Filtration sieve filters

NMe4[CBnMe12]. A solution of Cs[CBnMe12] (2g) in ether (250 mL) is extracted with a 20% aqueous solution of NMe4Cl (3 x 100 mL). Combined aqueous fractions are washed with ether (3 x 50 mL), dried with activated molecular sieves, filtered, and rinsed with dry ether (3 x 20 mL). The filtrate is evaporated, and the resulting powder is washed with warm (40-50°C) hexane under vigorous stirring (3 x 100 mL). The residue is dried under reduced pressure at... 

The chief disadvantages of a Buchner funnel for filtration are (i) it is impossible to see whether the underside of the perforated plate is perfectly clean, and (ii) the larger sizes are top heavy. The first drawback is absent in the Jena slit-sieve funnel (Fig. 11,1, 7,/) this is an all-glass funnel provided with a sealed-in transparent plate, perforated by a series of angular slots, upon which the filter paper rests. The sintered glass... 

Direct interception refers to a sieve-type mechanism in which contaminants larger than the filter pore size are directly trapped by the filter. This sieve retention mechanism of particle arrest is the mechanism of choice and occurs owing to geometric or spatial restraint. This type of particle arrest is considered to be absolute, that is, it is independent of filtration conditions. 

The purity of oxygen from chlorate candles before and after gas filtration is indicated in Table 2. A particulate filter is always used. Filter chemicals are HopcaUte, which oxidizes CO to CO2 molecular sieves (qv), which remove chlorine compounds and basic materials, eg, soda lime, which removes CO2 and chlorine compounds. Other than H2O and N2, impurity levels of <1 ppm can be attained. Moisture can be reduced by using a desiccant (see Desiccants). Gas purity is a function of candle packaging as well as composition. A hotter burning unit, eg, one in which steel wool is the binder, generates more impurities. 

The theory of filtration of aerosols from a gas stream is much more involved than the sieving action which removes particles in a liquid medium. Figure 29-1 shows three of the mechanisms of aerosol removal by a filter. In practice, the particles and filter elements are seldom spheres or cylinders. 

Pressure filters are worth noting. These are usually set up in the form of steel cylinders positioned vertically. Another variation consists of using horizontal filtration groups. This has the drawback that the surface loading is variable in the different layers of the filter bed moreover, it increases with greater penetration in the filter bed (the infiltration velocity is lowest at the level of the horizontal diameter of the cylinder). The filter bottom usually consists of a number of screens or mesh sieves that decrease in size from top to bottom or, as an alternative, perforated plates supporting gravel similar to that used in the filter bottoms of an open filter system. 

One of the oldest, simplest, and most efficient methods for removing solid particulate contaminants from gas streams is by filtration through fabric media. The fabric filter is capable of providing high collection efficiencies for particles as small as 0.5 pm and will remove a substantial quantity of particles as small as 0.01 pm. In its simplest form, the industrial fabric filter consists of a woven or felted fabric through which dust-laden gases are forced. A combination of factors results in the collection of particles on the fabric filters. When woven fabrics arc used, a dust cake eventually forms. This, in turn, acts predominantly as a sieving mechanism. When felted fabrics are used, the dust cake is minimal or nonc.xistent. 

Aminocephalosporanic acid (5.00 g) which passed through a 100-mesh sieve was suspended in boiling ethyl acetate (200 ml), and 2-thienylacetyl chloride (Cagniant, Bull. Soc. Chim. France, 1949,847) (4.42 g, 1.5 equiv.) was added in ethyl acetate (20 ml). The mixture was boiled under reflux for 40 minutes, cooled, and filtered. Aniline (5.03 ml) was added, and after 1 hour the mixture was extracted with 3% sodium hydrogen carbonate solution (1 x 150 ml, 2 X 100 ml, 1 x 50 ml) and the alkaline extracts washed with ethyl acetate (3 x 100 ml). The aqueous solution was acidified to pH 1.2, and extracted with ethyl acetate (2 x 150 ml). The ethyl acetate extract was washed with water (4 x 40 ml), dried (MgS04), and concentrated in vacuo to low volume. The crude 7-2 -thienylacetamidocephalosporanic acid (2.5 g) which separated was collected by filtration. Evaporation of the filtrate gave a further 2.68 g (71%) of the product, which was purified by crystallization from ethyl acetate, then aqueous acetone, MP 150°Cto 157°C (decomp.). 

A mixture of 7 (0.200 g. 0.97 mmol) and molecular sieves type 3A, 1/16 inch pellets (1 g) in benzene (40 mL) was refluxed for 6 h. The molecular sieves were filtered of) and the filtrate was evaporated in vacuo to leave 6c yield 0.130g (75%) pale-yellow prisms mp 46-49 C (acetone/hexanes). 

With Aromatic Aldehydes. To a solution of 10.3 g (20 mmol) of 2,3,4,6-tetra O-pivaloyl-/ -i>galactopyra-nosylaminc in 50 rnL of /-PrOI 1 or heptane are added 30 mmol of the corresponding aromatic aldehyde and 30 drops of acetic acid. After 30 min to 2 h, the Schiff base precipitates from the /-PrOH solution. When the reaction is carried out in heptane, 2 g of Na2S04 or 3 g of 3 A molecular sieves are added after 15 min, and the mixture is filtered. On cooling to 0 °C the Schiff base crystallizes from the heptane solution. The aldimines are collected by filtration and rapidly washed with ice-cold /-PrOH or pentane, respectively. Generally, they are pure enough for further transformations. 

To a solution of the titanocene(II) reagent 29 in THF (42 mL) in a 300-mL round-bottomed flask, prepared from titanocene dichloride (6.54 g, 26.3 mmol), magnesium turnings (0.766 g, 31.5 mmol), triethyl phosphite (8.96 mL, 52.5 mmol), and finely powdered 4 A molecular sieves (1.31 g) according to the procedure described above, was added a solution of l,l-bis(phenylthio)cyclobutane (63 2.29 g, 8.40 mmol) in THF (14 mL). The reaction mixture was stirred for 15 min. and then a solution of (S)-isopropyl 3-phenylpro-panethioate (91 1.46 g, 7.00 mmol) in THF (21 mL) was injected dropwise over a period of 10 min. The reaction mixture was refluxed for 1 h, then cooled, whereupon 1 m aq. NaOH solution (150 mL) was added. The insoluble materials produced were removed by filtration through Celite and washed with diethyl ether. The aqueous layer was separated and extracted with diethyl ether. The combined ethereal extracts were dried (Na2S04), filtered, and concentrated. The residual liquid was purified by column chromatography (silica gel, hexane) to afford 1.33 g (77%) of (l-isopropylthio-3-phenylpropan-1 -ylidene) cyclobutane (92). 

To a solution of thioglycoside (1.0 equiv), 1-benzenesulfinyl piperidine (1.0 equiv), TTBP (2.0 equiv), and freshly activated 3 A powdered molecular sieves in dichloromethane (25.0 ml mmol-1) was added trifluoromethanesulfonic anhydride (1.1 equiv) at —60 °C under an argon atmosphere. The reaction mixture was stirred for 5 min, after that a solution of the glycosyl acceptor (1.5 equiv) in dichloromethane (4.0 ml mmol-1) was added. The reaction mixture was stirred at — 60 °C for 2 min, after that it was slowly warmed to room temperature and quenched by the addition of saturated aqueous NaHC03. The organic layer was washed with brine, dried (MgS04), filtered and the filtrate was concentrated to dryness. Purification of the crude product by column chromatography over silica gel afforded the product. 

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