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There are three isomers of toluidine, which are discovered and named by James Sheridan Muspratt and August Wilhelm von Hofmann in 1845. These isomers are O-Toluidine, m-toluidine, and p-toluidine, with the prefixed letter abbreviating, respectively, ortho; meta; and para. All three are aryl amines whose chemical structures are similar to aniline except that a methyl group is substituted onto the benzene ring. The difference between these three isomers is the position where the methyl group (–CH3) is bonded to the ring relative to the amino functional group (–NH2); see illustration of the chemical structures below.
| Methyl position | ortho | meta | para |
| Common name | O-Toluidine | m-toluidine | p-toluidine |
| Other names | o-methylaniline | m-methylaniline | p-methylaniline |
| Chemical name | 2-methylaniline | 3-methylaniline | 4-methylaniline |
| Chemical formula | C7H9N | ||
| Molecular mass | 107.17 g/mol | ||
| Glass transition temperature | 189 K | 187 K | Glass not formed |
| Melting point | −23 °C | −30 °C | 43 °C |
| Boiling point | 199–200 °C | 203–204 °C | 200 °C |
| Density | 1.00 g/cm3 | 0.98 g/cm3 | 1.05 g/cm3 |
| Magnetic susceptibility | 76.0 × 10−6 cm3/mol | 74.6 × 10−6 cm3/mol | 72.1 × 10−6 cm3/mol |
| CAS number | 95-53-4 | 108-44-1 | 106-49-0 |
| SMILES | Cc1ccccc1N | Cc1cccc(N)c1 | Cc1ccc(N)cc1 |
| Disclaimer and references | |||
The chemical properties of the toluidines are quite similar to those of aniline, and toluidines have properties in common with other aromatic amines. Due to the amino group bonded to the aromatic ring, the toluidines are weak base. The toluidines are poorly soluble in pure water but dissolve well in acidic water due to formation of ammonium salts, as usual for organic amines. ortho- and meta-toluidines are viscous , but para-toluidine is a flaky solid. This difference is related to the fact that the p-toluidine are more symmetrical. p-Toluidine can be obtained from redox of p-nitrotoluene. p-Toluidine reacts with formaldehyde to form Tröger's base.
In some patients o-toluidine is a metabolite of prilocaine, which may cause methemoglobinemia. This is then treated with methylene blue.
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