Residues in the

Add dil. HjS04 to the residue in the flask until definitely acid to litmus. Distil off 1 2 ml., and perform tests on this aqueous distillate for acetic acid. 

A considerable amount of the formic acid, however, still remains behind in the distilling-flask as the unhydrolysed monoformate. Therefore, if time allows, dilute the residue in the flask with about an equal volume of water, and then steam-distil, the monoformate ester being thus completely hydrolysed and the formic acid then driven over in the steam. Collect about 400 ml. of distillate. Add this distillate to that obtained by direct heating of the reaction mixture and then treat with lead carbonate as described above. Total yield of lead formate is now about 40 g. 

Fit securely to the lower end of the condenser (as a receiver) a Buchner flask, the side-tube carrying a piece of rubber tubing which falls well below the level of the bench. Steam-distil the ethereal mixture for about 30 minutes discard the distillate, which contains the ether, possibly a trace of unchanged ethyl benzoate, and also any biphenyl, CeHs CgHs, which has been formed. The residue in the flask contains the triphenyl carbinol, which solidifies when the liquid is cooled. Filter this residual product at the pump, wash the triphenyl-carbinol thoroughly with water, drain, and then dry by pressing between several layers of thick drying-paper. Yield of crude dry product, 8 g. The triphenyl-carbinol can be recrystallised from methylated spirit (yield, 6 g.), or, if quite dry, from benzene, and so obtained as colourless crystals, m.p. 162. ... 

Steam-distil the ethereal solution and discard the distillate. The residue in the flask is triphenyl-carbinol and solidifies on cooling. Filter at the pump, wash with water, drain and dry. Yield of crude product 0 6 g. Recrystallise when dry from benzene to obtain colourless crystals m.p. 162°. 

Sulphur. Moisten the centre of a filter-paper with lead acetate solution. Then add about 10 ml. of dilute hydrochloric acid to the residue in the evaporating-basin, and at once cover the latter with the paper. If zinc sulphide is present in the residue, the hydrogen sulphide evolved will give a definite daA brown coloration with the lead acetate paper. The presence of hydrogen sulphide can often be confirmed by its odour. 

Next cool the alkaline residue in the flask and add dil. H2SO4 until definitely acid. 

It must be emphasised that there is no universal cleaning mixture. The student must take into account the nature of the substance to be removed and act accordingly. Thus if the residue in the flask is known to be basic in character, dilute hydrochloric or sulphuric acid may dissolve it completely similarly, dilute sodium hydroxide... 

The phosphoric acid may be recovered by diluting the residue in the three-necked flask with water, filtering, and then evaporating with a little nitric acid to a concentration of about 85 per cent. 

The residue in the flask may be mixed with the aqueous layer of the first distillate, 40 g. of isopropyl alcohol added, and the slow distillation repeated. The yield of crude isopropyl bromide in the second distillation is only slightly less than that obtained in the original preparation. Subsequently most of the residual hydrobromic acid may be recovered by distillation as the constant boiling point acid (126°). 

A further quantity of wopropyl iodide, only slightly less than that obtained in the first distillation, may be prepared by combining the residues in the distilling flask, adding 30 g. (38 ml.) of isopropyl alcohol, and repeating the distillation. Finally, the residues should be distUled and the 67 per cent, constant boiling point acid recovered. 

Allyl Iodide. Use 29 g. (34 ml.) of allyl alcohol and 340 g. (200 ml.) of 57 per cent, hydriodic acid 84 g. of crude iodide are obtained. Upon adding 29 g. (34 ml.) of allyl alcohol to the combined residue in the flask and the aqueous layer and distilling as before, a further 72 g. of crude allyl iodide may be isolated. B.p. 99-101° (mainly 100°). The compound is very sensitive to light the distillation should therefore be conducted in a darkened room and preferably in the presence of a little silver powder. 

In a 1-litre three-necked flask, fitted with a mechanical stirrer, reflux condenser and a thermometer, place 200 g. of iodoform and half of a sodium arsenite solution, prepared from 54-5 g. of A.R. arsenious oxide, 107 g. of A.R. sodium hydroxide and 520 ml. of water. Start the stirrer and heat the flask until the thermometer reads 60-65° maintain the mixture at this temperature during the whole reaction (1). Run in the remainder of the sodium arsenite solution during the course of 15 minutes, and keep the reaction mixture at 60-65° for 1 hour in order to complete the reaction. AUow to cool to about 40-45° (2) and filter with suction from the small amount of solid impurities. Separate the lower layer from the filtrate, dry it with anhydrous calcium chloride, and distil the crude methylene iodide (131 g. this crude product is satisfactory for most purposes) under diminished pressure. Practically all passes over as a light straw-coloured (sometimes brown) liquid at 80°/25 mm. it melts at 6°. Some of the colour may be removed by shaking with silver powder. The small dark residue in the flask solidifies on cooling. 

The evil>smelling residue in the reaction flask is best removed by the cautious addition of concentrated nitric acid. 

To obtain a maximum yield of the acid it is necessary to hydrolyse the by-product, iaoamyl iaovalerate this is most economically effected with methyl alcoholic sodium hydroxide. Place a mixture of 20 g. of sodium hydroxide pellets, 25 ml. of water and 225 ml. of methyl alcohol in a 500 ml. round-bottomed flask fitted with a reflux (double surface) condenser, warm until the sodium hydroxide dissolves, add the ester layer and reflux the mixture for a period of 15 minutes. Rearrange the flask for distillation (Fig. II, 13, 3) and distil off the methyl alcohol until the residue becomes pasty. Then add about 200 ml. of water and continue the distfllation until the temperature reaches 98-100°. Pour the residue in the flask, consisting of an aqueous solution of sodium iaovalerate, into a 600 ml. beaker and add sufficient water to dissolve any solid which separates. Add slowly, with stirring, a solution of 15 ml. of concentrated sulphuric acid in 50 ml. of water, and extract the hberated acid with 25 ml. of carbon tetrachloride. Combine this extract with extract (A), dry with a httle anhydrous magnesium or calcium sulphate, and distil off the carbon tetrachloride (Fig. II, 13, 4 150 ml. distiUing or Claisen flask), and then distil the residue. Collect the wovaleric acid 172-176°. The yield is 56 g. 

Stopper the side arm of a 25 or 50 ml. distilling flask and fit a vertical water condenser into the neck. Place 0-5-1 -0 g. of the dry acid (finely powdered if it is a solid) into the flask, add 2-5-5 0 ml. of redistilled thionyl chloride and reflux gently for 30 minutes it is advisable to place a plug of cotton wool in the top of the condenser to exclude moisture. Rearrange the condenser and distil off the excess of thionyl chloride t (b.p. 78°). The residue in the flask consists of the acid chloride and can be converted into any of the derivatives given below. 

The solid residue in the flask dissolves readily in cold water. 

The tarry residue in the flask may be removed by warm diiute sodium hydroxide solution. 

Acidify the residue in the flask with dUute sulphuric acid and distil off 10-15 ml. of the solution. Test a smaU portion of the distillate for acidity, and also observe the odour. Neutralise the main portion with sodium hydroxide solution (add a drop of phenolphthalein to act as indicator), evaporate to smaU bulk, and convert the sodium salt into the p-bromophenacyl ester or into some other suitable derivative (Section 111,85) determine the m.p. of the derivative. 

The residue in the flask will contain the sodium (or potassium) salt of the acid together with excess of alkali. Just acidify with dilute sulphuric acid and observe whether a crystalline acid separates if it does, filter, recrystallise and identify (Section 111,85). If no crystaUine solid is obtained, the solution may be just neutralised to phenolphthalein and the solution of the alkali salt used for the preparation of a crystaUine derivative. This wiU confirm, if necessary, the results of hydrolysis by method 1. If the time factor is important, either method 1 or the product of the caustic alkali hydrolysis may be used for the identification of the acid. 

Di-n-hexyl sulphide. Use 83 g. (71 ml.) of n-hexyl bromide (Section III.37), 56 g. of finely-powdered, anhydrous sodium sulphide and 100 ml. of rectified spirit. Reflux on a water bath for 20 hours. Distil ofiF the alcohol from a water bath very Uttle sulphide is obtained upon adding excess of water to the distiUate. Add excess of water to the residue in the flask and separate the upper layer of crude n-hexyl sulphide. Purify as for n-propyl sulphide, but distil under reduced pressure. CoUectthe n-hexyl sulphide at 113-114°/4 mm. The yield is 45 g. 

Method 1. Arrange the flask containing the reaction mixture for steam distillation as in Fig. II, 40, 1. Proceed with the steam distillation until crystals of p-dibromobenzene appear in the condenser. Change the receiver and continue with the distillation until all the p-dibromobenzeiie has passed over from time to time run out the water from the condenser so that the crystals melt and run down into the receiver. Reject the residue in the flask. Transfer the first distillate to a separatory funnel, wash it with a httle water, and dry the lower layer with a little anhydrous magnesium sulphate or anhydrous calcium chloride filter. Distil slowly from a small distilling flask use a wire gauze or an air bath (Fig. II, 5, 3). Collect the fraction which passes over at 150-170° pour the residue (R), while it is still hot, into a small beaker or porcelain basin for the isolation of p-dibromobenzene. Redistil the fraction of b.p. 150-170° and collect the bromobenzene at 154-157° (3). The yield is 60 g. 

Isolate the pure p-dibromobenzene from the residue in the basin by the procedure described in Method 1. The yield is about 10 g. 

Fit up a 1 -litre round-bottomed flask for steam distillation (Fig. II, 40,1) and place in it 22 g. of iodosobenzene (Section IV.25) made into a thin paste with water (1). Steam distil until almost all the iodobenzene has been removed (about 9 g.) cool the residue in the flask at once, filter the white solid with suction and dry in the air. Wash it with a little chloroform, filter with suction, and dry in the air upon filter paper. The yield is 10-5 g. It may be recrystallised from 800-900 ml. of water, lodoxybenzene melts with explosive decomposition at 237°,... 

Pure dimethylaniline from commercial dimethylaniline. Into a 250 ml. round-bottomed flask fitted with a reflux condenser place 50 g. (52-5 ml.) of a good commercial sample of dimethylaniline and 25 g. (23 ml.) of acetic anhydride. Heat vmder reflux for 3 hours, and allow to cool. Transfer to a 100 ml, Claisen flask equipped for distillation, and distil using a wire gauze or, better, an air bath (Fig. II, 5, 3). Some acetic acid and the excess of acetic anhydride passes over first, followed by pure dimethylaniline (a colourless liquid) at 193-194°, There is a small dark residue in the flask. The yield depends upon the purity of the commercial sample, but is usually 30-40 g. 

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