Pd/C: A Recyclable Catalyst for Cyanation of Aryl Bromides

Abstract

Aryl cyanides have been prepared from the corresponding aryl bromides with potassium hexacyanoferrate(II) usingPd/C as a catalyst. It is shown that the addition of Bu3N is the key factor in obtaining the corresponding aryl cyanides. Furthermore, the catalyst can be recycled by filtration and washing sequences, making the method also attractive for industrial applications.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Potassium Hexacyanoferrate(II)

“…7 A wide range of aryl bromides, iodides, and some activated chlorides were cyanated smoothly by using K 4 [Fe(CN) 6 )] as cyanide source.…”

“…The cyanation of aroyl chlorides by using K 4 [Fe(CN) 6 )] instead of strongly toxic metal cyanides provides a convenient method to prepare aroyl cyanides. 19 The reactions could be efficiently catalyzed by the AgI-PEG 400-KI system under mild conditions.…”

“…K 4 [Fe(CN) 6 )] is non-toxic {the LD 50 of K 4 [Fe(CN) 6 ] is lower than that for NaCl} and even used in food industry for metal precipitation. It has also been used as anti-agglutinating auxiliary for table salt (NaCl).…”

“…2 The lower basicity and nucleophilicity of the hexacyanoferrate(II) anion compared to the free cyanide ion may help to prevent side reactions. 3 It has been extensively used as highly efficient cyanation reagent in the synthesis of benzonitriles [4][5][6][7][8][9][10][11][12][13][14][15][16][17] and (oligo)phenothiazinyl nitriles. 18 It has also reported to be used as the cyanide source for cyanation of aroyl chlorides, 19 heteroaryl halides, 20 aryl perfluorooctylsulfonates 21 and aryl triflates.…”

“…22 It has been employed in the oxidation of N-phenyl-2,5-diarylamino-1,4-benzoquinone imines to 2-(ptolylamino)-5-(p-tolyl)phenazin-3-one. 23 K 4 [Fe(CN) 6 )] is commercially available on a ton scale. It can be readily prepared by the reaction of hydrogen ferrocyanide and potassium hydroxide.…”