Triphenylphosphine oxide, formation

In the chlorination of 2,4-dichlorophenol it has been found that traces of amine (23), onium salts (24), or triphenylphosphine oxide (25) are excellent catalysts to further chlorination by chlorine ia the ortho position with respect to the hydroxyl function. During chlorination (80°C, without solvent) these catalysts cause traces of 2,4,5-trichlorophenol ( 500 1000 ppm) to be transformed iato tetrachlorophenol. Thus these techniques leave no 2,4,5-trichlorophenol ia the final product, yielding a 2,4,6-trichlorophenol of outstanding quaUty. The possibiUty of chlorination usiag SO2CI2 ia the presence of Lewis catalysts has been discussed (26), but no mention is made of 2,4,5-trichlorophenol formation or content. 

The initial step of olefin formation is a nucleophilic addition of the negatively polarized ylide carbon center (see the resonance structure 1 above) to the carbonyl carbon center of an aldehyde or ketone. A betain 8 is thus formed, which can cyclize to give the oxaphosphetane 9 as an intermediate. The latter decomposes to yield a trisubstituted phosphine oxide 4—e.g. triphenylphosphine oxide (with R = Ph) and an alkene 3. The driving force for that reaction is the formation of the strong double bond between phosphorus and oxygen ... 

P-coupling occurs in the formation of azophosphonic esters [ArN2PO(OCH3)2] from diazonium salts and dimethyl phosphite [HPO(OCH3)2] (Suckfull and Hau-brich, 1958). P-coupled intermediates are formed in the reaction between diazonium salts and tertiary phosphines, studied by Horner and Stohr (1953), and by Horner and Hoffmann (1956). The P-azo compound is hydrolyzed to triphenylphosphine oxide, but if a second equivalent of the tertiary phosphine is available, phenyl-hydrazine is finally obtained along with the phosphine oxide (Scheme 6-26 Horner and Hoffmann, 1958). It is likely that an aryldiazene (ArN = NH) is an intermediate in the hydrolysis step of the P-azo compounds. 

Wittig reactions are versatile and useful for preparing alkenes, under mild conditions, where the position of the double bond is known unambiguously. The reaction involves the facile formation of a phosphonium salt from an alkyl halide and a phosphine. In the presence of base this loses HX to form an ylide (Scheme 1.15). This highly polar ylide reacts with a carbonyl compound to give an alkene and a stoichiometric amount of a phosphine oxide, usually triphenylphosphine oxide. 

When a phosphite is used as a catalyst modifier, it is susceptible to oxidation in the same manner as a phosphine. Unlike triphenylphosphine oxide, which is relatively innocuous except for precipitation when the solubility limit is reached, phosphite oxidation products may hydrolyze to give phosphoric acid. Since phosphites are esters, phosphoric acid can catalyst additional hydrolysis. Other than limiting formation of phosphite oxidation products, the best approach is to include some acidity control technology in the separation or reaction system. 

The mechanism for the Mori-Ban indole formation is representative of many Pd-catalyzed pyrrole annulation processes [123], Reduction of Pd(OAc)2 by PPh3 generates Pd(0) species accompanied by triphenylphosphine oxide and acetic anhydride. 

Kennedy and Stock reported the first use of Oxone for many common oxidation reactions such as formation of benzoic acid from toluene and of benzaldehyde, of ben-zophenone from diphenyhnethane, of frawi-cyclohexanediol Ifom cyclohexene, of acetone from 2-propanol, of hydroquinone from phenol, of e-caprolactone from cyclohexanone, of pyrocatechol from salicylaldehyde, of p-dinitrosobenzene from p-phenylenediamine, of phenylacetic acid from 2-phenethylamine, of dodecylsulfonic acid from dodecyl mercaptan, of diphenyl sulfone from diphenyl sulfide, of triphenylphosphine oxide from triphenylphosphine, of iodoxy benzene from iodobenzene, of benzyl chloride from toluene using NaCl and Oxone and bromination of 2-octene using KBr and Oxone . Thus, they... 

Hydroxy amides undergo cyclodehydration to oxazolines under very mUd conditions with triphenylphosphine and carbon tetrachloride. Carbon tetrabromide can also be used. The formation of the corresponding p-chloro amide is generally not a significant problem. The major disadvantage is that removal of the byproduct triphenylphosphine oxide may be difficult at times. Representative examples are shown in Table 8.14 (Fig. 8.5).n4,i4o,i73-i8i... 

If the assumption of this reaction sequence is correct, the photolysis of tetraphenylphosphonium chloride must then only lead to biphenyl, diphenylphosphine, ethyl diphenyl-phosphinate and triphenylphosphine and its oxidation products. After 2 h of irradiation, biphenyl, diphenylphosphine and its oxidation products, triphenylphosphine and triphenylphosphine oxide, in a ratio of 3 1 5, along with raw material, are obtained. Ethyl diphenylphosphinate was detected in trace amounts7. These results support the postulate of the reversibility of phosphoranyl radical formation in such systems and indicate one-electron transfer processes15 in the formation and decomposition of the tetraarylphosphonium cation. This reaction is comparable to the observation of an electron transfer from halide ions to hydroxyl radicals or hydrogen atoms in aqueous solutions16,... 

Mitsubishi Kasei introduced a process to manufacture isononyl alcohol, an important PVC (polyvinyl chloride) plasticizer, via the hydroformylation of octenes (a mixture of isomers produced by dimerization of the C4 cut of naphtha cracker or FCC processes).95 First a nonmodified rhodium complex exhibiting high activity and selectivity in the formation of the branched aldehyde is used. After the oxo reaction, before separation of the catalyst, triphenylphosphine is added to the reaction mixture and the recovered rhodium-triphenylphosphine is oxidized under controlled conditions. The resulting rhodium-triphenylphosphine oxide with an activity and selectivity similar to those of the original complex, is recycled and used again to produce isononanal. 

Reaction of the iminotriphenylphosphorane 27 with dimethyl acetyl-enedicarboxylate gives a mixture of the quinoxalines 28 and 29. The formation of compound 28 can be rationalized as shown, ring closure involving Wittig-like elimination of triphenylphosphine oxide. The formation of compound 29 is thought to involve a phosphazacyclo-butene intermediate.35... 

Dehydration of diols to cyclic ethers. The reagent dehydrates a variety of diols to cyclic ethers with formation of triphenylphosphine oxide as the co-product. Yields of cyclic ethers are high from 1,2-, 1,4- and 1,5-diols. Although (Z)-2-butene-1,4-diol is converted into 2,5-dihydrofuran in 95% yield, the (E)-isomer is converted in 35-40% yield into 3,4-epoxy-l-butene.1... 

One well-known drawback with the Wittig reaction in solution is the formation of 1 equiv. of triphenylphosphine oxide, which is inherently difficult to separate from the final product. Thus, Westman23 developed a one-pot multi-step microwave-assisted... 

Although terminal oxo complexes of the late-transition-metal elements have been proposed as possible intermediates for oxidations catalyzed by these elements, late-transition-metal-oxo complexes were scarcely known. Hill and coworkers reported the synthesis and characterization of Pt4 + -, Pd4 + - and Au3 + -oxo complexes, [M(0)(0H2) W0(0H2) (PW9034)2]m (M = Pt, Pd and Au, n = 0-2), stabilized by electron-accepting polyoxotungstate ligands [109-111]. The stoichiometric reaction of the Au-oxo complex [Au(0)(0H2) W0(0H2) 2 (PW9034)2]9 with triphenylphosphine led to the formation of triphenylphosphine oxide. 

The treatment of [bis(phenyliodonium)]ethyne ditriflate with triphenylphosphine has also been investigated40,41. The products depend on the stoichiometric ratios of the reactants. Thus, with one equivalent of triphenylphosphine, a monoiodonium-monophos-phonium derivative of acetylene is obtained, but with two equivalents of the phosphine, [bis(triphenylphosphonium)]ethyne ditriflate is produced (equation 72). When three equivalents of triphenylphosphine are employed in acetonitrile spiked with H20 or D20, a fram -alkenediyl bisphosphonium salt is generated (equation 73)41. The reduction of the triple bond and formation of triphenylphosphine oxide in this reaction is thought to proceed at the bisphosphonium alkyne stage41. 

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