Crystallization from concentrated mixtures

An analysis of the overall crystallization rate with composition requires that the comparison be made either at constant undercooling or at one of the nucleation temperature quantities, T / T AT or T /T(AT). This requirement is essential because of the importance of nucleation to the crystallization process. The overall crystallization kinetics of a variety of polymer-diluent systems have been reported. Many different relations between the overall crystallization rate and composition have been observed. For example, as is shown in Fig. 13.17 there is a continuous decrease in the crystallization rate with dilution for linear polyethylene-a-chloronaphthalene mixtures.(42) The results for poly(trans-1,4-isoprene) in methyl oleate follow a similar pattem.(80) In contrast, the rates for poly(dimethyl siloxane) crystallizing from toluene, at compositions V2 = 0.32 to 0.79, are the same at all undercoolings, but are faster than that of the pure polymer.(78) Another example is found with poly(ethylene oxide)-diphenyl ether mixtures.(77) In this case the crystallization rates for the pure polymer and composition = 0.92 to 0.51 are the same. However, the rates for the more dilute mixtures, V2 = 0.04 and 0.30 are lower. For poly(decamethylene adipate)-dimethyl formamide mixture the rates for the pure polymer and V2 = 0.80 are the same.(77) The mixture of isotactic poly(propylene) with dotricontane shows interesting behavior.(81) At all undercoolings studied, the crystallization rate initially decreases with dilution, reaches a minimum in the range V2 — 0.7 (a maximum in ti/2) and then slowly increases with further dilution, up to V2 = 0.10. 

The examples cited above indicate a wide diversity in the overall crystallization rate-composition relations among the different mixtures studied. A general pattern has not emerged from these studies. These results may reflect either specific differences between the different systems studied or may be a consequence of inadequate values being used for the equilibrium melting temperatures at the different compositions. 

In order to obtain the product of the interfacial free energies for nucleation from the slopes of the straight lines in Fig. 13.31 (as well as for other systems) both the effective volume fraction and reliable equilibrium melting temperature need to be known. For these reasons values of the product OenCTun cannot be obtained in a routine manner even for crystallization from dilute solutions. Even if the proper value of aenO un could be obtained from experimental data there is a problem that has been discussed previously. It is the matter of obtaining aen- To obtain this important quantity the value of needs to be independently known. As 

Polymers that show a rate maximum with respect to temperature in the pure state do so also when crystallizing from diluent mixtures.(42a,67,88) Two examples are shown in Figs. 13.32 and 13.33 for isotactic poly(styrene) crystallizing from ether benzophenone or dimethyl phthalate respectively.(42a,67) Characteristically, the addition of the diluent causes a shift of the crystallization range to lower temperatures. A similar effect was observed with bisphenol-A poly(carbonate).(88) In addition, the growth rate maximum increases with the initial addition of diluent. This phenomenon is observed up to about 20% diluent in the case of benzophenone (Fig. 13.32) and about 50% with dimethyl phthalate (Fig. 13.33). A similar pattern is also indicated for the poly(carbonate)-diluent mixture.(89) With further additions of diluent there is a continuous decrease in the growth maxima up to very dilute 

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Upon being concentrated and cooled the mother liquor yields a further quantity of the hydrochloride. The combined quantities of hydrochloride are treated with a small quantity of cold water, dried with care, and washed with ethyl acetate. The product is then crystallized from a mixture of alcohol and ethyl acetate, and there is obtained a hydrochloride melting at 239°-240°C. 

The mother liquor was concentrated to dryness after separation of the first fractio and the residue was crystallized from a mixture of ether and n-hexane (7 3) at -15°C. T1 crystals obtained were combined with the residue obtained after crystallization of 3. Tv consecutive crystallizations from the same solvent gave the second pure diastereoisomer ester 4 1.65 g, mp 72°-75°C, [ct]578 + 26.2° (c 1.8, CgHg). 

The resulting precipate of triethylamine hydrochloride (41.4 g., 81%) is filtered and washed with 100 ml. of dry ether. The solvent is removed from the combined filtrate by rotary evaporation under reduced pressure. The semi-solid residue crystallizes to an orange-red solid after refrigeration for several hours at ca. 5°. Crystallization from a mixture of 150 ml. of pentane and 120 ml. of dry ether affords 38.8 g. of diazoaceto-phononc as yellow square plates, m.p. 44-48°. Concentration of... 

Crude 5 -butyramido-2 -(2,3-epoxypropoxy)acetophenone (16 g), isopropylamine (20 g) and ethanol (100 ml) were heated together under reflux for 4 hours. The reaction mixture was concentrated under reduced pressure and the residual oil was dissolved in N hydrochloric acid. The acid solution was extracted with ethyl acetate, the ethyl acetate layers being discarded. The acidic solution was brought to pH 11 with 2 N aqueous sodium hydroxide solution and then extracted with chloroform. The dried chloroform extracts were concentrated under reduced pressure to give an oil which was crystallized from a mixture of ethanol and diethyl ether to give 5 -butyramido-2 -(2-hydroxy-3-isopropylaminopropoxy)acetophenone (3 g), MP 119-123°C. 

The following is an alternate method of preparation A mixture of 3-(l-piperazinyl)carbonylmethyl-5-chloro-2(3H)-benzothiazolinone (500 mg), anhydrous potassium carbonate (400 mg), 2-hydroxyethyl bromide (300 mg) and anhydrous ethanol (20 ml) is heated while refluxing for 5 hours. The reaction mixture is concentrated under reduced pressure. The residue is extracted with chloroform. The chloroform layer is dried over magnesium sulfate and concentrated. The residue is crystallized from a mixture of ethyl acetate and ethanol to give 3-[4-(2-hydroxyethyl]-l-piperazinylcarbonylmethyl]-5-chloro-2(3H)-benzothiazolinone (370 mg) as crystals, MP 159° to 160°C. 

Diamantanedicarboxylic acid and excess thionyl chloride were refluxed until a clear solution was obtained and then concentrated. The crude 4,9-diamantanedi-carboxylic acid chloride (0.0211 mole) was slowly added to a chilled solution of AICI3 (6.75 g) and anisole (22.8 g), and the mixture was stirred overnight at ambient temperature. The product was precipitated by pouring into O.IM aqueous HCl, then stirred, filtered, and the solid further stirred in methanol to remove unreacted anisole. The white solid was re-crystallized from a mixture of 700 ml toluene and 100 ml THF and the product was isolated in 72% yield, MP = 213-214°C. 

Hydroquinone and A-methyl-p-aminophenol (Metol) form superadditive mixtures and a complex, Metoquinone , consisting of one hydroquinone and two Metol molecules, was proposed by Lumiere, Lumiere and Seyewtz [44] to be the species with higher activity than the separate agents. A similar complex between hydroquinone and l-phenyl-3-pyrazolidinone (Phenidone) consisting of one molecule of hydroquinone and one molecule of Phenidone has been observed in the solid state by Kurosaki [45] and Mutter and Schneider [46]. Although these complexes can be crystallized from concentrated solutions of hydroquinone and Metol, and hydroquinone and Phenidone, there is no evidence of their existence in solution. 

To 20 mL ethyl acetoacetate heated to 160-165°C was added 5.5 g 4-amino-6-bromoveratrole over 3 min. After continuing the heating for an additional 30 min, the excess ethyl acetoacetate was distilled off under reduced pressure, and the residue was washed with light petroleum ether, leaving a thick oil in an apparently quantitative yield. This thick oil was mixed with 8 mL concentrated H2SO4, and the mixture was heated for 2 min at 60-70°C. The mixture immediately solidified, which was thrown into water. The solid was filtered out and crystallized from a mixture of chloroform and alcohol to give 60% 2-hydroxy-5-bromo-6,7-dimethoxylepidine as long white needles, m.p. 274-276°C (dec.). 

The technique for the isolation of nicotinic acid depends on the starting material. In most cases, a preliminary hydrolysis is required either with acids or alkalies. The extractions are more complete if the material is rendered free of lipids, a necessary step when working with animal products. The free acid is extracted from the hydrolysate with organic solvents such as hot alcohol. It may then be separated as such from the organic solvent extract or in the form of an ester or as the copper salt the free acid can be recovered from the copper salt by H2S treatment. Purification is carried out by crystallization from concentrated water or alcohol solutions. Nyc et al. extracted nicotinic acid from the mycelium of Neurospora with acetone. Subsequent purification steps included the formation of the barium salt, acidification with H2SO4 and adsorption of the free nicotinic acid on charcoal. Elution was accomplished with 4% aqueous aniline and the final purification step involves recrystallization from a i 4 mixture of acetic acid and benzene. Leifer et al. have applied paper chromatography with M-butanol saturated with ammonia to separate nicotinic acid from contaminating materials. 

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