Bromine chloride molecule

When nicotinic acid is heated for 8 hours at 180° with thionyl chloride, a low yield of 5-chloronicotiriic acid is obtained.182 The orientation observed in this case suggests an electrophilic attack, perhaps on a complexed nicotinic acid chloride molecule (which would thus behave somewhat like a pyridine A-oxide). If the reaction is carried out at 150° and the reaction time lengthened to 50 hours, a 30% yield of 5,6-dichloronicotinic acid is obtained.182 Both mechanistic pathways may be involved here. Isonicotinic acid reacts with thionyl chloride at 180-220°, presumably by, way of an electrophilic attack since 3-chloro-and 3,5-dichloroisonicotinic acid are formed.182 Nicotinoyl chloride (from nicotinic acid and thionyl chloride—probably in the complexed form) gives an 87% yield of 5-bromonicotinic acid on reaction with bromine for 10 hours at 150-1700.185... 

Alkyl bromides react at lower temperamres than chlorides in dehydrohalo-genation reactions, but the reactions are complex since brominated precursor molecules appear, indicating that some bromine is formed from the hydrogen bromide [182], It is worthwhile mentioning that carbons also catalyze hydrogenol-ysis of C-Hal bonds in monosubstituted benzenes and substituted chlorobenzenes [183,184],... 

Both fix one bromine molecule on the double bond of the cyclohexenyle cycle. We can also mention etacrynic acid, which fixes one molecule of bromine chloride, which is an interhalogen compound and in which bromine plays the part of the electrophilic species due to the electronegativities of the two different halogen atoms ... 

The trans-effect can be used synthetically. In the reaction of Br- with Au(NH3)4+, the introduction of the first bromine weakens the Au—N bond trans to it so that the introduction of a second bromine is both sterospecifically trans and rapid. (A similar effect occurs in the corresponding chloride.) The third and fourth ammonia molecules are replaced with difficulty, permitting the isolation of AuBr2(NH3)2 (second-order rate constants at 25°C are k] = 3.40, k2 = 6.5, k2 = 9.3 x 10-5 and k4 — 2.68 x 10 2lmor s l at 25°C) [141]. 

The estimation of reactivity of polyhalomethanes in the reactions with the same monomer shows that the quantity of halogen atoms in a molecule is the most essential factor affecting the easiness of homolysis of even one C— Br bond in molecule, and the influence of the halogen nature (chlorine or bromine) is of less significance. For instance, the analysis of the data on relative kinetics of some polyhalomethanes reactions with vinyl chloride allows us to grade the studied polyhalomethanes according to their reactivity, as follows ... 

This enzyme [EC 1.11.1.10], also called chloride peroxidase, catalyzes the reaction of hydrogen peroxide with two RH and two Cl to produce two R—Cl and two water molecules. A heme group is one of the cofactors. This enzyme can also catalyze bromination and iodin-ation, but not fluorination. 

The oxidative metabolism leads to the formation of reactive species (epoxides, quinone-imines, etc.), which can be a source of toxicity. Consequently, slowing down or limiting these oxidations is an important second target in medicinal chemistry. Thus, the metabolism of halothan (the first modern general anaesthetic) provides hepatotoxic metabolites inducing an important rate of hepatitis the oxidation of the non-fluorinated carbon generates trifluoroacetyl chloride. The latter can react with proteins and lead to immunotoxic adducts [54], The replacement of bromine or chlorine atoms by additional fluorine atoms has led to new families of compounds, preferentially excreted by pulmonary way. These molecules undergo only a very weak metabolism rate (1-3%) [54,55]. 

Hydrate Isomerism.—As its name implies, this depends on the position of water in the molecule, just as in the case of the acido compounds. If two or more molecules of water are present in a molecule of ammine, the water may be present within the co-ordination complex or outside of it. For instance, the compound Cr en2.(H20)2.Br3 exists in isomeric forms. It may have all the water within the complex, in which case the formula will be [Cr en2(H20)2]Br3. In solution the whole of the bromine is precipitated by silver nitrate. On the other hand, the compound may have one molecule of water in the complex and the other outside, in which case the formula is [Cr en2(IT20)Br]Br2.H20, and only two-thirds of the bromine are precipitated by silver nitrate. Another example of this kind occurs in the cobalt series chloro-aquo-tetrammino-cobaltic chloride, [Co(NTI3)4Cl.H20]Cl2, is violet in colour, and is isomeric with dichloro-tetrammino-cobaltie chloride monohydrate, [Co(N1I3)4CI2]C1.H20, which is green. 

Dibromo-tetrammino-platinic Chloride, [Pt(NH3)4Br2]Cl2, is isomeric with dichloro-tetrammino-platinic bromide. It is formed by double decomposition between ammonium chloride and dibromo-tetrammino-platinic nitrate, when the salt separates as a yellow crystalline powder. Silver nitrate precipitates all the chloride and one atom of bromine in the molecule. 

---