Phosphonium tosylate

In this context, the use of ionic liquids with halogen-free anions may become more and more popular. In 1998, Andersen et al. published a paper describing the use of some phosphonium tosylates (all with melting points >70 °C) in the rhodium-catalyzed hydroformylation of 1-hexene [13]. More recently, in our laboratories, we found that ionic liquids with halogen-free anions and with much lower melting points could be synthesized and used as solvents in transition metal catalysis. [BMIM][n-CgHi7S04] (mp = 35 °C), for example, could be used as catalyst solvent in the rhodium-catalyzed hydroformylation of 1-octene [14]. 

While it is clear that acidic chloroaluminate ionic liquids give very good results, their use is often not practicable and alternatives are desirable. Excellent stereoselectivity was obtained with phosphonium tosylate ionic liquids, [R3PR ][OTs], in the reaction between isoprene and methyl acrylate affording essentially exclusively the 1,4-isomcr.1 081 However, with... 

In bmim BF4 and CIO4 l-butyl-3-methylimidazolium tetrafluoroborate and perchlorate Fischer, T. Sethi, A. Welton, T. Woolf, J. Tetrahedron Lett. 1999, 40, 793. In chloroaluminates Lee, C.W. Tetrahedron Lett 1999, 40, 2461. In phosphonium tosylates Ludley, P Karodia, N. Tetrahedron Lett. 2001, 42, 2011. In pyridinium salts Xiao, Y MaUiotra, S.V. Tetrahedron Lett. 2004, 45, 8339. In HBuIm, hydrogenbutylimidazolium tetrafluoroborate and DiBuIm, 1,3-dibutylimidazolium, tetrafluoroborate Jaegar, D. A. Tucker, C. E. Tetrahedron Lett. 1989, 30, 1785. 

Hydroformylation. Using RhjCOAc) in phosphonium tosylates for hydro-formylation of 1-alkenes at 120°, the catalyst recovery is facilitated. Thus, on cooling of the reaction mixture the rhodium acetate is completely retained in the solid phase and the liquid products are obtained by simple decantation. Variation of substituents at the phosphorus atom of ionic solvents [e.g., (PhjPEt) OTs vs. (BUjPEO OTs ] has remarkable effects on the ratio of alkanals and 2-methylalkanals. 

Scheme 5.1-6 Diels-Alder reactions of isoprene with methyl acrylate, acrylic acids, but-3-en-2-one and acrylonitrile in phosphonium tosylates.

It is finally worth noting that phosphonium tosylates [31], and more recently pyridinium-based ionic liquids [32], have also been used as solvents for the Diels-Alder reactions of isoprene with methyl acrylate, acrylic acids, but-3-en-2-one and acrylonitrile (Scheme 5.1-6). 

The use of molten salts based on phosphonium tosylates has also been reported for Diels-Alder reactions [175]. These salts have higher melting points than most ionic liquids in common use and hence the reactions were performed in a sealed tube. The authors claim very high selectivities in the reaction of isoprene with MVK or methyl acrylate. The effect of temperature on the selectivity in phosphonium tosylates gave reduced endoxxo ratios at higher temperatures [176]. The Diels-Alder reactions of isoprene with acrylonitrile, acrylic acid and methacrylic acid in pyridinium ionic liquids ([EtPy][BF4] or [EtPy][F3CC02]) were found to give the expected cyclohexene structures [177]. The authors show that... 

Phosphonium salts manufactured by the above metathesis route will typically contain a few ppm of halogen anion. In many cases, this may be irrelevant, but if a totally halogen-free salt is required, they can readily be prepared in a simple one-pot procedure by heating a tertiary alkylphosphine with a tosylate, sulfate, or phosphate ester [51,59,60[. Examples are triisobutyl(methyl)phosphonium tosylate (CYPHOS IL 106),tributyl(methyl)phosphoniummethylsulfate (CYPHOS IL 108), and tributyl(ethyl)phosphonium diethylphosphate (CYPHOS IL 169). 

In general, salts with alkylphosphonium cations are less dense than water. Densities as a function of temperature for trihexyl(tetradecyl)phosphonium chloride (CYPHOS IL101), trihexyl(tetradecyl)phosphonium dicyanamide (CYPHOS IL105) and trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate (CYPHOS IL 104) are found in Figure 5. Phosphonium salts with aromatic anions such as triisobutyl(methyl)phosphonium tosylate (CYPHOS IL 106) have densities greater than that of water. The density of trihexyl(tetradecyl)phosphonium hexa-fluorophosphate (CYPHOS IL 110) is unique in that, depending on the temperature, it may be greater or less than that of water. 

Karodia N, Guise S, Newlands C, Andersen J (1998) Clean catalysis with ionic solvents-phosphonium tosylates for hydroformylation. Chem Commun 2341-2342. 

Petra L, Nazira K (2001) Phosphonium tosylates as solvents for the Diels-Alder reaction. Tetrahedron Lett 42(10) 2011-2014... 

The compounds triisobutyl (methyl) phosphonium tosylate (a) and trihexyl (tetradecyl) phosphonium bis 2,4,4-(trimethylpentyl)phosphinate (b) were synthesized (Fig. 4.14), and their surface-active properties studied.The polar compound (a) is water soluble and surface active, does not form micelles, but affects the micelliza-tion properties of ionic, nonionic, and zwitterionic surfactants more strongly than conventional electrolytes. The less polar compound (b) forms micelles and has very low aqueous solubility. Both compounds form mixed micelles with Triton X-100 nonionic surfactant in aqueous solution. Compound (a) replaces water to form microemulsions with isopropyl myristate as oil, stabilized by (b). Compound (a) showed a clear antitumor activity, for example, 5mg (a)mH in 0.9% NaCl solution caused 100% killing of Sarcoma-180 cell line in 1 h. More diluted solutions were still active 2.5 and 1 mg (a) mT caused 81 and 53% killing of the same cells, respectively. On the other hand, compound (b) was less active than (a) lOmg (b)mT in 0.9% NaCl solution caused 89% killing of Sarcoma-180 cell line in 2h. Note that the concentration of (b) employed was 33 times higher than its cmc (0.03 x 10" moll ). The efficiency of (a) with respect to (b) may be due to the fact that the former does not form micellar aggregates [89]. 

In addition, phosphonium salts have also been reported as coBaylis-Hillman reaction of methyl acrylate with benzaldehyde [77]. Good results were found with triethyl(n-butyl)phosphonium tosylate, affording up to quantitative yields in some cases. The authors proposed that the phosphonium salt stabilizes the intermediate 34, shown in Scheme 16.28, and thereby increases its concentration rather than activating the benzaldehyde. 

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