of water were added to the residue, and the mixture mas acidified with acetic acid. The chloride ion was titrated b j the Mohr method, or potentiometrically when excessive color interfered with visual end points. The presence of the regenerated cellulose did not interfere. The numbers of acetyl and chloroacetyl groups per anhgdroglucose unit are readily calculated from the percentage values by the use of equations or nomographs analogous to those described in the literature ( 7 ) . Table I shows the composition of the starting materials and products obtained by each of these methods. Most of the products used in this work were prepared by method A-1 or by A-1 followed by method D. Some of the materials were found to contain more acetyl groups per anhydroglucose unit than the starting materials. This was traced to the presence of small amounts of acetic or acetic-chloroacetic anhydrides in the chloroacetic anhydride used. The latter was prepared by the action of acetic anhydride on chloroacetic acid and purified by distillation a t reduced pressure (boiling point, 123" a t 20 mm.) ( 2 ) . This material contained 1 to 37, acetyl, which is sufficient t o cause the increase observed in the cellulose derivative since acetyl is introduced preferentially in the presence of chloroaeetyl. This introduction of acetyl along i+ith the desired chloroacetyl did not interfere with the preparation of a variety of cellulose acetate-chloroacetates, since the acetyl content of the starting material could be varied readily. Figure 1 shows the composition of typical mixed esters prepared, the designations within the circles indicating the preparatory method employed. The cellulose acetate-chloroacetates are quite stable t o heat, developing negligible color on heating at 180" C. for 8 hours. They have moisture resistance comparable to the cellulose acetate-butyrates of similar composition (20). Their solubility and compatibility ranges are greater than those of cellulose acetates, but are less than those of the cellulose acetate-butyrates
Vol. 42, No. 8
(20). The chlorine of the chloroacetyl group is resistant to boiling water, is only slowly removed by acictic hydrolysis, but is removed by saponification. This has been the basis of the chlorine analysis described above. PYRIDINIUM SALTS
The halogen atom of the chloroacetyl group is sufficiently reactive to form salts with amines The reaction that occurs may such as pyridine. __ be shown as follows:
Cell-OCOCH2Cl
O 'H
+ C&N
---f
(Cell-OCOCH~KC;Il~)+C1-
O 'H
One of the most important conditions for the formation of the quaternary ammonium salt is the maintenance of an anhydrous state; otherwise the halogen atoms or entire acyl groups may be removed by hydrolysis. The reaction is carried out by dissolving the ester in anhydrous pyridine, or in pyridine plus another solvent, or by suspending the ester in pyridine and a nonsolven L such as xylene. The latter method has becu the preferred modc of operation in most of this n ork. Twenty grams of a cellulose acetate-chloroacetate containing 1.89 acetyl and 0.81 chloroacetyl groups per anhydroglucose unit were suspended in 200 ml. of xylene containing the desired amount of pyridine, and the mixture was heated on a steam bath. The product was isolated by filtration and was washed frrc of xylene and excess pyridine with acetone. The quaternization occurs a t room temperatures but reaction times are excessive. Ordinarily, therefore, steam h t h temperatures were employed. Table I1 clearly shows the effects of pyridine conccntratioxi and reaction time on the composition of the products. All these products were readily soluble in cold water with the exception of the first, which dissolved in hot water and set to a gel on cooling. h'onaqueous solvents for these materials include methanol, methanol-acetone mixtures, methylene and ethylene dichloride-methanol mixtures, and methyl Cellosolvc. Ethanol,
Figure 1.
Compositions of Cellulose AcetateChloroacetate
Letters i n circles indicate method of preparation as dcscribed in text; E = far-hydroIyaed cellulobc acetate (containing no chloroaeetyl) prepared by hydrolysis i n aqueous AcOH; shaded area indioutcs watersolubility of pyridinium salts
August 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
OF CELLULOSE ACETATETABLE 11. QUATERXIZATION CHLOROACETATE WITH PYRIDINE IN XYLENE
Quaternization, % N: C1 From From Hours %N % C1 Ratio %N % C1 8.6 0.47 52 53 2 1.6 0.74 78 8.2 78 2.4 8 8.1 84 0.81 2.6 84 24 72 8.3 2.6 0.81 84 2 6 94 0.90 78 8.2 8 2.9 7.9 6 97 0.96 96 24 3.0 a Molar ratio of pyridine to chlorine available in sample. b Microanalyses accuracy within 1 0 . 1 % . N , 3.09; Cl, 7.83. c Calculated for’complete quaternization:
~~l~~
Heating,
Amount of Pyridinea 1.5 1.5 1.5 6
b’
thr propanols, Cellosolve, diacetone alcohol, and ethylene formal all become good solvents when mixed with varying amounts of methanol or water. Acetone and hydrocarbons are nonsolvents for the quaternized esters. Aqueous solutions of the pyridinium salts gel irreversibly on standing, the gelling time being dependent on the composition of the cellulose ester. This phenomenon will be dealt with in a later section of this paper. The aqueous dispersions tolerate little organic or inorganic salts, additions resulting in precipitation of the cellulose derivative. Pyridinium salts were prepared from the mixed esters shown in Figure 1, using xylene as a diluen t and using sufficient pyridine t o ensure reasonably complete quaternization, the amount being dependent on the chlorine content of the chloroacetate. In all cases, pyridination was complete to the extent of 90% or greater as determined by molar nitrogen t o chlorine ratios and by comparison of the calculated and theoretical nitrogen and chlorine contents. The compositions of the acetate-chloroacetates yielding water-soluble pyridinium salts are shown as the shaded area in Figure 1. One preparation was made of the pyridinium salt of cellulose acetate-8-chloropropionate t o test the properties of a pyridiniuin salt in a position other than alpha on the alkyl radical and t o test the possibility of preparing the salt and the mixed ester simultaneously. This was done by reacting a partially substituted cellulose acetate with p-chloropropionyl chloride in the presence of excess pyridine. Fifty grams of a cellulose acetate containing 31.1% of acetyl (1.68 acetyl per anhydroglucose unit) were dissolved in 144 ml. of 1,4-dioxane containing 62.5 grams of pyridine, and 50 grams of P-chloropropionyl chloride in 7 5 ml. of dioxane were added slowly. The temperature rose rapidly to about 95” C. and the reaction mixture soon set to a tcugh gel. This was immediately dissolved by the addition of water and the derivative was isolated by precipitation into acetone. Analysis: Calculated for 1.68 acetyl and 1.32 (CsHbNCH,CH,CO-) +C1- groups/anhydroglucose unit: N, 4.06%; C1, 10.28%. Found: N , 4.2%; C1, 9.870. The product was substantially completely esterified and was readily soluble in water and in methanol. The result indicates the feasibility of the reaction, although a few trials with chloroacetyl chloride yielded unsatisfactory products. INSTABILITY OF THE PYRIDINIUM SALTS
The irreversible gelling of aqueous dispersions of the pyridinium salts has already been mentioned. Measurement of the p H of these dispersions showed them to be of the order of 2.5. Therefore, hydrolysis of the esters t o split off either acetyl or the A‘-carboxymethylpyridinium chloride groups was suspected. Since this p H would require acetic acid concentratiohs of 0.5 t o 1 molar, the presence of a much stronger acid (N-carboxymethylpyridinium chloride) was indicated. A few attempts were made t o stabilize the dispersions by the addition of various quantities of aqueous ammonia or of pyridine to bring the p H t o a more nearly neutral point. These attempts
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failed; the porkions t o which alkaline reagents had been added gelled more rapidly than the unadjusted solutions. Other buffering agents were not tested because of the low tolerance of the dispersions t o salts. The degree of hydrolysis occurring was determined in a semiquantitative manner by preparing 5% aqueous dispersions of the cellulose derivatives, allowing them t o stand, and then isolating the derivative for reanalysis. The results obtained on the pyridinium salt of a cellulose acetate-chloroacetate are shown in Table 111, sample A. I n this case, gelling of the dispersion occurred in about 12 hours after preparation of the solution. The loss in the nitrogen and chlorine contents is apparent, and since their molar ratio remains essentially constant, loss of the N-carboxymethylpyridinium chloride group is indicated. The small change in the total acy1 content shows only slight loss of the acetyl groups. The main reaction occurring on hydrolysis thus appears to be: /OCOCH8 (Cel\-OCOCHaNC6Hs) +C1-
+ H20--+
\
OH OCOCHa
/
Cell-OH
+ (CSH5NCH2COOH)+C1-
O ‘H As a comparison, the hydrolysis experiment was repeated with the cellulose acetate-pchloropropionate derivative, the results being shown in Table I11 as sample B. Again, the constancy of the nitrogen to chlorine ratio shows the loss of the quaternized acyl group, although in this p-chloroester the loss was less rapid than in the a-(chloroacetic) ester. No gelling of the solution occurred during the 3.5-month period of the hydrolysis.
TABLE 111. EFFECTO F HYDROLYSIS ON P Y R I D I N I U h l
SALTS O F
CELLULOSEACETATE-CHLOROACYLATES IN AQUEOUS SOLUTION A
Sample Type
From AcetsteChloroacetate 240
B From Acetate8-Chloropropionate 2500
Hydrolysis time, hours Nitrogen, yo Before hydrolysis 2.2 After hydrolysis 1.5 Chlorine, % Before hydrolysis 5.7 After hydrolysis 3.7 Molar N : C1 ratio Before hydrolysis 0.98 After hvdrolvsis 1.03 Apparent-acet$l5, % Before hydrolysis 31.1 After hydrolyais 29.0 a Ap arent acetyl is sum of acetyl and other acyl groupings acetyl $&valent weight 43).
4.2 2.9 9.8 7.2 1.09 1.02
calculated as
LITERATURE CITED
Bass, S.L., Barry, A. J., and Young, A. E., in E. Ott, “Cellulose and Cellulose Derivatives,” PP. 787-8, New York, Interscience Publishers, Inc., 1943. Clarke, H. T., and Malm, C. J., U. S.Patent 1,648,540 (Nov. 8 , 1927). Cross, C. F . , Bevin, E . (1905).
J., and Briggs, J. F., Ber., 38,1859, 3531
Dreyfus, H., British Patent 320,842 (Oct. 18, 1929). Drya, Swiss Patent 145,979 (1930). Fordyce, C. R., U. S. Patent 2,129,052 (Sept. 6 , 1938). Fordyce, C. R., Genung, L. B., and Pile, M. A., IND.ENC. CHEM.,ANAL.E D . , 18,547 (1946). Frank, G., Belgian Patent 448,249 (June 1943). Tbid., 461,916 (Jan. 31, 1946). Genung, L. B., and Mallatt, R. C., IND. ENG. CHEM.,ANAL. E D . , 13,369 (1941).
Gesell. fiir chem. Ind., Basel, French Patent 717,524. Gesell. fur ahem. Ind., Basel, German Patent 550,259 (May 5, 1932).
INDUSTRIAL AND ENGINEERING CHEMISTRY
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(13) Gesell. fur chem. Ind., Basel, Swiss Patent 148,491 (Oct. 10, 1931). (14) Ibid., 150,789 and 150,790 (Feb. 2, 1932). (15) Goldberg, M. W., and Heineman, S. D., U. S.Patent 2,430,051 (Nov. 4,1947). (16) Hollabaugh, C. B., Burt, L. H., and Walsh, A. P., IXD.ENG. CHEK, 37, 943 (1945). (17) I. G. Farbenindustrie, A,-G., British Patent 306,132 (1932). (18) Izard, E. F., and Morgan, P. W., IND.ENG. CHEhf., 41, 617 (1949). (19) Malm, C. J., and Fordyce, C. R., Ibid., 32,405 (1940). (20) Malm, C. J., Fordyce, C. R., and Tanner, H. A., I b i d . , 34,430 (1942).
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(21) Malm, C. J., Genung, L. B., TTilliams, R. F., Jr., and Pile, hl. A, IND.ENG.CHEW, A N ~ LED., . 16, 501 (1944). (22) Olpin, H. C., Gibson, S. A., and Jones, J. E., U. S.Patent 2,348,305 (May 9,1944). (23j Soc. des usines chimiques Rhone-Ponlenc, French Patent 672,220 (1929). (24) Staud, C. J., and Febber, C. S., U. S.Patent 1,900,871(Mar. 7, 1933). (25) Yackel, E. C., and Kenyon, W. O., J . Ant. Chem. SOC.,64, 121 (1942). RECEIVED January 16, 1950. Presented before the Division of Cellulose Chemistry a t the 116th 3Ieeting of the AVERICAS CHEWCALSOCIETY, Atlantic City, N. J.
Desulfurization of Coal during Carbonization U
HIGH-SULFUR INDIAN COAL J. I
