Phosphines oxidation systems

Litvina, M.N., Chmutova, M.K., Myasoedov, B.F., Kabachnik, M.1.1996. Extraction and separation factors of lanthanides and americium in aqueous nitric acid- diaryl(dialkyl)-(dialkylcarbamoyl-methyl)phosphine oxide systems. Radiochemistry 38 (6) 494 -99. 

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

A method for determining the basicities of phosphoryl compounds has been decribed which is based on 31P n.m.r. chemical shift measurement and a two phase system consisting of an organic solvent and 12H sulphuric acid.245 The gas-phase protonation of aliphatic phosphine oxides have been determined by cyclotron resonance. There was a good correlation of pK4 with Kabachnik constants and HO... 

The reaction of alcohols with CO was catalyzed by Pd compounds, iodides and/or bromides, and amides (or thioamides). Thus, MeOH was carbonylated in the presence of Pd acetate, NiCl2, tV-methylpyrrolidone, Mel, and Lil to give HOAc. AcOH is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a Pd compound, an ionic Br or I compound other than HBr or HI, a sulfone or sulfoxide, and, in some cases, a Ni compound and a phosphine oxide or a phosphinic acid.60 Palladium(II) salts catalyze the carbonylation of methyl iodide in methanol to methyl acetate in the presence of an excess of iodide, even without amine or phosphine co-ligands platinum(II) salts are less effective.61 A novel Pd11 complex (13) is a highly efficient catalyst for the carbonylation of organic alcohols and alkenes to carboxylic acids/esters.62... 

Korkisch and Koch [106,107] determined low concentrations of uranium in seawater by extraction and ion exchange in a solvent system containing trioctyl phosphine oxide. Uranium is extracted from the sample solution (adjusted to be 1 M in hydrochloric acid and to contain 0.5% of ascorbic acid) with 0.1 M trioctylphos-phine oxide in ethyl ether. The extract is treated with sufficient 2-methoxyethanol and 12 M hydrochloric acid to make the solvent composition 2-methoxyethanol-0.1 M ethereal trioctylphosphine acid-12 M hydrochloric acid (9 10 1) this solution is applied to a column of Dowex 1-X8 resin (Cl" form). Excess of trioctylphosphine oxide is removed by washing the column with the same solvent mixture. Molybdenum is removed by elution with 2-methoxyethanol-30% aqueous hydrogen peroxide-12 M hydrochloric... 

Photoinitiators 2-hydroxy-2-methyl propiophenone and diphenyl-(2,4,6-trimethylbenzoyl) phosphine oxide both gave at least 100 MEKDR with no damage to the film surface when cured at a dosage as low as 0.5 J/cm2. This preference in photoinitiators has been observed in other studies of the maleate/vinyl ether system.1011... 

A Michael-type addition reaction of phosphine generated from red phosphorus in concentrated aqueous KOH solution has been noted to provide moderate isolable yields of pure organophosphorus products.27 For example, tris-(2-cyanoethyl)phosphine is produced in 45% isolable yield from acrylonitrile, and tris-(2-[y-pyridyl]ethyl) phosphine oxide is isolated in 40% yield from 4-vinylpyridine under these conditions. Excellent yields of the tertiary phosphine oxide, tris-(2-cyanoethyl)phosphine oxide, have been reported using white phosphorus in absolute ethanol with KOH at ice/salt-bath temperatures.28 A variety of solvent systems were examined for this reaction involving a Michael-type addition to acrylonitrile. Similarly, tris-(Z-styryl)phosphine is produced from phenylacetylene under these conditions in 55% isolated yield. It is noteworthy that this last cited reaction involves stereospecific syn- addition of the phosphine to the alkyne. 

The resultant material (isolated in low yield) is an intriguing tricyclic system that could be viewed as an overall antiaromatic system or as two aromatic rings with two phosphorus sites connecting them. In any event, this tricyclic product readily undergoes addition of water in even trace amounts to generate a bis-secondary phosphine oxide (Equation 4.26). 

In conclusion, it may be said that the agreed system seems to be entirely logical, although it often results in a certain degree of cacophony. It may be noted that two workers1 independently at a very early stage found it convenient to describe all these compounds as derivatives of either phosphine oxide or phosphine for example 0... 

As expected, hydrogen phosphinate, which is a hybrid structure of hydrogen phosphonate and secondary phosphine oxide, adds to alkynes in the presence of the Pd-diphenylphosphinic acid catalyst system (Scheme 44) [36]. Normally, branched isomers are the major products, while trimethylsily-lacetylene exceptionally affords the corresponding terminally phosphinylat-ed product. Diphenylacetylene also reacts to afford the corresponding adduct in 99% yield. 

Many other modifications, particularly of the Rh and Mel catalysed carbonylation of MeOH, have been proposed and some of these have been operated commercially or may have been tested at significant pilot plant scale. These include, for example, the use of phosphine oxide species such as PPh30 [20] as promoters and systems involving immobilizing the Rh on ion exchange resins [21]. Numerous examples of ligand modified catalysts have been described, particularly for Rh, though relatively few complexes have been shown to have any extended lifetime at typical process conditions and none are reported in commercial use [22, 23]. The carbonyl iodides of Ru and Os mentioned above in the context of the Cativa process are also promoters for Rh catalysed carbonylation of MeOH to AcOH [24]. 

The spectra are clearer in substituted compounds, especially in para-and poly-substituted aromatic systems. In the former case sign determination is feasible and McFarlane has obtained the values for some typical compounds as shown in Table XXII the data (without signs) for the tris(4-fluorophenyl)phosphine oxide are also included. 

The use of expensive catalysts, sometimes difficult to prepare and recover, is a concern, especially when working in large scale. Also, as previously mentioned, the very common use of phosphine-based catalysts oftentimes brings along undesired oxidation side-reactions and formation of difficult-to-remove phosphine oxides. To overcome these problems, ligandless systems are of interest for this and other cross-coupling reactions. 

Iodide-promoted reactions in phosphine oxide solvents have been observed under some conditions to produce ethanol from H2/CO with good rates and high selectivities (193-195) (Table XVI, Expts. 1-3). Experimental evidence suggests that the ethanol is a secondary product, although its selectivity is high even after very short reaction times (193). An acid component is believed to be involved in alcohol homologation by this system, which will be described in more detail below. 

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