Laboratory heating under reflux

The following procedure is an operatively simple route for the synthesis of bromotrimethylsilane on a preparative laboratory scale from reagents that are readily accessible and inexpensive. This could be a method of choice in some laboratories despite the fact that bromotrimethylsilane is now commercially available (Petrach Systems, Aldrich, or Alpha). Moreover, the procedure also serves as a suitable method for the synthesis of azidotrimethylsilane and isocyanatotrimethylsilane, and is specially useful for the preparation of cyanotrimethylsilane. Thus a mixture of triphenylphosphine dibromide, hexamethyldisiloxane, and a catalytic amount of powdered metal zinc in 1,2-dichlorobenzene is heated under reflux to produce bromotrimethylsilane in nearly quantitative yield, which is simultaneously distilled over a suspension of the corresponding pseudohalogenoacid salt in N, /V-dimethylformamide as solvent.6... 

Small Quantities. Wear nitrile rubber gloves, laboratory coat, and eye protection. Work in the fume hood. Place 25 mL of concentrated hydrochloric acid in a 100-mL, three-necked, round-bottom flask equipped with a stirrer, water-cooled condenser, dropping funnel, and heating mantle or steam bath. Heat the solution to gentle reflux and add the acrylonitrile (5.3 g, 0.1 mol) dropwise at such a rate to maintain gentle reflux. Heat under reflux while stirring (to prevent bumping) for 5-10 hours. Cool, dilute the reaction mixture with water, and wash down the drain with at least 50 times its volume of water.9... 

Metal chloride hydrates, such as CrClj.bH O, can be efficiently dehydrated to the anhydrous material in the laboratory by heating under reflux in the presence of an excess of SOClj (c/. Section 9.10.3.1). 

Synthesis of the previously unreported W(tbq)4 chelate initially involved a Schraup synthesis of Htbq. Previous attempts in other laboratories had failed because of the acid cleavage of the tert-hutyl group in the arsenic acid oxidation step (16). We have successfully used picric acid and 4-tgrt-butyl-2-nitrophenol as oxidants with yields of 5-10%. The procedure is similar to that used for Hmq (3,6). The W(tbq)4 chelate was prepared by the decarbonylation of W(CO)e in mesitylene heated under reflux, followed by sublimation of unreacted material and crystallization from chloroform. Chromatographic separation on silica gel with 1 1 v/v CHCI3 hexane produced an analytically pure W(tbq)4 chelate. 

How Do I Know How Hot to Heat It A common problem that inexperienced students encounter when they assemble an apparatus for heating under reflux is that it is difficult to decide what temperature setting to use for heating the contents of a vial or flask fo fhe desired temperature. This problem becomes more acute when the students attempt to reproduce the temperatures that are specified in the laboratory procedures of a fextbook. 

ETHANOLAMINE. H,N CHj CH--OH. Limited laboratory tests under refluxing conditions indicate that ethanolamine caused mild attack (-4 mpy) of 3003 alloy. Aluminum alloy heat exchangers have been used for handling a ethanolamine-diethylene glycol mixture to remove CO . H S, and water from natural gas. Aluminum alloy tanks have been used to transport ethanolamine. See also Ref (1) p. 131. 

Finally, another related study from the Sun laboratory concerned the synthesis of hydantoins utilizing acryloyl chloride to prepare a suitable polymer support [87]. All steps were carried out under reflux conditions in a dedicated microwave instrument utilizing 50-mL round-bottomed flasks. Identical reactions under classical thermal heating did not proceed in the same time period. 

Wear protective gloves, laboratory coat, goggles, and breathing apparatus if necessary. Cover spill with a 1 1 1 mixture by weight of soda ash, clay cat litter (bentonite), and sand. Scoop the mixture into a plastic container and either label and send for disposal by burning7 or, in the fume hood, add the mixture to a solution of 85% potassium hydroxide pellets in ethanol, allowing 0.36 mol (23.7 g) of potassium hydroxide and 100 mL of ethanol for each 0.1 mol (23.7 g) of 1, 2-dibromo-3-chloropropane to be destroyed. Heat the mixture under reflux for 8 hours. Decant the solution into the drain with a large volume of water. Treat the solid as normal refuse.6-8... 

Small Quantities. Wear eye protection, butyl rubber gloves,10 and laboratory coat. Work in the fume hood. For each 1 mL of dimethylformamide, add 10 mL of 10% sodium hydroxide solution. Heat the mixture under reflux for 30 minutes, or allow to stand at room temperature for 48 hours. Wash the liquid into the drain.10... 

Next to distillation, the most important purification method, especially in the laboratory, is recrystallization. In this operation, the substance to be purified is dissolved by heating with a suitable solvent, usually by boiling under reflux, and the hot solution is filtered to remove any undissolved impurities. The clear filtrate is cooled slowly, whereupon most of the main product crystallizes out, leaving the more soluble impurities in solution. If crystallization occurs slowly, it may be hastened by stirring. Some substances tend to form supersaturated solutions, and with these it may be necessary to induce... 

Reflux is one of the most common techniques you will encounter in your chemistry laboratory classes. Since many reactions between covalent compounds are slow processes rather than instantaneous reactions, prolonged heating forces the equilibrium to give an acceptable amount of product. In the reflux process, the reactants are dissolved or suspended in a suitable solvent, the solvent is boiled and then condensed so that it returns to the reaction flask. Once set up, a reaction carried out under reflux can be run for minutes, hours or even days to promote the required reaction. The basic components for a reflux apparatus are ... 

Because volatile and flammable solvents are used in this experiment, flameless heating should be used for heating the reaction under reflux and for distilling the product. However, if it is necessary to use a small microburner to distill the product, be sure that no one is using flammable solvents in the laboratory. 

DIETHANOLAMINE. HN(CH CHrOHlj. Laboratory tests showed that alloy 3003 was resistant to diethanolamine at ambient temperature. However, at the boiling temperature and under refluxing conditions diethanolamine caused moderate attack. While aluminum alioy heat exchangers have been used to handle diethanolamine solutions, tests under the anticipated conditions should be made prior to use In service. See also Ref (3) p. 145. 

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