Charcoal filter

Fig. 3.2. Activity of radioiodine in air of reactor shell. O, First charcoal paper A, second charcoal paper x, membrane filter , charcoal pack.

Figure 1.1-1. Construction of a two layer filter, a) inlet b) outlet c) bottom d) sand e) filter charcoal f) water distribution...

Filtering charcoal - never attempt to remove finely divided charcoal, used in decolourization during recrystallization or as a catalyst support, by suction filtration. It is a very fine powder and will always leak into the filtrate. Filter off charcoal by gravity filtration. 

Decolorisation by Animal Charcoal. It sometimes hap pens (particularly with aromatic and heterocyclic compounds) that a crude product may contain a coloured impurity, which on recrystallisation dissolves in the boiling solvent, but is then partly occluded by crystals as they form and grow in the cooling solution. Sometimes a very tenacious occlusion may thus occur, and repeated and very wasteful recrystallisation may be necessary to eliminate the impurity. Moreover, the amount of the impurity present may be so small that the melting-point and analytical values of the compound are not sensibly affected, yet the appearance of the sample is ruined. Such impurities can usually be readily removed by boiling the substance in solution with a small quantity of finely powdered animal charcoal for a short time, and then filtering the solution while hot. The animal charcoal adsorbs the coloured impurity, and the filtrate is usually almost free from extraneous colour and deposits therefore pure crystals. This decolorisation by animal charcoal occurs most readily in aqueous solution, but can be performed in almost any organic solvent. Care should be taken not to use an excessive quantity... 

Dissolve 5 g. of aniline hydrochloride in 120 ml. of hot water contained in a 200 ml. conical flask and then add 4 g. of potassium cyanate. Heat the solution on a water-bath for 30 minutes, adding about 1-2 g. of animal charcoal towards the end of the heating if a slight turbidity has developed. Now bring the solution quickly to the boil over a gauze, and filter it at the pump, using a Buchner funnel and flask which have been preheated by the filtration of some boiling distilled water. The clear... 

The p-dibromobenzene formed as a by-product in the above reaction usually solidifies when the undistilled residue obtained in the first distillation is chilled. It may then he isolated by adding about lo ml. of methylated spirit and some animal charcoal to the flask, boiling for a few minutes, and filtering hot. On cooling the filtrate in ice-water, crystals of p-dibromobenzene, m.p. 89°, separate recrystallise a second time if necessary to obtain colourless crystals. 

SULPHANILAMIDE. (Reaction C.) Add 15 g. of the above thoroughly drained sulphonamide to 10 ml. of concentrated hydrochloric acid diluted with 20 ml. water, and boil the mixture gently under reflux for i hour. Then add 30 ml. of water and heat the mixture again to boiling, with the addition of a small quantity of animal charcoal. Filter the boiling solution, and add powdered sodium carbonate in small quantities to the filtrate with stirring until all eflFervescence ceases and the sulphanilamide is precipitated as a white powder. Cool the mixture thoroughly and filter oflF the sulphanilamide at the pump, wash with water and dry. Yield, ca. 10 g. 

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. 

Prepare a mixture of 30 ml, of aniline, 8 g. of o-chloro-benzoic acid, 8 g. of anhydrous potassium carbonate and 0 4 g. of copper oxide in a 500 ml. round-bottomed flask fitted with an air-condenser, and then boil the mixture under reflux for 1 5 hours the mixture tends to foam during the earlier part of the heating owing to the evolution of carbon dioxide, and hence the large flask is used. When the heating has been completed, fit the flask with a steam-distillation head, and stcam-distil the crude product until all the excess of aniline has been removed. The residual solution now contains the potassium. V-phenylanthrani-late add ca. 2 g. of animal charcoal to this solution, boil for about 5 minutes, and filter hot. Add dilute hydrochloric acid (1 1 by volume) to the filtrate until no further precipitation occurs, and then cool in ice-water with stirring. Filter otT the. V-phcnylanthranilic acid at the pump, wash with water, drain and dry. Yield, 9-9 5 g. I he acid may be recrystallised from aqueous ethanol, or methylated spirit, with addition of charcoal if necessary, and is obtained as colourless crystals, m.p. 185-186°. 

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. 

Amino-4 -methylthiazole slowly decomposes on storage to a red viscous mass. It can be stored as the nitrate, which is readily deposited as pink crystals when dilute nitric acid is added to a cold ethanolic solution of the thiazole. The nitrate can be recrystallised from ethanol, although a faint pink colour persists. Alternatively, water can be added dropwise to a boiling suspension of the nitrate in acetone until the solution is just clear charcoal is now added and the solution, when boiled for a short time, filtered and cooled, deposits the colourless crystalline nitrate, m.p. 192-194° (immersed at 185°). The thiazole can be regenerated by decomposing the nitrate with aqueous sodium hydroxide, and extracting the free base with ether as before. 

Schiff s Reagent. Dissolve 1 g. of rosaniline in 50 ml. of water with gentle warming. Cool, saturate with SO, add about i g. of animal charcoal, shake and filter make up to i litre with water. If the pink colour reappears on standing, add a few drops of SOj-water carefully with stirring until the colour Just disappears. 

To isolate pure p-dibromobenzene, filter the second portion of the steam distillate through a small Buchner funnel with suction press the crystals as dry as possible. Combine these crystals with the residue (R) and recrystaliise from hot ethyl alcohol (for experimental details, see Section IV,12) with the addition of 1-2 g. of decolourising charcoal use about 4 ml. of alcohol (methylated spirit) for each gram of material. Filter the hot solution through a fluted filter paper, cool in ice, and filter the crystals at the pump. The yield of p-dibromobenzene, m.p. 89°, is about 12 g. 

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