Sulphur-34, commercial separation

Commercial benzene may contain thiophene C H S, b.p. 84°, which cannot be separated by distillation or by fractional crystallisation. The presence of thiophene may be detected by shaking 3 ml. of benzene with a solution of 10 mg. of isatin in 10 ml. of concentrated sulphuric acid and allowing the mixture to stand for a short time a bluish-green colouration is produced if thiophene is present. The thiophene may be removed from benzene by any of the following methods —... 

Bromine. The commercial product may be dried (and partially purified) by shaking with an equal volume of concentrated sulphuric acid, and then separating the acid. Chlorine, If present, may be removed by fractionation in an all-glass apparatus from pure potassium bromide the b.p. is 59°/760 mm. The analytical reagent grade is satisfactory for most purposes where pure bromine is required. 

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. 

The products betu a strong formal resemblance to styrene and may be polymerised. For commercial purposes the monomers are not separated but are polymerised in situ in the crude naphtha, sulphuric acid acting as an ionic catalyst to give polymers with a degree of polymerisation of 20-25. 

Commercial acetic acid is manufactured fiom pyroligneous acid obtained in the destructive distillation of wood. The latter is neutralised with lime, and separated by distillation from wood-spirit and acetone. The crude calcium acetate, which has a dark colour, is then distilled with the requisite quantity of concentrated hydrochloric acid. Anhydrous or glacial acetic acid is obtained by distilling fused sodium acetate with concentrated sulphuric acid. 

Pure Commercial Benzene, obtained from coal-tai naphtha, should distil w lthin one degiee (80—Si ), and solidify completely when cooled to 0°. Other tests are as follow s shaken with concentrated sulphuric acid for a few minutes, the acid should not darken, and a drop of bromine water should not be immediately decolourised. A single distillation over a few small pieces of sodium, which absorb any traces of water, is usually a sufficient purification. If the benzene impart a brown or black colour to the sulphuric acid, it must be repeatedly shaken with about 20 per cent, of the acid until the lattev becomes only slightly yellow on standing. This is done in a stoppered separating funnel, and after shaking fora few minutes the mixture is allow ed to settle, and the low er layer of acid diawn off. The benzene is then shaken tw o 01 three times with water to free it from acid, carefully separated from the aqueous layer, and left in contact with fused calcium chloride until the liquid becomes clear. It is then decanted, frozen in ice, and any liquid (carbon bisulphide, paraffins) carefully drained off, and die benzene finally distilled over sodium. 

Y Picoline. Commercially pure y-picoline contains )S-picoline and 2 6-lutidine and sometimes traces of non-basic impurities (aromatic hydrocarbons) which cannot be separated by fractionation. The non-basic impurities are removed by steam distillation of the base in dilute hydrochloric or sulphuric acid solution (for details, see under a Picoline). The impure y-picoline is converted into the zinc chloride complexes of the component bases the 2 6-lutidine - ZnClj complex is the least stable and upon steam distillation of the mixture of addition compounds suspended in water, 2 6-lutidine passes over flrst. The complete separation of the 2 6-lutidine may be detected by a determination of the density and the refractive index of the dry recovered base at varioiu stages of the steam distillation. The physical properties are —... 

The distillate is at once extracted with ether and the extract, after having been separated from the water, is heated on the water bath until most of the ether has distilled. The residue, which contains unchanged phenol as well as the salicylaldehyde, is now vigorously shaken in a small glass-stoppered bottle with two volumes of concentrated commercial sodium bisulphite solution. A thick paste of the bisulphite compound of the aldehyde is formed. After this paste has stood for from half an hour to one hour the bisulphite compound is separated by filtration at the pump, pressed well on the filter funnel, and washed several times, first with alcohol and finally with ether, until completely free from adherent phenol. The crystals (small plates, iridescent like mother-of-pearl) are then decomposed with dilute sulphuric acid in a small round-bottomed flask whi( h is fitted with an air condenser and gently warmed on the water bath. After the liquid thus produced has cooled, the aldehyde which separates is extracted with ether and the ethereal solution is dried with anhydrous sodium sulphate. The pure aldehyde which remains when the ether is evaporated distils at 196°. The yield amounts to 10-12 g. 

Preparation of Zinc.—To obtain perfectly pure zinc is a task of some difficulty, so much so that the commercial article is never met with in a puro state, hut rather with variable quantities of arsenic, cadmium, tin, lead, manganese, iron, cobalt, and nickel. In order to obtain perfectly pure metal, the purest commercial ziuo should be dissolved in dilute sulphuric acid, filtered from any residue, and the foreign metals thrown down by Immersing plates of zinc in the liquid till no further deposit takes place. After separating the precipitated metals, which may be tin, lead, copper, cadmium, antimony, and a trace of arsenic, the solution is treated with carbonate of soda, and the carbonate of zinc, which Falls after filtration and thorough washing, Is dried, heated to redness to expel carbonic acid, mixed with charcoal or lampblack, and introduced into a crucible as represented in Fig. 23, placed in a furnace,... 

In some commercial acids selenium is present in the form of the monoehloride, produced when seleniferous sulphuric acid is heated with salt. On the addition of ferric chloride, the monoehloride gradually separates.5... 

The main reason why this procedure has not been developed commercially is that during the precipitation of nitrostarch by means of sulphuric acid a sticky intermediate product separates. This is difficult to mix, hence it is not easy to keep its temperature constant and correct, and its composition uniform. In consequence... 

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