Dichloromethane, purification

To a solution of 4-nitrobenzaldehyde (151 mg, 1.0 mmol) and zinc(Il) chloride (0.15 mL, 1 M in dichloromethane, 0.15 mmol) in dichloromethane (5 mL) is added a freshly-prepared solution of ri -allyl-Fp (5 mL, 0.5 M, 2.5 mmol) under an argon atmosphere. The reaction is stirred at room temperature for 14 h and then added dropwise over a 30-min period to a solution of ceric ammonium nitrate (4.1 g, 7.5 mmol) in methanol (20 mL) at -78 °C under a carbon monoxide atmosphere. After the solution is stirred at -78 °C for an additional 30 min, the solvent is warmed to room temperature and allowed to stir for an additional 30 min, and then it is evaporated in vacuo. The residue is triturated several times with small portions of dichloromethane until the washings are colorless. After removal of the solvent, the residue is purified by column chromatography (Si02, dichloromethane and then 2% acetone in dichloromethane). Purification by a second chromatography affords the tetrahydrofuran ester (3.1 1 mixture of diastereoisomers) as a yellow oil 178 mg (71%). ... 

A mixture of 1.759 g of 2a.3a-epithio-5Q -endrostan-17 3-ol, 2.3 ml of 1-methoxycyclopen-tene, 20 mg of pyridine salt of p-toluenesulfonic acid and 20 ml of t-butanol is stirred for 4 hours at room temperature. The reaction mixture is poured into an aqueous solution of sodium carbonate and the whole extracted with dichloromethane. The extract is dried over anhydrous sodium sulfate and evaporated to remove solvent. Purification of the residue by chromatography over alumina gives 1.487 g of 17/3-(1-methoxycyclopentyl)oxy-2a,3a-epi-thio-50 -androstane. Yield68.2%. MP98°Cto 101°C. 

The submitters used reagent-grade dichloromethane without purification. The checkers dried dichloromethane by distillation from phosphorous pentoxide. 

This procedure provides a convenient method for the esterification ol a wide variety of carboxylic acids. The reaction proceeds smoothly with sterically hindered acids6 and with acids which contain various functional groups. Esters are obtained in high purity using Kugelrohr distillation as the sole purification technique. In cases where traces of dichloromethane present no problems, the crude product is usually pure enough to be used directly in subsequent reactions. Methyl and ethyl ethers of phenols may also be prepared by this procedure (see Note 8). 

A solution of mcpba (11.5 mmol) in dichloromethane (30 ml) was added to a stirred solution of the vinylsilane (10 mmol) in dichloromethane (50 ml) at 0°C. After stirring for 1 h, the mixture was washed with aqueous sodium hydrogen sulphite (50 ml), saturated sodium hydrogen carbonate solution and brine. The organic solution was then dried and concentrated, prior to purification by distillation or chromatography. 

To a stirred solution of the alkynylsilane (20 mmol) and triethylbenzyl-ammonium chloride (0.7 mmol) in MeCN (15 ml) cooled to 0°C was added aqueous sodium hydroxide (15 ml, 12m). After 5-10min, the mixture was diluted with ether and extracted with ether/dichloromethane. Drying, concentration and suitable purification gave the free alkyne (80-90%). 

Hexen-l-ol and triethylamine were purchased from Acros Organics and used without further purification. Alternatively, 5-hexen-l-ol may be prepared from 2-(chloromethyl)tetrahydropyran according to the literature procedure for the preparation of 4-penten-l-ol (Brooks, L. A. Snyder, H. R. Org. Synth. Coll. Vol. Ill 1955, 698). Dichloromethane (certified ACS) was purchased from Fisher Scientific and was used as received. 

Diisopropylethylamine was purchased from Alfa-Aesar chemical Company and used without further purification. Dichloromethane was purified by pressure filtration through activated alumina. 

Soluble support-based synthetic approaches offer the advantages of both homogeneous solution-phase chemistry (high reactivity, ease of analysis) and solid-phase synthesis (large excess of reagents, simple product isolation and purification) [98,99]. As a representative example, PEG, one of the most widely used soluble polymers, has good solubility in most organic solvents (i.e., dichloromethane, acetonitrile, dimethylformamide, and toluene), but it... 

Reagent-grade dichloromethane was used without further purification. 

Catalytic incineration has been appHed in the abatement of chlorinated VOC emissions in the pharmaceutical industry. The major compounds in the emission mixture are dichloromethane, perchloroethylene, dimethylformamide, oxitol, and toluene. The incinerator operates normally at 400-500 °C, but when emissions contain perchloroethylene the temperature is increased up to 500-600 °C. The emission mixture also contains water, which pushes the selectivity further toward HCl formation instead of formation of CI2. After oxidation, the product gases are washed with NaOH scrubbers. The purification level of over 99% can be achieved with the incinerator, the activity of which has been shown to be very stable after one year of continuous operation [69-71]. 

For example, an alumina layer with a nonaqueons mobile phase was optimized for the separation of the taxoid fraction from ballast snbstances [5]. Figure 11.3 shows the densitogram obtained for Taxus baccata cmde extract chromatographed on the alnmina layer developed with nonaqueous elnents. The nse of ethyl acetate and dichloromethane enables elntion of nonpolar fractions (chlorophylls and waxes) and purification of the starting zone (Figure 11.3a). In this system, all taxoids are strongly retained on the alumina layer. The use of a more polar mobile phase... 

Synthesis of Allylic Alcohol Xa. A 3.84 g sample of olefin VII was treated with m-chloroperoxybenzoic acid (MCPBA) in dichloromethane for 1.5 hours at 0°C and 2.5 hours at 20°C. The NMR spectrum of the crude product indicated a mixture of approximately 75% epoxide VIII and 25% IX (structural assignments based upon assumed epoxidation preferentially from the less hindered side). Purification by column chromatography furnished 0.61 g of IX and 2.58 g of VIII. The separation was performed for characterization purposes the crude epoxidation mixture was suitable for subsequent transformations. 

General Considerations. The following chemicals were commercially available and used as received 3,3,3-Triphenylpropionic acid (Acros), 1.0 M LiAlH4 in tetrahydrofuran (THF) (Aldrich), pyridinium dichromate (Acros), 2,6 di-tert-butylpyridine (Acros), dichlorodimethylsilane (Acros), tetraethyl orthosilicate (Aldrich), 3-aminopropyltrimethoxy silane (Aldrich), hexamethyldisilazane (Aldrich), tetrakis (diethylamino) titanium (Aldrich), trimethyl silyl chloride (Aldrich), terephthaloyl chloride (Acros), anhydrous toluene (Acros), and n-butyllithium in hexanes (Aldrich). Anhydrous ether, anhydrous THF, anhydrous dichloromethane, and anhydrous hexanes were obtained from a packed bed solvent purification system utilizing columns of copper oxide catalyst and alumina (ether, hexanes) or dual alumina columns (tetrahydrofuran, dichloromethane) (9). Tetramethylcyclopentadiene (Aldrich) was distilled over sodium metal prior to use. p-Aminophenyltrimethoxysilane (Gelest) was purified by recrystallization from methanol. Anhydrous methanol (Acros) was... 

The crude product is dissolved in a minimum amount of dichloromethane and adsorbed onto 25 g of silica gel (32-63 micron) by subsequent evaporation of the dichloromethane under reduced pressure. The sample of dry, dark brown silica gel is added to the top of a column containing 500 g of silica gel (32-63 micron) with a mobile phase of hexanes. The polarity of the mobile phase is gradually increased from hexanes to 95 5 hexanes-ethyl acetate. The fractions containing the desired product (Rf = 0.26, 95 5 hexanes-ethyl acetate) are combined and concentrated under reduced pressure to yield 6.9 g of 3 as a yellow solid. Additional purification is required to remove traces of tin by-products. Compound 3 is dissolved in 70 mL of... 

For this purpose, perfluorooctanesulfonyl-tagged benzaldehydes were reacted with 1.1 equivalents of a 2-aminopyridine (or 2-aminopyrazine), 1.2 equivalents of an isonitrile, and a catalytic amount of scandium(III) triflate [Sc(OTf)3] under micro-wave irradiation in a mixture of dichloromethane and methanol (Scheme 7.85). A ramp time of 2 min was employed to achieve the pre-set temperature, and then the reaction mixture was maintained at the final temperature for a further 10 min. The fluorous tag constitutes a multifunctional tool in this reaction, protecting the phenol in the condensation step, being the phase tag for purification, and serving as an acti-... 

All the procedures described were performed using dry solvents which were freshly distilled under nitrogen. Tetrahydrofuran and ether were distilled from sodium benzophenone ketal under nitrogen, and dichloromethane from calcium hydride under nitrogen. Petroleum ether (b.p. 40-60 °C) was distilled. Starting materials and solvents were used as obtained from commercial suppliers without further purification unless specified otherwise. 

The reaction mixture was stirred for 2h at room temperature until TLC analysis indicated that the reaction was complete. The solution was filtered through Celite and washed with dichloromethane. The filtrate was washed with saturated aqueous NaHC03 and H20. The organic phase was dried (MgS04), filtered and the filtrate was concentrated to dryness. Purification of the crude product by column chromatography over silica gel afforded the target compound. 

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