Aryl -, onium

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... 

All lation of Garbanions. Concentrated N a OH—hen syl triethyl amm onium chloride is the base/catalyst system normally used for this type of process (20). Classes of compounds alkylated in this way include phenylacetonitriles, ben2ylketones, simple aUphatic ketones, certain aldehydes, aryl sulfones, P-ketosulfones, P-ketoesters, malonic esters and nitriles, phenylacetic esters, indene, and fluorene (see Alkylation). 

Onium-Salze sind in der Literatur nur vereinzelt beschrieben worden, so bei der Ringoffnung von 1,3-Benzoxazinen mit Hydroxylamin358 oder als stabile Zwischenprodukte bei der Isomerisierung von 3-(Aryl-nitrono-mcthyl)-l,2,4-oxadiazolcn, die mit Diazomethan N-methyliert werden konnen253 ... 

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... 

Five different types of halogen exchange reactions are known (R and R are alkyl, aralkyl or an aryl groups, M is usually a metal cation but can also be an onium cation). 

The coordinatively unsaturated aryl tellurium halides, when refluxed with an onium halide in an organic solvent, accept a halide ion to form salts of aryldihalotellurates(II)3 4 (p. 298). 

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. 

Onium Aryltetrahalotelluratcs(IV) [Organic Medium]1 3 mmol of the aryl tellurium tri halide are dissolved in dry methanol or ethanol, a solution of 3 mmol of the onium halide in the same alcohol is added dropwise at 20°, and the precipitated product is filtered yield > 85%. 

Onium Aryltetrahalotelliirates(TV) [Aqueous Medium]2 1 mmol of the aryl tellurium trichloride (or tribromide) is dissolved in 6 molar hydrochloric acid (or 3 molar hydrobromic acid) and a solution of 1 mmol of the onium halide in 20 ml of water is added dropwise with stirring. The product precipitates immediately yield 100%... 

Thioynamines are discussed as being formed via onium rearrangement from aryl and alkylthio dichlororethylenes 44,), but alternatively chlorothioalkylacetylenes may be formed in a simple 1,2 elimination process. The ensuing chlorine substitution by lithium amides has been documented +3). 

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). 

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