Polyisobutylene-bound sulfonic acid are effective homogeneous Brønsted acid catalysts and they and a poly(alpha-olefin) (PAO) solvent are readily recyclable with simple product removal by extraction or distillation.
Polyisobutylene (PIB) oligomers containing terminal alkene groups depolymerize rapidly at room temperature in the presence of trifluoromethanesulfonic acid and an arene solvent like benzene. This dramatically lower temperature depolymerization behavior is due to an enthalpically driven process wherein the isobutylene groups formed by a chain scission event after reacting a strong Brønsted acid with alkene groups at the polyisobutylene oligomer terminus are trapped by the solvent. In an arene solvent like benzene or toluene, tert-butyl carbocations formed from this isobutylene group rapidly react with benzene or toluene in a thermodynamically favorable process to form tert-butylarene products. This process is presumably favored in part because the C sp2 −C sp3 bond that forms tertbutylarene is stronger than the C sp3 −C sp3 bonds in the polyisobutylene polymer. These studies show that polyisobutylene oligomers depolymerize in only a few minutes at ambient or even sub-ambient temperature using this chemistry.
Unactivated α-branched primary and secondary aliphatic alcohols have been successfully transformed into their corresponding alkyl chlorides in high yields upon treatment with a mixture of triphosgene and pyridine in dichloromethane at reflux. These mild chlorination conditions are high yielding, stereospecific, and well tolerated by numerous sensitive functionalities. Furthermore, no nuisance waste products are generated in the course of the reactions.
The use of polyisobutylene and poly(4-dodecylstyrene) bound catalysts that contain transition metal or organocatalysts for cyclopropanation, ring-closing metathesis, and nucleophilic catalysis in flow chemistry schemes is described and compared with similar catalysts used in batch reactions. These Rh(II) carboxylate catalysts, N-heterocyclic carbene-ligated Ru(II) benzylidene catalysts, and analogs of 4-dimethylaminopyridine catalysts were used in reactions in heptane in flow and then separated in a gravity based liquid/liquid separation using a biphasic heptane/acetonitrile mixture. The less dense catalyst-containing phase in that separation was continuously used in flow with fresh substrate solution. Leaching of catalysts, yields, and turnover frequencies in these flow reactions were comparable with prior results obtained with the same phase isolable catalysts in batch reactions.
Covalent and noncovalent chemical methods that use oligomeric lipophilic agents to solubilize silica nanoparticles in heptane and poly(α-olefin) (EPAO) solvents are described. While only modest solubilization efficiencies are seen with an octadecyl group, a variety of terminally functionalized polyisobutylene (PIB) derivatives are more efficient. Both covalent and noncovalent chemistry was found to be effective. Covalent modification solubilized up to 34 wt% of silica nanoparticles (SiNPs) as stable solutions in heptane or PAOs.Noncovalent modification was however more effective, solubilizing up to 70% of SiNPs in heptane or PAOs. The most successful covalent approach used PIB oligomers containing terminal triethoxysilane groups to covalently modify SiNPs. Alternatively, SiNPs that were first functionalized with amine groups could be solubilized in heptane or PAOs with polyisobutylene containing sulfonic acid groups using acid-base chemistry. Studies of these and other solubilization chemistry was also carried out using fluorescent labels, studies that confirmed the gravimetric analyses of the heptane-solubilized SiNPs. Transmission electron microscopy of a PAO solution of these solutions showed that these SiNPs were present as small aggregates dispersed in the PAOs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.