Solvent-Free Sonochemical Preparation of Ionic Liquids

Namboodiri, Vasudevan; Varma, Rajender S.

doi:10.1021/ol026608p

Cited by 198 publications

(91 citation statements)

References 26 publications

(16 reference statements)

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“…General: The preparation of complexes 1-4 [5] and 3-methyl-1-propylimidazolium bromide [27] was reported previously. CH 2 Cl 2 was dried with P 2 O 5 and distilled before use.…”

Section: Methodsmentioning

confidence: 99%

Transfer Hydrogenation of Ketones and Activated Olefins Using Chelating NHC Ruthenium Complexes

2011

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N‐Heterocyclic carbene (NHC) ruthenium complexes consisting of different donor substituents attached to the NHC ligand efficiently catalyse the transfer hydrogenation of ketones and of activated olefins in α,β‐unsaturated ketones to give saturated alcohols. The most active catalyst precursor contains a tethered olefin as a hemilabile donor site. This complex also converts nitriles and, depending on the reaction conditions, either benzylamines are produced by means of transfer hydrogenation, or amides from formal addition of H2O. Kinetic analysis of the double hydrogenation of α,β‐unsaturated ketones indicates fast isomerisation of the enol intermediate to its saturated ketone tautomer prior to the second hydrogenation.

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“…General: The preparation of complexes 1-4 [5] and 3-methyl-1-propylimidazolium bromide [27] was reported previously. CH 2 Cl 2 was dried with P 2 O 5 and distilled before use.…”

Section: Methodsmentioning

confidence: 99%

Transfer Hydrogenation of Ketones and Activated Olefins Using Chelating NHC Ruthenium Complexes

2011

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“…However, as reaction time is somewhat too long, several trials to reduce it were attempted. Sonochemistry (Namboodiri & Varma, 2002;Estager et al, 2007;Levêque et al, 2007) and microwave chemistry Varma & Namboodiri, 2001b) which are well described in the literature and often named as a good way to shorten reaction times, were used to try to improve our reaction. In the previous synthetic method the quaternarisation of 3-bromopropyl methacrylate with N-methylimidazole leads to 99 % yield in 24 hours.…”

Section: Synthetic Methods Modifying the Esterifying Chain: Waymentioning

confidence: 99%

Ionic Liquids from (Meth) Acrylic Compounds

Sindt¹,

Mieloszynski²,

Harmand³

2011

Ionic Liquids - Classes and Properties

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“…Consequently, several newer strategies have appeared, such as solvent-free *Corresponding author. Email: varma.rajender@epa.gov (dry media), solid-supported with and without microwave (MW) irradiation (2Á6), and mechanochemical mixing (grinding) (7Á9); and the use of room temperature ionic liquids (10,11), supercritical carbon dioxide, and water (12) as reaction media that can be combined with MW or ultrasonic irradiation for rapid synthesis. Indeed, the best solvent is ''no solvent,'' but in such cases the problems of handling of materials and heat and mass transfer aspects persist and need to be addressed in close co-operation with chemical engineers.…”

Section: Introductionmentioning

confidence: 99%

“Greener” chemical syntheses using mechanochemical mixing or microwave and ultrasound irradiation

Varma

2007

Green Chemistry Letters and Reviews

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Various emerging ''greener'' strategic pathways, researched primarily in the author's own laboratory, are summarized. They include solvent-free mechanochemical methods that involve the use of hypervalent iodine reagents at room temperature for the synthesis of heterocyclic entities, and useful conversion of ketones into b-keto sulfones and their a-tosyloxy derivatives in high yields. A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable mineral supports, such as alumina, silica, clay, or ''doped'' surfaces, is described; it is applicable to a wide range of cleavage, condensation, cyclization, rearrangement, oxidation, and reduction reactions, including rapid one-pot assembly of heterocyclic compounds from in situ generated reactive intermediates. The strategy is adaptable to multi-component reactions, e.g. Ugi and Biginelli reactions, for rapid assembly of a library of compounds. Synthesis of a wide variety of significant precursors and intermediates, namely enones, imines, enamines, nitroalkenes, and oxidized sulfur species, is possible and their value in concise MW synthesis of 2-aroylbenzofurans and thiazole derivatives is illustrated. Ultrasound-and MW-assisted solventless preparation of ionic liquids and their application in alkylation and metal-catalyzed multi-component reactions are described. With a view to consume greenhouse gas, carbon dioxide (CO 2 ), efficient reaction of epoxides with CO 2 provides ready access to cyclic carbonates using only a catalytic amount of recyclable indium-based ionic liquid. MW heating in aqueous reaction media enables expeditious N-alkylation reactions of amines and hydrazines to afford a series of heterocyclic ring systems, such as N-azacycloalkanes, 4,5-dihydropyrazoles, and pyrazolidines. A general and expeditious MW-enhanced nucleophilic substitution approach uses easily accessible starting materials such as halides or tosylates in reaction with alkali azides, thiocyanates, or sulfinates in the absence of any phase transfer catalyst to produce azides, thiocyanates, and sulfones, respectively, wherein a variety of reactive functional groups are tolerated. A three-component condensation (MCC) approach for the synthesis of useful 2-amino-2-chromenes is described using a recyclable nanosized magnesium oxide catalyst in aqueous poly (ethylene glycol) (PEG) medium at room temperature. A general greener approach to shape-selective generation of nanomaterials is summarized including their potential application as nanocomposites.

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Solvent-Free Sonochemical Preparation of Ionic Liquids

Cited by 198 publications

References 26 publications

Transfer Hydrogenation of Ketones and Activated Olefins Using Chelating NHC Ruthenium Complexes

Transfer Hydrogenation of Ketones and Activated Olefins Using Chelating NHC Ruthenium Complexes

Ionic Liquids from (Meth) Acrylic Compounds

“Greener” chemical syntheses using mechanochemical mixing or microwave and ultrasound irradiation

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