Tetra-n-butylammonium hydrogen sulphate

The highest yields in the Ciamician-Dennstedt reaction have been achieved using phase transfer catalysts (Table 8.3.1). In the reaction, the pyrrole or indole and a phase transfer catalyst (PTC, in this case benzyltriethylammonium chloride) are dissolved in chloroform and aqueous sodium hydroxide is added. Yields are typically in the 40s to 60s (rather than in the 20s for a typical Ciamician-Dennstedt reaction). More recently, yields as high as 80% have been reported using tetra-n-butylammonium hydrogen sulphate as the phase transfer catalyst. ... 

Polymeric aryl ethers have been obtained from, for example, bisphenol and 1,4-dichlorobut-2-ene or 1,4-bis(chloromethyl)benzene in a basic medium in the presence of tetra-n-butylammonium hydrogen sulphate [22],... 

Trichloroacetimidates, CCl,C(NH)OR, have been prepared under mild conditions by the reactions of alcohols with trichloroacetonitrile under basic conditions promoted by catalytic amounts of tetra-n-butylammonium hydrogen sulphate [72]. The procedure is far superior to the standard methods which normally require anhydrous reaction conditions. 

In contrast, liquidiliquid phase-transfer catalysis is virtually ineffective for the conversion of a-bromoacetamides into aziridones (a-lactams). Maximum yields of only 17-23% have been reported [31, 32], using tetra-n-butylammonium hydrogen sulphate or benzyltriethylammonium bromide over a reaction time of 4-6 days. It is significant that a solidiliquid two-phase system, using solid potassium hydroxide in the presence of 18-crown-6 produces the aziridones in 50-94% yield [33], but there are no reports of the corresponding quaternary ammonium ion catalysed reaction. Under the liquidiliquid two-phase conditions, the major product of the reaction is the piperazine-2,5-dione, resulting from dimerization of the bromoacetamide [34, 38]. However, only moderate yields are isolated and a polymer-supported catalyst appears to provide the best results [34, 38], Significant side reactions result from nucleophilic displacement by the aqueous base to produce hydroxyamides and ethers. 

It can be assumed that the azoles are deprotonated by the interfacial exchange mechanism, but it is noteworthy that it has been suggested that the rate of alkylation of indole under liquiddiquid two-phase conditions decreases with an increase in the concentration of the sodium hydroxide [8]. The choice of catalyst appears to have little effect on the reaction rate or on the overall yields of alkylated azole. Benzyltriethylammonium chloride, Aliquat, and tetra-n-butylammonium hydrogen sulphate or bromide have all been used at ca. 1-10% molar equivalents (relative to the concentration of the azole) for alkylation reactions, but N-arylation of indole with an activated aryl halide requires a stoichiometric amount of the catalyst [8]. 

Tungsten-catalysed oxidation of alcohols by hydrogen peroxide is achieved in high yield in the presence of tetra-n-butylammonium hydrogen sulphate [20-22]. Secondary alcohols are converted into ketones (>90%) [e.g. 21], but primary alcohols generally are oxidized completely to the carboxylic acids [21], Aldehydes are also oxidized to the carboxylic acids [e.g. 21]. In contrast, using procedure 10.7.8.B, which is adaptable to scale up, benzyl alcohols are converted into the aldehydes benzoic acids are only formed with an excess of hydrogen peroxide [22],... 

Tetra-n-butylammonium hydrogen sulphate facilitates the enantiomeric epoxida-tion of alkenes by persulphates in the presence of chiral ketones (10.6.8). The reaction proceeds via the initial formation of chiral dioxiranes [23]. 

A similar dependence of the first-order rate constants with respect to the quantity of added water has been reported for the reaction of sodium formate with 1,4-dichlorobutane and related displacement reactions, In these studies tetra- n-butylammonium hydrogen sulphate and tetra- n-butylammonium bromide were used as catalysts and chlorobenzene as the solvent. 

Tetra-n-butylammonium hydrogen sulphate [32503-27-8] M 339.5, m 171-172 . Crystd from acetone. 

N-Substituted amides can be N-alkylated by alkyl halides using a two-phase system of solid NaOH-KaCOs in refluxing benzene with tetra-n-butylammonium hydrogen sulphate as phase-transfer catalyst." This method works well for the limited range of compounds studied. Potassium t-butoxide in ether containing small amounts of a crown ether has similarly been used to N-alkylate some iV-arylbenzanilides." N-Aryl-jS-keto-amides can be N-alkylated under standard conditions (NaH-DMF-RX) after first blocking the sensitive jS-keto-amide function by formation of a difluoro-oxyborane complex with BFs-EtjO. ... 

An alkylation-deprotection two-step sequence offers a new approach to the synthesis of pure monoakylhydrazines from diphenylphosphinic hydrazide (53). The phase-transfer procedure involves the use of a powdered NaOH-KgCOa mixture in refluxing benzene (Scheme 33). Although the reaction proceeds in the absence of a catalyst, a rate enhancement is observed in the presence of tetra-n-butylammonium hydrogen sulphate (TBAH). 

The cleavage of benzyl ethers using hydrobromic acid is promoted by tetra-n-butylammonium bromide [38]. Selective cleavage of aryl silyl ethers can be effected in the presence of aliphatic silyl ethers using solid sodium hydroxide with tetra-n-butyl-ammonium hydrogen sulphate [39]. 

Tetra-n-butylammonium cyanoborohydride has been prepared by metathesis from the quaternary ammonium hydrogen sulphate and sodium cyanoborohydride. Other tetraalkylammonium cyanoborohydrides have also been synthesized [10]. 

Allylic nitro compounds are reduced by carbon disulphide under mild basic catalytic conditions to yield the conjugated oximes (Scheme 11.7) [8]. The reaction is sensitive to the amount of base used, and benzyltriethylammonium chloride appears to be a better catalyst than tetra-n-butylammonium bromide or hydrogen sulphate. Saturated nitro compounds are not reduced under these conditions. 

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