Ionic liquids BMIMPF

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... 

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. 

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]. 

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. 

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 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. 

A doped Si substrate with as-grown multiwalled (MW) CNTs synthesized through a thermal chemical vapor deposition (CVD) method was attached to a stainless steel working electrode, as shown in Fig. 27a [141]. A P3HT layer with a thickness of 20 nm was directly deposited on the surface of the MWCNTs using an electrochemical polymerization method. The electrolyte for the electrochemical polymerization consisted of 3-HT monomers, BMIMPFs as the ionic liquid, and anhydrous acetonitrile as the solvent. 

Zhang J, Bond AM (2003) Comparison of voltammetric data obtained for the /ra/w-[Mn(CN) (CO)2 P(OPh)3 (Ph2PCH2PPh2)]° process in BMIMPFe ionic liquid under microchemical and conventional conditions. Anal Chem 75(24) 6938-6948. doi 10.1021/ac034921e... 

In 2008, Yu and coworkers [31 ] reported the Au nanoparticle-supported Pd(II) microwave-assisted tilkyne cyclotrimerization reaction in ionic liquids. The Pd complexes were immobilized onto Au nanoparticles via chelation to the surface-bound dipyridyls. The catalysis was performed in bmimPF under microwave irradiation and the recovered catalysts could be recycled many times. The conversions were excellent, the regioselectivity was good, and the scope was broad. 

The potential super acid capability of excess aqueous HBF4 and HPFe in ionic liquid may facilitate formylation reactions of aromatics and were subsequently investigated. Toluene, being highly susceptible to CO formylation under acidic conditions, was therefor subjected to treatment with excess HPFe and HBF4 in BmimPFe and BmimBF4 respectively (Table 2.16, Runs 1 and 2). No formylation products were obtained which... 

It should be noted that in BmimPFg at temperatures above 410-420°K, partial destruction of the biradicals takes place, with the appearance of the superimposed three-line EPR spectrum, for all the systems I-III. This was revealed by the noticeable increase of the main "nitroxide" lines amplitude in EPR spectra (lines 1, 3 and 1 in Fig. 2). It seems, that thermal decomposition of BmimPFe started at 415-420°K (Huddleston et al., 2001) and the generated products react with biradical paramagnetic centers of I-III with formation of the appropriate radicals. The temperature at which such biradical "decay" starts depends on the ionic liquid. 

We assume that the experimental AH and e values for I in different liquids including ionic liquids qualitatively should correlate, first of all, with the viscosity of the solvent, though the viscosity of BmimPFe, for example, is reported as q = 257.1 cP at 298 K (Chiapp>e Pieraccini, 2004) Indeed, the E, values, which characterize temperature dependence of q ... 

Ionic liquid microemulsions have both the advantages of ionic liquids and microemulsion, which can overcome the inability of ionic liquids to dissolve a number of chemicals including some hydrophilic substances and then broaden the utilization of ionic liquids. Some papers reported that ionic liquid could substitute water to form nonaqueous ionic liquid microemulsion and exist as nanosized polar domains dispersed in cyclohexane with the aid of surfactant (Li et al., 2007). Gao, et al. prepared and characterized TX-IOO/H2O/I-butyl-3-methylimidazolium hexafluorophosphate (bmimPFs) microemulsion using different techniques. Their research results showed that water domains existed in the water-in-bmimPFa microemulsion, which could dissolve salts (Gao et al., 2005). 

---