Cellulose Esters of Dibasic Organic Acids Eastman Kodak Company, Rochester, N. Y.
CARL J. MALM ~ S DCHARLES R. FORDYCE Cellulose may be esterified with dibasic acids to give three types of derivatives : (1) those in which both carboxyl groups are combined with the cellulose, (2) those with one carboxyl group combined with cellulose and the other with another organic radical, (3) those having one carboxyl combined with cellulose and the other in free acid form. Derivatives of the first class are insoluble in solvents and do not lend themselves to useful applications. Those of the second
class exhibit a wide range of solubility, a high degree of resistance to moisture, and, in general, a low melting point. The third class of compounds, being organic acids, offer unique properties of water solubility as alkali metal salts, while salts of most heavier metals are water insoluble. Cellulose acetate acid phthalates represent an easily available group of the third class of compounds and present themselves as useful materials for special purposes.
ELLULOSE esters of dibasic organic acids have been
the general procedure of Clarke and Malm ( 2 ) . Chloroacetic anhydride will not esterify cellulose to give the chlorostudied but little as compared with the more widely acetate, but will act as an impelling agent to bring about known esters of monobasic acids. Although cellulose esterification of other monocarboxylic acids. It is not effecacetate has been known since its first preparation by Schutzentive with dicarboxylic acids but, as described by Stinchfield, berger in 1865, little was published concerning esters of dibasic is effective with half esters of these acids: acids before Stinchfield’s description in 1929 (17) of the esterification of cellulose with half esters of dicarboxylic acids and the work of COOR’ C1.CHZCO. r00C.R.COOR’ Frank and Caro (6) on esters of oxalic ‘0 t00C.R.COOR’ + 6 Cl.C!Hz.COOH +3R’ t 3 acid in 1930. Published work previ/ ous to these dates ( I ) disclosed no ‘COOH Cl.CH2CO’ LOOC.R.COOR~ derivatives soluble in organic solvents; Cellulose Cellulose alkyl the investigations were largely condicarboxylate cerned with the superficial treatment of cellulose by mixtures containing dibasic A variety of cellulose alkyl esters have been prepared in this acids or anhydrides and resulted in products containing small way; their physical properties are listed in Table I. The prodamounts, if any, of combined dicarboxylic acid. ucts have a wide range of solubility in organic solvents, but Reaction of acid chlorides of dibasic acids with cellulose in for many commercial uses the melting points are too low to be the presence of pyridine yields insoluble and infusible derivaof interest. tives. This is doubtless due to cross linking of the type usually obtained with polyhydroxy compounds and polybasic acids, Similar derivatives were obtained by use of partially hydrolyzed cellulose acetate as a starting material and esterification and the products are therefore of little interest. More useful cellulose esters are those in which only one carboxyl of the of the free hydroxyl groups with half esters of dibasic acids. dibasic acid is combined with the cellulose, the other acid Cellulose “diacetate” (35 per cent acetyl) was used, which regroup being esterified with an alkyl group or remaining in the sulted in a fully esterified product containing a proportion of acid form. two acetyl groups for each alkyl dibasic radical. The physical Frank and Car0 (5) prepared oxalic acid esters by reaction properties of these products are listed in Table 11. These of acid chlorides of half esters of oxalic acid with cellulose in the presence of pyridine a t elevated temperatures. A similar type of reaction TABLEI. PROPERTIES OF CELLULOSE ALKYLESTERS OF DIBASIC ACIDS is described in the patent literature (3) in which Solubility in: acid chlorides of half esters of dibasic acids are Methyl E t h y l ButJ.1Ethylene P., Aceethyl aceaceDioxreacted with cellulose without the use of pyridine. Cellulose Ester M,. c. tone ketone tate tate dichlo- Bensene Toluene 831e Cellulose Alkyd Esters X e t h y l succinate 195 + + + + Ethyl succinate 128 + + + + + - ++ I n the present work cellulose alkyl esters were ~ ~ $~ $ $\ $ ~$ ~ $ $ ~ prepared by a method described by Stinchfield hZethyl phthalate + + + + - +$ (17) and based upon the use of chloroacetic anB:b;;~$,t$;~~ $ $ $ $ $ $ ; hydride to bring about the esterification of the Butyl phthalate 155 + + + + + + + + free carboxyl of the dibasic acid half ester, following
C
[
-
7
2
;;!
405
~
INDUSTRIAL AND ENGIXEERING CHEMISTRY
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VOL. 32, NO. 3
TABLE11. PROPERTIES O F CELLULOSE MIXED ESTERSCONTAISINg ALKYLDICARBOXYL GROUPS Solubility in. Ethy!ene dichloride Benzene
7
Ester of Cellulose Acetate with: Methyl succinate Benzyl succinate Methyl phthalate E t h y l phthalate Butyl phthalate
M. p., C. 195
175 175
...
168
Methyl ethyl ketone
Acetone
+ +++ +
Ethyl acetate
++ + ++
Butyl acetate
+++ ++
+
+-
-
++
++
+
-
Toluene: alcohol,
-
-
+:
+-
+
Benzene: alcohol,
2:l
Toluene
2:l
+i-
Dioxane
++ i++
TABLE111. PROPERTIES OF CELLULOSE ACID DICARBOXYLATES Methyl 3:. P., ethyl Estex C. Acetone ketone Cellulose diacetate monosuccinate 172 -k Cellulose diacetate monophthalate 178 4Cellulose diethyl ether monophthalate 195 Cellulose diphthalate 168
+
% 10
15 20
35
-TABLEIv. PROPERTIES M. P
OC.”
243 211 201 178
Acetone
+ +++
Methyl ethul ketone
Ethyl acetate
++ ++
+ +++
OF
Butyl acetate
--
++
+ +
+-
Phthalyl Content,
Ethyl acetate
Solubility in: , Ethylene Benzene: Toluene: dichloalcohol, alcohol, ride Benzene Toluene 2:l 2:l
---
--
-
-
-
--
-
+ +-
-
+ +-
Dilute
Dilute
++ ++
++
NHdOH
NaOH
++
CELLULOSE ACETATEPHTHALATE O F VARYING PHTHALYL CONTEXT Solubility in:
Butyl acetate
Ethylene dichloride
Benzene
-
-
-
--
+-
--
Toluene
--
-
Benzene: alcohol,
Toluene: alcohol,
-+
2:l
++
2:l
--
Dioxane
Dilute NHaOH
-
+
i-
++
++ +
-
Dilute NaOH
++ +
soluble in dilute alkaline solutions. They may be isolated as salts which are readily water soluble (14). The cellulose acid dicarboxylates as a class are very limited in solubility in organic solvents, and mixed esters containing both acetyl and dicarboxylic acid groups are of greater interest. I n the acid Cellulose Acid Dicarboxylates form these esters, like cellulose acetate, are soluble in organic solvents and give solutions which can be used to form films or Special consideration has been given to cellulose dibasic coatings with or without the use of plasticizers. I n general, acid esters in which one carboxyl group remains unesterified. the mixed esters or ether esters containing dibasic acid groups These derivatives are conveniently prepared by the method have a wider range of solubility in organic solvents than of Malm and Waring (IS) and of Schulze (16) in which cellucellulose acetate and are somewhat lower in melting point lose or its derivatives are reacted with dibasic acid anhydrides (Table 111). in the presence of pyridine. Diglycolic anhydride was shown Representative of these cellulose derivatives is cellulose to react as a normal dibasic anhydride in this process ( 9 ) , acetate phthalate. This ester is easily accessible because of At more elevated temperatures the reaction may be made t o the availability of phthalic anhydride, and by introduction proceed without pyridine if a cellulose ester or ether soluble of increasing amounts of combined phthalyl into cellulose in the reaction solvent is employed as a starting material (6). acetate, a series of varying physical properties is obtained The reaction follows the equations: from which we may choose the composition particularly 0 H adapted to any given use. Variations in solubility of fully OOC.R.COOKCsH, // esterified cellulose acetate phthalate with increasing phthalyl C content are shown in Table 1V. These data apply to prodH + 3R’ ‘ 0 C5HsN ucts of moderate viscosity; somewhat increased solubilities are obtained if low-viscosity materials are employed. LOOC.R.COONCEH5 H Only minor changes in solubility are obtained up to ap. . proximately 15 per cent phthalyl content, a t which point the Cellulose Pyridine Cellulose products become soluble in dilute sodium hydroxide and in pyridine dicarboxylate organic solvents such as mixtures of benzene and alcohol. At slightly higher phthalyl content the ammonium salts become The pyridine salt obtained in the reaction may be acidified soluble in water, and still wider ranges of solubility are obto liberate the free acid: tained in organic solvents. Solutions of cellulose acetate phthalate in organic solvents H rOOC.R.COONCsH5 r00C.R.COOH may be prepared in varying concentrations which increase in viscosity as the concentration increases; Figure 1, H for example, shows the viscosity-concentration ;elation OOC.R.COONC5H5 + 3HC100C.R.COOH 3C5H5N.HC1 of acetone solutions. The ammonium salts are easily prepared in water solution by adding dilute ammonia [OOC.R.COOPC& H LC.R.CooH to a water suspension of the free acid, or in the dry state Cellulose hydrogen Cellulose pyridine by treating the dried free acid with dry ammonia gas. dicarboxylate dicarboxylate Organic bases such as pyridine or triethanolamine (4) also produce water-soluble salts. A similar reaction was shown to take place in the presence of It is often desirable to prepare neutral aqueous solutions benzyl pyridinium halides (16) or pyridine hydrochloride (7). of the sodium salts; in this case sodium bicarbonate is psrThe resulting compounds are insoluble in water but are products as a class are very soluble, have high qualities of moisture resistance, and may be of advantage for special purposes, but are not expected to obtain widespread use because of their manufacturing cost and tendency toward brittleness.
c
I
+
-
I
+
MARCH, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
ticularly useful (11) since it readily dissolves the cellulose ester but is not a strong enough base to de-esterify the ester groups. The resulting aqueous solutions may be prepared in high concentrations which are viscous, can be used for coating or impregnating fabrics or surfaces ( l a ) , and can either be allowed to remain as the water-soluble salt or be converted b y acid treatment to the water-insoluble acid. A viscosityconcentration curve of the aqueous sodium salt solution is given in Figure 2. Films of the water-soluble salts, formed by evaporation of aqueous solutions, are transparent, nonhygroscopic, and flexible except at low humidities, where brittleness results unless prevented by addition of a suitable water-soluble plasticizer.
SO7
metals which form complex ammonium ions may be carried into water solution by addition of ammonia. Characteristics of a number of these salts are shown in Table VI. TABLE VI. METALLIC S.4LTS O F C E L L U L O S E ACETATE I'HTHALATE ---Soly. Metal C o per a cium Cobalt Zinc Barium Iron
c
P.
Color Blue White Purple \?hire Jlhite Brown
in.-Dilute K a t e r h-HaOH -
++ +-
+
+++ --
-Sob. Metal
Color
Silver Cadmium Nickel Chromium Lead
White White Green Green White
Water
----
in:Dilute SHIOH
++-
The physical properties of the cellulose dibasic acid esters TABLEV. SOLUBILITY OF CELLULOSE ACETATEPHTHALATE OF are not such that they should be expected to attain the com35 PER CENT PHTHALYL CONTEXT IN SOLUTIONS OF VARYIXG mercial prominence of the more commonly known cellulose ACIDITY p H of Soluacetate or nitrate, but rather they should be expected to be Composition of Buffer S o h . bility useful for purposes where unique solubilities or other physical Citric acid-disodium hydrogen phosphate 2.75 properties present themselves as especially desirable. Potassium dihydrogen phosphate-disodium hydrogen phosphate 5.82 Cellulose acetate phthalate is useful for application of Potassium dihydrogen phosphate-disodium hydrogen phosphate 6.97 + water-insoluble surface coatings or sizings which are later to Citric acid-disodium hydrogen phosphate 7.50 + be removed by treatment with dilute alkaline solution. Potassium dihydrogen phosphate-disodium hydrogen phosphate 6.34 4Aqueous solutions of the water-soluble salts are useful for binding agents in water dispersions or for purposes where film-forming properties of aqueous solutions are required. I n its acidic form cellulose acetate phthalate of 20-40 per cent phthalyl content offers itself as a film-forming material; i t Preparation of Cellulose Derivatives is quite resistant to neutral water but readily soluble in alkaline CELLULOSE ALKYLDICARBOXYLATES. A mixture of 100 media, or even in solutions as low in p H as 6.0-6.5 if alkali grams of cotton linters, 500 grams of chloroacetic anhydride, 2.0 metal ions are available by which salt formation is possible. grams of magnesium perchlorate catalyst, and slightly over the The effect of p H on solubility is shown in Table V. Cellulose calculated quantity of the half dibasic acid ester corresponding to the cellulose ester to be prepared, was heated with continued acetate phthalate is compatible in all proportions with cellustirring at 70" C. until a uniform solution of the cellulose derivalose acetate and, when added in small quantities to t h a t mative was obtained. In most cases from 2 t o 5 hours were required. terial, greatly increases the affinity of the acetate for basic The solution was then precipitated into a large volume of methyl dyes (8). alcohol t o isolate the product, which was extracted with methyl alcohol until free from uncombined acid. CELLULOSE ACETATEALKYL DICARBOXYLATES. A mixture of 100 grams of cellulose acetate of 35 per cent acetyl content, 200 grams of chloroacetic acid, and 100 41grams of chloroacetic anhydride was stirred at 60" C. until a uniform solution resulted. There were then added 100 grams of the half dibasic acid ester corresponding to theproduct to be prepared and 0.10 gram of magnesium perchlorate, and the reaction mixture was heated with stirring at 60" C. for 2 hours. The resulting cellulose derivative was precipitated by pouring the reaction solution into a large volume of methanol, and the product was extracted with methanol until free from uncombined acid. CELLULOSE PHTHALATE. A mixture of 100 grams of low-viscosity cotton linters, 500 grams of pyridine, and 400 grams of phthalic anhydride was heated with continuous stirring at 100" C. for 12 hours, during which time the cellulose dissolved to give a uniform solution. An equal volume of acetone was added to reduce the viscosity, and the cellulose acid phthalate was then isolated by pouring the mixture into a large volume of water to which had been added 500 cc. of concentrated hydrochloric acid. The product was washed with warm distilled water until free from uncombined phthalic acid. The isolated product was found to contain 66 per cent CONC€N TRA T/ON (ET? GENT BY WT) combined phthalyl. CELLULOSE ACETATEACID DICARBOXTLATES. To a FIGUF~E 1. VISCOSITY OF ACETONE FIGURE2. VISCOSITY OF solution of 100 grams of cellulose acetate of the desired SOLUTIONE? OF CELLULOSE ACETATE AQUEOUS SOLUTIONSOF 400 grams of pyridine were added 200 acetyl content in PHTHALATE CELLULOSEACETATESograms of the dibasic acid anhydride corresponding t o DIUM PHTHALATE the cellulose derivative to be prepared. The resulting solution was heated a t 100' C. for 12 hours, after which Insoluble metal salts call also be prepared from these time the solution was precipitated into a large volume of water to which been added 400 cc of concentrated hydrochloric cellulose derivatives by use of heavier metals (10). This is acid. Thehad product was then lTith distilled wateruntil free from uncombined acids. easily accomplished by addition of water-soluble salts of the A similar procedure was used to prepare cellulose diethvl ether h e a w metals to aaueous solutions of the sodium salt of the celluioseester. ~i~ heavy metal salt of the ce~lu~ose ester 'monophthalate; ethylcellulose of 22 -per cent ethoxyl content was the starting material. is precipitated and may be isolated. These salts are colorless cELLULosE A~~~~~~ soDrUM pHTHALATE.900 cc. of disor colored, depending upon the metal employed. Salts of tilled water were suspended 100 grams of cellulose acetate acid
408
INDUSTRIAL .4ND ENGINEERING CHEMISTRY
phthalate of 33 per cent phthalyl content. Very small portions of sodium bicarbonate were added with continuous stirring from a weighed quantity of 20 grams. After somewhat over half of the bicarbonate had been added, the cellulose ester was largely in solution. Further additions of sodium bicarbonate were made at intervals, and the solution was tested after each addition with bromothymol blue indicator. A colorless aqueous solution of the cellulose acetate sodium phthalate 7 m s finally obtained; it was adjusted to a pH of 7.0-7.5, where it was kept for determination of viscosity data and preparation of the metallic salts listed in Table VI.
Literature Cited (1) Briggs, J. SOC.Chem. Ind., 31, 521 (1912); Levy, J. IXD. EXG. CHEU., 12, 743 (1920) ; Swiss Patent 142,173 (Nov. 1, 1930). (2) Clarke and Malm, U. S.Patent 1,880,808 (Oct. 4 , 1932) ; British Patent 313,408 (Aug. 27, 1929). (3) Deutsche Celluloid-Fabrik, U. S. Patent 2,003,408 (June 4 , 1935); British Patent 355,172 (Aug. 20, 1931); French Patent 709,958 (May 26, 1931).
VOL. 3 2 , NO. 3
(4) Fordyce, G. S. Patent 1,969,741 (Aug. 14, 1934). (5) Frank and Caro, Ber., 63, 1532 (1930) ; German Patent 499,053 (May 30, 1930). (6) Genung, U. S.Patent 2,126,460 (;1ug. 9, 1938). (7) Haskins and Schulze, U. S. Patent 1,967,405 (July 24, 1934). (8) Malm and Fordyce, U. S.Patent 2,011,345 (Aug. 13, 1935). (9) Ibid., 2,024,238 (Dee. 17, 1935); British Patent 410,125 (May 10, 1934). (10) Malm and Fordyce, U. S. Patent 2,040,093 (May 12, 1936); British Patent 410,126 (May 10, 1934). (11) Malm and Fordyce, U. S. Patent 2,082,804 (June 8 , 1937). (12) Malm and Stone, Ibid., 2,108,458 (Feb. 15, 1938). (13) Malm and Waring, Ibid., 2,093,462 and 2,093,464 (Sept. 21, 1937); British Patent 410,118 (May 10, 1934). (14) Malm and Waring, U. 5 . Patent 2,093,463 (Sept. 21, 1937). (15) Schulze, Ibid., 2,069,974 (Feb. 9, 1937). (16) SociBti! industrie chimique Blle, British Patent 359,249 (Oct. 22, 1931); French Patent 723,661 (Jan. 18. 1932). (17) Stinchfield, U. 5 . Patent 1,704,306 (March 5, 1929). PRESENTED before the Division of Cellulose Chemistry at the 97th Meeting of the American Chemical Society, Baltimore, hId.
Sulfonation and Nitration Reaction Promoted b-y Boron Fluoride' J
R. J. THOMAS, W. F. ANZILOTTI, AND G. F. HENNION University of Notre Dame, Notre Dame, Ind.
B
ORON fluoride is a remarkable catalyst (or promoter)
for many organic reactions, particularly those of addition or where water is a product of the reaction. I n the latter cases boron fluoride may both accelerate the reaction and drive it to completion by combining with the water produced. Combination with water may be by coordination or by hydrolysis. The complex BF3.2H20 is a heavy, waterwhite, distillable liquid ('?'). With large excesses of water, orthoboric acid, hydrofluoric acid, and fluoboric acid may be obtained. Tendency to form coordination complexes is particularly characteristic of boron fluoride. It combines directly with many oxygen- and nitrogen-containing compounds to form such substances as NH,. BF,, CH3CN.BF3, (CH8COOH)2.BF,, and (CH3CO)20.BF3. The remarkable properties of boron fluoride have merited considerable study by industrial chemists. Since about 1927 several score of patents have been issued covering its many catalytic uses, as in polymerization of olefinic hydrocarbons and in organic condensation reactions. The literature in these fields is too extensive to permit proper review in this paper. The highly important unit processes of sulfonation and nitration are frequently slow and also proceed incompletely unless the water formed is removed (4). It was felt, therefore, that these processes might be promoted to a great extent by using boron fluoride along with the required sulfuric or nitric acid. These expectations have been fulfilled in many. 1 This is the twenty-first paper in a series on organic reactions with boron fluoride: the previous paper appeared in J . Am. Chem. Sac., 60, 654 (1938).
Boron fluoride is shown to be a remarkably effective promoter and dehydrating agent for many sulfonation and nitration processes. In a number of such reactions the boron fluoride may be recovered by distillation as the dihydrate. This work is being continued.
instances. I n fact, it has been found possible to sulfonate and/or nitrate many organic compounds quickly and almost completely with stoichiometric amounts of sulfuric or nitric acid when sufficient boron fluoride was added. This is significant particularly since boron fluoride has recently been made available commercially (by the Harshaw Chemical Company) and because in many of the reactions i t may be recovered for re-use. The amounts of boron fluoride required indicate that the reactions proceed as follows : R-H R-H
+ H2S04 + BFa +R-SO3H + BFs.Hz0
+
+ BF3 +R-NOQ + BF3.H20
"03
If, at the completion of the reactions, sufficient water is added to convert the B F 3 . H 2 0to BF3.2H20,the latter may be distilled out under vacuum as a heavy, water-white liquid. Boron fluoride may be recovered from the dihydrate in various ways. I n a patented method (6) calcium fluoride is added t o form calcium fluoborate which, upon heating, releases gaseous boron fluoride :
+
2BF3.2H20 CaFz +Ca(BFI)z f 4 Ca(BF4)z +2BFa CaF2
+
H ~ 0
