HALOGENATED DERIVATIVES

The most important of the halogenated derivatives of acetic acid is chloroacetic acid. Fluorine, chlorine, bromine, and iodine derivatives are all known, as are mixed halogenated acids. For a discussion of the fluorine derivatives see Fluorine compounds, organic. 

Physical Properties. Pure chloroacetic acid [79-11-8] (CICH2COOH), mol wt 94.50, C2H2CIO2, is a colorless, white dehquescent soHd. It has 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Chemical Properties and Industrial Uses. Chloroacetic acid has wide appHcations as an industrial chemical intermediate. Both the carboxyhc acid group and the cx-chlorine are very reactive. It readily forms esters and amides, and can undergo a variety of cx-chlorine substitutions. 

Electron withdrawing effects of the cx-chlorine give chloroacetic acid a higher dissociation constant than that of acetic acid. 

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Halogen derivatives of silanes can be obtained but direct halogena-tion often occurs with explosive violence the halogen derivatives are usually prepared by reacting the silane at low temperature with a carbon compound such as tetrachloromethane, in the presence of the corresponding aluminium halide which acts as a catalyst. 

Picrates. Some halogen derivatives of the higher aromatic hydrocarbons form picrates (for experimental details, see under Aromatic Hydrocarbons, Section IV,9, 1), for example, a-chloronaphthalene (m.p. 137°), a-bromonaphthalene (m.p. 134°), and p-bromonaphthalene (m.p. 86°). 

Concentrated sulphuric acid. The paraffin hydrocarbons, cych-paraffins, the less readily sulphonated aromatic hydrocarbons (benzene, toluene, xylenes, etc.) and their halogen derivatives, and the diaryl ethers are generally insoluble in cold concentrated sulphuric acid. Unsaturated hydrocarbons, certain polyalkylated aromatic hydrocarbons (such as mesitylene) and most oxygen-containing compounds are soluble in the cold acid. 

Hydroxyalkylthiazoles are also obtained by cyclization or from alkoxyalkyl-thiazoles by hydrolysis (36, 44, 45, 52, 55-57) and by lithium aluminium hydride reduction of the esters of thiazolecarboxylic acids (58-60) or of the thiazoleacetic adds. The Cannizzaro reaction of 4-thiazolealdehyde gives 4-(hydroxymethyl)-thiazole (53). The main reactions of hydroxyalkyl thiazoles are the synthesis of halogenated derivatives by the action of hydrobroraic acid (55, 61-63), thionyl chloride (44, 45, 63-66), phosphoryl chloride (52, 62, 67), phosphorus penta-chloride (58), tribromide (38, 68), esterification (58, 68-71), and elimination that leads to the alkenylthiazoles (49, 72). 

Halogen Derivatives. Using substitutive nomenclature, names are formed by adding prefixes listed in Table 1.8 to the name of the parent compound. The prefix perhalo- implies the replacement of all hydrogen atoms by the particular halogen atoms. 

Halogenated and 4,5-halogenated derivatives of 1,8-naphthalenedicarboxyHc acid anhydride are useful intermediates for dyes, pigments, and fluorescent whiteners for polymers. 

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