Chlorobenzoic acid

The chlorobenzoic acids form a group of substances derived from both the benzoic acid as well as from chlorobenzene in chemistry. The structure consists of a benzene ring with an added carboxy group (-COOH) and chlorine ( -Cl) as a substituent. Due to their different arrangement of three structural isomers arise with the empirical formula C7H5ClO2.

Representation

4 -chlorobenzoic acid is prepared from 4 -chlorotoluene by oxidation of the methyl group with potassium permanganate in alkaline solution ( in the presence of a phase transfer catalyst). The Preparation of 2- chlorobenzoic acid from the reaction of a diazonium salt (which has previously [ turn, prepared in situ from sodium nitrite and a strong acid, such as hydrochloric acid ] from 2- aminobenzoic acid and nitrous acid freshly prepared at <5 ° C) with hydrochloric acid and copper ( I) chloride as a catalyst store ( Sandmeyer reaction).

Properties

The chlorobenzoic acids are colorless to beige crystalline solids. The melting points differ significantly. 4- chlorobenzoic acid, which has the highest symmetry, has the highest melting point. The chlorobenzoic acids have due to the -I effect of the chlorine substituents are more acidic in comparison to benzoic acid. The pKa values ​​are therefore correspondingly lower ( benzoic acid: 4,20 ).

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