Temperature control melting-point baths

The Friedlander annulation is one of the most straightforward approaches towards poly-substituted quinolines. Thus, a 22-membered library of quinolines was synthesized in a TsOH-catalyzed cyclocondensation-dehydration of 2-aminoaryl ketones and 2-aminoarylaldehydes with ketones in a household microwave oven (with power control) under solvent-free conditions [112]. It was observed that the Friedlander reaction occurred readily also in an oil-bath (at 100 °C). To compare the conventional and dielectric heating conditions precisely, a purpose-built monomode microwave system with temperature control was employed instead of the household oven. The experiments at 100 °C under otherwise identical conditions demonstrated that the dielectric heating protocol was only slightly faster. Products were isolated by a simple precipitation-neutralization sequence (in the case of solid products) or neutralization-extraction for oily or low melting point products (Scheme 43). 

A Wood s metal bath contains a metal alloy (50 per cent bismuth, 25 per cent lead, 12.5 per cent tin, and 12.5 per cent cadmium) with a low melting point ( 70°) which may be used up to quite high temperatures ( 400°). The metal is easily oxidized at the higher temperatures and, therefore, is usually covered with a protective layer of carbon. An electrically heated bath is recommended, since the temperature is then easily controlled. This may be made by taking an ordinary tin can (preferably low and wide), covering it with asbestos paper, and winding a coil of nichrome wire around it. The wire is covered with more asbestos paper held in place by some coils of copper wire. The entire assembly is placed inside a metal container such as... 

The rapid-water-quenching system produces good optical properties, has low equipment cost, but can be difficult to use to get precise control over the water temperature. Vibrations and currents can cause little marks on the film. A critical point is the necessity for maintaining a smooth surface in the water quench tank where the melt first enters. Different devices are used to control the flow of water such as baffles with openings. It has serious limitations when high production speeds are attempted the water must be kept from carrying over into any on-line pretreatment and the finished roll. However, these problems can be controlled. This liquid bath system has been used for blown tubular film inside the blown film to improve... 

Calibration of the CTD temperature sensor to better than 2mK accuracy thus requires three units (i) a reference temperature bridge that is accurate to 1 mK at a resolution of at least 0.5 mK, (ii) a thermostat bath to obtain the two oceanic primary fixed-point temperatures with a water triple point cell and a gallium melting point cell to control the drift of the reference sensor and (iii) a temperature controlled bath that is stable to better than 0.5 mK while taking a calibration point with the reference thermometer and the immersed CTD. 

In a Pasteur pipette loosely place a very small piece of cotton followed by 2.5 g of alumina. Add to the top of the pipette 1.5 mL of styrene and collect 1 mL in a disposable 10 x 75-mm test tube. Add to the tube 50 mg of benzoyl peroxide and a thermometer and heat the tube over a hot sand bath. When the temperature reaches about 135°C polymerization begins and, since it is an exothermic process, the temperature rises. Keep the reaction under control by cautious heating. The temperature rises, perhaps to 180°C, well above the boiling point of styrene (145°C) the viscosity also increases. Pull the thermometer from the melt from time to time to form fibers when a cool fiber is found to be brittle remove the thermometer. A boiling stick can be added to the tube and the polymer allowed to cool. It can then be removed from the tube or the tube can be broken from the polymer. Should the polymer be sticky the polymerization can be completed in an oven overnight at a temperature of about 85°C. 

The EMF measured by a readout device reflects the difference between the temperatures of the measuring junction and the reference junction thus, the temperature at the reference junction must be properly controlled. It is usually maintained at the freezing point of water (0°C) by using an ice bath (Fig. 16.23). The ice bath should be a mixture of crushed ice and pure water in a Dewar flask with considerably more ice than liquid. It can be very accurate but not too convenient in some applications, since frequent replacement of melted ice is required. With a thermoelectric refrigeration system [36], ice can be maintained by cooling the bath of water with thermoelectric cooling elements. 

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