Funnel, Buchner sintered glass

Rhodium(III) chloride trihydrate (2 g.) is dissolved in 70 ml. of ethanol (95%) in a 500-ml. round-bottomed flask fitted with gas inlet tube, reflux condenser, and gas exit bubbler. A solution of 12 g. of triphenylphosphine (freshly crystallized from ethanol to remove triphenylphosphine oxide) in 350 ml. of hot ethanol is added and the flask purged with nitrogen. The solution is refluxed for about 2 hours, and the crystalline product which forms is collected from the hot solution on a Buchner funnel or sintered-glass filter. The product is washed with small portions of 50 ml. of anhydrous ether yield 6.25 g. (88% based on Rh). This crystalline product is deep red in color. 

If a funnel with sintered-glass disk is not available, a Buchner funnel may be equipped with a porous Filtros plate sealed in with Insalute cement, f Filter paper cannot be used because of the swelling action of the hot solution on the fibers. Gentle suction may be applied to withdraw the liquid, but care must be taken to allow no air to pass through the crystals. 

The chief disadvantages of a Buchner funnel for filtration are (i) it is impossible to see whether the underside of the perforated plate is perfectly clean, and (ii) the larger sizes are top heavy. The first drawback is absent in the Jena slit-sieve funnel (Fig. 11,1, 7,/) this is an all-glass funnel provided with a sealed-in transparent plate, perforated by a series of angular slots, upon which the filter paper rests. The sintered glass... 

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. 

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. 

The crude o-phenylenediamine may be converted into the dihydrocliloride and the salt purified in the following manner. Dissolve it in 60 ml. of concentrated hydrochloric acid and 40 ml. of water containing 2 g. of stannous chloride, and treat the hot solution with 2-3 g. of decolourising carbon. Filter, add 100 ml. of concentrated hydrochloric acid to the hot colourless filtrate, and cool in a freezing mixture of ice and salt. Collect the colourless crystals of the dihydrochloride on a Buchner or sintered glass funnel, wash with a small volume of concentrated hydrochloric acid, and dry in a vacuum desiccator over sodium hydroxide. The yield is 61 g. 

As an alternative to the Buchner funnel for collecting crystalline solids, a funnel with a sintered glass-plate under suction may be used. Sintered-glass funnels with various porosities are commercially available and can be easily cleaned with warm chromic or nitric acid (see above). 

This material may be filtered conveniently by means of a sintered glass funnel, or by using a pad of pure wool flannel in an 8-cm. Buchner funnel. 

---