Aryl onium salts

The photocatalyst was a mixture of diphenyl carbonyl and triethyl-amine. Other photocatalysts, such as aryl onium salts (benzene iodonium fluoroborate and benzene arsonium fluoroborate) can also be used successfully. The monomer mixture was irradiated at 366 nm to form a polymer. The 2-hydroxy group can be regenerated to have an UV-absorbing group in the polymer by irradiation at 310 nm. 

Simple aryl onium salts (structures a-c in Fig. 10) absorb in the wavelength range of 200-330 nm, making them well-suited for applications requiring DUV... 

Onium salts of azaaromatics, such as 2-chloro-3-ethylbenzoxazolium tetrafluoroborate (380), have proven to be useful dehydrating agents (79CL1117). Aryl ketones are, for example,... 

In the reaction of activated aryl halides with phenoxide and thiophenoxide in chloro- or o-dichloro-benzene at reflux, pyridinium salts (48 R, R = —-CH2CH2CHMeCH2CH2— R = Me, Bu", n-C6Hi3 R = CH2CHEtBu, CH2BU1) proved to be superior catalysts to simpler onium salts, like TBAB, due mainly to their greater thermal stability.162... 

Halide displacement by thioanions such as thioalkoxides, thiocyanate and sulfite, can be readily carried out under PTC conditions in activated arenes. The reaction of nitro- and dinitro-aryl halides with thiophenol and NaOH in the presence of an ammonium or phosphonium salt catalyst proceeds readily in toluene at room temperature to give the phenyl aryl sulfides in nearly quantitative yield.189 Excellent yields of thiocyanoarenes were obtained from the reaction of the 2,4-dinitrohalobenzenes with KSCN in toluene at 90 C with a tetraalkyl onium salt PTC catalyst.190... 

Symmetrical diaryl sulfides were produced in fair yield from the PTC reaction of sodium sulfide with molten aryl chlorides activated by a cyano, nitro, phthalimido or anhydrido group.193 Typical conditions require use of a 3 1 mole ratio of aryl chloride to Na2S and 10% of catalyst (crown ethers and onium salts) at 200 C for 24 h. 

Conversion of saturated, primary alkyl and aryl alkyl alcohols into the corresponding aldehydes can be achieved by this method provided that the alcohols are entirely dissolved in the organic phase. Relatively unstable protective groups are not affected, as in the oxidation of the acetonide of 1,2,6-hexanetriol, whereas conjugated and isolated double bonds give rise to side reactions which considerably decrease selectivities and yields.4 Some examples of aldehydes synthesized with this method are reported in Table 1. Under the same conditions, secondary alcohols are oxidized to ketones. Addition of catalytic amounts of quaternary onium salts allows fast and total conversion of primary alcohols and aldehydes into carboxylic acids making this methodology very versatile 4... 

Mixed tetrahalotellurates(IV) result from the combination of an aryl tellurium trihalide with an onium salt containing a halide different from that in the tellurium compound. 

Alkylation, arylation, and acylation, at the heteroatom, lead to substitution of an NH or to onium salts. Three-membered ring onium salts are difficult to isolate, and very weakly nucleophilic counterions must be used, such as BF4. 

On the other hand, onium salts based in N (or S or P) are commercially available in abundance. Extended by introducing a variety of alkyl and aryl groups, they present a large variety of properties, being all liquid electrolytes. 

Cleavage of ethers, Dialkyl and alkyl aryl ethers are cleaved by 47% hydro-bromic acid in an aqueous organic solvent in the presence of an onium salt (hexadecyltributylphosphonium bromide, tetraoctylammonium bromide) that is completely soluble in the organic phase. Dialkyl ethers are converted into alkyl bromides (65-90% yield),whereas a phenol and an alkyl bromide are obtained from alkyl aryl ethers (85-90% yields). 

Onium salts have many of the characteristics required of photosensitive initiators for light-curable coatings. Aryl-diazonium, aryliodonium and arylsulfonium salts all initiate rapid cure. Storage life of photosensitized formulations ranges from a few hours to more than six months, depending upon structure of the photoinitiator, composition of the coating and storage conditions. 

Dialkylphenacylsulfonium salts are also known to be highly photosensitive [3b, c] and have been adapted to photoinitiated cationic polymerization [9]. These salts have a higher intrinsic quantum yield for photoinitiation of cationic polymerization on direct photolysis than the simple aryl or aryl-alkyl onium salts [10], but do not appear to undergo the same photodecomposition as the other onium salts [1-4]. 

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