Solvents doping with ionic liquids

Applying the concept of using solvents doped with ionic liquids in order to allow microwave heating to high temperatures (see Section 4.3.3.2), Leadbeater and Tore-nius studied the Diels-Alder reaction between 2,3-dimethylbutadiene and methyl acrylate (Scheme 6.91) [190]. This reaction is traditionally performed in toluene or... 

Table 4.3 Microwave heating effects of doping organic solvents with ionic liquids (IL) A and B (data from [63]). a ...

Inter- and intramolecular hetero-Diels-Alder cycloaddition reactions in a series of functionalized 2-(lH)-pyrazinones have been studied in detail by the groups of Van der Eycken and Kappe (Scheme 6.95) [195-197]. In the intramolecular series, cycloaddition of alkenyl-tethered 2-(lH)-pyrazinones required 1-2 days under conventional thermal conditions involving chlorobenzene as solvent under reflux conditions (132 °C). Switching to 1,2-dichloroethane doped with the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) and sealed-vessel microwave technology, the same transformations were completed within 8-18 min at a reaction temperature of 190 °C (Scheme 6.95 a) [195]. Without isolating the primary imidoyl chloride cycloadducts, rapid hydrolysis was achieved by the addition of small amounts of water and subjecting the reaction mixture to further microwave irradia-... 

Makote, R. D., Luo, H. M., Dai, S., Synthesis of ionic liquid and silica composites doped with dicyclohexyl-18-crown-6 for sequestration of metal ions. In Clean Solvents, ACS Symposium Series 819, 26-33, 2002. 

In many of the more recent reports of IMDA and IMHDA cydoadditions, the reactions are performed at high temperature under microwave activation. Different conditions have been used, including closed-vessel processes [56-60] with highly polar solvents or ionic liquids as doping agents in nonpolar solvents, or indeed, microwave irradiation under open-vessel reflux conditions [61-63, 36). 

Microwave-assisted thionation of amides using a polymer-supported thionating reagent has also been studied [110]. The polymer-supported amino thiophosphate serves as a convenient substitute for its homogeneous analog in microwave-induced rapid conversion of amides to thioamides. Under microwave conditions the reaction is complete within 15 min as opposed to conventional reflux in toluene for 30 h (Scheme 16.72). Use of the ionic liquid l-ethyl-3-methylimidazolium hexafluorophosphate (emimPF ) to dope nonpolar solvents such as toluene and assist with heating under microwave irradiation conditions was described for the first time (Chapter 7). 

PPy doped with protonic acid shows a higher electrical conductivity compared to that doped with organic sulfonic acid (Lee et al., 2014), and a PPy film with electrical conductivity up to 2000 S cm 1 was prepared (Qi et al., 2012). For PEDOTrPSS, many secondary dopants, commonly called conductivity enhancement agents, such as, polyols, alcohols, surfactants, salts, acids, and organic solvents, have been widely used to enhance the electrical conductivity (McCarthy et al., 2014). It reached 2084 S cm with the use of a nonvolatile ionic liquid (Badre et al., 2012) and 3065 S cm or even higher after H2SO4 treatment at high temperature (Xia et al., 2012). 

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. 

---