Tetra-n-butylammonium salts

The catalyst anion has also been shown to have a large influence on the reaction rate. The extraction constant of tetra-n-butylammonium salts between water and chloroform decreases with different anions as follows picrate CIO4 > T > toluene sulphonate > NO.-i > Br > benzoate > Cf > acetate > OH (Esikova, 1997 Dehmlow, 1993). 

Leadbeater NE, Pillsbury SJ, Shanahan E, Williams VA (2005) An assessment of the technique of simultaneous cooling in conjunction with microwave heating for organic synthesis. Tetrahedron 61 3565-3585 Lee CKY, Holmes AB, Ley SV, McConvey IF, Al-Duri B, Leeke GA, Santos RCD, Seville JPK (2005) Efficient batch and continuous flow Suzuki crosscoupling reactions under mild conditions, catalysed by polyurea-encapsulated palladium (II) acetate and tetra-n-butylammonium salts. J Chem Soc Chem Commun 2175-2177... 

The interfacial mechanism provides an acceptable explanation for the effect of the more lipophilic quaternary ammonium salts, such as tetra-n-butylammonium salts, Aliquat 336 and Adogen 464, on the majority of base-initiated nucleophilic substitution reactions which require the initial deprotonation of the substrate. Subsequent to the interfacial deprotonation of the methylene system, for example the soft quaternary ammonium cation preferentially forms a stable ion-pair with the soft carbanion, rather than with the hard hydroxide anion (Scheme 1.8). Strong evidence for the competing interface mechanism comes from the observation that, even in the absence of a catalyst, phenylacetonitrile is alkylated under two-phase conditions using concentrated sodium hydroxide [51],... 

Hydrogen bromide, trimethylsilyl bromide and acetyl bromide have all been proven to be suitable bromide transfer agents [e.g. 12, 13]. Tetra-n-butylammonium salts catalyse the interconversion of dichloroalkanes into bromochloroalkanes and chloroiodoalkanes upon reaction with an excess of bromo- and iodobutane, respectively [14]. Similarly, mixed bromochloromethanes are obtained from the reaction of dibromochloromethane with benzyltriethylammonium chloride under basic conditions [15]. 

As an alternative to the oxidation of sulphides and sulphoxides (see Chapter 10), sulphones can be prepared by the nucleophilic substitution reaction of the sulphinite anion on haloalkanes. In the absence of a phase-transfer catalyst, the reaction times are generally long and the yields are low, and undesirable O-alkylation of the sulphinite anion competes with S-alkylation. The stoichiometric reaction of the preformed tetra-n-butylammonium salt of 4-toluenesulphinic acid with haloalkanes produces 4-tolyl sulphones in high yield [1], but it has been demonstrated that equally good... 

It is noteworthy that benzyltriethylammonium chloride is a slightly better catalyst than the more lipophilic Aliquat or tetra-n-butylammonium salts (Table 5.2). These observations obviously point to a mechanism in which deprotonation of the amine is not a key catalysed step. As an extension of the known ability of quaternary ammonium halides to form complex ion-pairs with halogen acids in dichloromethane [8], it has been proposed that a hydrogen-bonded ion-pair is formed between the catalyst and the amine of the type [Q+X—H-NRAr] [5]. Subsequent alkylation of this ion-pair, followed by release of the cationic alkylated species, ArRR NH4, from the ion-pair and its deprotonation at the phase boundary is compatible with all of the observed facts. 

Dichlorocarbene has also been generated by the reaction of tetrachloromethane, hexachloroethane, or bromotrichloromethane using 60% aqueous or solid potassium hydroxide in the presence of a tetra-n-butylammonium salt [15, 16]. Yields of insertion products are similar to those obtained by Makosza s procedure. 

Chromium trioxide is also solublized in dichloromethane in the form of complex chromates Q+[X(CrO,) ] by the addition of an appropriate tetra-n-butylammonium salt [9-14],... 

Much emphasis has been placed on the selectivity of quaternary ammonium borohydrides in their reduction of aldehydes and ketones [18-20]. Predictably, steric factors are important, as are mesomeric electronic effects in the case of 4-substituted benzaldehydes. However, comparison of the relative merits of the use of tetraethyl-ammonium, or tetra-n-butylammonium borohydride in dichloromethane, and of sodium borohydride in isopropanol, has shown that, in the competitive reduction of benzaldehyde and acetophenone, each system preferentially reduces the aldehyde and that the ratio of benzyl alcohol to 1-phenylethanol is invariably ca. 4 1 [18-20], Thus, the only advantage in the use of the ammonium salts would appear to facilitate the use of non-hydroxylic solvents. In all reductions, the use of the more lipophilic tetra-n-butylammonium salt is to be preferred and the only advantage in using the tetraethylammonium salt is its ready removal from the reaction mixture by dissolution in water. 

The deep blue chromophore ca. 580 nm) formed by deprotonation of S NH was isolated as its tetra-n-butylammonium salt and identified as the S N" anion in 1973 but the structure of this unusual anion remained uncertain until an X-ray crystal structure determination of PPN S N", prepared by the thermal decomposition of PPN SjN in boiling acetonitrile, was reported in 1979... 

With respect to the oxygenation of methyl 4-hydroxybenzoate (as its tetra-n-butylammonium salt) to methyl 3,5-dihydroxybenzoate, remarkable differences in activity for this test reaction were observed with the three ligand sys-... 

Oxidative lactonization of unsaturated diacids (9, 265). Further study of this reaction indicates that it is general and can be controlled to result in cts-addition of two carboxylic oxygens to the double bond. Two experimental conditions are satisfactory (I) treatment of the diacid in CHClj or CII3CN with a large excess of Pb(0Ac)4 and (2) treatment of the tetra-n-butylammonium salt of the diacid in CH3CN with 6 15 equivalents of PbfOAc).,. Yields by the latter procedure are generally higher. 

Although the treatment of a phosphorodichloridate with the tri-n-butylammonium salt of phosphoric acid seems a plausible route to nucleoside diphosphates, this has recently been shown instead to be a means of preparing the triphosphate.8 Probably the most reliable method for preparing diphosphates is that described by Poulter,9 in which the tetra-n-butylammonium salt of a nucleophilic phosphorus component, for example, pyrophosphate is reacted with a nucleoside 5 -tosylate in acetonitrile (Figure 9.2). 

The synthesis of nucleoside diphosphates is best achieved using the Poulter reaction,9 which involves reaction of the tris(tetra-n-butylammonium) salt of pyrophosphate with a nucleoside 5 -tosylate in acetonitrile. A general procedure for the synthesis of nucleoside tosylates of thymidine and 2 -deoxyadenosine is included (Protocol 15), whilst the syntheses of the other tosylates (including ribonucleosides) have been described using related procedures. Simple modification of the protocol, whereby the tetra-n-butylammonium salt of pyrophosphoric acid is replaced by methylene or difluomethylene bis phosphonate, allows the synthesis of hydrolytically stable dNTP analogues.10... 

In the first synthesis of the potent antitumor agent may famine 131) by Corey et al. [75], linear amino acid 129 was first converted to the soluble tetra-n-butylammonium salt and then slowly added to a solution of excess mesitylene-sulfonyl chloride and diisopropylethylamine in benzene at 40 °C for 28 h to afford macrolactam 130 in 71% yield (Scheme 44). 

Examination of the Sn2 reaction between ethyl tosylate and halide ions in hexamethylphosphoric triamide (fir = 29.3) with a variety of counter ions [Li , [n-C4H9)4N ] has shown that the rates obtained with Hthium salts are always higher than those with the corresponding tetra-n-butylammonium salts [341]. This is in contrast to the situation observed in acetone [279]. This means that, in this particular solvent, lithium salts are more dissociated than tetraalkylammonium salts. This has indeed been confirmed by conductivity measurements [341, 342], The lithium cation apparently has specific interactions with strong EPD solvents such as [(CH3)2N]3PO cf. Section 3.3.2). 

Reetz studied the polymerization of nBuA initiated by tetrabutylammonium thiolates, which are easily prepared by reaction of thiols with tetrabutylammonium hydroxide ". Nevertheless, only polymers of molecular weight under 2000 were formed " ". This problem was overcome by using the tetra-n-butylammonium salt of diethyl 2-ethylmalonate (37) as initiator (equation 42). PnBuA was obtained with a predictable molecular weight and a low polydispersity index (1.1 < M /M < 1.2). 

Table 6). Where the expense of tetra-n-butylammonium hydroxide is a consideration, or in cases where the product carboxylic acid is poorly soluble in ether (making extractive removal of tetra-n-butylammonium salts difficult), an alternative procedure employing sodium hydroxide in a mixture of water, methanol, and ferf-butyl alcohol can be used. The mechanism of the base-induced hydrolysis reaction is believed to involve initial rate-limiting intramolecular N- O acyl transfer, followed by rapid saponification of the resulting (3-amino ester. ... 

The excellent solubility of MogCl tetra-n-butylammonium salt in nonaqueous solutions permits investigations in various organic solvents, with the most important conclusion that the observed ECL efficiency (4>es in the range 0.014-0.50) depends strongly on the reaction medium [199]. The es efficiency obtained is quite small (0.065) in ACN solutions but increases with lowering of the solvent polarity in a similar way to what is observed for organic ECL systems (up to 0.50 in dichloromethane or 1,2-dichloroethane solutions). 

The blue species formed from heptasulphur imide, S7NH, in basic media has been isolated as the tetra-n-butylammonium salt and characterized as the NS4 anion.100101 The addition of tetra-n-butylammonium hydroxide to a solution of S7NH in diethyl ether at —78 °C produced a yellow-green precipitate which turned purple-blue after 3 days at room temperature. The precipitate was shown to be a mixture of orthorhombic cyclo-Sg and a blue solid of composition Bu"N(S4N). Since solution of the blue solid in HMPA or THF gave an identical visible spectrum to that of S7NH in HMPA, the following equilibria were proposed ... 

Quaternary ammonium salts of amino acids can be formed in the usual way (Equation (4.1) Lansbury et al., 1989) and have the particular advantage that they are soluble in aprotic organic solvents (particularly the tetra-n-butylammonium salts), so opening up to amino acids (which are not significantly soluble in these solvents) a wider range of reactions (Nagase et al., 1993). 

We examined catalytic properties of cobalt-containing compounds having different nature, namely, the simple salt, Co(N03)2-6H20, tetra-n-butylammonium salts of PWnCoO ... 

Catalysts. Co(N03)2-6H20 was of pure grade. CoNaY zeolite and tetra-n-butylammonium salts of PWiiCo and CoW 12 heteropolyanions were obtained as described in [19] and [25], respectively. The content of cobalt in the CoNaY zeolite was 3.29 % wt. The formation of the Keggin structure and the purity of C0W12 and PWuCo were confirmed by 0 and P NMR, respectively. 

Lithium chloride is an effective promoter (no organic ligand added) for the Cul-catalysed N-1 arylation of 5- and 7-azaindoles. Very clean and high-yielding V-arylation results from the use of the tetra-n-butylammonium salt of 2-pyridone as substrate for Cul-catalysed reactions with iodides. ... 

The reaction of tetra-n-butylammonium fluoride (TBAF) (available as a THF solution although it always contains some water) with benzylsilanes in, the presence of an aldehyde or ketone provided homobenzyl alcohols111 (equation 109). It is presumed that the reaction proceeds through the tetra-n-butylammonium salt of the benzyl anion. This... 

An additional relationship between the gas hydrate and the salt hydrate structures has been revealed by the discovery that bromine hydrate, Br2- 8.5H20, crystallizes in neither of the cubic gas hydrate structures but rather is nearly isostructural with the tetragonal tetra-n-butylammonium salt hydrates. Its ideal limiting composition would be Brj S.bHjO. 

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