Imidazolium ionic liquids, oxidation

Odourless and non-volatile organosulfur compounds grafted to an imidazolium ionic liquid scaffold has been synthesized. The sulfoxides have been used for an efficient oxidation of primary allylic and benzylic alcohols into aldehydes and secondary alcohols to ketones under Swern oxidation conditions and the corresponding sulfides can be recovered and recycled.110... 

Farmer V. and Welton, T. (2002) The oxidation of alcohols in substituted imidazolium ionic liquids using ruthenium catalysts. Green Chem., 4, 97-102. 

Whitehead JA, Zhang J, Pereira N et al (2007) Application of l-alkyl-3-methyl-imidazolium ionic liquids in the oxidative leaching of sulphidic copper, gold and silver ores. HydrometaUurgy 88 109-120... 

Most importantly, [bmim][Br] could be recycled and reused in further reactions without any significant loss of its activity. This method is compatible with different functional groups, and the oxidation reactions were carried out in neutral conditions. Use of imidazolium ionic liquids as solvents for organic transformations with... 

Mehdi H, Bodor A, Lantos D, Horvath IT, De Vos DE, Binnemans K (2007) Imidazolium ionic liquids as solvents for cerium(IV)-mediated oxidation reactions. J Org Chem 72 517-524... 

Not only platinum forms carbene complexes by oxidative addition of 1,3-dialkylimidazolium salts. CaveU and coworkers also reported the formation of stable carbene complexes of nickel and palladium by reaction with imidazolium ionic liquids [53]. Even in cases where the imidazolium was protected with a methyl group in the 2-position of the imidazolium ring, carbene formation has been observed in the 4- or 5-position in some cases [54]. 

The application of ionic Hquids in catalysis has been reviewed by Hardacre and Parvulescu [127] hence, only selected examples are discussed herein. Molten salts have been used as an immobilization medium for homogeneous selox catalysis [128], for example, RuClj [129], Cu(C104)2 [130], or CuCl [131] (the latter in conjunction with molecular sieve 3A as a heterogeneous solid acid promoter). Van Doorslaer et al. [132] also reported the use of imidazolium ionic liquids for Pd(II)-acetate-catalyzed oxidation of alcohols to ketones, wherein, for... 

Mao, L., Y. Li, C. Y. Chi, H. S. O. Chan, and J. S. Wu. 2014. Conjugated polyfluorene imidazolium ionic liquids intercalated reduced graphene oxide for high performance supercapacitor electrodes. Nano Energy 6 119-128. 

A review of oxidation reactions in imidazolium ionic liquids has addressed oxidations of alcohols, aromatics, alkanes, and sulfur-containing compounds and the Baeyer-Villiger and Corey-Chaykovsky methods. ... 

Similarly, Au NPs have also been supported on r-GO an N-doped r-GO and the materials have been tested as catalysts for the aerobic oxidation of benzyl alcohol [40-41]. It was found that the presence of nitrogen as dopant is beneficial to obtain Au NPs with small size, therefore exhibiting enhanced catalytic activity [41]. The use of Au NPs and Au-Pd NPs supported on r-GO has also been reported to promote the aerobic oxidation of alcohols and oxidation of methanol to methyl formate [42]. In one of these examples, r-GO has been functionalized with imidazolium ionic liquid covalently anchored to the r-GO in order to increase the affinity of the support for Au NPs. 

Navarro-Suarez AM, Hidalgo-Acosta JC, Fadini L, Feliu JM, Suarez-Herrera MF (2011) Electrochemical oxidation of hydrogen on basal plane platinum electrodes in imidazolium ionic liquids. J Phys Chem C 115 11147-11155... 

Alkyl, cycloalkyl, arylalkyl and related acids. It was found that room temperature, imidazolium ionic liquids promote the Michaelis-Arbuzov rearrangement in high yields under mild conditions. A simple, efficient and new method for the synthesis of acetoxyphosphonates via one-pot reaction of aldehydes with dialkylphosphite in the presence of acetic anhydride using magnesium oxide has been developed. A unique [3,3]-rearrangement of phosphonium ylides has provided access to phosphonates (120) that have a wide range of synthetic utility (Scheme 41). ... 

Vicente JA, Mlonka A, Gunaratne HQN, Swadzba-Kwasny M, Nockemann P (2012) Phosphine oxide functionalised imidazolium ionic liquids as tuneable ligands for lanthanide complexatitm. Chem Conunun 48(49) 6115-6117... 

Wang, Y. Yang, H. (2009). Synthesis of iron oxide nanorods and nanocubes in an imidazolium ionic liquid. Chemical Engineering Journal, Vol.147, No.l, (April 2009), pp. 71-78, ISSN 1385-8947... 

Different solvents can be used for reactions with ammonium hexanitratocerate(IV) as reagent. The most popular solvents are (in decreasing order of importance) water, acetonitrile, dichloromethane, THF and methanol. Often mixtures of these solvents are used. Solvents of less importance are DMF, toluene, diethyl ether, ethanol, pyridine, acetone, benzene, ethyl acetate, hexane, acetic acid, chloroform, dioxane, DMSO, carbon tetrachloride and 1,2-dichloroethane. Other solvents have found only marginal use for this type of reactions. One report describes CAN-mediated oxidation reactions in a mixture of dichloromethane and an imidazolium ionic liquid (Bar et al., 2003). Methanol is a better solvent than ethanol for CAN (Cho and Romero, 1995) whereas methanol reacts only very slowly with CAN, the reaction between ethanol and CAN is fast. It should be mentioned that in many reactions in apolar solvents, CAN is used as a suspension thus under heterogeneous reaction conditions. Also reactions of CAN in acetic acid are often done under heterogeneous conditions. It was observed that for heterogeneous reactions of CAN in acetic acid, the nitrate/acetate ratio in the reactions mixture depends on the amount of solid CAN dispersed in acetic acid as the amount of undissolved CAN increases, the nitrate/acetate ratio increases significantly (Baciocchi et al., 1977). 

Phosphine oxide-functionalized imidazolium ionic liquids (ILs) were synthesized as tuneable ligands for lanthanide complexation. The task specific ILs were prepared in three steps, by reacting allq l bromide-functionalized 1,2-dimethyl imidazolium ILs with (TfzN) or (PFg) anions and potassium diphenylphosphide. The final step was oxidation of the phosphine to the P-oxide (Scheme 8). ... 

Another means of in situ metal-carbene complex formation in an ionic liquid is the direct oxidative addition of the imidazolium cation to a metal center in a low oxidation state (see Scheme 5.2-2, route b)). Cavell and co-workers have observed oxidative addition on heating 1,3-dimethylimidazolium tetrafluoroborate with Pt(PPli3)4 in refluxing THF [32]. The Pt-carbene complex formed can decompose by reductive elimination. Winterton et al. have also described the formation of a Pt-car-bene complex by oxidative addition of the [EMIM] cation to PtCl2 in a basic [EMIM]C1/A1C13 system (free CP ions present) under ethylene pressure [33]. The formation of a Pt-carbene complex by oxidative addition of the imidazolium cation is displayed in Scheme 5.2-4. 

The ease of formation of the carbene depends on the nucleophilicity of the anion associated with the imidazolium. For example, when Pd(OAc)2 is heated in the presence of [BMIM][Br], the formation of a mixture of Pd imidazolylidene complexes occurs. Palladium complexes have been shown to be active and stable catalysts for Heck and other C-C coupling reactions [34]. The highest activity and stability of palladium is observed in the ionic liquid [BMIM][Brj. Carbene complexes can be formed not only by deprotonation of the imidazolium cation but also by direct oxidative addition to metal(O) (Scheme 5.3-3). These heterocyclic carbene ligands can be functionalized with polar groups in order to increase their affinity for ionic liquids. While their donor properties can be compared to those of donor phosphines, they have the advantage over phosphines of being stable toward oxidation. 

Lee, C.M., Jeong, H.J., Lim, S.T., Sohn, M.H. and Kim, D.W. (2010) Synthesis of iron oxide nanopartides with control over shape using imidazolium-based ionic liquids. ACS Applied Materials S, Interfaces, 2 (3), 756-759. 

Ionic liquids based on imidazolium cations and either [BF4]- or [PF6] anions have been used to immobilize transition metal based oxidation catalysts developed... 

Various solid-supported perruthenate reagents have been designed for the oxidation of alcohols.Solid-supported NMO has also been used. A number of perruthenate systems employing O2 as the terminal oxidant have also been reported. The use of ionic liquids based upon substituted imidazolium cations as alternative solvent media for the selective oxidation of alcohols to aldehydes and ketones has also been investigated. ... 

The ionic liquid [bmim][BF ] is known to catalyze the aza-Diels-Alder reaction in the synthesis of pyrano- and furanoquinolines [190]. This reaction was also catalyzed by the enantiopure bis-imidazolinium salt 67 in 67% yield with an endo. exo ratio of 60 40 (Scheme 69) [191]. The product was obtained as a race-mate. In addition the aza-Diels-Alder reaction with imines and Danishefsky s diene was catalyzed by the salt 67 giving racemic product. The salt and its analogues could be easily prepared via the oxidation of the corresponding aminals [192]. Investigation of the influence of the counter anion in achiral C2-substituted imidazolinium salts, which can be also described as 4,5-dihydroimidazolium or saturated imidazolium salts, in the aza-Diels-Alder reaction showed, that the catalytic activity increased, the more lipophilic the counter anion and therefore the more hydrophobic the salt was [193]. 

The carbene complexes can also be formed by direct oxidative addition of ze-rovalent metal to an ionic liquid. The oxidative addition of a C-H bond has been demonstrated by heating [MMIM]BF4 with Pt(PPh3)4 in THF, resulting in the formation of a stable cationic platinum carbene complex (Scheme 15) (189). An effective method to protect this carbene-metal-alkyl complex from reductive elimination is to perform the reaction with an imidazolium salt as a solvent. 

Aerobic oxidation of primary alcohols to aldehydes and secondary alcohols to ketones was accomplished in ionic liquids (bmim, l-butyl-3-methyl-imidazolium cation) as RuCl2(PPh3)j/(bmim)V80°C RuClj or [RuCl Cp-cymene)] were also used... 

New 2-hydroxypropyl-functionalized imidazolium cation ionic liquids (containing an appended hydroxyl functionality) have been made [116] by use of an atom efficient one-pot reaction befween 1-mefhylimidazole and acid with propylene oxide. Unfortunately the systems were not studied... 

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