Solid bottom-filtration techniques

A prototype of a microwave reaction vessel that takes advantage of bottom filtration techniques was presented by Erdelyi and Gogoll in a more recent publication. Therein, the authors described the use of a modified reaction vessel (Fig. 7.2) for the Emrys instruments (see Section 3.5.1) with a polypropylene frit, suitable for the filtration /cleavage steps in their microwave-mediated solid-phase Sonogashira coupling (see Scheme 7.19) [21]. 

A recent article describes the construction and use of a parallel polypropylene reactor comprising of cylindrical, expandable reaction vessels with porous frits at the bottom (Fig. 7.4)21. This is the first description of reaction vessels for microwave-assisted synthesis that may be useful for carrying out solid-phase synthesis using bottom filtration techniques in conjunction with microwave heating. However, at the time when tins chapter was being written no application of this system for solid-phase synthesis had been reported. 

The combination of microwave-assisted chemistry and solid-phase synthesis applications is a logical consequence of the increased speed and effectiveness offered by microwave dielectric heating. While this technology is heavily used in the pharmaceutical and agrochemical research laboratories already, a further increase in the use of microwave-assisted solid-phase synthesis both in industry and in academic laboratories can be expected. This will depend also on the availability of modern microwave instrumentation specifically designed for solid-phase chemistry, involving for example dedicated vessels for bottom filtration techniques. 

Clarity. In some soy processing plants, high levels of HI may partition with the lecithin gums on separation from the oil. This lipid-insoluble material can cause haziness in fluid lecithins. With modem miscella and oil filtration techniques, lecithins with very low HI contents can be produced. Consequently, modern lecithins are clear. Additionally, moisture can also contribute to lack of clarity. Generally, moisture levels over 1% can cause haziness. Besides being an aesthetic problem, if haziness is caused by HI material, it can result in sediment over time solid particles may appear on the bottom of an otherwise clear liquid product containing lecithin. 

Upon completing the distillation, extract the distillate with two 15-mL portions of dichloromethane and put the extract in the 50-mL round-bottom flask. Use a few milliliters of dichloromethane to rinse any solid in the condenser into the flask containing the dichloromethane extract. Remove the dichloromethane by simple distillation. Alternatively, use rotary evaporation or other techniques to remove the solvent. Recrystallize the residue from methanol, and isolate the product by vacuum filtration. 

A. Benzamides. In a small round-bottom flask equipped for magnetic stirring, dissolve 0.3 g of the amine in 3 mL of dry pyridine. Slowly add 0.3 mL of benzoyl chloride to this solution. Affix a drying tube dlrectlyto the flask and heat the reaction mixture to 60-70 °C for 30 min then pour the mixture into 25 mL of water with stirring. If the solid derivative precipitates at this time, isolate it by vacuum filtration, and dissolve it in 10 mL of diethyl ether when it is nearly dry. If no precipitate forms, extract the aqueous mixture twice with 5-mL portions of diethyl ether. Combine the extracts. Wash the ethereal solution sequentially with 5-mL portions of water, 1.5 M HCI, and 0.6 A//sodium bicarbonate solution. Dry the ethereal layer over anhydrous sodium sulfate, filter or decant the dried solution, and remove the diethyl ether by one of the techniques described in Section 2.29. Recrystallize the solid derivative from one of the following solvents cyclohexane-hexane mixtures, cyclohexane-ethyl acetate mixtures, 95% ethanol, or aqueous ethanol. 

In a dinitrogen-filled glove box, 1 (0.420 g, 1.2 mmol) and ortAo-tolyllithium (0.18 g, 1.8 mmol) are transferred to a 50 mL round-bottomed flask fitted with a swivel frit assembly. The reaction mixture is stirred for 12 h at room temperature, and the volatile materials are removed under reduce pressure. Petroleum ether (10 mL) is transferred onto the solid in vacuum, and the resulting solution is filtered to remove LiCl. The residue is washed with additional pentane (2 X10 mL) using standard swivel frit techniques. The filtered washings are combined, concentrated to 3 mL, and cooled to —78°C. The resulting off-white precipitate is isolated by cold filtration. Yield 0.285 g (59%). 

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