Copper amine complexes oxidations with

Polymerization Mechanism. The mechanism that accounts for the experimental observations of oxidative coupling of 2,6-disubstituted phenols involves an initial formation of aryloxy radicals from oxidation of the phenol with the oxidized form of the copper—amine complex or other catalytic agent. The aryloxy radicals couple to form cyclohexadienones, which undergo enolization and redistribution steps (32). The initial steps of the polymerization scheme for 2,6-dimethylphenol are as in equation 6. 

The oxidative coupling of 2,6-dimethylphenol to yield poly(phenylene oxide) represents 90—95% of the consumption of 2,6-dimethylphenol (68). The oxidation with air is catalyzed by a copper—amine complex. The poly(phenylene oxide) derived from 2,6-dimethylphenol is blended with other polymers, primarily high impact polystyrene, and the resulting alloy is widely used in housings for business machines, electronic equipment and in the manufacture of automobiles (see Polyethers, aromatic). A minor use of 2,6-dimethylphenol involves its oxidative coupling to... 

It is well known that 2,6-dimethylphenol is oxidatively polymerized to poly(2,6-dimethyl-l,4-phenyleneoxide) with a copper amine complex as catalyst in the presence of oxygen at room temperature (Eq. 1)... 

Organic compounds having labile hydrogens, such as phenols [41,42], phenylene-diamines [43], and acetylenes [44], can be oxidatively coupled in the presence of specific metal complexes to form polymeric compounds. The oxidative polymerization of 2,6-disubstituted phenols with a copper-amine complex produces poly(2,6-disubstituted phenylene ether) [45-51], Poly(2,6-dimethylphenylene ether) and poly(2,6-diphenylphenylene ether) are commercially produced from 2,6-dimethyl phenol and 2,6-diphenylphenol, respectively (Figure 5). These polymers exhibit excellent performance as engineering plastics. 

Dimethylphenol is oxidatively polymerized to poly(2,6-dimethyl-1,4-phenyl-ene ether) with a copper-amine complex by a laccaselike reaction. The activated phenols are coupled to form a dimer. The dimer is activated by a mechanism similar to that by which the polymerization proceeds. The effects of the amine ligands are to improve the solubility and the stability of the copper complex as well as the phenol-coordinated complex and to control the redox potential of the copper complex. 

Many amine-copper complexes, as well as a few amine complexes of other metals, and certain metal oxides have since been shown to induce similar reactions (17, 18, 22, 23, 30). This chapter is concerned largely with the mechanism of oxidative polymerization of phenols to linear polyarylene ethers most of the work reported has dealt with the copper-amine catalyzed oxidation of 2,6-xylenol, which is the basis for the commercial production of the polymer marketed under the trade name PPO, but the principal features of the reaction are common to the oxidative polymerization of other 2,6-disubstituted phenols. 

Tsuchida, E. Kaneko, M. Nishide, H. The Kinetics of the Oxidative Polymerization of 2,6-Xylenol with a Copper-Amine Complex. Maknmtol. Otem. 1972.151, 221-234. 

Polyphenylene oxide (PPO) ru A thermoplastic, linear, non-crystalline polyether obtained by the oxidative polycondensation on 2,6-dimethylphenol in the presence of a copper-amine complex catalyst. The resin has a wide useful temperature range, from below —170 to +190°C, with intermittent use to 205° C possible. It has excellent electrical properties, unusual resistance to acids and bases, and is pro-cessable on conventional extrusion and injection-molding equipment. Because of its high coat PPO is also marketed in the form of polystyrene blends (see Noryf ) that are lower-softening (Tg of PS is about 100°C vs 208°C for PPO), and have working properties intermediate between those of the two resins. 

The reaction of alcohols and dioxygen in the presence of metal complexes often gives rise to aldehydes or ketones [307]. An early patent reports that methanol may be converted to formaldehyde in 80% yield by reaction with oxygen at 25 °C in the presence of copper-amine complexes [308]. Gas phase oxidation of 2-propanol to acetone and water was catalyzed by j3-Cu-phthalocyanine [309]. 

The oxidative polymerization of substituted phenols to poly(phenylene oxides is another example where a polymeric chain is formed by carbon-heteroatom coupling. " Thus, the reaction of 2,6-dimethylphenol with oxygen, in the presence of a copper-amine complex, yields high molecular weight poly(2,6-dimethyl-l,4-phenylene oxide). 

Oxidations with copper-amine complexes—o-Oxidation s. 

Trilialophenols can be converted to poly(dihaloph.enylene oxide)s by a reaction that resembles radical-initiated displacement polymerization. In one procedure, either a copper or silver complex of the phenol is heated to produce a branched product (50). In another procedure, a catalytic quantity of an oxidizing agent and the dry sodium salt in dimethyl sulfoxide produces linear poly(2,6-dichloro-l,4-polyphenylene oxide) (51). The polymer can also be prepared by direct oxidation with a copper—amine catalyst, although branching in the ortho positions is indicated by chlorine analyses (52). 

We were interested in the behaviour of polymeric catalysts in order to confirm that typical polymer effects may occur. Oxidative coupling of 2,6-disubstituted phenols, as developped by Hay (7), was chosen as a model reaction and the catalytic activities of coordination complexes of copper with several polymeric tertiary amines were compared with the activities of their low molecular weight analogs. The overall reaction scheme is presented in scheme 1. 

Amines such as diethylamine, morpholine, pyridine, and /V, /V, /V, /V -tetramethylethylene-diamine are used to solubilize the metal salt and increase the pH of the reaction system so as to lower the oxidation potential of the phenol reactant. The polymerization does not proceed if one uses an amine that forms an insoluble metal complex. Some copper-amine catalysts are inactivated by hydrolysis via the water formed as a by-product of polymerization. The presence of a desiccant such as anhydrous magnesium sulfate or 4-A molecular sieve in the reaction mixture prevents this inactivation. Polymerization is terminated by sweeping the reaction system with nitrogen and the catalyst is inactivated and removed by using an aqueous chelating agent. 

An unusual oxo-transfer to an amine has been observed, besides other products that originate from oxidative N-dealkylation chemistry, when the di-copper(I) complex of hgand 24 was reacted with O2 at 0 °C (Scheme 11) [169]. A labeling experiment showed that the O atom in 25 is derived from molecular dioxygen. 

Polymerization also takes place when 4-halo-2.6-disubstituted phenols are oxidized with copper-amine catalysts and oxygen (5,35). In this case, stoichiometric amounts of copper salt or some other chloride acceptor (inorganic bases or strongly basic amines) are necessary since the amine complexes of copper (II) halides are not catalysts for the polymerization. Blanchard (5) has also described the polymerization of these 4-halo-phenols under conditions similar to those used by Price using certain copper (II) complexes as initiators. 

When 2,6-dimelhylphenol is oxidized with oxygen in the presence of an amine complex of a copper salt as catalyst a high-molecular weight polyether (PPO) is formed. 

T isubstituted phenols react with oxygen in the presence of amine complexes of copper to yield linear poly(arylene oxides) the molding resin marketed under the trade name PPO is produced in this way by the oxidative polymerization of 2,6-dimethylphenol (14) ... 

Recently, White (32) observed that under certain conditions ( —15°C., large excess of amine base) oxidation of the dimer derived from 2,6-xylenol with a limited amount of preoxidized copper complex yielded the tetramer as the major product, with small amounts of hexamer and only traces of monomer and trimer. The two rings are indistinguishable in this case, but there is little doubt, in view of the results of Mijs, that... 

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