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

摘要

Background: The aryldiazonium salts (ArN_2~+X-) are useful intermediates in organic synthesis. Although well stablished, the generation of ArN_2~+X- from anilines usually requires the use of corrosive and hazardous strong acids (HCl, H_2SO_4 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 NaNO_2, 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 NaNO_2 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, NO_2) 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.