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AZERBAIJAN CHEMICAL JOURNAL № 2 2022
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 547.2/4; 547.917/.918; 544.4 A STUDY OF THE KINETICS AND MECHANISM OF LIQUID-PHASE OXIDATION OF ETHYLBENZENE IN THE PRESENCE OF COBALT-BASED POLYMER CATALYSTS WITH ACTIVE CENTERS TUNED TO HYDROCARBON SUBSTRATES
R.H.Suleymanova, N.A.Zeynalov, L.N.Qulubayova, A.R.Guliyeva, KJ.Hasanova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
suleyman.rena@gmail.com
Received 12.01.2022 Accepted 28.01.2022
The focus of the present study is liquid-phase oxidation of alkylaromatic hydrocarbons, particularly that of ethylbenzene, in the presence of cobalt-based polymer complexes tuned to ethylbenzene and obtained based on cobalt salts and a copolymer of diethyl ether of phenylphosphonic acid with acrylic acid. The reaction was carried out without solvent at atmospheric pressure and 900C temperature in a glass temperature-controlled equipped reactor. Oxidation was carried out by bubbling gaseous oxygen through the reaction mass. It is shown that tuning leads to a significant increase in the rate of formation of oxidation products. The heterogeneous-homogeneous mechanism of the process, the formation of radicals on the surface with their subsequent release into the liquid volume and the formation of products based on the radical-chain mechanism have been established. We also studied the specificity of the complex's ability to tune to a-phenylethyl hydroperoxide in a way identical to its ability to tune to ethylbenzene. As a result of our study, a-phenylethyl hydroperoxide, methylphenylcarbinol and acetophenone were obtained.
Keywords: ethylbenzene, oxidation, liquid-phase, metal-polymer complexes.
doi.org/10.32737/0005-2531-2022-2-6-10
Introduction
The process of oxidation of organic substances is one of the most widespread types of chemical transformations. A significant part of monomeric organic products and intermediates contains oxygen and can be obtained by oxidation of various substrates with molecular oxygen [1-3].
It is known that in many cases processes using bound oxygen (KMnO4, K2Cr2O7, NaOCl, various peroxides) as oxidizing agents are more selective and less powerful. However, such oxidizing agents are used only for the production of small-tonnage products, since, as a rule, they are quite expensive and scarce. In addition, their usage often leads to the formation of non-recyclable waste, which requires additional costs for environmental protection.
In this regard, the creation of new systems allowing to carry out of oxidation under mild conditions using molecular oxygen as oxidation remains relevant.
Complex-forming polymers are widely used for the selective sorption of metals from solutions, and the complexes formed by them with transition metals are effective catalysts for various chemical processes.
The development of new methods for the synthesis of polymers containing various active functional groups capable of entering into complex formation with metals is very important. Similar studies will significantly expand the scientific conceptions about the reactivity of macro-molecules and are dictated by the urgent need for modern chemical technology in specific and high-capacity sorbents and highly active and selective catalysts that exhibit these qualities at relatively low temperatures and pressures.
The new principle of obtaining metal-polymer complexes developed in our laboratory provides for the use of the "memory" of the polymer composition and consists of the conformational tuning of the macromolecules of the non-crosslinked polymeric complex-forming agent to a position favorable for complex formation with the metal and subsequent fixation of the resulting conformations optimal for complex formation by intermolecular cross-linking [4-8]. Macromolecules cross-linked in this way can fill their conformations preferred for significantly increasing the comp-lexing ability of the cross-linked polymeric ligand.
An example of such tuning is the copo-lymer of diethyl ether of vinylphosphonic acid
6
(DEVA) obtained by us with acrylic acid (AA), macromolecules of which were tuned for com-plexation with cobalt and substrates [9-11]. It has been shown that the complexing ability of the polymer towards cobalt is increased due to tuning by more than three times.
Experimental part
To obtain cobalt polymer complexes and tune them to ethylbenzene, the DEVA copoly-mer with AA was dissolved in ethanol, and an ethanol solution of cobalt chloride (CoCl2) was added dropwise to the solution at the rate of 3-4 mg-eq/g of copolymer. The resulting solution was mixed with an excess of ethylbenzene (EB) and kept for 8-16 hours, during which the mac-romolecules, having still sufficient mobility, take on a conformational structure favorable for EB.
To fix the conformational tuning, the heterogeneous mixture was frozen with liquid nitrogen, and ethanol and the substrate were removed under continuous vacuumizing. This "drying" operation was carried out by repeated (5-6 times) freezing and slow unfreezing at -30^-50°C until a dry complex of constant volume was obtained. Vacuumizing was stopped after reaching room temperature. The complex was additionally dried in a thermostat at 60-800C for 3-5 hours.
The dried complexes were mixed with the cross-linking agent N,N'-methylene-bis-acryl-amide (10-20% by weight of the complex) and from the resulting mixture tablets were prepared, which, at vacuumizing up to 10-4-10-5 Torr, were heated up to 1400C and withstood for 3 hours. Cross-linked in this way and tuned to EB, samples were crushed in a ball mill, a fraction of 0.06-0.09 mm was selected and used as a catalyst in the reaction of liquid-phase oxidation of EB with molecular oxygen.
The EB oxidation kinetics was carried out in a glass reactor at a constant pressure of molecular oxygen on the gas-liquid phase boundary. The apparatus, including the device - a volumeter, made it possible to automatically maintain the oxygen pressure and register its consumption in the oxidation reaction [12-17].
The process is controlled both by the oxygen consumption and by taking aliquot samples of
the oxidate, the composition of which was analyzed by the chromatographic method. The reaction was carried out without a solvent at atmospheric pressure and 900C temperature in a thermostatically controlled glass reactor equipped with a stirrer, gas inlet and outlet pipes, and a system of reflux condensers. The oxidation was carried out by gas oxygen bubbling through the reaction mass. The identification of the obtained samples was carried on the Agilent 7890B gas chro-matography with column HP-5 with a gas carrier velocity (H2 and N2) of 1.2 mL min-1 and pressure of 5.41 psi (pound-force square inch). As a catalyst for the oxidation of ethylbenzene, we used cobalt-polymer complexes obtained based on divalent cobalt salts and the DEVA+AA copolymer.
Results and discussion
The kinetic curves of ethylbenzene oxidation are shown in Figure 1. The figure shows that the rate of the oxidation reaction on the catalyst, the structure of which was formulated in the presence of ethylbenzene, is significantly higher than the rate of this reaction on the same catalyst obtained in the usual way.
Figures 2 and 3 show the kinetic curves for the formation of ethylbenzene oxidation reaction products - a-phenylethyl hydroperoxide, methyl-phenylcarbinol, and acetophenone in the presence of complexes tuned to ethylbenzene and obtained in the usual way. It can be seen from the Figures that the tuning leads to a significant increase in the rate of formation of all three oxidation products, and the initial rate of hydroperoxide formation increases to a much greater extent than the rate of its decomposition into methylphenyl-carbinol and acetophenone. We also studied the specificity of the tuning of the complex to a-phenylethyl hydroperoxide using a procedure similar to the tuning to ethylbenzene.
Kinetic curves for the formation of ethyl-benzene oxidation products in the presence of complexes tuned to a-phenylethyl hydroperoxide are shown in Figure 4. A comparison of this Figure with Figure 3 shows that such tuning leads to a significant increase in the rate of hydroperoxide decomposition in the EB oxidation reaction.
£ 3
ri o
Ê 2 o U
0
2.5 2.0
1.5
1.0 0.5
2.5 2.0 1.5
1.0 0.5
1 2 3 i, h
4 5 6
1 2 3 i, h
4 5 6
0 1 2 3 4 5 6 7 i, h
Fig.1. Kinetic curves of ethylbenzene oxidation in the presence of untuned (1) and tuned to ethylbenzene (2) complexes.
Fig.2. Kinetic curves of the formation of acetophenone (1), methylphenylcarbinol (2), and a-phenylethyl hydroperoxide (3) in the presence of untuned complexes.
Fig.3. Kinetic curves of the formation of acetophenone (1), methylphenylcarbinol (2), and a-phenylethyl hydroperoxide (3) in the presence of complexes tuned to ethylbenzene.
Fig.4. Kinetic curves of the formation of acetophenone (1), methylphenylcarbinol (2), and a-phenylethyl hydroperoxide (3) in the presence of complexes tuned to a-phenylethyl hydroperoxide.
0 1 2 3 4 5 6 i, h
1
0
1
3
1
Thus, the structural tuning of the active centers of metal-polymer complexes to hydrocarbon substrates leads to a significant increase in the activity and selectivity of the catalyst. In this case, it turns out to be possible to increase the specificity of metal-polymer complexes aimed at performing a catalytic function towards the substrate on which the catalyst is tuned. The methods of such tuning can also be an additional tool for studying the mechanism of catalytic processes occurring on metal-polymer complex catalysts. For the majority of heterogeneous catalysts of the liquid-phase oxidation of hydrocarbons, including ethylbenzene, a heterogeneous-homogeneous mechanism of the process has been established, namely the formation of radicals on the surface with their subsequent release into the liquid volume and the formation of products by the radical-chain mechanism.
If there is no thermal initiation, then at heterogeneous oxidation the generation of free radicals occurs in three ways: 1. At activation of oxygen molecule:
k
k • o,
+rh,
HR + [ K]OOH
2. At activation of hydrocarbon molecule:
k
+0,
+ rh2—». [k]-rh2—».hr'+[k]ooh
3. At decomposition of initially introduced or intermediate hydroperoxides on the catalyst surface (degenerate chain branching):
K
K
+ HROOH
+ HROOH
HRO+ K-OH
• HROo + K • H
Most of the studied heterogeneous catalysts take part in the stage of degenerate chain branching. The first step of the catalytic decomposition of hydroperoxide is the formation of intermediate complexes - [K] HROOH, the existence of which has been confirmed for homogeneous catalysis. However, the process of heterogeneous catalytic oxidation of ethylbenzene, which proceeds mainly by activation of oxygen without the participation of hydroperoxide, is also described. The portion of homogeneous reactions did not exceed 25%. The mechanism of such non-chain (heterogeneous) oxidation is represented by the scheme:
■ o 2
+
rh2
hrooh
Such mechanism was confirmed by the absence of decomposition of the introduced hydroperoxide, and by the equality of the rate of formation of alcohol and ketone as well. Kinetic studies of the mechanism of action of heterogeneous catalysts in liquid-phase oxidation made it possible to establish the possibility of their participation in all elementary stages of a chain radical process, characteristic of homogeneous catalytic processes (initiation, chain continuation, degenerate chain branching, chain termination).
References
1. Emanuel' N.M., Denisov Ye.T., Mayzuk Z.K. Tsepnyye reaktsii okisleniya uglevodorodov v zhidkoy faze. M.: Nauka, 1965. 375 s.
2. Emanuel' N.M., Zaikov G.Ye., Mayzuk Z.K. Rol' sredy v radikal'no-tsepnykh reaktsiyakh okisleniya organicheskikh soyedineniy. M.: Nauka, 1973. 379 s.
3. Emanuel' N.M., Gal D. Okisleniye etilbenzola, model'naya reaktsiya. M.: Nauka, 1984. 376 s.
4. Kabanov V.A., Efendiyev A.A., Orudzhev D.D. Sposob polucheniya sorbenta. A.s. № 502907 SSSR. B.I. 1976. № 6. S. 58.
5. Kabanov V.A., Efendiyev A.A., Orudzhev D.D., Samedova N.M. Dokl. AN SSSR. Sintez i issle-dovaniye komlleksoobrazushchego sorbenta s "na-stroyennym" na sorbtsiyu ionov raspolozheniyem makromolekul. 1978. T. 238. № 2. S. 356-358
6. Kabanov V.A., Efendiev A.A., Orujev D.D. Complex-forming polymeric sorbents with macro-molecular arrangement favorable for ion sorption. J. Appl. Pol. Sci. 1979. V. 24. P. 259-267.
7. Bernhard Gutmann, Petteri Elsner, Dominique Roberge, Kappe C.Oliver. Homogeneous LiquidPhase Oxidation of Ethylbenzene to Acetophe-none in Continuous Flow Mode. ACS Catal. 2013. 3. 12. P. 2669-2676.
8. Efendiev A.A., Kabanov V.A. Pure & Appl. Chem. Selective polymer complexons prearranged for metal ions sorption. 1982. V. 54. № 11. P. 2077-2092.
9. Jin Gao, Xinli Tong, Xiaoqing Li, Hong Miao, JieXu. The efficient liquid-phase oxidation of aromatic hydrocarbons by molecular oxygen in the presence of MnCO3. Chemical Technology and Biotechnology. 2007. V. 82. Iss. 7. P. 620-625.
10. Galiyeva D.D., Mentbayeva A., Tashmukham-betova Zh.kh., Shokorova L.A. Sposoby polu-cheniya effektivnykh katalizatorov dlya protsessov
zhidkofaznogo okisleniya uglevodorodov. Tezisy dokl.mezhd.konf.stud. i molodykh uchenykh «Mir nauki». Almaty, 2011. S. 60. 3.
11. Mukhambetova G.Ye., Tashmukhambetova Zh. Kh., Shokorova L.A. Zhidkofaznoye okisleniye uglevodorodov na metallokompleksnykh katali-zatorakh. Tezisy dokl.mezhd.konf.stud. i molodykh uchenykh «Mir nauki». Almaty, 2011. S. 100.
12. Vasil'yeva E.A., Mukhamedzyanov R.R., Sitmu-ratov T.S., Akhmedyanova R.A., Petukhov A.A., Beskrovnyy D.V., Miloslavskiy D.G. Gomogen-noye kataliticheskoye okisleniye etilbenzola kis-lorodom vozdukha v prisutstvii organicheskikh soley kobal'ta(II). Vest. Kazanskogo Tekhnol. Unta. 2017. T. 20. №15. S. 5-7.
13. Suleymanova R.H., Zeynalov N.A., Badalova O.T., Qulubayova L.N., Guliyeva A.R., Kerimova N.A. Research into kinetic regularities of catalytic liquid-phase oxidation of n-hexadecane in the presence of metalcomplexes catalysts. Chemical problems. 2019. No 3(17). P. 417-422.
14. Vasu Chaudhary, Sweta Sharma. Study of ethyl-benzene oxidation over polimer-silica hibrid supported Coand Cu(II) complexes. Catalyses Today. 2021. V. 375. P. 601-613.
15. Tagiev D.B., Mammadova U.A., Asadov M.M., Isazade A.F., Zeynalov N.A., Badalova O.T., Ba-girov Sh.T. Catalitic oxidation of N-hexane on immobilized manganese containing polymer catalyst. J. Chem. Techn. and Metallurgy. 2021. V. 56. Iss. 5. P. 979-987.
16. Sulejmanova R.G., Zejnalov N.A., Badalova O.T., Kulibekova L.N., Kulieva A.R., Isazade A.F. Is-sledovanie reakcii okislenie ciklogeksanona v pri-sutstvii nastroennnyh na med' i nikel' polimernyh kompleksov polietilenimina. Azerb. Chem. Journ. 2017. No 4. S. 55-59.
17. Sulejmanova R.G., Zejnalov N.A., Badalova O.T., Kulibekova L.N., Kulieva A.R., Isazade A.F. Is-sledovanie reakcii zhidkofaznogo okislenie ciklogeksanona na metallopolimernyh kompleksakh. Chemical Problems. 2017. No 4. S. 442-447.
KARBOHtDROGEN SUBSTRATLARINA KÖKLONMt§ AKTtV MORKOZLORl OLAN KOBALT POLtMER KATALtZATORLARININ t§TIRAKI ILO ETtLBENZOLUN MAYE FAZADA OKStDLO§MOSt REAKStYASININ KlNETlKA VO MEXANtZMtNtN TaDQtQt
R.H.Süleymanova, N.A.Zeynalov, L.N.Qulubayova, A.R.Quliyeva, KX.Hasanova
Vinilfosfon turjusunun dietil efiri ila akril turjusunun sopolimeri va kobalt duzlari asasinda alinmij etilbenzola köklanmij kobalt polimer komplekslari ijtiraki ila alkilaromatik karbohidrogenlarin xüsusan, etilbenzolun maye fazada oksidlajmasi reaksiyasi öyranilmijdir.Reaksiya halledici olmadan 900C temperaturda, atmosfer tazyiqinda temperaturu tanzimlayan jüja reaktorda apanlmijdir. Oksidlajma prosesi oksigenin barbotaj üsulu ila reaksiya kütlasindan kegirilmasi yolu ila baj tutur. Göstarilmijdir ki, polimerin etilbenzola köklanmasi reaksiya mahsullannin alinma süratini ahamiyyatli daracada artirir. Müayyan edilmijdir ki, prosesin heterogen-homogen mexanizmi radikallann sathda amala galmasi, onlann da öz növbasinda maye fazaya kegarak, radikal-zancir mexanizmi ila reaksiya mahsullanna gevrilmasi müayyan edilmijdir. Kompleksin a-feniletil hidroperoksidina köklanma prosesinin xüsusiyyatlari tadqiq olunmujdur.Aparilan tadqiqatlarin naticasinda a-feniletil hidroperoksidi, metilfenilkarbinol va asetofenon alinmijdir.
Agar sözlar: etilbenzol, oksidh§ma, maye faza, metalkompleks katalizatorlari.
ИССЛЕДОВАНИЕ КИНЕТИКИ И МЕХАНИЗМА ЖИДКОФАЗНОГО ОКИСЛЕНИЯ ЭТИЛБЕНЗОЛА В ПРИСУТСТВИИ КОБАЛЬТПОЛИМЕРНЫХ КАТАЛИЗАТОРОВ С АКТИВНЫМИ ЦЕНТРАМИ, НАСТРОЕННЫМИ НА УГЛЕВОДОРОДНЫЕ СУБСТРАТЫ
Р.Г.Сулейманова, Н.А.Зейналов, Л.Н.Кулибекова, А.Р.Кулиева, К.Дж.Гасанова
Изучено жидкофазное окисление алкилароматических углеводородов, в частности этилбензола в присутствии кобальтполимерных комплексов, настроенных на этилбензол, полученные на основе солей кобальта и сополимера диэтилового эфира финилфосфоновой кислоты с акриловой кислотой. Реакцию осуществляли без растворителя при атмосферном давлении и температуре 90°С в стеклянном термостатируемом реакторе. Окисление проводили путем барботирования газообразного кислорода через реакционную массу. Показано, что настройка приводит к существенному повышению скорости образования продуктов окисления. Установлен гетерогенно-гомогенный механизм процесса, образованием радикалов на поверхности с последующим выходом их в объем жидкости и образованием продуктов по радикально-цепному механизму. Была исследована специфичность настройки комплекса на гидропероксид a-фенилэтила по методике аналогичной настройке на этилбензол. В результате проведенных исследований были получены гидропероксид a-фенилэтила, метилфенилкарбинол и ацетофенон.
Ключевые слова: этилбензол, окисление, жидкая фаза, металлокомплексные катализаторы.
