Single displacement reaction halogens

The second type of single displacement reaction involves a non-metal (usually a halogen) replacing an anion in a compound, as follows ... 

Non-metals, typically halogens, can also take part in single displacement reactions. For example, molecular chlorine can replace bromine from KBr, an ionic compound, producing bromine and potassium chloride. 

In the same way as you used the activity series for metals, you can use the activity series for halogens to predict whether substances will undergo a single displacement reaction. For example, fluorine is above chlorine in the activity series. So, given the reactants fluorine and sodium chloride, you can predict that the following reaction will occur ... 

Using the activity series for halogens, write a balanced chemical equation for each single displacement reaction. If you predict that there will be no reaction, write NR . 

Displacing One Element by Another Activity Series As we said, displacement reactions have the same number of reactants as products. We mentioned doubledisplacement (metathesis) reactions in discussing precipitation and acid-base reactions. The other type, single-displacement reactions, are all oxidation-reduction processes. They occur when one atom displaces the ion of a different atom from solution. When the reaction involves metals, the atom reduces the ion when it involves nonmetals (specifically halogens), the atom oxidizes the ion. Chemists rank various elements into activity series—one for metals and one for halogens— in order of their ability to displace one another. 

In another type of single-displacement reaction, one halogen replaces another halogen in a compound. Fluorine is the most-active halogen. As such, it can replace any of the other halogens in their compounds. Each halogen is less active than the one above it in the periodic table. Therefore, in Group 17 each element can replace any element below it, but not any element above it. For example, while chlorine can replace bromine in potassium bromide, it caimot replace fluorine in potassium fluoride. The reaction of chlorine with potassium bromide produces bromine and potassium chloride, whereas the combination of fluorine and sodium chloride produces sodium fluoride and solid chlorine. 

Both of these types of organometallics have the disadvantages of difficulties in preparation and extreme toxicity. Their major advantage is that they provide a controlled reaction, allowing a single halogen of the phosphorus halide to be displaced, leaving the others untouched. 

One of the two classic schemes for constructing the thiazole ring involves the condensation of a thioamide or its equivalent with an a-haloketone. The reaction can be visualized as involving, as the first step, the displacement of halogen by sulfur from the enol form of the amide imine formation will then close the ring. Thus, reaction of bromoketone (99-2) obtained from the bromination of the corresponding keto-acid with thioamide (99-1) affords thiazole (99-3) in a single step. There is thus obtained the NSAID fentiazac [109]. 

Nucleophilic substitution reactions. Nucleophilic displacement of a halogen In compounds such as 2-acetamldo-4-chloromethylthlazole under reflux of an alkaline ethanol solution Is a straight foreward reaction (219). Nucleophilic aromatic substitution reactions are more complex but under certain conditions they can be used for single step synthesis of aryl methyl sulfides. A number of 4-methylthlo-polychlorobiphenyls were synthesized from... 

How can these reactions be explained The reaction with f-butyl chloride cannot be a simple nucleophilic displacement, which should have yielded isobutene. Nor can it be a single-electron transfer, free radical reaction, which should have produced many side products. A clue may come from the reactions of the carbene analogous to 1, which forms weak complexes with some halogen compounds, in which the carbene acts as a Lewis base and the halogen as a Lewis acid [12]. 

A single electron transfer mechanism seems also to best explain the synthesis of poly(thio-l,4-phenylene) from 1,4-dichlorobenzene and sodium sulfide. The mechanism of the halogen displacement phase transfer-catalyzed polycondensation of 4-bromo-2,6-dimethylphenol occurs by a single electron transfer reaction which leads to a telechelic PPO containing one bromophenyloxy and one phenolic chain end of controllable molecular weight. 

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