Microsoft Word - 2 Torosyan 2013 corectat.doc 12 journal homepage: www.fia.usv.ro/fiajournal Journal of Faculty of Food Engineering, Ştefan cel Mare University of Suceava, Romania Volume XII, Issue 1 – 2013, pag. 12 - 17 PHASE TRANSFER CATALYSIS FOR GREEN CHEMISTRY Yeva TOROSYAN1, Andranik AVETISYAN1, *Gagik TOROSYAN2 1 European regional educational academy, Yerevan, Armenia, gagiktorosyan@seua.am 2 Faculty of chemical technology and environmental engineering, State engineering university of Armenia, * Corresponding author Received 10 February 2013, accepted 5 March 2013 Abstract: The problem of “Green Chemistry” using like example phase transfer catalysis has been discussed in the present paper. Nowadays catalysis plays a very important role in the new green chemical industry. Catalysis can reduce the environmental impact of processes and therefore can reduce the costs of these processes. Application of new catalysts and catalytic systems aim to achieve both environmental protection and economical benefits. The PTC technology has been chosen and is used in these applications, because it provides many compelling benefits, primarily related to the cost reduction of organic manufacture chemicals and secondly because it prevent the environmental pollution. Keywords: Green chemistry, sustainable development, phase transfer catalysis PTC, pollutions. 1. Introduction Globalization and countries industrial development creates fast changes on environment fact that conduct to the opportunity of occurrence of new principles for definition of tasks of a society. Moreover, the increases changes of the extreme climatic phenomena are worsening more and more the situation on a global scale. It is widely acknowledged that there is a increase need of the human society for a more environmentally acceptable processes in the chemical industry. In the present paper the idea of green chemistry develops as a philosophy of chemical research that tried to minimize the use and the production of dangerous substances. The focus is to minimize the substance chemical danger and to maximize the efficiency of any chemical choose. Catalysis has played such a vital role in the success of the chemical industry in the 20th century, the application of this process ranging from pharmaceuticals to petroleum processing fields. More than 90% of all industrial processes are based on catalysis process. The widespread utilization by industry of catalytic processes has a positive influence on the economic and environmental safety [1]. One of the best way to realize of chemical processes, specially in organic reactions is the phase transfer catalysis - PTC [2,3]. Cost reduction and pollution prevention are the two most powerful driving forces in the chemical industry today, and they match precisely the strengths and benefits provided by phase transfer catalysis. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 1 – 2013 YEVA TOROSYAN, ASHOT AVETISYAN, GAGIK TOROSYAN , PHASE TRANSFER CATALYSIS FOR GREEN CHEMISTRY , Food and Environment Safety, Volume XII, Issue 1 – 2013, pag. 12 - 17 13 Phase transfer catalysis conduct to high productivity, increase environmental performance, improved safety environment, and increase plant operability in hundreds of commercial manufacturing processes for organic chemicals in dozens of reaction categories [2, 3]. 2. Materials and methods Green chemistry and the principles The developing of green chemistry methodologies is a challenge that can be presented through the framework of the “Twelve Principles of Green Chemistry” [4]. The principles of Green Chemistry [4] compared with the advantages of PTC are presented in table 1. The principle number 9 identifies the catalysis as one of the most important tools for implementing green chemistry. Nowadays, organic synthesis, especially fine chemicals and pharmaceuticals use “stoichiometric” technologies. Some of these reactions types were transformed in phase transfer catalytic (PTC) system. PTC is one of the most efficient methodologies in organic synthesis and therefore it. It was widely used for the synthesis of organic compounds. PTC uses as phase transfer catalyst onium salts (as quaternary or phosphonium ammonium salts /Quat/, crown ethers and others/, who facilitate the transport of one reactant into the other and interaction between reagents in two immiscible phases. PTC is widely used in the organic chemicals synthesis for both two and tri- phase systems. The use of PTC can be combined with other rate enhancement techniques like microwaves, sonochemistry and others. PTC has made possible to use cheaper and easily available alternative raw materials, avoiding in these way the need of using severe anhydrous conditions, expensive solvents, and dangerous bases such as metal hydrides and organo-metallic reagents. PTC uses much fine organic chemistry instead of toxic alkali metal alkoxides, amides, and hydrides. Table 1 A comparison of the principles of Green Chemistry and PTC advantages N Principles of Green Chemistry 1. Waste prevention instead of remediation 2. Atom efficiency 3. Less hazardous and toxic chemicals 4. Safer products by design 5. Innocuous solvents and auxiliaries 6. Energy efficient by design 7. Preferably renewable raw materials 8. Shorter syntheses 9. Catalytic rather than stoichiometric reagents 10. Design products for degradation 11. Analytical methodologies for pollution prevention 12. Inherently safer processes N Advantages of PTC 1. Minimization of industrial wastes 2. High reactivity and selectivity 3. Less dangerous, inconvenient and expensive reactants 4. High yields and purity of products 5. Less inconvenient and expensive organic solvents 6. Low energy consumption 7. Simplicity of technology 8. Possibility to mimic counter-current process An important issue in organic chemistry technology is the use of organic solvents. The principle of PTC also proposes the use of usual and environmental friendly solvent that coincides with the number 5 principle for green chemistry. For both of them it necessary to use the solvents with different characteristics like: low toxicity, easy recyclability (no disposal) and further desirable characteristics - easy removal from the product and. In this case some solvents should never be used: tetrachlorocarbon, 1,2-dichloroethane, 1,1-dichloroethane and some solvents are preferred like water, CO2 , heptane, tert- butyl methyl ether, ethyl acetate, tert-butyl alcohol, ethanol. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 1 – 2013 YEVA TOROSYAN, ASHOT AVETISYAN, GAGIK TOROSYAN , PHASE TRANSFER CATALYSIS FOR GREEN CHEMISTRY , Food and Environment Safety, Volume XII, Issue 1 – 2013, pag. 12 - 17 14 We are mentioned bellow the solvents are more convenient to be used for green chemistry technologies: 2.1. Water as a reaction medium Economically and Environmentally attractive - Inexpensive and abundantly available - Non-inflammable and non-toxic - Odorless and colorless Highly polar reaction medium - Facile product separation - Reduced product contamination. 2.2. Supercritical CO2 as a reaction medium Tc 31.0 °C, pc 73.8 bar, dc 0.477 kg L-1 • Low viscosity (more like a gas than like a liquid); hence, fast mass transfer • Cheap and abundantly available • Easy to remove • Non-toxic, non-inflammable, inert. PTC tries to use no toxic reagents, solvents and other materials as we seen in the number 3 principle for green chemistry. One of the other advantages of PTC is it lower energy and simplified technology – as we can see from the number 6 principle. However, the main disadvantages of PTC, especially in commercial applications, are the necessity to separate the catalyst from the organic phase. Further, is important to show the difference between homogenous and heterogeneous catalysis. Phase transfer catalysts can be either homogeneous (soluble in one or both solvents) or heterogeneous. The place PTC in catalytic systems between homogenous and heterogeneous, because of its catalytic system allowed to transfer heterogeneous system into the homogenous one – as in PTC liquid-liquid system. In this case appeared the possibility to use the advantages of homogenous catalysis. Quaternary ammonium and similar onium salts (Quat), crown ethers with alkaline metal cation and other provide a source of singly charged lipophilic cations. Generally, catalyst efficiency is influenced by the large number of carbon atoms and the symmetry of the carbon atom chains around the heteroatom that provide high lipophilicity [2,3]. Homogenous PTC is based on the mechanism proposed [2]. Table 2 Advantages and disadvantages of catalytic systems Catalytic system Advantages Disadvantages Homogeneous Mild reaction condition, High activity and selectivity, Efficient heat transfer Cumbersome separation and recycling of catalyst Heterogeneous Facile separation of catalyst Continuous processing Product contamination Heat transfer problems Low activity and selectivity products Not readily adapted Biphasic homogeneous catalysis integrates reaction and products and catalyzes separation into one single operation: - Other possible solutions; - Supported liquid phase catalysis; -Thermo-regulated biphasic catalysis supported liquid phase catalysis. PTC is used also in solid-liquid system, which is coming more as a heterogeneous system and even more heterogeneous when we have tri-phase system. PTC linked to a polymer or inorganic matrix are described as heterogeneous catalysis In this system the catalysts play role as like a third system, for instance, the immobilized on alumina / and other inorganic material/ or polymers quaternary ammonium salts or crown ethers. Here can include also polyethylenglicols (PEG) [2, 3] and polypropargyl alcohols [2]. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 1 – 2013 YEVA TOROSYAN, ASHOT AVETISYAN, GAGIK TOROSYAN , PHASE TRANSFER CATALYSIS FOR GREEN CHEMISTRY , Food and Environment Safety, Volume XII, Issue 1 – 2013, pag. 12 - 17 15 For Quat and crown ethers the situation is: catalyst is bonded to a matrix forming a third immiscible solid phase between the organic and aqueous ones involving a swelling, mixing and diffusion during the reaction. Due to diffusion retardation, reactions with slow intrinsic reaction rates are much slower with a tri-phase catalyst than with its homogeneous counterpart [2,3]. The use of tri-phase PTC simplifies the removal of the catalyst after the reaction which can be re-used until they lose their mechanical stability. Here we discussed about C–C Bond formation as Michael condensation in PTC system. 3. Results and discussions PTC is efficiently applicable for base- induced reactions of organic anions as Michael reaction. This reaction mentioned concern the chemists from the perspective point of view. Unsaturated compounds (acceptor groups), and compounds with donor group (CH-acid) receive new connections with the most different groups [5, 6]. O H2N NuH + Nu H2N O NuН – the molecule of conforming СН - acid (see table 3). This reaction one of two major categories of PTC reaction, when anion generated in situ/there is an anion from acetoacetic acid ethyl ether that reacts with acrylamide. Here is studied the interaction of acrylamide with some accessible classic СН - acids – malonic ester or diethylmalonate (ME), acetoacetic ester or ethyl acetoacetate (AAE), ethyl ether of cyanaoacetic acid (ECA) and acetylacetone or pentanedione-2,4 (AA). All these reagents react with acrylamide as the type of 1,4-addition for Michael reaction. The conversion of acrylamide with СН - acids is implemented in a water-alcaline medium, in conditions of PTC as catalyst of phase transfer carry were applied with different Quats. Table 3 The molecule of conforming СН - acid NuH Nu- malonic ester (ME) OEt OEt O O - ethyl ether of cyanoacetic acid (ECA) OEt NC O - acetoacetic ester (AAE) Me OEt O O - Acetylacetone (AA) Me Me O O - Influencing of СН - acids structure and catalysts on a reaction rate constant and yields of product is studied. It is visible from the results in table 4 ME and ECA in conditions of Michael addition to acrylamide are very close on reactivity. The AAE reacts with acrylamide a little bit more slowly, than ECA or, in particular ME. The reaction for AA is more slowly. At the same time, outgoing from values of dissociation constants of this CH acids, diverse sequence of reaction speeds was expected: ME (рК~13) < CAE (рК~11) < AAE (рК~11) < of an AA (рК~9). Probably, the main role in the control of reaction speed is played by solvation of СH-acids or their complexes with catalyst in aqueous phase, where an addition reaction flows past. In this case, the anion of more strong acid and slowing down for Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 1 – 2013 YEVA TOROSYAN, ASHOT AVETISYAN, GAGIK TOROSYAN , PHASE TRANSFER CATALYSIS FOR GREEN CHEMISTRY , Food and Environment Safety, Volume XII, Issue 1 – 2013, pag. 12 - 17 16 reacting, because of solvation effects is most solvated for that is also more. The speed of Michael addition in PTC conditions depends not only on a СH-acid, but also, at largely, from used catalyst (table 4). Table 4 The yield of addition products of СH-acids to acrylamide The yield Michael addition product (%) Catalysts ME CAE AAE AA Without catalyst 4.0 3.0 3.75 1.75 TMACl 60 40 75 28 TMHACl 80 58 80 40 TMBACl 85 70 80 45 TMDHACl 90 85 90 60 Outgoing from an extreme length of radical alkyl chain of l, the best catalytic activity shown trimethylhexa- decylammonium or trimethylcetyl- ammonium chloride (TMDHACl), is objective, as well as least, shown by tetramethylammonium chloride. To activity of chlorides trimethylhexyl and trimethylbenzylammonium (TMBACl) are rather close, despite of a little bit large length hexyl radical, as contrasted to benzyl. Despite of a little bit smaller, than for TMDHACl catalytic activity, (TMDHACl), nevertheless, is perspective catalyst because of the availability that can have crucial importance, in case of organization for a commercial production. On our point of view, in a reduced example of Michael addition, the important organic reaction, PTC demonstrates actual chance for an approaching to principles Green Chemistry. It is necessary to mark also, that here for the first time is described new reaction of acrylamide for synthesis of the very relevant products, in particular for synthesis physiologically and bacteriological active compounds. In this paper have not gone deep into mechanistic estimations of the conducted reaction, as it implements in called of an inverse PTC. 4. Conclusion The experiments were conducted in the reactor of ideal mixture at 300С. Initial concentrations of a СH-acid and acrylamide at 1,5-1,75 mol/L; it was compared yields of experiments by confrontation constants of reaction speeds in the supposition, that at enough high concentration of catalyst - 0,1 mol/L, what, for utilized of Quat, in 1,7- 5 times for above critical concentration micelle formation (CMF) - change of concentration for catalyst cease is appreciable to have an effect for reaction speed. Current concentration of the conforming СH-acid determined (GLCh) through 10 minutes from a beginning of reaction. The yields of addition reaction product was determined on expiration of an estimated time of reacting indispensable for achievement of 95% transformation for reagents (receiving conditionally selectivity for reacting equal 100 %). In tab. 4 the yields of addition products for investigated СH-acids to acrylamide are described. Due to the features and advantages of PTC here was considered as an efficient for green chemistry. 5. References [1]. M.S. SIMMONS, in: P.T. Anastas, T.C. Williamson (Eds.), Green Chemistry: Designing Chemistry for the Environment, American Chemical Society, Washington, DC, (1996), Ch. 10, p. 116 [2]. A.T. BABAYAN., G.H. TOROSYAN., The phase transfer catalysis development stages. Journal of Mendeleeev society, (1986) n.12, p. 129 [3]. STARKS, C.; LIOTTA, C.; HALPERN, M.; "Phase-Transfer Catalysis: Fundamentals, Applications and Industrial Perspectives," Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XII, Issue 1 – 2013 YEVA TOROSYAN, ASHOT AVETISYAN, GAGIK TOROSYAN , PHASE TRANSFER CATALYSIS FOR GREEN CHEMISTRY , Food and Environment Safety, Volume XII, Issue 1 – 2013, pag. 12 - 17 17 Chapter 16, Chapman & Hall, New York , (1994). [4]. P.T. ANASTAS, J.C. WARNER, Green Chemistry: Theory and Practice, Oxford University Press, New York, (1998), p. 30. [5]. TOROSYAN G., HARUTYUNYAN A., ISAKOVA L., BEYLERYAN N., CHOBNYAN J., SIMONYAN G., Reaction of acetoacetic acid ethyl ester with acryl- and α- methylacrylamides in conditions of inverse phase transfer catalysis. Effect of sufractant's type// Oxid. Commun.-2007.- V. 30, №3, pр. 548-552.