Reflux Apparatus

To bring about a successful reaction between two substances, it is often necessary to mix the materials together intimately and to maintain a specific temperature.The mixing operation is conveniently achieved by dissolving the materials in a solvent in which they are mutually soluble. If the reaction is carried out in solution under reflux conditions, the choice of solvent can be used to control the temperature of the reaction. Many organic reactions involve the use of a reflux apparatus in one arrangement or another. 

What do we mean by reflux The term means to return, or run back.  

This return is exactly how the reflux apparatus functions. When the temperature of the reaction system is raised to the solvent s boiHng point (constant temperature), all vapors are condensed and returned to the reaction flask or vial this operation is not a distillation and the liquid phase remains at a stable maximum temperature. In microscale reactions, two basic types of reflux condensers are utilized the air-cooled condenser, or air condenser (Chapter 3W, Fig. 3.6W), and H[www] the water-]acketed condenser (see Fig. 3.13 and Chapter 3W, Fig. 3.7W).The air 

Air condensers can occasionally be used with lower boiling systems however, the water-jacketed condenser is more often employed in these situations. 

The water-jacketed condenser employs flowing cold water to remove heat from the vertical column and thus facilitate vapor condensation. It is highly effective at condensing vapor from low-boiling liquids. 

---

After heating in a reflux apparatus for one-half hour, the mixture is poured into ice in the presence of ammonium chloride. 

Figure 2.4. (a) Typical Schlenk-line and (b) distillation/reflux apparatus used in sol-gel synthesis of film precursor solutions. [Reprinted from Ref. 71, with permission.]... 

Care should be taken not to allow the solution to evaporate, thereby changing the concentration of the components. A siliconized 250-mL volumetric flask works well. Alternatively, a reflux apparatus can be used. 

Like all the malonic acids, this acid loses carbon dioxide on heating, yielding butyric acid, B.P. 163°. The reaction is carried out by heating 10 gms. of the acid in a reflux apparatus to 180° until carbon dioxide is no longer evolved (J, hour). The residue is fractionated for butyric acid between 160° and 165°. 

To 80 gms. (excess) of finely powdered potassium or sodium dichromate, and 100 gms. of 50% sulphuric acid placed in a reflux apparatus (see p. 212), 70 gms. (1 mol.) of 25% alcohol are slowly added. The mixture is heated for 30 minutes and distilled until only very little acid passes over. The distillate is neutralised with caustic potash, and evaporated to dryness on a water bath. The residue is powdered and distilled with cone. 

The methylacetanilide is boiled with concentrated alcoholic potash solution for about 24 hours in a reflux apparatus. The alcohol is distilled off, and the residue neutralised by addition of hydrochloric acid. The residual xylene is then distilled off in steam, the solution made alkaline, and the methylaniline steam distilled. It is taken up with ether, dried over anhydrous sodium sulphate or potassium hydroxide and fractionated. 

To investigate the colouring matter added,1 15-20 grams of the butter are boiled in a reflux apparatus with about 40 c.c. of methyl alcohol. When thoroughly cold (best in ice) the liquid is filtered and to the residue from a few drops of the alcoholic solution evaporated in a porcelain capsule is added drop by drop down the side of the dish, cone, sulphuric, nitric or hydrochloric acid, the colour manifested being observed. 

The finely ground material is heated in a reflux apparatus with petroleum ether and ammonium carbonate, the mass being afterwards filtered and the petroleum extract shaken with methyl alcohol. The latter is separated and evaporated on a water-bath the presence of egg is then detectable by the odour of the residue. 

Pure alcohol. Pure alcohol of commerce of at least 96% strength is neutralised exactly, boiled for an hour in a reflux apparatus with 1-2% of metaphenylenediamine hydrochloride and then distilled, the first and last portions of the distillate being discarded. The sp. gr. of the alcohol thus obtained is determined and the strength adjusted to 90% or 50% (see Tables XXV and XXVII). This alcohol should not colour either with Schiff s reagent or when heated for an hour with an equal volume of concentrated sulphuric acid in a bath at 120°. 

Preparation op the liquid to be tested. The spirit must be freed from other impurities, such as esters, acids and aldehydes, which might influence the test, and is also brought to a definite strength (30%). To this end 100 c.c. of the spirit are boiled for an hour in a reflux apparatus with a few drops of concentrated potassium hydroxide solution, the greater part of the liquid being then distilled and the distillate made up to xoo c.c. 

Detection and Determination of Ketones in Presence of Aldehydes.—(A) Qualitative Test. A certain amount of the distilled alcohol is diluted so as to obtain about 50 c.c. of about 50% alcohol and then boiled with 10 c.c. of 10% sodium hydroxide solution in a reflux apparatus for 15 minutes. The liquid is afterwards allowed to cool a little and then distilled, about 30-40 c.c. of distillate being collected. The distillate is diluted to 50 c.c. and boiled with 0-5 c.c. of syrupy phosphoric acid and 0 5 c.c. of colourless aniline in a reflux apparatus for about half an hour. By this treatment the aldehydes in the spirit are destroyed or fixed. After cooling to some extent, the liquid is distilled slowly, two portions of distillate of 5 c.c. each being collected and tested for ketones by one of the two methods given above (see p. 252). If ketones are present in more than mere traces, positive reactions should be given by both portions of the distillate. 

Insoluble Impurities.—From 1 to 2 grams of the substance, previously dried, are heated with about 100 c.c. of chloroform in a reflux apparatus on a water-bath, the liquid being afterwards filtered—preferably through a glass-wool filter, previously tared—and the insoluble residue washed with chloroform, dried and weighed. 

A piece of the material is boiled in a reflux apparatus successively with ether, carbon tetrachloride, benzene, and alcohol, the treatment being stopped when the waterproofing material passes into solution in one of the solvents. This may be tested by ascertaining if the material treated in this way and well dried in the air has lost its impermeability totally or in part, and also by evaporating the extract in a porcelain dish on a water-bath and examining the residue the latter should consist of oil or fat, tar or fatty acids. 

According to Perrin,1 a piece of the fabric is boiled in a reflux apparatus... 

A solution of 2.5 parts of sodium in n-butylalcohol is boiled with 30 parts of a-chloro-y-quinoline-carboxylic acid diethyl-amino-ethylene-amide in a reflux apparatus, and when the reaction is over the excess of butylalcohol is distilled. The remaining base is taken up with ether the solution is washed with water and dried. The solvent is then distilled. The a-n-butoxy- quinoline-carboxylic acid diethyl-amino-ethylene-amide forms as colorless crystals, after recrystallization from petroleum ether melting point of it 64°C. 

A solution of 5.0 g of l-methyl-3-pyrrolidinol and 12.5 g of methyl phenyl-2-thienylglycolate in 200 ml of n-heptane is heated to reflux temperature, a trace of sodium methylate is added, and refluxing of the mixture is continued for 3 h. A Dean-Stark trap is incorporated in the reflux apparatus to separate and withdraw the methanol produced by the reaction. At the end of the reflux period, the reaction mixture is cooled and extracted two times with 100 ml portions of 2 N hydrochloric acid. The acid extracts are combined, basified with potassium carbonate, and extracted three times with 50 ml portions of benzene. The benzene extracts are combined, washed two times with 25 ml portions of water, and dried. The benzene is removed from the dried extract by evaporation at reduced pressure. The residue is l-methyl-3-pyrrolidylphenyl-2-thienylglycolate in the form of a clear liquid. 

A) Obtaining a p-Ketonic Ester by Reacting Ethyl Bromoisobutyrate with Cyanonerolin 9 g of cyanonerolin are heated in a reflux apparatus for 40 minutes with 7 g of zinc and 19 g of ethyl bromoisobutyrate in the presence... 

The p-benzyloxypropiophenone used for the transformation is prepared by adding to a solution of 6.9 g of sodium in 230 ml of absolute alcohol 45.0 g of p-hydroxypropiophenone and 54.0 g of benzyl bromide, and boiling for 1 h in a reflux apparatus. The excess of alcohol is then distilled and the residue is extracted with ether and water. After drying it the ethereal solution is evaporated and the residue is recrystallized from alcohol of 95% strength. The yield amounts to 60.0 g. The p-benzyloxypropiophenone melts at 100°-101°C. 

Figure 010. Reflux apparatus equipped with drying tube for the extraction of pipeline from black pepper. Cold water should... 

Into a suitable reflux apparatus, place 13 grams (0.45 oz.) of catechol, followed by 14 grams (0.49 oz.) of allyl bromide, and then add in 22 milliliters (0.74 fluid oz.) of dry acetone. Then stir the entire mixture to form a uniform mixture. Immediately thereafter, gradually add in 17 grams (0.59 oz.) of finely divided anhydrous potassium carbonate, and stir the mixture while adding this potassium carbonate. After the addition of the potassium carbonate, reflux the entire reaction mixture at 60 Celsius for about 3 hours. Note fit a calcium chloride drying tube to the top of the reflux condenser to keep moisture out from the apparatus. After refluxing for about 3 hours, quickly remove the reflux condenser, and replace it with a conventional cold water condenser, fitted with a receiver... 

Into a suitable flask, add 135 milliliters of 98% sulfuric acid, followed by 82 grams of N,N -diphenylurea. Thereafter, stir the mixture to dissolve most of the N,N -diphenylurea. Afterwards, place 250 milliliters of 99% nitric acid into a clean reflux apparatus fitted with a motorized stirrer, and then gently reflux the nitric acid at 40 Celsius using a hot plate or oil bath. When the temperature of the nitric acid reaches 40 Celsius, slowly add drop-wise, the N,N -diphenylurea/sulfuric acid mixture to the 99% nitric acid while rapidly stirring the nitric acid and maintaining its temperature around 40 Celsius. After the addition of the N,N -diphenylurea/sulfuric acid mixture, reflux the entire reaction mixture at 65 Celsius for 2 hours with constant stirring. After 2 hours, remove the heat source, and allow the reaction mixture to cool to room temperature. Thereafter, drown the entire reaction mixture into 500 milliliters of ice water, and allow this entire mixture to stand at room temperature for 24 hours. Thereafter, filter-off the precipitated solid (composed of tetranitro, and trinitro isomers of N,N -diphenylurea), and then vacuum dry or air dry this solid. 

---