Tetraalkylammonium bromide

Table 3.1-3 Changes in melting points for symmetric tetraalkylammonium bromide salts with increasing size of alkyl substituents.

Another catalytic system which has been successfully applied to the autoxidation of substituted toluenes involves the combination of Co/Br" with a quaternary ammonium salt as a phase transfer catalyst (ref. 20). For example, cobalt(II) chloride in combination with certain tetraalkylammonium bromides or tetraalkylphosphonium bromides afforded benzoic acid in 92 % yield from toluene at 135-160 °C and 15 bar (Fig. 19). It should be noted that this system does not require the use of acetic acid as solvent. The function of the phase transfer catalyst is presumably to solubilize the cobalt in the ArCH3 solvent via the formation of Q + [CoBr]. ... 

Ammonium salts are commonly used to stabilize aqueous colloidal suspensions of nanoparticles. The first such example was reported in 1983-84 by Januszkie-wicz and Alper [96, 97], who described the hydrogenation of several benzene derivatives under 1 bar H2 and biphasic conditions starting with [RhCl(l,5-hexa-diene)]2 as the metal source and with tetraalkylammonium bromide as a stabilizing agent Some ten years later, Lemaire and coworkers investigated the cis/... 

Tetraalkylammonium bromide was found to be a good catalyst for the conjugate addition of thiols to a,p-unsaturated nitriles, carboxylic esters, ketones, aldehydes, and nitro alkenes. The reactions proceeded rapidly and gave high yields of products (typically, 90%) (160). 

The salt effects of potassium bromide and a series office symmetrical tetraalkylammonium bromides on vapor-liquid equilibrium at constant pressure in various ethanol-water mixtures were determined. For these systems, the composition of the binary solvent was held constant while the dependence of the equilibrium vapor composition on salt concentration was investigated these studies were done at various fixed compositions of the mixed solvent. Good agreement with the equation of Furter and Johnson was observed for the salts exhibiting either mainly electrostrictive or mainly hydrophobic behavior however, the correlation was unsatisfactory in the case of the one salt (tetraethylammonium bromide) where these two types of solute-solvent interactions were in close competition. The transition from salting out of the ethanol to salting in, observed as the tetraalkylammonium salt series is ascended, was interpreted in terms of the solute-solvent interactions as related to physical properties of the system components, particularly solubilities and surface tensions. 

Tables IV-XVI show that the tetraalkylammonium salts have a large effect on both solvents in the binary solvent mixture, especially the larger tetraalkylammonium bromides, i.e., (n-C3H7)4NBr and (n-C4Hg)4NBr. This can be seen from consideration of the boiling temperature alone. This observation is also borne out by the surface tensions and solubilities at 25°C of the individual salts studied, the results of which are tabulated in Table XVII in water, in ethanol, and in an ethanol-water mixture at x = 0.206. For the higher homologs of the R4NBr series, these salts exert a large effect on the surface tensions of the solvent systems studied and show a marked increase in their solubility in ethanol.

Table XVII. Physical Properties of Saturated Solutions of Potassium Bromide and Various Tetraalkylammonium Bromides...

Table XVIII. Salt Effect Parameters and Reliability of Equation 1 to Predict the Salt Effect for Potassium Bromide and Tetraalkylammonium Bromides in Ethanol—Water Mixtures at Various Values of x...

The densities and volumetric specific heats of some alkali halides and tetraalkylammonium bromides were undertaken in mixed aqueous solutions at 25°C using a flow digital densimeter and a flow microcalorimeter. The organic cosolvents used were urea, p-dioxane, piperadine, morpholine, acetone, dime thy Isulf oxide, tert-butanol, and to a lesser extent acetamide, tetrahydropyran, and piperazine. The electrolyte concentration was kept at 0.1 m in all cases, while the cosolvent concentration was varied when possible up to 40 wt %. From the corresponding data in pure water, the volumes and heat capacities of transfer of the electrolytes from water to the mixed solvents were determined. The converse transfer functions of the nonelectrolyte (cosolvent) at 0.4m from water to the aqueous NaCl solutions were also determined. These transfer functions can be interpreted in terms of pair and higher order interactions between the electrolytes and the cosolvent. 

In recent years we have undertaken a systematic investigation of the volumes and heat capacities of transfer of alkali halides and tetraalkylammonium bromides from water to mixed aqueous solvents (1-6). These properties are important because, when combined with enthalpies and free energies, they can be used to calculate the temperature and pressure dependences of various equilibrium properties of electrolytes in mixed solvents. Since the properties of electrolytes in mixed aqueous solvents are closely related to the corresponding properties of the nonelectrolyte in an electrolyte solution, infor-... 

The enthalpy of solution measurements of n-Bu4NBr in DMF-water were made in very dilute solutions (0.02-0.001 mole kg-1) so that, in view of the experimental error, any concentration dependence of the enthalpies of solution in these solutions was neglected. Consequently, the enthalpy of solution at infinite dilution, AH°(sol.), was taken to be the average of three or more independent measurements agreeing within 150 J mol-1. Final results of AH°(sol.) of n-Bu4NBr with their mean deviations at 5°, 25°, and 55°C are given in Table I. The results for the other tetraalkylammonium bromides, for RbCl, and for urea in DMF-water at 25 °C are summarized in Table II. 

Fig. 14. Transition temperatures of NIPA polymer in aqueous solutions in the presence of tetraalkylammonium bromides. The monomer unit concentration in the NIPA polymer solution is 3.0 x 10 1 [molL-1]...

MCM-41 samples with increased hydrothermal stability could be successfully synthesized by adding additional salts like tetraalkylammonium bromide or sodium bromide to the synthesis gel. The increased stability is related to the increased condensation of the silanol groups during the formation of the mesostructure. Hydrothermally stable MCM-41 structures with different pore diameter can also be synthesized by this method using surfactants with varied chain length. 

Quaternary amines, such as tetraalkylammonium bromides and hydroxides (the alkyl group being Q to C4) are the typical zeolite templates. Quaternary amines fulfill the above-mentioned requirements of stability, specific interaction with the precursor (electrostatic interaction between quaternary amines and silicate), and easy removal (by calcination). 

Additives, in some cases, are used to modulate the stereochemistry of glycosylation by directly participating in the reaction process. Raymond Lemieux and coworkers, for example, demonstrated that a-pyranosyl bromides would transform into the P-pyranosyl bromides in situ in the presence of tetraalkylammonium bromide [7], The more reactive p-pyranosyl bromides would react with glycosyl acceptors in an SN2-type manner to give the kinetically controlled a-linked glycosides. 

The standard formation enthalpy of msny compounds ( H20( j, (03117)311 ( jd, etc.) taking part in the cycles are taken from the literature. The standard enthalpy of formation of TPABr (taking part in the cycles relative to the TPA[Si] -MFI and TPA Si, Al]-MFI samples is not available therefore, it had to be determined. Following the synthesis of tetraalkylammonium bromides and iodides (28.), the reaction of formation of TPABr was carried out in butanone on starting with tripropylamine and propyl bromide. The other reactions that were considered are the dissolution of TPABr, (0307)311, and C3H7Br in butanone. The value obtained for AfH°( TPA Br) is -322. 9 1.0 kJ. mol-1. 

Addition of one equivalent of ammonia to 1-bromoheptane gives a mixture of heptan-1-amine, some dialkylamine, some trialkylamine, and even some tetraalkylammonium bromide. 

In a related case, Maier and coworker [153] have recently also demonstrated that vinylogous enolates can enter into a cross-coupling step. However, the final products of Pd-catalyzed reactions of the hexahydro naph-thalenone and aryl bromides or iodides in the presence of cesium carbonate and tetraalkylammonium bromide in DMF at room temperature are 7-aryltetralones 208 (Scheme 85). This process can be readily interpreted as a Pd-catalyzed /-selective arylation of the thermodynamic enone enolate with a concomitant dehydrogenation-aromatization of the initial crosscoupling product. 

The enthalpy of solution values determined at different temperatures, by analogy with the results for N-methylformamide, suggest170 a slight degree of breaking of the NMA solvent structure by the two tetraalkylammonium bromide solutes studied. 

Tributylstannyl ethers are covalent derivatives with the nucleophilic properties of soft metal alkoxides they react with benzyl bromide on heating in non-polar solvents in the presence of tetraalkylammonium bromides or iodides to give the O-benzyl ether [Scheme 4.166]. 309 310 The moisture sensitive tributylstannyl ethers are formed by reaction of an alcohol with bis(tributyltin) oxide (bp... 

Figure 2. AH° of tetraalkylammonium bromides in mixtures of water with DMF as a function of the mole fraction of water...

Thermodynamic Behavior of Tetraalkylammonium Bromide and Hydrobromic Acid in Aqueous Media at 298.15 K... 

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