Electrosynthesis of 5-chloro- and 5-azido-4-pyrazole carboxylic acid at the nickel hydroxide electrode

Article abstract of DOI:10.1246/bcsj.67.1879

Pyrazole derivatives are valuable intermediates for drugs and agrochemicals. The literature seems to be almost devoid of suitable methods, from environmental point of view for the preparation of simple pyrazole carboxylic acid derivatives which could be prepared from aldehydes with oxidizing agents such as NaCIO₄. These reagents are partially toxic and large scale conversions create waste disposal problems. A clean oxidation technique would be the indirect electrochemical oxidation at the nickel hydroxide anode. Until recently there have been few examples of oxidation of heterocyclic aldehydes to the corresponding acids. We represent here an electrochemical method for oxidizing 5-chloro-4-pyrazole carbaldehyde (1) and 5-azido-4-pyrazole carbaldehyde (2) to their corresponding acids (3 and 4) at a nickel hydroxide anode in good yields (80-85%) (scheme 1).