3,5-Dinitrobenzoic acid

Synthesis

3,5-dinitrobenzoic acid is obtained from benzoic acid by the nitration reaction with nitric acid in the presence of concentrated sulfuric acid.

:[[File:3_5_Dinitrobenzoesäure.svg|400px]]

The nitration can also be started with 3-nitrobenzoic acid, which leads to yields of approximately 98%.

Properties

3,5-Dinitrobenzoic acid is an odorless, yellowish solid. Due to the mesomeric effect of the two nitro groups, it is more acidic (pK = 2.82) than benzoic acid (pK = 4.20) and 3-nitrobenzoic acid (pK = 3.47).

Uses

3,5-Dinitrobenzoic acid finds use in the identification of various organic substances, especially alcohols, by derivatization. For such an analysis, the substance to be analyzed is reacted with 3,5-dinitrobenzoic acid in the presence of sulfuric acid in order to form a derivate. By doing so, many substances that are liquid or have a low melting point are converted to easily crystallized derivates with sharp melting points. For instance, alcohols can be identified by the melting point of their esters with 3,5-dinitrobenzoic acid. This method is also applicable to a large number of amines.

:[[File:3-5-Dinitrobenzoesäure-2-propylester.svg|thumb|none|450px|Identification of [[isopropanol]] as a derivate of 3,5-dinitrobenzoic acid: 3,5-dinitrobenzoic acid-2-propylester (mp.: 123 C)]]

Compared to 4-nitrobenzoic acid, another acid that is used similarly, derivates of 3,5-dinitrobenzoic acid have higher melting points, so that it is preferred when the 4-nitrobenzoic acid derivate has a melting point too low to be accurately identified.

For more sensitive compounds, the reaction is carried out using the acid chloride, 3,5-dinitrobenzoyl chloride. This allows for example the identification of amino acids.

Explosives

Various heavy metal salts (including barium, lead, and silver) of 3,5-dinitrobenzoic acid are known to be high explosives. The lead salts are (relatively) stable and were patented for use in priming compositions.

References

References

1. {{Sigma-Aldrich
2. (25 March 2024). "3,5-dinitrobenzoic acid SDS". ThermoFisher Scientific.
3. "Antifoggant concentrate for preparing or replenishing a photographic color developer".
4. (1942). "The Preparation of 3:5-Dinitrobenzoic Acid and 3:5-Dinitrobenzoyl Chloride – Observations on the Acylation of Amino-acids by means of 3:5-Dinitrobenzoyl Chloride and certain other Acid Chlorides". [[Biochem. J.]].
5. (1942). "3,5-Dinitrobenzoic Acid".
6. (1988). "Preparation of 3,5-dinitrobenzoic acid from meta-nitrobenzoic acid". Pharmaceutical Chemistry Journal.
7. (1985). "CRC handbook of tables for organic compound identification". CRC Press.
8. (1 January 1962). "Encyclopedia of Explosives and Related Items: Volume 2 - B (Explosif) through Chloric Acid". Army Armament Research Development And Engineering Center, Picatinny Arsenal - Warheads Energetics And Combat Support Armaments Center.