The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Kinetics of pyrrole substitutions. Iodination reaction》. Authors are Doak, Kenneth W.; Corwin, Alsoph H..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).Name: Ethyl 3,5-Dimethyl-2-pyrrolecarboxylate. Through the article, more information about this compound (cas:2199-44-2) is conveyed.
The rates of iodination of 4 substituted pyrroles, measured in aqueous dioxane (28% dioxane by weight) at 26.5 ± 0.1°, follow 2nd-order equations. The substituents are methyl and carbethoxy groups. Reduction rates of 2 iodopyrroles with HI are also reported, one of which follows a 3rd order. From the data obtained it is shown that the α-position is about 25 times as reactive as the β-position. N-Methyl substitution increases the reactivity of the pyrrole ring 8 to 15% thus the effect is smaller than that of Me substitution on benzene. Similar studies of the reduction rates show the α-position to be 20 times as reactive towards reduction as the β-position. The iodination equilibrium constant K = [RI] [HSolv+] [I-]/[RH] [Solv] [I2], assuming the solvent as 48.2 M, is 24 for α-iodination and 21 for β-iodination, thus apparently little affected by structural changes.
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Reference:
Thiazolidine – Wikipedia,
Thiazolidine – ScienceDirect.com