Catalysts bromide

The success of the Bart reaction when applied to nuclear- substituted anilines is often much affected by the pH of the reaction-mixture. Furthermore, the yields obtained from some m-substituted anilines, which under the normal conditions are usually low, arc considerably increased by the modifications introduced by Scheller, and by Doak, in which the diazotisation is carried out in ethanolic solution followed by reaction with arsenic trichloride in the presence of a cuprous chloride or bromide catalyst. 

Catalysts other than the above cobalt salts have been considered. Several patents suggest that cobalt bromide gives improved yields and faster reaction rates (12—16). The bromide salts are, however, very corrosive and require that expensive materials of constmction, such as HastaHoy C or titanium, be used in the reaction system. Only one faciHty, located in the UK, is beHeved to uti1i2e cobalt bromide catalyst in the production of ben2oic acid. 

Zinc chloride was used as a catalyst in the Friedel Crafts benzylation of benzenes in the presence of polar solvents, such as primary alcohols, ketones, and water.639 Friedel-Crafts catalysis has also been carried out using a supported zinc chloride reagent. Mesoporous silicas with zinc chloride incorporated have been synthesized with a high level of available catalyst. Variation in reaction conditions and relation of catalytic activity to pore size and volume were studied.640 Other supported catalytic systems include a zinc bromide catalyst that is fast, efficient, selective, and reusable in the /wa-bromination of aromatic substrates.641... 

Cobalt bromide is used as a catalyst in the technology of production of arylcarboxylic acids by the oxidation of methylaromatic hydrocarbons (toluene, p-xylene, o-xylene, polymethyl-benzenes). A cobalt bromide catalyst is a mixture of cobaltous and bromide salts in the presence of which hydrocarbons are oxidized with dioxygen. Acetic acid or a mixture of carboxylic acids serves as the solvent. The catalyst was discovered as early as in the 1950s, and the mechanism of catalysis was studied by many researchers [195-214],... 

These reactions result in an additional route of chain propagation, which allows one to exceed the rate limit due to the mechanism of action of only variable-valence ions. In fact, the initial rate of RH transformation in the presence of the cobalt bromide catalyst is determined by the rate of two reactions, namely, R02 with RH (kp) and R02 with Co2+ (kp), followed by the reactions of Co3+ with Br and Br with RH. The general scheme proposed by Zakharov includes the following steps (written in the simplified form) [206] ... 

Generalizing the known data and established experimental peculiarities of the action of the cobalt bromide catalyst, we have to emphasize the following advantages of cobalt bromide catalysis ... 

TRIMETHYLPENTANAL, 51, 4 TRIMETHYLSILYL AZIDE, 50, 107 Triphenylphosphine-cobalt(II) bromide, catalyst, 53, 30,... 

The regio- and diastereo-selectivity of the Michael addition of 2-phenylcyclo-hexanone with a,p-unsaturated ketones are dependent on the reaction conditions. Mixtures of all six diastereoisomers resulting from reaction at either the 2- or 6-position of the cyclohexanone ring can be obtained using solid potassium hydroxide with tetra-n-butylammonium or A-benzylephcdrinium bromide catalysts. At 20°C with tetra-n-butylammonium bromide, the ratio of the 2,2- and 2,6-disubstituted cyclohexanones is ca. 3 2, but at higher temperatures with solid potassium f-butoxide the kinetically formed 2,6-isomer predominates (ca. 5 1) with the (2S,6R, R )-stereoisomer dominant, whereas greater amounts of the thermodynamically preferred 2,2-(2S,lR )-isomer are obtained with the chiral catalyst [61]. 

The terms in Equation 1.3 (Malkin s autocatalytic model) are described in Nomenclature. In Malkin s autocatalytic model, the concentration of the activator, [A], is defined as the concentration of the initiator times the functionality of the initiator. For a difimctional initiator [e.g., isophthaloyl-bis-caprolactam, the concentration of the activator (acyllactam) is twice the concentration of the initiator]. The term [C] is defined as the concentration of the metal ion that catalyzes the anionic polymerization of caprolactam. In a magnesium-bromide catalyzed system, the concentration of the metal ion is the same as the concentration of the caprolactam-magnesium-bromide (catalyst) because the latter is monofunctional. 

Aryl chlorides Aryl chlorides will substitute alkenes only under very special conditions, and then catalyst turnover numbers are generally not very high. Palladium on charcoal in the presence of triethylphos-phine catalyzes the reaction of chlorobenzene with styrene,58 but the catalyst becomes inactive after one use.59 Examples employing an activated aryl chloride and highly reactive alkenes, such as acrylonitrile, with a palladium acetate-triphenylphosphine catalyst in DMF solution at ISO C with sodium acetate as base react to the extent of only 51% or less.60 Similar results have been reported for the combination of chlorobenzene with styrene in DMF-water at 130 C, using sodium acetate as the base and palladium acetate-diphos as a catalyst.61 Most recently, a method for reacting chlorobenzene with activated alkenes has been claimed where, in addition to the usual palladium dibenzilideneacetone-tri-o-tolylphosphine catalyst, nickel bromide and sodium iodide are added. It is proposed that an equilibrium concentration of iodobenzene is formed from the chlorobenzene-sodium iodide-nickel bromide catalyst and the iodoben-zene then reacts in the palladium-catalyzed alkene substitution. Moderate to good yields were reported from reactions carried out in DMF solution at 140 C 62... 

Oxidation of a mixture of equivalent weights of the two low-molecular-weight homopolymers at 25°C with a diethylamine-cuprous bromide catalyst yielded a copolymer that formed stable solutions in methylene chloride and could not be caused to crystallize by stirring with a 3 1 methanol/toluene mixture, a procedure that results in crystallization of DMP homopolymer or of the DMP portion of DMP-DPP block copolymers. The NMR spectrum was identical with that of the polymer obtained by simultaneous oxidation of the two monomers. 

DMP homopolymer at the time the second monomer was added consisted of dead molecules, incapable of redistribution or of further normal polymerization. When the same procedure was followed, but with the less active diethylamine-cuprous bromide catalyst, only random copolymer was obtained, identical to that obtained by oxidation of the two monomers together. The same result was observed when DMP was oxidized with the diethylamine-cuprous bromide catalyst and tetramethyl-butanediamine-cuprous bromide was added along with DPP to increase the polymerization rate (Figure 5). 

Block copolymers were also produced by oxidizing mixtures of the two homopolymers. A summary of the effect of polymerization conditions on the structures of polymers prepared using equimolar amounts of the two monomers is presented in Table III. The preformed blocks used in these examples were a DMP homopolymer prepared with a diethylamine-cuprous bromide catalyst and a DPP polymer prepared with tetramethyl-butanediamine-cuprous bromide at 60°C. Each had an average degree of polymerization of approximately 50 units. 

The synthesis of some new substituted thieno[2,3-Z>]thiophenes (369)-(372) has been achieved <93BCJ201l> in a one-pot reaction employing solid-liquid phase transfer catalysis (PTC) conditions (K2C03, benzene, tetrabutylammonium bromide catalyst) and starting from acetylacetone, CS2, and a-chloro compounds in 1 1 2 molar ratio. The reaction of acetylacetone and CS2 with ethyl chloroacetate, chloroacetonitrile, 2-(chloroacetylamino)thiazole, or chloroacetanilide was carried out under PTC conditions by stirring the reactants reaction times and temperatures were optimized. The corresponding thieno[2,3-6]thiophenes (369)-(372) were obtained in excellent yields (51-93%). 

Partenheimer W. The aerobic oxidative cleavage of lignin to produce hydroxyaromatic benzaldehydes and carboxylic acids via metal/bromide catalysts in acetic acid/water mixtures. Adv Synth Catal. 2009 351 456-66. 

Copper(i) bromide catalyst. Related examples have been described [12]. 

C.C mlfPFe] Pd-bis-imidazole complexes Et3N NaOAc Na2C03 120-160 °C. Phosphine-free arylation of butyl acrylate and other olefins with aryliodides and bromides catalyst recycled five times without loss of activity product extracted with Et20. [78]... 

The a-hydroxy acid-derived 2,4-oxazolidinediones have been successfully utilized as substrates for asymmetric alkylations with a chiral phase-transfer catalyst (Scheme 40). Using 1 mol% of the N-spiro chiral quaternary ammonium bromide catalyst 153, oxazolidinedinone 152 was alkylated in high yield and enantioselectivity and hydrolyzed in situ to give a-hydroxy amides 154 <2006AGE3839>. 

---