Imidazolium Hydroxide Research Articles

Hydrolysis of Imidazole-2-ylidenes

The direct reaction of an imidazole-2-ylidene in a predominantly aqueous environment [about 0.1 M solution in a H(2)O (>60%)/THF solvent system] was investigated for the first time. The reaction yielded a stable solution of the corresponding imidazolium-hydroxide of pH 13, which is in agreement with results from an ab initio molecular dynamics simulation. In contrast, hydrolysis of the carbene in a mainly aprotic environment (>80% THF) gives a hydrogen-bridged carbene-water complex which could be detected by NMR and IR spectroscopies for the first time. This complex converts slowly to two isomeric ring opened products and is at higher water concentration in dynamic equilibrium with the imidazolium hydroxide. A computational mechanistic study of the carbene hydrolysis with a gradually increasing number of water molecules revealed that the imidazolium-hydroxide structure can only be optimized with three or more water molecules as reactants, and with the increasing number of water molecules its stability is increasing with respect to the carbene-water complex. In agreement with the experimental results, these findings point out that solvent stabilization and basicity of the hydroxide ion plays a crucial role in the reaction. With increasing number of water molecules the barriers connecting the reaction intermediates are getting smaller, and the ring opened hydrolysis products can be derived from imidazolium-hydroxide type intermediates. Computational studies on the hydrolysis of a nonaromatic imidazolidine-2-ylidene analogue clearly indicated the analogous ring-opened product to be by 10-12 kcal/mol more stable than the appropriate ion pair and the carbene-water complex, in agreement with the known aromatic stabilization of imidazol-2-ylidenes. Accordingly, these molecules hydrolyze with exclusive formation of the ring-opened product.

An ester appending multifunctional ionic liquid for Pd(II) catalyzed Heck reaction

A basic, ester functionalized, imidazolium based ionic liquid (IL2), 3-Methyl-1-(ethoxycarbonylmethyl)imidazolium hydroxide was designed eyeing in situ generation and stabilization of palladium nanoparticles for palladium catalyzed Heck reaction of haloarenes and olefins. This phosphine-free Pd-IL catalyst demonstrated excellent activity and reusability at relatively low reaction temperature (80 °C) for a wide spectrum of haloarenes including chloroarenes. The relatively low reaction temperature could be attributed to in situ generation of uniform and spherical palladium nanoparticles (~ 5 nm).

One‐pot synthesis of polyfunctionalized pyrans catalyzed by basic ionic liquid in aqueous media

Abstract magnified image An efficient and convenient method for the synthesis of polyfunctionalized 4H‐pyrans has been achieved through the one‐pot condensation of aromatic aldehydes, malononitrile, and 4‐hydroxycoumarin, phenols or active methylene carbonyl compounds such as 1, 3‐cyclohexanedione and dimedone in the presence of 1‐butyl‐3‐methyl imidazolium hydroxide ([bmim]OH) as catalyst in aqueous media. This method offers several advantages short reaction time, high yields, and simple procedure. J. Heterocyclic Chem., (2009).

Synthesis of quinazoline-2,4(1 H,3 H)-diones from carbon dioxide and 2-aminobenzonitriles using [Bmim]OH as a homogeneous recyclable catalyst

A green protocol for the synthesis of quinazoline-2,4(1 H,3 H)-diones from carbon dioxide and 2-aminobenzonitriles using a basic ionic liquid, 1-butyl-3-methyl imidazolium hydroxide ([Bmim]OH) as a catalyst have been reported. The effects of various reaction parameters like catalyst screening, catalyst loading, reaction time, solvent, temperature and pressure on the reaction system were investigated. A wide variety of aromatic aminobenzonitriles and five/six member N-heterocyclic carbonitriles were synthesized using this protocol. All these reaction were carried out under solvent-free condition. The ionic liquid was recovered and reused successfully for the title reaction. 6,7-Dimethoxyquinazoline-2,4(1 H,3 H)-diones, which is a key intermediates for several drugs (Prazosin, Bunazosin and Doxazosin) was synthesized successfully.

Efficient and green synthesis of tetrasubstituted pyrroles promoted by task-specific basic ionic liquids as catalyst in aqueous media

Synthesis of tetrasubstituted pyrroles by the three-component condensation reaction of acid chlorides, dialkyl acetylenedicarboxylates, and amino acids in the presence of various room-temperature ionic liquids (RTILs) as catalysts in water is reported. Among the ionic liquids used, the basic functionalized ionic liquid, butyl methyl imidazolium hydroxide [bmim]OH, was the most effective catalyst. The influence of reaction temperature, reaction time, and amount of ionic liquid on the reaction was investigated. The [bmim]OH/H(2)O catalyst system could be reused for at least five recycles without appreciable loss of efficiency.

ChemInform Abstract: Green Synthesis of 5‐Benzylidene Rhodanine Derivatives Catalyzed by 1‐Butyl‐3‐methyl Imidazolium Hydroxide in Water.

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Green synthesis of 5-benzylidene rhodanine derivatives catalyzed by 1-butyl-3-methyl imidazolium hydroxide in water

A basic functionalized ionic liquid, 1-butyl-3-methyl imidazolium hydroxide ([bmim][OH]), catalyzed the Knoevenagel condensation of rhodanine with aromatic aldehydes. It proceeded smoothly in water to afford the 5-benzylidene rhodamine derivatives in high yields at room temperature. This new method offers several advantages, such as excellent yields, short reaction times, and simple procedure. The catalyst can be reused at least 5 times without significant loss of activity.

Solvent-free synthesis of substituted ureas from CO2 and amines with a functional ionic liquid as the catalyst

The synthesis of disubstituted ureas from amines and CO2 were carried out using a basic ionic liquid (IL) 1-n-butyl-3-methyl imidazolium hydroxide ([Bmim]OH) as the catalyst. The effects of reaction time, amount of [Bmim]OH, reaction temperature, pressure, and solvent on yields of the products were investigated. The results indicated that aliphatic amines, cyclohexylamine, and benzylamine could be converted to the corresponding ureas selectively in moderate yields under solvent-free conditions without using any dehydrating regent. The IL could be reused after a simple separation procedure.

Basic ionic liquid as catalyst for the rapid and green synthesis of substituted 2-amino-2-chromenes in aqueous media

Abstract A basic functionalized ionic liquid, 1-butyl-3-methyl imidazolium hydroxide ([bmim]OH), catalyzed three-component condensation reaction of aromatic aldehydes, malononitrile and α- or β-naphthol proceeded rapidly in water at reflux to afford corresponding 2-amino-2-chromenes in high yields. The greener protocol was found to be fairly general and the aqueous reaction media was reused in subsequent reactions with consistent activity.