Protected Reaction Apparatus

Many organic reagents react rapidly and preferentially with water. The success or failure of many experiments depends to a large degree on how well atmospheric moisture is excluded from the reaction system. The drying tube, which is packed with a desiccant such as anhydrous calcium chloride, is a handy way to carry out a reaction in an apparatus that is not totally closed to the atmosphere, but 

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Standard Experimental Apparatus Moistiore Protected Reaction Apparatus... 

In a 100-ml round-bottomed flask place 16.1 g (O.lOmol) of 3-bromocyclo-hexene (Expt 5.68), 38.7 g of dried, redistilled quinoline and a magnetic stirrer follower. Attach to the flask a Claisen still-head fitted with a thermometer and a condenser set for downward distillation. Protect the apparatus from atmospheric moisture by a calcium chloride guard-tube attached to the side-arm of the receiver. Support the reaction flask in an oil bath which rests on a magnetic stirrer/hotplate, commence stirring rapidly and heat the oil bath to 160-170 °C. The cyclohexadiene steadily distils as colourless liquid, b.p. 80-82 °C, over a period of about 30 minutes, yield 5.4 g (68%). The product is 99 per cent pure by g.l.c. analysis use either a 2.7 m column of 10 per cent polyethyleneglycol adipate on Chromosorb W held at 60 °C with a flow rate of carrier gas of 40ml/minute, tR 2.4 minutes, or, a 1.5 m column of 10 per cent Silicone oil on Chromosorb W held at 6 °C with a flow rate of carrier gas of 40ml/minute, tR 1.5 minutes. 

A 2-1. round-bottomed three-necked flask is fitted with a reflux condenser, a dropping funnel, and an efficient mechanical stirrer. A calcium chloride tube is attached to the condenser to protect the apparatus from moisture. To the flask are added 800 ml. of absolute ether and 13.9 g. (2 gram atoms) of lithium chips or shavings (Note 1). The stirrer is started, and 105 ml. (157 g., 1 mole) of dry bromobenzene is placed in the dropping funnel. About 5-15 ml. of the bromobenzene is added to initiate the reaction when the ether begins to reflux, the balance is added at such a rate that the solvent refluxes continuously (1 hour) (Note 2). I he mixture is then stirred and refluxed until rriost of the lithium di.s i ) )ears (15 90 min.). Wliile stirring is con-... 

The apparatus is assembled as indicated and the oil baths under B and D are heated to about 190-200° (Note 4), and the oil bath under F to about 110-120°. The bath under I is filled with ice. The volatile [iroducts are collected in I which is kept carefully protected from light. After the first violent reaction has... 

The most convenient setup for hydrogenation on an intermediate synthetic scale is the Parr low-pressure shaker-type apparatus (Fig. A3.9), in which variable pressures of from 1 to 5 atmospheres (60 psi) may be safely employed. The compound to be hydrogenated (approx. 100 g) is dissolved or suspended in 200 ml of a suitable solvent in a heavy-walled 500-ml bottle. The bottle is placed in the apparatus and clamped in place inside the protective mesh. The flask is briefly evacuated, then filled with hydrogen to the desired pressure. The reaction is initiated by starting the shaker, and the course of the reaction is easily followed by observing the drop in pressure in the bottle and... 

While a current of dry nitrogen is passed through the apparatus, 400 cc. of dry ether and 6.9 g. (1 gram atom) of lithium (in small pieces) (Note 1) are placed in a 1-1. three-necked flask fitted with a dropping funnel, mechanical stirrer, and reflux condenser protected from moisture. The. stirrer is started, and 10-15 cc. of a solution of 79 g. (0.5 mole) of dry bromobenzene in 100 cc. of dry ether is added from the dropping funnel. The reaction usually starts immediately if not, the flask may be warmed, and the remainder of the mixture is then added at such a rate that the ether refluxes gently. The mixture is stirred until the lithium disappears (Note 2). 

The apparatus is dismantled, and the reaction mixture is filtered quickly by suction through a 1.5-cm. layer of filter aid on an 11-cm. Buchner funnel placed on a 2-1. filter flask. The filter cake is pressed down well and washed with three 50-ml. portions of methylene chloride. The filtrate is immediately protected from moisture by calcium chloride tubes, and the solvent is removed by distillation from a 2-1. flask. After the solution has been concentrated to about 225 ml., the hot liquid is poured into a suitable container (Note 6), and the remaining solvent is removed under reduced pressure (Note 7). The yield is 192-199 g. (81-84%) of a white, crystalline solid which melts at 155-156°. 

Carrying out the Determination.—After introducing the substance connect the gas inlet tube of the reaction flask with the Kipp apparatus and immediately before attaching the flask to the apparatus pour in 5 c.c. of hydriodic acicl (d 1 7). Protect the receivers from radiant heat with an asbestos shield and for the same reason use the smallest possible glycerol bath (beaker) for heating the acid. 

The apparatus and the special accessories necessary for this work are schematically illustrated in the Fig. 22. The reaction chamber used for the Knudsen effusion method is positioned above the balance. The reaction chamber is thermostatically controlled and connected with a cold trap. Both of them are protected from outside temperature effects by an insulating material. This protection leads to a more constant temperature and a straight line in the recorded loss in weight. 

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