Bromides bifunctional ammonium

Although quaternary onium bromides and chlorides as phase-transfer catalysts are generally beUeved to require base additives for phase-transfer reactions of active methylene and methine compounds, which were discussed above, we have recently discovered an hitherto unknown base-free neutral phase-transfer reaction system in asymmetric conjugate additions (Scheme 14.5) [23]. The reactions were efficiently promoted by chiral bifunctional ammonium bromide (S)-7 under neutral conditions with water-rich biphasic solvent. The role of hydroxy groups in the bifunctional catalyst was clearly shown in the transition-state model of the reaction based on the single-crystal X-ray structure of ammonium amide [23b] and nitro-nate [23c]. 

In the presence of chiral phosphonium salt 61 and potassium benzoate, the Michael addition reactions between 3-arylindoles 93 and alkylvinyl ketones worked very well with outstanding enantioselectivity [95], whereas chiral bifunctional ammonium bromide (S)-43a delivered high diastereo- and enantioselectivity for the... 

The reaction of the isocyanate and the epoxide group, to produce an oxazolidone ring, was studied through the model reaction between the monofunctional epoxide, PGE and the bifunctional isocyanate MDI. Their reaction was followed by DSC. Two catalysts for the reaction were evaluated tetraethyl ammonium bromide (R NBr) and ethylmethylimidazole (EMI). 

Polymerisation of vinyl toluene in quaternary microemulsions containing cetyltrimethylammonium bromide as the cationic surfactant was studied using laser Raman spectroscopy and dilatometry. The influences of water soluble (potassium peroxodisulphate, ammonium peroxodisulphate) and oil-soluble (azobisisobutyronitrile, benzoyl peroxide) initiators, monomer, surfactant, cosurfactants (n-alcohol and bifunctional alcohols) and temperature on the rates of polymerisation, energy of activation, particle diameter, number of polymer particles, molecular weight of polyvinyl toluene and number of polymer chains per latex particle were investigated. The dependencies of the kinetic and latex size parameters on the initiators and co-surfactants are discussed in terms of the efficiency of the initiators in initiating the polymerisation and on the interfacial partitioning behaviour of various co-surfactants. 19 refs. 

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