Crystallization from solution yield

The pentahydrate Bi(N03)3.5H20 can be crystallized from solutions of Bi oxide or carbonate in cone HNO3. Dilution causes the basic salt BiO(N03) to precipitate. Attempts at thermal dehydration yield complex oxocations by reactions which have been formulated as follows ... 

The most stable solid hypochlorites are those of Li, Ca, Sr and Ba (see below). NaOCl has only poor stability and cannot be isolated pure KOCl is known only in solution, Mg yields a basic hypochlorite and impure Ag and Zn hypochlorites have been reported. Hydrated salts are also known. Solid, yellow, hydrated hypobromites Na0Br.xH20 (x = 5, 7) and K0Br.3H20 can be crystallized from solutions obtained by adding Br2 to cold cone solutions of MOH but the compounds decompose above 0°C. No solid metal hypoiodites have yet been isolated. 

A) A mixture of 333 parts of 4-(1 -piperazinyDphenol dihydrobromide, 11.2 parts of acetic acid anhydride, 42 parts of potassium carbonate and 300 parts of 1,4-dioxane is stirred and refluxed for 3 days. The reaction mixture is filtered and the filtrate is evaporated. The solid residue is stirred in water and sodium hydrogen carbonate is added. The whole is stirred for 30 minutes. The precipitated product is filtered off and dissolved in a diluted hydrochloric acid solution. The solution is extracted with trichloromethane. The acid aqueous phase is separated and neutralized with ammonium hydroxide. The product is filtered off and crystallized from ethanol, yielding 5.7 parts of 1 acetyl-4-(4-hydroxyphenyl)piperazine MP 181.3°C. 

A mixture of 5.2 parts of 4-chloro-3-nitrobenzophenone, 5 parts of ammonia, 72 parts of methanol and 13 parts of sulfolane is heated overnight at 125°C in a sealed tube. The reaction mixture is evaporated in vacuo. The semisolld residue is boiled in 100 parts of a diluted hydrochloric acid solution. After cooling, the precipitated product Is filtered off and dissolved in chloroform. The chloroform phase is dried and evaporated. The residue is crystallized from toluene, yielding 4-amino-3-nitrobenzophenone MP 141°C. 

A mixture of 2.65 g. of freshly distilled 2,3-O-isopropylidene-D-glycerose, 1.5 ml. of ethyl acetoacetate, 0.7 g. of zinc chloride, 20 ml. of N sulfuric acid, and 20 ml. of 96% ethyl alcohol is kept at room temperature for twenty-four hours. After addition of 3 g. of crystalline sodium acetate and keeping for a further 48 hours at room temperature, the mixture is heated for 15 minutes at 90°. It is then repeatedly extracted with ether, and the united extracts are successively washed with water, an aqueous solution of sodium bisulfite, and a small quantity of aqueous sodium hydroxide solution. The ether layer is dried with anhydrous sodium sulfate and the solvent is evaporated, yielding an oil which is saponified with aqueous sodium hydroxide solution (4 ml. of 10%) by heating on a steam bath for one hour. The aqueous solution is extracted with ether, acidified (to Congo Red) with phosphoric acid, and then repeatedly extracted with ether the united extracts are dried with anhydrous sodium sulfate and the solvent is evaporated, giving a residue which crystallizes from water yield, 0.2 g. of the product (X) m. p., 153-155°. 

N-Acetyl-2,5-dimethoxy-4-iodophenylisopropylamine. 5 g of the diazonium salt is prepared as described immediately above and cooled to 0° then added gradually to a solution of 8 g of potassium iodide in 10 ml of water. After reaching room temp the reaction is set until the evolution of nitrogen has stopped. The dark brown viscous semi-solid that will separate is dissolved in ethanol with heat and then eooled. On cooling the title material separates out and is crystallized from ethanol. Yield 1.97 g, mp 167-168°. 

Nitrosonitrocyanomethanides (NNtCM) can easily be synthesized in a two-step reaction (Scheme 18) (i) formation of the metastable cyanomethylnitrolic acid by nitrosation of nitroacetonitrile in water and extracting the cyanomethylnitrolic acid with ether, (ii) treating the dried ether solution of cyanomethylnitrolic acid with a solution of MOR (M = alkali metal, NR4 R = H, alkyl) in isopropanol results in a red precipitate of MNNtCM. The beautiful red alkali NNtCM salts can easily be purified by re-crystallization from methanol (yield 50-60%). 

For many molecular materials, crystallization from solution does not yield single crystals of suitable size and quality for single-crystal XRD, and instead produces only microcrystalline powders. In such cases, structure determination from powder XRD data provides a viable route for establishing structural understanding of the resultant materials. 

The water lattice may be an important element in forming the ordered thymine structure necessary for dimerization, as pointed out by Beukers and Berends.37 Thymine can crystallize from solution as a monohydrate (a real hydrate)38 in whose crystal lattice one thymine is directly above another. The influence of humidity upon dimer yield in dry films may be connected with monohydrate formation, and monohydrate formation in frozen solutions may be the reason for the almost theoretically maximum quantum yields for dimer formation.31 The possible existence of aggregates in frozen aqueous solutions is supported by a tenfold increase in purine phosphorescence at 44°K produced by the presence of 1% ethanol and by a blue shift of excitation and emission spectra.39... 

The product solution is dried with anhydrous magnesium sulfate, filtered, and then freed from solvent by evaporation under reduced pressure. The oily residue is crystallized from ethanol yield 3 gm (67 %), m.p. 42°-43°C. 

A solution of 0.55 gm (2.8 mmoles) of pentafluoronitrosobenzene and 1 ml of triethyl phosphite in benzene is warmed for 30 min at 60°C. The reaction mixture is cooled to room temperature and extracted several times with water. The organic layer is then evaporated to dryness and the residue is crystallized from methanol yield 0.42 gm (81 %), m.p. 48°C. 

Dean-Stark trap. During this period the yellow reaction mixture turned first crimson and then dark brown. Toluene was removed under reduced pressure and the residual enamine crystallized from acetone as discolored crystals (8 g). The enamine (10 g) was treated with concentrated HC1 (1 ml) in methanol (200 ml). The crimson solution was evaporated and the residual dark oil crystallized from acetone, yielding the intermediate ketopyran (8.4 g, yellow needles from acetone). The crystals were added to methanol and an excess of sodium borohydride was gradually added to the solution, yielding on standard workup 7.47 g of the hydroxypyran. The crystalline hydroxy intermediate was well mixed with 4.5 g of anhydrous copper sulfate and heated to 150-160°C in a carbon dioxide current for 10 min. Upon cooling, the product was extracted into methylene chloride. Removal of the solvent under reduced pressure gave 6.3 g of discolored solid that was decolorized with carbon and recrystallized from acetone (melting point not reported). 

Concomitant crystallization is by no means limited to crystallization from solution, nor to preservation of constant molecular conformation. As noted in Section 2.2.5 the classic pressure vs temperature phase diagram for two solid phases (Fig. 2.6) of one material exhibits two lines corresponding to the solid/vapour equilibrium for each of two polymorphs. At any one temperature one would expect the two polymorphs to have different vapour pressures. This, in fact, is the basis for purification of solids by sublimation. Nevertheless there are examples where the two have nearly equal vapour pressures at a particular temperature and thus cosublime. This could be near the transition temperature or simply because the two curves are similar over a large range of temperatures or in close proximity at the temperature at which the sublimation is carried out. For instance, the compounds 3-VI and 3-Vn both yield two phases upon... 

To a solution of 4-amino-3-[2 -deoxy-3, 5 -di-0-(4-toluoyl)-/ -D-ribofuranosyl]-l//-imidazole-5-carboni-trile (400 mg, 0.87 mmol) in anhyd MeCN (15 mL) was added benzoyl isocyanate (90% purity, 0.6 mL, 4.3 mmol) under stirring at rt. A precipitate formed within 15 min. The mixture was stirred overnight and then refluxed for 30 min. The solvent was evaporated, the residue dissolved in 25% aq NHj/i-PrOH (1 1, lOOmL) and the solution stirred for 2 d at rt. Upon evaporation, the residue was extracted with EtjO (2 X 50 mL) under stirring. The precipitate was dissolved in HjO (100 mL) containing a few drops of 25% aq NHj and filtered. The volume of the filtrate was reduced to 30 mL and applied to an XAD-4 column (2 X 20 cm). lIjO (200 mL) removed inorganic material the title compound was eluted with HjO/i-PrOH (9 1). Evaporation yielded a residue which gave colorless crystals from EtOH yield 100 mg (43%) mp > 230 "C (dec.). 

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