Ullmann ether reaction

The most convenient method of preparing the flexible (low Tg) system is to employ the Ullmann ether reaction of dibromobenzene and aromatic bis-diols followed by catalytic replacement of the bromine atoms by terminal acetylene groups. A host of commercially available bis-diols have been used in the synthesis with both meta and para dibromobenzene. Low Tg arylether oligomers have been prepared containing sulfone, sulfide, carbonyl, isopropyl and perfluoroisopropyl groups in the backbone (9). 

The reaction sequence used to synthesize these flexible systems involved four steps which are outlined in Figure 1. The first of these was an aromatic nucleophilic substitution, a polymer forming reaction in which 4,4 -dichlorodiphenyl sulfone reacts with various diols. The second step, an Ullmann ether reaction, gives bromine terminated products in which the bromines can be replaced by ethynyl end groups in the final stages. 

Ullmann ether reaction The synthesis of diaryl ethers by the coupling of an aroxide anion with an aryl halide in the presence of copper. 

Mix I gram of phenol with i c.c. of dimethyl sulphate and add 4 c.c. of a lo per cent, solution of caustic soda. Warm and shake. The odour of phenol is replaced by that of anisole, which can be extracted from the licjuid by ether (Ullmann s reaction). See Appendix. p. 294. 

A new Ullmann ether protocol to install the pyrrolidinylethanol 10 was developed, obviating the need for the Mitsunobu reaction. 

The syntheses of 1 utilized the Ullmann ether synthesis.13 Reaction of 2 mol of 1-bromonaphthalene with 4,4-(hexafluoroisopropylidiene)diphenol afforded the desired product 1. The reaction was carried out in DM Ac at 160°C in the presence of potassium carbonate as the base and copper (I) iodine as the reaction catalyst to yield 1, as depicted in Scheme 1. The reaction proceeded slowly but in good yield with easy isolation of the desired compound. Acylation of 1 with 4-fluorobenzoyl chloride to prepare 2 was carried out under modified Friedel-Crafts reaction conditions14 using dimethyl-sulfone as catalyst moderator. Both 1 and 2 were easily recrystallized to yield high-purity monomers suitable for polymerizations. 

An Ullmann ether condensation was used in the reaction sequence in an effort to obtain very flexible systems which would have low initial Tg s for ease of processing. 

All of the sulfone diols were able to form oligomers in the second step of the reaction sequence, the Ullmann ether synthesis. As with the synthesis of the mono(bromophenoxy)phenol products, two methods were used to form the dibromo materials. Method A used pyridine, potassium carbonate and cuprous iodide, while Method B employed collidine and cuprous oxide with the dibromobenzene and higher molecular weight diol (IV). The major difference between the syntheses of the mono(bromophenoxy)phenols described earlier and these lies in the stoichiometry of the reactions. In order to... 

Substitution reactions at aromatic carbon (see also Reduction reactions, Ullmann ether coupling, specific reactions such as Nitration) Arene(tricarbonyl)chromium complexes, 19... 

Ullmann ether synthesis, 1, 361 for enantioselective reactions characteristics, 1, 366 hydroformylation, 1, 371 hydrogenation, 1, 368 hydrosilylation, 1, 371... 

V-Alkylated analogues 19b-d (see Scheme 4.5) were prepared using a modified procedure. To this end, sulfenyl diaryl ether 27 was prepared from phenol and 26 using an Ullmann-type reaction [26], and was then oxidized to sulfoxide 28. Lithiation and... 

UUmann ether synthesis. The original Ullmann ether synthesis9 involved melting the salt of a phenol with an aryl bromide in the presence of copper metal. Yields are low. Williams et al.10 found that the reaction can be carried out at lower temperatures by using as solvent pyridine, which forms a complex with copper salts (cuprous chloride preferred), which provides catalysis for the reaction reflux temperature is then sufficient. 

Coupling reactions. Nanosized copper is a good catalyst for Ullmann ether synthesis, using CS2CO3 as base in MeCN at 50-60°. Carbon-supported copper in the presence of 1,10-phenanthroline shows similar activities with the aid of microwave irradiation. A -Arylation of A-heterocycles (benzimidazole, triazole,...) by ArSi(OR)3 is mediated by Cu-FeCls and TBAF in the air. ... 

Diaryl ethers are an important class of compounds in pharmaceuticals and agricultural chemicals. The Ullmann ether formation reaction provides direct access to diaryl ethers. However, harsh reaction conditions, such as high temperatures (125-220 °C), stoichiometric quantities of the copper catalyst, and low to moderate yields, have greatly limited the utility of the reaction. The use of soluble copper salts and some effective ligands made it possible to carry out these reactions under mild reaction conditions. 

Ueda and co-workers [183] synthesized poly-(phenylene ether)s with pendant perfluoroal-kyl sulfonic acid groups with lEC values of 1.17-1.83 mEq./g by nucleophilic polycondensahon reachon of a perhuoromonomer such as decafluo-robiphenyl or hexahuorobenzene with 2,5-bisip-iodophenyl)hydroquinone, followed by the Ullmann coupling reaction with potassium 1,1,2,2-tetrafluoro... 

Halophenols without 2,6-disubstitution do not pol5unerize imder oxidative displacement conditions. Oxidative side reactions at the ortho position may consume the initiator or interrupt the propagation step of the chain process. To prepare polyCphenylene oxide)s from unsubstituted 4-halophenols, it is necessary to employ the more drastic conditions of the Ullmann ether synthesis. A cuprous chloride-pyridine complex in 1,4-dimethoxybenzene at 200° C converts the sodium salt of 4-bromophenol to poly(phenylene oxide) (1) ... 

Yoshimiu-a and Iwasaki of Sumitomo Chemical Co. have synthesized aromatic ionomers containing pendant perfluorosulfonic acid groups (Fig. 7.29) [79]. Poly (arylene ether sulfone) was brominated and then perfluorosulfonated via Ullmann coupling reaction in the presence of copper catalyst. The lEC was controllable up to 1.58 meq/g. The obtained ionomer membranes behaved very differently from the typical sulfonated aromatic ionomer membranes. Characteristic hydrophobic/hydro-philic separation (ca. 3-4 nm) was observed in the smaU-angle X-ray scattering (SAXS) analyses of the hydrated samples. The ionic clusters were slightly smaller... 

More recent studies have been concerned with the utilization of acetylene functionality and designing a system which would have all the processing criteria of an epoxide system. Materials which process analogously to the state-of-the-art epoxides require a very flexible backbone which will exhibit a low Tg before cure. The study provided a flexible aryl-ether system which Incorporates a phenylsul-fone backbone and has been referred to as ATS. The initial synthesis of ATS Involved the nucleophilic displacement reaction of various leaving groups in the 4,4 positions of diphenylsulfone with the metallic salt of m-hydroxyphenylacetylene. Research in our laboratory for lower cost precursors to ATS has led to the synthesis of bromo end-capped phenylsulfone oligomers via the Ullmann ether synthesis. 

The benzophenone system was also prepared by the reaction of m-hydroxyphenylacetylene with 4,4 -difluorobenzophenone. The S3nithe-sis allowed an independent method of obtaining pure monomer which could be compared with the monomer obtained from the Ullmann ether synthesis. 

A series of acetylene-terminated, aryl-ether thermoset systems were prepared by an Ullmann ether synthesis involving the condensation of various salts of aromatic bis—diols with m—dibromobenzene. The bromo end-capped oligomers were converted to the acetylene-terminated systems by the catalytically-induced, bromo-displacement reaction with 2-methyl-3-but3m-2-ol, followed by base hydrolysis. 

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