Catalytic two-phase systems

Makosza, M. and Wojciehowski, K., Synthesis of phosphonic acid esters in a solid-liquid catalytic two-phase system, Bull. Pol. Acad. Sci. Chem., 32, 175, 1984. 

Reactions of carbanions, anions of weak organic acids (e.g., indole or carbazole), and dihalocarbenes may be carried out in liquid-liquid systems, in which concentrated aqueous sodium hydroxide is the aqueous phase. The term phase transfer catalysis is mechanistically incorrect these are often referred to as catalytic two-phase systems. Numerous reactions of carbanions including alkylation, nitroarylation, addition, the Darzens condensation, cyclopropanation, and also a variety of reactions of dihalocarbenes are conveniently carried out in this way. 

Allylic sulfonyl carbanions react with electrophiles such as alkyl halides and aldehydes at the a-position. Although relatively strong bases like Bu"Li and LDA are usually used for deprotonation of allylic sulfur compounds, including sulfones, a catalytic two-phase system that consists of a concentrated aqueous NaOH solution and a quaternary ammonium salt can be used to generate allylic sulfonyl carbanions. 1,1-Dilithiated allyl phenyl sulfone (equation 20) reacts with excess benzaldehyde to afford the 1,3-( )-diadduct, while l,ort/io-dilithiated allyl phenyl sulfone gives the l,ort/io-diadduct predominantly. Other examples of sulfur-substituted allylic anions are summarized in Table 1. 

The direct addition of ammonia and amines across the tmsaturated CC bond of alkenes, dienes, and alkynes is a promising and atom-economical route to organo-nitrogen compounds. A catalytic two-phase system wherein Lewis acidic catalysts immobilized in a highly polar IL are employed [56,74] has been transferred successfully to the supported IL system, whereby the catalyst was used in the slurry phase [24, 43] or as a fixed-bed catalyst [63]. 

Thioalkyl substituent (RS) is often introduced via the reaction of carbanions with alkyl disulfides. The catalytic two-phase system is unsuitable for this reaction since thiolate anions produced during the thioalkylation are highly extractible, so the catalysts do not operate. These difficulties are eliminated by the addition of an alkylating agent to the system, which reacts irreversibly with thiolate anions liberating the catalyst. 

Although heterogeneity of the catalytic two-phase system prevents alkaline hydrolysis of the reacting compounds, there are many cases in which aqueous sodium hydroxide cannot be used as a base. 

Thus the use of solid alkali carbonates considerably expands the area of application of the catalytic two-phase systems in organic synthesis. 

Reactions of organic anions. Part LXVIIL An improved method of synthesizing dibromocyclopropane derivatives in a catalytic two-phase system M. Makosza and M. Fedorynski, Rocz. Chem. 50, 2223 (1976)... 

Reactions of organic anions. LXXL Reactions of enol esters with carbanions and dihalocarbenes in catalytic two-phase systems. M. Fedorynski, I. Gorzkowska and M. Makosza, Synthesis, 120 (1977)... 

Butanes are recovered from raw natural gas and from petroleum refinery streams that result from catalytic cracking, catalytic reforming, and other refinery operations. The most common separation techniques are based on a vapor—Hquid, two-phase system by which Hquid butane is recovered from the feed gas. 

Such a reaction is controlled by the rate of addition of the acid. The two-phase system is stirred throughout the reaction the heavy product layer is separated and washed thoroughly with water and alkaU before distillation (Fig. 3). The alkaU treatment is particularly important and serves not just to remove residual acidity but, more importantiy, to remove chemically any addition compounds that may have formed. The washwater must be maintained alkaline during this procedure. With the introduction of more than one bromine atom, this alkaU wash becomes more critical as there is a greater tendency for addition by-products to form in such reactions. Distillation of material containing residual addition compounds is ha2ardous, because traces of acid become self-catalytic, causing decomposition of the stiU contents and much acid gas evolution. Bromination of alkylthiophenes follows a similar pattern. 

Cationic phosphine ligands containing guanidiniumphenyl moieties were originally developed in order to make use of their pronounced solubility in water [72, 73]. They were shown to form active catalytic systems in Pd-mediated C-C coupling reactions between aryl iodides and alkynes (Castro-Stephens-Sonogashira reaction) [72, 74] and Rh-catalyzed hydroformylation of olefins in aqueous two-phase systems [75]. 

An unusual enhancement of catalytic activity in a two-phase system has been reported by Fremy et al. (1998) for the hydroformylation of acrylic esters using Rh complex of TPTS as catalyst. Even though acrylic esters have reasonable solubility in water, rate enhancements in two-phase systems by a factor of 2 to 14 have been reported. It seems that water is not an inert solvent but also acts as a reactant or a co-ordinating solvent which can modify elementary steps of the catalytic cycle (Cornilis, 1997). 

Hydroaminomethylation of alkenes occurred to give both n- and /. so aliphatic amines catalyzed by [Rh(cod)Cl]2 and [Ir(cod)Cl]2 with TPPTS in aqueous NH3 with CO/H2 in an autoclave. The ratio of n-and /.soprimary amines ranged from 96 4 to 84 16.178 The catalytic hydroaminomethylation of long-chain alkenes with dimethylamine can be catalyzed by a water-soluble rhodium-phosphine complex, RhCl(CO) (Tppts)2 [TPPTS P(m-C6H4S03Na)3], in an aqueous-organic two-phase system in the presence of the cationic surfactant cetyltrimethy-lammonium bromide (CTAB) (Eq. 3.43). The addition of the cationic surfactant CTAB accelerated the reaction due to the micelle effect.179... 

Phenols are easily mononitrated by sodium nitrate in a two-phase system (water-ether) in the presence of HC1 and a catalytic amount of La(N03)3.13 Various lanthanide nitrates have been used in the nitration of 3-substituted phenols to give regioselectively the 3-substituted 5-nitrophenols.14... 

Heterogeneously catalyzed reactions are rather complex processes. In a two-phase system, either liquid/solid or gas/solid, several steps are needed to complete the catalytic cycle ... 

Recently, Dupont and coworkers described the use of room-temperature imi-dazolium ionic liquids for the formation and stabilization of transition-metal nanoparticles. The potential interest in the use of ionic liquids is to promote a bi-phasic organic-organic catalytic system for a recycling process. The mixture forms a two-phase system consisting of a lower phase which contains the nanocatalyst in the ionic liquid, and an upper phase which contains the organic products. Rhodium and iridium [105], platinum [73] or ruthenium [74] nanoparticles were prepared from various salts or organometallic precursors in dry 1-bu-tyl-3-methylimidazolium hexafluorophosphate (BMI PF6) ionic liquid under hydrogen pressure (4 bar) at 75 °C. Nanoparticles with a mean diameter of 2-3 nm... 

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