Extraction with solvents, continuous continuous, of solids


Cyanuric chloride (which may or may not contain the usual commercial impurities) is dispersed into ice water by stirring in a ratio of 18.8 g of cyanuric chloride to a mixture of 100 g of ice and 100 g of water. The slurry may conveniently be prepared directly in a 3-necked flask equipped with an agitator, dropping funnel, and thermometer. The temperature of the flask and contents is maintained within the range of 2°C to 5°C, with an ice-salt mixture. A solution of ethylenimine in an aqueous solution of potassium carbonate prepared in the proportions of 14 g ethylenimine, 44.5 g potassium carbonate, and 150 g of water, is added drop-wise to the cyanuric chloride slurry. The reaction solution is then clarified with a little activated charcoal, filtered, and extracted with chloroform. Despite the fact that triethylene-melamine is more soluble in water than in chloroform, in a two-phase system (water-chloroform) nearly 75% of the triethylenemelamine is distributed in the chloroform, and hence a few extractions with that solvent suffice to separate the material from the original reaction medium. Five extractions with 50 ml portions of chloroform gave 19 g of product, and an additional 3 extractions with 25 ml portions gave 0.5 g, a total yield of 95.7%. The product obtained by evaporating such an extract is a white microcrystalline powder.  [c.1538]

It is useful to devote some conments to the following work-up procedure, which is often prescribed in the case of compounds, prepared in THF, that have a volatility comparable to that of THF (b.p. between 35 and 100 C at normal pressure). The problem is to remove the THF, the amount of which exceeds many-fold that of the product, and yet to isolate all of the volatile product which has been formed. The procedure to be followed consists in adding a high-boiling solvent (b.p. > 170 C at 760 mraHg) to the reaction mixture and subsequently extracting with water or, more efficiently, with dilute hydrochloric acid (if the compound is stable in acidic medium), until no more THF is present in the organic layer. As a rule this requires washing several times. The many aqueous layers obtained in this operation, may contain some of the product, but even this can be isolated by shaking the combined washings once or twice with the extraction solvent and subsequently removing the THF from these extracts by washing 5-6 times with water or dilute acid. It should be pointed out that the partition coefficient of the pmdacL between the extraction solvent and water (or the acid) must be large, but that of THF and the mentioned phases in the order indicated must be small. High-boiling ethers (e.g. diisoamyl ether) therefore seem unsuitable, and hydrocarbons (light petroleum fractions) are the solvents of choice. The further isolation procedure involves heating the dried extract in vacuo and condensing the vapour of the product in a strongly cooled receiver (see Fig. 5). The contents of the receiver always contain some extraction solvent and should therefore be redistilled, either at normal or under reduced pressure.  [c.2]


See pages that mention the term Extraction with solvents, continuous continuous, of solids : [c.3]   
Textbook on organic chemistry (1974) -- [ c.153 , c.154 , c.222 , c.223 ]