Effect of polyethylene glycol 400 on the allylation of phenoxide in a homogeneous phase

Abstract

The allylation of sodium phenoxide was carried out by using polyethylene glycol 400 (PEG-400) as a promoting agent in the homogeneous phase. The experiments were conducted in two ways, either in EtOH solvent or in PEG-400 solvent. A reaction mechanism, from which the sodium phenoxide will dissociate into free ions and a complex will form from the sodium cation with PEG-400, is proposed. The free ion of the dissociated phenoxide is verified as the active component in the allylation. The formation of a complex from PEG-400 with the sodium cation will loosen the interaction between the sodium cation and the phenoxide anion and enhance the reaction rate. The observed experimental data were satisfactorily explained by the present proposed reaction mechanism.In organic chemistry, Pedersen (1967) first found the formation of a complex from crown ethers with group I and I1 cations. This complex is able to carry the alkali salts to the organic solvents. After this, noncyclic polyethylene glycol (PEG) was found to have a similar structure to that of crown ether (Liu, 1968; Yanagida et al., 1977) and could also act as a phase-transfer catalyst. The biggest advantage for using PEG as a phase-transfer catalyst is its cheap price (Freedman, 1986) and easy recovery by conventional separation methods (Harris et al., 1982;Santaniello et al., 1979).In the past, several papers (Harris et al., 1982;Hanis et al., 1985) only discussed the promotion of the reaction rate by PEG. Several methods (Yanagida et al., 1978;Poonia et al., 1979;Ono et al., 1979;Haymore et al., 1982;Harris et al., 1982) have been proposed for understanding the interaction between polyethylene glycol and cations and their cation-binding characteristics in a nonreacting system. However, few research works have concerned themselves with the reaction mechanism in a PEG-catalyzed reaction system. In the two-phase catalyzed reaction, water-soluble reactants are usually dissociated with ion forms in the aqueous phase, and the ion-exchange reaction is conducted. However, the interaction between PEG and a reacting agent in an organic phase is not well-understood. Therefore, the study of the reaction promoted by PEG is very important in understanding the overall reaction.The purpose of this paper is to study of the role of PEG-400 in the allylation of sodium phenoxide with allyl chloride in an organic phase. It is assumed that PEG-400 is used to promote the dissociation of sodium phenoxide in the organic phase. Then, PEG-400 will associate with the sodium cation to form a complex by loosening the interaction between the phenoxide anion and the sodium cation. The discrete site-binding model (Ono et al., 1979) and the dissociation of sodium phenoxide are used to build up the reaction model. The proposed reaction mechanism is verified by the experimental data. The reaction is carried out by reacting allyl chloride with sodium phenoxide and with PEG-400 in an EtOH solvent. The dissociation constant of sodium phenoxide in the reacting system was determined by the conductometr...

Effects of solvents and molecular weights of polyethylene glycols on the allylation of phenoxide

“…Previous studies [25,26] of the allylation of phenoxide using PEG-400 indicate that the role of PEG-400 is to promote the dissociation of sodium phenoxide in the homogeneous phase reaction, to augment the solubility of sodium phenoxide in the organic phase and to augment the solubility of allyl chloride in the aqueous phase of the two-phase reaction. The free ion of the dissociated phenoxide has been verified as the reactive component in the allylation.…”

“…In most cases, sodium phenoxide proceeded to the O-allylation in a homogeneous solution. As indicated by Wang and Chang [25], the O-allylation of the phenoxide anion takes place in an EtOH solution. The work of Akabori et al [1] indicates that C-alkylation occurs only in the aqueous phase and that the O/(O + C) ratio (i.e., O-allylation/(Oallylation+C-allylation)) is about 70% in the absence of a phase transfer catalyst in the two-phase reaction.…”

“…The reactivity of the reactants in these aprotic solvents is increased by augmenting the polarity of the solvents. Nevertheless, the reaction mechanism of two-phase catalytic reaction by PEG is to form a complex of PEG with cation [6,25]. This leads to a different result from that of the catalytic reaction by quaternary salts in finding the reactivity of the reactants.…”

“…The capability of forming a complex from PEGs with metallic cations in a methanol solvent was discussed by many scientists [3,7,10,16,18]. Very recently, Wang and Chang [25,26] identified the reaction mechanism for synthesizing allyl phenyl ether by polyethylene glycol-400 (PEG-400) either in a homogeneous phase or in a twophase reaction using allyl chloride as the reactant and solvent. They concluded that the role of PEG in the homogeneous phase reaction was to promote the dissociation of sodium phenoxide and to enhance the reaction rate.…”

“…Based on the reaction mechanism proposed by Wang and Chang [25,26], the effects of the organic solvents and the molecular weights of PEGs on the reaction rate were examined in the present study. The reactions were carried out in a homogeneous phase using EtOH as the solvent and in a two-phase reaction using dichloromethane, ethyl ether, chlorobenzene, cyclohexane and n-decane as the organic solvents.…”