Role of Third Phase in Intensification of Reaction Rates and Selectivity: Phase-Transfer Catalyzed Synthesis of Benzyl Phenyl Ether (original) (raw)
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Selectivity engineering in multiphase transfer catalysis in the preparation of aromatic ethers
Journal of Molecular Catalysis A: Chemical, 2004
Phase transfer catalysis (PTC) is a very mature discipline now. However, there are hardly any studies on the theoretical and experimental analysis of the effect of nature and number of phases on enhancement of rates and selectivities. PTC reactions can be carried out in liquid-liquid (L-L), solid-liquid (S-L), and liquid-liquid-liquid (L-L-L) and solid-liquid-liquid (S-L-L) conditions bringing into picture dominance of mass transfer effects. The current work addresses these issues in the alkylation reaction of -naphthol with benzyl chloride with the C-and O-alkylation being the competing reactions. The role of various phases in enhancing the selectivity towards benzyl-2-naphthyl ether has been extensively investigated. The L-L-L PTC process has been found to be the most effective and economical route giving only the desired ether within a short reaction times and high catalyst reusability, unlike the L-L PTC process. A mathematical model is developed to establish the rate constant.
Applied Catalysis A: General, 2005
Reactions in three immiscible liquid phases (L-L-L) are attractive, and one of the phases can be the locale of reaction which will have a dramatic effect on product distribution in complex reactions. Thus, converting a bi-liquid system into a tri-liquid phase is of considerable scientific and commercial interest. 4-Benzyloxy-vanillin is used as a perfume and also as a starting material for synthesis of thalifoline and ephedradine as alkaloids and in synthesis of flavonoid compounds. Etherification of vanillin with benzyl chloride under biphasic phase transfer catalysis leads to formation of 4-benzyloxy-vanillin, but selectively suffers due to side reactions. Waste minimization is a major theme of green chemistry. In the traditional liquid-liquid phase transfer catalysis, the catalyst is not recovered but disposed off causing load on environment. However, the transformation of two-liquid phases into three-liquid phases L-L-L, PTC leads to 100% conversion of the limiting reactant benzyl chloride with 100% selectivity to 4-benzyloxy-vanillin, using TBAB as a catalyst. The rates of reactions are very high under L-L-L PTC, and reaction can be completed within 1 h as against 8 h required in L-L PTC. The catalyst-rich middle phase is recycled many times, thereby leading to profitability. The current work deals with effect of different kinetics and process parameters leading to enhancement in rates and selectivities and greener aspects of phase transfer catalysis. #
Novelties of liquid–liquid–liquid phase transfer catalysis
Catalysis Today, 2001
Liquid-liquid-liquid phase transfer catalysis (L-L-L PTC) offers orders of magnitude intensification of rates of reaction and better selectivities than the biphasic PTC. The catalyst-rich middle phase is the main reaction phase. The etherification or alkoxylation of p-chloronitrobenzene (PCNB) was conducted by using alkanol and alkali instead of the metal alkoxide. A kinetic model is presented and validated.
Industrial & Engineering Chemistry Research, 2005
Studies in the preparation of aromatic ethers have proven to be quite attractive because of the extensive use of these compounds in the dyestuff, perfume, flavor, agriculture, and pharmaceutical industries. The novelties of phase-transfer-catalyzed alkylation of p-methoxyphenol with allyl bromide were studied in detail in a biphasic system with tetrabutylammonium bromide (TBAB) as the catalyst, and the selectivity of O-versus C-alkylation was compared. The effects of various parameters were studied systematically to understand the conversion patterns; product distribution; and selectivity of the desired product, 1-methoxy-4-(2-propenyloxy)benzene, which is an important perfumery compound. A mechanistic model has been proposed on the basis of the theory of mass transfer with chemical reaction in two liquid phases. The desired product is produced by the O-alkylation reaction between the quaternary 4-methoxyphenoxide and allyl bromide, which takes place instantaneously at a reaction plane in the organic film next to liquidliquid interface, conforms to the so-called regime 4, and is an example of normal liquid-liquid phase-transfer catalysis (L-L PTC). The isomerization of the desired product to give the first byproduct, the C-alkylated derivative 4-methoxy-2-(2-propenyl)phenol, takes place in the aqueous film by a fast pseudo-first-order reaction (regime 3) and is an example of so-called inverse L-L PTC. This byproduct also has fragrance value. The second byproduct, 1-allyloxy-2-allyl-4methoxybenzene, is formed by a slow reaction between 4-methoxy-2-(2-propenyl)phenol and allyl bromide in the bulk organic phase and conforms to the so-called regime 1. A 100% selectivity of the desired product is obtained when a stoichiometrically deficient quantity of the base is used at 30°C. This system is a unique example of mass transfer with complex chemical reactions. It has provided insight into a practical problem with academic excitement, and it also happens to be the first reported case of a PTC reaction in which both normal L-L PTC and inverse PTC are at play.
Chemical Engineering Journal, 2001
The conventional method of producing benzaldehyde by direct oxidation of toluene has a major drawback: low conversion to achieve high selectivity. Phase-transfer catalysis (PTC) may be used as an alternative route for benzaldehyde production. In the present study, routes to produce benzaldehyde from benzyl chloride in the liquid phase by using PTC have been examined based on the kinetic data obtained.
Kinetic study of phenol recovery using phase-transfer catalysis in horizontal membrane reactor
Chemical Engineering Journal, 2008
Quaternary ammonium membrane was made from polymerizing chloromethylstyrene crosslinking with divinylbenzene by the paste method, and immobilized with tertiary amine (tri-methylamine, triethylamine, tripropylamine or tri-n-butylamine). Phenol was recovered from 2500 ppm to 2 ppm from the simulated waste water in the form of useful product allyl phenyl ether using quaternary ammonium salt as phase-transfer catalyst in a horizontal membrane reactor. The ion-exchange capacity, water content and thickness in the membrane were determined. The turnover numbers of the phenol allylation for different quaternary ammonium membranes were also calculated by means of response surface methodology method.
Phase Transfer Catalysis for Green Chemistry
The problem of "Green Chemistry" using like example phase transfer catalysis has been discussed in the present paper. Nowadays catalysis plays a very important role in the new green chemical industry. Catalysis can reduce the environmental impact of processes and therefore can reduce the costs of these processes. Application of new catalysts and catalytic systems aim to achieve both environmental protection and economical benefits. The PTC technology has been chosen and is used in these applications, because it provides many compelling benefits, primarily related to the cost reduction of organic manufacture chemicals and secondly because it prevent the environmental pollution.
One-step production of phenol by selective oxidation of benzene in a biphasic system
Catalysis Today, 2006
Phenol production through the direct hydroxylation of benzene with hydrogen peroxide using a catalytic membrane reactor has been studied. The reaction was carried out in a biphasic system separated by a membrane. This new system showed a high selectivity to phenol, minimizing its over-oxidation in over-oxygenated by-products. The effect of various reaction parameters such as the addition of hydrogen peroxide mode, amount of hydrogen peroxide, type of membrane, type of catalyst and organic acid was investigated. The results showed that iron(II) sulphate as the catalyst, 18 mmol of hydrogen peroxide pumped for 4 h in the aqueous phase as oxidant feeding, acetic acid and polypropylene hydrophobic porous support gave the best system performance in terms of produced phenol (17.42 mmol), selectivity to phenol (99.94%), benzene conversion to phenol (1.20%), and hydrogen peroxide conversion to phenol (96.78%).
Journal of Molecular Catalysis A-chemical, 2008
The kinetics of dichlorocarbene addition to allyl phenyl ether have been studied under phase-transfer catalytic conditions using aqueous sodium hydroxide as the base and benzyltriethylammonium bromide as a phase-transfer catalyst. The reaction was carried out at 35 • C under pseudo-first-order conditions by keeping aqueous sodium hydroxide and chloroform in excess and was monitored by GC. The effect of various experimental parameters on the rate of the reaction has been studied and based on the results obtained, a suitable mechanism is proposed.