Diazotization of Anilines in Vinegar: A Very Simple and Low-cost Synthesis of Iodoarenes and Arylfurans

Background: The aryldiazonium salts (ArN2+X-) are useful intermediates in organic synthesis. Although well stablished, the generation of ArN2+X- from anilines usually requires the use of corrosive and hazardous strong acids (HCl, H2SO4 or HBF4). The use of weak acids from a renewable source for diazotization reaction is infrequent and not well investigated. Methods: The goal of this work is to verify if vinegar, an easily available solution of acetic acid can act both as a acid source and as a solvent to promote the diazotation reaction. The reactivity of the aryldiazonium acetates was evaluated by addition of KI (Sandemeyer reaction) or furan (Gomberg-Bachmann reaction). Results: Using 1 equivalent of KI and 1.2 equivalents of NaNO2, substituted iodoarenes were obtained with poor to good yields. We observed in this two-step iodination protocol, the anilines that contained electron withdrawing groups performed better than those with electron donating groups. For the arylation reaction, higher amounts of furan and NaNO2 were required. In this case, the corresponding substituted arylfurans were also obtained with poor to good yields. Similar to the diazotization-iodination reaction, this arylation of furan with anilines containing electron withdrawing groups (Br, NO2) performed better than the same reaction with anilines containing electron donating groups. Conclusion: Substituted iodoarenes and arylfurans can be synthesized directly from anilines in vinegar, without the use of metals, additives or catalysts. The dual role of vinegar (acting as a solvent and acid source) combined with the green aspects (low cost, low toxicity, renewable) and the simplicity makes this method attractive.