With onium salts

Buijsen, P, Electron Beam Induced Cationic Polymerization with Onium Salts (Thesis, Delft University of Technology), Delft University Press (1996). 

Alkylation with Onium Salts Alkoxy-de-hydroxylation... 

Reaction between alkoxides or arox-ides and alkyl halides (Williamson) 0-14 Reaction between alkoxides or arox-ides and inorganic esters 0-15 Alkylation of alcohols or phenols with diazo compounds 0-16 Dehydration of alcohols 0-17 Transetherification 0-19 Alkylation of alcohols with onium salts... 

PTC with onium salts (TBAB or TBPB) in a two-phase system (HzO/NaOH/CIfcCh) afforded bis(aryloxynitrophenyl) sulfones (47) in good yields at room temperature, from the reaction of the coire-sponding chlorides with several phenols.159... 

Crivello, J. V, Heat Curable Cationically Polymerizable Compositions and Method of Curing Same with Onium Salts and Reducing Agents, U.S. Patent No. 4,216,288, 1980. 

It can be concluded that cationic photopolymerization of glycidyl ethers with onium salt initiators should be considered as a dual-step process 1) liberation of the active initiator species by irradiation and 2) heat treatment to complete the polymerization reaction... 

Another example is thermally depolymerizable polycarbonates that are sensitized with onium salt cationic photoinitiators (139). As discussed previously (Section 3.2.3), one of the positive-negative resists based on polystyrene with pendant tertiary butyl carbonate protecting groups undergoes acid-catalyzed thermolysis to generate poly( p-vinylphenol), carbon dioxide, and isobutene. Therefore, if the tertiary butyl carbonate moiety is incorporated in the polymer backbone as a repeating unit, such polymers will... 

Another method used for recycling TSOSs consists in using the so-called supported ionic liquid phase (SILP) [44-49], The general principle is using an OS with a trialkoxysilane moiety that can be grafted covalently to a particle of silica. The particle, now coated with onium salt, has a special affinity for other onium salts, especially ILs. ILs can therefore get immobilized on a solid particle and subsequently be used for immobilizing other reagents (transition metal complexes, proline, etc.). This method has recently been reviewed and employs mostly non-functional ILs, so it won t be explained in more detail [44-49] (Fig. 17). 

Oxetane undergoes ring-opening polymerization under the action of MAD in conjunction with onium salts, including quaternary ammonium and phosphonium halides, giving a narrow MWD polyether (Scheme 6.173) [221]. Use of MesAl in place of MAD resulted in no polymerization. The aluminum ate complex seemed to be an initiator, which underwent a trigger reaction involving halide transfer to the aluminum-oxetane complex. 

Electron Transfer Via Exciplexes. Sensitizers such as anthracene, perylene, or phenothiazone form exciplexes with onium salts. Being formed in the consequence of light absorption by the sensitizer, these energy-rich complexes consist of nonexcited onium salt and electronically excited sensitizer molecules. In the complexation state, electron transfer to the onium salt is observed, giving rise to positively charged sensitizer species [85,86]. 

There has been an evolution in the development of new coupling reagents and their application to solid-phase methodology. The formerly predominant carbodiimide reagents are being replaced by onium (phosphonium and aminium) salts. As discussed later, depending on the conditions, the activation step with onium salts occurs faster than with carbodiimides and usually leads to less perishable intermediates. 

A highly reactive ion pair may, therefore, be obtained by using a quaternary cation soluble in a low dielectric constant organic solvent. This is usually accomplished with onium salts with at least one long alkyl chain or symmetrical Bu4N. ... 

The hydration of the complexed polyether under two-phase conditions includes the specific hydration of anions, similar to that found with onium salts, and two molecules of water associated with the uncomplexed ligand. Removal of the hydration sphere of the anions in going from two phase to anhydrous conditions is balanced by a larger cation-anion interaction. This behavior causes very little variation in anionic reactivity in contrast with that observed with onium salts [40]. The hydration sphere determines in both cases the anomalous nucleophilicity scale found under PTC conditions with respect to dipolar aprotic solvents. 

Non-crosslinked polystyrene with salen ligand Non-crosslinked polystyrene with onium salt residues Non-crosslinked polystyrene copolymerised with a chiral phosphine ligand 14,765 0.5-3.8" 0.7-2.3 CH2Cl2,THF, EtOAc, DMF DMF,DMSO,DMA, toluene, anisole, MeOH,MeCN, diglyme Asymmetric epoxidation Regioselective addition reaction of phenyl glycidyl ether with S-phenyl thioacetate Pt-catalysed asymmetric hydroformylation of olefins Precipitation (methanol) (r) Precipitation (diethyl ether) (r) [68] [142] [143]... 

Chart 10.5 Typical electron-transfer photosensitizers that may be applied in conjunction with onium salts [54]. 

It was considered previously that the most effective phase transfer catalysts are quaternary ammonimn bases. However, preliminary experiments with crown-ethers had already shown that these compounds are more powerful phase transfer catalysts than quaternary ammonium bases and are more selective [106, 177]. This is explained by differences in the mechanism of catalytic action. The mechanisms of reaction acceleration in two-phase systems with crown-ethers are as yet little studied, but simple examination of salt extraction with crown-ethers shows that the salt in the aqueous phase G>oth anion and cation) passes into the organic layer, whereas only anions paired with the onium cation pass from the aqueous into the organic phase during extraction with onium salts. This considerable difference in the mechanism of action of the two groups of ion-carrying catalysts is the basis for the prospective use of crown-ethers and their analogs instead of quaternary ammonium bases in many fields. 

The first system involves polymerization initiated with onium salts in the presence of Al(i-Bu)3 [133-136] whereby, in addition to the formation of a 1 1 complex of Al(i-Bu)3 with the initiator, a second complex between Al(i-Bu)3 and the monomer greatly increases the reactivity of the monomer, allowing a rapid and controlled polymerization of propylene oxide (Mn 20kgmol ) and epichlorohydrin (M 80 kg mol ), with narrow molecular weight distributions (Mw/M 1.2). 

The coumarin derivative used with onium salts can be... 

SEE 01] Selvaraju C., Sivakumar A., Rammamurthy P., Excited state reactions of acridinedione dyes with onium salts mechanistic details , Journal of Photochemistry and Photobiology A Chemistry, vol. 138, no. 3, pp. 213-226, 2001. 

SYNTHESIS OF ULTRAHIGH MOLECULAR WEIGHT NYLON 4 WITH ONIUM SALT AND CROWN ETHER-CONTAINING CATALYSTS... 

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