Co solvents

The alkylations proceeded much more slowly, when ethyl- or butyllithium in diethyl ether, prepared from the alkyl bromides, had been used for the metallation of allene, in spite of the presence of THF and HMPT as co-solvents. 

Note 1. If the lithiation of the allenic ether is performed with butyllithium in hexane and THF as a co-solvent, subsequent alkylation (in the presence of a small amount of HMPT) is much faster. The separation of the volatile product from the hexane and THF is difficult, however. 

Note 1. This yield is lower than that reported in the literature. In our procedure no low-boiling light petroleum is used as co-solvent, so that the temperature of the boiling reaction mixture can become considerably higher, which may give rise to the formation of polymeric products and tars. Our reaction time is much shorter than that in the literature. The reaction with HCECCH2OH and HC=C-CH(CH3)0H failed. 

Note 1. This co-solvent is used in order to increase the solubility of the allenic sulfide (compare Exp. 1). 

The alkene is allowed to react at low temperatures with a mixture of aqueous hydrogen peroxide, base, and a co-solvent to give a low conversion of the alkene (29). These conditions permit reaction of the water-insoluble alkene and minimise the subsequent ionic reactions of the epoxide product. Phase-transfer techniques have been employed (30). A variation of this scheme using a peroxycarbimic acid has been reported (31). 

Medium Boiling Esters. Esterificatioa of ethyl and propyl alcohols, ethylene glycol, and glycerol with various acids, eg, chloro- or bromoacetic, or pymvic, by the use of a third component such as bensene, toluene, hexane, cyclohexane, or carbon tetrachloride to remove the water produced is quite common. Bensene has been used as a co-solvent ia the preparatioa of methyl pymvate from pymvic acid (101). The preparatioa of ethyl lactate is described as an example of the general procedure (102). A mixture of 1 mol 80% lactic acid and 2.3 mol 95% ethyl alcohol is added to a volume of benzene equal to half that of the alcohol (ca 43 mL), and the resulting mixture is refluxed for several hours. When distilled, the overhead condensate separates iato layers. The lower layer is extracted to recover the benzene and alcohol, and the water is discarded. The upper layer is returned to the column for reflux. After all the water is removed from the reaction mixture, the excess of alcohol and benzene is removed by distillation, and the ester is fractionated to isolate the pure ester. 

The checkers distilled the anisole from calcium sulfate before use. This reagent functions not only as a reactant, but also as solvent. In some similar preparations the intermediate trichloride is rather insoluble, as in the case of bis(3-methyl-4-methoxyphenyl)tellurium dichloride. The addition of co-solvents such as bis-(2-methoxyethyl) ether is beneficial. ... 

A widely used procedure for the reduction of conjugated enones to saturated ketones is that of Bowers, Ringold and Denot, Procedure 5 (section V). Ether-dioxane (1 1) is used as the organic co-solvent and solid ammonium... 

Toluene is a useful co-solvent in metal-ammonia reductions as first reported by Chapman and his colleagues. The author has found that a toluene-tetrahydrofuran-ammonia mixture (1 1 2) is a particularly useful medium for various metal-ammonia reductions. Procedure 8a (section V) describes the reduction of 17-ethyl-19-nortestosterone in such a system. Ethylene dibromide is used to quench excess lithium. Trituration of the total crude reduction product with methanol affords an 85% yield of 4,5a-dihydro-17-ethyl-19-nortestosterone, mp 207-213° (after sintering at 198°), reported mp 212-213°. For the same reduction using Procedure 5 (section V), Bowers et al obtained a 60% yield of crude product, mp, 196-199°, after column chromatography of the total reduction product. A similar reduction of 17-ethynyl-19-nortestosterone is described in Procedure 8b (section V). The steroid concentration in the toluene-tetrahydrofuran-ammonia system is 0.05 M whereas in the ether-dioxane-ammonia system it is 0.029 M. 

In this case, the co-solvent dosage rate is programmed in order to control the transient level of supersaturation in an effort to improve on the product crystal size distribution from simply dumping in all the solvent at the start of the batch. An experimental crystallizer within which a programmed microcomputer determines the set point of a variable speed-dosing pump is shown in Figure 7.7. Controlled co-solvent dosing improves the product crystal size, with a consequent increase in the filterability of the product. These process concepts are developed further in Chapter 9. 

A variety of media have been used for the Wallach fluorination reaction anhydrous hydrogen fluoride alone or with cosolvents such as methylene chloride, benzene, or tetrahydrofuran and hydrogen fluoride-pyridine alone or with co solvents such as benzene, glyme, or acetic acid [42,43, 46 50] Solutions of cesium fluoride, tetraethylammonium fluoride, or tetrabutylammonium fluoride in strong acids such as methanesulfonic acid or trifiuoroacetic acid with numerous cosolvents have also been studied [48, 49]... 

In an extension of this work Scheeren et al. studied a series of derivatives of N-to-syl-oxazaborolidinones as catalysts for the 1,3-dipolar cycloaddition reaction of 1 with 2b [29]. The addition of a co-solvent appeared to be of major importance. Catalyst 3b was synthesized from the corresponding amino acid and BH3-THF, hence, THF was present as a co-solvent. In this reaction (-)-4b was obtained with 62% ee. If the catalyst instead was synthesized from the amino acid and... 

While partially concurrent eluent evaporation is easier to use, and is preferred for the transfer of normal phase solvents, concurrent eluent evaporation with co-solvent trapping is the technique of choice for transfer of water-containing solvents, because wettability is not required. 

Figure 2.7 (11) shows a gas chromatogram obtained by co-solvent trapping and concurrent eluent evaporation after injecting 500 p.1 of diluted gasoline. The main solvent was -pentane with 5% of -heptane as co-solvent. It is noteworthy that without the co-solvent, higher-boiling compounds could be lost. 

Figure 2.7 Gas clnomatogram obtained for 500 jl1 of diluted gasoline in -pentane inti O-duced by concunent eluent evaporation, using w-heptane as the co-solvent. Reprinted from Journal of High Resolution Chromatography, 11, K. Grob and E. Muller, Co-solvent effects for preventing broadening or loss of early eluted peaks when using concunent eluent evaporation in capillary GC. Part 2 w-heptane in w-pentane as an example , pp. 560-565, 1988, with permission from Wiley-VCH.

DIRECT INJECTION BY USING CONCURRENT SOLVENT EVAPORATION WITH A CO-SOLVENT... 

A partial solution to the problem of producing sharp peaks at low elution temperatures is to add a small amount of a higher-boiling co-solvent to the main solvent. As suggested by Grob and Muller (23, 24), butoxyethanol can be used as a suitable cosolvent for aqueous mixtures in such cases. 

K. Grob, Concurrent eluent evapor ation with co-solvent Capping for on-line reversed-phase liquid cliromatography-gas clir omatogr aphy. Optimization of conditions , J. Chromatogr. 477 73-86 (1989). 

This is a highly efficient barrier against evaporative losses of volatile compounds, which also improves the peak width of the early eluting compounds. This system has been successfully applied to a group of pesticides, using -decane as the co-solvent and has enabled a group of volatile phosphorus pesticides to be determined (95). The experimental conditions used in this work are shown in Table 13.2. 

While certain TSILs have been developed to pull metals into the IL phase, others have been developed to keep metals in an IL phase. The use of metal complexes dissolved in IL for catalytic reactions has been one of the most fruitful areas of IL research to date. LLowever, these systems still have a tendency to leach dissolved catalyst into the co-solvents used to extract the product of the reaction from the ionic liquid. Consequently, Wasserscheid et al. have pioneered the use of TSILs based upon the dissolution into a conventional IL of metal complexes that incorporate charged phosphine ligands in their stmctures [16-18]. These metal complex ions become an integral part of the ionic medium, and remain there when the reaction products arising from their use are extracted into a co-solvent. Certain of the charged phosphine ions that form the basis of this chemistry (e.g., P(m-C6H4S03 Na )3) are commercially available, while others may be prepared by established phosphine synthetic procedures. 

The addition of co-solvents to ionic liquids can result in dramatic reductions in the viscosity without alteration of the cations or anions in the system. The haloaluminate ionic liquids present a challenge, due to the reactivity of the ionic liquid. Nonetheless, several compatible co-solvents including benzene, dichloromethane, and acetonitrile have been investigated [33-37]. The addition of as little as 5 wt. % acetonitrile or 15 wt. % benzene or methylene chloride was able to reduce the... 

The physical properties of ionic liquids can often be considerably improved through the judicious addition of co-solvents [55-58]. Flowever, surprisingly, this approach has been relatively underutilized. Flussey and co-workers investigated the effect of co-solvents on the physical properties of [EMIM]C1/A1C13 ionic liquids [55, 56]. They found significant increases in ionic conductivity upon the addition of a variety of co-solvents. Figure 3.6-5 displays representative data from this work. The magnitude of the conductivity increase depends both on the type and amount of the co-solvent [55, 56]. 

BMIM][PFg] as co-solvent during distillative product isolation - apparatus for distillative product isolation from the ionic catalyst layer. 

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