Pyridine, 3-bromo-, complex with

Bromination of pyridine is much easier than chlorination. Vapour phase bromination over pumice or charcoal has been studied extensively (B-67MI20500) and, as with chlorination, orientation varies with change in temperature. At 300 °C, pyridine yields chiefly 3-bromo-and 3,5-dibromo-pyridine (electrophilic attack), whilst at 500 °C 2-bromo- and 2,6-dibromo-pyridine predominate (free radical attack). At intermediate temperatures, mixtures of these products are found. Similarly, bromination of quinoline over pumice at 300 °C affords the 3-bromo product, but at higher temperatures (450 °C) the 2-bromo isomer is obtained (77HC(32-1)319). Mixtures of 3-bromo- and 3,5-dibromo-pyridine may be produced by heating a pyridine-bromine complex at 200 °C, by addition of bromine to pyridine hydrochloride under reflux, and by heating pyridine hydrochloride perbromide at 160-170 °C (B-67MI20500). 

There is a very extensive range of complexes [AuC13L], which are easily prepared by reaction of either [AuCU]- or [Au y with the corresponding nitrogen donor ligand L. Bromo derivatives [AuBr3L] are prepared similarly. Complexes with L = pyridine are most commonly studied and the cationic [AuCl2L2]+ may be prepared by further displacement of chloride by pyridine or its derivatives.571-573 The vibrational spectra, electronic spectra and mechanisms of substitution of pyridine for chloride (and the reverse reaction) have been studied.92,574"580... 

Pyridines react quite readily with bromine to give crystalline derivatives that have some N-bromo characteristics, but that are related to the tribromide anion. In nonpolar solvents the species are largely undissociated. Positive bromine gives stable 1 2 salts and 1 1 complexes with pyridine [74HC(14-S2)416 86TL3271], but, in contrast to the chloro derivatives, N-bromo-2-pyridones are not known (82JA4142 84JOC4784). 

Values of molar Kerr constants and dipole moments of nitrogen azoles and their complexes with phenols have been obtained. " These complexes are formed by an intermolecular hydrogen bond between the pyridine-type nitrogen of the azole and the phenolic proton. " The use of dipole moments in conformational studies has shown that A-aryl- and C-aryl- and A-furyl- and C-furyl imidazoles (and benzimidazoles) are nonplanar, but l-(a-furyl)-4,5-diphenylimidazoles do have a planar bicyclic fragment. The dipole moments and conformations of azolides (A-acylazoles) have been studied. In the 1-arylimidazoles the dipole is toward the aryl group. In 4,5-di-t-butylimidazole the molecule is essentially planar, but the C-4—C-5 bond is slightly stretched. Among other imidazole derivatives which have been studied by X-ray are histidine hydrochloride, 4-acetyl-amino - 2 - bromo - 5 - isopropyl -1 - methylimidazole, 4- acetyl - 5 - methyl - 2 -phenylimidazole, and imidazole-4-acetic acid hydrochloride. 

Thiadiazines lacking the 5,5-dioxide function are much less common. They have been prepared by reaction of f/ -allylmetal complexes with A,A -dimesylsulfamide (Section 6.16.9.2.1.1), by treatment of 1,3-diaminopropanes with A,A-thiobisphthalimide (Section 6.16.9.2.3.1), and, in high yield, by cyclization of 4-arylamino-3-bromo-l-aza-1,3-butadienes with thionyl chloride in cold pyridine (Section 6.16.9.2.3.1). 

Cyclopenta[b]indole gave 5-bromo (61%), 7-bromo (9%) and the 5,7-dibromo products on treatment with excess pyridine-Br2 complex followed by Zn [55]. This reaction is thought to proceed through a 2,3-adduct. C-5-substituted analogs behave similarly, with both donor and acceptor substituents giving the C-7 product. These results are consistent with a controlling directive effect by the indoline-type nitrogen in the adduct. Unfortunately, these reactimis are not applicable to tetrahydrocarbazoles. 

In 1997, a new synthetic route [30-34,43] made available a range of heterocyclic-substituted metallo-l,2-enedithiolate complexes (Scheme 1). The heterocycle (Het) and R group are readily varied using this method. Metallo-1,2-enedithiolate complexes with appended pyridines, 2-pyrazine, and 2-quinoxaline are now available. While the R group is limited only by the availability of the a-bromo- or tosyl ketone required for this synthesis, to date only complexes where R = H, Me, and CH2CH2OAC (and several derivatives of CH2CH2OH) [34] have been prepared. 

Fluorination of pyridine by complex AIF3 and CuF2 at 450-5(X) C forms a mixture of 2-fluoropyridine and 2,6-difluoropyridine in yields 32 and 11 % accordingly [47]. 3-Bromo-2-nitropyridine reacts with Bu4NT in DMF at 20 °C to form... 

The pyridine-bromine complex or its hydrochloride, heated at 200°, gives 3-bromo- and 3,5-dibromo-pyridinei 7, Later workers Tt obtained more complex results, the 3-bromopyridine probably being contaminated with 3,4-dibromopyridine or other reactive halogen derivatives which subsequently decomposed to polymeric salt-like material. More practicable is the preparation of 3-bromo- and 3,5-dibromo-pyridine by adding bromine to pyridine hydrochloride under reflux (a reaction in which iron and mercuric chloride have been used as catalysts) 3-Bromopyridine in good... 

---