BmimPF

One year later the same team described the rapid alkenylation of 3-chlo-ropyridine and 6-chloroquinohne with butyl acrylate based on Herrmann s palladacycle employing a mixture of dioxane and bmimPFe as a mediiun... 

However, most of the reactions are reported to be slow, taking up to 12 h for complete conversion of the starting materials. A Diels-Alder reaction of the pyrazinone scaffold with dimethyl acetylenedicarboxylate (DMAD) [57] has been studied in view of investigating the swiftness of this cycloaddition-fragmentation protocol (Scheme 20). The authors investigated the reaction with DMAD (lOequiv) under microwave irradiation at an elevated temperature of 190 °C, using small amounts of ionic liquid (bmimPFe) in... 

Figure 9.5 Sammon map representing similarity of extraction ability of solvents (with respect to extraction of neutral organic compounds). The closer the points are on the map, the more similar are the corresponding solvents. Conventional solvents are designated by numbers, some representative numbers are m-xylene—35, butyl acetate—9, 1-octanol—40. The point marked BMImPF, represents l-butyl-3-methyl-imidazolium hexafluorophosphate ([C4CiIm][PF5]).

Fletcher, K.A., Storey, L, Hendricks, A.E., Pandey, S., Pandey, S., Behavior of the solvatochromic probes Reichardt s dye, pyrene, dansylamide, Nile Red and 1-pyrenecarbaldehyde within the room-temperature ionic liquid bmimPF(6), Green Chem., 3, 210-215, 2001. 

Analogous to epoxides, aziridines can be prepared by the methylenation of imines. In this case, ethyl diazoacetate is the most common source of carbenes. For example, the imine derived from p-chlorobenzaldehyde 148 is converted to the c/j-aziridinyl ester 149 upon treatment with ethyl diazoacetate in the presence of lithium perchlorate <03TL5275>. These conditions have also been applied to a reaction medium of the ionic liquid l-n-butyl-3-methylimidazolium hexafluorophosphate (bmimPFe) with excellent results <03TL2409>. An interesting enantioselective twist to this protocol has been reported, in which a diazoacetate derived from (TJ)-pantolactone 150 is used. This system was applied to the aziridination of trifluoromethyl-substituted aldimines, which were prepared in situ from the corresponding aminals under the catalysis of boron trifluoride etherate <03TL4011>. 

The anodic oxidation of the tetrafluoroborate anion occurs at potentials higher than 2.1 V and the remaining hexafluorophosphate and imide anions are oxidised at potentials higher than 2.0 V. Hence, the stability window of the EMImBF4 and BMImBF4 is 4.2 V. Ionic liquids BMImPFe and EMImN(Tf)2 shows a similar stability window of ca. 4.1 V. However, the window of the BMPyN(Tf)2, is considerably lower ca. 3.0 V. This is consistent with data (ca. 4.1-4.2 V) found for a series of ionic liquids based on EMIm and DMPIm (l,2-dimethyl-3-propylimidazolium) cations [12]. 

Li and Niu et al. [69] employed the BmimPF -supported SWCNT electrode to execute electrografting poly(V-succinimidyl acrylate) (PNSA) onto their surfaces. 

Fig. 15.6 Environmental scanning electron microscope (ESEM) images of (a) the BmimPF -MWCNT gel modified the graphite electrode surface (inset high-magnification ESEM image) and (b) the BmimPF -MWCNT gel modified the GC electrode surface after immersing in water for 10 h (Reproduced from Ref. [99] with kind permission of Elsevier)...

The hetero Diels-Alder reaction of a series of functionalized 2(li-f)-pyrazinones was studied in detail by Van der Eycken et al. [58, 65]. For example, in a series of intramolecular cycioadditions of alkenyl-tethered 2(li-f)-pyrazinones 27 the reaction required 1-2 days under conventional thermal conditions (chlorobenzene, reflux, 132 °C) whereas use of 1,2-dichloroethane doped with the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPFe) and use of micro-waves up to a temperature of 190 °C (sealed vessels) enabled the same transformations to be completed within 8-15 min. The primary imidoyl chloride cycloadducts were not isolated, but were rapidly hydrolyzed under the action of microwaves by addition of small amounts of water (130 °C, 5 min). The overall yields of 28 were in the same range as reported for the conventional thermal procedures (Scheme 11.8) [58]. 

A significant advance in DA reactions is use of a recyclable organotungsten Lewis acid, readily employed in water or ionic liquid ([bmimjPFe) as solvent, in conjunction with microwave technology [21c]. In the DA reactions shown in Scheme 11.21, 3 mol% organotungsten Lewis acid catalyst [0=P(2-py)3W(CO)(NO)2](BF4)2 was used. The authors showed that such DA reactions could be performed very efficiently with the combined effects of the Lewis acid catalyst in water (or in bmimPFe) and controlled microwave irradiation. Full conversion was achieved under such conditions at 50 °C within 50-60 s in water (25-60 s in bmimPFg) compared with thermal heating which required 1-8 h in water or 1-48 h in bmimPFg. 

Water and the ionic liquid bmimPF act as powerful reaction media not only for rate acceleration (for adduct 80, in water, conversion = 92-99%, yield = 83-97%, and in bmimPF, conversion = 81-99%, yield = 71-96%) and chemoelectivity enhancement but also for facilitating catalyst recycling in the [0=P(2-py)3W(CO)(NO)2](BF4)2-catalyzed Diels-Alder reaction systems. A key feature of this catalyst-water or catalyst-ionic liquid system is that the catalyst was recycled many times. In addition, the authors illustrated the development of the catalyst by conventional heating or under the action of microwave irradiation, the results of which are summarized in Scheme 11.21. 

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