DABCO-based ammonium

Similar to the biguanide structures, Dizman et al. created l,4-diazabicyclo[2.2.2]octane (DABCO)-based stmctures carrying two quaternary ammonium charges with butyl and hexyl alkyl extensions (C12). The monomer was assembled by multiple nucleophilic substitution reactions. Polymers were formed by free radical polymerization in water. These polymers, much like the biguanide acrylate and pyridinium polymers, combined hydrophobidty and cationic charge on the same monomer. One difference is that the cationic charge was also separated from the backbone of the polymer by a long alkyl chain. As with the pyridine polymers, the hexyl alkyl monomers were found to be the most effective biocides. 

An important aspect of AEMs is the chemical stability of the cationic groups against OH" attack. Bauer et al. [45] compared the stability of different benzylammonium groups for AEM synthesis in relatively harsh conditions (160 °C and [KOH] =2M, under nitrogen atmosphere). They noticed that a molecule that carried two proximate ammoniums, called bis-(ammonium) compound, is less stable than its monoammonium homolog. For instance, they compared two different membranes based on DABCO that they considered the most stable amine in alkaline conditions (Fig. 5.35). They synthesized a monoquaternized DABCO-based polymer and a bis-quatemized DABCO polymer. The monoquaternized one was much more stable tyi = 42 min) than the bis-quatemized DABCO-based polymer ty = 2.3 min). The degradation of... 

Strong bases, such as potassium acetate, potassium 2-ethylhexoate, or amine—epoxide combinations are the most useful trimerization catalysts. Also, some special tertiary amines, such as 2,4,6-tns(A7,A7-dimethylarninomethyl)phenol (DMT-30) (6), l,3,5-tris(3-dimethylaminopropyl)hexahydro-j -triazine (7), and ammonium salts (Dabco TMR) (8) are good trimerization catalysts. 

The reaction of l,4-diazabicyclo[2.2.2]octane (DABCO)-derived quaternary ammonium salts with electrophilic alkenes in the presence of a base opens a stereoselective route to highly substituted 2,3-dihydrofurans <2005S2188>. An ammonium ylide is initially formed that attacks the Michael acceptor. The resulting enolate finally expels DABCO in an O-alkylation reaction, affording fra j -2,3-disubstituted dihydrofurans as the major products (Equation 65) <2005S2188>. 

Dizman and co-workers [27] prodnced new methacrylate monomers enclosing pendent biquaternary ammonium moieties based on l,4-diazabicyclo-[2.2.2]-octane (DABCO)... 

Diazabicycloundecene (DBU) is shown to be a superior catalyst to DABCO in a typical Baylis-Hillman reaction. The finding downplays the importance of the nucleophilicity of the base, as DBU is generally considered to be both non-nucleophilic and hindered. Rather, it appears to stabilize better the -ammonium enolate intermediate of the reaction. 

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