CC BY
15
UDC 542.9:547.21
N. Chkhubianishvili, L. Kristesashvili, G. E. Zaikov
INVESTIGATION OF REACTION OF TELOMERIZATION OF ETHYLENE AND TRICHLORACETIC ACID ETHYL ESTER Keywords: reaction, telomerization, ethylene, trichloracetic acid, ethyl ester, mechanism, reactivity.
The reaction of telomerization of ethylene and trichloracetic acid ethyl ester have been investigated. In order to study this reaction, a series of autoclave experiments were conducted. Samples were analyzed on air-liquid chromatograph, on heat-conducting detector. Besides chromatographic analysis, identity of telomers was established by boiling temperature, density, refraction, infra-red spectroscopy and element analysis.
Ключевые слова: реакция, теломеризация, этилен, трихлоруксусная кислота, этиловый эфир, механизм, реакционная
способность.
Исследованы реакции теломеризации этилена и этилового эфира трихлоруксусной кислоты. С целью изучения этой реакции проведены серии экспериментов в автоклаве. Образцы анализировали на газо-жидкостном хроматографе и приборе для определения теплопроводности. Кроме хроматографического анализа использовались методы инфракрасной спектроскопии и элементного анализа, идентификация теломеров проведена по температуре кипения, плотности, показателю преломления.
Introduction
The interest towards radical telomerization is caused by the fact that it enables to obtain comparably low-molecular long-chain organic substances with various functional groups that are hard to obtain with ordinary methods and that can be widely applied in practice. The reaction of telomerization of ethylene and trichloracetic acid ethyl ester [1] is especially interesting. The reaction proceeds in the precense of initiator in the following way: nCH2 = CH2 +CCl3COOEt ^ Cl (CH2CH2)nCCl2COOEt. Telomers, received from ethylene and trichloracetic acid esters, are utilized to obtain the psychotropic drug Gamalon, e-Capron (e-hexanoic acid) and biological active substances Lysin and methion.
Experimental
Telomerization of Ethylene and Trichlororoacetic
acid
In order to study this reaction, a series of autoclave experiments were conducted: we had an experiment with the equipment which is presented on Figure 1. It was a 200cm3 volume stainless steel autoclave (1) which was equipped with electromagnetic stirrer (2) and a pocket of thermocouple. We added solution of initiator to telogen. During each experiment 103.5gr (75ml) trichloracetic acid ethyl ester was loaded into the autoclave under the conditions of high pressure and closed valves (4, 5, 11). The autoclave was cooled at up to -20-250C and the vacuum in the system was created through the valve (6) connected to a vacuum line. The residual pressure was 5-10mmHg. Then we closed the valve (6), opened valves (4, 11) and delivered ethylene to evacuate air. Ethylene was delivered from the balloon (7). The autoclave was warmed up to room temperature, electromagnetic stirrer was turned on and telogen was saturated with ethylene to defined pressure of manometer (9). Once pressure decay was stopped, the autoclave was placed into the thermostat (8) and heated to the reaction temperature. Liquid silicone was used as a heat transmitter. The stirring in the autoclave
was done with nitrogen sparging. The temperature was regulated via contact thermometer connected to the network through electromagnetic switch. The control over telomerization was implemented according to the pressure decay on the manometer (9). The reaction was conducted until the drop of ethylene pressure was finished. Calculation of the amount of ethylene loaded into the autoclave was determined by ethylene amounts reacted (based on the data of telomers composition) and returned after the reaction or by solubility of ethylene.
Fig. 1 - The scheme of the equipment to carry out the reaction of telomerization in the intermittently operational autoclave
For security reasons, the equipment was outfitted with blasting plate (10) designed for 200 atmosphere pressure and emergency valve (11).
After finishing the reaction, autoclave was cooled down to room temperature. Throttling of non-reacted ethylene was done in fixer (12). It was cooled down to -15-200C in Dewar vessel and was collected in gasometer (14). The fixer was installed to hold the reaction mass taken away during throttling. After throttling of air, reaction products were removed, non-reacted initial ester was removed by distillation and the mix of telomeres was distilled on the rectifying column of 7-10 theoretical plate effectiveness.
Samples were analyzed on air-liquid chromatograph, on heat-conducting detector.
35 20 to i>
т, horns
Fig. 2 - Chromatogram of telomer mix 1 - nt; 2 - n2; 3 - ns; 4 - n4
It was established that the product chromatogram had 4 peaks (see Figure 2):
1 - corresponded to telomer n1; 1,1,3-thrichlorerbor acid ethyl ester;
2 - corresponded to telomer n2, 1,1,5-thrichlorcapron acid ethyl ester;
3 - corresponded to telomer n3, 1,1,7-thrichlorcapril acid ethyl ester;
4 - corresponded to telomer n4, high molecule esther.
Besides chromatographic analysis, identity of telomers was established by boiling temperature, density, refraction, infra-red spectroscopy and element analysis.
Result and Discussions
Thermodynamics of the Reaction of Telomerization of Ethylene and Trichloracetic Acid Ethyl Ester
The telomerization reaction is an exothermic process. The approximate estimation of thermal effect of the reaction is possible through the energy of chemical bonds. The total thermal effect of telomerization reactions is mostly determined by the energies of breaking double C=C bonds and generation of single c-c bonds.
There is no data available in the literature about thermodynamic characteristics of the reaction of telomerization of ethylene and trichloracetic acid ethyl ester. That was why we estimated standard thermal effect of the reaction, coefficients of heat capacity equation cp = ^(T), and entropy for initial and final products of the reaction based on molecular structure with group revision method [2]. Results are reported in Table 1. Figure 3 shows dependence of AF and Lg Kp values on temperature. Approximate values of temperature allowing the reaction to be conducted thermodynamically are determined graphically.
As long as the reaction of telomerization takes place in liquid but not in air phase, calculations of thermal effects of reaction should take into account heat of phase transition - heat of condensation of trichloracetic acid ethyl ester and telomers, and heat of
dilution of ethylene into the telogen. The heat of dilution of telomers in telogens can be ignored. Combination of reaction equation and phase transformation equation leads to the following:
1. For 1,1,3 - trichlor butyric acid ethyl ester (telomer n1):
AHC(5 _AHC6 ~AHtei0g.dUut. + AHtelog.evapor.
~^^c6evapor.
2. For 1,1,5 - trichlor hexanoic acid ethyl ester: AHCg = AHCg — 2AHester.diiut.
+ AHteiofi(.
evapor.
AH,
cBevapor.
3. For 1,1,7 - trichlor hexyl acetic acid ethyl ester
AHCio =AHCiq — 3AHesterdaut. +
AHtelog.evapor. ~ AHc10evapor.
\gKJ
kK) 200 >41 TOO MHI
VK
Fig. 3 - The dependence of equilibrium constant logarithm and AF isobaric potential on temperature for A, B, C telomerization reactions
Table 1 - Standard thermal effects and entropy increment of reactions
# Reaction AH298 kcal/ mol AS298 kcal/ mol
A CCl3COOC2H5+ C2H4 ^ Cl(CH2CH2)CCl2COOC2H5 -27.7 -31.1
B CCl3COOC2H5+2C2H4 ^ CKCH2CH2hCChCOOC2H5 -50.8 -65.5
C CCl3COOC2H5+3C2H4 ^ Cl(CH2CH2)3CCl2COOC2H5 -73.9 -100.1
The heat of evaporation of trichloracetic acid and telomers is calculated with respective empirical
formula through extrapolation of boiling temperature data:
AHevapor = (8.75 + 4.575 lg7"boil.)*Tboil.
On Figure 3, the heat of ethylene dilution in trichloracetic acid ethyl ester is ~ 3.5kcal/mol=14.5kj/mol.
ДЯс6 = 27.7 + 3.5 + 9.5 - 10.5 = 30.2 kcal/mol = 126.5 kj/mol
AHçs = 50.8 + 23.5 + 9.5 - 11.4 = 55.9 kcal/mol = 234.2 kj/mol
ДЯ; = 73.9 + 3.35 + 9.5 - 11.9
c10
= 82.0 kcal/mol = 343.6 kj/mol
The data shows that thermal effect of these reactions in liquid phase is slightly different from that in air phase. Therefore, thermal effect of telomerization of ethylene and trichloracetic acid ethyl ester is on average 28.5 kcal (119.3 kj/mol) on 1 mol ethylene which is close to polymerization heat of ethylene (30 kcal/mol).
Solubility of Ethylene in Trichloracetic Acid Ethyl Ester
To study kinetics of telomerization reactions the condition of air and liquid phases is of big importance as it determines liquid and air phase composition, dependence of reaction speed on components' concentration.
The solubility of ethylene was studied on special equipment (Figure 4).
Fig. 4 - The scheme of the equipment to study ethylene solubility
Creation of vacuum in the equipment was done under the condition of opened valves of both systems. We closed valves (10) and (7) and loaded trichloracetic acid ethyl ester into the autoclave. The thermostat of the autoclave was cooled down to -15 ^20°C. Then we opened valve (7) and created vacuum in the system. Subsequently we closed the vacuum line and supplied the systems with ethylene. Required temperature was reached in both thermostats and the stirrer was turned
on. We turned the equipment off from ethylene delivery line and observed the termination of the saturation of trichloracetic acid ethyl ester with ethylene by ending the pressure decay. After that, we closed the stirrer, opened the valve (10) and the systems remained under similar temperature during one hour. Then the valves (7-10) were closed and the second system was separated from the first. The solubility of ethylene was studied under different pressure and temperature.
Air solubility depends on the nature of air and solvent, temperature and pressure. The association between air solubility and partial pressure is expressed by Henry's Law:
=kP2,
Where N2 - is a molar fraction of liquid soluble air; P2 - partial pressure of a given air above solution; k -Henry's law constant (atmospheric/molar fraction).
Ethylene solubility under different pressure and temperature is shown on Figure 5. The figure shows that ethylene solubility is directly proportional to ethylene pressure and responds to Henry's law. Out of experimental data, we calculated Henry's law constant at 25, 90, 100, 1200C and it was respectively 0.428, 1.195, 1,395 and 1. 725.
2 - 1000C; 3 - 900C; 4 - 250C
Based on these data we found the heat of ethylene dilution in trichloracetic acid ethyl ester. For this reason, we designed the curve representing association between logarithm of Henry's law constant and inverse of absolute temperature. This association is shown on Figure 6, which is drawn as a straight line and tangent of its angle is a thermal heat of ethylene.
The diagram and Arrhenius equation help determine ethylene dilution heat, which is approximately 3.5kcal/mol.
Figure 7 shows the dependence of molar volumes of studied solutions on pressure and temperature. It is clear that the change of molar volumes of solutions is directly proportional to pressure in the area of temperature and pressure of the research interest.
2,5 2,6 2,7 2,8 h p in-1 Fig. 6 - Dependence of logarithm of Henry's law constant on inverse of absolute temperature in the system - ethylene trichloracetic acid ester
F.atm
solution on pressure at 25, 90, and 1000C temperature
The goal of conducted series of autoclave experiments of telomerization of Ethylene and trichloracetic ethyl ester was to study the following issues:
1. Effect of temperature on the yield and composition of telomers.
2. Effect of concentration of initiator on the yield and composition of telomers.
3. Effect of mixture of initial reagents on the composition of telomers.
Effect of Temperature
One of the important factors for telomerization reactions is reaction temperature. It determines the velocity of dissociation of the initiator and reaction potential of reacting components and affects the chain transmission constants. The effect of temperature on ethylene conversion was studied under the condition of loading equal quantities of reagents. Figure 8 depicts the dependence of ethylene conversion on temperature.
The highest conversion of ethylene is achieved at 1000C (12.3mol%). Conversion is reduced through decreased temperature, which can be attributable to incomplete dissociation of initiator. Temperature increase above 1000C apparently considerably raises the recombination velocity of initiator's free radicals.
Figure 9 describes the dependence of pressure decay on time at various temperatures. As far as velocity of telomerization reaction is limited by the velocity of dissociation of initiator, the data of pressure decay can be used to determine the velocity of telomerization. As shown on Figure 9, the duration of reaction at 700C is 10.5 hours, while the reactions at 100 and 1200C end in ~ 4.5 and 1.5 hours, respectively.
Fig. 8 - Dependency of ethylene conversion on temperature
Fig. 9 - Pressure drop dependence on time at various temperatures
Effect of Initiator
According to kinetic equation of telomerization, the velocity of telomer yield is proportional to initiator concentration in power / (for squared discontinuity and disproportionation) or 1 (for allylic discontinuity). The study of effect of quantity of initiator on telomer compositions and yields was conducted in the following telogen concentration intervals - BP(Benzoyl Peroxide) 11-10-3 - 82-10-3 mol/liter and AIBN (azo-bis-izobutironitrile) 24-10-3 -163-10-3 mol/liter.
As we see from Figure10, with the increase of concentrations of initiators BP and AIBN up to some limit, the linear dependence between telomer yield and square root of initiator concentration takes place. It is found that the linear dependence takes place up to 27.5-10-3mol/liter for BP and up to 121.9-10-3 mol/liter for AIBN. Above these concentrations, linear dependence is no longer in place.
Based on Figure 11, for BP with average concentration of 27.5T0-3mol/liter telomers are received with ~49 mol yield and for AIBN with similar concentration telomers are received with ~18 mol yield per mole of initiator. Therefore, BP is 2.7 times as effective as AIBN. Thus, the length of kinetic chain for BP is ~100 and for AIBN it is ~40. Derived from experimental data, chain transmission constants are calculated at 1000C: d=94-10-3± 12.6-10-3; c2=1.76± 0.24; c3=3.26±0.42.
telomer yield %
40
1
30 * ~ *
s 2
20,. / * " /
io- /
0 2 4 6 8 10 v'7
Fig. 10 - Effect of initiator on telomer yields 1 -Benzoyl peroxide t=1200c, t =2.5 hours, 2 - AIBN t=1000c, t =1.5 hours
2 4 6 8 10 (/]-1,J(:moi/i;i-u
Fig. 11 - Effectiveness of initiator: 1 - Benzoyl peroxide, t=1200c, t =2.5 hours, 2 - AIBN, t=1000c, t =1.5 hours
Effect of Ethylene Molar Concentration on the Composition of Telomers
Fig. 12. describes the dependence of telomer composition change on molar composition of ethylene in the mixture at 1000C.
As we see from the diagram, when ethylene concentration goes to zero in the original mixture, telomer n1 composition reaches 100%. In case of significant increase of ethylene concentration in initial mixture, the quantity of lower order telomers approaches zero and upper order telomers (n>3) will be the major products of telomerization reaction.
The curves n=2 and n=3 have maximums. Therefore, the adequate composition of ethylene in the mixture to receive n=2 (70 weight %) is 45mol % and to receive telomer n=3 (33 weight %) is 80 mol %.
I
j 80 ■a
H
60 40 20
0 20 40 60 80 CiHi moL°/o Fig. 12 - I - telomer n=l; II - Telomer n=2; III -telomer n=3
According to the data from this study, it is recommended to conduct telomerization reaction of ethylene and trichloracetic acid ethyl ester under the following conditions:
- Initiator---------------BP (0.5 mol/l telogen)
- Telogen/Oliphin ratio-----------1:0.8
- Temperature-----------------1000C
- Reaction time----------------1 hour.
References
1. Thermodynamics of telomerization reaction of ethylene and trichloracetic acid ethyl. Georgian Chemical Journal, 9, #2, 130-132, 2009 (in Georgian)
2. Karapetyants M.Kh. Chemical thermodynamics, edition 4, 2013, 584 c. ISBN 987-5-397-03700-6. (in Russian)
3. Chkhubianishvili N., Kristesashvili L. Study of ethylene dilution in trichloracetic acid ethyl ester. The works of Georgian Technical University. #6 (445), 58-60. 2002 (in Georgian).
© N. Chkhubianishvili - Doctor of Chemistry, Full Professor, Georgian Technical University, Tbilisi, Georgia, E.mail: rusikoch@yahoo.com, L. Kristesashvili - Georgian Technical University, Tbilisi, Georgia, G. E. Zaikov - Doctor of Chemistry, Full Professor, Plastics Technology Department, Kazan National Research Technological University, Kazan, Russia.
© Н. Чхубианишвили - доктор химических наук, профессор, Грузинский технический университет, Тбилиси, Грузия, E.mail: rusikoch@yahoo.com, Л. Кристесашвили - Грузинский технический университет, Тбилиси, Грузия, Г. Е. Заиков - доктор химических наук, профессор, каф. технологии пластических масс, Казанский национальный исследовательский технологический университет, Казань, Россия.
