Phosphonium salts periodates

The action of water on cyanines 8d for longer periods of time (with or without careful exclusion of oxygen) leads to 1,3-diefhyl-benzimidazolium-tetrafluoroborate 19. This corresponds to the hydrolytic cleavage of quaternary phosphonium salts. 

TABLE 26. Half-life periods r1/2 for the degradation of quaternary phosphonium salts R4P+ Y" in a chlorobenzene-50% aqueous NaOH two-phase system under phase-transfer catalysis in the absence (A)a and presence (B)fc of a molar excess of the corresponding inorganic salt (NaY)727... 

Hogen-Esch stressed that the MMA polymerization initiated by PhsCPPlu is very fast (0.3 s < half life < 1 s) with a very short induction period (0.05 to 0.2 s). Therefore, it is mandatory that the polymerization medium be very rapidly homogenized for the polymerization to be controlled. The dropwise addition of a MMA solution in THE to a solution of the phosphonium salt in the same solvent was recommended. ... 

One of the earliest reports on use of a phosphonium salt as an IL in such a process was that of Kaufmann and co-workers (9). In this work, the use of tri-butyl(hexadecyl)phosphonium bromide as a recyclable medium for the palladium-mediated Heck coupling of aryl halides with acrylate esters was reported (9). While these reactions proceeded without the use of an additive ligand, elevated temperatures (100 °C) were required and the process was most efficient only with more activated aryl halides [Eq. (1)]. More recently, the use of trihexyl(tetradecyl)-phosphonium chloride (Cyphos IL 101) has been reported as a useful medium for the Suzuki cross-coupling of aryl halides with boronic acid derivatives [Eq. (2)] [10]. In this process, a soluble palladium precursor such as Pd2(dba)3-CHCl3 was dissolved in the phosphonium salt, forming a dark orange solution. This solution was stable in the absence of oxygen for an extended period of time and could be... 

Introduction. Sodium periodate is widely used for the oxidation of a variety of organic substrates and as a cooxidant in other oxidation reactions (see Sodium Periodate-Osmium Tetroxide and Sodium Periodate-Potassium Permanganate) f The Nal04 oxidation is usually conducted in water however, for organic substrates that are insoluble in water, an organic cosolvent (e.g. MeOH, 95% EtOH, 1,4-dioxane, acetone, MeCN) is used. Alternatively, the oxidation can be conducted either with phase-transfer catalysis (PTC) using quaternary ammonium or phosphonium salts in a two-phase system, or in an organic solvent if the oxidant is first coated on an inert support. ... 

A mixture of 760 mg of phosphonium salt (0.92 mmol), 0.90 g activated 4-A powdered molecular sieves, 7.1 mL anhydrous THF, and 4.7 mL anhydrous HMPA was stirred at room temperature for 10 min and then cooled to -20°C. The stirred mixture was treated with 580 /xL 1.6 M -BuLi in hexanes (0.92 mmol), warmed to 0°C, stirred for an additional 30 min, and then cooled to -20°C. To the stirred mixture was added 336 mg Garner aldehyde in 7.1 mL anhydrous THF over a 15-min period. The mixture was allowed to reach 0°C in 2.5 h, stirred at 0°C for an additional 1 h, and then diluted with 200 mL Et20 and filtered through a pad of Celite. The ethereal solution was washed with 1 M phosphate buffer at pH 7 (3 x 30 mL), dried over Na2S04, and concentrated. The residue was eluted from a column of silica gel with 5 1 cyclohexane/EtOAc to give 457 mg 6,10-anhydro-7,8,9-tri-(9-benzyl-2-fert-butoxycarbonylamino-2,3,4,5,ll-pentadeoxy-l,2-N, 0-isopropylidene-L-f/ re(9-D-t(i(9-undec-4-(Z)-enitol as a syrup, in a yield of 75%. 

Place 0.480 g of benzyltriphenylphosphonium chloride (MW = 388.9) in a dry 5-mL conical vial. Add a magnetic spin vane. Transfer 2.0 mL of absolute (anhydrous) ethanol to the vial and stir the mixture to dissolve the phosphonium salt (Wittig salt). Add 0.75 mL of sodium ethoxide solution to the vial using a dry pipette while stirring continuously. Cap the vial and stir this mixture for 15 minutes. During this period, the cloudy solution acquires the characteristic yellow color of the ylide. 

An ylide is a neutral species whose Lewis structure contains opposite charges on adjacent atoms. The atoms involved are carbon and an element from either group 15 (VA) or 16 (VIA) of the periodic table, such as N, P, or S. The Wittig reaction uses phosphorus ylides, which are obtained by deprotonation of a phosphonium salt with a strong base. Phosphorus ylides are relatively stable, but reactive species, for which the following resonance structures may be written the phosphorus atom can exceed an octet by accommodating electron donation into its 3d orbitals. 

Phosphorus is the second element in Group 5A of the Periodic Table and, like nitrogen, has five electrons in its valence shell. Examples of trivalent phosphorus compounds are phosphine, PH3, and triphenylphosphine, PhjP. Phosphine is a highly toxic, flammable gas. Triphenylphosphine is a colorless, odorless solid. Because phosphorus is below nitrogen in the Periodic Table, phosphines are weaker bases than amines and good nucleophiles (Section 9.3E). Treatment of a phosphine with a methyl, primary, or secondary all l halide gives a phosphonium salt by an Sj 2 pathway. 

On the other hand, the chemistries of silicon (lying below carbon in the periodic table) and phosphorus (lying beneath nitrogen) are strikingly different. Phosphorus, like nitrogen, can be expected to be found as phosphine (PH3), and as with amines, substituted phosphines and phosphonium salts should be capable of formation. While it might be (correctly) anticipated that with more electrons the chemistry of phosphorus would be more complicated, it might also be (correctly) anticipated that some similarities could be found. 

The present review is aimed at describing the state-of-the-art, for the period January-December 2014, of two pillar classes of phosphorus-containing compounds, the phosphonium salts and ylides. The importance of these derivatives is revealed by the very high number of references cited herein. For the Reader s convenience, topics are organized to offer an introductory survey on the methods of preparation and characterisation of both types of compounds, followed by an analysis of applicative and curiosity driven research. A special section is devoted to phosphonium-based ionic liquids (PILs). 

The quaternisation of phosphines with electrophiles or Bronsted acids is doubtlessly the most typical and simple reaction for the preparation of phosphonium salts. The preparation of most phosphonium salts reported in the period surveyed by this review followed this approach. The structures of these compounds are summarised in Fig. 1. 

The octet rule does not apply to elements of higher periods. Oxidation levels of +3 and +4 stand for normal oxidation levels of phosphines or phosphonium salts, but the valence shell can be expanded beyond that. Tetraphenylphosphonium iodide readily combines with phenyllithium to afford the colorless and crystalline but ether soluble pentaphenylphosphorane (62). Would it be possible to produce a lithium hexaphenylphosphate (63) by merely using phenyllithium in excess (Scheme 1-44) Such an expansion of the valence shell of pentaphenylstiborane to the electron dodecet of lithium hexaphenylantimonate is possible indeed.However, the smaller phosphorus atom tolerates steric congestion not as well. When a series of pentaarylphosphoranes was incubated with the corresponding aryllithiums, no high-field P nmr signal testifying the presence of an ate complex was detected. ... 

Quaternisation of the corresponding phosphine by reaction with an electrophile or a Bronsted acid is the most typical and simple procedure for the preparation of phosphonium salts. Besides this classic approach, new interesting synthetic pathways have been described in the period... 

A number of methods used for preparing phosphonium compounds has already been indicated on p. 7. Some tetra-alkylphosphonium hydroxides may be produced by heating white phosphorus and the corresponding alcohol above 250° C. for a long period. The compound PgHgg reacts with alkyl iodides to form quaternary compounds, and the latter also occur when trialkylphosphines react with alkyl halides. There are also special methods of preparation applying only to individual derivatives. The iodides are converted into the hydroxides by treatment with moist silver oxide, and bromides, cyanides, carbonates, acetates, oxalates and sulphates are similarly obtained when the appropriate silver salt is used. Such salts also result when the hydroxides are treated with the corresponding acids. 

Thiophen Analogues of Helicenes.— The photocyclization with iodine as oxidant of 1,2-di(diheteroaryl)ethenes, in which the heteroaryl group is derived from benzo[fe]thienyl or from tricyclic systems such as (434) or (440), is the key step in the synthesis of heterohelicenes. The ethylenes in turn are prepared from the aldehydes and the chloromethyl derivatives via phos-phonium salts or phosphonates through the Wittig reaction. The Bestmann method was also used for the synthesis of symmetrically substituted ethylenes from phosphonium periodates. Thus from (443) the heterohexahelicene (444) was obtained, (445) gave (446), and the hetero-heptahelicene (448) was obtained from (447). The undecahelicene (450) was prepared from (449). - These syntheses illustrate the fact that heterohelicenes are more easily available than helicenes, as the necessary aldehyde is prepared by metalation of (448) with butyl-lithium followed by reaction with iV-methylformanilide. The heptahelicene (452) was obtained by a double photocyclization of (451). 

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