Traps: gas absorption

TLe gas traps depicted in Fig. II, 8,, a and b are used when limited quantities of gas are to be absorbed. For larger volumes of gas, or where 

The comparatively inexpensive long-scale thermometer, widely used by students, is usually calibrated for complete immersion of the mercury column in the vapour or liquid. As generally employed for boiling point or melting point determinations, the entire column is neither surrounded by the vapour nor completely immersed in the liquid. The part of the mercury column exposed to the cooler air of the laboratory is obviously not expanded as much as the bulk of the mercury and hence the reading will be lower than the true temperature. The error thus introduced is not appreciable up to about 100°, but it may amount to 3-5° at 200° and 6-10° at 250°. The error due to the column of mercury exposed above the heating bath can be corrected by adding a stem correction, calculated by the formula  

Stem correction (in degrees) = KN(t — t ) where K = the apparent expansion coefficient of mercury in glass  

N - - the length, measured in degrees, of the part of the thermometer not heated to the temperature of the bulb, t.e., the length of the exposed column  

The stem correction may be avoided by employing a thermometer with a short scale (sometimes termed an Anschutz thermometer) and of such size that the entire column of mercury is immersed in the vapour or in the liquid. In practice, it is generally more convenient to use thermometers which have been graduated for partial immersion for a short and con- 

6-10° at 250°. The error due to the column of mercury exposed -above the heating bath can be corrected by adding a stem correction, calculated by the formula  

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Dihydroxyacetophenone. Finely powder a mixture of 40 g. of dry hydroquinone diacetate (1) and 87 g. of anhydrous aluminium chloride in a glass mortar and introduce it into a 500 ml. round-bottomed flask, fitted with an air condenser protected by a calcium chloride tube and connected to a gas absorption trap (Fig. II, 8, 1). Immerse the flask in an oil bath and heat slowly so that the temperature reaches 110-120° at the end of about 30 minutes the evolution of hydrogen chloride then hegins. Raise the temperature slowly to 160-165° and maintain this temperature for 3 hours. Remove the flask from the oil bath and allow to cool. Add 280 g. of crushed ice followed by 20 ml. of concentrated hydrochloric acid in order to decompose the excess of aluminium chloride. Filter the resulting solid with suction and wash it with two 80 ml. portions of cold water. Recrystallise the crude product from 200 ml. of 95 per cent, ethanol. The 3 ield of pure 2 5-dihydroxyacetophenone, m.p. 202-203°, is 23 g. 

The considerable quantities of hydrogen chloride and hydrogen bromide evolved are best handled by means of a gas-absorption trap.- The insertion of a calcium chloride tube between the trap and the reflux condenser is recommended. 

In a r-1. three-necked flask fitted with a mechanical stirrer, a reflux condenser, a thermometer, and a dropping funnel is placed LOO g. (0.58 mole) of -bromotoluene (Org. Syn. Coll. Vol. i, 131). The stem of the dropping funnel and the thermometer should reach nearly to the bottom of the flask. The upper end of the condenser is connected to a gas absorption trap (Org. Syn. 14, 2). The flask is heated with stirring in an oil bath until the temperature of the liquid reaches 105. The liquid is illuminated with an unfrosted 150-watt tungsten lamp, and 197 g. (61.8 cc., 1.23 moles) of bromine is added slowly from the separatory funnel (Note i). About one-half of the bromine is added during the first hour, during which time the temperature is kept at 105-110°. The rest is added during about two hours, while the temperature is raised to 135°. When all the bromine has been added the temperature is raised slowly to 150°. 

The apparatus should be set up under a hood, or the top of the condenser connected to a gas absorption trap for the removal of bromine vapor, a small amount of which escapes continually under the conditions of the experiment. 

In a dry 2-1. three-necked round-bottomed flask, fitted with a gas-tight stirrer and a reflux condenser carrying at the top a calcium chloride drying tube connected to a gas-absorption trap (a good hood is preferable), are placed 98.5 g. (0.6 mole) of... 

A 5-1. three-necked flask is fitted with a mechanical rubbersleeved stirrer, a dropping funnel, and a reflux condenser capped with a calcium chloride tube leading to a gas-absorption trap.2 The system is flame-dried, and the flask is charged with 308 g. (1 mole) of dibromohydrocinnamic acid (Note 1) and 800 ml. of dried (by distillation) thiophene-free benzene. While the dibromohydrocinnamic acid is maintained in suspension by stir-... 

A 500-ml. three-necked round-bottomed flask is provided with a small dropping funnel, a sealed mechanical stirrer, a reflux condenser connected to a gas-absorption trap, and a hydrogen chloride delivery tube which extends, to the bottom of the flask. 

In a 5-1. three-necked, round-bottomed flask, fitted with a sealed stirrer, dropping funnel, and air condenser, the open end of which is connected to a gas-absorption trap, arc placed 188 g. (2 moles) of phenol and 268 g. (2 moles) of ethyl acetoacetate in... 

A) 2-Bromophthalide.—The apparatus shown in Fig. 6 is used for the bromination. Flasks A and B are of 200-cc. capacity. Bromine is introduced by means of a current of carbon dioxide, which passes through mineral oil or sulfuric acid in the bubble counter, then through the bromine in flask B, and finally through the drying tower. The tower is conveniently made from a condenser jacket and is filled with anhydrous calcium chloride. Flask A is surrounded by an oil bath and is equipped with a thermometer, an outlet tube of wide bore connected to a gas absorption trap, and a gas inlet tube having an inside diameter of 2 mm. The inlet tube reaches to the bottom of the flask. 

A. 2-Chloro-2-methylcyclohexanone. A 3-1. three-necked flask, fitted with a sealed mechanical stirrer with glass blade, a dropping funnel, and an outlet tube connected to a gas-absorption trap,1 2 is charged with... 

The preparation should be conducted in a well-ventilated hood or provision should be made for an exhaust tube and attachment to a gas-absorption trap. 

A mixture of 150 g. (2.5 moles) of urea, 125 g. (1.25 moles) of reprecipitated calcium carbonate, and 150 ml. of water in a 2-1. three-necked flask is tared and cooled in an ice-salt bath. The flask is equipped with a thermometer which extends into the reaction mixture, a gas inlet tube, an outlet tube leading to a gas-absorption trap, and a slip- or mercury-sealed mechanical stirrer which will disperse chlorine gas below the surface of the liquid (Note 1). 

A. a,a,ot, a -Tetrabromo-o-xylene. In a 2-1. three-necked flask equipped with an oil-lubricated Trubore stirrer, a dropping funnel, a thermometer extending nearly to the bottom of the flask, and a reflux condenser (Note 1) attached to a gas absorption trap 2 is placed 117 g. (1.1 moles) of dry o-xylene (Note 2). An ultraviolet lamp such as a General Electric R.S. Reflector Type 275-watt sun lamp is placed about 1 cm. from the flask so as to admit the maximum amount of light. The stirrer is started, and the o-xylene is heated to 120° with an electric heating mantle. A total of 700 g. (4.4 moles) of bromine (n.f. grade) is added in portions from the dropping funnel to the reaction flask at such a rate that the bromine color is removed as fast as it is added. 

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