Fischer, H.; Ernst, Paul published an article in 1926, the title of the article was Halogen-substituted pyrroles. IV. New preparation of pyrrole-α-aldehydes and stable tripyrrylmethanes.Formula: C7H8BrNO And the article contains the following content:
2,4-Dimethyl-5-carbethoxypyrrole and Br in CCl4 give nearly quant. the 3-Br derivative (IV), m. 150°, which, on further bromination, gives 85% of 2-bromomethyl-3-bromo-4-methyl-5-carbethoxypyrrole (V), decomposing 165-7°. The free acid (VI) from IV treated with 3 mols. Br in a little CCl4 gives [2,4-dimethyl-3-bromopyrryl][2,4-dibromo-3-methylpyrryl]methene, dark red, m. 192°. VI (5 g.), through the Gattermann aldehyde synthesis, gives 1 g. 2,4-dimethyl-3-bromo-5-formylpyrrole (VII), m. 166-7° (decomposition) (phenylhydrazone, decomposes 99-100°; semicarbazone, m. 223-4° (decomposition)). VII, warmed with EtOH-HCl, gives bis-[2,4-dimethyl-3-bromopyrrole-5]-methene, decomposes 187°. All attempts to prepare the corresponding alc. from V by heating with H2O failed. With AcOK there results quant. 2-acetoxymethyl-3-bromo-4-methyl-5-carbethoxypyrrole, m. 107-9°; the Ehrlich reaction is negative. The corresponding 2-chloroacetoxymethyl derivative, m. 150-3°, decomposes 172°; the 2-formoxymethyl derivative, m. 146-8° (decomposition). 2-Anilinomethyl derivative, m. 128-9° (50-60% yield); dehydration with KMnO4 in Me2CO-H2O gives 70% of the Schiff base, C15H15O2N2Br, m. 127-8°, which is catalytically reduced to the anilide and adds HCl, giving the compound C15H16O2N2BrCl, decomposes 216°. In boiling H2O containing the calculated amount of HCl, the base gives 70% of 2-carbethoxy-3-methyl-4-bromo-5-formylpyrrole (VIII), m. 134-6° (phenylhydrazone, m. 144°; oxime, m. 155-6°; semicarbazone, decomposes 260°). The free acid has no characteristic decomposition point, gives a positive Ehrlich reaction in the hot and on boiling with concentrated HCl gives a violet-red color. The Schiff base, C13H20O4N2, m. 82°, from 2-anilinomethyl-4-methyl-3,5-dicarbethoxypyrrole, gives 2-formyl-4-methyl-3,5-dicarbethoxypyrrole (IX), m. 124°; 1 l. boiling H2O dissolves 0.65 g.; it reduces NH4OH-AgNO3 but not Fehling solution; 1 g. in EtONa (1 g. Na and 10 cc. EtOH) gives 2-formyl-3-carbethoxy-4-methyl-5-pyrrolecarboxylic acid, decomposing 195°; 1 l. boiling H2O dissolves 6.5 g. Excess alkali gives 2-formyl-4-methylpyrrole-3,5-dicarboxylic acid, does not decompose at 250°. 2-Anilinomethyl-3-carbethoxy-4-methyl-5-pyrrolecarboxylic acid, decomposes 186°; dry distillation gives a non-crystalline oil, giving positive PhNH2 and Ehrlich aldehyde reactions. 2-Anilinomethyl-3-bromo-4-methyl-5-pyrrolecarboxylic acid, decomposes 197°. IX and 2,4-dimethyl-3-carbethoxypyrrole give [bis-(2,4-dimethyl-3-carbethoxy)]-3,5-dicarbethoxy-4-methylpyrryl-2-methane, m. 179°. The corresponding 3-Ac derivative, m. 254-5° the 5-carbethoxy derivative, m. 109-200°. VIII gives [bis-(2,4-dimethyl-3-carbethoxy)]-3-bromo-4-methyl-5-carbethoxypyrryl-2-methane, m. 227-8°. They readily take up EtOH of crystallization and are best crystallized from H2O. The AcOH solution gives a deep red color with K2Cr2O7 but does not show an absorption spectrum. Ehrlich’s reagent in the hot gives a positive reaction but is accompanied by a hydrolysis; they are stable towards concentrated HCl. Catalytic reduction of IX gives 2-hydroxymethyl-3,5-dicarbethoxy-4-methylpyrrole, m. 116°; Ac derivative, m. 113°; CrO3 oxidizes it to IX. HBr gives the 2-bromomethyl derivative, m. 156°. Upon heating, HCHO is slowly evolved with the formation of II’. Heating with pyrroles gives the corresponding methanes. 2,4-Dimethyl-3-ethyl-5-carbethoxypyrrole and Br in AcOH at 35-40° give about 75% of the 2-bromomethyl derivative, m. 132-4° (decomposition); 2-anilinomethyl derivative, m. 144-5° (40-50% yield); the Schiff base, C17H20O2N2, yellow, m. 133°; the HCl addition product, light yellow, m. 196° (decomposition); with aqueous AcONa there results a compound, m. 119-20°; boiling with a large amount of H2O gives 90% of 2-formyl-3-ethyl-4-methyl-5-carbethoxypyrrole, m. 90°; 500 g. hot H2O dissolves about 0.2 g.; oxime, m. 150°. With 2 mols. 2,4-dimethyl-3-carbethoxypyrrole in EtOH-HCl there results the HCl salt of the methene. The experimental process involved the reaction of 4-Bromo-3,5-dimethyl-1H-pyrrole-2-carbaldehyde(cas: 89909-51-3).Formula: C7H8BrNO
4-Bromo-3,5-dimethyl-1H-pyrrole-2-carbaldehyde(cas:89909-51-3) belongs to organobromine compounds. Most organobromine compounds, like most organohalide compounds, are relatively nonpolar. Bromine is more electronegative than carbon (2.9 vs 2.5). Consequently, the carbon in a carbon–bromine bond is electrophilic, i.e. alkyl bromides are alkylating agents. Formula: C7H8BrNO
Referemce:
Bromide – Wikipedia,
bromide – Wiktionary