Calix[4]pyrrole: Synthesis and Anion-Binding Properties. An Organic Chemistry Laboratory Experiment

• Published in: Journal of chemical education 2006-09, Vol.83 (9), p.1330
• Main Authors: Shriver, James A, Westphal, Scott G
• Format: Article
• Language: English
• Subjects: Acetone; Binding; Chemical bonds; Chemical synthesis; Experiments; Hydrogen bonds; Molecular structure; Organic chemistry; Porphyrins; Science education
• ISSN: 0021-9584; 1938-1328
• DOI: 10.1021/ed083p1330

The study of synthetic macrocycles capable of interacting with small anionic species is an emerging field in organic chemistry. One specific example is a class of compounds known as calixpyrroles. The most common formulation of this system is a result of the condensation of acetone and pyrrole, which leads to the formation of a tetrapyrrolic macrocycle structurally similar but electronically different than porphyrins. This system is different from porphyrin in that you cannot form an 18π electron aromatic structure, which imparts drastically different properties. Instead, each pyrrole is electronically independent and consequently, each can donate one hydrogen bond. Their solid state structure also suggests that these meso-octamethylporphyrinogens are more aptly named calixpyrroles to emphasize their structural similarities to other members in the calixarene family. These observations led to the development of these systems as anion binding agents used to target a multitude of useful functions. Herein is described a three to four hour procedure introducing students to this system during their second term of organic chemistry. It has been optimized to have a completion time of three hours while allowing for optional characterization. The exploration of the anion-binding properties of calixpyrroles also makes this laboratory suitable for more advanced students.