Dichloromethane-methanol solvent

The subsequent Wittig olefination of 79 with the Cio-dialdehyde 58 is carried out with an equivalent amount of sodium methoxide in dichloromethane/methanol. After aqueous workup, astaxanthin (403) is crystallized by simultaneous dichloromethane —> methanol solvent exchange triphenylphosphine oxide (56) remains in solution. Thermal isomerization gives (all-E)-4Q3 in a yield of approximately 80% and a purity of 98% according to HPLC (Scheme 25). 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

Fluoride ion catalyzes the hydrosilylation of both alkyl and aryl aldehydes to silyl ethers that can be easily hydrolyzed to the free alcohols by treatment with 1 M hydrogen chloride in methanol.320 The most effective sources of fluoride are TBAF and tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF). Somewhat less effective are CsF and KF. Solvent effects are marked. The reactions are facilitated in polar, aprotic solvents such as hexamethylphosphortriamide (HMPA) or 1,3-dimethyl-3,4,5,6-tetrahydro-2(l //)-pyrirnidinone (DMPU), go moderately well in dimethylformamide, but do not proceed well in either tetrahydrofuran or dichloromethane. The solvent effects are dramatically illustrated in the reaction of undecanal and dimethylphenylsilane to produce undecyloxyphenyldimethylsi-lane. After one hour at room temperature with TBAF as the source of fluoride and a 10 mol% excess of silane, yields of 91% in HMPA, 89% in DMPU, 56% in dimethylformamide, 9% in tetrahydrofuran, and only 1% in dichloromethane are obtained (Eq. 164).320... 

The identification of bromocriptine mesilate in the dosage form can be carried out by thin layer chromatography using Merck plates with dichloromethane/methanol/formic acid 78 20 2 (v/v/v) and subsequent uv-visualization at 254 and 360 nm. Using this method, it is important to only air-dry the spot after application to the plate, since more vigorous evaporation of the solvent will give rise to artifacts (32). 

For a recovery of (S)-a,a-diphenylprolinol, which is the hydrolysis product of the CBS-catalyst (S)-5 (and likewise its synthetic precursor ), the aqueous phase is carefully adjusted to pH 10 with concentrated ammonia and extracted with diethyl ether (3 x 50 ml). The combined organic layers are washed with brine (50 mL) and dried over MgS04. Removal of the solvent by rotary evaporation yields 1.68 g (79%) of crude (S)-a,a-diphenylprolinol. This material is dissolved in dichloromethane / methanol 9 1 (3 ml) and filtered over Alox B (act. Ill, 80 g) with dichloromethane / methanol 9 1 as the eluent, to yield 1.64 g (77%) of (S)-a,a-diphenylprolinol as a white solid. 

Carotenoids A large number of solvents have been used for extraction of carotenoids from vegetables matrices, such as acetone, tetrahydrofuran, n-hexane, pentane, ethanol, methanol, chloroform [427-431], or solvent mixtures such as dichloromethane/methanol, tetrahydrofuran/methanol, -hexane/acetone, or toluene or ethyl acetate [424,432-435], SPE has been used as an additional purification step by some authors [422,426], Supercritical fluid extraction (SEE) has been widely used, as an alternative method, also adding CO2 modifiers (such as methanol, ethanol, -hexane, water, methylene chloride) to increase extraction efficiency [436-438], In addition, saponification can be carried out, but a loss of the total carotenoid content has been observed and, furthermore, direct solvent extraction has been proved to be a valid alternative [439],... 

The purification of bacterial constituents usually starts in a very conventional way with an extraction step of the crude broth at neutral or slightly acidic pH. Mycelium-forming organisms are separated by filtration, and the cell mass and the filtrate are extracted separately. For the liquid phase, adsorber resins allow high recovery rates of metabolites and low process costs due to repeated use of the resins. If liquid-liquid extraction has to be applied, medium or highly polar solvents are favored. Ethyl acetate is the solvent of choice, and only in few cases is butanol superior. To extract the moist cell material, ethyl acetate, acetone or dichloromethane/methanol can be used. 

The complexes were prepared from [CODRhCl]2 and 1.1 equiv of chiral diphosphine in dichloromethane as solvent. The chiral complex was added to a suspension of the support in dichloromethane. After being stirred for 24 h, the solid was filtered, washed with dichloromethane until the solvent showed no color, and afterward dried at room temperature for 16 h. In order to remove the excess of Rh complex not fixed to the solid carrier, the catalysts were extracted with methanol in a Soxhlet apparatus under reflux for 24h (Scheme 2.1.6.1). Both ICP-AES analysis and FTIR spectra of the remaining solvent indicated no content of homogeneous complex. The resulting catalysts had a pale yellow color similar to that of the homogeneous complex. 

To a solution of 2-(trimethylsilyl)ethyl CMmethyl 5-acetamido-4,7,8,9-tetra-0-acetyl-3,5-dideoxy-D-g/ycero-a-D-galacto-2-nonulopyranosylonate)-(2->3)-2,4,6-tri-0-benzoyl-P-D-galactopyranose (295 mg, 0.28 mmol) in 2 mL of dichloromethane was added trifluoro-acetic acid (2 mL) at 0°C, and the stirring was continued for 2 h at 0°C. Ethyl acetate (3 mL) and toluene (3 ml) were added and the solvents were evaporated. A second portion of toluene was added and the evaporation was repeated. Purification by flash chromatography on silica gel column with dichloromethane-methanol (20 1) gave the hemiacetal 21 (267 mg, quantitative) mp 85°C. 

Studies of the reactions of quinoxaline N-oxides under Reissert reaction conditions have led to some very interesting and unusual results. Thus, treatment of quinoxaline IV-oxide with PhCOCl/KCN in methanol or water under standard Reissert conditions gave 6-chloroquinoxaline as the major product (ca. 45%), and only small amounts of the desired 2-cyanoquinoxaline. Use of 3 equivalents of TMSCN in place of KCN and dichloromethane as solvent, however, gave 2-cyanoquinoxaline in 72% yield. When 2,3-diphenylquinoxaline iV-oxide was treated with 1 equivalent of PhCOCl in the presence of 3 equivalents of either KCN or TMSCN a mixture of products was always obtained irrespective of the solvent used. The most interesting of these products was the ring cleaved compound 1. 

The samples were ground and extracted with the solvent mixture 9 1 dichloromethane/methanol for 48 hours in a soxhlet system. The extracted samples were then demineralized to isolate kerogens using a detailed procedure described in (3). Hie kerogen was next solvent extracted a second time and treated with 0.2 N nitric acid at room temperature to separate pyrite from the organic matter and the solution was kept for determination of pyrite S content and isotopic composition. X-ray diffraction was used to verify the removal of pyrite from the kerogen. 

A study compared ASE and SFE to Soxhlet and sonication in the determination of long-chain trialkylamines (TAMs) in marine sediments and primary sewage sludge [89], The recoveries of these compounds by SFE at 50°C and 30 MPa with CO2 (modified dynamically with methanol or statically with triethylamine) were 10 to 77% higher than those by Soxhlet or soni-cation with dichloromethane methanol (2 1). ASE at 150°C and 17 MPa with the same solvent mixture as Soxhlet showed the highest extraction efficiency among the extraction methods evaluated. SFE exhibited the best precision because no cleanup was needed, whereas Soxhlet, sonication, and ASE extracts required an alumina column cleanup prior to analysis. SFE and ASE used less solvent and reduced the extraction time by a factor of 3 and a factor of 20 compared to sonication and Soxhlet, respectively. 

Olefins undergo a two-step oxidative process, with the first step leading to an epoxide that, in the presence of excess oxidant, subsequently is cleaved to afford aldehydes or ketones, dependent on the position of the olefinic bond. Oxidative reactions by peroxovanadates tend to be retarded by protic solvents such as water or methanol. For instance, oxidation of norbomene by picolinatooxomonoperoxo-vanadate in acetonitrile affords 22% of the product epoxide in 9 min. After 120 min in methanol solvent, only 1.8% yield was obtained. In dichloromethane, even cyclohexane is oxidized faster than this, giving 4% cyclohexanol and 9% cyclohexanone in 120 min, whereas benzene in acetonitrile yields 56% of phenol [23],... 

A mixture of 100 kg of 8-benzyltheophilline, 36 L of N-ethylethanolamine, 300 L of 1,2-dichlorethane and 71 kg of sodium carbonate was refluxed for 24 hours. Then 36 L of N-ethylethanolamine was added and the reaction mixture was refluxed. After cooling to the mixture was added the water and hydrochloric acid. The organic phase was extracted with hydrochloric acid. The acidic phase was neutralized with sodium carbonate and the 7-(N-ethyl-N-p-hydroxyethylaminoethyl)-8-benzyltheophilline was extracted with dichloromethane. The solvent was evaporated and the free base of 7-(N-ethyl-N-p-hydroxyethylaminoethyl)-8-benzyltheophilline was dissolved in methanol. Hydrochloride of 7-(N-ethyl-N-p-hydroxyethylaminoethyl)-8-benzyltheophilline was obtained by addition to the solution the hydrochloric acid yield 81%, melting point 185-186°C. 

A solution of 561 mg of 2-[3(S)-amino-2(R)-hydroxy-4-phenylbutyl]-N-tert-butyl-decahydro-(4aS,8aS) -isoquinoline-3(S)-carboxamide and 372 mg of N-(benzyloxycarbonyl)-L-asparagine in 20 ml of dry tetrahydrofuran was cooled in an ice/salt mixture. 189 mg of hydroxybenzotriazole, 161 mg of N-ethylmorpholine and 317 mg of dicyclohexylcarbodiimide were added and the mixture was stirred for 16 h. The mixture was then diluted with ethyl acetate and filtered. The filtrate was washed with aqueous sodium bicarbonate solution and sodium chloride solution. The solvent was removed by evaporation and the residue was chromatographed on silica gel using dichloromethane/methanol (9 1) for the elution to give 434 mg of 2-[3(S)-[[N-(benzyloxycarbonyl)-L-asparaginyl]amino]-2(R)-hydroxy-4-phenyl butyl]-N-tert-butyl-decahydro-(4aS,8aS)-isoquinoline-3(S)-carboxamide as a white solid from methanol/diethyl ether. 

---