Inert atmosphere methods

Inert atmosphere reactions - these should be done in the fume cupboaTd, since j most c)f the solventsend reagents t ed- ta/e flammable and/dfltoxic. 

Safety note Gas cylinders must be supported safely either by clamping to tiie bench using a special cylinder clamp or in a cylindei tiulley. 

The source of the inert atmosphere is usually a cylinder of nitrogen or argon gas under pressure, which should be placed as close to the apparatus as possible to avoid long runs of connecting rubber tubing. 

The gas flow rate from the cylinder is controlled by the cylinder head regulating valve (Fig. 18.1). Before you start make sure that the regulator outlet tap is off (turn anti-clockwise until it feels free ) and then open the valve to the cylinder with the cylinder spanner (turn anti-clockwise) and the cylinder pressure should be indicated on the right-hand pressure dial. Switch on the gas at the regulator (turn slowly clockwise) until there is a reading on the left-hand dial. Use the minimum pressure required to provide a steady flow of gas. The gas flow rate from the regulator can be controlled further by a needle valve on the regulator outlet, if one is fitted. To switch off, reverse the instructions above. 

Use clean, dry, thin-walled rubber tubing and special adapters with ground-glass joints to connect the tubing to your reaction flask or to the inlet pipe of a bubbler . Where a single cylinder supplies several outlets, e.g. in a fume cupboard, the gas flow rate may change markedly when someone turns off one of the outlets, resulting in an increase in gas pressure to your equipment. You should, therefore, fit a gas blow-off valve between your gas supply and 

Nitrogen atmospheres - note that lithium metal reacts slowly with nitrogen. 

Use of argon - reactions carried out under argon can be opened to the atmosphere briefly ( 5 s), for the addition of other chemicals, without degradation of the inert atmosphere. 

Inert gas flow rate - only low flow rates are required to provide an inert atmosphere, once the apparatus has been swept with the gas. 

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The transition-metal anions present the main experimental problem and precautions must be taken against oxidation or hydrolysis. However, handling by vacuum line or inert atmosphere methods is sufficient safeguard and extraordinary precautions are not required. 

Rubidium can be liquid at room temperature. It is a soft, silvery-white metallic element of the alkali group and is the second most electropositive and alkaline element. It ignites spontaneously in air and reacts violently in water, setting fire to the liberated hydrogen. As with other alkali metals, it forms amalgams with mercury and it alloys with gold, cesium, sodium, and potassium. It colors a flame yellowish violet. Rubidium metal can be prepared by reducing rubidium chloride with calcium, and by a number of other methods. It must be kept under a dry mineral oil or in a vacuum or inert atmosphere. 

Shipment Methods and Packaging. Pyridine (1) and pyridine compounds can be shipped in bulk containers such as tank cars, rail cars, and super-sacks, or in smaller containers like fiber or steel dmms. The appropriate U.S. Department of Transportation (DOT) requirements for labeling are given in Table 4. Certain temperature-sensitive pyridines, such as 2-vinylpyridine (23) and 4-vinylpyridine are shipped cold (<—10°C) to inhibit polymerisation. Piperidine (18) and certain piperidine salts are regulated within the United States by the Dmg Enforcement Agency (DEA) (77). Pyridines subject to facile oxidation, like those containing aldehyde and carbinol functionaUty, can be shipped under an inert atmosphere. 

Heating and Cooling. Heat must be appHed to form the molten zones, and this heat much be removed from the adjacent sohd material (4,70). In principle, any heat source can be used, including direct flames. However, the most common method is to place electrical resistance heaters around the container. In air, nichrome wine is useflil to ca 1000°C, Kanthal to ca 1300°C, and platinum-rhodium alloys to ca 1700°C. In an inert atmosphere or vacuum, molybdenum, tungsten, and graphite can be used to well over 2000°C. 

A convenient method for assessing the extent of surface oxidation is the measurement of volatile content. This standard method measures the weight loss of the evolved gases on heating up to 950°C in an inert atmosphere. The composition of these gases consists of three principal components hydrogen, carbon monoxide, and carbon dioxide. The volatile content of normal furnace blacks is under 1.5%, and the volatile content of oxidized special grades is 2.0 to 9.5%. 

Direct Reduction with Metals. PoUucite can be directly reduced by heating the ore in the presence of calcium to 950°C in a vacuum (20), or in the presence of either sodium or potassium to 750°C in an inert atmosphere (21). Extraction is not complete. Excessive amounts of the reducing metal is required and the resultant cesium metal is impure except when extensive distiUation purification is carried out. Engineering difficulties in this process are significant, hence, this method is not commerciaUy used. 

Copper Oxides. Coppet(I) oxide [1317-39-17 is a cubic or octahedral naturally occurring mineral known as cuprite [1308-76-5]. It is ted or reddish brown in color. Commercially prepared coppet(I) oxides vary in color from yellow to orange to ted to purple as particle size increases. Usually coppet(I) oxide is prepared by pytometaHutgical methods. It is prepared by heating copper powder in air above 1030°C or by blending coppet(II) oxide with carbon and heating to 750°C in an inert atmosphere. A particularly air-stable coppet(I) oxide is produced when a stoichiometric blend of coppet(II) oxide and copper powder ate heated to 800—900°C in the absence of oxygen. Lower temperatures can be used if ammonia is added to the gas stream (27-29). 

The most general preparative route to phosphides (Faraday s method) is to heat the metal with the appropriate amount of red P at high temperature in an inert atmosphere or an evacuated sealed tube ... 

Three operations usually accompany the carrying out of a reaction on a synthetic scale stirring, addition of a reagent, and temperature control. Most often, a threenecked round-bottom flask allows simultaneous execution of these operations along with certain other controls that may be desirable, such as introduction of an inert atmosphere or maintenance of reflux. In what follows, a short description of a suitable method of carrying out each of the operations is given. 

Volkov and Sushko [335] described a technique that is based on the use of nets. This method provides direct absorption spectra, but is very complex to perform The net must be placed in a chamber that ensures a pure inert atmosphere so as to avoid hydrolysis of the melt, and the temperature and geometry of the net must be kept very stable. Other major limitations of the method are the requirements that the surface tension of the melt be such that its position on the net is ensured, and that the vapor pressure of the material in molten state be as low as possible... 

For very high melting polymers (Tm > 300°C), a solution polymerization is normally employed. If this is started from the reactive acid chloride, the reaction temperature can be low. Polymers from acid chlorides can also be prepared by the interfacial method. Semicrystalline PA can be postcondensed in the solid state to higher molecular weights. To do this, the polymer powder/particles are heated for many hours below their melting temperature in an inert atmosphere. 

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