Reactivity of functional groups of nitrate esters of cellulose in the presence of Lewis acids

2144

g . I . SARYBAYEV&and L.S. SKcK~LOKHOVA

10. S. S. IVANCHEV, Yu. L. ZHEREBIN, V. I. KUZNETSOV and Yu. I. DERKACH, U.S.S.g. Pat. 35925l, Byul. izobret., 35, 53, 1972 11. B. N. PRONIN, Ye. N. BARANTSEVICH, L. V. SHUMNYI and S. S. IVANCHEV, Vysokomol, soyed. A19: 16] 5, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 7, 1850, 1977)

PolymerScienceU..%~.R.Vol.25, No. 9, pp. 2144~2151,1983 Printcdin Poland

REACTIVITY

OF FUNCTIONAL

CELLULOSE

GROUPS

IN THE PRESENCE

0032-3950/83$10.00+.00 © 1981PergamonPress Ltd.

OF NITRATE OF LEWIS

ESTERS

OF

ACIDS*

P~. I. SAI'CYBAYEVA ~nd L. S. ~HCHELOKHOVA Institute of Organic Chemistry, Kirg.S.S.R. Academy of Sciences

(Received 24 February 1982) Kinetic investigations of the reaction of donitration of cellulose nitrate esters have been made allowing one t.o make a quantitative estimation of the reactivity of the nitrate groups at the C-6, C-2 and C-3 atoms of the elementary unit of cellulose nitrate. The thermodynamics of the process has been studied. The participation of the hydroxyl groups in the acylation of cellulose dinitrates is demonstrated. SYNTHESIS of mixed nitric and c a r b o x y l i c acid esters of cellulose b y the reaction of reesterification of cellulose nitrates (CN) is of scientific and practical i n t e r e s t as the resulting cellulose derivatives possess good physicomechanical characteristics combined with reduced combustibility [ 1, 2]. F o r this purpose we studied the interaction of the cellulose nitrates (degree of substitution ~ 1.72-2.90) w i t h different acid chlorides of carboxylic acids in p resencc of a series of Lewis acids (SnCli, ZnCl.,, TiCl4, SbCls, BF3" 0 (C2H.~).,, A1C13). I t has been shown [3, 4] t h a t such interaction reduces tile c o n t e n t of the n i t r a t e groups (denitration) w i t h appearance of acyl groups (Fig. l). ])epending o n ' t h e conditions o f synthesis it is also possible to obtain highly s u b s t i t u t e d cellulose acylates (Table 1). geesterification proceeds in mild conditions and is practically no t complicated b y s e c o n d a r y pr ocesses. T h e mechanism of the reaction on the basis of the k n o w n published findings and e x p e r i m e n t m a y be represented b y the following scheme: f o r m a t i o n of t h e active acylating complex of MCln a c i d w i t h the acid chloride RCOC1 + MCln -~ (RCO) +MCI~+1 * Vysokomol. soyed. A25: :No. 9, 1844-1849, 1983.

• :Reactivity of fimctional groups of nitrate esters of celhdoso TABLE

l.

SYNTIIESIS

OF

SO~E

IIIGIILY

SUBSTITUTED

ACYLATES BY R E E S T E R I F I C A T I O I ~ OF C E L L U L O S E N I T R A T E S

2145

CELLULOSE

(IN] =

10.86-

12.70°,o) B Y ACID C H L O R I D E S OF C A R B O X Y L I C ACIDS ([SnCI ~]= 1 mole/elementary cellulose nitrate unit) Complex cellulose esters

Conditions of reaction T° time, rain 20 30 40 50

Acetates Butyrates Valeratos Benzoates

30 60 60 60

296 280 286 292

and the attack of the ester bond ousting the nitro group and formation of a new bond Cell -- O -- :NO ~+ (RCO) +MCI~+1-~ Cell -- O -- CO R + M C1n + NO =CI T h e f o r m a t i o n o f h i g h l y s u b s t i t u t e d ( 7 ~ 300) c e l l u l o s e a c y l a t e s e v e n w i t h u s e as starting compound of its dinitrates suggests that the hydroxyl groups take part in esterification. I n t h e I R s p e c t r a i f t h e p r o d u c t s o b t a i n e d ( F i g . 2) t o g e t h e r w i t h t h e a p p e a r a u c e o f a n a b s o r p t i o n b a n d a t 1750 e m -1 d u e t o t h e v a l e n t v i b r a t i o n s o f t h e C - ~ O

c~ rco;% 10

Iv

-#0

8 I

[

l

10 2O 30 T/me, rain FIG. 1

,I

34

I

I 30

17

13 v~lO,Zcm-~

Fl(~. 2

FIe. 1. Kinetics of accumulation of CtI3CO groups in denitration products of cellulose nitrate ([N]=10'86°/o) by acetyl chloride. Fl(:. 2. I N spectra of cellulose a~etonitrates obtained in the ra~.t.i,m of celhdese nitrate ( [ N ] : 10.68~}o) with aeetyl chloride at 20°C with content of b(,uml nitr~gen t;.41 (l), 4.89 (2) and 1.86 (3)00 .

2146

1~. I. SAItYBAYEVAand L. S. SHCHELOKIIOVA.

TABLE 2. ELEI~ENTAL A N D

COI~I~ES:POlgDING F U N C T I O N A L C O } r P O S I T I O N OP C E L L U L O S E N I T r t A T E

ltEACTION ~ PI~ODI/CTS

C

iElemental composition, ~o H N

30.79 32.32 34-26 34.36 36.28 36.90 36.86 37.91 41.88 45.09 48.30

3.54 3.45 4.04 3.86 4.24 4.02 4.12 4-56 4.52 5.19 5.40

9.81 8.97 7"96 7.91 7.00 6.62 6.40 5.98 4.09 2.27 0.82

(y = 1"88) W I T H

ACETYL

CIILOIIIDE

Functional composition of elementary unit

--ONO, 1'76 1'58

1 '40 1 '40 1"30 1'20 1"20

1"10 0"90 0"45 0'20

CHACO-0'12 0'32 0"50 0"54 0"91 0'90 1"10 1'10 1"70

2'25 2'80

OH-1'12 l'10 1'10 1 "06 0"80 0"90 0'70 0"81 0"40 0'30

c o m p l e x e s t e r g r o u p t h e r e is fall i n t h e i n t e n s i t y o f t h e b a n d i n t h e r e g i o n 3 2 0 0 3600 c m 1 c h a r a c t e r i s t i c o f t h e v a l e n c e v i b r a t i o n s o f t h e h y d r o x y l g r o u p s . T h e r e s u l t s o f e l e m e n t a l a n a l y s i s o f a n u m b e r o f c e l l u l o s e a c y l n i t r ~ t e s ( T a b l e 2) c o n firms the conclusion drawn. The reactivity of the nitrate groups differing in position in the elementary unit was studied on model compounds in which ~70-100% of nitrate groups w e r e a t t h e a t o m s C-6, C-2, 3 o r C-3. T o e x c l u d e t h e p o s s i b l e p a r t i c i p a t i o n i n t h e reaction of the hydroxyl groups present the latter were first acetylated by the known technique. The model compounds were synthesized fi'om cotton cellulose purified after Corey a n d ~h'ey by the techniques ill references [5, 6]. The nitrate ester was obtained denoted b y us cellulose-6-nitrate in ,~hich 68.6% of the nitrate groups were s t the C-6 atom (nitrogen content 6.000/0) and also cellulose 2,3-dinitrate and eellulose-3-nitrate the number of nitrate groups in which at the secondary carbon atoms was 99.8 and 99-9~o respectively (content of bound nitrogen 11.28 and 7"31% respectively). The hydroxyl groups in the synthesized compounds were protected b y acetylation with a mixture of acetic acid and acetic anhydride in presence of chlorie acid [7], This gave cellulose-2,3-diacetyl-6-nitrate, cellulose-2,6-diacetyl-3-nitrate and cellulose-6-acetyl-2,3-dinitrate with a nitrogen content 3'97, 4.14 a n d 8.85°/0 respectively. The I R spectra of the model compounds were characterized b y distinct absorption bands at I750 and 600 cm -1 belonging to the valence vibrations of the C - - O complex ester bond and the deformation vibrations of the aeetyl groups and also absorption bands a t 1640, 1280 and 840 cm -1 characteristic of the valence vibrations of the nitrate groups: the b a n d 3200-3600 em-* belonging to the valence vibrations of the OH-groups was absent. The content of bound nitrogen in the cellulose tritfitrate used in the work was 13.91~,. The investigation of reactivity were b y the m e t h o d of isomolar series (time interval between adjacent points in the kinetic curve 2-3 rain, total duration of process 60--90 rain). Re-esterification was carried (mr b y the fellowing technique. The test sample was first "loosened" to ensure uniform wetting ,)f the whole mass of the sample. A weighed sample of dried cellulose acctyluitrate or trinitrate was immersed in freshly distilled acetyl

R e a c t i v i t y of f u n c t i o n a l g r o u p s of n i t r a t e esters o f cellulose

2147

c h l o r i d e ix, a p e a r - s h a p e d flask f i t t e d o n t o a s h a k e r . T h e flask was t h e r n m s t a t t e d a t t h e fixed t e m p e r a t u r e w i t h a c t i v e a g i t a t i o n of t h e r e a g e n t s for 10 15 rain. T h e n t h e a n h y d r o u s SnCI4 s a l t w a s i n t r o d u c e d (1 m o l e p e r n i t r a t e g r o u p ) first dissolved i n a p o r t i o n o f a e e t y l c h l o r i d e . M o d u l u s 1 : 40. A t t h e e n d o f a fixed t i m e t o t h e flask h e x a n e was a d d e d t o d i l u t e t h e r e a c t i o n m e d i u m a n d irdaibit t h e process. T h e p r o d u c t was s e p a r a t e d f r o m t h e e s t e r i f y i n g m i x t u r e i n a S e h o t t filter a n d s u c c e s s i v e l y w a s h e d w i t h h e x a n e , e t h a n o l a n d w a t e r to a neg a t i v e r e a c t i o n for t h e c o n t e n t o f c h l o r i n e io~m i n t h e f i l t r a t e a n d to a n e u t r a l r e a c t i o n of t h e m e d i u m a n d d r i e d a t r e d u c e d p r e s s u r e o v e r P20~ a n d o v e r c a l c i u m chloride. T h e p r o d u c t s were a n a l y s e d for t h e c o n t e n t o f b o u n d n i t r o g e n b y t h e D u m a s m e t h o d . T h e n u m b e r of n i t r a t e g r o u p s a t t h e C-6 a t o m was d e t e r m i n e d b y i o d i n a t i o n [8] a n d t h e n u m b e r o f n i t r a t e g r o u p i n g s a t t h e s e c o n d c a r b o n a t o m by s a p o n i f i c a t i o n w i t h h y d r o x y l a m i n e [9]. T h e c o n t e n t of a c e t y l g r o u p s i n t h e esters w i t h a low c o n t e n t of b o u n d n i t r o g e n was d e t e r m i n e d b y a l k a l i n e s a p o n i f i c a t i o n [10] a n d also e l e m e n t a l analysis. T h e II-I s p e c t r a of t h e c o m p o u n d s were r e c o r d e d w i t h t h e U R - 2 0 s p e e t r o p h o t o m e t e r . T h e r e a c t i o n r a t e c o n s t a n t s were c a l c u l a t e d f r o m t h e e q u a t i o n fi)r first o r d e r r a c t i o n s u s i n g t h e d a t a o n t h e c o n t e n t o f r e s i d u a l n i t r o g e n in t h e d e r i v a t i v e s o b t a i n e d . TABLE 3. t~ATE CONSTANTS AND ACTIVATION PARAMETERS OF REACTION OF DENITRATION OF CELLULOSE ACETYLNITRATES IN I~RESENCI~I O:P SnCl 4 /c × l03, see ~1

Celhflose e s t e r s t u d i e d

2,3-Diacetyl-6-nitrate 6-Acetyl-2,3-dinitrate 2,6-Diacetyl-3-nitrate

20°C

30°C

40°C

2.63 0.19 0'06

5.14 0.38 0.20

9.42 0.74 0.62

Activation Activation energy, entropy, J/mole J / m o l e . °C • 48-5 51.9 89-9

136.8 146-8 27.6

The course of the kinetic curves (Fig. 3) indicates that the primary and secondary nitrate groups differ in their reactivity: denitration of the samples cellulose 2,3-diacetyl-6-nitrate occurred at a rate far exceeding the substitution of the secondary nitrate groups; an appreciable difference is also observed in the reactivity of the latter, which does not conflict with the known data Ill, 12] and suggests that the O51"O2groups are more reactive at. the C-2 atom than the groups at the C-3 atom of the elementary units of the maeromolecule. The quantR.ative evaluation of the denitration of the cellulose nitrates is given in Table 3 noting that the effective rates of denitration of the primary and secondary nitrate groups differ almost b y an order of 1.5. From comparison of the values of activation of reesterifieation of model compounds it follows that the temperature factor has a much more profound influence on the reactivity of the nitrate groups at the C-3 atom than is the case for the C-2 and C-6 atoms, which are subject to the temperature influence practically to the same degree. Moreover, the difference in the reactivity of the nitrate groups at the C-2 and C-3 atoms with rise in temperature, in fact, disappears and reesterifleation proceeds almost at, the same rate. The sign and the value of the activation entropy according to the theory of the transitional state indicates that reesterifieation proceeds by an associative mech--

2148

lZ. I. SAI~¥BAX'EV)~and L. S. S~el~ELOK~OVA

anism, the formation of the new C - - O --C bond instead of the C - O - N present m a y be explained not only b y the weakening of the O --~T bond as a result of the possible coordination interaction of the oxygen atom with the central atom of the Lewis acid b u t also b y the high reactivity of the complex formed [CH3CO+.SnCl~]. The influence of the catalyst on the kinetic parameters of the reaction is not in doubt since in its absence denitration practically does not occur and rise in the concentration of this complex promotes acceleration of the reaction (Table 4), the maximum effect being observed for cellulose, 2,6-diacetyl-3nitrate. In addition, as shown above, in presence of Lewis acids there is also esterification of the OH-groups, which does not occur if in carrying out the reaction protonic acids ~re used as catalysts. In b ~-X

1.01

O.E 2

o

0"2 O

I

3

6

9

Time ~, lO'Z~eo

12

~Ia. 3. Kinetics of reesberification of 2,3-diaeetyl-6-nitrate (1), 6-acetyl-2,3-dillitrate (2) and 2,6-diaeetyl-3-nitrate (3) of cellulose by CH3COCI in coordinates corresponding to the equation of first order reactions, b - - I n i t i a l concentration of bound nitroge aud (b--x) its currant concen~at~ion, e/o.

Mathematical treatment of the experimental data of acylation of cellulose lritrates in presence of different concentrations of Lewis acids (from 0.01 to 12 moles per elementary unit) enabled us to identify the exponential character of the dependence of the content of residual nitrogen in the mixed acylnitrate on the concentration of acid used. In general form for the series of acids the equation has the form [N] = a exp (--b [MXn]), where [~N~] is the content of bound nitrogen in the acylnitrates, %; [MXn] is the concentration of the Lewis acid; a and b are empirical contents for each acid calculated t)y the method of legist squares. Since denitratio,~ is fastest at, the C-6 atom the reaction by these groups is omcpleted first and the results of iodination of the samples with a nitrogen con-

2149

1Reactivity o f flmetiona.1 g r o u p s o f n i t r a t e esters o f celluloso T A B L E 4. EFtTCT OF CONCI,:,~T.R, A T I O N

OF

SIICI~ ON RATE OF SUBSTI-

TUTIO~N" OF N I T R A T E GROUPS AT 2 0 ° C

Celhdosc e s t e r 2, 3 -Diacetyl- 6 - n i t r a t e 6-Acetyl-2,3-dinitrate 2,6 -Diacetyl- 3- n i t r a t e

k x 103 s e e -1 kl* k,¢

k,/kl

2.63 0.19 0. O6

2.26 2"74 4"36

5.94

0.52 0.26

* ('oncentration of' catalyst 1 mole. "t 8 moles.

TABLE

5. ]:~ESULTS OF ANALYSIS OF T H E PRODUCTS OF

INTERACTIO:N OF CELLULOSE T R I N I T R A T E * V¢ITIt CI~-~3COCl IN PRESENOE OF SDCI t

Percentage i P e r c e n t a g e iodine I N i t r o g e n c o n t e n t content after nitrogen content after hydroxyl of sample iodination amine treatment 12.88 8.67 6.53 6.29

24.2 3.3 Not ~mld

10.33 7.54 4.99 4-32

* h)dine content in iodinatitm product of cellulose trinitrate 3 P6 %.

tent of less than 7% clearly confirm this conclusion (Table 5). Then the reaction by the nitrate groups at the C-2 atom terminates; reesterification over C-3 ends last. The series-parallel character of the reaction may be schematically represented as follows: CH20NO2

x

Clt20Ac

O ONO2

---~

CH2OAc

~ ONO 2

CH2OA¢

O,,, OAc

0A¢

where Ae is tile acetyl group. This may evidently explain wily the kinetics of denitration of cellulose trinitrate cannot be expressed by a straight line and has an inflexion point (Fig. 4). The results of thin layer and paper chromatography of the products of total hydrolysis of the saponified mixed acylnitrates revealed 11o other, apart from glucose, monosaccharide. This suggests that during reesterification of the cellulose nitrates there is no inversion of the configuration of the secondary carbon atoms of the macromolecu]e with formation of mixed polysaccharides. (!omparison of the kinetics of reesterification of cellulose trilfitrate and dinitrate with the initially acetylated hydroxyl groups (Fig. 5) discloses a slight dif-

R. I. SARYBAYEVAand L. S. SHOHELOKHOYA

2150

ference in the rates in the initial period of the reaction which we are inclined to explain by structural hindrances namely the considerable rigidity of the cellulose trinitrate maeromolecules. 2, I'#0

0.6 i

i

5

15

I

I

0

30 ~,~ Time f ~lO~Zsec

I

I

/5

30

Time ~rain

Fro. 4

FIG. 5

Ft(~. 4. Kinetics of the interaction of eelhdose triniLratc ([N]=13.91o/o) with CHaCOC1 at 20°C in coordinates of the equation of a first order reaction. FIG. 5. Kinetics of the reesterification of cellulose trinitrate ([N])= 13.91%) (1) and nitrate ([N]=10.86%) (2) by aeetyl chloride at 20°C ([SnC14]=l mole).

Thus, kinetic analysis of the reaction and also the results on the elemental composition of t h e p r o d u c t s of i n t e r a c t i o n of the cellulose n i t r a t e s w i t h a c e t y l ehloride in presence of Lewis acids help to establish t h e relative r e a c t i v i t y o f t h e p r i m a r y a n d s e c o n d a r y n i t r a t e groups a n d also t h e free h y d r o x y l groups p r e s e n t in t h e cellulose n i t r a t e s which diminishes in t h e series --

0(6)-- NO~ > --O(~)NO~ > -- OH >i 0(3)-- NO 2

T h e kinetic p a t t e r n s established a n d the a c t i v a t i o n p a r a m e t e r s allow t h e process t o b e r u n in a t a r g e t t e d fashion a n d the reaction for o b t a i n i n g m i x e d cellulose a e y l n i t r a t e s to be e n d e d a t a definite point.

'REFERENCES

1. S, N. USHAKOV, Efiry tseilyulozy i plastietmskiye massy na ikh osnove (Cellulose Esters and Plastics Based on Them). p. 289, Goskhimizdat, Moscow-Leningrad, 1941 2. S. N. DANILOV, M. A. SOKOLOVSKII and A. I. YEVDOKIMOVA, Zh. obsh. khim. 17: 1 8 8 8 , 1947 3. R. I. SARYBAYEVA, L. S. SHCHELOICJ~IOVAand V. A. AFANAS'YEV, I. Vscs. konL po ldlim, i fiz. tsellyulozy. I. Khimiya (Ist All-Union Conference on the Chemistry and Physics of Cclhdose. I. Chemistry). p. 125, Zanatiyc, Riga, 1975 4. R. I. SARYBAYEVA and L. S. SIICHELOKHOVA, U.S.S.R. Pat. 883058, Byul., izobret., 43, 1981; IY,S.S.R. Pat. 523109, Byul. izobret., 28, 1976

Synthesis of altcrnating and random copolymers of ethylene with MA

2151

5. A. V. OBOLENSKAYA, V. P. StICtIEGOLEV, E. L. AKIM, N. L. KOSOVICH a n d L Z. YEMEL'YANOVA, Praktich. raboty po khimii drevesiny i tsellyulozy (Practical Work on Wood and Cellulose Chemistry). p. 365, Lesn. promyshlennost', 1965 6. Z. I. KUZNETSOVA and V. S. IVANOVA, Vysok(),nol. soyed. A9: 1930, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 9, 2177, 1967) 7. A. I. POLYAKOV and L. N. SPIRIDONOVA, Izv. Akad. Nauk SSSR, Oral. khim. n., 7, 1562, 1969 8. G. E. MURREY and C. B. PURVES, Caned. J. Chem. 62: 3194, 1940 9. G. H. SEGALL and C, B. PURVES, Canad. J. Chem. 30: 860, 1952 10. L.J. TANGHE, L. B. GENUNG and J. W. MEZCH, In: Whistler. Methods in Carbohydrate Chemistry, Acad. Press, N . Y . - L , 1963 l l . E. J. ROBERTS a n d S. P. ROWLANDS, Carbohydr. Res. 5: 1, 1967 12. C. P. WADE, E. J. ROBERTS and S. P. ROWLAND, J. Polymer Sei. B6: 673, 1968

Pvlymcr Science U.S.S.R. Vol.25, No. 9, I'P. 2151-2160,1963 Printed i n Poland

003'2-395(;/83$10.00+.00 © 1984PergamonPress Ltd,

SYNTHESIS OF ALTERNATING A N D R A N D O M COPOLYMERS OF ETHYLENE W I T H MALEIC A N H Y D R I D E * I¢. A. TEIeTERYAN a n d V. S. KHICAPOV All-Union Petroleum Processing Research Institute

(Received 4 March 1982) The radical copolymerization of ethylene with maleic aifl~ydride has been investigated over a wide range of pressure (10-150 MPa), temperature (70-235 °) a n d comonomer concentrations (0.1-60 mole ~o) in the presence of various solvents a n d initiators. Olfly albernating copolymers are formed at 150 °, irrespective of the initial ratio of monomers and pressure, a n d irrespective of the medium. Above 200 ° random copolymers containing 0.4-13 mole°~ anhydride units are formed. The relative reactivity of ethylene in the random copolymerizatiou was equal to 0'0454-0.019. The dependence of t.he rate of formation of alternating copolymers on the maleic anhydride concentration was expressed b y an extremal type of relationship, a maxim m n being obtained at an equimolar ratio of monomers. I t was found t h a t the rate and degree of eopolymerization depend on pressure and temperature, on the polarity of the solvent, and on the initiator concentration.

JNVESTIGATORS have long been investigating the radical copolymerization of various monomers with mMeic anhydride (MA). This is because MA, being a difficultly polymerizable monomer, enters readily into copolymerization reactions * Vysokomo]. soyed. A25: :No. 9, 1850-1857, 1983,