Amines deprotonation

We mention Williams work briefly here because it may also explain Blangey s observations strongly basic primary amines unequivocally form 7V-nitrosoanilinium ions in strongly acidic media. In contrast to the rate-limiting deprotonations of the less basic aromatic and heteroaromatic nitrosoamine cations discussed in this section, the TV-nitroso cation of a strongly basic amine deprotonates extremely slowly. Therefore, the nitroso rearrangement, the Fischer-Hepp reaction, competes effectively with the 7V-deprotonation. 

It appeared that triethylamine is the base of choice for generating nitrosals (343). However, sterically less hindered amines deprotonate the C-4 atom to give, after retro-[4 + 2]-cycloaddition of the intermediate enamines (346), the corresponding conjugated enoximes (347). 

Besides the dependence of peak potential with solution pH, there is other evidence of the acid-base and redox coupling, namely the prediction of amine deprotonation during film oxidation. Deprotonation is a response to the creation of Os(III) sites that increment the concentration of positive charges in the film. This is an example of charge regulation a chemical equilibrium at the interface is displaced as the system tries to reduce its electrostatic charge. 

Thermodynamic equilibrium constant for amine deprotonation Thermodynamic equilibrium constant for thiol sulfonate protonation... 

The photoreactions of aliphatic amines with aromatic hydrocarbons have also been reported by several groups. With tertiary amines, deprotonation occurs from the radical cations of amines at the a-carbon to generate carbon radicals which react with the radical anion of aromatic hydrocarbons. With secondary amines, deprotonation from the radical cations of amines occurs both at the a-carbon and at the nitrogen atom, so that the reaction becomes complicated [64-65]. 

It was mentioned in the discussion of equation 56 that the presence of certain amines leads to nearly perfect chemoselectivity in the hydrogenation of the C=0 group adjacent to a Mef group. It has also been shown that in solution the amine deprotonates the enol and generates an ammonium cation and an enolate anion. This was modeled by the interaction between the trimethylammonium ion and the enolate derived from 223 in the presence of... 

Tertiary ammonium radicals are also acidic so, if (x-CH protons are present in the amine, deprotonation of these intermediate products stabilizes the a-amino radicals... 

The regiochemistry of deprotonation of imines derived from unsymmetrical ketones is of special significance for the synthetic applications of these anions for carbon-carbon bond formation. This selectivity is sensitive to both the amine moiety and the base used. With imines derived from cyclohexyl- or r-butyl-amine, deprotonation with either Grignard reagents or lithium dialkylamide bases will result in high selectivity (>98 2) for removal of the proton on the less substituted a-carbon as in equations (39) and (40). 3i... 

Brensted Base Quenching. The trans-Rh(cyclam)(CN)2+ ion (cyclam = 1,4,8,11-tetraazacyclotetradecane) displays luminescence from a ligand field excited state (3LF ) at room temperature, in an aqueous solution with a lifetime (8.1 /is) [53] several orders of magnitude longer than generally observed for rhodium(III) amine complexes [54]. As was observed for some other Rh(III) amines, the 3LF emission from trans-Rh(cyclam)(CN)2 is quenched by OH- in solution (Eq. (13)), a process attributed to amine deprotonation [55],... 

With unsymmetrically substituted tertiary aliphatic amines, deprotonation can occur at different sites, and CIDNP spectroscopy was employed to measure relative group reactivities [94d]. For these complex reaction mechanisms, where two deprotonation routes can lead to the same products,... 

The two amines were efficiently debenzylated with Pd/C in acidic methanol at room temperature, and the remaining tryptamine bridge carbons inserted by double alkylation at the indole /3 -position and the secondary amine. Deprotonation of the resulting indolenine gives the / -anilinoacrylate, minovine (506 Scheme 27) (226, 227). 

It is tempting to try and react the amine directly with the acid, but unfortunately the only product this would give is the ammonium carboxylate salt the amine deprotonates the acid, and the carboxylate anion that results is no longer electrophilic. With alcohols, esters can be formed from carboxylic acids under acid catalysis, but with amines the acid catalyst just protonates the amine, and it is no longer nucleophilic The simplest... 

Scheme 3 Possible structures for the deprotonated Pb glycine complex. The amine-deprotonated structure (1) is identified spectroscopically as the predominant form for glycine and the other aliphatic amino acids including Pro. Reproduced with permission from [84]...

Amines deprotonate water to a small extent to form ammonium and hydroxide ions. Thus, amines are more strongly basic than alcohols but not nearly as basic as alkoxides. Protonation occurs at the site of the free electron pair as pictured in the electrostatic potential map of A,A-dimethylmethanamine (trimethylamine) in the margin. 

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