Pyridine acid ionic liquids

Scheme 51 An acidic ionic liquid catalyzes the direct alkylation of the methyl pyridines.

Acid ionic liquids will catalyze the addition of the sp C-H bond of methyl pyridines to aromatic aldehydes (Scheme 51) (14TL5462).The best yields where found with a co-solvent of water and dioxane and using [Hmim] [H2PO4] as the acid. Sterics appeared to be irrelevant to the reaction as ortho-, meta-, and para-substituted aryl aldehydes combined with methyl pyridines in relatively the same yields. The reaction was also robust if the pyridine was swapped for quinolines. However, when the methyl group was moved to C-4 on the pyridine, no reaction was observed. Finally, the acidic ionic liquid could be recycled with very little loss in yield. 

Each sample was mixed with the ionic liquid matrix (2,5-dihydroxybenzoic acid/pyridine) containing C-labelled glucose as internal standard and spotted on the target. MALDI-MS analysis generated reaction profiles by the simultaneous determination of product and substrate concentrations for each enzyme variant. The reaction profiles could be used to sort the enzyme variants into five different classes. 

Lecocq et al. [108] studied ionic liquids formed between zinc chloride and TbutyT2,3-dimethylimidazolium chloride [BMMIMJC1 with the amount of Zn(H2 between 0 and 0.75 mol%. Analysis using NMR, and mass spectrometry showed Cl and [ZnCl j] in Lewis basic liquids and [ZnCh] and [Zn>,Cl7] in Lewis acidic liquids. Infrared spectra with pyridine were used to quantify the Lewis acidity and high temperature (110 °C) NMR experiments showed that the structure varies with time from [BMMIM][ZnCl3] to [BMMIM... Cl... ZnCy. 

Ionic liquids based on salts of alkylimida-zoles and pyridines have been used for the synthesis of esters of ascorbic acid and other sugars on the laboratory scale and show particular advantage in their ability to dissolve otherwise incompatible substrates. One of the key features of these solvents is their extremely low vapor pressures and excellent ability to dissolve both polar and nonpolar materials. Reactions can be run under vacuum allowing the removal of volatile byproducts such as water and enable one to... 

Recently, Ni and group [66] introduced a new type of chiral ionic liquid based on pyridinium cation having a chiral moiety tethered to a urea unit. The synthesis of salt involves a reaction of 2-aminomethyl pyridine with chiral 2-isocyanate-3-methylbutyrate and then heating in the presence of alkyl halide to form salt (Scheme 17.18). In total, nine chiral pyridinium salts were synthesized with varying amino acids. Currently, the authors are using these salts for asymmetric induction in organic transformation. 

Zhao et al. have synthesized novel ionic liquids 307 and 308, which contain (3-chloro-2-hydroxypropyl)-functionalized pyridinium cations, by the ultrasound-assisted reaction of pyridine with acid (HCl and HBF4) and 3-chloro-propylene oxide at room temperature, in excellent yields and purity, in whieh the acid provided the eorresponding anionic component of the ionic Uquids. Furthermore, they examined the appheation of new ionic liquids as solvents in the MBH reaction and found that IL-BF4 308 showed a better effect in rate enhanee-ment and an improved yield than IL-Cl 307 in some cases (Scheme 1.121). ... 

Hydroxyphenylazo)-benzoic acid was employed as a matrix for MALDl-MS analysis of Rhizobium cells, which yielded a maximum number of signals in the 1-10 kDa range (Mandal et al. 2007). Ionic liquid matrices (ILMs) based on S A and DHB in conjugation with various bases including aniline, dimethyl aniline, diethylaniline, dicyclohexylamine, and pyridine have been reported for the analysis of intact bacteria in MALDl-MS (Abdelhamid et al. 2013). 

IC-MS has also been applied for the characterization of ionic liquids (IL) and for the investigation of their long-term stability under process-like conditions. The term ionic liquid commonly refers to a class of molten salts that are by definition liquid below 100 °C. They usually consist of bulky organic cations such as alkylated imidazole, pyrrole, or pyridine derivatives, or quatemized alkyl amines and alkyl phosphines. Common counterions are halides, alkyl sulfates, fluorinated hydrocarbons, carboxylic acids, or amino acids [268]. The physical and chemical properties of ILs are customizable by different cation-anion combinations and by the length of the alkyl chain of the cation. Depending on the... 

Pibiri I, Pace A, Buscemi S, Causin V, RastreUi F, Saielli G (2012) Oxadiazolyl-pyridines and perfluoroalkyl-carboxyUc acids as building blocks for protic ionic liquids crossing the thin line between ionic and hydrogen bonded materials. PCCP 14 14306-14314... 

Different solvents can be used for reactions with ammonium hexanitratocerate(IV) as reagent. The most popular solvents are (in decreasing order of importance) water, acetonitrile, dichloromethane, THF and methanol. Often mixtures of these solvents are used. Solvents of less importance are DMF, toluene, diethyl ether, ethanol, pyridine, acetone, benzene, ethyl acetate, hexane, acetic acid, chloroform, dioxane, DMSO, carbon tetrachloride and 1,2-dichloroethane. Other solvents have found only marginal use for this type of reactions. One report describes CAN-mediated oxidation reactions in a mixture of dichloromethane and an imidazolium ionic liquid (Bar et al., 2003). Methanol is a better solvent than ethanol for CAN (Cho and Romero, 1995) whereas methanol reacts only very slowly with CAN, the reaction between ethanol and CAN is fast. It should be mentioned that in many reactions in apolar solvents, CAN is used as a suspension thus under heterogeneous reaction conditions. Also reactions of CAN in acetic acid are often done under heterogeneous conditions. It was observed that for heterogeneous reactions of CAN in acetic acid, the nitrate/acetate ratio in the reactions mixture depends on the amount of solid CAN dispersed in acetic acid as the amount of undissolved CAN increases, the nitrate/acetate ratio increases significantly (Baciocchi et al., 1977). 

Poly(ionic liquid) brushes with terminated ferrocene units acted similarly, while the interfacial resistance was probed by hexacyanoferrate [457]. Chemical and electrochemical switching of local pH at an electrode-grafted poly(vinyl pyridine) brush again allowed modulation of hexacyanoferrate chemistiy (Fig. 43) [458]. Octacyanomolybdate was used as catalyst for the oxidation of ascorbic acid [459]. Even heteropolyanions (Keggin ions) could be entrapped in polymer films electrochemicaUy [460]. Further, thermoresponsive or pH-responsive cationic copolymer films modulated the hexacyanoferrate or ferrocenedicarboxyUc acid electrochemistry by temperature or variatimi of pH and perchlorate concentration, respectively [461-463]. Besides these complexes with cationic polyelectrolyte films, electroactive cationic counterions (e.g., the europium couple) interacted with anionic networks [464]. Similarly, copper ions within a PAA matrix [367] allowed the construction of actuators [465]. Besides these binary systems (poly-electrolyte/electroactive counterions), multiresponsive electrode modification with an interpenetrating gel network of poly(acrylic) acid and poly(diethyl acrylamide) allowed the modulation of hexacyanoferrate electrochemistry [368]. 

Biginelli reaction (combining ArCHO, MeCOCH2COEt, and urea) has been catalysed by a combination of a chiral bifunctional primary amine-pyridine and HCl in dioxane/CHCl3 to form dihydropyrimidines with up to 99% ee Lewis-acid-promoted formations of dihydropyrimidinones via Biginelli reactions catalysed by imidazolium-based ionic liquids have been found by NMR, ESI-MS, and theoretical studies to proceed via stabilized charged intermediates. ... 

---