Tetraglyme solvent

Fig. 8. Plot of rates as a function of Cst/Rh ratio ( ) methanol ( ) ethylene glycol. Reaction conditions 75 ml tetraglyme solvent, 3 mmol Rh, 10 mmol 2-hydroxypyridine, 544 atm, H2/CO = 1, 220 C, cesium formate promoter as indicated, 4 hr (88). Methanol and ethylene glycol rates at Cs+/Rh = 0 are 5.21 and 1.34 hr-1, respectively.

Two equivalents of ethyl fluorosulfonate must be used (one ethylates the triflu-oroacetate ion) to avoid complications arising from ethylation of ether oxygens in the tetraglyme solvent. The product must be distilled out of the reaction mixture on a vacuum line within 5 min after addition is complete. The hydri-... 

The second method involves the direct reaction ofbromo- or lodofluoroolefinx with zinc powder [110] (equation 81) in solvents such as DMF, NJV-dimethyl-acetamide (DMAC), tnglyme, tetraglyme, THF, and CH3CN. In all cases, the stereochemistry is retained Table 4 shows some typical examples of this method ology Similar results are obtained with l-chloro-2 lodotetrafluorocyclobutene [III] and l-iodo-2-chlorohexafluorocyclopentene [112]... 

Several high-boiling, inert solvents have been reported in various steps of the Gould-Jacobs reaction. Dowtherm, f Ph20, cumene, tetraglyme, diphenyl methane, ... 

Rhodium losses can also be reduced by using a two-phase system to separate the polyol products from the catalyst solution (64). In this modification the reaction is carried out in a production solvent (e.g., tetraglyme). In order to separate the products, water and an essentially water-immiscible organic extraction solvent (e.g., dichloromethane or chloroform) are added. The resulting two-phase system then consists of a water phase containing the alcohol products and an organic phase containing essentially all the rhodium complex. 

The solvents used in these rhodium-catalyzed reactions may also act as complexing agents for counterions of the anionic rhodium complexes. For example, tetraglyme is known to coordinate alkali metal cations. Such solvation decreases the possibility of the cation interacting with the anionic rhodium catalyst and lowering its activity or solubility. The crown ethers, such as [18]-crown-6... 

Since the crown ethers are very effective complexing agents, the amount of free M+ in solution, as in (33)—(36), is expected to be small the crown ether competes very well with Rh and X for M +. Indeed, it is found that the addition of excess salt causes a much lower degree of rate inhibition in [18]-crown-6 as compared to some other solvents. For example, Fig. 10 illustrates the differences between [18]-crown-6 and tetraglyme as the level of salt promoter is increased. The capability of using an excess of salt reduces the criticality of precisely controlling the salt concentration and is beneficial for the stability of the catalyst (92). 

Fig. 10. Effect of cesium concentration on ethylene glycol rates in 8-crown-6 ( ) and tetraglyme ( ) (92). Reaction conditions 75 ml solvent, 3 mmol Rh, cesium benzoate, 544 atm, Hj/CO = 1, 220°C, 4 hr.

For complex III, the Na+ Is probably as accessible to solva-tlon by solvent molecules as is the Na In the tight Fl-,Na+ Ion pair. Hence, no externally bound solvent molecules need to be removed. This may be different In other systems. For example, the formation constant of a loose Ion pair complex between FI", Na+ and tetraglyme (tetraethylene glycol dimethyl ether) Is nearly four times lower In dloxane than In THF (10). This may be caused by specific solvent effects rather than by the difference In solvent dielectric constant. The flexible glyme ligand wraps Itself around the Na+ Ion, and this may make It more difficult for solvent molecules to remain bound to Na+ In the glyme-separated Ion pair. 

Tertiary carbanions have been isolated, but secondary and primary structures do not exhibit sufficient kinetic stability. The lifetimes of the former is highly dependent on structure, counterion, solvent and other factors. One of the simpler tertiary carbanions is present in (perfluoro-fer/-butyl)cesium obtained as a solid from the reaction of perfluoro(2-methyl-propene) and cesium fluoride in tetraglyme.36 The structure of the salt was analyzed by 19F and l3C NMR spectroscopy. 

Alkali metal hexafluoroantimonates arc used, like hexafluorophosphate or tetrafluoroborate salts, to effect halogen-exchange fluorination in organosilanes both in the presence and in the absence of solvents. Fluorotriphenylsilane and difluorodiphenylsilane are obtained in 87 and 95 % yield by heating the corresponding chlorides with sodium hexafluoroantimonate in tetra-ethylene glycol dimethyl ether (tetraglyme).102 Tetrafluoroborates react with chlorosilanes faster than hexafluorophosphate or hexafluoroantimonate salts. 

DiaJkyl-J, S-cyelohexadienes. The diylidc of I [KOC(CHj)3, tetraglyme] reacts with ot-dicarbonyl compounds to form 2,3-dialkyl- 1,3-cyclohexadienes, albeit In modest yields. Tetraglyme is used as solvent, since the products arc rather volatile and are isolated by distillation. 

Fig. 52. Molecular structures of the disodium perylene Na[C2oH,2] complexes with mono-, di-, and tetraglyme showing the change from solvent-shared to solvent-separated ion pairs. (Reprinted with permission from H. Bock ei at, J. Am. Chem. Soc. 1995,117, 3869. Copyright 1995 American Chemical Society.)...

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