4-Nitrobenzoic acid

Yellowish to light green odorless crystalline solid

Fixed

1.61 g · cm -3

239-242 ° C

3.42

0.42 g / l (20 ° C)

Attention

1960 mg · kg -1 ( LD50, rat, oral)

-392.2 KJ / mol

Template: Infobox chemical / molecular formula search available

The 4-nitrobenzoic acid is an organic chemical compound and is one of the aromatics. The structure consists of a benzene ring with an added carboxy group (-COOH) and nitro ( - NO2) as a substituent. It is derived from both the benzoic acid as well as from nitrobenzene and belongs to the group of nitrobenzoic acids. 4-nitrobenzoic acid is mainly used in the analysis of organic substances.

Representation

4-nitrotoluene is oxidized with sodium dichromate in the presence of concentrated sulfuric acid to 4-nitrobenzoic acid.

Properties

The 4-nitrobenzoic acid is a yellowish crystalline solid. It has due to the -M effect of the nitro group to a higher acidity compared to benzoic acid. The pK a value of 3.42 is therefore correspondingly lower ( benzoic acid: 4,20 ).

Use

4-nitrobenzoic acid is mainly used in the analysis of organic substances by derivatization. Liquid substances or those with a low melting point can be converted to a slightly crystallized derivatives: alcohols can be identified, for example by measuring the melting points of its esters of 4-nitrobenzoic acid, or 3,5- dinitrobenzoic. For this purpose the substance to be analyzed is reacted with 4-nitrobenzoic acid in the presence of small amounts of sulfuric acid.

The melting points of these derivatives are usually sharp. This reaction is also suitable for many amines.

The derivatives of 3,5- dinitrobenzoic generally have higher melting points than that of 4-nitrobenzoic acid. You are then preferably selected when the melting point of 4-nitrobenzoic acid is too low and no more accurate determination is possible.

If the substance in question is more sensitive, and instead they direct reaction with the corresponding acid chloride, 4- nitrobenzoyl chloride. In this way, for example, derivatives of amino acids are available.