Multiple halogen substitution

An electronegative substituent, particularly if it is attached to the a carbon, increases the acidity of a carboxylic acid. As the data in Table 19.2 show, all the rnono-haloacetic acids are about 100 times more acidic than acetic acid. Multiple halogen substitution increases the acidity even more trichloroacetic acid is 7000 times more acidic than acetic acid ... 

The reduction of basicity of benzene by halogen substitution similarly applies to the case of toluene, as deduced by Tamres (1952) from I.R. measurements and by Ogimachi et al. (1955) from complex formation with ICl. The basicity decreases even more for multiple halogen substitution (Tamres, 1952). 

In the case of mono-olefins halogen substituents again reduce the basicity, as in the case of benzene. Unfortunately no information is available which would permit a comment as to whether the halogen atom causes this effect only if it is directly linked to the C=C double bond or whether an effect is also still exerted by an adjacent saturated halogen-substituted C-atom. With multiple halogen substitution the basicity falls even more as may be seen from the examples of chlorine-substituted ethylenes in Table 17. 

When hydrogen abstraction or electrophilic addition reactions may be inhibited by multiple halogen substitutions or steric hindrance, a hydroxyl radical can be reduced to a hydroxide anion by an organic substrate shown in Equation (7.28) ... 

Multiple-halogen substituted methanes usually contain both chlorine and fluorine, better known as chlorofluorocarbons (CFCs). Chlorofluorocarbons are gases that are nonflammable, nontoxic, and extremely stable. Because of their properties, CFCs are used mainly as refrigerants and fire extinguishing agents, although some are used as solvents. The total production of CFCs for 1990 was 1.1 million tons [162],... 

PHENYL OR SUBSTITUTED ARYL COMPOUND - GENERAL 276 PARA ARYL, ARYLOXY OR ARYLAMINO COMPOUND 2211 AROMATIC COMPOUND - POSSIBLY MULTIPLE HALOGEN SUBSTITUTION... 

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