Funnel , addition clogging

Another method involves the use of a hopper for the solid (Fig. 5-18) which has a rubber stopper or a glass valve as a seal between the reaction flask and the funnel. Addition is effected by raising the rod attached to the stopper. If the solid clogs the neck of the flask, it may be dislodged by the part of the rod which passes through the stopper. 

In order for this filtration to proceed smoothly, the funnel and its contents must remain hot to avoid premature crystallization of the product and clogging of the funnel. Minor clogging can be remedied by addition of a 100-mL portion of boiling distilled water to the funnel. Major clogging may require addition of boiling water and agitation of the filtration media with a spatula. This addition, however, may reduce the yield of the crystallized product. 

The addition of 2,4-pentanedione to liquid ammonia is a highly exothermic process. Also, ammonia vapor reacts with the /3-diketone to produce an insoluble ammonium salt, which tends to clog the tip of the addition funnel. Cooling the reaction mixture in dry ice-acetone reduces the vigor of the reaction and minimizes the dogging of the addition funnel. The 2,4-pentanedione should be added in spurts which fall on the surface of the reaction mixture rather than on the wall of the flask... 

After cooling slightly, the reaction mixture is transferred to a large flask and treated with 3.5 1. of water. Part of this is used to rinse out the reaction flask. The mixture is boiled with 30 g. of Norite for about ten minutes and is filtered while still hot with suction, using a preheated Buchner funnel. Furylacrylic acid tends to separate quickly and sometimes offers trouble in clogging the funnel. The filtrate is acidified to Congo red by the addition of a 1 1 solution of concentrated hydrochloric acid in water. 

This prevents clogging of the funnel during the subsequent addition of methyllithium solution. 

The addition of 2,4-pentanedione to liquid ammonia is a highly exothermic process. Also, ammonia vapor reacts with the fi diketone to produce an insoluble ammonium salt, which tends to clog the tip of the addition funnel. Cooling the reaction... 

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