Solution crystallization procedures

Already, more than 25 years ago, Toda et al. reported the mechanochemical preparation of crystalline host-guest inclusion compounds and of charge-transfer (CT) systems. CT systems have also been studied by Kuroda et al., who were able to obtain multicomponent systems based on racemic bis-)8-naphtol, benzoquinone, and anthracene the cocrystal formation could be easily followed by the change in color of the solid mixtures. Importantly, this material was not accessible from conventional solution crystallization procedures and required structure determination from X-ray powder diffraction. ... 

Solution Crystallization Procedures Most 8 clathrate and intercalate co-crystals can be easily prepared by solution crystallization procedures (e.g., casting, spin-coating, gel desiccation [76-88]) or by solvent-induced crystallization in amorphous SPS films [89-92],... 

Films and Three Different Uniplanar Orientations of the Cocrystalline Phases Film processing in the presence of suitable solvents can lead to the formation of co-crystalline films exhibiting three different kinds of uniplanar orientations of the co-crystalline phases [69-75,95], The degree and the kind of uniplanar orientation depends on the selected technique (solution crystallization procedures or solvent-induced crystallization in amorphous... 

The visible crystals that develop during a crystallization procedure are built up as a result of growth either on nuclei of the material itself or surfaces of foreign material serving the same purpose. Neglecting for the moment the matter of impurities, nucleation theory provides an explanation for certain qualitative observations in the case of solutions. 

The e.s.r. spectra obtained for several oxovanadium (iv) complexes, including [VO(acac)2], orientated in nematic glasses, compare favourably with those obtained by dilute single-crystal procedures.X-Band e.s.r. spectra of magnetically dilute glasses at 77 K show that EtOH and py form weak complexes with [VO(P-dik)] molecules [P-dik = acac, bzac, tropolone, 3-bromotropolone, (35), or (36)], and that vanadium(iv) in solutions of these... 

The (S)-amine 23 was synthesized after 1 day and the enzyme was recovered from the reaction by filtration, then washed and reused. The residual amine was extracted from the MTBE solution with dilute phosphoric acid (pH 2.9-4.4). The aqueous extract was concentrated to give a phosphate salt of the (S)-sec-butylamine with 99.7%. This was followed by a crystallization procedure in ethanol to give 99.8% and 50% yield. 

Synthesis of MCM-41 with Additives. The hydrothermal crystallization procedure as described earlier [10] was modified by adding additional salts like tetraalkylammonium (TAA+) bromide or alkali bromides to the synthesis gel [11]. Sodium silicate solution ( 14% NaOH, 27% Si02) was used as the silicon source. Cetyltrimethylammonium (CTA) bromide was used as the surfactant (Cl6). Other surfactants like octadecylltrimethylammonium (ODA) bromide (C,8), myristyltrimethylammonium (MTA) bromide (C,4) were also used to get MCM-41 structures with different pore diameter. Different tetralkylammonium or alkali halide salts were dissolved in little water and added to the gel before addition of the silica source. The final gel mixture was stirred for 2 h at room temperature and then transferred into polypropylene bottles and statically heated at 100°C for 4 days under autogeneous pressure. The final solid material obtained was washed with plenty of water, dried and calcined (heating rate l°C/min) at 560°C for 6 h. 

The crystallization procedure employed by Pasteur for his classical resolution of ( )-tartaric acid (Section 5-1C) has been successful only in a very few cases. This procedure depends on the formation of individual crystals of each enantiomer. Thus if the crystallization of sodium ammonium tartrate is carried out below 27°, the usual racemate salt does not form a mixture of crystals of the (+) and (—) salts forms instead. The two different kinds of crystals, which are related as an object to its mirror image, can be separated manually with the aid of a microscope and subsequently may be converted to the tartaric acid enantiomers by strong acid. A variation on this method of resolution is the seeding of a saturated solution of a racemic mixture with crystals of one pure enantiomer in the hope of causing crystallization of just that one enantiomer, thereby leaving the other in solution. Unfortunately, very few practical resolutions have been achieved in this way. 

The high stability of the aluminate ion allows the production of concentrated solutions of aluminum with the virtual exclusion of the main metallic impurity, viz. iron as an oxide residue. The resultant impure aluminate solution is clarified and its temperature reduced when the reverse of the above reaction occurs with the formation of A1203,3H20 by a slow crystallization procedure. The high-purity alumina trihydrate product is calcined and then reduced electrochemically in a molten fluoride bath by the well-known Hall-Heroult process. The major problems in the Bayer process have their origin in the coordination chemistry of aluminum in alkaline solutions. The... 

A solution containing 442 g of N,N-dimethyl-3-phenyl-3-hydroxypropylamine in 5 L of chloroform was saturated with dry gaseous hydrogen chloride. 400 ml of thionyl chloride were then added to the chloroform solution at a rate sufficient to maintain reflux. The solution was refluxed an additional 5 h. Evaporation of the chloroform and other volatile constituents in vacuo yielded N,N-dimethyl-3-phenyl-3-chloropropylamine hydrochloride which was collected by filtration, and the filter cake washed twice with 1500 ml portions of acetone. The washed crystals weighed about 500 g and melted at 181°-183°C with decomposition. An additional 30 g of compound were obtained from the acetone wash by standard crystallization procedures. The structure of the above compound was verified by NMR and titration. 

Compound 50c was obtained in ca. 25% yield as a precipitate from the acid-catalyzed condensation of pyrogallol and isovaleraldehyde. No evidence of any hexamer was found in the solid material. To convert this material into the hexamer (50c)6, the original precipitate can be dissolved in Et20, acetone, or methanol, with a few drops of nitrobenzene or o-dinitrobenzene, followed by crystallization upon slow evaporation. The hexamer may also be obtained by thermal treatment of the initial precipitate or the initial filtrate. The product in the initial filtrate may be converted into hexamer by extraction in Et20, followed by evaporation to dryness with subsequent dissolution in methanol. The methanol solution is then heated to 120-150 °C for at least 12 h. Methanol may be removed under vacuum to yield a red-brown solid. Colorless hexameric spherical capsules are obtained from this solid utilizing the crystallization procedure described for the initial precipitate. 

Combined Synthesis and Crystal Growth (a) Solution Reaction Procedures... 

Catalyst. One catalyst, prepared to contain equi-atomic amounts of lead, magnesium, and aluminum, was prepared for this study. Synthesis was accomplished by the hydrotalcite preparation procedure reported by Reichle 12). It is a standard aqueous precipitation and crystallization procedure that avoids filtering and washing problems associated with gel precipitates. A solution of Pb, Mg, and Al nitrates was added under agitation to a solution of NaOH and Na2C03 and maintained at 70 C for thirty hours. This caused precipitation of crystalline material. 

The second method of disposing of the completed nitration mixture consists in cooling the products while stiU in the nitrating kettle, and thus forcing out the TNT from its acid solution. This procedure, of course, results in more dissolved TNT in the spent acid, but the time saved in the separation is very great, since the crystallization in pans requires about four days, while the nitrator separation requires but a few minutes. The nitrator separation is used especially in plants where the spent acid goes into the next charge of... 

Crystallization of polymers can be carried out from the molten state or from solutions. These procedures lead to different morphologies. Starting from solution, single crystals are obtained with the shape of lamella (plates). Starting form the melt, small crystalline lamellae or crystallites are formed that are organized into complex structures known as spherulites. 

Various techniques have been used to prepare single crystals of polydiacetylene. Bulk crystals obtained by conventional crystallization procedures (e.g., slow cooling or evaporation from solution) tend to be riddled with defects such as grain boundaries or stacking faults, and are not suitable for optical applications. The LB technique, on the other hand, has been... 

The mixture of MoCl4(Ph2PCH2CH2PPh2) (6.80 g, 0.01 mmol) thus formed and diphos (4.78 g, 0.12 mol) dispersed in dry ethanol (150 mL) is stirred at 50 °C for 30 min. To the solution, NaBH4 (3.0 g, 0.08 mol) is added with stirring over a period of 5 min. The solution is heated under reflux for 30 min and then cooled slowly to room temperature. The yellow precipitate thus formed is collected by filtration and dissolved in benzene at 50 °C. Addition of ethanol (200 mL) to the solution crystallizes the product. Repetition of this crystallization procedure yields yellow crystals of MoH4(Ph2PCH2CH2PPh2)2, which are dried in vacuo at 25 for 5 h. Yield 1.5 g. 

The experimentally determined S-L-V equilibrium data for salicylic acid (2-hydroxy-benzoic acid)-l-propanol-C02 were correlated by using the Stryjek-Vera modification of the Peng Robinson EOS in conjunction with Eq. (35) for the solid state fugacity of the solute (58,62), as described earlier. This procedure also yielded good agreement of the liquid phase compositions of salicylic acid in the temperature and pressure ranges of 273 to 367 K and 1.0 to 12.5 MPa. The P-Ttraces of S-L and L-V equilibria were calculated for a fixed solute concentration on C02-free basis, and subsequently the P-T trace for the S-L-V equilibrium was found from the point of intersection of these two lines. The liquid phase compositions of the solute as a function of pressure at a constant temperature at the condition of S-L-V equilibrium were calculated to assess the effect of pressure or addition of antisolvent on solute crystallization. It was reported that two isobaric points of the CO2 mole fraction could be observed on the curve of the S-L equilibrium temperature vs the CO2 mole fraction at constant temperature as it passes through a mini-... 

Crystallization Method. Such methods as mechanical separation, preferential crystallization, and substitution crystallization procedures are included in this category. The preferential crystaUization method is the most popular. The general procedure is to inoculate a saturated solution of the racemic mixture with a seed of the desired enantiomer. Resolutions by this method have been reported for histidine (43), glutamic acid (44), DOPA (45), threonine (46), A/-acetyl phenjialanine (47), and others. In the case of glutamic acid, the method had been used for industrial manufacture (48). 

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