Sodium sulfate concentration, added

The mixture is distilled until most of the ether has been removed and then refluxed for 8 hr. Ethyl acetate is added to decompose the excess reagent and concentrated aqueous sodium sulfate is then added until the precipitate begins to adhere to the sides of the flask. Finally ca. 100 g of solid sodium sulfate is added, the salts are removed by filtration and washed well with dioxane. Evaporation of the solvent gives a solid residue which is dissolved in 60 ml of chloroform and shaken with 3.5 g of manganese dioxide for 16 hr. Subsequently another 3.5 g of manganese dioxide is added and shaking continued for a further 16 hr. The solid is removed by filtration and washed well with hot chloroform. Evaporation of solvent and crystallization of the residue from acetone-hexane affords 0.51 g (72%) of 17a-hydroxy-17jff-ethylandrost-4-en-3-one mp 145-148°. 

For some nonionic, nonpolar polymers, such as polyethylene glycols, normal chromatograms can be obtained by using distilled water. Some more polar nonionic polymers exhibit abnormal peak shapes or minor peaks near the void volume when eluted with distilled water due to ionic interactions between the sample and the charged groups on the resin surface. To eliminate ionic interactions, a neutral salt, such as sodium nitrate or sodium sulfate, is added to the aqueous eluent. Generally, a salt concentration of 0.1-0.5 M is sufficient to overcome undesired ionic interactions. 

Electrostatic effects have long been recognized in commercial HPLC columns for SEC of proteins (15,21,22). The usual remedy is to add 100 mM salt to the mobile phase. This works here too the Lys and Asp peaks collapse into the Gly peak with 100 mM salt (Eig. 8.8). High concentrations of sodium sulfate were added to determine the role played in SEC by hydrophobic interactions (sodium sulfate, a structure-forming salt, strengthens such interactions). Sodium sulfate increased the retention only of the most hydrophobic amino acids to any extent, and then only when the concentration approached 1 M. Clearly, hydrophobic interaction cannot account for the elution order of amino acids on PolyHEA. 

Strontium sulfate (SrS04) will precipitate when a solution of sodium sulfate is added to a strontium nitrate solution. What will be the strontium ion, Sr2+, concentration remaining after 30.0 mL of 0.10 M Na2S04 solution are added to 70.0 mL of 0.20 M Sr(N03)2 solution ... 

Trimethylaluminum (20 mL of a 2 M solution in toluene, 40 mmol) is added to titanocene dichloride (5.0 g, 20 mmol) under inert gas. The resulting mixture is stirred at room temperature for 3 d with evolution of methane. The mixture is then cooled to 0 °C and a solution of phenyl benzoate (4.0 g, 20 mmol) in THE (20 mL) is added over 5 min. The resulting mixture is left to warm to room temperature within 45 min and is then diluted with anhydrous diethyl ether (50 mL). Approximately 50 drops of a 1 M aqueous sodium hydroxide solution are carefully added over 10-20 min. When gas evolution has ceased anhydrous sodium sulfate is added and the slurry is filtered through a pad of Celite. After rinsing with diethyl ether the combined filtrates are concentrated and the product is purified by column chromatography (150 g basic alumina, pentane/diethyl ether 9 1). 2.8 g (70%) of the title compound is obtained. NMR (250 MHz, CDCI3) 5 4.45 (d, 2.3 Hz, IH), 5.05 (d, 2.3 Hz, IH), 7.06-7.11 (m, 3H), 7.29-7.38 (m, 5H), 7.66-7.70 (m, 2H). 

The surrogate compounds were mono-, tetra-, octa-, deca- C-PCBs, dg-naphthalene, C-PCP and C-phenol. The soil samples were dried with Na2S04 (60 g) and then Soxhlet extracted with hexane acetone (9 1) for 16 h. The extract was dried with sodium sulfate, concentrated, and split. While one portion was held for other analyses, the other portion was placed on a 3% deactivated silica gel column and eluted with increasing solvent polarity systems [hexane, followed by methylene chloride hexane (1 1), and then methylene chloride acetone (95 5)]. The extracts were combined and reduced to 1 mL, split and two internal standards added (tetrafluorobiphenyl and di2 Chrysene). The extracts were chromatographed on a 15-m DB-5 fused silica capillary column and detected with flame ionization (FID). Sludge samples were extracted according to the EPA sludge protocol (2) developed at Midwest Research Institute. 

The flask is placed in an ice-salt mixture and the contents decomposed by the gradual addition of 300 cc. of saturated ammonium chloride solution and 100 cc. of water (Note 4). The aqueous layer is removed by means of a 1500-cc. separatory funnel and sufficient ether is added to dissolve the yellow precipitate. The total volume of ether solution is about one liter. This is washed with two 200-cc. portions of water, and the three aqueous layers are extracted consecutively with a 100-cc. portion of ether. The combined ether solution is dried over 30 g. of anhydrous sodium sulfate, concentrated on the steam bath to a volume of about 200 cc., and cooled to room temperature. The product which crystallizes is collected with suction and washed with two 25-cc. portions of ether. The yield is 35-38 g. of light yellow product, m.p. 122-123°. The ether is completely removed from the combined filtrates by heating on the steam bath, and the black oil is allowed to stand overnight. The semi-solid mass is filtered with suction and washed with a minimum amount of cold ether. In this way an additional 6-7 g. of yellow material is obtained which melts at 119-121°. 

The liquid monomers were stored with a trace of iodine (0.01-0.1%) to prevent polymerization. When such a monomer was used to prepare a polymer, the charge of monomer or mixed monomers was washed with a few drops of concentrated aqueous sodium thiosulfate to remove the iodine. Then a small amount of sodium sulfate was added and the monomer charge was decanted. 

Typical procedure. 2,3,4,6-Tetra-0-acetyl-a.-D-glucopyranosfl isocyanide 1644 [1225] To a solution of 2,3,4,6-tetra-O-acetyl-a-n-glucopyranosyl formamide 1643 (2.80 g, 7.47 mmol), triethylamine (4.48 mL, 32.2 mmol), and tetrabromomethane (8.00 g, 24.1 mmol) in dichloromethane (85 mL) cooled to —20 °C under nitrogen atmosphere was added a solution of triphenylphosphine (6.30 g, 24.1 mmol) in dichloromethane (5 mL). After stirring at —20 °C for 3 h, the solution was diluted with diethyl ether, washed with aqueous ammonium chloride solution, water, and brine, and dried over anhydrous sodium sulfate. Concentration and purification by chromatography on silica gel (diethyl ether/hexane, 2 1) gave 2,3,4,6-tetra-O-acetyl-a-o-glucopyranosyl isocyanide 1644 (0.86 g, 79%). 

For example, let s consider a solution containing 10 mol/L of barium chloride and 10 mol/L of strontium chloride. A saturated solution of sodium sulfate is added to it. The problem is to calculate the concentration of the remaining ion (the most insoluble) when the second begins to precipitate. The solubility products are /fs(BaS04) = 1.1 X 10 ° and /fs(SrS04) = 2.8 x 10 . An examination of the solubility products shows that barium ions precipitate first. Just at the beginning of the strontium precipitation, both solubility products are satisfied simultaneously and [Sr +l = 10 mol/L. Therefore, we can write... 

Benzene (4.0 mL), JV,Ar-dimethylethane-1,2-diamine (13.2 mg, 0.15 mmol), and 4-bromoanisole (93.5 mg, 0.5 mmol) are added to a Schlenk tube charged with iron(lII) chloride (12.1 mg, 0.075 mmol) and lithium bis(trimethylsilyl)amide (167 mg, 1.0 mmol) under an argon atmosphere at room temperature. The resulting reaction mixture is stirred at 80 °C for 48 h. After cooling to room temperature, the mixture is quenched and extracted with ethyl acetate (3 x 10 mL). The organic layers are combined, dried over sodium sulfate, concentrated under reduced pressure, and then purified by column chromatography on silica gel (ethyl acetate/petroleum ether = 1 100) to yield 4-methoxybiphenyl mp 86-87 74.5 mg (81%) colorless solid. ... 

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