Reflux, heating under

A skilled worker can use a micro-Bunsen burner for most types of heating. Nevertheless, as there is a tendency for a liquid to shoot out of a small test tube when heated, it is preferable to place the tube in a hot water-bath or in a metal heating block. A small glycerol bath is suitable for distillations and heating under reflux, the glycerol being subsequently easily removed from flasks, etc., by washing with water. 

Reflux Distillation Unit. The apparatus shown in Fig. 38 is a specially designed distillation-unit that can be used for boiling liquids under reflux, followed by distillation. The unit consists of a vertical water-condenser A, the top of which is fused to the side-arm condenser B. The flask C is attached by a cork to A. This apparatus is particularly suitable for the hydrolysis of esters (p. 99) and anilides (p. 109), on a small scale. For example an ester is heated under reflux with sodium hydroxide solution while water is passed through the vertical condenser water is then run out of the vertical condenser and passed through the inclined condenser. The rate of heating is increased and any volatile product will then distil over. 

Dissolve 10 g. of chloro- 2,4-dinitrobenzenet in 50 ml. of dioxan in a 250 ml. conical flask. Dilute 8 ml. of hydrazine hydrate with an equal volume of water and add this slowly with shaking to the dioxan solution, keeping the temperature between zo " and 25°. Heat under reflux for 10 minutes to complete the reaction and then add 5 ml. of ethanol and heat again for 5 minutes. Cool and filter oflF the orange 2,4-dinitrophenylhydra-zine. Recrystallise the dry product from ethyl acetate m.p. 200° (decomp.). Yield, 7 g. 

Mix 1 g. of quinaldine and 1 g. of powdered />-dimethylaminobenzab dehyde, add 2 -3 drops of 10% etl nolic zinc chloride solution, and heat under reflux in an oil-bath at 150 for 1 hour. Cool the product in ice-water, and reciystallise it from ethanol. p-Dimethylaminostyryl-quinoline (I) separates as bright yellow crystals, m.p. 177-178°. 

B) Sulphonamides. Mix 0 5 g. of the sulphonic acid or its alkali salt with 15 g. of phosphorus pentachloride, and heat under reflux in a silicone- or oil-bath at 150° for 30 minutes then allow it to cool. 

In general the method is more satisfactory with esters of aromatic acids than with esters of aliphatic acids. Esters of alcohols other than methyl and ethyl are best treated by first converting them into methyl esters thus Heat together under reflux i ml. of the higher ester, 5 ml. of methanol and 0-2 g. of sodium methoxide. [In place of the sodium methoxide, it suffices to add o i g. of metallic sodium to the methanol.] After refluxing, distil off the excess of methanol (b.p, 65 ). The residue is then heated under reflux with benzylamine as described above. 

Example. Heat under reflux 0 5 g. of ammonium benzoate and 1 5 ml. of benzylamine for 1 hour. Shake with water to remove unchanged benzylamine and filter off the benzylamide. Recrystallise from ethanol m.p., 105 . 

Alkaline permanganate. Heat under reflux i g. of i,2 naph thoquinone, 50 ml. of saturated aqueous KMn04 solution and 2 g. of anhydrous NajCO for 30 minutes. Then proceed as for oxidation of benzyl chloride (p. 393). 1,2-Naphthoquinone gives phthalic acid, m.p. 195°. Phenanthraquinone gives diphenic acid, HOOC CeH CeH COOH, m.p. 229°. 

D) Phenylurea Derivatives. This reaction usually proceeds readily when cold solutions of the dried amine and of phenyl isocyanate, each in petroleum (b.p. 100-120 ), are mixed if no reaction is obvious, heat under reflux for 30 minutes. Care in using the isocyanate, p. 336.)... 

The above diamines can alternatively be identified as their diacetyl derivatives. Heat under reflux 0 5 g. of the diamine with 3 ml. of acetic acid—NaOH solution will cause the separation of the diacetyl derivative. Recrystallise from ethanol. M.ps. of the diacetyl derivatives of 0-, m-, and />-phenylene diamine are 185 , 191 , and 304 respectively (p. 551). 

Heat under reflux i g. of anisole and 10 ml. of constant-boiling hydrogen iodide for 30 minutes. Now distil off the volatile methyl iodide and identify it in the distillate (see pp. 390-391). 

For alcohols of b.p. below 150°, mix 0- 5 g. of 3-nitrophthalic anhydride (Section VII,19) and 0-5 ml. (0-4 g.) of the dry alcohol in a test-tube fitted with a short condenser, and heat under reflux for 10 minutes after the mixture liquefies. For alcohols boiling above 150°, use the same quantities of reactants, add 5 ml. of dry toluene, heat under reflux until all the anhydride has dissolved and then for 20 minutes more remove the toluene under reduced pressure (suction with water pump). The reaction product usually solidifies upon cooling, particularly upon rubbing with a glass rod and standing. If it does not crystallise, extract it with dilute sodium bicarbonate solution, wash the extract with ether, and acidify. Recrystallise from hot water, or from 30 to 40 per cent, ethanol or from toluene. It may be noted that the m.p. of 3-nitrophthalic acid is 218°. 

Into a 500 ml. three-necked flask, provided with a mechanical stirrer, a gas inlet tube and a reflux condenser, place 57 g. of anhydrous stannous chloride (Section 11,50,11) and 200 ml. of anhydrous ether. Pass in dry hydrogen chloride gas (Section 11,48,1) until the mixture is saturated and separates into two layers the lower viscous layer consists of stannous chloride dissolved in ethereal hydrogen chloride. Set the stirrer in motion and add 19 5 g. of n-amyl cyanide (Sections III,112 and III,113) through the separatory funnel. Separation of the crystalline aldimine hydrochloride commences after a few minutes continue the stirring for 15 minutes. Filter oflF the crystalline solid, suspend it in about 50 ml. of water and heat under reflux until it is completely hydrolysed. Allow to cool and extract with ether dry the ethereal extract with anhydrous magnesium or calcium sulphate and remove the ether slowly (Fig. II, 13, 4, but with the distilling flask replaced by a Claisen flask with fractionating side arm). Finally, distil the residue and collect the n-hexaldehyde at 127-129°. The yield is 19 g. 

Mix 50 ml. of formalin, containing about 37 per cent, of formaldehyde, with 40 ml. of concentrated ammonia solution (sp. gr. 0- 88) in a 200 ml. round-bottomed flask. Insert a two-holed cork or rubber stopper carrying a capillary tube drawn out at the lower end (as for vacuum distillation) and reaching almost to the bottom of the flask, and also a short outlet tube connected through a filter flask to a water pump. Evaporate the contents of the flask as far as possible on a water bath under reduced pressure. Add a further 40 ml. of concentrated ammonia solution and repeat the evaporation. Attach a reflux condenser to the flask, add sufficient absolute ethyl alcohol (about 100 ml.) in small portions to dissolve most of the residue, heat under reflux for a few minutes and filter the hot alcoholic extract, preferably through a hot water fuimel (all flames in the vicinity must be extinguished). When cold, filter the hexamine, wash it with a little absolute alcohol, and dry in the air. The yield is 10 g. Treat the filtrate with an equal volume of dry ether and cool in ice. A fiulher 2 g. of hexamine is obtained. 

If only the monocarboxybc acid is required, the ester after hydrolysis with potash may be strongly acidified with sulphuric acid and the mixture heated under reflux the mineral acid promotes decarboxylation at a temperature just above 100°. The net result is the replacement of the halogen atom of the alkyl halide by —CH COOH thus in the above example ... 

Di lve 20 g. of the cyano ester in 100 ml. of rectified spirit and add a solution of 19 2 g. of pure potassium cyanide in 40 ml. of water. Allow to stand for 48 hours, then distil oflF the alcohol on a water bath. Add a large excess of concentrated hydrochloric acid and heat under reflux for 3 hours. Dilute with water, saturate the solution with ammonium sulphate, and extract with four 75 ml. portions of ether. Dry the combined ethereal extracts with anhydrous sodium or magnesium sulphate, and distil off the ether. RecrystaUise the residual acid from excess concentrated hydrochloric acid, and dry in the air. The yield of pure ew-dimethyl-succinic acid, m.p. 141-142°, is 12 g. 

Into a 500 ml. round-bottomed flask, fitted with a reflux condenser, place 42 g. of potassium hydroxide pellets and 120 g. (152 ml.) of absolute ethyl alcohol. Heat under reflux for 1 hour. Allow to cool and decant the liquid from the residual solid into another dry 500 ml. flask add 57 g. (45 ml.) of A.R. carbon dtsulphide slowly and with constant shaking. Filter the resulting almost solid mass, after cooling in ice, on a sintered glass funnel at the pump, and wash it with two 25 ml. portions of ether (sp. gr. 0-720), followed by 25 ml. of anhydrous ether. Dry the potassium ethyl xanthate in a vacuum desiccator over silica gel. The yield is 74 g. If desired, it ma be recrystallised from absolute ethyl alcohol, but this is usually unneceasary. 

Suspend in a round-bottomed flask 1 g. of the substance in 75-80 ml. of boihng water to which about 0 -5 g. of sodium carbonate crystals have been added, and introduce slowly 4 g. of finely-powdered potassium permanganate. Heat under reflux until the purple colour of the permanganate has disappeared (1-4 hours). Allow the mixture to cool and carefully acidify with dilute sulphuric acid. Heat the mixture under reflux for a further 30 minutes and then cool. Remove any excess of manganese dioxide by the addition of a little sodium bisulphite. Filter the precipitated acid and recrystallise it from a suitable solvent (e.g., benzene, alcohol, dilute alcohol or water). If the acid does not separate from the solution, extract it with ether, benzene or carbon tetrachloride. 

The experimental conditions for conducting the above reaction in the presence of dimethylformamide as a solvent are as follows. In a 250 ml. three-necked flask, equipped with a reflux condenser and a tantalum wire Hershberg-type stirrer, place 20 g. of o-chloronitrobenzene and 100 ml. of diinethylform-amide (dried over anhydrous calcium sulphate). Heat the solution to reflux and add 20 g. of activated copper bronze in one portion. Heat under reflux for 4 hours, add another 20 g. portion of copper powder, and continue refluxing for a second 4-hour period. Allow to cool, pour the reaction mixture into 2 litres of water, and filter with suction. Extract the solids with three 200 ml. portions of boiling ethanol alternatively, use 300 ml. of ethanol in a Soxhlet apparatus. Isolate the 2 2- dinitrodiphenyl from the alcoholic extracts as described above the 3ueld of product, m.p. 124-125°, is 11 - 5 g. 

Dissolve 50 g. of piperonal and 75 g. of malonic acid in a mixture of 160 ml. of pyridine and 2-5 ml. of piperidine contained in a 500 ml. round-bottomed flask, and heat under reflux for 1 hour on a water bath. A rapid evolution of carbon dioxide takes place. Complete the reaction by boiling the solution for 5 minutes. Cool, pour into excess of water containing enough hydrochloric acid to combine with the pyridine, filter ofiFthe piperonylacrylic acid, wash with a little water, and dry. The yield is almost quantitative and the acid is practically pure. It may be recrystallised from glacial acetic acid m.p. 238°. 

The horon difluoride coordination complex is decomposed by heating under reflux with an aqueous solution of 2 mols of sodium acetate per mol of anhydride, whereupon the p diketone (acetylacetone) is liberated. 

Methyl crotonate. Purify commercial crotonic acid by distiUing 100 g. from a 100 ml. Claisen flask attached to an air condenser use an air bath (Fig. II, 5, 3). The pure acid passes over at 180-182° and crystallises out on cooling, m.p. 72-73° the recovery is about 90 per cent. Place 75 g. of absolute methyl alcohol, 5 g. (2 -7 ml.) of concentrated sulphuric acid and 50 g. of pure crotonic acid in a 500 ml. round-bottomed flask and heat under reflux for 12 hours. Add water, separate the precipitated ester and dissolve it in ether wash with dilute sodium carbonate solution until effervescence ceases, dry with anhydrous magnesium sulphate, and remove the ether on a water bath. Distil and collect the methyl crotoiiato at 118-120° the yield is 40 g. 

In a 500 ml. Pyrex round-bottomed flask, provided with a reflux condenser, place a mixture of 40 g. of freshly-distUled phenylhydrazine (Section IV.89) and 14 g. of urea (previously dried for 3 hours at 100°). Immerse the flask in an oil bath at 155°. After about 10 minutes the urea commences to dissolve accompanied by foaming due to evolution of ammonia the gas evolution slackens after about 1 hour. Remove the flask from the oil bath after 135 minutes, allow it to cool for 3 minutes, and then add 250 ml. of rectified spirit to the hot golden-yellow oil some diphenylcarbazide will crystallise out. Heat under reflux for about 15 minutes to dissolve the diphenylcarbazide, filter through a hot water funnel or a pre-heated Buchner fuimel, and cool the alcoholic solution rapidly in a bath of ice and salt. After 30 minutes, filter the white crystals at the pump, drain well, and wash twice with a little ether. Dry upon filter paper in the air. The yield of diphenylcarbazide, m.p. 171 °, is 34 g. A further 7 g. may be obtained by concentrating the filtrate under reduced pressure. The compound may be recrystallised from alcohol or from glacial acetic acid. 

Add 10 ml. of concentrated sulphuric acid cautiously to 45 ml. of water contained in a 200 ml. round-bottomed flask, introduce 3 g. of Nylon 66 polymer into the hot solution, and heat under reflux for 6 hours. Allow to stand for 1 hour and cool in ice for a further hour. Filter off the solid and keep the filtrate. Recrystalhse the sohd (adipic acid) from water m.p. 152°. 

Reduction of a nitro compound to a primary amine. In a 50 ml. round-bottomed or conical flask fitted with a reflux condenser, place 1 g. of the nitro compound and 2 g. of granulated tin. Measure out 10 ml. of concentrated hydrochloric acid and add it in three equal portions to the mixtiue shake thoroughly after each addition. When the vigorous reaction subsides, heat under reflux on a water bath until the nitro compound has completely reacted (20-30 minutes). Shake the reaction mixture from time to time if the nitro compound appears to be very insoluble, add 5 ml. of alcohol. Cool the reaction mixture, and add 20-40 per cent, sodium hydroxide solution imtil the precipitate of tin hydroxide dissolves. Extract the resulting amine from the cooled solution with ether, and remove the ether by distillation. Examine the residue with regard to its solubility in 5 per cent, hydrochloric acid and its reaction with acetyl chloride or benzene-sulphonyl chloride. 

Heating under reflux.—A water condenser of total length 25 cm, (cooling jacket 15 cm.) may be used. If the upper end is provided with a long side arm as in Fig. XII, 2, 9, refluxing may be followed by distillation without transferring the contents of the flask it may be necessary to surround part of the side arm with a short water condenser (compare... 

The flask was charged with 48 g of magnesium and 200 ml of dry diethyl ether. 1,2-Dibromoethane (4 ml) was added. After a few minutes a vigorous reaction started and the diethyl ether began to reflux. When this reaction had subsided, 500 ml of dry diethyl ether were added. Stirring was started and 1.0 mol of chlorocyclohexane (note 1) was added from the dropping funnel at a rate such that the diethyl ether gently refluxed (note 2). After this addition, which was carried out in 1 h, the flask was heated under reflux for a further 1 h. 

To a solution of 0.50 tnol of ethyllithium in about 450 tnl of diethyl ether (see Chapter II, Exp. 1) was added 0.20 mol of 1-heptyne or butylallene (see Chapter VI, Exp. 1) with cooling below Q°C. After the addition the cooling bath was removed and the thermometer-gas outlet combination was replaced with a reflux condenser. The solution was heated under reflux for 6 h. The thermometer-gas outlet was again placed on the flask and the yellow suspension was cooled to -50°C. Trimethylchlorosilane (0.20 mol) was added dropwise in 10 min, while keeping the temperature between -40 and -35°C. After having kept the mixture for an additional 30 min at -30°C, it was poured into 200 ml of ice-water. The aqueous layer was extracted three times with small portions of diethyl ether. 

The flask was charged with 2.0 mol of dry, freshly distilled (note 1) methyl propargyl ether (VIII-6, Exp. 7), potassium iert.-butoxide (note 2) (5 g) was added with stirring and the mixture was heated under reflux. The reaction was... 

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