Phase transfer catalysis amines

Quaternary ammonium compounds (quats) are prepared - by moderate heating of the amine and the alkyl halide in a suitable solvent - as the chlorides or the bromides. Subsequently conversion to the hydroxides may be carried out. Major applications of the quat chlorides are as fabric softeners and as starch cationizing agent. Several bio-active compounds (agrochemicals, pharmaceuticals) possess the quat-structure. Important applications of quat bromides are in phase transfer catalysis and in zeolite synthesis. 

The reaction with ammonia or amines, which undoubtedly proceeds by the SnAt mechanism, is catalyzed by copper and nickel salts, though these are normally used only with rather unreactive halides. This reaction, with phase-transfer catalysis, has been used to synthesize triarylamines. Copper ion catalysts (especially cuprous oxide or iodide) also permit the Gabriel synthesis (10-61) to be... 

Phase-transfer catalysis is a special type of catalysis. It is based on the addition of an ionic (sometimes non-ionic like PEG400) catalyst to a two-phase system consisting of a combination of aqueous and organic phases. The ionic species bind with the reactant in one phase, forcing transfer of this reactant to the second (reactive) phase in which the reactant is only sparingly soluble without the phase-transfer catalyst (PTC). Its concentration increases because of the transfer, which results in an increased reaction rate. Quaternary amines are effective PTCs. Specialists involved in process development should pay special attention to the problem of removal of phase-transfer catalysts from effluents and the recovery of the catalysts. Solid PTCs could diminish environmental problems. The problem of using solid supported PTCs seems not to have been successfully solved so far, due to relatively small activity and/or due to poor stability. 

Heteropoly acids can be synergistically combined with phase-transfer catalysis in the so-called Ishii-Venturello chemistry for oxidation reactions such as oxidation of alcohols, allyl alcohols, alkenes, alkynes, P-unsaturated acids, vic-diols, phenol, and amines with hydrogen peroxide (Mizuno et al., 1994). Recent examples include the epoxidations of alkyl undecylenates (Yadav and Satoskar, 1997) and. styrene (Yadav and Pujari, 2000). 

In addition, there are a few examples of heterogeneous nonaqueous sonochemistry, in both liquid-liquid and liquid-solid systems. Two recent reports have utilized ultrasonic agitation in place of or along with phase transfer catalysis for the preparation of dichlorocarbene from aqueous NaOH/CHCl3 (166), and for N-alkylation of amines with alkyl halides (167). Along the same lines, several papers have appeared in which... 

Phase transfer catalysis has been widely employed in commercial synthetic applications, primarily because of its ability to replace organic amine and alkoxides bases with low cost metal hydroxides. An example of this from PTC Organics... 

Fig. 21. Schematic illustration of phase-transfer catalysis using an amine-terminated den-drimer-encapsulated nanoparticle complexed with a fatty acid (present in the organic phase). The fatty acid surrounds the dendrimer, yielding a monodisperse inverted micelle which is soluble in the organic phase. After catalysis, the catalyst can be reclaimed by changing the pH of the aqueous phase...

Aromatic nitroso compounds combine with primary arylamines in glacial acetic acid to give symmetrical or unsymmetrical azo compounds (the Mills reaction).554 A wide variety of substituents may be present in both aryl groups. Unsymmetrical azo compounds have also been prepared by the reaction between aromatic nitro compounds ArN02 and N-acyl aromatic amines Ar NHAc.555 The use of phase transfer catalysis increased the yields. 

Phase-transfer catalysis has been developed by the combination of Keggin-type heteropolyanions and quaternary countercations such as tetrahexyl-ammonium or cetylpyridinium ion. The oxidations of alcohols (306), allyl alcohols (307), olefins (308), alkynes (309), /J-unsaturated acids (310), v/ c-diols (311), phenol (312), and amines (313) are the examples. 

In particular, it is not only the cinchona alkaloids that are suitable chiral sources for asymmetric organocatalysis [6], but also the corresponding ammonium salts. Indeed, the latter are particularly useful for chiral PTCs because (1) both pseudo enantiomers of the starting amines are inexpensive and available commercially (2) various quaternary ammonium salts can be easily prepared by the use of alkyl halides in a single step and (3) the olefin and hydroxyl functions are beneficial for further modification of the catalyst. In this chapter, the details of recent progress on asymmetric phase-transfer catalysis are described, with special focus on cinchona-derived ammonium salts, except for asymmetric alkylation in a-amino acid synthesis. 

Various allylic amines and protected allylic alcohols were tested using different cyclodextrins. Although only low to moderate enantioselectivity was obtained, the method demonstrated for the first time an enantioselective inverse phase-transfer catalysis hydration reaction via an oxymercuration-demercuration process. 

The reaction of ethyl 2-phenyl-4//-furo[3,2-/>]pyrrole-5-carboxylate (94) with 2-nitrobenzyl-oromide afforded ethyl 4-(2-nitrobenzyl)-2-phenylfuro[3,2-6]pyrrole-5-carboxylate (269) under conditions of phase transfer catalysis by utilization of sodium carbonate and tetrabutylammonium bromide. This product (269) was hydrogenated using palladium-on-charcoal catalyst to give the amine (270), which cyclized in the presence of 2-hydroxypyridine to give 2-phenylfuro[2, 3 4,5]pyrrolo[2,l-c]benzo[l,4]diazepin-l 1-one (271) <92CCC1487>. 

The chloramine derivatives (ArS02NClNa) of a variety of other aryl-sulfonamides (Ar = phenyl, o-tolyl, p-chlorophenyl,/>-nitrophenyl, and o-carboalkoxyphenyl) have been used successfully in these catalytic oxy-aminations. Since only chloramine-T (Ar = p-tolyl) and chloramine-B (Ar = phenyl) are commercially available, we have developed a convenient procedure for generating the chloramines in situ for use in the modification involving phase-transfer catalysis. One simply stirs a suspension of the arylsulfonamide with an equivalent of sodium hypochlorite (Clorox) until a homogeneous solution is obtained. When this solution is used in the PTC method (see Ref. 2 for experimental details), the yields of oxyaminated product are comparable with those obtained with isolated chloramine salts. 

Peroxidic initiators, like dibenzoyl peroxide, are too reactive with phenolic and aminic moieties and can be applied only exceptionally [50], Inorganic peroxides, like potassium persulfate, were used for emulsion polymerization of functionalized monomers [51]. Phase transfer catalysis may be also applied using persulfate initiation. To circumvent problems with the peroxide initiation, 4,4 -azobis(4-cyanovaleric acid), a water soluble initiator, was successfully used [48]. 

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