Zinc, chloride, concentrating distillation

Pure pyridine may be prepared from technical coal-tar pyridine in the following manner. The technical pyridine is first dried over solid sodium hydroxide, distilled through an efficient fractionating column, and the fraction, b.p. 114 116° collected. Four hundred ml. of the redistilled p)rridine are added to a reagent prepared by dissolving 340 g. of anhydrous zinc chloride in a mixture of 210 ml. of concentrated hydrochloric acid and 1 litre of absolute ethyl alcohol. A crystalline precipitate of an addition compound (probable composition 2C5H5N,ZnCl2,HCl ) separates and some heat is evolved. When cold, this is collected by suction filtration and washed with a little absolute ethyl alcohol. The yield is about 680 g. It is recrystaUised from absolute ethyl alcohol to a constant m.p. (151-8°). The base is liberated by the addition of excess of concentrated... 

Reflux a mixture of 68 g. of anhydrous zinc chloride (e.g., sticks), 40 ml. (47 -5 g.) of concentrated hydrochloric acid and 18-5 g. (23 ml.) of sec.-butyl alcohol (b.p. 99-100°) in the apparatus of Fig. 777, 25, 1 for 2 hours. Distil oflF the crude chloride untU the temperature rises to 100°. Separate the upper layer of the distillate, wash it successively with water, 5 per cent, sodium hydroxide solution and water dry with anhydrous calcium chloride. Distil through a short column or from a Claisen flask with fractionating side arm, and collect the fraction of b.p. 67-70° some high boiling point material remains in the flask. Redistil and collect the pure cc. butyl chloride at 67-69°. The yield is 15 g. 

Allyl Chloride. Comparatively poor yields are obtained by the zinc chloride - hydrochloric acid method, but the following procedure, which employs cuprous chloride as a catalyst, gives a yield of over 90 per cent. Place 100 ml. of allyl alcohol (Section 111,140), 150 ml. of concentrated hydrochloric acid and 2 g. of freshly prepared cuprous chloride (Section II,50,i one tenth scale) in a 750 ml. round-bottomed flask equipped with a reflux condenser. Cool the flask in ice and add 50 ml. of concen trated sulphuric acid dropwise through the condenser with frequent shaking of the flask. A little hydrogen chloride may be evolved towards the end of the reaction. Allow the turbid liquid to stand for 30 minutes in order to complete the separation of the allyl chloride. Remove the upper layer, wash it with twice its volume of water, and dry over anhydrous calcium chloride. Distil the allyl chloride passes over at 46-47°. 

The amine (Imol) is added to a solution of anhydrous zinc chloride (Imol) in concentrated hydrochloric acid (42mL) in ethanol (200mL, or less depending on the solubility of the double salt). The solution is stirred for Ih and the precipitated salt is filtered off and recrystallised from ethanol. The free base is recovered by adding excess of 5-ION NaOH (to dissolve the zinc hydroxide that separates) and is steam distilled. Mercuric chloride in hot water can be used instead of zinc chloride and the salt is crystallised from 1% hydrochloric acid. Other double salts have been used, e.g. cuprous salts, but are not as convenient as the above salts. 

Preparation of the Leuco-Base—Zinc chloride (10 g.) is fused in a porcelain basin, cooled, and powdered. It is then added to a mixture of 25 g. of dimethylaniline and 10 g. of benzaldehyde (both freshly distilled) and the whole is heated in a porcelain basin on the water bath with frequent stirring for four hours. By the addition of hot water the viscous mass is liquefied on the water bath and the hot liquid is poured into a half-litre flask into which steam is passed until drops of oil cease to distil. After the liquid has cooled the water is poured off and the residue is washed several times with water. When as much as possible of the water has been removed the material in the flask is dissolved by adding alcohol and warming on the water bath, and the solution is filtered. On leaving the filtrate over night in a cool place the base separates in colourless crystals which are collected at the pump, washed with alcohol and dried in air on several folds of filter paper. A second crop of crystals can be obtained by concentrating the mother liquor. Should the base not crystallise, but separate as an oil—as often happens after the filtered solution has stood for a short time—it follows that too little alcohol has been used. In such cases somewhat more alcohol is added and the mixture is heated until the oil dissolves. Yield 20-24 g. 

Chemicals used were of analytical/laboratoiy grade procured either from Merck or Aldrich. Stock lead and zinc solutions 1,000 mg/L for adsorption stndy were prepared from AR grade lead nitrate [PbCNOj) ] and from zinc chloride [ZnCy. Different concentrations of Pb and Zn solutions were prepared from the stock solntions. All working solutions were prepared by diluting the stock solutions with distilled water. 

A solution of LDA is prepared by the addition of 12 mmol of 1.6 M butyllithium in hexane to a stirred solution of 1.5 g (15 mmol) of diisopropylaminc in 15 mL of THF at 0°C, then cooled to —78 °C. A solution of 10 mmol of the benzyloxy boronic ester and 10-17 g (60-100 mmol) of dibromomethane is stirred at — 78 °C during dropwise addition of the LDA solution via a cannula. The solvent is distilled at <0.75 Torr <0 °C. The solid residue of borate complex is cooled to — 78 CC and treated with a 0.5-0.7 M solution of anhyd zinc chloride (Section 1.1.2.1.1.1.) [(1 On + 8) mmol, where n is the number of benzyloxy groups in the boronic ester] in THF. The mixture is stirred for 16-20 h at 20-25 °C. An equal volume of petroleum ether (bp 30-60 °C) is added, followed by 100 mL of sat. aq NH4C1. The aqueous phase is further extracted with 4 1 petroleum cthcr/diethyl ether, and the combined organic phase is filtered through a 5-cm column of MgS04 with the aid of additional petroleum ether/diethyl ether. After concentration, the residue of labile a-bromo boronic ester should be used promptly in the next step. 

Method I.—50 gms. dimethylaniline, 20 gms. of benzaldehyde and 20 gms. of pulverised anhydrous zinc chloride (see p. 509) are heated in a porcelain dish, with frequent stirring, on a water bath for 4 hours. The mass is then melted by the addition of hot water and transferred to a large flask, where it is steam distilled until no more dimethylaniline passes over. The leuco-base of the dye remains in a viscous form on the sides of the flask after cooling the aqueous solution is decanted and the base washed a few times by decantation with cold water. The base is dissolved in boiling alcohol, the solution filtered hot, and the filtrate left overnight in an ice chest. Colourless crystals separate, which are collected and dried in air on filter paper. A second crop may be obtained by concentrating the mother liquor. If the base separates as an oil, instead of crystals, more alcohol should be added, and heat applied until the oil redissolves. 

To 190 g. (2 moles) of cold concentrated hydrochloric add (sp. gr. 1.19) is added 272 g. (2 moles) of anhydrous zinc chloride. The mixture is kept cold to avoid loss of hydrogen chloride. To this solution, 74 g. of 71-butyl alcohol (1 mole) is added (Note 1). The mixture is then refluxed over a free flame for three and one-half to four hours (Note 2). After cooling, the upper layer is separated (Note 3) and placed in a distilling flask with an equal volume of concentrated sulfuric acid (Note 4). The side arm of the flask is closed and the neck is connected with a reflux condenser. After refluxing gently for one-half hour, the chloride is distilled. The distillate is washed with water, dried over calcium chloride, filtered, and distilled. The fraction boiling at 76-78° weighs 59-61 g. (64-66 per cent of the theoretical amount). 

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