Recrystallization colored compounds

The high reactivity of the 5-position in 1.3-selenazoles toward electrophilic substitution was also observed on azocoupling. By reacting molar quantities of an aqueous solution of a diazonium salt with an ethanolic solution of a 2-arylamino selenazole. for example, the corresponding 2-arylamino-5 azoselenazoles are formed in a smooth reaction (100). They deposit from the deeply colored solution and form intenselv red-colored compounds after their recrystallization from a suitable solvent (Scheme 36l. 

Hydrazine hydrate dissolves many inorganic salts readily most of these salts recrystallize from the solution to form stable solvates or adducts that do not dissolve further. Additionally, the reaction of hydrazine with mineral adds/organic acids also leads to the formation of crystalline solids. These colored compounds are mostly single crystals although polycrystalline products can also be obtained. In metal complexes, hydrazine appears as either singly or doubly protonated cation and plays an important role in forming various hydrogen bond networks in their derivatives. For this reason, it is of interest to determine their crystal structures. 

Compound 6 crystallizes from cyclohexane as colorless needles which have no definite melting point there is a change of color to yellow at 128-134 C and the compound then melts sharply at 187-189 r C. When the colorless form is kept for a long time or recrystallized from pyridine or dimethyl sulfoxide it is changed into the yellow modification of mp 187-189 C recrystallization from cyclohexane reverses the process. It has been suggested that the yellow stable form has structure 6A and that the colorless metastable compound is the tautomer 2-methyl-l//-pyrido[2,3-6][l, 4]diazepin-4(5//)-one (6B). There is evidence from 1H NMR spectroscopy that the isomeric pyridodiazepin-2-one, yellow crystals, mp 195—197 " C, exists as an inseparable mixture of the tautomers 4-methyl-l//-pyrido[2,3-6][l,4]diazepin-2(3//)-one (7 A) and 4-methyl-l H-pyrido[2,3-6][l, 4Jdiazepin-2(5//)-one (7B) in the ratio 1 3. 

Information in the notebook (which came from a handbook) for your compound might say, for alcohol (meaning ethyl alcohol), s.h. Since this means soluble in hot alcohol, it implies insoluble in cold alcohol (and you wondered what the i meant). Then alcohol is probably a good solvent for recrystallization of that compound. Also, check on the color or crystalline form. This is important since... 

The BF2 chelates are hydrolytically stable (the majority of them may be recrystallized from water) whereas the BC12 chelates are easily hydrolyzed. The boric acid ester complex triptych boroxazolidines are also stable towards hydrolysis as are other aminoalcohol esters.83 A great number of the boron chelates are colored several spectrophotometric methods are based on chelate formation81 84 for the analytical determination of boric acid, organoboric acids and chelating organic compounds. The boron chelates are remarkable for their pharmacological properties as well.84 Various aspects of the boron chelates have been reviewed.81,83-86... 

Equimolar quantities of the aldehyde 1 (4 mmol) and the active methylene compound 2 were stirred in CH2C12 (30 mL) in the presence of K10, ZnCl2 (4 g). The solvent was evaporated in vacuo and the obtained solid was subjected to microwave irradiation in an open Erlenmeyer flask (25 mL). The condensation product was extracted into acetonitrile. The extract was filtered and the solvent was evaporated in vacuo. The colored solid was washed with ethanol-water (1 1) and recrystallized from ethanol. 

Compound 1 was recrystallized in two different forms one was yellow colored crystal la (benzene), and the other was orange crystal lb (a mixture of THF and acetonitrile). Photoirradiation on la in the single crystals at 366 nm for 15 h gave mainly the insoluble polymer and small amounts of 2, but lb did not react at all. 

The filtrate is treated with concentrated aqueous ammonia until the mixture gives a pink color on phenolphthalein paper. The liquid is extracted seven times with 100 cc portions of chloroform, the extracts are combined, dried with anhydrous sodium sulfate and evaporated. The residue is dissolved in ethanol by refluxing and the ethanol evaporated nearly to dryness. 100 cc of benzene are then added, the mixture is refluxed for Vi hour and set aside for crystallization. After cooling, the desired compound is collected by filtration, 2.3 grams of a white crystalline powder are obtained MP 245° to 247°C. This powder consisting of 14-hydroxydihydromorphinone can be purified by recrystallization from benzene, ethylacetate or ethanol. From benzene it generally forms diamond shaped platelets, while needles are obtained from ethylacetate. 

When it is difficult to remove traces of azo compounds from the biaryl by distillation or recrystallization, chemical means may be employed. Colorless 4-bromobiphenyl was obtained by treating an alcoholic solution of the yellow product with a little zinc dust and hydrochloric acid.60 In the preparation of 3-bromobiphenyl, the crude reaction mixture was shaken with portions of concentrated sulfuric acid until the red color of the solution was removed.61... 

Dry clean tanshen rhizomes were powdered and extracted with hexane for three days at room temperature. The hexane solution was kept overnight and then filtered. After removal of the solvent a residue was obtained which was separated into seven colored fractions by column chromatography with silica gel. Miltirone was isolated by preparative tic from fraction 1 (light red) using hexane ethyl acetate (4 1) followed by benzene-acetone (20 1). The product obtained was recrystallized from ethylacetate, m.p. 100-101°C. Its structure was confirmed by mass spectrum, NMR, IR and UV spectra which agree quite closely with those of Ho et al [76], Miltirone showed antioxidant behavior comparable to that of the commonly used phenolics BHT and BEA [77], The antioxidant activity of miltirone in lard at 100°C was determined with a Rancimat. Miltirone and other related compounds may have the potential of being used as natural antioxidants in food and cosmetics. 

Phenyl THphenylgcrmyl Tellurium2 2.56 g (6.25 mmol) of diphenyl ditellurium are dissolved in a mixture of 3 ml of benzene plus 9 ml of ethanol, the solution is heated on a water bath, and, at reflux, a solution of 0.38 g (10 mmol) of sodium borohydride in 9 ml of 1 molar aqueous sodium hydroxide is added dropwise. When the red color of the mixture has faded, 5.1 g (15 mmol) of solid chlorotriphenylgermane are added quickly, the mixture is stirred for 5 min, and poured into 50 ml of water. The resultant mixture is extracted with three 70 ml portions of diethyl ether, the organic phases arc combined, dried with anhydrous sodium sulfate, filtered, and evaporated to dryness. The residue is recrystallized from hexane yield 3.9 g (61 %) m.p. 107°. Examples of similarly prepared compounds are ... 

Bis[2-benzoylphcnyl] Ditellurium [Potassium Hydroxide Method]3 To 200 ml of ethanolic potassium hydroxide are added 16.5 g (48 mmol) of 2-benzoylphenyl tellurium chloride and the mixture is heated until the reddish color disappears and potassium chloride precipitates. The mixture is poured into cold water and the ditellurium compound is extracted with chloroform. The extract is dried, evaporated to dryness, and the residue is recrystallized from benzene yield 12.3 g (83%) m.p. 139°. 

The residue was recrystallized twice from MeCN to yield 930 mg of 12 as a cream-colored solid, mp 245-248° dec. Compound 11 was obtained in a similar fashion. 

The trichlorocyclotrithiazene is obtained11 by stirring tetrasulfur tetranitride or S3N2C12 with excess sulfuryl chloride (2-3 mL per gram of sulfur compound) for ca. 24 hr at room temperature, in a flask fitted with an exit bubbler. After excess solvent has been removed by distillation (at ca. 20° under reduced pressure) and the residue has been pumped dry, the (NSC1)3 is obtained as a pale-yellow powder. Further purification is usually unnecessary but if analyses or a darker color indicate that some decomposition has occurred (e.g., through exposure to atmospheric moisture), it can be recrystallized from thionyl chloride or sulfuryl chloride. To obtain a good recovery, the mixture should be filtered at ca. —10°. 

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