Crystallization from solution crystallizers with fines removal

Into a 1500 ml. round-bottomed flask place 97-5 g. of finely-powdered sodium cyanide (1), 125 ml. of water, and a few chips of porous porcelain. Attach a reflux condenser and warm on a water bath until all the sodium cyanide dissolves. Introduce a solution of 250 g. (196 ml.) of n-butyl bromide (Sections 111,35 and 111,37) in 290 ml. of pure methyl alcohol, and reflux gently on a water bath for 28-30 hours. Cool to room temperature and remove the sodium bromide which has separated by filtration through a sintered glass funnel at the pump wash the crystals with about 100 ml. of methyl alcohol. Transfer the filtrate and washings to From n caproamide by SOClj method. 

To a solution of 16.3 g 2,5-dimethoxy-3,4-dimethylbenzaldehyde in 50 mL nitromethane there was added 3.0 g anhydrous ammonium acetate, and the mixture was heated on the steam bath overnight. There was then added an equal volume of MeOH, and with cooling there was obtained a fine crop of yellow crystals. These were removed by filtration, washed with MeOH, and air dried to provide 4.4 g of 2,5-dimethoxy-3,4-dimethy 1-6-nitrostyrene with a mp of 120-121 °C which was not improved by recrystallization from MeOH (50 mL/g). The mother liquors of the above filtration were diluted with H20 to the point of per-manent turbidity, then set aside in a cold box. There wasachunky, granular, tomato-red crystal deposited which weighed 2.5 g when dry. It had a mp of 118-119.5 °C, which was undepressed in mixed mp with the yellow sample. Both forms had identical NMR spectra (2.20, 2.25 CH, 3.72, 3.84 OCH, 6.80 ArH 7.76, 8.28 CH=CH, with 14 cycle splitting), infrared spectra, ultra violet spectra (max. 324 nm with shoulder at 366 nm in EtOH, two peaks at 309 and 355 nm in hexane), and microanalyses. Anal. (C HlsN04) C,H,N. 

To a solution of 10 g impure 2,5-dimethoxy-(t-butylthio)benzaldehyde in 75 mL of nitromethane there was added 1.0 g of anhydrous ammonium acetate, and the mixture was heated on the steam bath 1.5 h. Removal of the excess solvent/ reagent under vacuum produced an orange oil that was (not surprisingly) complex by TLC and which would not crystallize. A hot hexane solution of this oil was allowed to slowly cool and stand at room temperature for several days, yielding a mixture of yellow crystals and a brown viscous syrup. The solids were separated and recrystallized from 40 mL MeOH to give 3.7 g 2,5-dimethoxy-4-(t)-butylthio-B-nitrostyrenc as fine lemon-yellow crystals, with a mp of93-94 °C. A second crop... 

Clear-liquor advance from what is called a double draw-off crystallizer is simply the removal of mother liquor without simultaneous removal of crystals. The primary action in classified-fines removal is preferential withdrawal from the crystallizer of crystals of a size below some specified value this may be coupled with the dissolution of the crystals removed as fines and the return of the resulting solution to the crystallizer. Classified-product removal is carried out to remove preferentially those crystals of a size larger than some specified value. In the following discussion, the effects of each of these selective removal functions on crystal size distributions will be described in terms of the population density function n. Only the ideal solid-liquid classification devices will be examined. It is convenient in the analyses to define flow rates in terms of clear liquor. Necessarily, then, the population density function is defined on a clear-liquor basis. 

Alanine 60 Ethyl cyanoacetate (30 g) is converted into / -alanine ethyl ester by catalytic hydrogenation on Pt02 in glacial acetic acid/sulfuric acid. After removal of the catalyst the solution is concentrated in a vacuum so far as possible, and the residue is poured into water (300 ml), treated with finely powdered barium hydroxide (100 g), and boiled for 3 h. Then, after cooling, the barium is precipitated with dilute sulfuric acid and separated by centrifugation. The solution is concentrated greatly in a vacuum, whereupon the -alanine rapidly crystallizes (17 g, 72%) recrystallized from aqueous alcohol-ether, it has m.p. 195°. 

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