Recrystallization experimental procedures

General Experimental Procedure. A mixture of the amine, 0.1 mole in 250 cc. of absolute alcohol, with 10 g. of sulfuric acid and 28 g. of arseni-ous chloride, cooled to 0°, is diazotized with a saturated aqueous solution of the calculated amount of sodium nitrite (starch-iodide end point). Then, and not before, 1 g. of cuprous bromide is added the mixture is thoroughly stirred, warmed to 60° until no more nitrogen is evolved, and then distilled with steam. The separated arsonic add is recrystallized. 

Filtration is the physical separation of a solid from a liquid and is a process encountered in experimental procedures such as gravimetric analysis (p. 139), recrystallization (p. 92), and solvent drying (p. 41). In principle, the mixture of the solid and liquid is passed through a porous material, filter paper or if sintered glass, and the solid is trapped on the porous material while the liquid passes through. 

Schiff base condensation reactions have also been widely used in the preparation of new imine-functionalized tertiary phosphines (64) (68).122-129 The most frequently used experimental procedure involves the condensation of a carbonyl compound (often 2-Ph2PCeH4CHO)176 and the appropriate amine in ethanol, benzene, or THF under refluxing conditions. To ensure complete reaction, a Dean-Stark trap or the addition of molecular sieves is often necessary, to remove water formed during the reaction. Evaporation of the solvent and recrystallization yield the desired ligand in good to excellent yields. This approach can be used to prepare bis-phosphines, e.g., (66)-(68).127- 29 The iminophosphine (69) was prepared by a series of coupling reactions at a palladium template, and was liberated from the metal by treatment with aqueous cyanide.130... 

Recrystallization solvent in parentheses (if given). b Compare with experimental procedure on p 335. c No data available. 

Acetyl Peroxide-Carbonyl-I80. Acetyl peroxide-lsO was prepared by a modification of the usual procedure (16). An apparatus was devised to allow purification of the peroxide by remote manipulation of stopcocks and valves controlling nitrogen pressure. Recrystallization, filtration, and the addition of fresh solvent were accomplished without exposing the experimenter to the hazard of direct manipulation of crystalline acetyl peroxide. 

The desired compound from a reaction is frequently part of a mixture, and its isolation in pure form can be a significant experimental challenge. Two of the more common methods for separating and purifying organic liquids and solids are recrystallization and distillation these procedures are discussed in Chapters 3 and 4, respectively. Two other important techniques available for these purposes are extraction and chromatography. As you will see here and in Chapter 6, both of these methods involve partitioning of compounds between two immiscible phases. This process is termed phase distribution and can result in separation of compounds if they distribute differently between the two phases. 

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