An Efficient Combined Electrochemical and Ultrasound Assisted Synthesis of Imidazole‐2‐Thiones

Feroci, Marta; Orsini, Monica; Inesi, Achille

doi:10.1002/adsc.200900359

Cited by 27 publications

(31 citation statements)

References 22 publications

(14 reference statements)

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“…Anolyte: 2 mL of the same solvent of catholyte. After 31 C, the current flow was stopped, the electrodes removed and 0.13 mmol of S 8 was added to the catholyte, which was subsequently sonicated for 5 min (22.5 kHertz) . Usual workup and flash column chromatography (eluent: AcOEt to AcOEt/MeOH 9/1) yielded the corresponding products (DTs and TILs).…”

Section: Methodsmentioning

confidence: 99%

Cathodic Behaviour of Dicationic Imidazolium Bromides: The Role of the Spacer

et al. 2019

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The cathodic reduction of dicationic imidazolium bromides, whose spacer is either an aliphatic chain or a xylyl group, leads to the formation of the corresponding N‐heterocyclic carbenes (NHCs), which were isolated as the corresponding thiones, after reaction with elemental sulfur. The behaviour of the dications was compared with the corresponding monocations. The behaviour of dicarbenes depends on the nature of the spacer. This study evidenced that dicarbenes deriving from xylyl dications are less stable than the corresponding aliphatic ones (giving lower yields in thiones), due to a debenzylation reaction. On the other hand, the yields in thiones starting from aliphatic dications are higher than the corresponding monocations, suggesting a cooperative reduction at the electrode of the two imidazolium moieties. The cathodic process was confirmed using the co‐electrogenerated hydrogen to reduce 2,2,2‐trifluoroacetophenone to the corresponding alcohol.

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Section: Methodsmentioning

confidence: 99%

Cathodic Behaviour of Dicationic Imidazolium Bromides: The Role of the Spacer

et al. 2019

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“…Imidazolin-2-ylidenes (carbenes) formed by deprotonation of the respective imidazolium cations were presumed to be intermediates in these reactions. In fact, some imidazoline-2-thiones were prepared from isolated carbenes [30], from electrolytically generated carbenes [31], and the imidazolium ion was designated as 'protocarbene' [32]. Some 1,3-dialkylimidazoline-2-thiones were reportedly prepared by alkylation of 2-mercapto-1-methylimidazole [33] and by thermal isomerization of S-alkyl compounds [21].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Crystal Structures of New 1,3-Disubstituted Imidazoline-2-thiones

Laus

Kahlenberg

Wurst

et al. 2013

Zeitschrift Für Naturforschung B

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Two methods (MeOH/K 2 CO 3 , pyridine/Et 3 N) were assessed for the introduction of sulfur into the 2-position of 1,3-disubstituted quaternary imidazolium salts 1-9 (Cl, I, BF 4 , PF 6 , CH 3 OSO 3 were used as anions) to yield nine 1,3-disubstituted imidazoline-2-thiones 10-18 (1, 10: R 1 = CH 3 , R 2 = CH 3 ; 2, 11: R 1 = OCH 2 Ph, R 2 = CH 3 ; 3, 12: R 1 = OCH 3 , R 2 = CH 3 ; 4, 13: R 1 = OCH 3 , R 2 = OCH 3 ; 5, 14: R 1 = NH 2 , R 2 = CH 2 Ph; 6, 15: R 1 = NCHPh, R 2 = CH 3 ; 7, 16: R 1 = NH 2 , R 2 = CH 3 ; 8, 17: R 1 = NCHPh, R 2 = NCHPh; 9, 18: R 1 = NH 2 , R 2 = OCH 3 ). Compounds 11-18 represent N-alkyloxy and N-amino imidazoline-2-thiones, whereas 10 served as reference compound. The first method was advantageous for the conversion 1 → 10 due to faster reaction, whereas in the reaction 2 → 11 considerable amounts of by-products were formed. Pure thiones 11, 14, 16, 17, and 18 were obtained only by the second method. Both methods worked for the synthesis of the methoxy derivatives 12 and 13 from 3 and 4, and the benzylideneamino derivative 15 from 6. 1-Amino-3-methylimidazoline-2-thione (16) was also prepared by hydrolysis of the benzylideneamino derivative 15. Crystal structures of seven 1,3-disubstituted imidazoline-2-thiones were determined by singlecrystal X-ray diffraction. Intermolecular C-H···S contacts were identified and, additionally, N-H···S interactions in aminothiones 14 and 16. The 1 H NMR shifts of 10 and 13 were satisfactorily correlated with the Kamlet-Abboud-Taft π * and β parameters in ten solvents. From the lack of correlation with the α parameter and from the C=S bond length (average 1.68Å) a significant contribution of a mesoionic imidazolium-2-thiolate resonance structure seems unlikely.

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“…115 For the synthesis of imidazole-2-thiones, electrochemistry and sonochemistry were combined, but successively. 116 Indeed, the electrochemical reduction of 1,3-dialkylimidazolium ILs gave first the corresponding N-heterocyclic carbenes that, after reaction with elemental sulfur under ultrasound (22.5 kHz, 100 W), yielded 1,3-dialkylimidazole-2-thiones in very high yields in very short times. The anodic substitution reaction of N-(methoxycarbonyl)-pyrrolidine with allyltrimethylsilane in [C 2 mim][BF 4 ] involving ultrasound illustrated the advantages of operating in a single reactor, trapping the carbocations in sub-micrometre range nucleophile droplets formed by ultrasound irradiation (3.2 mm diameter horn, 20 kHz, 150 W cm À2 ).…”

Section: Electrochemical Processesmentioning

confidence: 99%

Ionic liquids and ultrasound in combination: synergies and challenges

2014

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Ionic liquids, as reaction media, and sonochemistry are two recently developing fields of chemistry that present some similarities. Firstly, they constitute separately unconventional approaches to reaction chemistry that, in many cases, generate improvements in yield, rate and selectivity compared to classical chemistry, or even change the mechanisms or products expected. In addition, both are often associated with green chemistry concepts as a result of their properties and their possible eco-friendly uses. A recent trend has been to combine these two technologies in a range of different applications and the results demonstrate very significant and occasionally surprising synergetic effects. Here we critically review the advantages and limitations of the ionic liquid/ultrasound combination in different applications in chemistry, to understand how, and in which respects, it could become an essential tool of sustainable chemistry in the future. Many practical and theoretical aspects associated with this combination of techniques are not understood or resolved and we discus where fundamental studies might further advance this field.

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An Efficient Combined Electrochemical and Ultrasound Assisted Synthesis of Imidazole‐2‐Thiones

Cited by 27 publications

References 22 publications

Cathodic Behaviour of Dicationic Imidazolium Bromides: The Role of the Spacer

Cathodic Behaviour of Dicationic Imidazolium Bromides: The Role of the Spacer

Synthesis and Crystal Structures of New 1,3-Disubstituted Imidazoline-2-thiones

Ionic liquids and ultrasound in combination: synergies and challenges

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