Powder crystallization

Feed condition solid, liquid, paste, powder, crystals. 

Ticks and fleas tend to concentrate in or migrate through the neck area of the animal. As they do this, they contact the active pesticide on or released by the collar and are killed. Powder-producing collars have an advantage over vaporous ones in that by the movement of the dog or cat, the powder crystals (bloom) are rubbed or wiped onto the fur, which expands the contact area allowing it to continue to control the ticks and fleas [20]. 

However, the findings of Prins and his coworkers were strongly criticised by Horse-field and Wasserman 147,148) who obtained esr spectra at 77 K for a number of Fe(Cp)2+ species, as powders, crystals, and glasses. All the systems gaveg = 3.15—3.35 andg = 1.82—1.90, and it was concluded that the Fe(Cp)2+ complexes were unstable under the conditions used by Prins et al. 72, 144) and that the observed signals were due to free Fe3+. Similar results were also obtained by Rowe and McCaffery 149) who studied Fe(Cp)2+ BF4 by MCD at 9 K and 290 K and by esr at 20 K in polymethacrylic acid. 

Irradiation of the powdered crystals of 6a-d with a high-pressure mercury lamp under argon at 0 °C showed a different photochemical behavior from that in benzene solution. Contrary to the photochemical results in solution media in which azetidin-2-ones 8 (y-hydrogen abstraction products) were formed as major products, thioketones 7 (P-hydrogen abstraction products) were obtained as major components in the solid-state photoreactions (Scheme 7). The... 

Fig. 5 Time dependence of X-ray diffraction profiles measured for the powder crystals of 1 at room temperature [51]...

White crystal or powder (crystal systems anhydrous BaCk is orthogonal, transition to cubic form occurs at 925°C, and the dihydrate, BaCl2 2H20 is monoclinic) hygroscopic hitter, salty taste density 3.856 g/cm (dihydrate 3.0979/cm3) melts at 962°C vaporizes at 1,560°C readily dissolves in water also dissolves in methanol, hut is insoluble in other polar organic solvents. 

Powder diffraction patterns. When a narrow monochromatic beam of X-rays passes through a small specimen of a powdered crystals... 

Artificial organic colouring matters may be in powder, crystals, lumps or more or less aqueous paste. They exhibit various tints often different from those they impart to the fibre they frequently show iridescence and metallic lustre, especially if crystallised. 

Powdered crystals of 1 (670 mg, 3.9 mmol) that were recrystallized from /r-hexane were evacuated in a 1 L flask and heated to 45 °C. Hydrogen gas was fed in from a steel cylinder (1 bar, 45 mmol) and the system kept at 45 °C for 2 days. The crystals changed their appearance and contained 67 mg (10%) unreacted 1, 502 mg (74%) 2 and 110 mg (16%) 3. The products were separated by preparative TLC on 200 g Si02 with dichloromethane. 

Finely powdered crystals of 1 (100 mg) were dispersed in 100 mL of water containing a few drops of a surfactant (Nikkol TL-10FF) and irradiated from outside the flask with a 500-W super-high-pressure mercury lamp (Ushio USH 500 D) through an optical filter (Kenko UV-32 (cut off nm)) with vigorous stirring under a nitrogen atmosphere. The products were separated and purified by preparative TLC (dichloromethane). 

Powdered crystals of 1, well ground and sandwiched by Pyrex glass plates, were irradiated with 500-W Hg lamp at 0 °C for 2 h, which led to the exclusive production of optically active / -thiolactam, l-benzyl-4-phenyl-azetidine-2-tliione-3-spiro-T-cyclohexane 2, in 96% yield at 58% conversion. The material was purified by column chromatography, and the structure was determined by spectroscopy. As expected, the thiolactam 2 showed optical activity ([a]D+109° c 1.0 CHC13, 94% ee). 

Recrystallization of the achiral oxo amide /V,/V-diisopropylphenylglyoxylamide (la) from benzene gave colorless chiral prisms [1], Each crystal is chiral and shows a CD spectrum in Nujol mulls (Fig. 1). One type of chiral crystal shows a (+)-Cotton effect and the other type shows a (-)-Cotton effect (Fig. 1). Crystals of (+)-la and (-)-la can easily be prepared in large quantities by seeding with finely powdered crystals of (+)-la or (-)-la during recrystallization of la from benzene. Measurement of the CD spectrum of chiral crystals as Nujol mulls is now well established [2],... 

Coumarin photochemistry has been recently employed to demonstrate that a frozen axial chirality can be used to induce the absolute configuration of stereogenic centers. Coumarin 103 was obtained as a single atropisomer by spontaneous crystallization (Scheme 6.37). Upon warming powdered crystals of 103 in MeOH to —20 °C, sensitized [2 + 2]-photocydoaddition to ethyl vinyl ether gave the almost enantiomerically pure products 104. The approach to the coumarin double bond occurred preferentially from the less-shielded face to which the amide carbonyl group... 

The 5-phenyl A -(benzoylformyl)thiocarbamate 118 crystallized in chiral space group P2X. Irradiation of the powdered crystals afforded optically active oxazolidinedione 119 and cis- 3-lactam 120 in moderate enantiomeric excesses... 

CDNTA form a white to bluish white powder, crystals, or granules. The crystals are sensitive to shock, friction, and percussion. CDNTA is a powerful primary explosive that demonstrates outstanding potential as a future replacement for mercury fulminate, lead styphnate, lead azide, and diazodinitrophenol for use in blasting caps and detonators. It should not be stored dry, and should be desensitized with dextrose, sulfur, starch, wood pulp, dextrin, or gum Arabic after preparation... 

Figure 2 Top The variation of the doublet splitting as a function of the angle 6 between a given C—D bond in a single crystal and the magnetic field. Bottom The Pake doublet. A powdered crystal will display this characteristic spectrum, which is the superposition of all the component doublets from C—D bonds, which are randomly oriented.

When powdered crystals of (V-(thiobenzoyl)methacrylanilide (11), which are chiral, are irradiated under nitrogen with UV light, a phototransformation to optically active /J-lactam 12 occurs. Its enantiomeric purity is strongly influenced by the reaction temperature. At 0 °C the /(-lactam 12 isolated in 75% yield has 10% ee when the reaction is carried out at —45 °C, the isolated product has 40 % ee140. 

Most of the supramolecular assemblies have been constructed from the solutions of each component. More recently, the authors found that CD formed inclusion complexes with PEG with high selectivity only by mixing powdered crystals of CDs and polymer samples without any solvents under ambient conditions (Scheme 2) [120]. When crystals of a-CD and PEG (Mw = 400) were mixed without solvent (a-CD ethylene glycol unit =1 2), the X-ray powder patterns changed a peak at 26 = 22° characteristic for the cage type decreased, and a peak at 26 = 20° characteristic for the channel type appeared... 

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