Removal of triphenylphosphine oxide

The first protocol describes the simple reduction of an organic azide employing triphenylphosphine and water in tetrahydrofuran 

Caution All procedures should be performed in a well-ventilated hood. Wear disposable vinyl or latex gloves and chemical-resistant safety goggles. 

Clean the apparatus and bake in an oven at a minimum of 120°C for 3-4 h. When required, allow the equipment to cool in a desiccator. 

Set up the flask with a stirrer bar, septum cap and a positive pressure of nitrogen from a balloon or line connected via a syringe needle. 

Dissolve /V-(3-azidopropyl)-1,4-diamino-2-butyne (340 mg, 2.04 mmol) in tetrahydrofuran (10 mL), then add triphenylphosphine (558 mg, 2.24 mmol) and water (40 m-L). 

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A modification of GSR has been reported by Classon and co-workers.190 The idea remains the same create a covalently bound phosphorus cation and displace with a nucleophile—in this case, a halogen. Both bromine and iodine have been used.190 Three different systems were evaluated (1) chlorodiphenylphophine, iodine-bromine, and imidazole (2) p-(dimethylamino)phenyldiphenylphosphine, iodine-bromine, and imidazole or (3) polymer-bound triphenylphosphine, iodine-bromine, and imidazole. The last two were found to be very similar to just triphenylphosphine itself, and displayed reactivity inferior to the first system. The polymer-bound reagent does allow for easier removal of triphenylphosphine oxide produced in the course of the reaction. As with the original procedure, and consistent with a Sn2 mechanism, inversion of configuration occurred. Again, as with the original method vicinal diols were readily converted into alkenes.191 This... 

Sulfonamides may be directly synthesized from sulfonic acid salts by treatment with triphenylphosphine ditriflate followed by an amine <2004JA1024>. This procedure, that avoids the generation of sulfonic acids, converts sulfonic acid salt 129 to sulfonamide 130 in 81% yield (Equation 92). Problems associated with the removal of triphenylphosphine oxide by-products can be alleviated by performing the reaction with polystyrene-supported phosphine. 

Scheme 12) (72). The preparation of 153 from oxazole was initially investigated via the Corey-Fuchs protocol. Low yields were observed, in part due to difficulties associated with the removal of triphenylphosphine oxide produced during the coupling process. Eventually, this problem was solved by employing hexamethylphosphorous... 

The precipitate of triphenylphosphine oxide is filtered and washed with 50 ml. of pentane. The solvent is removed from the combined filtrate at the rotary evaporator under water aspirator pressure at room temperature. Distillation of the residue through a 2-cm. Vigreux column attached to a short-path distillation apparatus (Note 4) provides 13.0-14.0 g. (75-81%) of geranyl chloride, b.p. 47-49° (0.4 mm.), w2Sd = 1.4794 (Note 5). 

RhCl(PPh3)3] (23) catalyzes the hydrosilylation of propylene (equation 168).618 The silyl complex [RhH(Cl)(SiEt3)(PPh3)3] (135) was present in the reaction mixture, but was not thought to be involved in the catalytic cycle. Small amounts of oxygen or peroxide were necessary for the hydrosilylation to proceed and this was attributed to the generation of coordinative unsaturation by removal of triphenylphosphine as the oxide. 

The mixture of reaction product and triphenylphospbine oxide (16), which mixture is gelatinous owing to the alkali metal salt formed, enters an extraction column e, in which the desired reaction product, after acidification with sulfuric acid, is extracted, in counter-current, by hydrocarbons. In a second column, the hydrocarbon extract is washed, also continuously, with aqueous alcohol in order to remove the last residues of triphenylphosphine oxide (16). After concentration, under mild conditions, of the hydrocarbon extract, the all-trans vitamin A acetate (9) formed in the reaction crystallizes out and is separated off. The cis isomer, which does not crystallize, remains in the mother liquor and can be converted, according to one of the above-mentioned techniques, into the all-trans compound. 

Polymer-supported Wittig reagents have recently been developed as an extension to the traditional reagents.29 For example, polystyryldiphenylphosphine has been developed in an attempt to replace the use of triphenylphosphine in the preparation of phosphoranes (see Protocol 1). The hope is that these polymer-bound regents will overcome the practical problem of removing the triphenylphosphine oxide by-product formed in Wittig reactions. Polymer supported phosphonates and Wittig substrates have also been prepared for use in solid phase synthesis and combinatorial chemistry.30... 

A solution of triflic anhydride (1.57 ml, 10 mmol) [84] in dichloroethanc (30 ml) at 0"C is added to a solution of triphenylphosphine oxide (5.55 g, 20 mmol) or equivalent phosphinamide in dichloroethanc. After appearance of a precipitate (usually in less than 15 min), a solution containing n-phcnylenediamine (0.44 g, 4 mmol) and benzoic acid (0.61 g, 5 mmol) in dichloroethanc (10 ml) is added drop wise. After stirring (0.5 h), the solution is washed with 5% sodium bicarbonate solution, dried (MgS04) and evaporated. The residue is passed through a short column packed with silica and eluted with bexanc-cthyl acetate (3 1) to remove excess phosphine oxide. Evaporation gives 2-phcnylbenzimida7.ole (0.66 g, 85%), m.p. 287°C. 

A related triazole synthesis utilizes phosphorous ylids, such as 264. The initially formed triazenes cyclize with elimination of triphenylphosphine oxide. The reaction proceeded sluggishly with phenyl azide, but good results have been obtained with acyl or sulphonyl azides. Tosyl azide and 264 yielded 98% of the 1-tosyl-triazole 265. The tosyl group could be removed by solvolysis in boiling ethanol... 

Iodo-N-BOC-piperidine 42 was obtained by iodination of 4-hydroxy-Af-BOC-piperidine 41 with iodine/triphenylphosphine/imidazole in THE. An extractive workup removed the triphenylphos-phine oxide, allowing a direct crystallization of the pure iodide from ethanol/water that typically contained <1 mol% of triphenylphosphine oxide and other by-products. DMAC was later identified as a better solvent to avoid the formation of THF-polymer or dimer impurities resulting from the interaction of I2/THF. 

Sodamide (60 mmoles) in liquid ammonia (300 ml) is mixed with methyltriphenylammo-nium bromide (55 mmoles), and the ammonia is evaporated. The residue is boiled in ether (200 ml) under reflux. o-Phthalaldehyde (28 mmoles) in ether (100 ml) is stirred during 15 min into the orange-yellow solution of methylenetriphenylphosphorane, and the mixture is boiled for 2 h. After removal of the triphenylphosphine oxide, concentration of the filtrate to 50 ml, and then removal of further oxide, the filtrate affords o-divinylbenzene, b.p. 75-78°/14 mm, in 75 % yield (2.7 g). 

A 500-ml rcund-bottom flask is equipped with a reflux condenser, a gas inlet tube, and a gas outlet leading to a bubbler. The flask is charged with a solution of rhodium (III) chloride trihydrate (2 g) in 70 ml of 95 % ethanol. A solution of triphenylphosphine (12 g, freshly recrystallized from ethanol to remove the oxide) in 350 ml of hot ethanol is added to the flask, and the system is flushed with nitrogen. The mixture is refluxed for 2 hours, following which the hot solution is filtered by suction to obtain the product. The crystalline residue is washed with several small portions of anhydrous ether (50 ml total) affording the deep red crystalline product in about 85% yield. 

Rhodium(III) chloride trihydrate (2 g.) is dissolved in 70 ml. of ethanol (95%) in a 500-ml. round-bottomed flask fitted with gas inlet tube, reflux condenser, and gas exit bubbler. A solution of 12 g. of triphenylphosphine (freshly crystallized from ethanol to remove triphenylphosphine oxide) in 350 ml. of hot ethanol is added and the flask purged with nitrogen. The solution is refluxed for about 2 hours, and the crystalline product which forms is collected from the hot solution on a Buchner funnel or sintered-glass filter. The product is washed with small portions of 50 ml. of anhydrous ether yield 6.25 g. (88% based on Rh). This crystalline product is deep red in color. 

The excess triphenylphosphine used in the preparation can be recovered by addition of water to the ethanol filtrates until precipitation begins. After allowing the solutions to stand 2 to 3 days in a stoppered flask, the triphenylphosphine crystallizes out. Recrystallization from ethanol and ethanol-benzene (1 1) removes triphenylphosphine oxide contaminant. 

When this distillation was replaced by a procedure in which the acetonitrile was removed with a rotary evaporator and steam bath, and the product was extracted from the triphenylphosphine oxide with small portions of acetonitrile totaling ca. 250 ml., the checkers obtained an improved yield (79%) of cinnamyl bromide. 

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... 

Several factors can influence the effectiveness of a metal scavenger, one of which is the oxidation state of the metal. In these studies the removal of Pd(II) as trans-di( j-acetato) bis [o-(di-o-tolylphosphino) benzyl] dipalladium (II) (3) and Pd(0) as tetrakis-(triphenylphosphine)palladium(0) (4) was investigated. 

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