C. Frank Show, Ill and A. L. Allred
Northwestern University Evonston, lllinois 60201
Crystallization and Filtration Apparatus for Low Temperatures and Inert Atmosphere
Equipment for low temperature crystallization, (1, 2 ) and for inert atmosphere filtration (1, 3, 4) has been described recently. The depicted apparatus is useful for both operations. It is a modification of the double Schlenk tube ( I ) , and is designed for use with Schlenk-ware techniques (1, S), but also can be used in conjunction with a vacuum line or a dry box. The sizes and fittings described are compatible with semi-micro scale Schlenk-ware but can be adapted to larger systems by changing the sizes of the joints. However, an appreciable increase in the overall dimensions will require an unusually large Dewar for the coolant. Crystallization takes place in leg A , not on the sintered glass disc. The angular design permits tipping of the apparatus in the coolant and removal of air-sensitive solids from the sintered glass disc by a spatula. The sample to be crystallized is introduced into tube A by a method appropriate to the materials involved: vacuum line (6),dry box (6), Schlenk-ware manipulations, or open-air transfer. With stopcocks closed and joints stoppered and fastened, the entire apparatus is immersed in an appropriate low temperature bath so that the entire sintered glass disc is covered by the bath. The apparatus is occasionally swirled to prevent the precipitate from clinging to the walls of the apparatus. When precipitation is complete, the immersed apparatus is tilted until the sintered glass is horizontal. (The apparatus drawn can be so tilted in a 200-mm i.d. Dewar; the same result can be achieved in a Dewar as
164 / Journol of Chemical Education
narrow as 120 mm by tilting the apparatus as far as possible and then tipping the Dewar.) Filtration can be effected by pressurizing A with an inert gas ("ears" are used in securing attachcd glassware), or by creating a partial vacuum in B. If B is evacuated, care must be
taken that the solvent truly filters through the sintered glass and does not merely boil through leaving behipd the impurities as well as the precipitate; this is especially important for volatile solvents such as ethyl ether. The stopcock on B can be attached to a bubbler to relieve pressure and facilitate the filtration. The filtrate can be removed from B by syringing under a nitrogen flow or by vacuum line transfer if the precipitate is relatively non-volatile. Additional solvent can he introduced to A for convenient.recrystallization. If the precipitate is a liquid a t room temperature, the apparatus should be repositioned before warming so that the liquid drains back into A rather than collecting on the frit, through which some product might be lost. The apparatus has been successfully used to crystallize low-melting room-temperature solids (e.g., tri-
methyl-tert-butyltin, m.p. 32°C) which tend to form oils if not chilled, to purify liquids by low-temperature crystallization (e.g., trimethylstannyltrimethylgermane, m.p. -7 to -g°C), and to filter air sensitive compounds (e.g., cesium trichlorogermanate(I1)). Literature Cited (1) I). F.. "The Martiodation of Air Sensitive Com, , SHRIVI:R. ponndb," ~cGraw- ill, I& New York, 1969, Chapter 7. (2) GII:SI.;,ll., J . C n m . Eouc., 45, 610 (1968). (3) HI:RZOG, S., h N D ~ H X I I R T ,J., r%. Chem., 4, 1 (1964); ITrlrJ., and L ~ ~ H D EX., R , in "Technique of zoc, S., I)I:I
