Periodate is an anion composed of iodine and oxygen. Technically, it is a monovalent inorganic anion obtained by deprotonation of periodic acid. Periodate has emerged as an important oxidizing agent in organic synthesis. In fact, a review of existing literature reveals that periodate enables a rich chemistry in the synthesis of active pharmaceutical ingredients. Unfortunately, its use in various technical applications is impeded by its scarcity coupled by its astronomical cost. This high cost is attributable to periodate’s purifications protocols. Electrochemistry is the most preferred method for periodate generation credit to its low environmental and financial costs. In this approach; however, lead dioxide (which is known to disintegrate slowly during electrolysis and cause contamination) is generally used as the anode. The toxicity of lead is inacceptable for regulated products, and its removal is cumbersome and economically prohibitive. To date, alternative anode materials have been investigated where most have yielded poorer results. Nonetheless, research for innovative electrode materials in the last decades has resulted in boron-doped diamond (BDD) anodes, which exhibit strongly improved properties.
Generally, BDD has been reported to be sustainable since it can be made from methane and possesses a similar overpotential for oxygen evolution at lead dioxide but a outstandingly superior durability. Previous experiments involving BDD revealed that salt used (mostly lithium iodate) and its pH have significant impact technically and cost-wise (the former refereeing to iodine precipitation and the latter; the exorbitant cost of the lithium salt). Therefore, to overcome these shortfalls, German researchers from the Department of Chemistry at Johannes Gutenberg University Mainz: Dr Sebastian Arndt, Dominik Weis and led by Professor Siegfried R. Waldvogel in collaboration with Dr. Kai Donsbach at the PharmaZell GmbH developed a clean and cost-efficient periodate synthesis at BDD. They focused on conducting oxidation at boron-doped diamond anodes, which are durable, metal-free, and nontoxic. Their work is currently published in the research journal, Angewandte Chemie International Edition.
The research team initiated their research with cyclic voltammetry, which suggested a hydroxyl radical based mechanism, which is well known for BDD anodes. More so, common alkali iodides were used as the commercial source and alkaline conditions were chosen to favor a high current efficiency and the solubility of iodine. Further, the use of toxic anti-reducing agents was avoided by using a Nafion membrane. Ultimately, the process was scaled up into a flow electrolysis.
The authors reported that under the working conditions they adopted, heat generation was moderate thereby contributing to an energy-efficient process and a yield of 94%. Overall, it was established that the avoidance of lead dioxide ultimately lowered the cost of purification and quality assurance. All in all, the direct electrochemical synthesis of periodate from common iodides was established at a BDD anode.
In summary, the study presented a direct and cost-efficient electrochemical synthesis of periodate from iodide, which is less costly and relies on a readily available starting material. Remarkably, the conventional use of nondurable metal-based electrodes, in particular lead dioxide, was hereby avoided altogether. In a statement to Advances in Engineering, Professor Siegfried R. Waldvogel emphasized that their presented electrochemical approach will promote the use of periodate in several fields where toxic heavy metals are considered to be critical. Additionally, he further highlighted that the presented method will accelerate future research in the field of hypervalent iodic species.
Sebastian Arndt, Dominik Weis, Kai Donsbach, and Siegfried R. Waldvogel. The “Green” Electrochemical Synthesis of Periodate Angewandte Chemie International Edition 2020, volume 59; page 8036 –8041.