Reaction of trimesic acid trichloride with glycols in solution

REACTION OF TRIMESIC ACID TRICHLORIDE WITH GLYCOLS IN SOLUTION* V. V. KORSHa~, YU. A. CHERNO~IORDIK and I. D. KIsxr~ovx Organomotallics Institute, U.S.S.R. Academy of Sciences D. I. Mendoleyev Institute of Chemical Technology, Moscow (Received 6 December 1965)

A SERIES of papers dealing with the clarification of the effects of the structure of monohydric alcohols and dicarboxylic acids on their mutual reactivity has appeared in the literature [1-3]. These established the influence of primary and secondary hydroxyl groups present in monohydric alcohols, and of the length of the methylene chain in diearboxylie acids on polycondensation kinetics. The aim of the work reported here was to study the effect of the structure and length of the glycol on its reactivity during polycondensation with a monobasic acid chloride, the effect of the initial component ratio and of the temperature on the reaction rate. We thought it desirable to determine the possibility of using the results of kinetic measurements to control the process of branched polyester production. We investigated the polycondensation kinetics of trimesie acid trichloride (TMTC) with glycols having different molecular weights (m.w.) and structures. The polycondensation was carried out in ditoluylmethane with an equivalent ratio of the starting components (3 moles glycol per 2 moles TMTC). The absence of water from the glycols and the solvent was established by a Fischer titration. The progress of the reaction was checked by determining the hydrogen chloride produced during polycondensation. The rate constants of polycondensation were calculated by using first-, second- and third-order equations; this showed t h a t constancy of values was preserved only when the rate constants were calculated on the basis of a secondorder reaction. The experimental points on the diagram (Fig. 1), in which 1/(a--x) was plotted against time (in which x-----amount of HC1 liberated up to the moment of reaction, a----amount of HC1 expected to be liberated on 100% reaction), showed the points to fall on a straight line [4]. The second order of the reaction was also established by calculating the experimental results by the Van't Hoff method. The rate constants of the reaction were determined at 120°C using TMTC with various hydroxyethylene glycols. I n , t h e reaction with diethylene glycol k--~ 10.89 X 10 -41.. mole -1- see -x, with triethylene glycol k-= 10.72 X 10 -41.. mole -1. * Vysokomol. soyod. Ag: No. 1, 195-199, 1967. 212

Reaction of trimesic acid trichloride with glycols

213

sec -1, the polyethylene glycol of m.w. 1550, had k = 10.96 × 10 -41.. mole -1. sec -1 and that with m . w . = 1 0 0 0 had k=10-89 × 10 -¢ 1..mole-l'sec -~. One can see that ethylene glycols with the same structure b u t different m.w. had the same rate constants for reaction with TMTC. •

1 x 4G- ~ 2 I

I

80

I

120 T/me, min

180

FIG. 1. 1~(a--x) as a function of the duration of polycondensation at 120°C; 1--with

polytetrahydrofuran (m.w. 1360), 2--with PEG (m.w. 1000), 3--polypropylene glycol (m.w. 1700), 4--with ethylene glycol. The rate constant was much smaller in the case of ethylene glycol (Fig. 1; k = 1.24 X 10 -41..mole -1. sec -1) than with hydroxyethylene glycols. The presence of the ester oxygen bond in the main hydroxyethylene glycol chain appears to affect the reaction rate. The reaction of ethylene glycol with TMTC was more rapid in the polar solvent diglyme (CHaOCH2CH~OCH~) , than in ditoluylmethane (k=7.73X X 10 -41..mole-l.sec-1). The reaction of ethylene glycol with TMTC can be schematized as follows:

r-~ g-N

t~ ~_

H---Q--R--O----H H--O--R--O~--H - - . .

OI (1) -

_

(m

IO--R--O--H

_

IQI e

0 (m}

in which R is CH~CH2, R I = C e H 3. The TMTC molecules contain strongly negatively charged chlorine atoms. This makes the nueleophilic attack on the carbonyl group easier. The negative charge on the substituent, i.e. chlorine, dissociates together with the electron pair of the bond b y an anionic t y p e mechanism and leaves the reaction sphere on reacting with the proton. The dissociation becomes possible as a result of the transition of the undivided electron pair which moves due to the primary attack [5]. The polar solvent solvates the dipolar complex (II), intensifies its polarization and makes the chlorine liberation easier [6].

V. V. KORSKAK et al.

214

Where TMTC is reacted with hydroxyethylene glycols in a non-polar solvent such as ditoluylmethane, internal solvation appears to take place. The reaction rate constant was smaller with butylene-2,3-glycol (k=0.89X X 10 -41..mole-l.sec -1) than with ethylene glycol, and also smaller with polypropylene glycol of m.w. 1700 (k~--2.09 × 10 -a 1..mole-l.sec -1) than with polyethylene glycol (Fig. 1). In this reaction in this case a second OH group is introduced. The presence of the edge methyl group gave a shielding effect making it difficult for the interaction of functional groups. The increase in the amount of methyl groups in the elementary links of the hydroxy glycol helps to increase the rate of the polyeondensation. The reaction rate was thus greater with polytetrahydrofuran of m.w. 1360 (k-~ 19.17 × 10 -a 1.. •mole-l.sec -~) than with polyethylene glycol (PEG). The reaction rate is influenced b y the ratio of starting components. An excess of glycol will increase the reaction rate, or it will decrease when TMTC is used in excess (Table 1). The low viscosity of a reaction product from PEG* (m.w. 100O) and polytetrahydrofuran (m.w. 1360) will increase in proportion to the amount of TMTC used. TABLE 1. REDUCED VISCOSITY OF THE POLYCONDElqSATION PRODUCTS R e a c t i o n of T M T C a t 120°C w i t h Glycol : T M T C

P E G (m.w. 1000)

p o l y - T H F (m.w. 1360)

molar ratio

time, min

reaction eric., %

t/red, dl/g

time, min

3:3 3:2.5 3:2 3:1.5 3:1

330 240 150 120 85

58"06 58"22 58"10 58"44 58'04

0-1370 0-1348 0"1320 0"0964 0"0918

10 45 00 85 60

reaction erie.,%

t/red, dl/g

59'62 59"86 58"42 60"30 59-79

0"1980 0"1940 0"1920 0"1616 0"1360

* 0"5% Dioxane solution.

A series of experiments was carried out to determine the effect of the reaction between 80 and 140°C on the rate of polycondensation. The rate constants, obtained on the basis of the experimental data, increased with increasing temperature of polycondensation. The plot of the logarithm of the reaction rate constant against the inverse value of absolute temperature was a straight line (Fig. 2). The results of the temperature dependence of the rate constant were processed mathematically (Table 2) b y the method of least squares and were then used to determine the activation energy. The efficiency of the polycondensation was determined as a function of temperature and reaction time (Fig. 3). The latter function gave curves with * Polyethylenoglycol.

Reaction of trimosio acid trichlorido with glycols

215

a slope which d e c r e a s e d w i t h increasing d u r a t i o n of t h e p o l y c o n d e n s a t i o n , i.e. corr e s p o n d i n g t o a decrease o f t h e r a t e a t which efficiency i m p r o v e d t o a p p r o a c h t h e gel p o i n t [7]. This a p p e a r s to be due to t h e decrease o f c o n c e n t r a t i o n of r e a c t i v e g r o u p s in t h e r e a c t i o n m e d i u m [8].

10g[K-t0*]

a' !

2 3

t',Y 50

f'O 0"5

02. 2

2"6

t/T " tO$

3"0

0

FIG. 2

I

I

I

/20

200

360

Time,rain FIG. 3

FIG. 2. Rate constant of polycondensation as a function of temperature using TMTC and PEG (m.w. 1000). FIG. 3. Efficiency o£ the polycondonsation of TMTC with PEG (m.w. 1000) as a function of temperature and reaction time: 1--140, 2--120, 3--100, 4--80°C. TABLE

2.

RATE

CONSTANTS

OF T H E

R E A C T I O N OF

TMTC

W I T H GLYCOLS AT

:DIFFERENT

TEMPERATURES

Reaction rate constants, k × 104, 1.mole -1 -sec -1

Glycols

Ethylene glycol PEG (m.w. 1000) Polypropylene glycol (m.w. 1700) Polytetrahydrofuran (m.w. 1360)

Activation energy, cal/mole

80 °

100 °

120°

140°

0"38 3"80

0"68 6"64

1"24 10"89

2"25 20"25

8600 7950

1'04

1"25

2"09

6"01

12,000

5"98

7"37

19"17

22"42

7100

T h e f a c t t h a t t h e process s t o p p e d a t high conversion efficiencies u p t o t h e gel p o i n t a n d t h e resulting p r o d u c t i o n of a b r a n c h e d p o l y e s t e r did not p r e s e n t a n y difficulties in this case. A lower process t e m p e r a t u r e w a s r e p r e s e n t e d b y a less s t e e p slope o f t h e curve, e v e n for t h e initial stage o f t h e reaction. I t is possible to stop t h e r e a c t i o n a t a n y s t a g e b y v a r y i n g t h e t e m p e r a t u r e conditions a n d t h e r e a c t i o n t i m e , a n d t h u s to p r o d u c e p r o d u c t s o f t h e desired quality.

216

V.V.

KoRs~

e~ al.

EXPERIMENTAL TMTC was synthesized b y oxidizing mesitylene with potassium permanganate, followed b y treating the trimosic acid with thionyl chloride b y known methods [9, 10]. The product was purified b y vacuum distillation at 145°C/2 mm. The saponification n u m b e r of the reaction product was found to be 922, 924; theoretical 904. The product melted at 34°C; the literature [10] gives m.p. 34-35°C. The initial glycols were subjected to azeotropie drying with absolute benzene. The m.w. of the glycols were determined b y the Verley method. The polycondensation of P E G (m.w. 1000) with TMTC was carried out in the apparatus illustrated in Fig. 4. A reaction flask with a bubbler for argon, a thermometer and an outlet tube was filled with 6.5 g of P E G dissolved in 60 ml ditoluylmethano and heated to the reaction temperature in a thermostatted chamber. Argon free from oxygen was bubbled t h r o u g h the solution at a rate of 15-20 ml/min. TMTC, 1-1505 g in 40 ml ditoluylmethano, all at reaction temperature, was then added in a single batch. The overall P E G concentration was 0.065 mole/1, that of the acid chloride 0.043 mole/1.

n

~

-

=

4

3

I 2

i

FIG. 4. Apparatus used for the polycondensation and the kinetic measurements: 1--reaction flask, 2--threeway tap, 3--systems of absorber bottles, 4--flow meter. The hydrogen chloride liberated during the reaction was absorbed alternately in two systems of absorber bottles filled with 0.1 N KOH. The alkaline solutions were titrate
CONCLUSIONS (1) T h e k i n e t i c s o f t h e p o l y c o n d e n s a t i o n o f t r i m e s i c a c i d t r i e h ] o r i d e w i t h various glycols were investigated.

(2) I t was f o u n d t h a t the p o l y c o n d e n s a t i o n has a bimolecular mechanism. (3) T h e r e a c t i o n r a t e w a s f o u n d t o b e i n d e p e n d e n t of t h e l e n g t h o f t h e i n i t i a l

Reactivity of hydroxyl end groups

217

h y d r o x y e t h y l e n e glycol molecule, b u t was affected b y t h e s t r u c t u r e o f t h e m a i n glycol chain, the ratio of t h e s t a r t i n g c o m p o n e n t s , a n d t h e process t e m p e r a t u r e . (4) A control of t h e s y n t h e s i s of b r a n c h e d p o l y e s t e r s is possible on t h e basis o f t h e results of kinetic m e a s u r e m e n t s . Translated by K. A. ALLEN REFERENCES

1. N. N. MENSHUTKIN, Zhur. Russ. fiz-khim. Obsh. 9: 316, 1877 2. G. S. PETROV, K. A. ANDRIANOV and P. A. MULYAR, Prom org. khim. 1: 265, 1936 3. P. P. PRICE, J. H. GIBBS and B. H. ZIMM, J. Phys. Chem. 62: 972, 1958 4. T. M. LAURI and S. SEGDEN, Kurs fizicheskoi khimii. (Physical Chemistry Course) Gos. khim. tekh. izdat, O.N.T.I., 231, 1934 5. Zh. MAT'E and A. ALLE, (Printsipy organicheskogo sinteza (Principles of Organic Synthesis) Izdat inostran. Lit. 189, 1962 6. A. Dzh. PARKER, Uspekhi khim. 32: 1282, 1963 7. P. FLORY, J. Am. Chem. Soc. 63: 3090, 1941 8. S. V. VINOGRADOVA, Dissertation, 384, 1959 9. F. ULLMANN and J. B. UZBACHIAN, Bet. 36: 1799, 1903 10. W. RIED and F. J. KONIGSTEIN, Chem. Ber. 92: 2537, 1959

REACTIVITY OF HYDROXYL END GROUPS IN A SERIES OF LOW MOLECULAR WEIGHT POLYESTERS* V. I. VALUYEV, R. A. SHLYAKttTER, N. 1:). APUKHTINA, R . P. TIGER, S. G. EI~TELIS a n d Z. S. KOROL'KOVA S. V. Lobodov All-Union Synthotic Rubbor Rosoarch Instituto (Received 7 December 1965)

THE question of t h e r e a c t i v i t y o f e n d g r o u p s in a h o m o l o g o u s series of condensat i o n p o l y m e r s is still u n d e r discussion a t t h e p r e s e n t t i m e . T h e i n v e s t i g a t i o n s m a d e b y R a u t e r k u s a n d K e r n [1] on p o l y e t h y l e n e glycol oligomers h a d s h o w n t h e r e a c t i o n r a t e s of these p o l y m e r s w i t h p h e n y l i s o c y a n a t e , c a t a l y s e d b y t r i e t h y l a m i n e , to be similar in t h e s t u d i e d series of oligomers. I n t h e case o f t h e r e a c t i o n o f p o l y e t h y l e n e glycol ( P E G ) w i t h n i t r o p h e n y l isoc y a n a t e , h o w e v e r , the a u t h o r s noticed some difference b e t w e e n t h e r a t e c o n s t a n t s w h e n a c a t a l y s t was n o t present. * Vysokomol. soyed. Ag: No. 1, 200-205. 1967.