While its iron complex is a reasonable model compound, it unfortunately does not have all the properties of heme. Other much more complex porphyrin systems have also been synthesized which attempt to more closely mimic the function of heme. Many other transition metal species are found to be important in biological systems. There is a class of very important cluster molecules which function as electron-transport agents. These are often clusters of iron with sulfur ligands and may also contain molybdenum.
Copper is important in cytochrome c oxidase.
Vanadium has been found in certain algae. Cobalt is found in vitamin B12. These are just a few examples. In many cases the protein portion of the active molecules is so complex that model compounds may be the only way that a clearer picture of what is happening in the biological system may be obtained. Heat 350 mL of propionic acid to reflux in a 500 mL roundbottom flask using a heating mantle, a stirrer, and a reflux condenser.