Use of the ester exchange reaction for the synthesis of cellulose stearates

Synthesis of cellulose strearates

761

R£FERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

It. E. NEIMAN, Dokl. AN SSSR 82: 419, 1952 A. V. NIKOLAYEV, It. E. NEIMAN and O. V. NEIMAN, Kolloid. zh. 19: 121, 1957 S. M. LIPATOV and S. M. MEEItSON, Kolloid. zh. 17: 230, 1955 T. N. BUItZHANADZE, P. I. PItIVALOV and I. I. TAVZHLIDZE, Vysokomol. soyed. 4: 1419, 1962 (Not translated ir~ Polymer Sci. U.S.S.R.) S. M. LEVI, Kolloid. zh. 22: 599, 1960 V. A. PCHELIN, V. I. IZMAILOVA and V. P. MEItZLOV, Dokl. AN SSSR 150: 1307, 1963 V. PAULI a n d E. VAL'KO, Koll. khimiya belkovykh veshchestv (Colloid Chemistry of Proteins). Izd. ONTI, 112, 1936 V. O. PAULI and E. WEISS, Biochem. Z. 203: 103, 1928 V. O. PAULI and I. SAFRIN, Biochem. Z. 233: 86, 1931 V. O. PAULI and I. WIT, Biochem. Z. 174: 308, 1926 V. O. PAULI and E. GEIGNEIt, Biochem. Z. 235: 271, 1931 S. M. LIPATOY, Problemy ucheniya liofilnykh kolloidov (Problems of Lyophilic Colloids). Izd. AN BSSR, Minsk, 1941 G. NEIRAT and K. BEILI, Proteins, vol. II, 431-512, Foreiga Lit. Pub. House, 1956 Y. O. PAULI and Th. STENZINGEIt, Biochem. Z. 205: 71, 1929 V. O. PAULI and D. V. KLOBUSIZKI, Biochem. Z. 260: 201, 1933

USE OF THE ESTER EXCHANGE REACTION FOR THE SYNTHESIS OF CELLULOSE STEARATES* A. I. LATETIN, L. S. GAL'BI~AIKH and Z. A. ROGOVlN Moscow Textile I n s t i t u t e

(Received 25 April 1967) T~E synthesis of cellulose esters and cabroxylie acids is generally effected b y means of the esterification of cellulose ~ i t h anhydrides or acid halides of these acids, or less frequently through the action of the acids themselves [1]. In the synthesis of cellulose esters with higher f a t t y acids, which are of some practical interest, acid chlorides are used as the esterifying agent. The need to use these reagents, and the fact that the reaction must be carried out in a medium of organic solvents binding the HC1 evolved in the esterification reaction, adds considerably to difficulties in carrying out the reaction, and limits its practical use. It was therefore desired to consider the use of other more suitable methods of esterifieation for synthesizing cellulose esters, and in particular cellulose stearates. Cellulose esters are obtainable b y means of ester exchange. Only separate experiments aimed at synthesizing cellulose esters and phosphorus-containing * Vysokomol. soyed. A19: No. 3, 652-656, 1968.

762

A.I. LA~'ETr~et al.

[2] and boron-containing [3] acids by this method have been described in the lit~ erature. Data on the use of this reaction in order to obtain esters of sugars and of higher fatty [4] and unsaturated [5] acids have also been published. Howevec, no systematic study has yet been made of the use of transesterification to synthesize cellulose esters. The present investigation is based on the production of cellulose stearate by the action of methyl stearate on cellulose by the scheme: [CeH~Oz(OH)s]n-~nx. C H s - - O ~ C 1 7 H u ,

catalyst

-~

[C,HTO2(0H)a-~(O--C--C~,H,,)~]~+nx.CH,OH O Cotton cellulose reprecipitated from euproammonium solution was used as the initial cellulose material. The ester exchange reaction was carried out in dimethylformamide enabling the cellulose hydrate to be kept in the swollen state, and making it possible for the methanol formed during the reaction to be distilled off. According to data in [6] the presence of traces of water (over 0.3%) in the reaction medium completely inhibits the effect of the catalyst in the ester exchange reaction. Therefore to remove water as far as possible benzene was added to the reaction system, and the azeotropic mixture of benzene and water distils off during the reaction. From a great variety of catalysts for the ester exchange reaction [7] we selected sodium methylate, cadmium acetate and ~-toluenesulphonie acid, which are soluble in dimethylformamide. The mechanism of the action of basic and acid catalysts in the aleoholysis of methyl stearate by cellulose may be represented by schemes I [8] and II [9] given below. There is no information in the literature regarding the eytalytie action of polyvalent metal salts. I [C6H,O~(OH),]n~-xn.CH,ONa~xn.CHsOH~[C6H,O2(OH)s-~(ONa)~]n

[CeH,02(OH)8-~(ONa)~]n~-xn. CHs--O--C--C1,Hu

/

o O--CH8

~[C6H,02(0H)s-~(0--~--C~,Hu)~]n OCHs I

[C6HT02(OH)a-x(0--~--Cl~Hss)~]n~zn. CHsONa+ |

ONa

+[C6H,O,(0H),-~(O---C--CI,H,,)~]n o/

Synthesis of cellulose stearates 0

763

0

+~

CHs--O--C---C17H85-]-H+~CH3--O--C--Cr'+Hss

L

H O +~ + CH..--O--C--Cr~IT,s '~CHsOH-P-O ~ C--C17Hss

i

H + -,I[C+H+O~(OH)+],,+xn. O= C--C~+Hsa~[C+H+O+(OH),-+. (O--C--C17Hs+)+]n

i

tt

]l

O

[C~HTO~(OH)s-~(O--C--CI,H3~)x]n ~ x n . I-I +-~-[C+H,O2(OI-I)s-~( O--C----C~,Hss)~],+ H

A study was made of the degree of substitution (DS) of cellulose stearates in relation to the amount of methyl stearate, the nature and amount of catalyst, and the time and temperature of the reaction. TABLE

1. ~ E G R E E

OF S U B S T I T U T I O N OF CELLULOSE STEARATE I N

RELATI01~ TO T H E AI~OUNT OF I~ETHYL S T E A R A T E $

Molar ratio methyl

stearate

cellulose

:

Amount of stearie acid bound, °/o

DS of cellulose stearate

1:1

29"0

0"23

2:1

3 5 "5

0"32

3:1

38"0

0"36

4:1

39"5

0"38

* Catalyst CHaO.~'a (1 x 10 -~ g-mole per 162 g of cellulose); reaction t i m e - 8 hr; temp. 120 ° .

On increasing the molar ratio of methyl stearate : elementary unit of cellulose molecule from 1 : 1 to 2 : 1 the DS for the cellulose stearate is increased b y approximately 50% (Table 1). Further increase in the above ratio has only an inappreciable effect on the degree of substitution of cellulose stearate. In subsequent tests therefore a methyl stearate/cellulose ratio of 2 : 1 was adopted. Figure 1 shows the effect of the reaction temperature on the DS of cellulose stearate. It will be seen that in the tempearture range investigated the DS of cellulose stearate has a maximum on carrying out the reaction at 130-140°; however, at this temperature there is considerable degradation of the cellulose material (the coefficient of polymerization is reduced from 1100 to 680). For cellulose stearate obtained at 120 ° the DS is slightly lower, b u t there is less degradat i o n - t h e coefficient of polymerization of the cellulose is reduced b y 12% during the reaction.

764

A.I. LATETrXet ul.

To obtain a rough estimate of the activation energy and order of the reaction the alcoholysis of methyl stearate by cellulose in the presence of sodium methylate was investigated (Fig. 2). This reaction is of the first order and the activation energy is 22.3 kcal/mole. D.8.

O"Z

0"2

#

0 ~lOO frO FIG. 1

f~O T,°C

1)

ZO

Z8

Time, hi' FIG. 2

FIG. 1. DS of cellulose stearate vs. reaction temperature. Catalyst CHsONa (1 × l0 -~ g-mole per 162 g of cellulose); methyl stearate/cellulose ratio=2 : 1; reaction time--8 hr. FIG. 2. DS of cellulose stearate vs. reaction time. Catalyst CH8ONa (1 × 10-~ g-mole per 162 g of cellulose). Temperature: 1-3--120°; 4--130°; 5--110; methyl stearate/eellulose ratio: 1--3 : 1; 2, 4, 5--2 : 1; 3--1 : 1. I n view of the data obtained it m a y be concluded t h a t the alcoholysis of methyl stearate by cellulose in the presence of sodium methylate has a nuro ber of special features. Generally the alcoholysis of esters by low molecular weight alcohols takes place by a second order reaction. The activation energy of these processes amounts to 12-14 kcal/mole [9, 10], while the activation energy for the alcoholysis reaction by iso-structure alcohols is slightly higher t h a n for the corresponding normal alcohols. The fact t h a t the alcoholysis of methyl stearate by cellulose takes place as a first order reaction is apparently the result of carrying out the reaction in a heterogeneous medium. The relatively high activation energy of the process m a y be attributed to the considerable steric hindrances resulting from the complexity of the structure of the high molecular weight alcohol (cellulose) and from the great size of the acid radical in the ester undergoing alcoholysis. A study was made of the effect of the type and amount of the catalyst on the DS of cellulose stearate. The data obtained are presented in Table 2. I t will be seen t h a t the amount of catalyst has a strong effect upon the DS of the reaction product; moreover for each catalyst there is a characteristic optimal concentration at which the maximal DS of cellulose stearate is obtained. When nitrobenzene

Synthesis of cellulose stearates

765

and toluene (differing in polarity from dimethylformamide) are used as solvents for the methyl stearate under identical conditions and with 1 × 10 -4 g-mole CH30Na there is insignificant change in the DS of cellulose stearate: Solvent

Dimethylformamide

Toluene

l~itrobenzene

35"3 0"31

37"8 0"35

32"0 0"27

Amount of stearic acid bound, ~o DS of cellulose stearate

The DS of cellulose stearates obtained through ester exchange depends on the structure of the initial cellulose: when cotton fabric (cheap cotton cloth) is used instead of reprecipitated cellulose, the DS of cellulose stearate is reduced by more t h a n one half. EXPERIMENTAL The methyl stearate used in the experiments contained C17H3~C00H~ 0"50/0. Found, 0/0 C 76.8; H 13.0. C19H3sO2. Calculated, %: C 76"5; t I 12"7. Cotton fluff was reprecipitated from cuproammonium solution, and carefully washed in a filter with distilled water until neutral reaction was obtained and no reaction to SOl ~ ions (with BaCI~); the water was carefully removed with dimethylformamide. T A B L E 2.

DS

o F C E L L U L O S E S T E A R A T E R E L A T I V E TO T H E A M O U N T A N D T Y P E OF CATALYST*

Catalyst Amount of catalyst, g-mole.10-2/

CHsONa

Cd(OCOCH3)2

n-CH3CsHdSO3I-t

amount

D S o f c e l - ofs~::r~tc D S o f c e l - a m o u n t DSofcel/162 g of cellulose acid°f steariCbound lulOSearateSte-acid bound, lulOS~arateSte- acid°f steariCbound lulOSearateSte-

% 0"005 0"01 0"05 0"1 0"25 0"5 1 2

%

11"5 35"7

0"07 0"32

34"7 34"0 31"7 16"0 11"0

0"31 0"30 0'26 0"11 0"07

8 35"7 35"8 24"0 18"8 18"0

% 0"05 0"32 0"32 0"19 0"14 0"13

14"0 26"6 31 "7 31"2 33"0 27"2

0"09 0"21 0"26 0"26 0"28 0"22

* Methyl stearate/cellulose r a t i o = 2 : 1; reaction time--8 hr; temp. 120%

Synthesis of cellulose stearate. I n t o a three-necked flask fitted with a stirrer and direct condenser were placed 2"5 g of cellulose (coefficient of polymerization 1100), 4"5--18 g of methyl stearate (depending on the required molar ratio of methyl stearate : cellulose), 200 ml of dimethylformamide and 100 ml of benzene. The catalysts were added in the form of 0"05 M and 0"5 M solutions in absolute methanol. On completion of the process the product was filtered off and vacuum-dried. Analysis of cellulose stearate. Determination of the amount of bound stearic acid was carried out using the procedure adopted to determine the bound CH3COOH in cellulose acetates. I n contrast to this method we used a 0.5 • solution of K O H in 80~o ethyl alcohol.

766

A . I . LATETIN ¢2 a/. CONCLUSIONS

(1) I t h a s b e e n s h o w n t h a t t h e synthesis o f cellulose s t e a r a t e is possible t h r o u g h e s t e r e x c h a n g e b y m e a n s o f t h e a c t i o n of m e t h y l s t e a r a t e on cellulose in a d i m e t h y l f o r m a m i d e m e d i u m in t h e presence of different catalysts. T h e m a x i m a l degree o f s u b s t i t u t i o n o f cellulose s t e a r a t e s s y n t h e s i z e d u n d e r t h e a d o p t e d r e a c t i o n conditions is 0.38. (2) A s t u d y h a s b e e n m a d e of t h e effect of r e a c t i o n conditions u p o n t h e degree o f s u b s t i t u t i o n of t h e cellulose s t e a r a t e s o b t a i n e d . T h e alcoholysis of m e t h y l stea r a t e b y cellulose t a k e s place as a first order r e a c t i o n w i t h a n a c t i v a t i o n e n e r g y o f 22.3 kcal/mole. Translated by R. J. A. HEI~DRY REFERENCES

1. Z. A. ROGOVIN and N. N. SHORYGINA, Khimiya tsellyulozy i eye sputnikov (Chemistry of Cellulose and its Derivatives). Goskhimizdat, p. 414, 1953 2. K. A. PETROV and Ye. E. NIFANT'EV, Vysokomol. soyed. 4: 242, 1962 (Not translated in Polymer Sci. U.S.S.R.); U. MEIYAN, M. A. TYUGANOVA, Ye. L. GEFTER and Z. A. ROGOVIN, Tsellyuloza i eye proizvodnyye (Cellulose and its Derivatives). Izd. AN SSSR, p. 37, 1963 3. Ya. Ya. MAKAROV-ZEMLYANSKH and V. V. HERTSEV, Zh. obshch, khimii 35: 272, 1965 4. L. OSIPOW, F. D. SNELL, W. C. YORK and A. FINCHLER, Industr. Engng. Chem. 48: 1459, 1956 5. U.K. Pat. 859305; Chem. Abstrs. 55: 12898, 1961 6. U.S.A. Pat. 2486444; Chem. Abstrs. 44: 2264, 1950 7. J. NEBKY, Chem. listy 46: 497, 1962; P. A. ARTAMONOV, Transesterification of Fats, publ. by Central Research Institute of the Food Industry, 1962 8. M. A. VERLAY, Bull. Soc. Chim. France 41: 788, 1927 9. D. BUESSI-THIERNAGAND and P. J. C. FIERENS, Bull. Soc. China. Belge 61: 405, 1952 10. D. BUESSI-THIERNAGAND and P. J. C. FIERENS, Industr. Chim. Belge 18: 9, 1953