Reaction methods drying tubes

Method B. In a 500 ml. round-bottomed flask, provided with a reflux condenser protected by a cotton wool (or calcium chloride) drying tube, place 59 g. of succinic acid and 102 g. (94-5 ml.) of redistilled acetic anhydride. Reflux the mixture gently on a water bath with occasional shaking until a clear solution is obtamed ca. 1 hour), and then for a further hour to ensure the completeness of the reaction. Remove the complete assembly from the water bath, allow it to cool (observe the formation of crystals), and finally cool in ice. Collect the succinic anhydride as in Method A. The yield is 45 g., m.p. 119-120°. 

Because atmospheric humidity must be avoided, the reaction flask is isolated from the atmosphere with drying tubes. Moreover, since the solvent is rarely perfectly anhydrous and will contain traces of water due to its hygroscopic nature, its water content must be measured prior to the determination. The equivalence point of the titration reaction is detected by an electrical method instead of a visual method. The current intensity that passes between two platinum electrodes inserted in the reaction medium is measured (see Fig. 19.10). The reagent, which is a mixture of sulphur dioxide, iodine and a base, is characterised by the number of mg of water that can be neutralised by 1 cm3 of this reagent. This is referred to as the equivalent mass concentration of water, or the titre T of the reagent. 

Random copolymers of L-Val and L-Glu(OBzl) containing 3-11% Val were synthesized by polymerization of the NCAs in 1,4-dioxane with TEA as an initiator. The two NCAs were dissolved in 1,4-dioxane [concentration either lOmmol total NCA/lOOmL solvent (Method 1) or lOmmol total NCA/ 80 mL solvent (Method 2)], in the molar ratio desired for the copolymer product. TEA was added [NCA/ initiator ratio either 25 1 (Method 1) or 12.5 1 (Method 2)]. The reaction flask was sealed with a Drierite drying tube and allowed to stand for 5 d (Method 1) or 3 h (Method 2) at rt. The viscous mixture was then introduced into vigorously stirred abs EtOH (500 mL). The white precipitate was collected on a filter funnel, washed thoroughly with EtOH, and dried (P205) in vacuo yield 45-80% average molecular weights 195 110 x 103. 

Syntheses of Bisphenol-A Carbonate Oligomers in Homogeneous Pyridine. Oligomers made by the pyridine method were prepared in the same apparatus except that drying tubes were added where necessary. It was also necessary to use carefully dried solvents since the undesirable side reaction with water converts chlorocarbonic acid to hydrochloric acid and carbon dioxide, thus upsetting the reaction stoichiometry. 

Method 2. It is often convenient to prepare the powdered sodium in the flask in which the subsequent reaction is to be carried out this is usually a three-necked flask. Into a 1-litre three-necked flask fitted with a reflux condenser (protected by a drying tube containing soda lime), a sealed stirrer and a dropping funnel are placed 23 g of clean sodium and 150-200 ml of sodium-dried xylene. The flask is surrounded by a mantle and heated until the sodium has melted. The stirrer is started and, after the sodium is suitably granulated, the mantle is removed. When the contents of the flask have cooled to the laboratory temperature, the stirrer is stopped. The xylene may then be decanted, and the sodium washed with two 100 ml portions of sodium-dried ether to remove traces of xylene as in Method 1. Large quantities of molecular sodium may be prepared by this method. 

This procedure has been previously described in connection with the Kiessling method for preparing pure boron. If BBra is desired, the apparatus shown in Fig. 238 is closed off by means of a drying tube inserted behind condensation trap o. Before the reaction the boron is thoroughly dried by prolonged heating at 600°C in a quartz tube flushed with a stream of Hg. Then dropwise Brg addition is started, and the temperature of the reaction tube is raised to 700-750°C. The product BBra is purified as in method I. 

One way to eliminate emissions is to place moistened glass wool in a drying tube, which is then attached to the reaction apparatus (Fig. 3.10W). What precautions must be taken when using this method ... 

Method 2. Mix 1 0 g. of 3 5-dinitrobenzoic acid with 1 5 g. of phosphorus pentachloride in a small, dry test-tube. Warm the mixture gently over a small smoky fiame to start the reaction when the reaction has subsided (but not before), boil for 1-2 minutes or until the solid matter has dissolved. Pour the mixture while still liquid on a dry watch glass (CAUTION the fumes are irritating to the eyes). When the product has solidified, remove the liquid by-product (phosphorus oxychloride) by transferring the pasty mixture to a pad of several thicknesses of filter paper or to a small piece of porous tile. Spread the material until the liquid has been absorbed and the residual solid is dry. Transfer the 3 5 dinitrobenzoyl chloride to a test-tube, add 0-5-1 ml. of the alcohol, and continue as in Method 1. 

Method 1. Use the apparatus depicted iu Fig. Ill, 56, 1, but omit the thermometer also attach a cotton wool (or calcium chloride) tube to the side arm of the filter fiask receiver in order to prevent the entrance of moisture into the apparatus. Mount the reaction fiask in a water bath e.g., a large beaker or other convenient vessel). It is important that all the apparatus be perfectly dry, since both phosphorus trichloride and acetyl chloride are decomposed by water. The set-up should be assembled in the fume eupboard. 

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