Hydrogen with halogen

The replacement of hydrogen with halogen takes place under thermal or photochemical conditions [J9, 20, 21] (equations 10-12). 

Replacement of hydrogen with halogen in fluoraarenes takes place by an ionic mechanism and is subject to the normal directing effects [27, 28, 29] (equations 13-15). 

Replacement of hydrogen with halogen can be carried out in the alpha position of fluorinated ethers, amines, aldehydes, or nitriles In 2,2,3,4,4,4 hexafluoro-bulyl methyl ether, chlorination occurs predominantly at the methyl, however, bromination occurs mostly at the internal position of the fluorobutyl group 133] (equation 20)... 

Table 8. Replacement of Hydrogen with Halogen in Benzotrifluoride...

C15-0125. At least three possible reaction mechanisms exist for the reaction of hydrogen with halogens, H2 + 2 2 H JT. Determine the rate law predicted by each of them ... 

In the compounds of hydrogen with halogens, an increase in the atomic radius of the halogens causes a decrease in the electronegativity which also causes the strengths of the bonds to become weaker. 

Other typical chain reactions include those of hydrogen with halogen in the gas phase and oxidation of organic substances at moderate temperatures (autoxidation). A special facet of the latter reactions is that the product or an intermediate can act as initiator, and the reaction then is autocatalytic. 

The reaction of sulfides bearing a-methylene hydrogens with halogenating agents, to form a-halo sulfides, can be classified as a Pummerer reaction of halosulfonium salts. With chlorine and bromine it is sometimes difficult to limit the reaction to monosubstitution. However, monosubstituted products are produced in high yields using N-halosuccinimides, sulfuryl and thionyl chloride and cyclic phosphoms... 

One compound is an alkane the other is an alkene. Alkenes characteristically undergo addition reactions with hydrogen, with halogens (CI2, Br2,12) and with hydrogen hahdes (HCl, HBr, HI). Alkanes do not react with these substanees nnder ordinary eonditions. 

It is often desirable to replace hydrogens with halogens. Fluorimtion of polyethylene can be carried out in the dark by simply exposing the polymer, either in sheet or in powder form, to fluorine gas. The reaction is exothermic and it is best to dilute the gas with nitrogen to allow a gradual introduction of the fluorine and avoid destruction of the polymer. In this manner, however, only the surface layers are fluorinated and the substitutions occur only a few molecular layers deep. 

Treatment of a ketone or an aldehyde containing an a hydrogen with halogen (X2, X = I, Cl, or Br) in acid results in the replacement of an a hydrogen with a halogen atom (Fig. 19.33). For the specific example shown in Rgure 19.33, the... 

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