Methoxybenzoic acids
In chemistry, methoxybenzoic acids form a group of substances that are derived from both benzoic acid and anisole . The structure consists of a benzene ring with attached carboxy (-COOH) and methoxy groups (-OCH 3 ) as substituents . Their different arrangements ( ortho , meta or para ) result in three constitutional isomers with the empirical formula C 8 H 8 O 3 . Primarily they can be viewed as methoxy-substituted benzoic acids. 4-Methoxybenzoic acid is mainly known by its common name anisic acid . In the English-language literature, the term anisic acid is also used for 2- and 3-methoxybenzoic acid.
Representatives and characteristics
| Methoxybenzoic acids | ||||||
| Surname | 2-methoxybenzoic acid | 3-methoxybenzoic acid | 4-methoxybenzoic acid | |||
| other names |
o -methoxybenzoic acid |
m -methoxybenzoic acid |
p -methoxybenzoic acid anisic acid |
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| Structural formula |
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| CAS number | 579-75-9 | 586-38-9 | 100-09-4 | |||
| ECHA InfoCard | 100.008.590 | 100.008.706 | 100,002,562 | |||
| PubChem | 11370 | 11461 | 7478 | |||
| Molecular formula | C 8 H 8 O 3 | |||||
| Molar mass | 152.15 g mol −1 | |||||
| Physical state | firmly | |||||
| Brief description | practically odorless, colorless crystal needles | |||||
| Melting point | 98-100 ° C | 105-107 ° C ( Polymorph I) 94 ° C (Polymorph II) |
182-185 ° C | |||
| boiling point | 200 ° C | 170–172 ° C (13 hPa ) | 277 ° C | |||
| pK s value | 4.08 | 4.09 | 4.47 | |||
| solubility | very sparingly soluble in water (0.3 g / l at 20 ° C) |
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GHS labeling |
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| H and P phrases | no H-phrases | no H-phrases | 302-315-319-335 | |||
| no P-phrases | no P-phrases | 261-305 + 351 + 338 | ||||
4-methoxybenzoic acid ( anisic acid ) has the highest melting point due to the greatest molecular symmetry. The methoxy group has little influence on the acidity of the COOH group, the pK s values have only minor differences from the benzoic acid (4.20) on.
See also
Derivatives
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Hydroxymethoxybenzoic acids C 8 H 8 O 4 - 10 isomers, e.g. B.
- Vanillic acid = 4-hydroxy-3-methoxybenzoic acid
- Isovanillic acid = 3-hydroxy-4-methoxybenzoic acid
- 5-methoxysalicylic acid = 2-hydroxy-5-methoxybenzoic acid
- Aminomethoxybenzoic acids C 8 H 9 NO 3 - 10 isomers, e.g. B.
- Fluoromethoxybenzoic acids C 8 H 7 FO 3 - 10 isomers, e.g. B.
- Di- and trifluorides as well as the corresponding chloro- and bromomethoxybenzoic acids also exist
Individual evidence
- ↑ a b Data sheet 2-Methoxybenzoic acid from Sigma-Aldrich , accessed on December 28, 2019 ( PDF ).
- ↑ a b c data sheet 3-Methoxybenzoic acid from Sigma-Aldrich , accessed on December 28, 2019 ( PDF ).
- ↑ a b Pereira Silva, PS; Castro, RAE; Melro, E .; Silva, MR; Maria, TMR; Canotilho, J .; Eusebio, MES: Structural evidence of polymorphism and conformational isomorphism of a somewhat flexible molecule: m-anisic acid in J. Therm. Anal. Calorim. 120 (22015) 667-677, doi : 10.1007 / s10973-014-4289-y .
- ↑ a b c Entry on 4-methoxybenzoic acid in the GESTIS substance database of the IFA , accessed on December 28, 2019(JavaScript required) .
- ↑ Entry on 2-methoxybenzoic acid in the ChemSpider database of the Royal Society of Chemistry , accessed on December 26, 2019.
- ↑ a b CRC Handbook of Tables for Organic Compound Identification , Third Edition, 1984, ISBN 0-8493-0303-6 .
- ↑ Data sheet 4-Methoxybenzoic acid from Sigma-Aldrich , accessed on December 28, 2019 ( PDF ).
- ↑ External identifiers or database links for 5-methoxysalicylic acid : CAS number: 2612-02-4, EC number: 220-037-8, ECHA InfoCard: 100.018.217 , PubChem : 75787 , ChemSpider : 68296 , Wikidata : Q15410212 .
- ↑ External identifiers of or database links to 2-amino-5-methoxybenzoic acid : CAS number: 6705-03-9, EC number: 628-679-4, ECHA InfoCard: 100.156.929 , PubChem : 277930 , Wikidata : Q72438652 .
- ↑ External identifiers or database links for 4-fluoro-2-methoxybenzoic acid : CAS number: 395-82-4, EC number: 630-039-4, ECHA InfoCard: 100.158.316 , PubChem : 2774545 , Wikidata : Q72474013 .