Sonochemical heating profile for solvents and ionic liquid doped solvents, and their application in the N-alkylation of pyrazoles

[Display omitted] •The dissipated ultrasonic power of 25 solvents was determined.•[BMIM][BF4] and water had the highest dissipated ultrasonic power.•Toluene and toluene doped with [BMIM][BF4] were evaluated in an SN2 reaction.•Conversion in neat toluene was 46%.•Conversions in toluene doped with [BM...

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Bibliographic Details
Published in:Ultrasonics sonochemistry 2016-09, Vol.32, p.432-439
Main Authors: Frizzo, Clarissa P., Bacim, Carolini, Moreira, Dayse N., Rodrigues, Leticia V., Zimmer, Geórgia C., Bonacorso, Hélio G., Zanatta, Nilo, Martins, Marcos A.P.
Format: Article
Language:English
Subjects:
Dissipated ultrasonic power
Ionic liquid doped solvents
N-alkylation reaction
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Summary:[Display omitted] •The dissipated ultrasonic power of 25 solvents was determined.•[BMIM][BF4] and water had the highest dissipated ultrasonic power.•Toluene and toluene doped with [BMIM][BF4] were evaluated in an SN2 reaction.•Conversion in neat toluene was 46%.•Conversions in toluene doped with [BMIM][BF4] was 100%. The heating profile for 25 solvents was determined in ultrasonic probe equipment at amplitudes of 20%, 25%, and 30%. Each solvent was heated in accordance with its boiling point. The effect of vapor pressure, surface tension, and viscosity of the solvents in dissipated ultrasonic power (Up) was evaluated. Multiple regression analysis of these solvent properties and dissipated Up reveals that solvent viscosity is the property that most strongly affected dissipated Up. Experimentation involving acetonitrile doped with [BMIM][BF4] indicated faster heating than MeCN. Aprotic polar solvents such as DMSO, DMF, and MeCN were tested in the N-alkylation of pyrazoles under ultrasonic conditions. After 5min at 90°C, the reactants had been totally converted into product in these solvents. Solvents, with low dissipated Up (e.g., toluene) were tested. Conversions were lower compared to those of aprotic polar solvents. When the reactions were done in hexane, no conversion to product was observed. To check the effect of doping in solvents with low Up, [BMIM][BF4], DMSO, and DMF were selected. The conversions for toluene doped with [BMIM][BF4], DMSO, and DMF were 100%, 59%, and 25%, respectively. These conversions were greater than when done in just toluene (46%). Thus, [BMIM][BF4] was the best polar doping solvent, followed by DMSO. DMF was not considered to be a satisfactory doping solvent. No conversion was observed for reactions in the absence of base performed in DMSO, DMF, and MeCN doped with [BMIM][BF4].
ISSN:1350-4177
1873-2828
DOI:10.1016/j.ultsonch.2016.03.014