The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Porphyrins. VI. The relative reactivities of substituted pyrroles》. Authors are Badger, G. M.; Harris, R. L. N.; Jones, R. Alan.The article about the compound:Ethyl 3,5-Dimethyl-2-pyrrolecarboxylatecas:2199-44-2,SMILESS:O=C(C1=C(C)C=C(C)N1)OCC).Safety of Ethyl 3,5-Dimethyl-2-pyrrolecarboxylate. Through the article, more information about this compound (cas:2199-44-2) is conveyed.
The comparative reactivities of a series of substituted pyrroles was examined by use of the diazo-coupling reaction and the Ehrlich reaction. The method used was that of Treibs and Fritz (CA 52, 13705g), but some modifications were introduced, p-AcNHC6H4N2Cl was used instead of p-PhNHC6H4N2Cl, and PhN2Cl and 2,4,6-Br3C6H2N2OAc were included to improve the accuracy of classification. Six aryldiazonium salts (I-VI) were used. With I-IV the reaction was carried out by mixing an alc. solution of the pyrrole (5 mL. 1.5 × 10-3M) with an aqueous solution of the diazonium salt (0.15 mL., 5 × 10-2M) and with V-VI an HOAc solution of the pyrrole was mixed with an HOAc solution of the Na salt of the anti-diazotate, both with and without the addition of HCl (0.15 mL., 2N). Tests were carried out at pH 3, 5, and 7 with the following pyrroles (substituents given): 3-Me; 2,4-Me2; 3-CO2Et; 2,4-Me2, 3-CO2Et; 2-Z, 3-Me, 4-CO2Et; 2-Q, 3-Me, 4-Ac; 3-CO2Et, 4-Me; 3-Ac, 4-Me; 2-CO2Et, 3,4-Me2; 2-CO2Et, 3,5-Me2; 2-CO2Et, 3,5-Me2; 2-CO2Et, 3-CH2CH2CO2Et, 5-Me; 2-CO2Et; 2-CH:C(CN)2, 3,4-Me2; 2-CH:C(CN)2, 3-CH2CH2-CO2Et, 4-Me; 2-CH:C(CN)2, 4-Me; 2-CH:C(CN)2, 3-Me; and 2-CH:C(CN)2. The results showed that the dicyanovinyl group exerted a very pronounced deactivating influence on pyrroles. The dicyanovinyl group was much more deactivating than an ethoxycarbonyl group. Most of the pyrroles used were prepared earlier. Other pyrroles were prepared as follows: A solution of 50 g. 2-carboxy-3-ethoxycarbonyl-4-methylpyrrole in ethanol-amine was refluxed 1 h. and poured into 1 l. H2O, the mixture extracted 24 h. with ether, and the aqueous solution acidified with dilute HCl to give 36 g. 2-carboxy-3-(2-hydroxyethylcarbonyl)-4-methylpyr-role (VII), m. 219° (decomposition) (EtOH). VII (2.5 g.) in 10 mL. 25% aqueous NaOH was heated 15 h. in a sealed tube at 140-50°, the mixture extracted with ether, and the extract dried and evaporated to yield 0.67 g. 3-methylpyrrole (VIII), b. 142-3°. Formylation of VIII by the Vilsmeier-Haack method at 0° yielded 2-formyl-3-methylpyrrole (IX), m. 92°. Condensation of 0.1 g. IX with 0.05 g. malononitrile in a few drops MeOH and I drop Et2NH yielded 2-(-dicyanovinyl)-3-methylpyrrole, m. 194.5-5.5° (decomposition) (MeOH). A mixture of 1 g. 2-ethoxycarbonyl-3,4-dimethylpyrrole, 1 mL. EtOH, and 10 mL. 10% aqueous KOH was refluxed 90 min. and the solution cooled and brought to pH 5-6 (HOAc) to yield 0.8 g. 2-carboxy-3,4-dimethylpyrrole (X). Refluxing 5 g. X and 5 mL. ethanolamine 1 h. and working up the mixture yielded 2.56 g. 3,4-dimethylpyrrole (XI), b760 164-6°, m. 32-3°. Formylation of XI (as in VIII) yielded 2-formyl-3,4-dimethylpyrrole (XII), m. 129-30°. XII was converted into 2-(-dicyanovinyl)-3,4-dimethylpyrrole by the method of Fischer and Hoefelman (CA 32, 33894).
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Reference:
Thiazolidine – Wikipedia,
Thiazolidine – ScienceDirect.com