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Synlett 2010(20): 3115-3116  
DOI: 10.1055/s-0030-1259048
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© Georg Thieme Verlag Stuttgart ˙ New York

Potassium Hexacyanoferrate(II)

Jun-Tao Hou*
The College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang 050016, P. R. of China
e-Mail: juntaohou@gmail.com;

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Publikationsdatum:
17. November 2010 (online)

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Biographical Sketches

Jun-Tao Hou was born in Handan, P. R. of China. He graduated from the College of Handan in 2004 and is currently working towards his M.Sc degree under the supervision of Professor Zhan-Hui Zhang at the Hebei Normal University. His research interest is focused on the development of new synthetic methodologies for green chemistry.

Introduction

Potassium hexacyanoferrate(II) has received considerable attention as an environmentally benign cyanaide source for the synthesis of a variety of important aryl nitriles. K4[Fe(CN)6)] is non-toxic {the LD50 of K4[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). It is soluble in ­water without decomposition even on addition of hydrochloric acid. [¹] In addition to its nontoxicity, cheapness, and easy handling, it allows for improved catalyst productivity and substrate scope. [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 [4-¹7] 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-(p-tolylamino)-5-(p-tolyl)phenazin-3-one. [²³]

K4[Fe(CN)6)] is commercially available on a ton scale. It can be readily prepared by the reaction of hydrogen ferrocyanide and potassium hydroxide.

Abstracts

(A) Cyanation of Aryl Halides: An efficient Pd/C-PEG-H2O system for the cyanation of aryl halides has been developed by Wan and co-workers. [7] A wide range of aryl bromides, iodides, and some activated chlorides were cyanated smoothly by using K4[Fe(CN)6)] as cyanide source.

(B) Cyanation of Aroyl Chlorides: The cyanation of aroyl chlorides by using K4[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.

(C) Cyanation of Aryl Perfluorooctylsulfonates: Zhu and co-workers have reported that aryl perfluorooctylsulfonates can be converted into benzonitriles in the presence of Pd(OAc)2, CuI, and Ph3P or 1,1-bis(diphenylphosphino)ferrocene (dppf) applying K4[Fe(CN)6)]. [²¹]

(D) Synthesis of Arylvinyl Nitriles: The preparation of various arylvinyl nitriles has be achieved by cyanation of the corresponding arylvinyl bromides using K4[Fe(CN)6)] in ionic liquid under microwave irradiation catalyzed by palladium. [²4]

(E) The Stereoselective Synthesis of Fully Substituted α,β-Unsaturated Nitriles: A convenient and practical method for one-pot stereoselective synthesis of fully substituted α,β-unsaturated nitriles from aryl bromides, internal alkynes and K4[Fe(CN)6)] catalzyed by palladium in N,N-dimethylacetamide (DMAc) has been developed. [²5]

(F) Synthesis of Functionalized 3-Alkyl-3-cyanomethyl-2-oxindo­leles: Zhu and colleagues reported an efficient synthetic method for various functionalized 3-alkyl-3-cyanomethyl-2-oxindoleles by a domino intramolecular Heck-cyanation sequence using K4[Fe(CN)6] as a cyanide donor in the presence of palladium acetate and sodium carbonate. [²6] The enantiomerically enriched 2-oxindoles were also obtained by this method using (S)-Difluorphos as a chiral supporting ligand.

(G) One-Pot Synthesis of 5-Substituted 1H-Tetrazoles: Cai and co-workers reported a new and general method for the one-pot synthesis of 5-substituted 1H-tetrazole through three-component reaction of aryl bromide, NaN3, and K4[Fe(CN)6)] in the presence of catalyst Pd(OAc)2, the additive ZnBr2 and 1,4-diazabicyclo- [2.2.2]octane (dabco). [²7]

(H) Synthesis of Polysubstituted Aromatic Nitriles: Lautens and co-workers also showed that a tandem intermolecular ortho-arylation-cyanation reaction can be achieved by combining an aryl iodide with an alkyl halide or an aryl bromide followed by cyanation. In this way, polysubstituted aromatic nitriles can be prepared in one step. [²8]

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