Nitrobenzoic acids
| Nitrobenzoic acids | ||||||
| Surname | 2-nitrobenzoic acid | 3-nitrobenzoic acid | 4-nitrobenzoic acid | |||
| other names | o -nitrobenzoic acid | m -nitrobenzoic acid | p -nitrobenzoic acid | |||
| Structural formula |
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| CAS number | 552-16-9 | 121-92-6 | 62-23-7 | |||
| PubChem | 11087 | 8497 | 6108 | |||
| Molecular formula | C 7 H 5 NO 4 | |||||
| Molar mass | 167.12 g mol −1 | |||||
| Physical state | firmly | |||||
| Brief description | White dust | yellowish crystalline powder |
light green crystalline powder |
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| Melting point | 146-148 ° C | 139-142 ° C | 239-242 ° C | |||
| boiling point | Decomp. | Decomp. | Decomp. | |||
| pK s value | 2.22 | 3.44 | 3.42 | |||
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Solubility in water |
7.8 g / l (25 ° C) | 3 g / l (25 ° C) | 0.42 g / l (20 ° C) | |||
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GHS labeling |
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| H and P phrases | 315-319-335 | 302-315-319-335-412 | 302-319 | |||
| no EUH phrases | no EUH phrases | no EUH phrases | ||||
| 261-305 + 351 + 338 | 262-273-305 + 351 + 338 |
301 + 330 + 331 264-280-337 + 313 |
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The nitrobenzoic acids form a group of substances in chemistry that is derived from both benzoic acid and nitrobenzene . The structure consists of a benzene ring with attached carboxy (-COOH) and nitro group (-NO 2 ) as substituents . Their different arrangement results in three constitutional isomers with the empirical formula C 7 H 5 NO 4 . The 4-nitrobenzoic acid found in the analysis of organic substances mainly use.
presentation
3-Nitrobenzoic acid is obtained from methyl benzoate by reaction with fuming nitric acid in the presence of concentrated sulfuric acid . After the nitration, the methyl 3-nitrobenzoate formed is saponified to form an acid .
However, if the benzoic acid is nitrated directly, 3,5-dinitrobenzoic acid is usually formed .
In general, the nitrobenzoic acids are accessible from the nitrotoluenes by oxidation of the methyl group . For example, 4-nitrotoluene is oxidized to 4-nitrobenzoic acid with sodium dichromate in the presence of concentrated sulfuric acid.
properties
The nitrobenzoic acids are colorless to yellowish crystalline solids. The melting points differ significantly. The 4-nitrobenzoic acid, which has the highest symmetry, has the highest melting point. The nitrobenzoic acids have a higher acidity compared to benzoic acid due to the −M effect of the nitro group. The pK s values are therefore correspondingly lower (benzoic acid: 4.20).
use
Analytics
The 4-nitrobenzoic acid is mainly used in the analysis of organic substances by derivatization . Liquid substances or those with a low melting point are converted into easily crystallizing derivatives: alcohols can be identified, for example, by measuring the melting points of their esters of 4-nitrobenzoic acid or 3,5-dinitrobenzoic acid . For this purpose, the substance to be analyzed is reacted with 4-nitrobenzoic acid in the presence of small amounts of sulfuric acid.
Detection of isopropanol as a derivative of 4-nitrobenzoic acid:
4-nitrobenzoic acid-2-propyl ester (melting point: 100.5 ° C.).
The melting points of these derivatives are usually sharp. This implementation is also suitable for numerous amines .
The derivatives of 3,5-dinitrobenzoic acid generally have higher melting points than those of 4-nitrobenzoic acid. They are preferred when the melting point of 4-nitrobenzoic acid is too low and an exact determination is no longer possible.
If the substance in question is more sensitive, the direct reaction with the corresponding acid chloride , 4-nitrobenzoyl chloride , takes place instead . In this way z. B. derivatives of amino acids also accessible.
synthesis
3-aminobenzoic acid can be obtained by the reduction of 3-nitrobenzoic acid. Elemental zinc in hydrochloric acid or hydrazine , for example, are suitable as reducing agents .
Individual evidence
- ↑ a b c d e Entry on 2-nitrobenzoic acid in the GESTIS substance database of the IFA , accessed on March 12, 2017(JavaScript required) .
- ↑ a b c d e Entry on 3-nitrobenzoic acid in the GESTIS substance database of the IFA , accessed on March 12, 2017(JavaScript required) .
- ↑ a b c d e Entry on 4-nitrobenzoic acid in the GESTIS substance database of the IFA , accessed on March 12, 2017(JavaScript required) .
- ↑ a b c d e CRC Handbook of Tables for Organic Compound Identification , Third Edition, 1984, ISBN 0-8493-0303-6 .
- ^ Beyer / Walter : Textbook of Organic Chemistry , 19th edition, S. Hirzel Verlag, Stuttgart 1981, ISBN 3-7776-0356-2 , p. 511.
- ↑ Oliver Kamm, JB Segur: Methyl m-nitrobenzoate In: Organic Syntheses . 3, 1923, p. 71, doi : 10.15227 / orgsyn.003.0071 ; Coll. Vol. 1, 1941, p. 372 ( PDF ).
- ↑ Oliver Kamm, JB Segur: m-Nitrobenzoic acid In: Organic Syntheses . 3, 1923, p. 73, doi : 10.15227 / orgsyn.003.0073 ; Coll. Vol. 1, 1941, p. 391 ( PDF ).
- ^ O. Kamm, AO Matthews: p-Nitrobenzoic acid In: Organic Syntheses . 2, 1922, p. 53, doi : 10.15227 / orgsyn.002.0053 ; Coll. Vol. 1, 1941, p. 392 ( PDF ).
- ↑ J. Wilbrand , FK Beilstein : About a new series of isomeric compounds of the Benzoë group. - Nitrodracylic acid and its derivatives , in: J. Liebigs Ann. Chem. , 1863 , 128 , pp. 257-273 ( doi: 10.1002 / jlac.18631280302 ).
- ^ T. Curtius : The action of hydrazine hydrate on nitro compounds. I. Treatise , in: J. Prakt. Chem. , 1907 , 76 , pp. 233-237 ( doi: 10.1002 / prac.19070760116 ).
