Buchner acids

The Buchner acids exemplified by 287 were originally formulated as norcaradienes. However, Doering s group, in work which probably kindled modern interest in this subject despite an enigmatic numbering system demonstrated that these compounds were cycloheptatrienes. Subsequently line broadening at low temperatures has been shown to occur for only C(l), C(6) and C(7) in the C-NMR spectrum. ... 

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 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. 

I. Oxidation to benzoic acid. Boil a mixture of i ml. of benzyl chloride, 50 ml. of saturated aqueous KMn04 solution and 2 g. of anhydrous Na.jCOj under reflux for 30 minutes. Acidify with cone. HCl and then add 25% Na SOj solution until the brown precipitate of MnOj has dissolved. On cooling, benzoic acid crystallises out. Filter through a small Buchner funnel, wash with water and identify (P 347) When recrystallised from water, benzoic acid has m.p. 121 . 

Add dil. H2SO4 until the solution is acid to litmus. Cool, and scratch the sides of the vessel with a glass rod a white precipitate indicates an aromatic carboxylic acid or uric acid, or a solid phenol insoluble in water (e.g., i- or 2-naphthol). If a precipitate is obtained, filter off through a Buchner funnel, wash with water, recrystallise if necessary and identify. 

Method 2 (from potassium bromide and sulphuric acid). Potassium bromide (240 g.) is dissolved in water (400 ml.) in a litre flask, and the latter is cooled in ice or in a bath of cold water. Concentrated sulphuric acid (180 ml.) is then slowly added. Care must be taken that the temperature does not rise above 75° otherwise a little bromine may be formed. The solution is cooled to room temperature and the potassium bisulphate, which has separated, is removed by flltration through a hardened Alter paper in a Buchner funnel or through a sintered glass funnel. The flltrate is distilled from a litre distilling flask, and the fraction b.p. 124 127° is collected this contains traces of sulphate. Pure constant boiling point hydrobromic acid is obtained by redistillation from a little barium bromide. The yield is about 285 g. or 85 per cent, of the theoretical. 

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. 

Red phosphorus. Commercial red phosphorus is usually contaminated with small quantities of acidic products. It should be boiled for 15 minutes with distilled water, allowed to settle, decanted through a Buchner funnel, and then washed two or three times with boiling water by decantation. Finally, the phosphorus is completely transferred to the Buchner funnel and washed with hot water untU the washings are neutral. It is dried at 100°, and kept in a desiccator or in a tightly stoppered bottle. 

Method A. In a 500 ml. round-bottomed flask, fitted with a reflux condenser attached to a gas trap (Fig. II, 13, 8), place 59 g. of succinic acid and 117-5 g. (107-5 ml.) of redistilled acetyl chloride. Reflux the mixture gently upon a water bath until all the acid dissolves (1-2 hours). Allow the solution to cool undisturbed and finally cool in ice. Collect the succinic anhydride, which separates in beautiful crystals, on a Buchner or sintered glass funnel, wash it with two 40 ml. portions of anhydrous ether, and dry in a vacuum desiccator. The yield of succinic anhydride, m.p. 118-119°, is 47 g. 

Place 18 g. (12 ml.) of fuming nitric acid, sp. gr. 1 5, and 30 g. (16-5 ml.) of concentrated sulphuric acid and a few fragments of broken glass in a 250 or 500 ml. round-bottomed flask. Add gradually, in small portions, 14 g. of p-nitrotoluene do not allow the temperature to rise above 50 and cool the flask, if necessary, by immersion in cold water. Place a small funnel in the mouth of the flask and heat on a water bath at 90-95° for 30 minutes. Allow to cool almost to the laboratory temperature and pour the reaction mixture slowly into about 500 ml. of ice water containing a few small pieces of ice. Filter the crude dinitrotoluene through a Buchner funnel at the pump, wash it thoroughly with cold water, and drain as completely as possible. RecrystalUse from the minimum volume of hot methyl alcohol (flask, reflux condenser, and water bath experimental details as in Section IV,12). The yield of pure 2 4-dinitrotoluene, m.p. 71°, is 12 -5 g. 

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