Aliquat as phase transfer catalyst

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. 

Quaternary alkylammonium salts, tertiary amines, and crown ethers have all been utilized as catalysts in the reaction of hydroxide with chloroform to yield dichlorocarbene. The most commonly utilized catalyst has been benzyltriethylammonium chloride (see Sect. 1.7) but other quaternary ammonium chloride catalysts have proved effective. Cetyltrimethylammonium chloride and tricaprylmethylammonium chloride (Aliquat 336) have both been used effectively in the cyclopropanation of simple alkenes. The use of Z e a-hydroxyethyltrialkylammonium hydroxides as phase transfer catalysts results in increased regioselectivity in the addition of dichlorocarbene to olefins [12]. Crown ethers such as dibenzo and dicyclohexyl-18-crown-6 have both been utilized in place of quaternary ammonium compounds. 18-Crown-6 has also been used as a catalyst in the phase transfer thermal decomposition of sodium trichloroacetate to yield dichlorocarbene [13]. 

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. 

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. 

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... 

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. 

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). 

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 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). 

Melville and Goddard [204] used rotating disk flow to measure the mass transfer coefficient between the solid and liquid phases in SLPTC for the reaction of benzyl chloride and solid potassium acetate using Aliquat 336 as the catalyst in acetonitrile as solvent. The concentration of quaternary ammonium acetate is expressed in the following equations ... 

Aliquat 336, a quaternary ammonium salt, has been used as a phase transfer catalyst for a solid-liquid interface. A comparison of its catalytic ability with that of 18-crown-6-ether and tetramethylethylenediamine shows that the quaternary ammonium salt is equivalent and sometimes superior in catalysing anion displacement reactions of acetate, fluoride and adeninyl anions. ... 

Polymer Studies. General Procedure. The desired amount of BPA (generally 45.35g), sodium or potassium hydroxide, phase transfer catalyst (Aliquat 336 or tetrabutylammonium bromide), p - t-butylphenol (0.75% as a chain stopper) and methylene chloride or methylene chloride/chlorobenzene (1/3) were heated at reflux for a period of 5 hr under nitrogen. At this point the reaction mixture was diluted with methylene chloride and filtered through Celite. The mixture was then either a) poured directly into methanol to precipitate the polymer or b) split into two portions one portion was precipitated by methanol, the second was reverse precipitated using methanol/acetone. (see below)... 

Since the solubility of COS into an aqueous alkaline solution has some importance here, and the reaction takes place only in the aqueous phase, Bhave and Sharma (1983) have introduced species such as tricapryl methyl ammonium chloride (Aliquat 336) into the organic phase. This species acts as a phase-transfer catalyst, transferring OH ions into the organic phase near the interface for reaction with COS. Thus COS reacts both in the organic and the aqueous phase, and the rate of COS extraction is increased considerably. 

Quaternary salts can be used in catalytic amount in liquid-sobd phase transfer conditions. For example, solid potassium acetate reacted with benzyl chloride in acetonitrile using A -methyl-MMA -trioctylammonium chloride (Aliquat 336) as the phase transfer catalyst (PTC) (Eq. 9.10) [38]. 

These alkylation procedures can benefit greatly from the use of microwave activation, which can reduce reaction times by a factor of 60. Moreover, the often tedious separation of high boiling solvents (DMF, DMSO, HMPA) can be omitted, if reactions are conducted under solvent-free conditions in the presence of ferf-BuOK as a base and a phase transfer catalyst such as Aliquat 336. Chemical yields are comparable to those obtained using classical procedures and only traces of dialkylated byproducts have been detected. Moreover, microwave treatment of the diester product with LLF or LiCl (Krapcho procedure) under solvent-free conditions provides the corresponding mono-ester by selective decarbalkoxylation . 

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