Synthetic organic experiments are conducted at temperatures ranging from -90 degrees to 200 degrees Celsius. It is important to know how to achieve and maintain the correct temperature for a reaction, especially over long time periods. Temperature should be monitored with a low-temperature alcohol thermometer.
See Also: The Complete List on the Hoveyda Group website.
For reactions that require heating to a temp below 140 degrees, a hot plate/oil bath apparatus with internal temperature control is most commonly used. Mineral oil polymerizes at ~150 degrees; for higher temperatures switch to silicone oil (up to 220 degrees C), white oil, or a heating mantle with sand (see below).
Paraffin oil can be used to heat reactions in solvent up to 300 degrees C. Please be aware that you should dry this oil beforehand (heating to 200 degrees over CaH2 while purging with nitrogen or argon).
For reactions requiring high temperatures, or large scale reactions, a heating mantle full of sand controlled by a Variac can be a good choice. Sand is less messy than oil and high temperatures are easy to attain. Put a thermometer in the sand and then experiment with the Variac until you achieve the correct temperature.
For gentle heating (35-80 degrees), a hot plate/water bath is sometimes convenient.
Don't forget: the temperature of the reaction will equal the boiling temperature of the solvent, unless the vessel is sealed.
See Also: Complete list of heat sources for chemical reactions