Preparation of meso-diethyl-2,2′-dipyrromethane in water


To synthesize meso-diethyl-2,2′-dipyrromethane in water with negligible subsequent purification.

Preparation of meso-diethyl-2,2'-dipyrromethane in water
Preparation of meso-diethyl-2,2′-dipyrromethane in water


Dipyrromethanes are used as intermediates for the synthesis of porphyrins and other value-added compounds such as fluorescent markers or coordination compounds. The syntheses of such compounds are generally based on the acid-catalyzed condensation of pyrrole with aldehydes or ketones in an organic solvent. Careful control over the reaction is necessary to stop it when the dipyrromethane concentration is at its maximum, and for the correct purification of the final product, distillation of the excess pyrrole is required. In particular, meso-diethyl-2,2′-dipyrromethane from pyrrole and 3-pentanone can be synthesized in water with very high efficiency. This green synthesis of the dipyrromethane derivative involves negligible subsequent purification, since the final product separates from the aqueous reaction media spontaneously in a one-pot reaction with good yields.

Experimental procedure

In a 250 ml round-bottom flask, place a solution of 3-pentanone (3.8 ml, 0.036 mol) in 100 ml of hot water (90-100 ºC) and 0.5 ml of 37 % aqueous HCl, followed by the dropwise addition of pyrrole (5 ml, 0.072 mol). Fit a reflux condenser and heat the reaction under reflux for 45–50 min: a suspension will form during the reaction time. After it is heated, let the crude cool to 40–50 ºC, and then transfer the upper layer to another flask using a separatory funnel and allow to cool to room temperatura. Over several hours (one day is preferable), let the product crystallize into large pale-white crystals, giving the desired meso-diethyl-2,2′-dipyrromethane (m.p. = 109 ºC; expected yield near 80 %).

Physico-chemical properties

This table collects data for the molecular weight (Mw), melting point (M.p.) boiling point (B.p.) and density of the reactives and compounds used in this laboratory experiment.

Name Mw (g/mol) M.p. (ºC) B.p. (ºC) Density (g/ml)
HCl 36.46-30>1001.200

GHS pictograms

Hazard pictograms form part of the international Globally Harmonized System of Classification and Labelling of Chemicals (GHS) and are collected in the followinf Table for the chemical compounds used in this experiment.

Name GHS
HCl ghs05  Danger Warning Corrosive cat. 1 pictogram ghs07  Warning Toxic cat. 4 Irritant cat. 2 or 3 Lower systemic health hazards pictogram
1H-Pyrrole ghs02  Danger Warning Flammable pictogram ghs06  Danger Toxic cat. 1–3 pictogram ghs05  Danger Warning Corrosive cat. 1 pictogram
3-Pentanone ghs07  Warning Toxic cat. 4 Irritant cat. 2 or 3 Lower systemic health hazards pictogram ghs02  Danger Warning Flammable pictogram

International Chemical Identifier

The IUPAC InChI key identifiers for the main compounds used in this experiment are provided to facilitate the nomenclature and formulation of chemical compounds and the search for information on the Internet for these compounds.



  • Isac-García, J.; Dobado, J. A.; Calvo-Flores, F. G.; and Martínez-García, H. (2015). Experimental Organic Chemistry Laboratory Manual. Elsevier Science & Technology. ISBN: 978-0-12-803893-2
  • A. J. F. N. Sobral, Synthesis of meso-diethyl-2,2′-dipyrromethane in water. An exper- iment in green organic chemistry., Journal of Chemical Education 83 (2006), no. 11, 1665–1666, DOI 10.1021/ed083p1665