Acetone-water solvent system

In addition to the reactions discussed above, there are still other alkyne reactions carried out in aqueous media. Examples include the Pseudomonas cepacia lipase-catalyzed hydrolysis of propargylic acetate in an acetone-water solvent system,137 the ruthenium-catalyzed cycloisomerization-oxidation of propargyl alcohols in DMF-water,138 an intramolecular allylindination of terminal alkyne in THF-water,139 and alkyne polymerization catalyzed by late-transition metals.140... 

Higher yields, almost quantitative, are reported when the solvent DMSO is used either in combination or without ion-exchange resins [23-27]. But from the ecological point of view the use of DMSO is unfavorable and furthermore the separation of the solvent DMSO from the desired product HMF is difficult. A different solvent approach utilizing a solvent with higher volatility and thus easier separation from HMF is the use of a sub- and supercritical organic solvent like acetone. In a 9 1 mixture of acetone/water - water is needed due to the low solubility of D-fructose in pure acetone - and sulfuric acid catalysis at a temperature of 180°C and a pressure of 20 MPa, high fructose conversion and HMF selectivity (up to 77%) could be achieved without the formation of insoluble humic acids [28-31]. The tremendous increase in selectivity for the acetone/water solvent system could be... 

We believe that the presence of free H in the acetone/water solvent system plays a role in the monocationic system. The rate determining step, once again, is the reductive elimination of aldehyde with a calculated barrier of 21.6 kcal (Fig. 14). Protonation of the monocationic dirhodium acyl is an alternate and likely pathway for eliminating aldehyde and forming the dicationic dirhodium catalyst Hr. Due to the very low activation barrier for the monocationic aUcyl-CO migratory insertion step, protonation of Rh-alkyl species to produce alkane is far less likely and consistent with the much lower alkane side reactions for 15r. 

Many procedures have been studied for detoxification of aflatoxkis, including heat and treatment with ammonia, methylamine, or sodium hydroxide coupled with extraction from an acetone—hexane—water solvent system. Because ki detoxification it is important to free the toxki from cellular constituents to which it is bound, a stabifi2ation of protekis uskig a tanning compound such as acetaldehyde (qv) or glutaraldehyde may be a solution to the problem (98). 

The most frequently used method for the preparation of isoquinoline Reissert compounds is treatment of an isoquinoline with acyl chloride and potassium cyanide in water or in a dichloromethane-water solvent system. Though this method could be successfully applied in a great number of syntheses, it has also some disadvantages. First, the starting isoquinoline and the Reissert compound formed in the reaction are usually insoluble in water. Second, in the case of reactive acyl halides the hydrolysis of this reaction partner may became dominant. Third, the hydroxide ion present could compete with the cyanide ion as a nucleophile to produce a pseudobase instead of Reissert compound. To decrease the pseudobase formation phase-transfer catalysts have been used successfully in the case of the dichloromethane-water solvent system, resulting in considerably increased yields of the Reissert compound. To avoid the hydrolysis of reactive acid halides in some cases nonaqueous media have been applied, e.g., acetonitrile, acetone, dioxane, benzene, while utilizing hydrogen cyanide or trimethylsilyl cyanide as reactants instead of potassium cyanide. 

Figure 9.18 has been obtained for the water-acetone mixture, and should be recalculated for different water-solvent systems the mixing time may be very weakly modified by changing the solvent if there is not a large variation in viscosity and diffiisivity, as in the case of acetone and THF, but the effect of density and viscosity on the energy dissipation must also be accounted for. 

DAG is treated with ethanol and hydrochloric acid in the presence of inert solvent, eg, chlorinated solvents, hydrocarbons, ketones, etc. The L-ascorbic acid precipitates from the mixture as it forms, minimising its decomposition (69). Cmde L-ascorbic acid is isolated through filtration and purified by recrystallization from water. The pure L-ascorbic acid is isolated, washed with ethanol, and dried. The mother Hquor from the recrystallization step is treated in the usual manner to recover the L-ascorbic acid and ethanol contained in it. The cmde L-ascorbic acid mother Hquor contains solvents and acetone Hberated in the DAG hydrolysis. The solvents are recovered by fractional distillation and recycled. Many solvent systems have been reported for the acid-catalyzed conversion of DAG to L-ascorbic acid (46). Rearrangement solvent systems are used which contain only the necessary amount of water required to give >80% yields of high purity cmde L-ascorbic acid (70). 

The effect of solvent concentration on the activity coefficients of the key components is shown in Fig. 13-72 for the system methanol-acetone with either water or methylisopropylketone (MIPK) as solvent. For an initial-feed mixture of 50 mol % methanol and 50 mol % acetone (no solvent present), the ratio of activity coefficients of methanol and acetone is close to unity. With water as the solvent, the activity coefficient of the similar key (methanol) rises slightly as the solvent concentration increases, while the coefficient of acetone approaches the relatively large infinite-dilution value. With methylisopropylketone as the solvent, acetone is the similar key and its activity coefficient drops toward unity as the solvent concentration increases, while the activity coefficient of the methanol increases. 

FIG. 13-72 Effect of solvent concentration on activity coefficients for acetone-methanol system, (a) water solvent, (h) MIPK solvent. 

FIG. 13-75 Number of theoretical stages versus solvent-to-feed ratio for extractive distillation, a) Close-boiling vinyl acetate-etbyl acetate system with phenol solvent, (h) A2eotropic acetone-methanol system with water solvent. 

Geraniol [106-24-1] M 154.3, b 230 , d 0.879, n 1.4766. Purified by ascending chromatography or by thin layer chromatography on plates of kieselguhr G with acetone/water/liquid paraffin (130 70 1) as solvent system. Hexane/ethyl acetate (1 4) is also suitable. Also purified by GLC on a silicone-treated column of Carbowax 20M (10%) on Chromosorb W (60-80 mesh). [Porter Pure Appl Chem 20 499 7969.] Stored in full, tightly sealed containers in the cool, protected from light. 

A similar technique, the so-called spontaneous emulsification solvent diffusion method, is derived from the solvent injection method to prepare liposomes [161]. Kawashima et al. [162] used a mixed-solvent system of methylene chloride and acetone to prepare PLGA nanoparticles. The addition of the water-miscible solvent acetone results in nanoparticles in the submicrometer range this is not possible with only the water-immiscible organic solvent. The addition of acetone decreases the interfacial tension between the organic and the aqueous phase and, in addition, results in the perturbation of the droplet interface because of the rapid diffusion of acetone into the aqueous phase. 

The bis pyridine complex [Ir(cod)py2][PF6], (314), is prepared by the reaction of [IrCl(cod)]2 with pyridine in the presence of NH4PF6.508 Best yields were achieved from a water/acetone (1 1) solvent system. Reaction of (314) with equimolar amounts of P(C6Hn)3 affords the substituted, air-stable species [Ir(cod) P(C6Hii)3 py][PF6]. 

In a related approach from the same laboratory, the perfluorooctylsulfonyl tag was employed in a traceless strategy for the deoxygenation of phenols (Scheme 7.82) [94], These reactions were carried out in a toluene/acetone/water (4 4 1) solvent mixture, utilizing 5 equivalents of formic acid and potassium carbonate/[l,T-bis(diphe-nylphosphino)ferrocene]dichloropalladium(II) [Pd(dppf)Cl2] as the catalytic system. After 20 min of irradiation, the reaction mixture was subjected to fluorous solid-phase extraction (F-S PE) to afford the desired products in high yields. This new traceless fluorous tag has also been employed in the synthesis of pyrimidines and hydantoins. 

PCBs in biological samples are usually extracted by a Soxhlet column and with a nonpolar solvent such as hexane. The sample is first mixed with sodium sulfate to remove moisture. The extraction of PCBs from sediments was tested with sonication, with two sonications interspersed at a 24-h quiescent interval, with steam distillation, or with Soxhlet extraction (Dunnivant and Elzerman 1988). Comparison of the recoveries of various PCB mixtures from dry and wet sediments by the four techniques and the extraction efficiency of four solvents showed that the best overall recoveries were obtained by Soxhlet extraction and the two sonication procedures. In comparisons of solvent systems of acetone, acetonitrile, acetone-hexane (1+1), and water-acetone-isooctane (5+1.5+1), recoveries of lower chlorinated congeners (dichloro- to tetrachloro-) were usually higher with acetonitrile and recoveries of higher chlorinated congeners (tetrachloro- to heptachloro-) extracted with acetone were superior (Dunnivant and Elzerman 1988). The completeness of extraction from a sample matrix does not seem to discriminate against specific isomers however, discrimination in the cleanup and fractionation process may occur and must be tested (Duinker et al. 1988b). 

The next step is to determine the solubility of the substrate (or its salts) in different solvents. This can also be performed by an automated liquid handling system. Depending upon the solubility of the substrate in water-miscible solvent (alcohols, acetone, tetrahydrofuran, etc.) and water-immiscible solvents (ethyl acetate, methyl-tert-butyl ether, heptane, etc.) the process chemist can identify one or many solvent systems from which the substrate (or its salts) could be ciystallized using the antisolvent addition strategy. 

Griesbeck et al. successfully transformed w-phthalimidoalkanoates via PET with concomitant decarboxylation and C,C combination leading to medium- and large-ring compounds with yields in the range 60-80%. Thereby, the solvent system acetone/water and K2CO3 employed for the deprotonation of the carboxylic acids were crucial (Scheme 45) [66]. 

Water is a possible axial ligand for the transient Ni(PP) in these systems and has been shown to form weak complexes with other nickel porphyrin species (18). While we cannot unequivocally rule out weak, transient ligation, the observation of similar transient behavior in Ni(OEP) and Ni(PPDME) in noncoordinating, nonaqueous, solvents (toluene, methylene chloride (9, unpublished results)) leads us to conclude that the transient behavior of the Ni(PP) in acetone/water is not predicated upon ligand binding. 

---