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Interfacial Processes—The Key Steps of Phase Transfer Catalyzed Review Interfacialcatalysts Processes—The Key Steps of Phase Transfer Catalyzed Reactions Review InterfacialMieczysław Mąkosza Processes—The 1,* and Michał Fedoryński 2 Key Steps of Phase Transfer1 Institute of Organic Catalyzed Chemistry, Polish Reactions Academy of Sciences, Kasprzaka 44/52, 01‐224 Warsaw, Poland 2 Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00‐664 Warsaw, Poland; Mieczysł[email protected] M ˛akosza 1,* and Michał Fedory ´nski 2 * Correspondence: [email protected]; Tel: +48‐22‐3432334 1 Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland 2Received:Faculty 18 of November Chemistry, 2020; Warsaw Accepted: University 5 December of Technology, 2020; Published: Noakowskiego 8 December 3, 00-664 2020 Warsaw, Poland; [email protected] *Abstract:Correspondence: After short [email protected]; historical introduction, Tel.: + interfacial48-22-3432334 mechanism of phase transfer catalyzed (PTC) reactions of organic anions, induced by aqueous NaOH or KOH in two‐phase systems is Received:formulated. 18 NovemberSubsequently 2020; experimental Accepted: 5 December evidence 2020; that Published: supports 8 the December interfacial 2020 deprotonation as the key initial step of these reactions is presented. Abstract: After short historical introduction, interfacial mechanism of phase transfer catalyzed (PTC) reactionsKeywords: of organiccarbanions; anions, dichlorocarbene; induced by aqueous sodium NaOH hydroxide; or KOH ininterfacial two-phase processes; systems is formulated.quaternary Subsequentlyammonium salts; experimental phase transfer evidence catalysis; that supports alkylation the interfacial deprotonation as the key initial step of these reactions is presented. Keywords: carbanions; dichlorocarbene; sodium hydroxide; interfacial processes; quaternary ammonium 1.salts; Introduction phase transfer catalysis; alkylation Phase‐Transfer Catalysis (PTC) is presently widely applied in chemical industry based on organic synthesis, such as pharmaceutical, agrochemical, cosmetical etc. The importance of this 1.catalysis Introduction is illustrated by value of sales of the PT catalysts that, according to the report of Market & Market Company in 2019, was exceeding 1 billion USD [1]. A particularly valuable variant of PTC Phase-Transfer Catalysis (PTC) is presently widely applied in chemical industry based on organic are reactions of organic anions, mostly carbanions, but also O‐ and N‐anions, generated and carried synthesis, such as pharmaceutical, agrochemical, cosmetical etc. The importance of this catalysis out in the presence of concentrated aqueous NaOH or KOH, catalyzed by tetraalkylammonium is illustrated by value of sales of the PT catalysts that, according to the report of Market & Market (TAA) salts. In this review we would like to discuss mechanistic features of these reactions, Company in 2019, was exceeding 1 billion USD [1]. A particularly valuable variant of PTC are reactions particularly interfacial processes that are key steps of generation of the reacting anions. of organic anions, mostly carbanions, but also O- and N-anions, generated and carried out in the The first example of industrial application of such catalytic processes was manufacturing of presence of concentrated aqueous NaOH or KOH, catalyzed by tetraalkylammonium (TAA) salts. 2‐phenylbutyronitrile via reaction of phenylacetonitrile with ethyl chloride carried out in the In this review we would like to discuss mechanistic features of these reactions, particularly interfacial presence of 50% aqueous NaOH and benzyltriethylammonium chloride (TEBA), 1 mol %, without processes that are key steps of generation of the reacting anions. solvent, by small Polish company, Isopharm, started in 1960 [2] (Scheme 1). The first example of industrial application of such catalytic processes was manufacturing of It should be stressed that carbanions associated with TAA cations in lipophilic ion pairs 2-phenylbutyronitrile via reaction of phenylacetonitrile with ethyl chloride carried out in the presence entering the organic phase exhibit much higher nucleophilic activity than those associated with of 50% aqueous NaOH and benzyltriethylammonium chloride (TEBA), 1 mol %, without solvent, potassium, sodium or lithium cations in organic solvents, thus the reactions proceed rapidly in spite by small Polish company, Isopharm, started in 1960 [2] (Scheme1). of their low concentrations that cannot exceed concentrations of the TAA salts (usually 1% molar). 50% NaOH aq Ph CN + Cl + Ph CN TEBA Ph CN 90–95% 3–5% Scheme 1. Production of 2 2-phenylbutyronitrile‐phenylbutyronitrile according to Polish Patent 46,030 (1962). ItThis should process be stressed was elaborated that carbanions on the basis associated of short with note TAA by a cations French in chemist lipophilic Jarrousse ion pairs [3]. entering At that thetime organic this nitrile phase was exhibit usually much manufactured higher nucleophilic via reaction activity of phenylacetonitrile than those associated with ethyl with bromide potassium, in sodium or lithium cations in organic solvents, thus the reactions proceed rapidly in spite of their low concentrationsCatalysts 2020, 10, x; that doi: cannotFOR PEER exceed REVIEW concentrations of the TAA salts (usuallywww.mdpi.com/jou 1% molar). rnal/catalysts This process was elaborated on the basis of short note by a French chemist Jarrousse [3]. At that time this nitrile was usually manufactured via reaction of phenylacetonitrile with ethyl bromide in the Catalysts 2020, 10, 1436; doi:10.3390/catal10121436 www.mdpi.com/journal/catalysts Catalysts 2020, 10, 1436 2 of 15 CatalystsCatalysts 20202020,, 1010,, xx FORFOR PEERPEER REVIEWREVIEW 22 ofof 1515 Catalysts 2020, 10, x FOR PEER REVIEW 2 of 15 presencethe presence of sodium of sodium amide amide in anhydrous in anhydrous toluene. toluene. Taking intoTaking account into costaccount of the cost starting of the materials, starting thethe presencepresence ofof sodiumsodium amideamide inin anhydrousanhydrous toluene.toluene. TakingTaking intointo accountaccount costcost ofof thethe startingstarting solventsmaterials, and solvents investment and investment assuring safe assuring operation safe with operation sodium with amide sodium and regenerationamide and regeneration of the solvent, of materials,materials, solventssolvents andand investmentinvestment assuringassuring safesafe operationoperation withwith sodiumsodium amideamide andand regenerationregeneration ofof costthe solvent, of the catalytic cost of the process catalytic was process below 30% was of below the cost 30% of of the the known cost of procedure. the known procedure. thethe solvent,solvent, costcost ofof thethe catalyticcatalytic processprocess waswas belowbelow 30%30% ofof thethe costcost ofof thethe knownknown procedure.procedure. Thus wewe can can presently presently celebrate celebrate 60 year60 year anniversary anniversary of introduction of introduction of PTC of into PTC chemical into chemical industry. ThusThus wewe cancan presentlypresently celebratecelebrate 6060 yearyear anniversaryanniversary ofof introductionintroduction ofof PTCPTC intointo chemicalchemical Thisindustry. patent This and patent subsequent and subsequent patents and publicationspatents and presentingpublications alkylation presenting of carbanions alkylation in of the carbanions presence industry.industry. ThisThis patentpatent andand subsequentsubsequent patentspatents andand publicationspublications presentingpresenting alkylationalkylation ofof carbanionscarbanions ofin aqueousthe presence NaOH of andaqueous TEBA NaOH catalyst and [4 –TEBA7] have catalyst not raised [4–7] wider have interest not raised to these wider catalytic interest processes. to these inin thethe presencepresence ofof aqueousaqueous NaOHNaOH andand TEBATEBA catalystcatalyst [4–7][4–7] havehave notnot raisedraised widerwider interestinterest toto thesethese Onlycatalytic the processes. 1969 report Only that the dichlorocarbene 1969 report that can dichlorocarbene be generated andcan be react generated efficiently and with react alkenes efficiently via catalyticcatalytic processes.processes. OnlyOnly thethe 19691969 reportreport thatthat dichlorocarbenedichlorocarbene cancan bebe generatedgenerated andand reactreact efficientlyefficiently treatmentwith alkenes of chloroform via treatment and of alkenes chloroform by concentrated and alkenes aqueous by concentrated NaOH in the aqueous presence NaOH of TEBA in [the8], withwith alkenesalkenes viavia treatmenttreatment ofof chloroformchloroform andand alkenesalkenes byby concentratedconcentrated aqueousaqueous NaOHNaOH inin thethe waspresence widely of recognizedTEBA [8], was and widely convinced recognized chemical and community convinced that chemical concentrated community aqueous that alkali concentrated and TAA presencepresence ofof TEBATEBA [8],[8], waswas widelywidely recognizedrecognized andand convincedconvinced chemicalchemical communitycommunity thatthat concentratedconcentrated catalystsaqueous inalkali two and immiscible TAA catalysts phase system in two is immiscible a general and phase effi systemcient way is a for general generation and efficient and reactions way for of aqueousaqueous alkalialkali andand TAATAA catalystscatalysts inin twotwo immiscibleimmiscible phasephase systemsystem isis aa generalgeneral andand efficientefficient wayway forfor carbanionsgeneration (Schemeand reactions2). of carbanions (Scheme 2). generationgeneration andand reactionsreactions
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