Tetra-n-butylammonium hydrogen

AcCl, NaOH, dioxane, Bu4N HS04 , 25°, 30 min, 90% yield. Phase-transfer catalysis with tetra-n-butylammonium hydrogen sulfate effects acylation of sterically hindered phenols and selective acylation of a phenol in the presence of an aliphatic secondary alcohol. 

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]. 

Cation exchange produces tetra-n-butylammonium hydrogen persulphate [6, 7] which, as with other peroxy compounds, should be treated as POTENTIALLY EXPLOSIVE. 

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. 

Amides from nitriles. One classical reagent for this reaction is H202-Na0H in a suitable solvent.3 This reaction can be carried out advantageously under phase-transfer catalyzed conditions.4 Tetra-n-butylammonium hydrogen sulfate is satisfactory the effectiveness varies with the structure of the nitrile. An excess of 30% H202 is used the solvent system is CH2C12 20% NaOH. Yields are 85-95%. 

A two-phase mixture of methyl propiolate (5.0 g, 59.5 mmol), boric acid (5.5 g, 89 mmol), sodium benzenesulfinate (9.75 g, 59.5 mmol), and tetra-n-butylammonium hydrogen sulfate (3.0 g, 8.75 mmol) (Note 1) in tetrahydrofuran water (200 mL, 1 1) is stirred vigorously at room temperature for 48 hr (Note 2). The solution is acidified to pH 4 (2 N hydrochloric acid) and extracted into diethyl ether (4 x 50 mL) (Note 3). The organic layer is dried (MgSCU) and concentrated under reduced pressure to afford 13.75 g of yellow oil (Note 4) which is subjected to flash column chromatography (1.5 1 hexanes-diethyl ether) to afford initially methyl (E)-3-(benzenesulfonyl)prop-2-enoate (400 mg, 2.9%) and then the desired Z-isomer (10.89 g, 81%) as a pale yellow solid, pure by spectral study (Note 5). 

Amino acid synthesis (8, 389). Alkylation of the aldimine (1) from glycine ethyl ester and /j-chlorobenzaldehyde under phase-transfer conditions offers a general route to amino acids. Either liquid-liquid phase-transfer or solid-liquid phase-transfer catalytic conditions are satisfactory with active halides, but alkylation with allylic halides and less active alkyl halides is best effected under ion-pair extraction conditions (6,41), with 1 equiv. of tetra-n-butylammonium hydrogen sulfate (76-95% yields).1... 

Fig. 4. Gradient elution separation of ribonucleotides. Mobile phase (A) 0.025 M tetra-n-butylammonium hydrogen sulfate, 0.050 M KHjP04,0.080 M NH4CI buffered at pH 3.90 (B) 0.025 tetravt-butylammonium hydrogen sulfate, 0.10 M KHjPO, 0.20 M NH4CI buffered at pH 3.4, 30% methanol. Operating conditions 40-min gradient program (concave 8) at 1 ml/min. Reprinted with permission from Hoffman and Liao (H19). Copyright by the American Chemical Society.

Dehydrohalogenation. Aryl vinyl ethers are prepared conveniently by dehy-drohalogenation of aryl 2-haloethyl ethers with aqueous sodium hydroxide with tetra-n-butylammonium hydrogen sulfate as phase-transfer catalyst (equation I). 

Solid-liquid phase-transfer catalysts. Diphenylphosphinic hydrazide (1) is not alkylated efficiently under usual phase-transfer conditions, but is alkylated by use of solid Na0H-K2C03 with benzene as solvent. The reaction is strongly accelerated by tetra-n-butylammonium hydrogen sulfate. The role of K2CO3 is not clear. The products are hydrolyzed by 15% HCl to pure monoalkylhydrazines. 

Tetra-n-butylammonium di-r-butyl phosphate, [(CH3)3CO]2PON[C4Hg-n]4 (1). Mol. wt. 451.7, m.p. 108-110°. The salt is prepared by reaction of potassium di-(-butyl phosphate with tetra-n-butylammonium hydrogen sulfate in aqueous NaOH-CHjCU (96% yield). 

Hydroxydithiocinnamic acids (1) can be converted into the monosalt by treatment with tetra-n-butylammonium hydrogen sulfate and NaOCHj, which on alkylation gives the dithioesters (2) in high yield. Mercaptals (3) can be prepared in 70-88% yield by treatment of (2) with thallous ethoxide (2, 407 411) and an alkyl halide. 

ALLYLIC PYROPHOSPHATES Tris-(tetra-n-butylammonium)hydrogen pyrophosphate. 

P-Lactams.1 /(-Amino acids are converted to /(-lactams by dehydration with methanesulfonyl chloride under phase-transfer conditions. Tetra-n-butylammonium hydrogen sulfate is the most useful ammonium salt (equation I). 

---