Cooling preheating

No preheating or postweld treatment Preheating to 260°C, welding at 260°C, slow cooling Preheating to 260°C, welding at 260°C, annealing... 

Add 5 g. of potassium hydrogen tartrate and 5 g. of antimony trioxide (each being finely powdered) to 30 ml. of water contained in a small flask, and boil the mixture under a reflux water-condenser for 15 minutes. Then filter hot, using a Buchner funnel and flask which have been preheated by the filtration of some boiling distilled water. Pour the clear filtrate into a beaker and allow to cool. Potassium antimonyl tartrate separates as colourless crystals. Filter, drain and dry. Yield, 5 g. The product can be recrystallised from hot water, but this is usually not necessary. 

When the ij hours boiling is complete, preheat a Buchner funnel and flask by pouring some boiling water through the funnel with the filter-paper already in position, and then quickly filter the boiling solution. Transfer the filtrate to a beaker to cool, and then wash the insoluble residue of diphenylurea on the filter twice with hot water, and drain thoroughly. Cool the filtrate in ice-water the monophenylurea separates as colourless needles. Filter at the pump and drain well. Recrystallise the crude product from boiling water, as in the previous preparation. Yield of monophenylurea, 2 5-3 g. m.p. 147°. 

The insoluble residue of diphenylurea from the original filtration is chemically almost pure. It may be recrystallised from hot rectified spirit or ethanol, a process which will be necessary if the material contains fragments of porcelain. When using either of these solvents, however, the hot solution should be filtered at the pump using a small Buchner funnel and flask which again have been preheated by the filtration of some of the hot solvent, as the solution when cooled rapidly deposits the diphenylurea. iSym-Diphenylurea (or carbanilide) is thus obtained as fine colourless crystals, m.p. 237° yield, 1-1 5 S ... 

For purification, transfer the acid to a 150 ml. flask containing 60 ml. of water, boil the mixture under reflux, and then add acetic acid in 5 ml. portions down the condenser until almost all the solid has dissolved avoid an excess of acetic acid by ensuring that the solvent action of each addition is complete before the next portion is added. A small suspension of insoluble impurity may remain. Add 2 g. of animal charcoal, boil the solution again for 10-15 minutes, and then filter it through a preheated Buchner funnel. Cool and stir the filtrate, which will deposit pale cream-coloured crystals of the acid. Collect as before and if necessary repeat the recrystallisation. Yield of pure acid, 9 g. m.p. 227-229°. 

Recrystallise from methylated spirit, using animal charcoal for this purpose, use about twice the minimum quantity of methylated spirit required to obtain a clear solution, and filter through a funnel preheated by the filtration of some boiling solvent, as the tribromobenzene separates very rapidly as the solution cools. The 1,3,5-tribromobenzene is thus obtained as colourless crystals, m.p. 122° yield, 3 g. 

To obtain the free acid, dissolve the potassium salt in 50 ml. of cold water, filter the solution if a small undissolved residue remains, and then boil the clear solution gently whilst dilute sulphuric acid is added until the separation of the acid is complete. Cool the solution and filter off the pale orange-coloured crystals of the benzilic acid wash the crystals on the filter with some hot distilled water, drain well, and then dry in a desiccator. Yield of crude acid, 4 g. Recrystallise from benzene (about 50 ml.) to which a small quantity of animal charcoal has been added, filtering the boiling solution through a preheated funnel fitted w ith a fluted filter-paper, as the benzilic acid readily crystallises as the solution cools alternatively, recrystallise from much hot water. The benzilic acid is obtained as colourless crystals, m.p. 150°. 

Recrystallise the remaining half of the crude anthraquinone from boiling acetic acid, using animal charcoal filter the hot solution through a Buchner funnel which has been preheated by the filtration of some of the boiling solvent, as the anthraquinone crystallises rapidly as the solution cools. Cool the filtrate in cold water and then filter at the pump, drain, wash with methylated spirit and dry. Yield, 4-5 g. 

Add 5 ml. (5 g.) of acetophenone, 1-25 g. of finely powdered paraformaldehyde, and 3 5 g. of dry dimethylamine hydrochloride to 8 ml. of absolute ethanol, and then boil the mixture under reflux for 1-5 hours. Filter the solution (which is now almost entirely clear) through a preheated filter-funnel, and cool the filtrate in ice-water with stirring. The propiophenone hydrochloride rapidly separates as white crystals filter oflF the crystals at the pump and recrystallise from a small quantity of ethanol m.p. 155-156°. Yield, 2 5 g. 

Anthracene and maleic anhydride. In a 50 ml. round-bottomed flask fitted with a reflux condenser, place 2 0 g. of pure anthracene, I 1 g. of maleic anhydride (Section 111,93) and 25 ml. of dry xylene. Boil the mixture under reflux for 20 minutes with frequent shaking during the first 10 minutes. Allow to cool somewhat, add 0 5 g. of decolourising carbon and boil for a further 5 minutes. Filter the hot solution through a small, preheated Buchner funnel. Collect the solid which separates upon coohng by suction filtration, and dry it in a vacuum desiccator containing paraffin wax shavings (to absorb traces of xylene). The yield of adduct (colourless crystals), m.p. 262-263° (decomp.), is 2-2 g. Place the product (9 10-dihydroanthracene-9 10-cndo-ap-succinic anhydride) in a weU-stoppered tube, since exposure to air tends to cause hydration of the anhydride portion of the molecule. 

In a 1 litre round-bottomed flask, equipped with an air condenser, place a mixture of 44 g. of o-chlorobenzoic acid (Section IV,157) (1), 156 g. (153 ml.) of redistilled aniline, 41 g. of anhydrous potassium carbonate and 1 g. of cupric oxide. Reflux the mixture in an oil bath for 2 hours. Allow to cool. Remove the excess of aniline by steam distillation and add 20 g. of decolourising carbon to the brown residual solution. Boil the mixture for 15 minutes, and filter at the pump. Add the filtrate with stirring to a mixture of 30 ml. of concentrated hydrochloric acid and 60 ml. of water, and allow to cool. Filter off the precipitated acid with suction, and dry to constant weight upon filter paper in the air. The yield of iV-phenylanthranilic acid, m.p. 181-182° (capillary tube placed in preheated bath at 170°), is 50 g. This acid is pure enough for most purposes. It may be recrystaUised as follows dissolve 5 g. of the acid in either 25 ml. of alcohol or in 10 ml. of acetic acid, and add 5 ml. of hot water m.p. 182-183°. 

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