Electrochemical Synthesis of Selected λ3- and λ5-Iodanes

Abstract

Numerous λ3- and λ5-iodanes are used as highly selective oxidants in organic synthesis and are considered as a green alternative to classical metal based (CrVI, MnVII, ...) oxidants. The main advantage of iodanes is substantially lower toxicity and environmental footprint. However, their synthesis is based on chemical oxidation of iodobenzenes which usually involves handling toxic or at least potentially unstable oxidants (e.g. bromate, chlorine, persulfate or percarboxylic acids). This represents safety issue which becomes significant especially when scale-up of the process beyond laboratory level is required. Application of electrochemical synthesis of iodanes offers substantial advantage over the classical chemical approach in a sence no chemical oxidants are required. However, up to this point, no cheap, sustainable and easily scalable process for electrochemical synthesis of λ3-iodanes has been published. The main problems is that majority of the authors use environmentally unfriendly solvents and often workup of the product is complicated or even missing. In the case of electrochemical synthesis of λ5-iodanes, the situation is even worse since there is just handfull of publications on the topic.In the present contribution, a process of electrochemical synthesis of selected λ3- and λ5-iodanes (based on our previous publications [1-3]) including solid product workup, will be presented. In particular, the electrochemical process is based on anodic oxidation of 2-iodobenzoic acid to 2-iodosylbenzoic acid and 2-iodylbenzoic acid (IBX) using boron-doped diamond electrode. This step proceeds with high current efficiency, selectivity and product yield. Separation involves precipitation, crystallisation and filtration. No product washing with organic solvents is required. It is important to note that during the process development the attention was paid to minimisation of the environmental footprint of the process (high atom efficiency, low amount of waste, absence of toxic chemicals), low price of the chemicals and process scalability.