Dihydrate, 3.24

Crystallizes as the dihydrate in colourless prisms, m.p. 253 C. Prepared by heating... 

Mercury [) nitrate, HgaCNOsji. Forms dihydrate from aqueous solution (Hg plus cold dilute HNO3). Useful source of mercury(I) compounds. 

Mercury(I) forms few complexes, one example is the linear [H2O-Hg Hg- H20] found in the mercury(I) nitrate dihydrate (above, p. 437), In contrast, mercury(II) forms a wide variety of complexes, with some peculiarities (a) octahedral complexes are rare, (b) complexes with nitrogen as the donor atom are common, (c) complexes are more readily formed with iodine than with other halogen ligands. 

It follows that liquids of high boiling point should not be distilled from drying agent systems which have appreciable vapour pressures. An extreme case of this action is the dehydration of oxalic acid dihydrate by distillation over toluene or over carbon tetrachloride. 

Cuprous bromide. The solid salt may be prepared by dissolving 150 g. of copper sulphate crystals and 87 5 g. of sodium bromide dihydrate in 500 ml. of warm water, and then adding 38 g. of powdered sodium sulphite over a period of 5-10 minutes to the stirred solution. If the blue colour is not completely discharged, a little more sodium sulphite should be added. The mixture is then cooled, the precipitate is collected in a Buchner funnel, washed twice with water containing a little dissolved sulphurous acid, pressed with a glass stopper to remove most of the liquid, and then dried in an evaporating dish or in an air oven at 100 120°. The yield is about 80 g. 

A solution of cuprous bromide may be prepared either by dissolving the solid in hot constant boiling point hydrobromic acid or by refluxing a mixture of 63 g. of crystallised copper sulphate, 20 g. of copper turnings, 154 g. of sodium bromide dihydrate, 30 g. (16-3 ml.) of concentrated sulphuric acid and 1 litre of water for 3-4 hours. If the colour of the solution has not become yellowish after this period of heating, a few grams of sodium sulphite should be added to complete the reduction. 

Propionaldehyde. Use 34 g. (42-6 ml.) of n propyl alcohol, and a solution containing 56 g. of sodium chromate dihydrate, 300 ml. of water and 40 ml. of concentrated sulphuric acid. The experimental details are identical with those for n-butyraldehyde, except that the addition of the dichromate solution occupies 20 minutes, the temperature at the top of the column is not allowed to rise above 70-75°, and during the subsequent heating for 15 minutes the liquid passing over below 80° is collected the receiver must be cooled in ice. The yield of propionaldehyde, b.p. 47-50°, is 12 g. 

Methyl ethyl ketone. Use the apparatus of Fig. Ill, 61, 1 but with a 500 ml. round-bottomed flask. Place 40 g. (50 ml.) of see. butyl alcohol, 100 ml. of water and a few fragments of porous porcelain in the flask. Dissolve 100 g. of sodium dichromate dihydrate in 125 ml. of water in a beaker and add very slowly and with constant sturing 80 ml. of concentrated sulphuric acid allow to cool, and transfer the resulting solution to the dropping funnel. Heat the flask on a wire gauze or in an air bath until the alcohol mixture commences to boil. Remove the flame and run in the dichromate solution slowly and at such a rate that the temperature... 

Polyhydric alcohols are compounds containing two or more hydroxyl groups in the molecule. The two most important are ethylene glycol HOCHjCHjOH (a dihydric alcohol) and glycerol HOCHjCH(OH)CH. OH (a trihydric alcohol). Ethylene glycol may be obtained by the hydrolysis of ethylene dibromide or ethylene dichloride with dilute aqueous sodium hydroxide or sodium carbonate solution ... 

Introduce 197 g. of anhydrous brucine or 215 g. of the air-dried dihydrate (4) into a warm solution of 139 g. of dZ-acc.-octyl hj drogen phthalate in 300 ml. of acetone and warm the mixture vmder reflux on a water bath until the solution is clear. Upon cooling, the brucine salt (dA, IB) separates as a crystalline solid. Filter this off on a sintered glass funnel, press it well to remove mother liquor, and wash it in the funnel with 125 ml. of acetone. Set the combined filtrate and washings (W) aside. Cover the crystals with acetone and add, slowly and with stirriug, a slight excess (to Congo red) of dilute hydrochloric acid (1 1 by volume about 60 ml.) if the solution becomes turbid before the introduction of... 

SULPHONATION OF AROMATIC AMINES If aniline is treated with excess of concentrated sulphuric acid and the resulting mixture, which contains aniline sulphate, is heated at 180° until a test portion when mixed with sodium hydroxide solution no longer liberates aniline, p-aminobenzenesulphonic acid or sulphanilic acid is formed this separates as the dihydrate upon pouring the cooled mixture into water. The reaction prohahly proceeds as follows ... 

In a 250 ml. conical flask place 10 -5 g. of sulphanilic acid dihydrate,... 

Dissolve 15-0 g. of A.R. barium nitrate and 130 g. of A.R. cupric nitrate trihydrate in 450 ml. of water at 80°. Prepare a solution of sodium chromate by dissolving 89 g. of recrystallised sodium dichromate dihydrate in 200 ml. of water and adding 112 5 ml. of cone, ammonia solution (sp. gr. 0-90). Add the warm solution (80°) of nitrates in a thin stream, with stirring, to the sodium chromate solution (at 25°). Collect the orange precipitate by suction Bltration, wash it with two 50 ml. portions of 5fiter, drain well, and dry at 75-80° for 12 hours powder finely. 

Alternatively, the equivalent quantity of palladium chloride dihydrate may be used. 

A cousin to this reduction is one using stannous chloride (a.k.a. SnCb, a.k.a. Tin chloride) which is done exactly as the calcium one except that about lOOg of SnCb is used in place of the Mg or Ca and the addition occurs at room temperature and the solution is stirred for one hour rather than 15 minutes. Some very good reductions that operate almost exclusively at room temperature with no pressure and give almost 100% yields are to follow. The only reason Strike did not detail these methods is that some of the chemicals involved are a little less common than Strike is used to but all are available to the public. These alternatives include acetlylacetone and triethylamine [73], propanedithlol and trieth-ylamine [74], triphenylphosphine [75], NaBH4 with phase transfer catalyst [76], H2S and pyridine [77], and palladium hydrox-ide/carbon with hydrazine [78], stannous chloride dihydrate [85]. 

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