Organic Bronsted bases

Organic Bronsted bases have been used to catalyze synthetically valuable carbon-carbon bond forming reactions of carbonyl and related compounds for decades. 

The cationic polymerization of 2-vinylfuran with strong acids can be allowed to proceed to black crosslinked resins which display a remarkable proton affinity when swelled in organic solvents (19). Their very high Lewis basicity can be exploited to scavenge Bronsted acids the insoluble resin is easily removed by filtration at the end of the operation and readily regenerated by neutralization with a strong Bronsted base. 

The carbide ion ( C=C 2 ) is a Bronsted base and is readily protonated by water, resulting in the formation of the organic compound ethyne (acetylene) ... 

The properties of superoxide anion have been well reviewed [45,46]. In water it is a relatively weak nucleophile, whereas in aprotic solvents, such as those commonly used for electrolysis, it is a powerful nucleophile. Its basic properties stem from the driving force of the disproportionation [45,46] depicted as Eq. (5), similar to the disproportionation discussed for organic radical anions in Sec. II.B. Thus, although superoxide anion itself is a relatively weak Bronsted base— pA a(H02) 12 in DMF [46]—the overall equilibrium... 

The C-C couphng of aromahc hahdes usually requires the addition of a base in stoichiometric amounts, and the most common Bronsted bases are water soluble and can be employed conveniently in biphasic aqueous/organic systems. 

Under alkaline conditions, the rate of this reaction is low (Fignre 11.7) [35], bnt superoxide ion, being a strong Bronsted base, may abstract a proton from an organic... 

Although the differences between the Bronsted and Lewis bases are minimal compared with that between the acids, Bronsted bases constitute, in fact, a small group of Lewis bases. Besides anions, Lewis bases consist of molecules with lone-pair electrons as well as Tr-electron systems, n Complexes play significant roles in organic and organometallic chemistry. Many of these can be detected spectroscopically or can be isolated. 

Amines are organic bases that have the general formula RfT, in which one of the R groups must be an alkyl group or an aromatic hydrocarbon group. Like ammonia, amines are weak Bronsted bases that react with water as follows ... 

I. Rodriguez, S. Iborra, F. Rey, A. Corma, Heterogeneized Bronsted base catalysts for fine chemicals production grafted quaternary organic ammonium hydroxides as catalyst for the production of chromenes and coumarins, Appl. Catal. A Gen. 194-195 (2000) 241-252. 

Gaseous Bronsted bases, B , usually react with organic analytes M by proton abstraction to produce... 

Amines are organic bases whose acid—base chemistry is like that of ammonia. For example, methyl-amine behaves as a Bronsted base because the nonbonded electron pair of the nitrogen atom can accept a proton from an acid such as hydronium ion. When methylamine accepts a proton, the conjugate acid, methyl-ammonium ion, is produced. 

The synthetic utility of the bifunctional catalysts in various organic transformations with chiral cyclohexane-diamine derived thioureas was established through the works of Jacobsen, Takemoto, Johnston, Li, Wang, and Tsogoeva. In the last decade, asymmetric conjugate-type reactions have become popular with cinchona alkaloid derived thioureas. The next section presents non-traditional asymmetric reactions of nitroolefins, enones, imines, and cycloadditions to highlight the role of chiral Bronsted base derived thiourea catalysts. 

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