Toluic acids
| Toluic acids | ||||
| Surname | 2-toluic acid | 3-toluic acid | 4-toluic acid | |
| other names |
o -Toluic acid 2-methylbenzoic acid |
m -toluic acid 3-methylbenzoic acid |
p -toluic acid 4-methylbenzoic acid |
|
| Structural formula |
|
|
|
|
| CAS number | 118-90-1 | 99-04-7 | 99-94-5 | |
| PubChem | 8373 | 7418 | 7470 | |
| Molecular formula | C 8 H 8 O 2 | |||
| Molar mass | 136.15 g mol −1 | |||
| Physical state | firmly | |||
| Brief description | yellow scales | yellowish scales with a faint aromatic odor |
white crystalline powder with a slightly aromatic odor |
|
| Melting point | 101-104 ° C | 110-111 ° C | 179-181 ° C | |
| boiling point | 260 ° C | 263 ° C | 274 ° C | |
| pK s value | 3.91 | 4.27 | 4.37 | |
|
Solubility in water |
1.2 g l −1 (25 ° C) | 1 g l −1 (20 ° C) | 0.3 g l −1 (20 ° C) | |
|
GHS labeling |
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|||
| H and P phrases | 315-319-335 | 315-319-335 | 302-319 | |
| no EUH phrases | no EUH phrases | no EUH phrases | ||
| 261-305 + 351 + 338 |
261-280-302 + 352 305 + 351 + 338 |
305 + 351 + 338 | ||
The toluic acids (or methylbenzoic acids) form a group of substances in chemistry that is derived from both benzoic acid and toluene . The structure consists of a benzene ring with attached carboxy (–COOH) and methyl (–CH 3 ) groups as substituents . Their different arrangement results in three constitutional isomers ( ortho , meta or para ) with the empirical formula C 8 H 8 O 2 . They are primarily to be regarded as methyl-substituted benzoic acids.
properties
The isomers of toluic acid are colorless to yellowish solids. The melting points differ characteristically.
The electron impact-induced mass spectrum of 2-toluic acid on the one hand differs significantly from that of the other two positional isomers, since the ortho effect promotes the splitting off of water from the molecular ion.
presentation
The corresponding toluic acids are obtained from the xylene isomers by oxygen oxidation (e.g. in the presence of cobalt stearate as a catalyst ). In this reaction, discovered by Ewald Katzschmann , only one methyl group is selectively oxidized. In a xylene isomer mixture, the para isomer is oxidized before the other isomers.
If stronger oxidizing agents such as potassium permanganate or chromosulfuric acid are used, both methyl groups are oxidized.
literature
Individual evidence
- ↑ a b c d e Entry for CAS no. 118-90-1 in the GESTIS substance database of the IFA , accessed on March 7, 2017(JavaScript required) .
- ↑ a b c d e Entry for CAS no. 99-04-7 in the GESTIS substance database of the IFA , accessed on March 7, 2017(JavaScript required) .
- ↑ a b c d e Entry for CAS no. 99-94-5 in the GESTIS substance database of the IFA , accessed on March 7, 2017(JavaScript required) .
- ↑ a b c CRC Handbook of Tables for Organic Compound Identification , Third Edition, 1984, ISBN 0-8493-0303-6 .
- ↑ Jürgen Martens , Klaus Praefcke and Helmut Schwarz : Mass spectrometric investigations on ortho effects and related rearrangements in benzoic and 2,2'-diphenic acid derivatives , in: Liebigs Ann. Chem. , 1975 , pp. 62-74 ( doi: 10.1002 / jlac.197519750107 ).