Collective recrystallization

While stirring at room temperature, l-bromo-4-chlorobutane (100 g, 0.5832 mole, 3 eq.) is added in one portion. The mixture becomes exothermic reaching around 35°C in approximately 30 min. The near-solution is heated a t approximately 80°C by steam bath for 4 h, cooled and stirred for approximately 8 h at room temperature (30°C). The cloudy mixture is filtered, removing a small amount of insoluble solid. The filtrate is concentrated under reduced pressure to a semi-solid residue. This residue is triturated with H20 (400 ml), collected, recrystallized from acetonitrile, and then air-dried to give 43.1 g (0.1467 mole) of l-phenylmethyleneamino-3-(4-chlorobutyl)-2,4-imidazolidinedione. 

Methylphenylthiosnlfooato Phenyl Tellurium2 Phenyl tellurium trichloride is dissolved in dry ethyl acetate, 3 molar equivalents of potassium 4-methylbenzenethiosulfonate dissolved in methanol are added, and the mixture is heated under reflux. The hot mixture is filtered, the filtrate is concentrated lo a volume of 5 to 10 m/, and cooled. The orange crystals are collected, recrystallized from methanol, dried, and stored under nitrogen m.p. 138°. 

A solution of pyridine-2,3-diamine (4 g, 36.6 mmol) and diethyl mesoxalate (10 mL) in EtOH (80 mL) and H20 (60 mL) was refluxed for 2 h, and the material which crystallized from the cold solution was collected. Recrystallization (EtOH) gave a mixture (5 g, 62%), which was separated by fractional crystallization (EtOH) into ethyl 3-oxo-3,4-dihydropyrido[2,3-6]pyrazine-2-carboxylate, pale-yellow, flat needles yield 2.5 g (31%) mp213-214°C, and ethyl 2-oxo-l,2-dihydropyrido[2,3-6]pyrazine-3-carboxylale, pale-yellow plates yield 0.09 g (1 %) mp 247-254°C (dec.). 

Due to high viscosity of continuous phase, collective recrystallization, related to the diffusional transport of inclusions through dispersion medium, is the principal and usually the only mechanism by which the degree of dispersion in these systems may be changed. Because of small diffusion coefficients of components, changes in the degree of dispersion are extremely slow and become noticeable only at sufficiently high temperatures. 

Zinc powder (1.75 g) was added within 10 min to a stirred suspension of 5-(chloromethyl)-uracil (0.2 g) in 6n-DC1 (75 ml) at 60-75°C, and the mixture was stirred at that temperature for 2.5 h. The liquid was then decanted from the excess of metal powder, and the zinc was washed several times with water. After cooling, the aqueous solution was exactly neutralized with ammonia, freed from precipitated zinc hydroxide, and concentrated in a vacuum. The crystals that separated were collected. Recrystallization from water gave [oc-Di]thymine (0.04 g), m.p. 327-329°C (dec.). 

B. Synthesis of m- 4-[o-(2-Chloro-5-fluorosulfonylphenylureido)-phenoxy]butoxy bematnidine (11).To 5.2 mmoles of 3-amino-4-chloro-benzenesulfonylfluoride (18) (Aldrich Chemical Co.) are added 25 ml of benzene (dry reagent grade) and 5.5 mmoles of p-nitrophenylchlorofor-mate (19) (Aldrich Chemical Co.). The mixture is stirred at reflux for 4 hr, at which point hydrochloric acid vapor is no longer detectable. The mixture is cooled, and i T-(2-chloro-5-fluorosulfonyl-0-(4-nitrophenyl) carbamate (W) is collected. Recrystallization is from methylene chloride. To a solution of m-[4-(o-aminophenoxy)butoxy]benzamidine p-toluenesulfonate (21) in 10 ml of DMF are added 10.0 mmoles of pyri-... 

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