Recrystallization fluted filter paper

In a 1-1. round-bottomed flask fitted with a reflux condenser are placed 192 g. (166 ml., 2 moles) of freshly distilled furfural (Note 1), 208 g. (2 moles) of malonic acid (Note 2), and 96 ml. (1.2 moles) of pyridine (Note 3). The flask is heated on a boiling water bath for 2 hours, and the reaction mixture is cooled and diluted with 200 ml. of water. The acid is dissolved by the addition of concentrated aqueous ammonia, the solution is filtered through a fluted filter paper, and the paper is washed with three 80-ml. portions of water. The combined filtrates are acidified with an excess of diluted (1 1) hydrochloric acid with stirring. The mixture is cooled by running water and then allowed to stand in an ice bath for at least 1 hour. The furylacrylic acid is filtered, washed with four 100-ml. portions of water, and dried. The yield of practically colorless needles melting at 141° is 252-254 g. (91-92%). If a purer product is desired, recrystallization is best effected from dilute alcohol (Note 4). On slow cooling of the solution, needles melting at 141° separate. 

The key to successful gravity filtration is the fluted filter paper. A fluted filter paper decreases the area of contact between the filter paper and the funnel, thus allowing rapid filtration. If you use traditional cone-folded filter paper, note that all sides of the paper are touching the sides of the funnel and on half the filter paper the liquid has to pass through three thicknesses of paper, all of which slow the rate of filtration. Slow filtration can lead to disaster in hot filtration during recrystallization (p. 100). 

The residue obtained above is filtered while hot through a fluted filter paper so as to get rid of the resinous matter and extract the cold filtrate with three successive quantities of ether (each of 25 ml). Distil off the ether, and the yellow solid thus obtained is eventually recrystallized firom hot water to which a few ml of sulphurous acid (HgSOg) has been added. The yield of the para-hydroxybenzaldehyde, obtained as colourless crystals, is 1.5-2.2 g, having mp ranging between 115-116°C. 

Cyanuric chloride recrystallization. Cyanuric chloride (30 g, 0.16 mol) is dissolved in hot petroleum ether (500 mL) with constant stirring in an oil bath. Heated petroleum ether is pomed over a fluted filter paper and the solution of cyanuric chloride filtered into a 1-L conical flask. The saturated solution of cyanuric chloride is left overnight, covered, to allow formation of crystals. The crystals are filtered and dried under reduced pressure. The dried crystals are stable at room temperature in an airtight container. The yield is about 95%. 

For recrystallization, a solution of the nitrile in 3-4 ml. of hot methanol per gram was treated with Darco G-60 and filtered on a fluted paper. Distilled water was added to the hot solution until incipient crystallization was observed. In general the final solvent was approximately 90% methanol. 

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