L-butyl-4-methylpyridinium

Chlorostannate ionic liquids have been used in hydroformylation reactions [23], Acidic [bmimjCl-SnCb and [l-butyl-4-methylpyridinium]Cl-SnCl2 were prepared from mixing the respective [cation]+ Cl with tin(II)chloride in a ratio of 100 104, much in the same way that the chloroaluminates are made (see Chapter 4). Both these chlorostannate ionic liquids melt below 25 °C. Addition of Pd(PPh3)2Cl2 to these chlorostannate ionic liquids leads to a reaction medium that catalyses the hydroformylation of alkenes such as methyl-3-pentenoate as shown in Scheme 8.9. The ionic liquid-palladium catalyst solution is more effective than the corresponding homogeneous dichloromethane-palladium catalyst solution. The product was readily separated from the ionic liquid by distillation under vacuum. This is an important reaction as it provides a clean route to adipic acid. 

The application of ionic liquids as a reaction medium for the copper-catalyzed aerobic oxidation of primary alcohols was reported recently by various groups, in attempts to recycle the relatively expensive oxidant TEMPO [150,151]. A TEMPO/CuCl-based system was employed using [bmim]PF6 (bmim = l-butyl-3-methylimodazolium) as the ionic liquid. At 65 °C a variety of allylic, benzylic, aliphatic primary and secondary alcohols were converted to the respective aldehydes or ketones, with good selectiv-ities [150]. A three-component catalytic system comprised of Cu(C104)2, dimethylaminopyridine (DMAP) and acetamido-TEMPO in the ionic liquid [bmpy]Pp6 (bmpy = l-butyl-4-methylpyridinium) was also applied for the oxidation of benzylic and allylic alcohols as well as selected primary alcohols. Possible recycling of the catalyst system for up to five runs was demonstrated, albeit with significant loss of activity and yields. No reactivity was observed with 1-phenylethanol and cyclohexanol [151]. 

Table 2.1 Standard ion transfer potentials of different A/yV-alkylimidazolium and l-butyl-4-methylpyridinium ionic liquid cations [29]...

Jiang et al. used another Cu complex for the promotion of the oxidation of primary alcohols with O. They applied a three-component system including acet-amido-TEMPO/CuCClO Jj/DMAP in the ionic liquid l-butyl-4-methylpyridinium hexafluorophosphate ([bmpy][PFg]) at room temperature (Scheme 14.29) [28]. 

A similar dimerization catalytic system has been investigated [42] in a continuous flow loop reactor in order to study the stability of the ionic liquid solution. The catalyst used is the organometallic nickel(II) complex (Hcod)Ni(hfacac) (Hcod=cyclooct-4-ene-l-yl and hfacac=l,l,l,5,5,5-hexafluoro-2,4-pentanedionato-0,0 ) and the ionic liquid is an acidic chloroaluminate based on the acidic mixture of l-butyl-4-methylpyridinium chloride and aluminum chloride. No alkylaluminum is added, but an organic Lewis base is added to buffer the acidity of the medium. 

Safarov J, Kul I, El-Awady WA, Nocke J, Shahverdiyev A, Hassel E (2012) Thermophysical properties of l-butyl-4-methylpyridinium tetrafluoroborate. J Chem Thermodyn 51 82-87... 

Fig. 3. Prediction of Log Kl at 298.15 K of organic compounds in two ionic liquids using the GC-LSER. l-butyl-4-methylpyridinium thiocyanate [BMPyr][SCN] and 1-butyl-l-methylpyrrolidinium thiocyanate [BMPYR][SCN].

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