Aryl bromination

Imidazole, 2-amino-1 -methyl-4,5-diphenyl-tautomerism, 5, 368 Imidazole, 2-aroyl-mass spectra, 5, 360 synthesis, 5, 391, 402 UV spectra, 5, 356 Imidazole, 4-aroyl-synthesis, 5, 474 Imidazole, C-aroyl-UV spectra, 5, 356 Imidazole, aryl-nitration, 5, 396, 433 oxidation, 5, 433 Imidazole, 1-aryl-dipole moments, 5, 351 dearylation, 5, 449 ethylation, 5, 448 H NMR, 5, 353 hydroxymethylation, 5, 404 rearrangement, 5, 108 synthesis, 5, 390 thermal rearrangement, 5, 363 Imidazole, 2-aryl-chlorosulfonation, 5, 397 synthesis, 5, 475 Imidazole, 4-aryl-bromination, 5, 399 Imidazole, C-aryl-electrophilic substitution, 5, 432-433 nitration, 5, 433 Imidazole, N-aryl-reactions, 5, 448-449 structure, 5, 448-449 Imidazole, arylmercapto-... 

Halogenatlon. Poly(2,6-dimethyl- and 2,6-diphenyl-l,4-phenylene ether) can be aryl-brominated simply by exposure to a bromine solution no catalyst is required.6 In fact, the use of Lewis acid catalysts to promote the chlorination of poly(2,6-dimethy1-1,4-phenylene ether) leads to substantial degradation of the molecular weight of the chlorinated products.7 Membranes produced from ring brominated PPO (40% wt Br) exhibited enhanced permeability to CHi and CO2 and proved to be more selective in separating CH4/CO2 mixtures.8... 

According to mechanistic considerations of Scheme 8, benzylamine arylation should also be feasible. The palladation of benzylamines in strong acid might be retarded due to protonation of the directing amino group. Employing a limited amount of trifluoroacetic acid solvent allowed efficient benzylamine arylation [63], Specifically, the benzylamine arylation reactions are the fastest if about five equivalents of trifluoroacetic acid solvent are used. A number of benzylamines and A-methy lbenzy I am i n e s were shown to be reactive under these conditions (Scheme 16). The reactions proceed well with both electron-rich and moderately electron-poor benzylamines. For unsubstituted or 4-substituted benzylamines, 2,6-diarylation is observed. Benzylamines substituted at the 3-position are monoarylated. As in the case of pyridine and anilide arylation, bromine is tolerated on the substrate, and even iodide is compatible with the reaction conditions, although the yield is reduced. The products are acylated after the reaction to facilitate isolation. 

Awwadi FF, Willett DD, Haddad SF, Twamley B (2006) The electrostatic nature of aryl—bromine—halide synthons the role of aryl—bromine—halide synthons in the crystal structures of the trans-bis(2-bromopyridine)dihalocopper(II) and trans-bis(3-bromopyridine)dihalocopper (II) complexes. Cryst Growth Des 6 1833-1836... 

Chern RT, Sheu FR, Jia L, Stannett VT, Hopfenberg HB, Transport of gases in unmodified and aryl-brominated 2,6-dimethyl-1,4 poly (phenylene oxide). J. Membrane Sci. 1987 35 103. 

Among the various chemical modifications on PPO, the most extensively studied reaction is bromination. The method of modification is simple and bromine may be selectively attached to the PPO backbone or the methyl group depending on the reaction conditions. Aryl bromination occurs when the reaction is carried out under mild conditions in chloroform solution and in the absence of catalysts . By this method bromination to varying degrees has... 

Table 5. Permeability and permeability ratio for the gas pair CO2/CH4 of dense films prepared from aryl brominated PPO (PPOBr) measured at 35 C...

Integrally skinned asymmetric hollow fibers were prepared from brominated PPO having a benzylic bromine level of 0.68 and an aryl bromine level of 1.02. Small test modules were prepared and tested. Membranes coated with polydimethylsiloxane showed improved performances compared to uncoated membranes. The coated membranes exhibited hydrogen permeance of 100 GPU and separation factor of 53 for hydrogen over methane. The CO2 permeance was 42 GPU and the separation factor for carbon dioxide over methane was 23. The hollow fibers were also exposed to ammonia gas so that crosslinking of the polymer took place. 

---