Recrystallizations, number

Amino alcohols can be resolved by a number of pathways including hydrolysis, esterification, and transesterification. For example, hydrolysis of Ai,0-diacet5l-2-amino-l-butanol with PPL followed by recrystallization results in (80a) with 95% ee (108). Hydrolysis of racemic acetates or butyrates of 2-[(aLkoxycarbonyl)amino]-l-aLkanols with PFL gives (R)-alcohol (81) with 95% ee (109). (3)-(81) can be obtained by transesterification of the racemic (81) with ethyl acetate which also serves as the reaction medium (109). 

A purified fatty acid is recommended for the preparation of a pure a-sulfo acid. Purified palmitic acid (m.p. 60.8-61.4°, neutralization equivalent 256.2) is prepared by twice recrystallizing a good commercial grade of palmitic acid from acetone at 0°, using a solvent ratio of 10 ml. to 1 g. However, the reaction may be applied to commercial saturated higher fatty acids, if the iodine number is sufficiently low. The checkers obtained similar results with recrystaUized Neo-Fat 1-56 (Armour and Company, Chicago, 111.) or Eastman white label palmitic acid. 

The p-methoxybenzylidene ketal can be prepared by DDQ oxidation of a p-methoxybenzyl group that has a neighboring hydroxyl. This methodology has been used to advantage in a number of syntheses. " In one case, to prevent an unwanted acid-catalyzed acetal isomerization, it was necessary to recrystallize the DDQ and use molecular sieves. The following examples serve to illustrate the reaction " ... 

The filtrates are combined, cooled, and extracted with three successive 200 cc portions of ether. The pH of the filtrate is then raised to 3.5 with sodium hydroxide and the filtrate extracted with six successive 200 cc portions of ether to yield the balance of the product. The crude para-aminobenzoic acid product is recovered by evaporation of ether and is suspended in hot benzene, cooled and filtered to remove benzoic and toluic acids together with small amounts of impurities soluble in the filtrate. Recrystallization of the product from 200 cc of water yields 14.5 grams of light tan needles of para-aminobenzoic acid having an acid number of 411 (theoretical value 409). 

This is separated, washed with petroleum ether, and dried in vacuo. After some time it hardens into a whitish solid, which if it was prepared from a 1-bromo-pentane which had some of its isomer 3-bromo-pentane copresent with it has a melting point of about 80° to 83°C. However, by using a pure 2-bromo-pentane, and/or by recrystallizing a number of times from dilute alcohol, the melting point may be raised to 98° to 100°C, corrected. 

Proton magnetic resonance (CDC13) 8, number of protons, multiplicity, coupling constant J in Hz. 1.5-2.2 (2, multiple ), 2.7-3.0 (4, multiplct), 7.0 (1, doublet, J = 2.5), 7.1-7.5 (6, multiplet), 7.7-8.2 (4, multiplet). A sample recrystallized from methanol-chloroform melted at 183-185°. The submitters also obtained pure product, m.p. 181-183°, after chromatography on basic alumina with 20% petroleum ether in dichloromethane as eluent. 

The caprolactam obtained must meet die specifications of permanganate number, volatile bases, hazen color, UV transmittance, solidification point, and turbidity in order to be used for repolymerization alone or in combination witii virgin CL.5 Reported CL purification methods include recrystallization, solvent extraction, and fractional distillation. One solvent extraction technique involves membrane solvent extraction. Ion exchange resins have been shown to be effective in the purification of aqueous caprolactam solutions. In one such process,... 

Fig. 4a. Resolution of racemic (67) by column chromatography on microcrystalline cellulose triacetate (column B) and by recrystallization 35) C = crystals M = mother liquor the index following C or M gives the number of recrystallizations the fraction has undergone. The value of [ot] ° is given, followed by the quantity obtained...

Fig. 7. Evolution of the diastereo-meric composition of methylphenyl-(2-phenylpropyl)stannyltriphenyl-phosphinetricarbonylcobalt (76) in function of the number n of fractional recrystallizations in n-hexane 18).

Polyurethane networks were prepared from polyoxypropylene (POP) triols(Union Carbide Niax Polyols) after removal of water by azeotropic distillation with benzene. For Niax LHT 240, the number-average molecular weight determined by VPO was 710 and the number-average functionality fn, calculated from Mjj and the content of OH groupSj determined by using excess phenyl isocyanate and titration of unreacted phenyl isocyanate with dibutylamine, was 2.78 the content of residual water was 0.02 wt.-%. For the Niax LG-56, 1 =2630, fn=2.78, and the content of H2O was 0.02wt.-%. The triols were reacted with recrystallized 4,4"-diphenylmethane diisocyanate in the presence of 0.002 wt.-% dibutyltin dilaurate under exclusion of moisture at 80 C for 7 days. The molar ratio r0H = [OH]/ [NCO] varied between 1.0 and 1.8. For dry samples, the stress-strain dependences were measured at 60 C in nitrogen atmosphere. The relaxation was sufficiently fast and no extrapolation to infinite time was necessary. 

The recrystallized materials are designated with letter R before zeolite symbol (BEA or MOR) the number given after zeolite symbol corresponds to the contribution of... 

No systematic study of the solubility characteristics of 1,2,3-thiadiazoles has been undertaken but most are freely soluble in methylene chloride and chloroform. The parent 1,2,3-thiadiazole 1 is soluble in alcohol, ether, and water. In contrast, a number of 1,2,3-thiadiazoles have been recrystallized from various alcohols and ethers <1985JME442, 1988JHC1873>. 

This stearolic acid has been thoroughly characterized 3 6 by the freezing-point curve, ultraviolet and infrared spectra, ozonization, and hydrogenation. It has been shown to be free both of positional isomers and of olefinic acids such as oleic and elaidic acids. Its properties include m.p. 46-46.5°, iodine number (Wijs titration, 30 minutes) 89.5, d 5 1.4510, d 5 1.4484, neutral equivalent 279.2-279.6 (theory 280.4), hydrogen uptake 95-100% of theory for a triple bond. The last trace of color is difficult to remove by recrystallization from petroleum ether. It can be removed, however, by crystallization from a 20-30% solution in acetone at —5 to —8°, or from an 8-10% solution at —20°, or by distillation (b.p. 189-190°/2mm.). 

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