Quaternary ammonium halides catalyst

Racemic epoxides are converted into optically active carbonates using a chiral Sa-lenCo(m) quaternary ammonium halide catalyst system . ... 

The phase-transfer catalyst (Q+X-) is usually a quaternary ammonium halide (R4N+X ) such as tetrabutylammonium halide (CH3CH2CH2CH2)4N+X. ... 

Lower molecular-weight quaternary ammonium halides, which partition across the two-phase system, transfer anions in measurable concentrations from the aqueous to the organic phase but, in contrast, many of the higher-molecular-weight quaternary ammonium halides with more than ca. 30 carbon atoms are virtually insoluble in aqueous media and their partition coefficients between aqueous and organic phases preclude the transfer of anions efficiently across the interface by the extraction process and yet catalysts, such as Aliquat 336 and Adogen 464, are extremely effective catalysts. 

It is noteworthy that benzyltriethylammonium chloride is a slightly better catalyst than the more lipophilic Aliquat or tetra-n-butylammonium salts (Table 5.2). These observations obviously point to a mechanism in which deprotonation of the amine is not a key catalysed step. As an extension of the known ability of quaternary ammonium halides to form complex ion-pairs with halogen acids in dichloromethane [8], it has been proposed that a hydrogen-bonded ion-pair is formed between the catalyst and the amine of the type [Q+X—H-NRAr] [5]. Subsequent alkylation of this ion-pair, followed by release of the cationic alkylated species, ArRR NH4, from the ion-pair and its deprotonation at the phase boundary is compatible with all of the observed facts. 

A compound whose addition to a two-phase organic water system helps to transfer a water soluble ionic reactant across the interface to the organic phase where a homogeneous reaction can take place is called a phase transfer catalyst. These catalysts enhance the rate of a reaction. A quaternary ammonium halide R4N+ X- e.g., tetrabutylammonium halide is phase transfer catalyst. It can cause the transfer of the... 

Propylene carbonate [108-32-7] M 102.1, b 110°/0.5-lmm, 238-239°/760mm, d 1.204, n 1.423. Manufactured by reaction of 1,2-propylene oxide with CO2 in the presence of a catalyst (quaternary ammonium halide). Contaminants include propylene oxide, carbon dioxide, 1,2- and 1,3-propanediols, allyl alcohol and ethylene carbonate. It can be purified by percolation through molecular sieves (Linde 5A, dried at 350° for 14h under a stream of argon), followed by distn under vac. [Jasinski and Kirkland AC 39 163 1967], It can be stored over molecular sieves under an inert gas atmosphere. When purified in this way it contains less... 

The use of mixtures of sodium hydroxide and benzyltrimethylammonium chloride or tetrabutylammonium bromide failed to enhance the DPGE alkylation of HEC by the in situ formation of the corresponding quaternary ammonium hydroxide phase transfer catalyst. These quaternary ammonium halides are too soluble in aqueous /-butyl alcohol and are preferentially extracted into the organic phase. Mixtures of benzyltrimethylammonium hydroxide and sodium acetate were also ineffective in enhancing the DPGE alkylation of HEC for the same reason, namely preferential solubility of benzyltrimethylammonium acetate in the organic phase. 

EMDE DEGRADATION. Modification of the Hofmann degradation method for reductive cleavage of the carbon-nitrogen bond by treatment of an alcoholic or aqueous solution of a quaternary ammonium halide with sodium amalgam. Also used as a catalytic method with palladium and platinum catalysts. The method succeeds with ring compounds not degraded by the Hofmann procedure. 

Ethylene carbonate can be prepared by a well-known process, from ethylene oxide and carbon dioxide with a catalyst such as a quaternary ammonium halide at 150-175°C. Addition of a cocatalyst such as zinc chloride to a quaternary ammonium iodide allows milder reaction conditions (50-100°C). ... 

In the two-phase alkylation using alkali hydroxides as bases and quaternary ammonium halides as catalysts (20) a reverse order (RCl > RBr > RI) of the customary alkylator reactivity prevails. Quaternary ammonium iodides exhibit little catalytic effect (21). Because the effective concentration of R4N Nu is low and limited by the initial amount of catalyst, the nucleophile cannot be expected to compete successfully for the alkylating agent with I , if its softness lies in between OH and I . 

Tanaka and his associates demonstrated for the first time how to use non-volatile ionic liquids (ILs) as solvents in palladium-catalyzed carbonylations [163], In the case of alkoxycarbonylation of bromobenzene, higher yields were obtained when 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] was used as the reaction medium compared with standard conditions. And the selectivity for the monocarb-onylation of iodobenzene with t -PrOH or Et2NH was significantly enhanced by [bmim][BF4]. After separation of the products, the solvent-catalyst system was easily recycled and exhibited catalytic activity up to seven times. Since then the replacement of traditional solvents with quaternary ammonium halides, imidazoli-um- or pyridinium-derived ILs has gained increasing importance [164—173]. Recently, the phosphonium salt IL trihexyl(tetradecyl)phosphonium bromide has proven to be an effective reaction medium for various carbonylation reactions of aryl and vinyl bromides or iodides under mild conditions (Scheme 2.17) [174]. 

Blum J. The versatility of metal halide-quaternary ammonium salt catalysts for organic processes. From homogeneous to glass-encapsulated ion pairs. Russ. Chem. Bull. 1993 42 1619-1627... 

The use of an extractor-type polymeric catalytic membrane reactor has also been described by Wu et for phenol allylation. Ion-exchange membranes, consisting of poly (styrene quaternary ammonium halide) cross-linked with divinylbenzene paste on polypropylene non-woven fabric, were assembled in a two-chamber flat membrane reactor, either in a horizontal configuration or in a vertical configuration. One of the chambers was filled with an aqueous solution of phenol and sodium hydroxide, while the other chamber was filled with a solution of allylbromide in dichloroethane, the membranes acting as phase transfer catalysts according to the mechanism depicted in Fig. 1.5. 

Polk et al. reported27 that PET fibers could be hydrolyzed with 5% aqueous sodium hydroxide at 80°C in the presence of trioctylmethylammonium bromide in 60 min to obtain terephthalic acid in 93% yield. The results of catalytic depolymerization of PET without agitation are listed in Table 10.1. The results of catalytic depolymerization of PET with agitation are listed in Table 10.2. As expected, agitation shortened the time required for 100% conversion. Results (Table 10.1) for the quaternary salts with a halide counterion were promising. Phenyltrimethylammonium chloride (PTMAC) was chosen to ascertain whether steric effects would hinder catalytic activity. Bulky alkyl groups of the quaternary ammonium compounds were expected to hinder close approach of the catalyst to the somewhat hidden carbonyl groups of the fiber structure. The results indicate that steric hindrance is not a problem for PET hydrolysis under this set of conditions since the depolymerization results were substantially lower for PTMAC than for die more sterically hindered quaternary salts. 

In some cases, the Q ions have such a low solubility in water that virtually all remain in the organic phase. ° In such cases, the exchange of ions (equilibrium 3) takes place across the interface. Still another mechanism the interfacial mechanism) can operate where OH extracts a proton from an organic substrate. In this mechanism, the OH ions remain in the aqueous phase and the substrate in the organic phase the deprotonation takes place at the interface. Thermal stability of the quaternary ammonium salt is a problem, limiting the use of some catalysts. The trialkylacyl ammonium halide 95 is thermally stable, however, even at high reaction temperatures." The use of molten quaternary ammonium salts as ionic reaction media for substitution reactions has also been reported. " " ... 

There are a number of industrially important reactions where two liquid phases are involved and the aqueous phase contains ionic species. Here the rate may be severely limited due to low solubiblity of the reactant, located in the organic phase, in water. We would benefit from using a pha.se-transfer (PT) catalyst, which ferries the ionic species into the organic phase thus overcoming a severe limitation. Such PT catalysts are typically quaternary ammonium compounds like tetrabutylammonium halides, trioctylmethylammonium chloride, etc. (see also Section 3.8). 

A thio-substituted, quaternary ammonium salt can be synthesized by the Michael addition of an alkyl thiol to acrylamide in the presence of benzyl trimethyl ammonium hydroxide as a catalyst [793-795]. The reaction leads to the crystallization of the adducts in essentially quantitative yield. Reduction of the amides by lithium aluminum hydride in tetrahydrofuran solution produces the desired amines, which are converted to desired halide by reaction of the methyl iodide with the amines. The inhibitor is useful in controlling corrosion such as that caused by CO2 and H2S. 

It has been shown that reaction of carboxylic acids with benzyl halides, which does not occur when heated conventionally, could be performed efficiently under the action of MW irradiation in the presence of a quaternary ammonium salt as a catalyst (Eq. 3) [15]. Typical results are given in Tab. 5.3. 

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