Diphenyl iodonium salt

Pyrylium and Thiopyrylium Salts In the presence of additives such as a perester and in conjunction with ketocoumarins and coumarins, pyrylium, and thiopyrylium salts allow to decompose peresters. Addition of a diphenyl iodonium salt or a bromo compound such as CBr4 to a thiopyrylium salt leads to an electron transfer process resulting in the generation of radicals [211]. 

The solution containing thiophene and diphenyl iodonium salt becomes dark and films are accumulated on the surface of the reaction tube when the tube is exposed to radiation. A conducting freestanding film is essentially obtained. 

Initial attempts to demonstrate UV-curability of epoxysilicones were unsuccessful because crystalline, high melting unsubstituted diphenyl iodonium salts and triphenylsulfonium salts were completely immiscible in silicone matrices without the use of solvents. 

Dye = benzophenone, isopropyl thioxanthone, merocyanine, etc. Dye/amine/maleimide widi Dye = benzophenone, etc. Dye/amine/diphenyl iodonium salt with Dye = eosin, ketocoumarin, methylene blue, thioxanthene dye, fluorone dye, etc. Dye orate salt/triazine derivative with Dye = cyanine dye, styiylquinolinium dye, etc. Dye/borate salt/alkoxypyridinium salt with Dye = carbocyanine dye, etc. Pl/amine/triazine derivative with Dye = pyrromethene dye. Rose Bengal, etc. Dye/hexabisimidazole derivative (e.g. Cl-HABI)/thiol with PI = styiylnaphtothiazole dye, diethylamino benzophenone, julolidine dye, etc. Dye/amine (or... 

To the more usual homolytic fragmentation of aryl halides (from the excited state or from the radical anion, the well known SrnI reaction, for a recent example see the arylation of aromatics), the heterolytic version of the reaction which produces phenyl cations has more recently joined. A theroretic study on the photodissociation of fluorinated iodobenzenes has been published. The perfluoroallgrlation of various alkenes has been obtained by irradiation in the presence of iodoperfluorobutane. The formation of phenyl cations is exemplified in many arylation reactions and, in the case of o-chlorostannane, also a benzyne has been reported. In the field of polymer chemistry, iodonium salts are model cationic photoinitiators. In particular the truxene-acridine/diphenyl iodonium salt/9-vinylcarbazole combination is able to promote the ringopening polymerization of an epoxide, whereas the truxene AD/allq l halide/amine system is very efficient in initiating the radical photopolymerization of an acrylate. ... 

The protonic add is formed upon irradiation, when the resists contain a small amount of an appropriate add generator such as an iodonium or sulfonium salt (Scheme 3.46). A detailed mechanism of the photolysis of a diphenyl iodonium salt is presented in Scheme 3.7. 

Most N-phenyl quaternary salts are not prepared by direct quater-nization but rather by introducing the nitrogen substituent before ring closure. It has recently been found that diphenyl iodonium boro-fluoride reacts smoothly with pyridine the phenyl carbonium ions formed give the 1-phenylpyridinium ion good yield. ... 

The initiating radicals are assumed to be SCN, ONO or N3 free radicals. Tris oxalate-ferrate-amine anion salt complexes have been studied as photoinitiators (A = 436 nm) of acrylamide polymer [48]. In this initiating system it is proposed that the CO2 radical anion found in the primary photolytic process reacts with iodonium salt (usually diphenyl iodonium chloride salt) by an electron transfer mechanism to give photoactive initiating phenyl radicals by the following reaction machanism ... 

The same salt from acetylene afforded similarly adducts with furan and 1,3-diphenyl i sobenzofuran. A number of alkynyl iodonium salts underwent also [2 + 3] cycloaddition with dipolarophiles such as a-diazocarbonyl compounds, nitrile oxides, etc., allowing the preparation of iodonium salts with an alkenyl or a heterocyclic moiety [7],... 

Phenylation, by using diphenyl lithium cuprate, was stereospecific in both E and Z isomers of appropriate alkenyl iodonium salt, proceeding with complete retention of configuration. 

The photochemistry of diphenyl- and bis(4-methylphenyl)iodonium salts has been investigated481,482. Diphenyliodonium halides (140, X = Cl, Br, I) exist as tight ion pairs in acetonitrile. Their photolysis gives almost exclusively iodobenzene by a homolytic cleavage from a charge-transfer excited state. In aqueous acetonitrile, however, the ion pairs are solvent-separated and substantial amounts of 2-, 3- and 4-iodobiphenyls (141) are formed in addition to iodobenzene (142), benzene (143), acetanilide (144) and biphenyl (145) (equation 126). In this medium the photodecomposition occurs via initial heterolysis of the molecule in its excited state, leading to iodobenzene and phenyl cation. 

The reactions of the lithium enolate of diethyl 2-[(diphenylmethylene)amino]malonate with several alkynyliodonium triflates are rare examples of enolate alkynylations with iodonium species other than the ethynyl(phenyl)- and (phenylethynyl)phenyliodonium ions (equation 125)16. Two experimental protocols were followed, i.e. addition of the enolates to the iodonium salts and vice versa, the former procedure giving higher yields of alkynylmalonates. As with other enolate alkynylations, these reactions are thought to involve alkylidenecarbene intermediates. It has been proposed, however, that the carbenes rearrange with migration of the diethyl 2-[(diphenyl) amino] malonate anion 16. 

Whether the iodonium salts are truly iodonium salts, and not highly-polarized, unsymmetrical i3-iodanes, has recently been questioned by Ochiai on the basis of X-ray evidence (03MI1). For example, diphenyl-iodonium chloride, or chloro(diphenyl)- 3-iodane [Ph2I + Cl or... 

Quantum yields of acid, and iodobenzene or phenyl sulfide were measured by irradiating. 03 molar acetonitrile solutions of diphenyl iodonium hexafluoroarsenate and triphenyl sulfonium hexa-fluoroarsenate. Photosensitizers were included at identical optical density (1.0) at the wavelength of irradiation (366 nm). Relative polymerization rates were calculated as a function of the gelation time of a solution of 50% acetone, and 50% cycloaliphatic diepoxide resin ARALDITE CY-179 (v/v) containing the photosensitizer and onium salt as above. Experimental details were published previously.(8,15) IRGACURE and ARALDITE are registered trademarks of the Ciba-Geigy Corporation. 

Among the reactions of diaryliodonium salts with inorganic compounds, their hydrolysis has been studied in detail.40.41,43,51-53 jhe hydrolysis reaction proceeds quite slowly in boiling water. However, in the presence of aqueous alkali, the hydrolysis takes place in a few days for diphenyl-iodonium bromide to afford a mixture of iodobenzene, bromobenzene and phenol. With weakly nucleophilic anions, the reaction affords iodobenzene, phenol and a small amount of diphenylether. The reaction was considered to involve an unstable hydroxydiaryliodane, which is likely to be in equilibrium with diaryliodonium hydroxide. Decomposition of the hydroxyiodane leads to the... 

The O-arylation of appropriate phenols using symmetrical iodonium salts has been employed in the synthesis of hydroxylated and methoxylated polybrominated diphenyl ethers, some of which are related to natural products [872,873]. For example, several polybrominated diphenyl ethers 680 have been prepared by the reaction of iodonium salt 678 with phenols 679 in iV,iV-dimethylacetamide (DMAC) solution in the presence of base (Scheme 3.272) [872]. 

In addition to iodonium, sulfonium and selenonium compounds, onium salts of bromine, chlorine, arsenic, and phosphoras are also stable and can act as sources of cation radicals as well as Bronsted acids, when irradiated with light. Performance of diaryl chloronium and diaryl bromonium salts was studied by Nickers and Abu. Also, aryl ammonium and aryl phosphonium, and an alkyl aryl sulfonium salt were investigated. It appears that the general behavior of these materials is similar to diphenyl iodonium and triphenyl sulfonium salts. These are formations of singlet and triplet states followed by cleavages of the carbon-onium atom bonds and in-cage and out of cage-escape reactivity. The anions of choice appear to be boron tetrafluoride, phosphorus hexafluoride, arsenic hexafluoride, and antimony hexafluoride. 

As a typical example, Scheme 3.7 presents the detailed mechanism of the photolysis of diphenyl iodonium ions. The initiation of the polymerization can be accomplished by both Bronsted acids and radical cations Many onium salts do not, or only weakly, absorb light at 1 > 300 nm, and in this case a photosensitizer (PS) that absorbs strongly at longer wavelengths may be employed in conjunction with an onium salt. Provided that the free energy, AG, has a sufficiently high negative value, excited PS molecules (PS ) are oxidized by the onium ions, such that radical cations PS are formed (Scheme 3.8). 

The photoinitiation of polymerization of pentaerythritol tetraacrylate using phenyl-(p-anisyl)-iodonium triflate or triphenylsulfonium hexafluorophosphate, sensitized with either l,6-diphenyl-l,3,5-hexatriene or 1,3-diphenyl-2-pyrazoline, was illustrated by Smith [111b] in 1981. Under his conditions, direct photolysis of the onium initiators failed to initiate polymerization. Baumann and co-workers, however, found conditions for initiation of radical polymerization on direct irradiation of onium salts [18,122], consistent with the hypothesized generation of radicals capable of cage escape in direct photolysis. 

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. 

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