Tetra-Alkylammonium Salt

Catalyst Cation. The logarithms of extraction constants for symmetrical tetra- -alkylammonium salts (log rise by ca 0.54 per added C atom. Although absolute numerical values for extraction coefficients are vastly different in various solvents and for various anions, this relation holds as a first approximation for most solvent—water combinations tested and for many anions. It is important to note, however, that the lipophilicity of phenyl and benzyl groups carrying ammonium salts is much lower than the number of C atoms might suggest. Benzyl is extracted between / -propyl and -butyl. The extraction constants of tetra- -butylammonium salts are about 140 times larger than the constants for tetra- -propylammonium salts of the same anion in the same solvent—water system. 

Whilst some organic compounds can be investigated in aqueous solution, it is frequently necessary to add an organic solvent to improve the solubility suitable water-miscible solvents include ethanol, methanol, ethane-1,2-diol, dioxan, acetonitrile and acetic (ethanoic) acid. In some cases a purely organic solvent must be used and anhydrous materials such as acetic acid, formamide and diethylamine have been employed suitable supporting electrolytes in these solvents include lithium perchlorate and tetra-alkylammonium salts R4NX (R = ethyl or butyl X = iodide or perchlorate). 

Additives such as acids, bases or tetra-alkylammonium salts ... 

Many examples of the phase-transfer catalysed epoxidation of a,(3-unsaturated carbonyl compounds using sodium hypochlorite have been reported [e.g. 7-10]. The addition of transition metal complexes also aids the reaction [11], but advantages in reaction time or yields are relatively insignificant, whereas the use of hexaethyl-guanidinium chloride, instead of a tetra-alkylammonium salt, enhances the rate of epoxidation while retaining the high yields (>95%) [10]. Intermediate (3-haloalkanols are readily converted into the oxiranes under basic conditions in the presence of benzyltriethylammonium chloride [12]. 

Bulky quaternary ammonium salts promote the ruthenium-catalysed oxidation of anilines by hydrogen peroxide to nitrobenzenes [25]. In the absence of the ammonium salt, the major product is the azoxybenzene, whereas lower molecular weight tetra-alkylammonium salts produce a mixture of products. 

As a rather strongly hydrophilic anion, nitrate requires an ISE membrane containing a strongly hydrophobic cation, as described on p. 169. This function was fulfilled in the first nitrate electrode from Orion Research by cation V [180] in nitro-p-cymene 5. The electrode can be used in the pH range 4-7. In other commercial electrodes, the ion-exchanger ion is a tetra-alkylammonium salt, for example in the electrode from Coming Co., substance XIII in solvent 6 [27]. An ISE with a renewable membrane surface was found to be very useful (see section 4.1 and fig. 4.4), in which the ion-exchanger solution contains the nitrate of crystal violet VII dissolved in nitrobenzene [191]. The NOj ISE also responds to nitrites that can be removed by addition of aminosulphonic acid. 

Chiral ligands XXXII and XXXIII are marked by slight but clear selectivity in ISEs with respect to chiral antipodes in tetra-alkylammonium salts [175, 209]. 

Hydrogen peroxide may be efficiently employed for the epoxidation of unfunctionalized aikenes in the presence of polyoxo complexes of tungsten and molybdenum . Venturello and coworkers first developed a phosphotungstate catalyst , with particular emphasis on the tetrakis(diperoxotungsto)phosphate anion P04[W(0)(02)2]4 , 37 , that in conjunction with H2O2 and a lipophilic tetra-alkylammonium salt Q+X as phase transfer... 

Retention of solutes and selectivity can be controlled by adjusting the type and concentration of the ion-pair reagent added and by selection of the type and concentration of the organic solvent in the mobile phase (135,168). The ion pair reagents most commonly used are tetra-alkylammonium salts such as cetrimide (155,156,177) and tetra-n-butylammonium (TBA). The TBA reagent can be used as TBA phosphate (159,184), TBA chloride (221), TBA hydrogen sulfate (188,189), or TBA hydroxide (168,175,183). 

The complex hydrate structure, 1.67 choline hydroxide-tetra-n-propyl-ammonium fluoride 30-33H2O (space group = R-3, a = 12.533, c = 90.525 A) was discovered by Udachin and Ripmeester (1999b). It should be noted that the tetra-n-propylammonium salt will not form a hydrate on its own (Dyadin et al., 1988), even though other tetra-alkylammonium salts will form a variety of hydrate structures. Similar to structures II, H, and IV, this complex structure consists of stacked sequences of layers, CABBCAABCCABBCAAB. That is,... 

Fig. 11. Inhibitory constants of tetra-alkylammonium salts, R4N, as function of n, the number of carbon atoms in the four substituents together (according to Table IV and V). O------O Eel esterase. ------ Human plasma ChE.

Even this is not all If the alkylation were to continue, the secondary and the tertiary amines would be produced all together in the reaction mixture. The reaction comes to an end only when the tetra-alkylammonium salt R4N+ is formed. This salt could be the product if a large excess of alkyl halide R1 is used, but other more controlled methods are needed for the synthesis of primary, secondary, and tertiary amines. 

Laidler has pointed out [11, 242] that Eq. (5-88) is best considered as a semi-quantitative formulation, which gives only a rough prediction of the effect of a change in fir on the rate of dipole-dipole reactions. This also applies to Eqs. (5-87) and (5-90). Nevertheless, in many cases a satisfactory correlation between rate constants and function of solvent relative permittivity has been obtained, as, for instance, in the Men-schutkin reaction between trialkylamines and haloalkanes forming quaternary tetra-alkylammonium salts [2, 56, 58, 60, 61, 64, 65, 245-247]. 

Macrolides. - Although many notable total syntheses of naturally occurring macrolides have been reported this year, most have used previously reported methods to effect the ring closure step. One of the oldest ways to form macrolides is by lactonisation of -halo-acids tetra-alkylammonium salts of 2-pyrrolidinone in DMP have been found to... 

Non-aqueous solutions of the XWuM complexes may be prepared from tetra-alkylammonium salts or by using phase transfer agents. The coordination of the organic solvent to M, replacing the water molecule, usually takes place with donor solvents. Dehydration of some (but not all) of the XWnM(H20) anions occurs after phase transfer for solvents like toluene with formation of species with a free... 

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