Aliphatic Acid Esters of Cellulose PREPARATION BY ACID CHLORIDE-PYRIDINE PROCEDURE C. J. MALM, J. W. MENCH, D. L. KENDALL', AND G. D. HIATT Eastman Kodak Co.,Rochester, N . Y . T h e literature describes attempts to prepare the higher homologs of cellulose acetate in which the esters are fully esterified and have the same degree of polymerization. None of these earlier references, however, shows analytical data to indicate that this was accomplished. I n this work, a series of cellulose esters from acetate through palmitate was prepared by the acid chloridepyridine procedure to meet the above requirements. This was accomplished by careful selection of conditions, including reagent ratios, tertiary amine, reaction diluent, and cellulose used. Acyl and hydroxyl analyses showed good agreement with calculated values, indicating substantially complete esterification. Intrinsic viscosity results on the esters varied with the acyl group and with the solvent used. Intrinsic viscosity values of their regenerated celluloses indicated, how-ever,that the esters were of substantially the same degree of polymerization The acid chloride-pyridine procedure thus was found to be capable, under certain conditions, of preparing esters which satisfy the requirements set for this work.
In the present work cellulose prepared by deacetylation of a medium viscosity cellulose acetate was chosen as a starting material. This is a cellulose already in the desired range of degree of polymerization and yields soluble esters directly. Because an esterification method was chosen which causes very little degradation of the cellulose, the products have the desired similarity of chain length. PREPARATIOK O F STARTING CELLULOSE
Twenty pounds of a commercial, medium-viscosity cellulosc acetate (40.4% acetyl content) were suspended in 200 pounds of 14% ammonia and allowed t o stand a t room temperature for 7 2 hours with occasional stirring. The regenerated cellulose was then thoroughly washed with distilled water and dried. Analysis : Acetyl content, 0.1 yo; viscosity, 2.5% in cuprammonium eolution, 11.0 cp. a t 25" C. The dried material was found to react as readily as material which had been dewatered by displacement with pyridine or other solvents. Consequently, the dried material was used for all reactions. DETERMINATION OF SATISFACTORY REACTIOS CONDITIONS
EFFECTOF EXCESSES OF PYRIDINE AND ACID CHLORIDE. Cellulose propionate was chosen as representative of the lowe1 members of the homologous series, and a number of preparations were made varying the amounts of reagents employed. These data are shown in Tablc I.
T
HE technology of the simple and mixed lo~verfatty acid esters of cellulose is well known, having been given much attention in the technical, trade, and patent literature in recent years. Knowledge of the higher esters, however, is more limited This is especially true of simple ester series which have a uniform degree of polymerization, are fully esterified, and are free from combined impurities arising from side reactions or impure reagents. The research described in this paper had as its purpose the preparation of a homologous series of fatty acid esters fulfilling these three requirements. Pringsheim, Lorand, and Ward ( 1 1 ) have critically reviewed the literature up to 1932 and have contributed certain improvements in laboratory procedures. A review of preparatory methods through 1942 has also been given by Malm and Fordyce
TABLEI. VARIATIOXOF MOLARRATIOSOF PYRIDIXE 4x11 PROPIOKYL CHLORIDE TO CELLULOSIC HYDROXYL Analyees ____ -.Sample 1 2 3 4
5 6 7 8 9 10
(6).
Because esterification methods employing anhydrides with either acidic or basic catalysts are not useful for the preparation of cellulose esters much higher than the butyrate, only two methods remain for making the higher esters. The "impeller" method of Clarke and Malm ( 1), utilizing chloroacetic anhydride to promote esterification by the desired acid, is very efficient. It, however, does not lend itself easily t o critical viscosity control and mag introduce small amounts of chloroacetyl, depending on reaction conditions and on the ester being prepared. The acid chloride-pyridine procedure was found t o be capable, under certain conditions, of preparing esters t h a t satisfy the requirements set for this work. For the most part, previous workers in the field have not studied complete series of esters, but have confined their work to one or two members. Little has been published on the effect of varying reaction conditions. Hagedorn and Moeller ( 4 , 5 ) reported the preparation of a homologous series of the fatty acid esters by the acid chloride-pyridine procedure, but gave no experimental details (except t o state that optimum conditions were employed) or analyses of the products. 1 Present address, Department of Chemistry, Purdue University, West Lafayette, Ind.
Pyridine 9.2 6.3
4 4 3.3 2.5 2 1.6 1
0.5
EtCOCl E t & - a 1.5
2
2
P 2 1.5
1.5 1.5 1.5
39.8 48.8 50.1 49.1 43.2 50.9 50.2 50.6 50.9 50.4
Waterb tolerance value Insol. 22.4 22.3 25.8 22.9 26.0 28.8 28.6 28.2 30.8
Melting point, 'C
CharC point, 'C,
236 158 165 205 173 196 223 224 228 202
270 225 200 215 260 276 305 305 295 275
[ql in CxH2Clr" Insol.
0.89 0.86 0,86 0.80 0.83 0.86 0.86 0.77 0.38
For analytical method see (8). Theoretical, 51.8%. See text. Char point is t h a t temperature where sample turns black. and is a meacjure of stability of ester. d Intrinsic viscosity determined a t 0.25 gram per 100 ml. a
b C
One-tenth mole quantities of cellulose were placed in a 500-ml. three-necked flask fitted with a sealed stirrer, and the desired amount of pyridine was added. Sufficient 1,4-dioxane was then added so that liquid-solid ratio would be 16 to 1when all additions were completed. The acid chloride was added over a period of 15 minutes and was always diluted with a n equal weight of dioxane. All reactions were run on a steam bath for 4 hours, which was found more than the time required for complete dissolution of the cellulose. The reaction mixtures were then diluted with acetone containing a small amount of water to destroy excess acid chloride and were filtered through felt and through filter paper, and the ester was precipitated into distilled water with good agitation. After distilled-water washing, the products were dried a t 65' C. Contrary to expectations, the data indicated that the use of Jarge amounts of pyridine (sample 1 used i t as a diluent as well as a reactant) gave products low in propionyl content and with
684
March 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
melting points considerably below the 230" to 250' C. considered normal for tripropionates (7). Samples 2, 3, 4, and especially 5 show t h a t large excesses of either reagent are undesirable, in that low melting points and low water-tolerance values are observed. [Water-tolerance value is a measure of the amount of water required, in milliliters, t o start precipitation of the ester from 125 ml. of a n acetone solution of 0.1% concentraa
*)
*
*
685
TABLE 11. VARIATIONOF REACTION DILUENT IN PREPARATION OF CELLULOSE PROPIONATE Samde 7 11 12 13 14 15 16 1 17 18 19
Diluent Dioxane Chlorobenzene Nitrobenzene Toluene Tetrachloroethane Ethyl propionate Iaophorone Pyridine Ethylene formal Propionic acid Dibutyl ether
Reaction Time, Hours 4 4 5 4 24 5 4 4 22 5 22
% EtCO50.2 50.6 49.8 45.1 44.3 43.5 40.2 49.8 10.6 6, Negligible
Analyses Water Melting tolerance point, value OC. 28.8 223 24.5 nonea 198 25.0 23.6 nonea 167 20.6 20.4 nonea 34.1 nonea Insol. 236
Char point, OC. 305 300 225 295 195 300 290 270
&l&,& 0.86 0.89 1.14 0.99 0.92 1.02 0.70 Insol.
tion. T h e initial point of turbidity formation is determined photometrically in a n apparatus similar t o those described in the literature (3, IO)]. These low values show the possible presence of Sample chars before melting. higher acyl groups such as a-propionylpropionyl arising from side reactions or of water-insoluble impurities, inasmuch as the water-to1erance TABLE111. VARIATION OF TERTIARY AMINEIN PREPARATION OF CELLULOSE has been fouvd to be a n indication of the nature PROPIONATE and number of the acyl groups attached t o the Analyses cellulose. Reaction Water Melting Char Time, tolerance point, polnt, [VI in I n general, the pyridine should be limited t o Sample Tertiary Amine Hours % EtCOvalue OC. OC. ClH&lr slightly over t h a t equivalent t o the acid chloride 7 Pyridine 4 50.2 28.8 223 305 0.86 20 @-Picoline 4 49.1 28.1 252 265 0.92 used, which in turn should be limited in amount. Quinoline 4 43.7 30.3 215 275 0.63 21 Smaller amounts of pyridine cause degradation, 22 Dimethylaniline 48 35.8 33.3 195 205 0.38 a-Picoline 5 Very poor reaction 23 as indicated b y intrinsic viscosity measurements 24 7-Picoline 24 Very poor reaction on samples 9 and 10. EFFECTOF TIMEA P ~ DTEMPERATURE. Using reagent ratios as for sample 7, experiments were made at temperatures varying from 40' t o 100" C. Reaction purification was given the Cs t o CIZacids; instead the resulting acid chlorides were fractionated through a column of 25 theoretitimes for complete solution of the cellulose varied from 4 t o over 200 hours. I n all cases, these variations appeared t o have no cal plates. I n all cases, the acid chlorides were collected over effect on the properties of the esters. Because the lower temless than a 1' boiling range. T h e commercial myristic and palmitic acids were recrystallized three times from acetone to remove peratures required excessive reaction times, steam bath temperatures were employed in the remainder of t h e work. unsaturated acids. They were then converted t o the methyl EFFECT OF DILUENT.It was expected t h a t any inert diluent esters, and these were fractionated at reduced pressure to separate which is a solvent for cellulose propionate would be suitable as a the lower and higher homologs. T h e pure methyl esters were then reaction medium. Table I1 shows the use of a n assortment of saponified t o the acids, which were in turn converted t o the correcompounds of varying solvent power, using reagent ratios as for sponding acid chlorides. These were distilled t o remove thionyl sample 7. chloride and free acid. Table IV shows the source and boiling Although the higher boiling aromatic solvents, such as chloropoints of the reagents used. benzene, nitrobenzene, and toluene gave products of relatively high acyl contents, most of the wqter tolerance values and melting behaviors were abnormal. I n addition, they have the disadTABLEIV. SOURCEAND CONSTANTS OF REAGENTS vantage of necessitating precipitation of the ester into organic solCompound Source B.P., oc. vents rather than water. Dioxane is, therefore, the preferred Pyridine E K 214a 115.5-116.0 diluent. E K 2144 101.1 1,4-Dioxane EK 4 139.0-140.0 Acetic anhydride EFFECT OF TERTIARY AYINESOTHERTHANPYRIDINE. The E K 788 78.2 Propionyl chloride E K 781 102.2-102.8 Butyryl chloride patent literature reports the effectiveness of almost all tertiary E K 271 Valeric acid amines t o promote cellulose esterification with acid chlorides. Acid 5 1 . 4 (50 mm.) Valeryl chloride E K P352 Caproic acid Quinoline and dimethylaniline have been most often mentioned. Acid 5 9 . 0 (27 mm.) Caproyl chloride E K 821 Heptylic acid Table I11 indicates the results obtained with other amines, using 7 2 . 0 (25 mm.) Hepto 1 chloride Acid dioxane as a diluent and reagent ratios as for sample 7. Of these, Neo-fat 7a CapryEc acid 89.0 (14 mm.) Acid Caprylyl chloride only 8-picoline approached pyridine in efficiency. Quinoline and Neo-fat 15 Capric acid 110-114 (14-16 mm.) dimethylaniline, in addition t o yielding low acyl contents, were Acid Capryl chloride Neo-fat 11 Lauric acid difficult t o remove from the precipitates even with methanol 1 3 2 . 0 (14 mm.) Acid Lauroyl chloride Neo-fat 13 Myristic acid washing. T h e esters always had both odor and color. 107-111 (0.3-0 5 mm.) Acid Methyl myristate Neut. eq. 228.3c Methyl ester The results of the foregoing experiments indicate t h a t pyridine Myristic acid 1 5 0 . 0 (6 mm.) Acid Myristoyl chloride with dioxane as a diluent is satisfactory for the preparation of Neo-fat 1-56 Palmitic acid 139.0 (1.5 mm.) Acid Methyl palmitate triesters of acceptable purity. It is possible, however, t h a t other Neut. eq. 256.2a Methyl eater Palmitic acid Acid combinations of amines and diluents might work as well. Palmitoyl chloride PREPARATION AND PURIFICATION OF REAGENTS
a b 0
d
T h e pyridine used was the best commercial grade available (2 ") and was carefully fractionated t o assure the absence of picolines and moisture. 1,4Dioxane was also fractionated t o remove water. T h e acid chlorides were prepared by the action of 20 t o 50% excesses of redistilled thionyl chloride on the corresponding acids. All the acids used were the best grade available commercially. No
s
Eastman synthetio chemicals. Armour a n d Co. chemicals. Calculated. 228.2. Calculated, 256.3.
PREPARATION OF CELLULOSE ESTERS
The use of acetyl chloride and pyridine does not yield satkfactory cellulose acetates, because of side reactions which cause the introduction of chlorine and nitrogen (6),and because of the lack
686
Vol. 43, No. 3
INDUSTRIAL AND ENGINEERING CHEMISTRY I .o-
lose). These products Fere isolated as from the first reaction mixtures after filtering the reaction mixtures through felt and paper. The only departures from this general procedure were in the case of the myristate and palmitate. Because these esters are not soluble in dioxane, a part of this solvent was replaced by toluene t o give a more active solvent system during the reaction.
(3
-
0.9
ANALYSIS OF PRODUCTS
ACYLCOSTEKTS. The acyl contents of the esters were determined by saponification with 0.25 N alcoholic alkali, as described by Genung and Mallatt ( 2 ) . This work was done by an experienced analyst usingextreme care. The esters were analyzed once a week for three consecutive weeks t o obtain a good average value and t o get an indication of the precision. The results are shown in Table T'.
0.6
0.5
TABLE V. ACYLCONTESTSOF ESTERS o.2 0
t .
-1st l
l
0 1
~
~
I
I
l
2 3 4 5 6 7 8
I
l I I
IO
I
I
I2
14
N u m b e r of c a r b o n a i o m s i n e s t e r i f y i n g acid'
Figure 1.
Intrinsic Viscosities of Triesters in Chloroform
of suitable reaction diluents in which the triacetate is soluble once it is formed. A triacetate was prepared by reaction of the commercial, medium-viscosity cellulose acetate (used for preparing the starting cellulose) with acetic anhydride.
PREPARATIOS OF CELLULOSE TRIACETATE. Four hundred grams of cellulose acetate (40.4% acetyl content) were dissolved in 3200 ml. of pyridine, and 550 grams of acetic anhydride and 600 grams of acetic acid were added. The reaction mixture was held on a steam bath for 24 hours with continuous stirring, and then was diluted with 3000 ml. of pyridine and precipitated into distilled water. The precipitate was given twelve 2-hour washes in distilled water with centrifuging between each change, and was then dried a t 65 C.
Triester Acetate Provionate Bucyrate Valerate Caproate Heptylate Caprylate Caprate Laurate Myristate Palmitate
Observed 2nd 3rd week week 44.7 44.5 51.7 51.7 57.1 57.1 61.6 61.6 64.7 65.4 67.8 68,3 70.6 70.9 74.2 75.0 77.6 78.7 79.0 80.0 81.2 82.8
week 44.9 51.7 57.3 61.6 66.4 68.3 70.9 74.6 78.3 79.0 82.8
Average yo acyl 44.7 51.7 57.2 61.5 66.2 68.1 70.8 74.6 78.2 79.3 82.3
Theoretical % Acyl 44.8 51.8 67.3 61.6 66.1 68.1. 70.6 74.5 77.6 79.9 81.9
Inasmuch as the precision of the analytical method is about =t0.2Oj, and the accuracy is about +0.4% n-hen the results are calculated as per cent apparent acetyl (molecular weight 43), good agreement can be said t o have been attained between the calculated and observed values of acyl contents. HYDROXYL COKTENTS.The unesterified hydroxyl content8 of the esters were determined as a check on the acyl analyses. This was accomplished by a modification of a published procedure (8), the only change consisting of the addition of toluene after the
O
The preliminary experiments described yielded conditions appearing satisfactory for the preparation of the lower triesters of cellulose. These were checked for the preparation of the caprate, which was considered as representative of the higher members of the series. It was found advisable, however, to subject the esters to a second esterification step to assure complete reaction of all the hydroxyls.
PREPARATION OF TRIESTERS. PROPIONATE THROUGH PALYIThe remainder of the esters were prepared by the following general procedure: One mole (162 grams) of cellulose was placed in a 3-necked flask and 4.2 moles of pyridine (1.4 times the theoretical amount, based on the hydroxyls) were added. Sufficient 1,4-dioxane was then added t o give a total liquid-to-solid ratio of 16 t o 1 after addition of the acid chloride. The cellulose suspension was stirred, and 3.6 moles of acid chloride (1.2 times the theoretical amount) diluted with an equal weight of dioxane were added over a period of 15 minutes. The reaction mixture was then raised t o steam bath temperature and held there with continuous stirring for 20 t o 24 hours. After cooling, the solution was diluted with acetone (or toluene in the case of the higher esters) containing a small amount of water or methanol to destroy excess acid chloride. Esters of water-soluble acids were precipitated into water, and the higher esters into methanol. After thorough washing, the esters were dried. They were then dissolved in a suitable solvent, the solution was filtered through felt and through paper, and the esters were reprecipitated, rewashed, and redried. By using these proportions and conditions, a fully esterified propionate (51.8y0 EtCO-) was obtained, but t o assure complete esterification, all esters were redissolved in dioxane and reacted at steam bath temperature for 20 t o 24 hours with 0.25 and 0.20 times the theoretical amounts of pyridine and acid chloride, respectively (based on the original hydroxyl content of the celluTATE.
1.1
I
.o
0)
0.9 c c al
0.8
-0
== V ?
f
2
0.7
2 n :
.e
& 0.6
2 5
'j;
w
0 0
.-In
0.5
>
.y
0.4
.-c c L
5
0.3 0.2 0. I
I 12
I 14 N u m b e r o f c o r b o n atoms i n e s t e r i f y i n g acid
I
I
I
I
I
I
I
I
0 1 2 3 4 5 6 7 8
Figure 2.
I
IO
Intrinsic Viscosities of Triesters in Tetrachloroethane
16
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1951
687
1.3 I .2
1.5 c
.-c ,gc
zz
acetate, s t o r t i n g material )
'I tn
1.2 -
.? .2 E
1.0-
'c
0.9 -
.L!
0
:.c
5
In€
-c
0.7
1.4,--1.3'5 ( D e a c e t y l a t e d cellulose 1.1
0
-
m
" 0 0 ,
A
0
0
0.8 5'0.7-
0.60 .E
I
I
I
I
I
3
4
5
6
7
0.5
I
l
l
l
l
l
l
'
I
I
I
0
N u m b e r of carbons in esterifying acid
Figure 3.
Intrinsic Viscosities of Triesters in Acetone
acetylation period to hold the ester in solution during destruction of the excess acetic anhydride and during titration. The values obtained by this procedure and those calculated from the observed acyl contents of the esters are shown in Table VI. The precision of the hydroxyl determination appears to be in the range of 10.3%. The results show observed values from -0.3% on the propionate to 0.3% on the butyrate and heptylate, with other values lying between these. In general, fair agreement exists between the two methods of determination of the extent of esterification. JNTRINSIC VISCOSITIES. Intrinsic viscosities were determined in the apparatus described by Wagner ( 1 9 ) using both chloroform and s-tetrachloroethane, which are solvents for the entire series. Acetone was also used over the range of propionate to caprylate. Intrinsic viscosity value8 are reported which were found by extrapolation to zero concentration. The measurements were made a t three concentrations and the calculation was made using Kramer's equation, [ T ] = In qr/c. The data are shown in Tables VII, VIII, and IX and in Figures 1, 2, and 3.
TABLE VIII.
INTRINSIC VISCOSITIESOF ESTERSIN S-TETRACHLOROETHANE
Triester Acetate Propionate Butyrate Valerate Caproate Heptylate Caprylate Caprate Laurate Myristate Palmitate Extrapolated. +
a
TABLE IX.
a
In % / c . Concn., G./100 0.50 0.25 0.10 1.08 1.01 1.12 0.83 0.81 0.84 0.76 0.74 0.77 0.74 0.77 0.76 0.70 0.66 .... 0.63 0.60 0.68 .... 0.58 0.56 0.53 0.54 .... 0.46 0.49 0.49 0.43 0.45 0.49 0.31 0.37 0.39
M1. O.Oa
1.15 0.86 0.78 0.78 0.73 0.68 0.59 0.55 0.50 0.49 0.42
INTRINSIC VISCOSITIES OF ESTERSIN ACETONE
Triester Propionate Butyrate Valerate Caproate Heptylate Caprylate Extrapolated.
In S V / C , 1.00 1.00 1.04 0.99 0.89 0.76 0.68
Concn., 0.50 1.06 1.12 1.04 0.94 0.79 0.70
G./100 M1. 0.25 O.Oa 1.10 1.13 1.19 1.14 1.07 1.10 0.96 0.99 0.81 0.83 0.71 0.72
TABLE VI. HYDROXYL CONTENTS OF ESTERS Triester Acetate Propionate Butvrate Valerate Caproate Heptylate Caprylate Caprate Laurate Myristate Palmitate
yo Hydroxyl Observed Calculated"
Intrinsic viscosity measurements on the esters cannot be entirely satisfactory for comparison of their relative degree of polymerization because of solvation effects and varying cellulose contents and axial ratios of the esters. All the esters were, therefore, deacylated under conditions approximating the saponification method used for the determination of their acyl contents.
Portions of the esters sufficient t o yield about 5 grams of regenerated cellulose were suspended in an excess of 0.25 N alcoholic alkali and nitrogen was bubbled through the suspensions t o re4 Calculated from observed average acyl content. move as much air as possible. After saponification had proceeded for 16 hours a t room temperature, the celluloses were filtered off, a fresh portion of the alcoholic alkali was added, and the suspenVISCOSITIES OF ESTERSIN CHLOROFORM sions were again flushed with nitrogen. After a second 16-hour TABLE VII. INTRINSIC saponification, the solutions were carefully neutralized with In n / c , Conon., G.1'100 M1. aqueous hydrochloric acid, and the celluloses were filtered off and Triester 1.00 0.50 0.25 O.Oa washed thoroughly with distilled water and methanol until free 0.92 0.95 0.98 Acetate 0.85 from salts and acidity. 0.75 0.77 0.80 Propionate 0.70 Butyrate Valerate Caproate Heptylate Caprylate CaDrate Laurate Myristate Palmitate
a
Extrapolated.
0.66 0.66 0.67 0.60
0.59 0.56 0.55 0.52 0.41
0.71 0.71 0.70 0.63 0.62 0.59 0.57 0.55 0.43
0.73 0.73 0.72 0.63 0.63 0.61 0.59 0.56 0.42
0.75 0.75 0.73 0.66 0.65 0.62 0.61 0.57 0.42
The intrinsic viscosity of the original deacetylated cellulose acetate used for the preparation of the esters was determined in cuprammonium solution. The measurements were made a t four concentrations, and the values were calculated by both the Staudinger and Kramer equations. These data are shown in Table X. The same cellulose was subjected to the alcoholic alkali treatment and showed no viscosity decrease. The cupram-
688
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE x.
INTRINSIC \‘ISCOSITY OF DEACETYLATED CELLULOSE ACBTATEIK CUPRAMMONIUM SOLUTION
Concn., G./100 M I .
(Kramer) In V F / C
(Staudinger) 78dC
Average
Vol. 43, No. 3
The above results indicate t h a t within esperiment,al error the esters fulfill the requirements set a t the beginning of the work. The properties of the triesters of similar degree of polymerization are described in the following paper (9). ACKNOWLEDGMEIYT
a
T h e authors wish t o express their appreciation t o ?*Ira. D. L. Kendall, who did much of the analytical work reported in this paper.
Extrapolated.
TABLE XI. INTRINSIC VISCOSITIESOF CELLULOSICS IS CUPRAMMONIUhC SOLUTION
LITERATURE CITED
Source of Cellulor e [?la Starting material 1.36 Acetate 1.17 Propionate 1.05 Butyrate 1.07 Valerate 1.10 Caproate 1.06 Heptylate 1.02 Caprylate 1.06 Caprate 1.02 Laurate 1.06 Myristate 0.99 Palmitate 0.72 a Determined a t 0 . 2 5 gram per 100 nil. Value reported is average of those calculated by Kramer and Staudingei equations, which gives close approximation of value found by extrapolation to infinite dilution by either equation.
monium intrinsic viscosities of the celluloses regenerated from the esters are shown in Table XI and Figure 4. These results indicate the acetate to be of slightly higher, and the palmitate of slightly lower degree of polymerization than that of the remainder of the series. All are lower than the starting material, giving a measure of the degradation occurring under the esterification and deacylation conditions employed.
Clarke, H. T., and Malm, C. J., U. S.Patent 1,880,808 (Oct. 4 , 1932).
Genung, L. B., and hIallatt, R. C., IND. ENG.CHCM.,A K A LED., . 1 3 , 3 6 9 (1941).
Greene, C. H., J . Am. Chem. Soc., 56, 1269 (1934). Hagedorn, M., and Moeller, P., Cellulosechemie, 12, 29 (1931). Hagedorn, M . , and Moeller, P., Veroffentl. wiss. Zentr-Lubs. phot., Abt. I . G.Fnrbenind. B.G. Agfa, 1, 150 (1930). Malm, C. J., and Fordyce, C. R., in Ott, E., “Cellulo3e and Cellulose Derivatives,” pp. 667-708, Xew York, Interscience Publishers. 1943. Malm, C. J.; Fordyoe, C . It., and Tanner, H. A , , IND.ENG. CHEM.,34, 430 (1942).
Malm, C. J., Genung, L. B., and Williams, R. F., Jr., IND. EKG. CHEX.,AKAL.ED., 14, 935 (1942). Malm, C . J., Mench, J. W., Kendall, D. L.. and Hiatt. G . D.. IND. ENG.CHEM.,43, 658 (1951). LIorey, D. R., and Tamblyn, J. IT., J . A p p l i e d P h y s , 16, 419 (1945).
Pringsheim, H., Lorand, E., and Kard, K., Jr., Cellulosechemie, 1 3 , 1 1 9 (1932).
Tagner, R. H., and Russell, J., A n d . Chem., 20, 151 (1948). RECEIVEDAugust 2 , 1950. Presented before the Division of Cellulose CHEWCALSocriwr, Chemistry a t the 118th hleeting of the AMERICAN Chicago, Ill.
stem of
atic Aci
PRQPERTIES C. J. MALM, J. W. RIENCH, D. L. KENDALL’, AKD G . D. HIATT E a s t m a n IQodak Co., Rochester, N . Y .
Certain discrepancies are observed in the literature relating to the properties o€ homologous series of aliphatic acid esters of cellulose. This work presents data on melting point behavior, moisture sorption, density, tensile strength, refractive index, solubilities, and specific rotation for a series of cellulose esters from acetate through palmitate. The esters used were fully esterified and had substantially the same degree of polymerization. As the number of carbon atoms
in the acid increases, density, tensile strength, specific rotation, and moisture sorption decrease. The melting points pass through a minimum at the Cg ester, while maximum solubility is reached with the Cs or Cg esters. The refractive index varies only slightly throughout the series, The data may be considered comparable, because all esters studied were fully esterified and of uniform degree of polymerization.
T
ment in high-boiling solvents containing acid catalysts. Obviously, this is a disadvantage if the properties of a series of esters are to be compared. Sheppard and Newsome (6) described a variety of properties of the fatty acid esters, and emphasized the necessity of having materials of comparable chain length and of uniform and high degree of esterification. They gave no data, however, t o show that these requirements were met, nor did they describe the method of preparing the esters. Certain properties of these esters were determined, and the results are summarized in Table I. The methods used and comments on the results are given below. BEHAVIOR ON HEATING. The melting behavior of the samples
H I S paper reports the properties of the series of cellulose esters whose preparation has been described ( 5 ) . The esters have been shown to be substantially fully esterified, and were prepared using pure reagents under conditions which minimized side reactions which cause combined impurities. The degree of polymerization is also relatively constant throughout the series. Hagedorn and Moeller ( 2 , 3 ) have reported tensile strengths and solubilities for a homologous series of fatty acid esters of cellulose. Most of their esters, however, were obtained in a fibrous, insoluble form and had to be solubilized by a heat treat1 Present address, Department of Chemistry, Purdue University, West Lafayette, Ind.
