Catalysts, phase transfer, with

In our previous paper [1], multicomponent nanometer particle Cu> Zn/Al20s catalyst has been prepared by phase transfer with cationic surfactant cethyltrimethyl ammonium chloride and some basic preparation conditions have been studied. The objective of the present paper is to study in detail the effect of sol preparation and phase transfer conditions on the particle size of the solid. 

A newer and equally effective way of swapping azides with halides (bromines or iodines) is in the use of phase transfer catalysts [68]. Strike wouldn t expect an underground chemist to purchase the exotic catalyst Aliquat 336 which the investigators in this reference used to get yields approaching 100% but an alternative catalyst of... 

A cousin to this reduction is one using stannous chloride (a.k.a. SnCb, a.k.a. Tin chloride) which is done exactly as the calcium one except that about lOOg of SnCb is used in place of the Mg or Ca and the addition occurs at room temperature and the solution is stirred for one hour rather than 15 minutes. Some very good reductions that operate almost exclusively at room temperature with no pressure and give almost 100% yields are to follow. The only reason Strike did not detail these methods is that some of the chemicals involved are a little less common than Strike is used to but all are available to the public. These alternatives include acetlylacetone and triethylamine [73], propanedithlol and trieth-ylamine [74], triphenylphosphine [75], NaBH4 with phase transfer catalyst [76], H2S and pyridine [77], and palladium hydrox-ide/carbon with hydrazine [78], stannous chloride dihydrate [85]. 

Recently, a nice bee named Quirks submitted an article from our new, favorite patron researcher Rajender S. Varma. This time the good doctor is tackling our azide problem with another novel use of his clay phase transfer catalyst system. This is just going to be... 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Halex rates can also be increased by phase-transfer catalysts (PTC) with widely varying stmctures quaternary ammonium salts (51—53) 18-crown-6-ether (54) pytidinium salts (55) quaternary phosphonium salts (56) and poly(ethylene glycol)s (57). Catalytic quantities of cesium duoride also enhance Halex reactions (58). 

Fluoroaliphatic Thermolytic Routes. The reaction of diduorocarbene (generated from CHCIF2 at 600°C) with cyclopentadiene to give duoroben2ene (70% yield) has been scaled up in a pilot-plant/semiworks faciUty (capacity = several dozen t/yr) (77,78). The same process can now be effected under Hquid-phase conditions in the presence of phase-transfer catalysts (79,80). 

The reaction of dihalocarbenes with isoprene yields exclusively the 1,2- (or 3,4-) addition product, eg, dichlorocarbene CI2C and isoprene react to give l,l-dichloro-2-methyl-2-vinylcyclopropane (63). The evidence for the presence of any 1,4 or much 3,4 addition is inconclusive (64). The cycloaddition reaction of l,l-dichloro-2,2-difluoroethylene to isoprene yields 1,2- and 3,4-cycloaddition products in a ratio of 5.4 1 (65). The main product is l,l-dichloro-2,2-difluoro-3-isopropenylcyclobutane, and the side product is l,l-dichloro-2,2-difluoro-3-methyl-3-vinylcyclobutane. When the dichlorocarbene is generated from CHCl plus aqueous base with a tertiary amine as a phase-transfer catalyst, the addition has a high selectivity that increases (for a series of diolefins) with a decrease in activity (66) (see Catalysis, phase-TRANSFEr). For isoprene, both mono-(l,2-) and diadducts (1,2- and 3,4-) could be obtained in various ratios depending on which amine is used. 

In this case, yields >95% of the tertiary phosphine are obtained. Tributylphosphine is readily converted to tetraalkylphophonium salts by reaction with an alkyl haUde. These compounds are used commercially as biocides and phase-transfer catalysts. 

A method for the polymerization of polysulfones in nondipolar aprotic solvents has been developed and reported (9,10). The method reUes on phase-transfer catalysis. Polysulfone is made in chlorobenzene as solvent with (2.2.2)cryptand as catalyst (9). Less reactive crown ethers require dichlorobenzene as solvent (10). High molecular weight polyphenylsulfone can also be made by this route in dichlorobenzene however, only low molecular weight PES is achievable by this method. Cross-linked polystyrene-bound (2.2.2)cryptand is found to be effective in these polymerizations which allow simple recovery and reuse of the catalyst. 

Pyrrohdinone can be alkylated by reaction with an alkyl haUde or sulfate and an alkaline acid acceptor (63,64). This reaction can be advantageously carried out with a phase-transfer catalyst (65). Alkylation can also be accompHshed with alcohols and either copper chromite or heterogenous acid catalysts... 

Nucleophilic Reactions. Useful nucleophilic substitutions of halothiophenes are readily achieved in copper-mediated reactions. Of particular note is the ready conversion of 3-bromoderivatives to the corresponding 3-chloroderivatives with copper(I)chloride in hot /V, /V- dim ethyl form am i de (26). High yields of alkoxythiophenes are obtained from bromo- and iodothiophenes on reaction with sodium alkoxide in the appropriate alcohol, and catalyzed by copper(II) oxide, a trace of potassium iodide, and in more recent years a phase-transfer catalyst (27). 

Direct Chlorination of Ethylene. Direct chlorination of ethylene is generally conducted in Hquid EDC in a bubble column reactor. Ethylene and chlorine dissolve in the Hquid phase and combine in a homogeneous catalytic reaction to form EDC. Under typical process conditions, the reaction rate is controlled by mass transfer, with absorption of ethylene as the limiting factor (77). Ferric chloride is a highly selective and efficient catalyst for this reaction, and is widely used commercially (78). Ferric chloride and sodium chloride [7647-14-5] mixtures have also been utilized for the catalyst (79), as have tetrachloroferrate compounds, eg, ammonium tetrachloroferrate [24411-12-9] NH FeCl (80). The reaction most likely proceeds through an electrophilic addition mechanism, in which the catalyst first polarizes chlorine, as shown in equation 5. The polarized chlorine molecule then acts as an electrophilic reagent to attack the double bond of ethylene, thereby faciHtating chlorine addition (eq. 6) ... 

Class (2) reactions are performed in the presence of dilute to concentrated aqueous sodium hydroxide, powdered potassium hydroxide, or, at elevated temperatures, soHd potassium carbonate, depending on the acidity of the substrate. Alkylations are possible in the presence of concentrated NaOH and a PT catalyst for substrates with conventional pX values up to - 23. This includes many C—H acidic compounds such as fiuorene, phenylacetylene, simple ketones, phenylacetonittile. Furthermore, alkylations of N—H, O—H, S—H, and P—H bonds, and ambident anions are weU known. Other basic phase-transfer reactions are hydrolyses, saponifications, isomerizations, H/D exchange, Michael-type additions, aldol, Darzens, and similar... 

In dihalocarbene generation by phase-transfer catalysis the following steps seem to be involved (15) formation of CX anions dynamically anchored at the boundary reversible detachment with the help of the catalyst reversible carbene formation [Q+ CX3 ] [Q + X ] + CX2 addition to olefin. 

Reactions of the Side Chain. Benzyl chloride is hydrolyzed slowly by boiling water and more rapidly at elevated temperature and pressure in the presence of alkaHes (11). Reaction with aqueous sodium cyanide, preferably in the presence of a quaternary ammonium chloride, produces phenylacetonitrile [140-29-4] in high yield (12). The presence of a lower molecular-weight alcohol gives faster rates and higher yields. In the presence of suitable catalysts benzyl chloride reacts with carbon monoxide to produce phenylacetic acid [103-82-2] (13—15). With different catalyst systems in the presence of calcium hydroxide, double carbonylation to phenylpymvic acid [156-06-9] occurs (16). Benzyl esters are formed by heating benzyl chloride with the sodium salts of acids benzyl ethers by reaction with sodium alkoxides. The ease of ether formation is improved by the use of phase-transfer catalysts (17) (see Catalysis, phase-thansfer). 

The terminal R groups can be aromatic or aliphatic. Typically, they are derivatives of monohydric phenoHc compounds including phenol and alkylated phenols, eg, /-butylphenol. In iaterfacial polymerization, bisphenol A and a monofunctional terminator are dissolved in aqueous caustic. Methylene chloride containing a phase-transfer catalyst is added. The two-phase system is stirred and phosgene is added. The bisphenol A salt reacts with the phosgene at the interface of the two solutions and the polymer "grows" into the methylene chloride. The sodium chloride by-product enters the aqueous phase. Chain length is controlled by the amount of monohydric terminator. The methylene chloride—polymer solution is separated from the aqueous brine-laden by-products. The facile separation of a pure polymer solution is the key to the interfacial process. The methylene chloride solvent is removed, and the polymer is isolated in the form of pellets, powder, or slurries. 

Reactions involving ions can be favored to occur in the organic phase by use of phase-transfer catalysts. Thus the conversion of 1-chlorooctane to 1-cyanooctane with aqueous NaCN is vastly accelerated in the organic phase by 1.3 percent of tributyl (hexadecyl) phosphonium bromide in the aqueous phase. (Starks and Owens, J. Am. Chem. Soc., 95, 3613 [1973]). A large class of such promotions is known. 

Soild-8quld phase transfer catalyst 2 (or aliphatic and arematic nudeophiftc substitution also synergistic effect with Cu in UHmann synthesis. 

Compound 1, 2,2-diniethyl-4-pentenal, has been prepared by the Claisen rearrangement route described above and by reaction of isobutyraldehyde with allyl chloride in the presence of aqueous sodium hydroxide and a phase-transfer catalyst. Both routes are applicable to the synthesis of a variety of substituted 4-pentenals. 

Tomoi and coworkers adopted a somewhat more direct approach in their synthesis of 16-crown-5 derivatives bearing a single alkenyl residue. They hoped to obtain precursors to polymers which could be used as phase transfer catalysts. In this approach I,I-bis-chloromethylethylene (a-chloromethallyl chloride) was allowed to react with the dianion of tetraethylene glycol (NaH/THF). By this method, methylene-16-crown-5 could be isolated in 66% yield after vacuum distillation. Ozonolysis led, in almost quantitative yield, to the formation of oxo-16-crown-5 as shown in Eq. (3.38). These authors prepared a number of other, closely related species by similar methods. 

Boujlel and Simonet used an electrochemical method to prepare a group of similar compounds, including compound ]5, shown in Eq. (3.41). In a typical case, benzil was reduced in DMF solution at the dropping mercury electrode in the presence of tetrabutylammonium iodide, used in this case as a supporting electrolyte rather than phase transfer catalyst. In the presence of diethylene glycol ditosylate, compound 15 (mp 77— 78°) was isolated in 10% yield. Using the same approach, acenaphthenedione was reduc-tively cyclized with triethylene glycol ditosylate to afford the product (mp 84—85°, 42% yield) shown in Eq. (3.42). 

Quite recently, Okahara and his coworkers have extended their method to the formation of long chain N-alkylmonoazacrowns. It was expected that such compounds as N-decylmonoaza-18-crown-6 may be useful as new surfactants with complexing ability with metal salts, phase transfer catalysts and selective ion carriers . ... 

With the discovery of the crowns and related species, it was inevitable that a search would begin for simpler and simpler relatives which might be useful in similar applications. Perhaps these compounds would be easier and more economical to prepare and ultimately, of course, better in one respect or another than the molecules which inspired the research. In particular, the collateral developments of crown ether chemistry and phase transfer catalysis fostered an interest in utilizing the readily available polyethylene glycol mono- or dimethyl ethers as catalysts for such reactions. Although there is considerable literature in this area, much of it relates to the use of simple polyethylene glycols in phase transfer processes. Since our main concern in this monograph is with novel structures, we will discuss these simple examples further only briefly, below. 

It was noted early by Smid and his coworkers that open-chained polyethylene glycol type compounds bind alkali metals much as the crowns do, but with considerably lower binding constants. This suggested that such materials could be substituted for crown ethers in phase transfer catalytic reactions where a larger amount of the more economical material could effect the transformation just as effectively as more expensive cyclic ethers. Knbchel and coworkers demonstrated the application of open-chained crown ether equivalents in 1975 . Recently, a number of applications have been published in which simple polyethylene glycols are substituted for crowns . These include nucleophilic substitution reactions, as well as solubilization of arenediazonium cations . Glymes have also been bound into polymer backbones for use as catalysts " " . 

Montanari and his coworkers used the interesting polypode ligands derived from sym-trichlorotriazine as phase transfer catalysts for a variety of transformations. These catalysts were quite successful and their formation is illustrated below in Eqs. (7.3)— (7.5). Comparisons were also made with certain pentaerythrityl derived polypodes as well. These latter compounds are listed in Table 7.1 as compounds 10—13. 

Landini, Montanari and Rolla ° were able to incorporate cyclohexyl residues in the strands and thereby increase lipophilicity. As with the compounds referred to above, these were effective phase transfer catalysts. 

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