Phase transfer catalysts Aliquat

A solution of 4-chloro-N-methyl-N-phenyl-2-(2-pyrrolyl)butanamide in toluene was added dropwise at 85°C over 40 min to 1 hour to a stirred suspension of ALIQUAT 336 (phase transfer catalyst, 2 mol % with respect to pyrrolylbutanamide) and granular sodium hydroxide (3 equivalents) in toluene (50 mL). After the addition was complete, the suspension was stirred under a nitrogen atmosphere at a temperature of 85°C for 30 min, then cooled to 35°C. Cooled water (200 mL) was rapidly added to the mixture and stirred for 15 min at 25°C. The solution was rinsed with water and the layers were separated. The organic layer was washed with water, then distilled under atmospheric pressure to recover the toluene and water. The resultant solution was cooled to 50°C and allowed to crystallize after the addition of hexane and a seed crystal. The suspension was cooled to 5°C and stirred for 15 minutes. The resultant precipitate was filtered, washed with 100 mL of hexane, and dried under vacuum at 25°C to yield approximately 38 g (63%) N-methyl-N-phenyl-2,3-dihydro-lH-pyrrolizine-l-carboxamide. This solid was recrystallized from toluene to yield colorless crystals of N-methyl-N-phenyl-2,3-dihydro-lH-pyrrolizine-l-carboxamide, melting point 112-112.5°C. 

Chlorobutanoyl chloride Phosphorus tribromide Methyl magnesium chloride ALIQUAT (phase transfer catalyst) Phosphorus oxychloride Benzoyl chloride... 

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... 

The diazo transfer reaction between p-toluenesulfonyl azide and active methylene compounds is a useful synthetic method for the preparation of a-diazo carbonyl compounds. However, the reaction of di-tert-butyl malonate and p-toluenesulfonyl azide to form di-tert-butyl diazomalonate proceeded to the extent of only 47% after 4 weeks with the usual procedure." The present procedure, which utilizes a two-phase medium and methyltri-n-octylammonium chloride (Aliquat 336) as phase-transfer catalyst, effects this same diazo transfer in 2 hours and has the additional advantage of avoiding the use of anhydrous solvents. This procedure has been employed for the preparation of diazoacetoacetates, diazoacetates, and diazomalonates (Table I). Ethyl and ten-butyl acetoacetate are converted to the corresponding a-diazoacetoacetates with saturated sodium carbonate as the aqueous phase. When aqueous sodium hydroxide is used with the acetoace-tates, the initially formed a-diazoacetoacetates undergo deacylation to the diazoacetates. Methyl esters are not suitable substrates, since they are too easily saponified under these conditions. 

The submitter obtained methyltri-n-octylammonium chloride (Aliquat 336) from General Mills Company, Chemical Division, Kankakee, Illinois. The phase-transfer catalyst used by the checkers, which was supplied by Fluka AG through Tridom Chemical Inc., was a mixture in which the alkyl chains varied in length from re-octyl to re-decyl with the former predominating. 

Solvent effect. Several different solvent systems were investigated for the coupling of 4-bromoanisole with 4-phenylboronic acid catalyzed by BaCeo 95Pdoo50295. The resnlts are summarized in Table 27.2. A phase-transfer catalyst (Aliquat 336) was added in the experiment involving toluene/H20. However, only the IPA/H2O solvent system was effective, resulting in a biaiyl yield of 100% all other solvents gave rather low yields. 

Potassium acetate, for example, can be readily alkylated by the use of an equivalent amount of an alkylating reagent (for example, an alkyl halide) in the presence of the phase-transfer catalyst Aliquat 336 (10 mol%) (Scheme 4.7) [16]. Yields are always near quantitative within a few minutes of microwave irradiation, irrespective of the chain length and the nature of the leaving group. This procedure has been scaled-up from 50 mmol to 2 mol scale in a large batch reactor [17]. 

It is worth mentioning at this point that according to Normant et al. (1975) simple polyamines such as tetramethylethylenediamine (TMEDA) are even more active than [2.2.2]-cryptand in the benzylation of acetates in acetonitrile under liquid-solid conditions. These authors suggested that the activity was due to salt solubilization by cation complexation and not to formation of a quaternary ammonium ion since the latter showed no activity. This statement, however, is not in line with the results of Cote and Bauer (1977), who were unable to detect any interaction between K+ and TMEDA in acetonitrile. Furthermore, Vander Zwan and Hartner (1978) found Aliquat 336 (tricaprylylmethylammonium chloride) to be almost as effective as TMEDA in this reaction (Table 30). It might well be, however, that in amine-catalysed benzylation reactions the quaternary salt formed in situ acts both as a reactant and as a phase-transfer catalyst, since Dou et al. (1977) have shown that the benzyltriethylammonium ion is a powerful benzylation agent. 

Rhodium(III) complexes [e.g. (i-Pr,P)2Rh(H)Cl2] in the presence of quaternary ammonium salts are excellent catalysts for the hydrogenolysis of chloroarenes under mild conditions [5] other labile substituents are unaffected. Hydrodehalogenation of haloaryl ketones over a palladium catalyst to give acylbenzenes is also aided by the addition of Aliquat [6]. In the absence of the phase-transfer catalyst, or when the hydrogenation is conducted in ethanol, the major product is the corresponding alkyl-benzene, which is also produced by hydrodehalogenation of the halobenzyl alcohols. 

These observations showed that the reaction can be simplified by preformation of the indanone enolate in toluene/50% NaOH and subsequent addition of catalyst and CH3CI (Figure 12). This eliminates the "induction period and most importantly the high sensitivity of rate and ee to the catalyst/indanone ratio. Detailed kinetic measurements on this preformed enolate methylation in toluene/50% NaOH determined that the reaction is 0.55 order in catalyst. This is consistent with our finding that the catalyst goes into solution as a dimer which must dissociate prior to com-plexation with the indanone anion. If the rate has a first order dependence on the monomer, the amount of monomer is very small, and the equilibration between dimer and monomer is fast, then the order in catalyst is expected to be 0.5. The 0.5 order in catalyst is not due to the preformation of solid sodium indanone enolate but is a peculiarity of this type of chiral catalyst. Vlhen Aliquat 336 is used as catalyst in this identical system the order in catalyst is 1. Finally, in the absence of a phase transfer catalyst less than 2% methylation was observed in 95 hours. 

A critical survey of the literature on free radical polymerizations in the presence of phase transfer agents indicates that the majority of these reactions are initiated by transfer of an active species (monomer or initiator) from one phase to another, although the exact details of this phase transfer may be influenced by the nature of the phase transfer catalyst and reaction medium. Initial kinetic studies of the solution polymerization of methyl methacrylate utilizing solid potassium persulfate and Aliquat 336 yield the experimental rate law ... 

Scission of Polysulfide Crosslinks in Scrap Rubber Particles. Throughout this study, we used a single lot of scrap rubber peelings having the average composition described in the Experimental Section. We began our studies with Aliquat 336 as the phase transfer catalyst because of its proven effectiveness in simple systems and its commercial availability. When devulcanization is performed in a refluxing benzene/aqueous NaOH mixture, the chemical crosslink density (M... 

Various methods can be used to prepare dihydro- 1,4-benzoxazines and -benzothiazines (B-78MI22701). A recent approach to the first group of compounds is to react 2-hydroxyacetanilides (279) with 1,2-dibromoethane and sodium hydroxide in acetonitrile containing the phase transfer catalyst Aliquat 336 (Scheme 122) (79S541). 1,1-Dioxides of dihydrobenzo-l,4-thiazines (281) are generated through the cyclization of imines (280) with methanesulphonyl chloride in the presence of triethylamine (79CI(L)26). 

Anelli s TEMPO-mediated oxidation can be accelerated by the addition of a quaternary ammonium salt, like Aliquat 336, acting as a phase transfer catalyst. This can be advisable in the oxidation of hindered secondary alcohols but can encourage the over-oxidation of primary alcohols to carboxylic acids.16... 

Using 1.1 equivalents of NaOCl, the selective oxidation of the primary alcohol occurs. With, 2.2 equivalents of NaOCl, the main reaction product results from the oxidation of both alcohols, giving a ketoaldehyde. Finally, employing 3.6 equivalents of NaOCl, and including Aliquat 336 as a phase-transfer catalyst that greatly accelerates the reaction, a complete oxidation of the secondary alcohol to ketone and the primary alcohol to a carboxylic acid occurs. 

Trimethylsilyl ethers.2 These protective derivatives of alcohols are conveniently prepared with K2COj or Na2C03 as base and Aliquat 336 as the phase-transfer catalyst (65 95% yield). r-Butyldimethylsilyl ethers can be prepared in the same way. 

Alkynes.10 Alkynes can be prepared by double dehydrobromination of pic-dibromides in petroleum ether by use of powdered KOH and catalytic amounts of a phase-transfer catalyst. Tetraoctylammonium bromide, 18-crown-6, or even Aliquat 336 are much more effective than more hydrophilic quarternary ammonium salts, such as tetrabutylammonium hydrogen sulfate, previously used (7, 354-355)." Isolated yields are 80-98%. Yields are generally lower when mc-dichlorides are used as the starting material. 

Ester interchange,3 Exchange of methyl or ethyl esters can be conducted with 1 equiv. of an alcohol and a base (K2CO,) in the presence of Aliquat or Bu4NHS04 and in the absence of an additional solvent. Indeed it can be carried out at 70° in the absence of a phase-transfer catalyst. 

Alcohols can be dehydrogenated to carbonyl compounds by exposure to a catalytic amount of a rhodium(I) complex under phase-transfer conditions. This reaction is particularly useful for benzylic alcohols such as 1-phenylethanol (50) which gave acetophenone (51) in 78% yield using chlorodicarbonylrhodium(I) dimer as the metal catalyst and benzyltrieth-ylammonium chloride or Aliquat 336 as the phase-transfer catalyst (52). 

Aliquat 336 (tri-n-alkylmethylammonium chloride) was obtained from Aldrich Chemical Company, Inc. The material is a mixture of Ca and C10 chains with Cs predominating. There is a slight initial exothermic reaction on adding the phase transfer catalyst. Intermittent cooling with a cold water bath is required to keep the temperature below 35°C. 

Gomberg-Bachmann biphenyl synthesis. Reaction of stable arenediazonium tet-rafluoroborates or hexafluorophosphates in an aromatic solvent with potassium acetate (2 equiv.) and a phase-transfer catalyst results in biar Is in high yield. Crown ethers, Aliquat 336, and tetrabutylammonium hydrogen sulfate arc all effective catalysts. The reaction is useful for synthesis of unsymmetrical biaryls. The ortho-isomer predominates in reactions with a monosubstituted benzene. The most selective method is to couple a substituted arenediazonium salt with a symmetrical arene. 

Later, phase-transfer catalysts such as Aliquat 336 [i.e., (C8H,)3N MeCl ] were used for the synthesis of benzyladenines 8 and 9 which improved the yield significantly. ... 

The solvated ion pair [(C8Hi7)3NMe] [RhCl4]", formed from aqueous rhodium trichloride and Aliquat-336 in a two-phase liquid system, hydrogenates a,p-unsaturated ketones and esters selectively at the C==C double bond. The reduction of benzylideneacetone follows first-order kinetics in substrate below 0.2 M, and approaches second-order in hydrogen at partial pressures below 0.12 atm (1 atm = 101.3 kPa). The catalysis also depends on the nature of the solvent, the phase transfer catalyst and stirring rates. 

The glycosylations of aryl alcohols using a phase transfer catalyst such as Et3N BnBr [23a, b], EtsN+BnCr [24], Me(CH2)i5N+Me3Br- [25,26], Bu4N+Br [27], Bu4NH+S04 [28], Aliquat 336 [29], and BnN" Bu3Cl [30] were also developed (O Table 3). 

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