Tetramethylammonium Bromid

Tetramethylammonium bromide [64-20-0] M 154.1, sublimes with dec >230°. Crystd from EtOH, EtOH/diethyl ether, MeOH/acetone, water or from acetone/MeOH (4 1) by adding an equal volume of acetone. It was dried at 110° under reduced pressure or at 140° for 24h. 

Fluoride ion is effective in promoting the reduction of aldehydes by organosil-icon hydrides (Eq. 161). The source of fluoride ion is important to the efficiency of reduction. Triethylsilane reduces benzaldehyde to triethylbenzyloxysilane in 36% yield within 10-12 hours in anhydrous acetonitrile solvent at room temperature when tetraethylammonium fluoride (TEAF) is used as the fluoride ion source and in 96% yield when cesium fluoride is used.83 The carbonyl functions of both p-anisaldehyde and cinnamaldehyde are reduced under similar conditions. Potassium bromide or chloride, or tetramethylammonium bromide or chloride are not effective at promoting similar behavior under these reaction conditions.83 Moderate yields of alcohols are obtained by the KF-catalyzed PMHS, (EtO SiH, or Me(EtO)2SiH reduction of aldehydes.80,83,79... 

Diepoxy 6 (0.84g, 1 mmol) and diimidediol 3 (1.07 g, 1 mmol) were mixed well and the mixture heated at 110°C overnight, during which time no change took place. Tetramethylammonium bromide in a catalytic amount was added, mixed well, and heated at 110°C. After one day a brittle transparent solid was obtained. During two more days it became a very hard solid 7. IR (KBr pellet) 3480 (OH), 1785 and 1730 (imide), 1452, 1388, 1300-1100 (F), 1050, 1018, 983, 750, 730, 716, 708 cm1. 

In addition to substitution N-bromosuccinimide also forms addition compounds although in small amounts. Such addition reactions are catalysed by tetra-alkyl ammonium salts. Thus while with cyclohexene allylic substitution occurs, in presence of tetramethylammonium bromide, 1 2 dibromocyclohexane is obtained as the main product. 

The ammonium catalyst can also influence the reaction path and higher yields of the desired product may result, as the side reactions are eliminated. In some cases, the structure of the quaternary ammonium cation may control the product ratio with potentially tautomeric systems as, for example, with the alkylation of 2-naph-thol under basic conditions. The use of tetramethylammonium bromide leads to predominant C-alkylation at the 1-position, as a result of the strong ion-pair binding of the hard quaternary ammonium cation with the hard oxy anion, whereas with the more bulky tetra-n-butylammonium bromide O-alkylation occurs, as the binding between the cation and the oxygen centre is weaker [11], Similar effects have been observed in the alkylation of methylene ketones [e.g. 12, 13]. The stereochemistry of the Darzen s reaction and of the base-initiated formation of cyclopropanes under two-phase conditions is influenced by the presence or absence of quaternary ammonium salts [e.g. 14], whereas chiral quaternary ammonium salts are capable of influencing the enantioselectivity of several nucleophilic reactions (Chapter 12). 

It was found that the sensitivity of the hydrolysis of substituted 1-benzoyl-1,2,4-triazoles 6a-f to added 1-propanol and tetramethylammonium bromide varied... 

Table 2 Molalities m and concentrations c of 1-propanol and tetramethylammonium bromide (TMAB) in solutions mimicking the Stern regions of DTAB and CTAB micelles...

A nuclear magnetic resonance method for chlorpromazine has been reported [178]. For tablets, capsules, and bulk chemical, the sample is shaken with CHCI3 containing cyclohexane or piperanol as an internal standard. For injectable solutions, tetramethylammonium bromide was used as the internal standard. The NMR spectrum was recorded between 0 and 7.0 ppm, and the drug resonance at 2.7 ppm (relative to TMS) measured. The signals for the respective internal standards were at 1.5, 6.0, and 3.3 ppm. 

Preparation of ortho esters by the reaction of diphenylacetylene, chloroform, and ethylene oxide at elevated temperatures in the presence of tetramethylammonium bromide [182]. 

Tetramethylammonium bromide [64-20-0] M 154.1, sublimes with dec >230 . Crystd from... 

An examination of Figures 1-6 indicates that Equation 1 is valid under conditions of constant x for potassium, ammonium, and tetramethylammonium bromides in ethanol-water mixtures. All three salts show an ability to salt out ethanol from these mixtures (i.e., increase its concentration in the equilibrium vapor) which is verified by their k values shown in Table XVIII. Also, the results for tetra-n-propylammonium bromide and tetra-n-butylammonium bromide in ethanol-water mixtures reveal that Equation 1 can be used to predict the salt effects of these systems however, these two salts demonstrate a propensity to salt in ethanol (i.e., decrease its vapor concentration) in ethanol-water mixtures. On the other hand, Figures 7-9 and the data in Table XVIII reveal that Equation 1 cannot be used to correlate the salt effects of tetraethylammonium bromide in ethanol-water. For this system, a linear dependence of log aja vs. z is observed initially however, a gradual levelling off occurs at higher concentrations. 

Table VII. Isobaric Vapor—Liquid Equilibrium Data for the Tetramethylammonium Bromide—Ethanol—Water System at x = 0.206 (757 3 Torr)...

In contrast to NaCl or tetramethylammonium bromide, also shown in Fig. 4, the concentration dependence of the density is less marked. However, the slopes of the density curves measured at 20 °C and 35 °C for DADMAC increase with the concentration. This indicates a change of the interaction with water is likely caused by the formation of ordered structures such as associates [32, 37]. The greatest change of the slope is located at approximately 1.5 mol L 1. The influence of this monomer structure formation on the polymerization behavior will be discussed in Sect. 4. The non-linear concentration dependence of the viscosity is illustrated in Fig. 5. Here, a strong increase of this solution parameter is observed at approximately 1.5 mol L 1 indicating a change of intermolecular interactions [32,37]. 

Fig. 4. Comparison of the concentration dependencies of the densities of aqueous salt solutions and DADMAC solutions (x NaCl, T=20 °C O tetramethylammonium bromide, T=20°C diallyldimethylammonium chloride, T=20°C diallyldimethylammonium chloride, T=35 °C) (Data taken from [32])...

Conductivities of the complexes in absolute ethanol were shown (38) to be very low when compared with tetramethylammonium bromide as a reference. This finding was interpreted to indicate that molecular adducts exist in solution. The absence of rs(Sn—C) from the IR spectra and the J( H—C—119Sn) magnitude (ca. 70 Hz) were interpreted in terms of planarity of the C3Sn site and a noticeable rehybridization of the tin orbitals. 

While the first transition metal carbene complex was reported in 1964, the first cyclo-propyIcsirhene complex salt [(C0)5Cr=C(0")(c-Pr)]NMe4 was only synthesized about a decade later, by addition of cyclopropyllithium to chromium hexacarbonyl, followed by tetramethylammonium bromide Subsequent reaction with trimethyloxonium fluoro-borate gave methoxycarbene complex (CO)5Cr=C(OMe)(c-Pr) (equation 62). ... 

Tetramethylammonium bromide Tetrabuty I ammonium iodide Tetrapropylammonium iodide (AlCljj-1 -butyl-pyridinium chloride... 

Cleavage of eyclopropyl ketones. Cyclopropyl ketones are cleaved under neutral conditions at 20 by the combined reaction of AcOMs and the nucleophile tetramethylammonium bromide or iodide (as a source of Br or r). CH3CN is somewhat superior to CH2CI2 as solvent. ... 

Most of the work is done with carbonyl complexes of group-VIA metals. Tungsten hexacarbonyl reacts at RT with methyllithium in solvents such as diethylether or THF almost quantitatively with addition of the carbanion to the carbon atom of a coordinated CO to give the lithium salt of acetylpentacarbonyl tungstate. This complex can be converted by aqueous tetramethylammonium bromide into the more stable tetramethyl-ammonium salt ... 

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