Stirrer

The influence of stirring on the nitration rate and the safety of the operation has already been emphasized. It is evident that special attention must be paid to the stirring equipment provided in a nitrator. Various types of stirrers are used. 

Horseshoe stirrers, the shape of which fits well into the inside of a nitrator, are the simplest type (Fig. 29). 

Another type of simple stirrer is one with a set of blades or bars mounted vertically on a vertical axis. A more complex form of this type of stirrer consists of two 

The types of stirrers mentioned are particularly useful when the contents of the nitrator are highly viscous or semi-liquid, for example a mixture of acid and a crystalline product. 

For liquids of low viscosity a spiral screw stirrer may be used (Fig. 30). Circulation can be facilitated by surrounding the stirrer (I) with a sheet metal cylinder 

Mostly the mechanical stirring machines (devices) essentially comprise of a variable-speed electric motor adequately clamped and strategically positioned just above the reaction vessel, which causes stirring due to a rotating vertical rod (normally glass, but can also be made up of stainless-steel or Teflon). Usually a paddle or vane (i.e., the blade of a propellar) is attached to the bottom end of this rod. The rotating action of the rod with the vane or paddle is solely responsible for agitation of the reaction mixture as shown in Fig. 3.9. 

Salient Features. The various salient features of a mechanical stirring assembly are as given below  

Both rod and vane are normally detachable so as to enable different length rods and different sized paddles may be employed as per the appropriate need and requirement. 

Speed of the stirrer can always be adjusted by the help of a variable-speed device on the motor. 

Various shapes and designs of vanes are available, the most frequently used being a crescent-shaped piece of TEFLON about 5 mm thick. It has a specific slot in it which permits it to he detached easily from the glass rod, as can be seen from Fig. 3.10. In this particular design the vane may be rotated about a horizontal axis. Therefore, it can be easily and conveniently inserted through the narrow neck of a round-bottomed flask, and subsequently, rotated into a horizontal position ready for use. 

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Figure Bl.27.4. Rotating bomb isoperibole calorimeter. A, stainless steel bomb, platinum lined B, heater C, thermostat can D, thennostat iimer wall E, themiostat water G, sleeve for temperature sensor H, motor for bomb rotation J, motor for calorimeter stirrer K, coimection to cooling or heating unit for thennostat L, circulation pump.

Figure Bl.27.5. A typical solution calorimeter with thennometer, heater and an ampoule on the base of the stirrer which is broken by depressing it against the ampoule breaker. (Reproduced with pennission from Suimer S and Wadso I 1959 Acta. Chem. Scand. 13 97.)...

Figure Bl.27.7. Schematic diagram of isothennal displacement calorimeter A, glass calorimeter cell B, sealed heater C, stainless steel stirrer D, thennistor E, inlet tube F, valve G, window shutters Ft, silver rod ...

Alternatively a mercury-sealed stirrer may be employed. Here again a short glass tube C is inserted through the cork of the flask to act as a collar for the stirrer. The tube C carries a short wide tube B which is either fused at its lower end to C, or is fixed to it by means of a cork as shown. The stirrer D carries a precisely similar tube E, the top of which however is now fixed to D the bore of the tube E allows it to fit easily within the annular space between the collar C and the tube B. Mercury... 

Fig. 23(C) shows a reflux assembly with a stirrer fitted. The stirrer A is both held in position in the tube B and allowed to rotate freely by the lubricated rubber sleeve C, as described on p. 39, and is connected to a vertical motor above. The extent to which the stirrer dips into the liquid in the flask can readily be adjusted. The condenser (not shown) is fitted into D. This constitutes for many purposes the best type of stirrer. If desired, the rubber sleeve C can be replaced by a metal fitting E for a horizontal drive. The gas-inlet F is closed when not in use.

The disc contains a hole, centrally placed, through which a small glass stirrer can be pushed. The stirrer should be smeared with a very small amount of silicone grease where it passes through the spring disc. A relatively powerful motor is required for this apparatus. 

A magnetic stirrer is also recommended for semi-micro work. A small bar of glass-covered steelf is placed in the liquid contained... 

Assemble in a fume-cupboard a 3-necked flask fitted with a stirrer, a reflux condenser, and a dropping-funnel, the apparatus... 

Place 80 g, of hydroxylamine sulphate (or 68-5 g. of the hydrochloride), 25 g. of hydrated sodium acetate, and 100 ml. of water in a 500 ml. flask fitted with a stirrer and a reflux water-condenser, and heat the stirred solution to 55-60°. Run in 35 g (42 nil,) of -hexyl methyl ketone, and continue the heating and vigorous stirring for ij hours. (The mixture can conveniently be set aside overnight after this stage.) Extract the oily oxime from the cold mixture twice with ether. Wash the united ethereal extract once with a small quantity of water, and dry it with sodium sulphate. Then distil off the ether from the filtered extract, preferably using a distillation flask of type shown in Fig. 41 (p. 65) and of ca, 50 ml, capacity, the extract being run in as fast as the ether distils, and then fractionally distil the oxime at water-pump pressure. Collect the liquid ketoxime, b.p. 110-111713 mm. Yield, 30-32 g. 

For this reduction use preferably a i litre round-bottomed flask having 3 necks (Fig. 23(G), p. 46), the two necks at the flanks being straight (to avoid the obstruction, during the addition of sodium, which a curved neck might cause). Fit the central neck with a stirrer, one of the side necks with a reflux water-condenser, and the other with a glass or rubber stopper. 

Assemble a 250 ml. three-necked flask, fitted with a stirrer, a reflux condenser and a dropping-funnel, as in Fig. 22(A) and (j), p. 43, or Fig. 23(c), p. 46 (or a two-necked flask, with the funnel fitted by a grooved cork (p. 255) to the top of the condenser). Place 40 ml. of ethanol in the flask, and then add 2-3 g. of sodium cut into small pieces. When all the sodium has dissolved, heat the stirred solution on the water-bath, and run in from the funnel 17 g. (17 ml.) of ethyl malonate and then (more slowly) io-2 g. (12 ml.) of mesityl oxide, the reaction-mixture meanwhile forming a thick slurry. Boil the stirred mixture under reflux for i hour, and then add a solution of 10 g. of sodium hydroxide in 50 ml. of water, and continue boiling the pale honey-coloured solution for ij hours more. 

A 1500 ml. flask is fitted (preferably by means of a three-necked adaptor) with a rubber-sleeved or mercury-sealed stirrer (Fig. 20, p. 39), a reflux water-condenser, and a dropping-funnel cf. Fig. 23(c), p. 45, in which only a two-necked adaptor is shown or Fig. 23(G)). The dried zinc powder (20 g.) is placed in the flask, and a solution of 28 ml. of ethyl bromoacetate and 32 ml. of benzaldehyde in 40 ml. of dry benzene containing 5 ml. of dry ether is placed in the dropping-funnel. Approximately 10 ml. of this solution is run on to the zinc powder, and the mixture allowed to remain unstirred until (usually within a few minutes) a vigorous reaction occurs. (If no reaction occurs, warm the mixture on the water-bath until the reaction starts.) The stirrer is now started, and the rest of the solution allowed to run in drop-wise over a period of about 30 minutes so that the initial reaction is steadily maintained. The flask is then heated on a water-bath for 30 minutes with continuous stirring, and is then cooled in an ice-water bath. The well-stirred product is then hydrolysed by the addition of 120 ml. of 10% sulphuric acid. The mixture is transferred to a separating-funnel, the lower aqueous layer discarded, and the upper benzene layer then... 

Fit a three necked 250 ml. flask with a central rubber-sleeved or mercury-sealed stirrer, c/. Fig. 23(c), p. 45, where only two necks are shown, and with a thermometer the bulb of which reaches as near the bottom of the flask as the stirrer allows the third neck will carry at first a dropping-funnel and later a reflux condenser. Place 20 g. (19-5 ml.) of ethyl acetoacetate and 45 ml. of glacial acetic acid in the flask and by ice-water cooling adjust the temperature of the stirred mixture to 5 -7° maintain this temperature whilst adding a solution of 5 4 g. of sodium nitrite in 8 ml. of water slowly from the dropping-funnel during 15 minutes. Continue the stirring for 20-30 minutes, and then... 

Fit a 250 ml. three-necked flask with a stirrer, a reflux condenser and a dropping-funnel. (Alternatively, use a two-necked flask, with the dropping-funnel fitted by a grooved cork into the condenser.) Place 15 g. of powdered thiourea and 40 ml. of water in the flask and stir the mixture whilst 18 5 g. (16 ml.) of chloroacetone are added dropwise over a period of 20 minutes the thiourea will dissolve and the temperature of the mixture... 

Now add the diazonium solution slowly from a dropping-funnel to the vigorously-stirred arsenite solution, keeping the temperature of the latter at 5 7°. The frothing caused by the evolution of nitrogen will probably be dispersed by the stirrer if not, the addition of 1-2 ml. of ether, preferably in a fine jet from a wash-bottle, will cause it to subside. 

If a small Beckmann thermometer, similar to that used in the Sucharda-Bobranski method (p. 442) is available, the above method can be readily modified by replacing the tube T (Fig. 79) by an ordinary small boiling-tube without the side-arm A. The thermometer B and the stirrer S are fitted as in Fig. 79. The volume of solvent (usually ca 5 ml.) must of course cover the bulb of the thermometer. 

Multi-necked flasks. Fig. II, 1, 8, a, illustrates a typical threenecked flask. This has numerous applications in organic chemistry for many operations, the central aperture carries a mechanical stirrer, and the two side apertures a dropping funnel and a reflux condenser respectively. 

Kestner Laboratory Stirrer supplied by Kestner Evaporator and Engineering Co. Ltd. 

A powerful stirrer, driven by a flexible driving shaft between the motor (I h.p.) and the stirrer, is depicted in Fig. II, 7, 3. The motor may be placed at a distance from the stirrer head and reaction vessel, thus enabling the assembly to be used for inflammable, corrosive or fuming liquids without damage to the motor. Furthermore, any laboratory retort stand and clamp may be used since the stirrer head weighs only about 250 grams. A variable speed control (500-2000 r.p.m.) is provided. 

Stirrers are usually made of glass, but those of monel metal, stainless steel or Teflon (a polyfluoroethylene) also find application in the labora tory. An important advantage of a stirrer with a Teflon blade is that it is... 

A useful stirrer—sometimes termed a Hershberg stirrer— Fig. 11,7,5. for efficient agitation in round-bottomed vessels, even of... 

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