Promoters sodium bromide

Formation of the P—N bond has been observed when the cross-coupling of dialkylphosphites (59) with amines (60) proceeds by an iodo cation [I]+-promoted electrooxidation, affording N-substituted dialkylphosphor-amidates (61) (Scheme 22) [76]. Lack of alkali iodide in the electrolysis media results in the formation of only a trace of (61), indicating that the iodide plays an important role in the P—N bond-forming reaction. In contrast, usage of sodium bromide or sodium chloride brings about inferior results since the current drops to zero before the crosscoupling reaction is completed. 

In the DMT process, the esterification is done by feeding a slurry of TPA crystals in methanol to a reactor with a catalyst of sulfuric acid at 220°F and 50 psi. DMT forms and can be purified by distillation. Yields exceed 95%, based on the TPA that ends up as DMT. In some later designs resulting in less severe operating conditions, MEK or acetaldehyde have been used as promoters in place of sodium bromide. 

The TPA process. The technology involves the oxidation of p-xylene, as shown already in Figure 18—2. The reaction takes place in the liquid phase in an acetic acid solvent at 400°F and 200 psi, with a cobalt acetate/ manganese acetate catalyst and sodium bromide promoter. Excess air is present to ensure the p-xylene is fully oxidized and to minimize by-products. The reaction time is about one hour. Yields are 90—95% based on the amount of p-xylene that ends up as TPA. Solid TPA has only limited solubility in acetic acid, so happily the TPA crystals drop out of solution as they form. They are continuously removed by filtration of a slipstream from the bottom of the reactor. The crude TPA is purified by aqueous methanol extraction that gives 99 % pure flakes. 

Soluble cobalt salts (acetate or naphthenate) are used as catalysts, most often together with manganese and bromide ions. Particularly in the presence of bromide source (as HBr, sodium bromide, or even organic bromides), the rate of the oxidation of methylbenzenes increases by up to 400 x. None of the other halogens approaches bromide in its promoting activity. The maximum effect is achieved with a 1 1 cobaltrbromine atomic ratio. 

Oxiranes can be prepared by electrochemical oxidation. " Regioselective w-epoxidation of polyisoprenoids will take place with excellent yields on sodium bromide-promoted electrochemical oxidation in neutral or basic medium. " " This has now been described as a general method. " " Hexafluoropropylene oxiranes have been produced by electrochemical means. " The deoxygenation of dioxetane to oxirane with triphenylphosphine has been described (Eq, 50). ... 

In the hydrogenation of p keto esters (R, R) tartaric acid gives the (R) alcohols and the (S, S) tartaric acid gives the (S) enantiomers. Raney nickel is more effective than supported nickel catalysts. It appears that the active catalyst is nickel tartrate which is adsorbed on the catalyst surface and that the sodium bromide is adsorbed on the non-chiral active sites, thus, keeping them from promoting the non-selective hydrogenations. 2,84 -pj is procedure has been used to prepare the chiral intermediate in the synthesis of the Pine Sawfly sex pheromone. ... 

Methyl or ethyl acetonacetate can be hydrogenated to (R)- or (5 )-methyl- or ethyl-3-hydroxybutyrate on nickel catalysts. With (/ )- or (5 )-tartaric acid and sodium bromide as promoters, the hydogenation can reach enantiomeric excess (ee) values over 90%. The ee value is defined as the excess of the major enantiomer to the minor one over the total yields. The products are vitamin precursors. The function of tartaric acid is believed to form nickel(II) tartarate, which is adsorbed on the metal surface. The asymmetric site... 

Wang G-W, Gao J. Solvent-free bromination reactions with sodium bromide and oxone promoted by mechanical milling. Green Chem 2012 14 1125-31. 

Sommer and coworkers have achieved selective carbonylation of propane in superacidic media promoted by halogen. When propane-carbon monoxide mixture (CO propane ratio = 3) was passed through HF-SbFg in a Kel-F reactor at — 10°C with the addition of a small amount of sodium bromide (Br"/Sb 0.5mol%), the NMR spectrum indicated the formation of isopropyloxocarbenium ion in 95% yield with a total conversion of 9% of the propane. This remarkable reaction can be rationalized as in equation 50. 

Torii S, Uneyama K, Ono M, TazawaH, Matsunami S (1979) A regioselective omega-epoxydation of polyisoprenoids by the sodium bromide promoted electrochemical oxidation. Tetrahedron Lett 20 4661 662... 

Torii S, Tanaka H, Ukida M (1979) Electrosynthesis of hetero-hetero atom bonds 3. Sodium bromide promoted electrolytic cross-coupling reaction of imides with disulfide. N-(cyclohexylthio)phthalimide, an important prevulcanization inhibitor. J Org Chem 44 1554-1557... 

Torii S, Tanaka H, Sayo N (1979) Electrosynihesis of hetero-hetero atom bonds 4. Direct cross-coupling of diaIkyl(or diaryl)phosphites with disulfides by a sodium bromide promoted electrolytic procesure. J Org Chem 44 2938-2941... 

Regioselective co-epoxidation of polyisoprenoids has been achieved by sodium bromide promoted electrochemical oxidation in a mixed solvent. Selectivity is extremely high ( 77—99%), and conversions range from 46 to 100%. A typical example is shown in Scheme 8. Hydrogen peroxide or t-butyl hydroperoxide in contact with basic alumina epoxidizes olefins but yields are low. ... 

Reaction conditions depend on the reactants and usually involve acid or base catalysis. Examples of X include sulfate, acid sulfate, alkane- or arenesulfonate, chloride, bromide, hydroxyl, alkoxide, perchlorate, etc. RX can also be an alkyl orthoformate or alkyl carboxylate. The reaction of cycHc alkylating agents, eg, epoxides and a2iridines, with sodium or potassium salts of alkyl hydroperoxides also promotes formation of dialkyl peroxides (44,66). Olefinic alkylating agents include acycHc and cycHc olefinic hydrocarbons, vinyl and isopropenyl ethers, enamines, A[-vinylamides, vinyl sulfonates, divinyl sulfone, and a, P-unsaturated compounds, eg, methyl acrylate, mesityl oxide, acrylamide, and acrylonitrile (44,66). 

Among the many methods of generating difluorocarbene, the treatment of bromodifluoromethylphosphonium bromides with potassium or cesium fluoride is particularly useful at room temperature or below [II, 12 13] The sodium iodide promoted decomposition of phenyl(trifluoromethyl)mercury is very effective at moderate temperatures [S, 14] Hexafluoropropylene oxide [/5] and chlorodifluo-roacetate salts [7] are excellent higher temperature sources of difluorocarbene... 

Apparently a substantial spacer is also allowable between I he aromatic ring and the carboxy group. Gemfibrozi 1 (52), a iiypotriglyceridemic agent which decreases the influx of steroid into the liver, is a cl ofibrate homologue. It is made readily liy lithium di isopropyl amide-promoted alkylation of sodium iso-propionate with alkyl bromide 51. 

Surfactants employed for w/o-ME formation, listed in Table 1, are more lipophilic than those employed in aqueous systems, e.g., for micelles or oil-in-water emulsions, having a hydrophilic-lipophilic balance (HLB) value of around 8-11 [4-40]. The most commonly employed surfactant for w/o-ME formation is Aerosol-OT, or AOT [sodium bis(2-ethylhexyl) sulfosuccinate], containing an anionic sulfonate headgroup and two hydrocarbon tails. Common cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB) and trioctylmethyl ammonium bromide (TOMAC), have also fulfilled this purpose however, cosurfactants (e.g., fatty alcohols, such as 1-butanol or 1-octanol) must be added for a monophasic w/o-ME (Winsor IV) system to occur. Nonionic and mixed ionic-nonionic surfactant systems have received a great deal of attention recently because they are more biocompatible and they promote less inactivation of biomolecules compared to ionic surfactants. Surfactants with two or more hydrophobic tail groups of different lengths frequently form w/o-MEs more readily than one-tailed surfactants without the requirement of cosurfactant, perhaps because of their wedge-shaped molecular structure [17,41]. 

Ester enolates are somewhat less stable than ketone enolates because of the potential for elimination of alkoxide. The sodium and potassium enolates are rather unstable, but Rathke and co-workers found that the lithium enolates can be generated at -78° C.69 Alkylations of simple esters require a strong base because relatively weak bases such as alkoxides promote condensation reactions (see Section 2.3.1). The successful formation of ester enolates typically involves an amide base, usually LDA or LiHDMS, at low temperature.70 The resulting enolates can be successfully alkylated with alkyl bromides or iodides. HMPA is sometimes added to accelerate the alkylation reaction. 

Fe. Iron metal was found to be able to mediate the allylation reactions of aryl aldehydes with allyl bromide using sodium fluoride as the promoter. The formation of an allyliron species was proposed as the reactive intermediate in the reaction (Scheme 8.20).187 In view of... 

A somewhat related microwave-promoted 5 -0-allylation of thymidine has been described by the Zerrouki group (Scheme 6.108) [215], While the classical method for the preparation of 5 -0-allylthymidine required various protection steps (four synthetic steps in total), the authors attempted the direct allylation of thymidine under basic conditions. Employing sodium hydride as a base at room temperature in N,N-dimethylformamide resulted in the formation of per-allylated compounds along with the desired monoallylated product (75% yield). The best result was achieved when both the deprotonation with sodium hydride (1.15 equivalents) and the subsequent allylation (1.2 equivalents of allyl bromide) were conducted under... 

Other approaches to tetrazoles were also recently published. Primary and secondary amines 195 were reacted with isothiocyanates to afford thioureas 196, which underwent mercury(II)-promoted attack of azide anion, to provide 5-aminotetrazoles 197 . A modified Ugi reaction of substituted methylisocyanoacetates 198, ketones, primary amines, and trimethylsilyldiazomethane afforded the one-pot solution phase preparation of fused tetrazole-ketopiperazines 200 via intermediate 199 <00TL8729>. Microwave-assisted preparation of aryl cyanides, prepared from aryl bromides 201, with sodium azide afforded aryl tetrazoles 202 . 

A detailed study of the formation of n-octyl ethers under solidrliquid two-phase conditions in the absence of an added solvent has been reported [10], Potassium alkoxides tend to produce higher yields of the ethers than do the corresponding sodium derivatives, but octene is the major product in the reaction of 1-bromooctane with potassium t-butoxide. High temperatures also tend to promote the preferential formation of octene and slightly higher yields of the ethers are obtained using n-octyl tosylate in preference to n-octyl bromide. p-Fluorinated acetals have been prepared either under basic catalytic liquidrliquid or solidrliquid conditions from the fluori-nated alcohol and dichloromethane [11] with displacement of the fluorine atoms. 

A novel aromatic substitution reaction with electron-deficient radicals, which avoids the use of stannanes, is promoted by the addition of tetra-n-butylammonium bromide [54]. Iodoacetonitrile and iodoacetic esters react with pyrroles and indoles in good to high yield upon photolysis in the presence of 2-methyloxirane and sodium thiosulphate (Scheme 6.34). 

The cleavage of benzyl ethers using hydrobromic acid is promoted by tetra-n-butylammonium bromide [38]. Selective cleavage of aryl silyl ethers can be effected in the presence of aliphatic silyl ethers using solid sodium hydroxide with tetra-n-butyl-ammonium hydrogen sulphate [39]. 

Electrochemical epoxidation of olefins has been developed for the production of ethylene and propylene oxides in aqueous sodium chloride or bromide solution. However, associated with these electrolyses are difficulties in achieving product selectivity as well as in obtaining high yields of the epoxides. Recently, a regiose-lective )-epoxidation of polyisoprenoids (23) to (24), promoted by electrooxidation in an MeCN/THF/H20-NaBr-(Pt) system, has been achieved (Scheme 10) [52]. 

As the supported glycol catalysts worked better in promoting reactions in a single solvent system, we explored the direct carbonylation of benzyl halides using an alcohol solvent, base, and cobalt carbonyl. Our initial experiments concentrated on the reaction of benzyl bromide at room temperature and one atmosphere carbon monoxide. We chose sodium hydroxide as the base, methanol as the solvent, and looked at the product distribution. We were interested in the selectivity to ester and the reactivity of this system. The results are given in Table III. 

The above-described solventless procedure has recently been promoted to a general method to prepare aryltellurium trichloride. The crude trichlorides can be converted in situ into the corresponding aryl butyl tellurides by sequential treatment with aqueous sodium borohydride and n-butyl bromide (see Section 3.1.3.2). 

Thiazolium ion based ionic liquids (OIL) have been used to promote the benzoin condensation of benzaldehyde. 4- And 5-methylthiazoles are readily alkylated with n-butyl bromide to give the corresponding bromide salt. Anion exchange with sodium tetrafluoroborate gave the tetrafluoroborate salt 53 as a stable yellow orange oil. When activated with a small quantity of triethylamine (5 mol%) the oil promotes the coupling of benzaldehyde to benzoin <99TL1621>. 

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