In the Laboratory
An Innovative Design of a Small Reactor1 P. A. Thomas Polymer Science and Engineering Group, Chemical Engineering Division, National Chemical Laboratory, Pune - 411 008 India
In chemical laboratories engaged in teaching as well as research, there is frequently a need to carry out reactions on a very small scale for reasons of cost, effort, or convenience. Reactions that simultaneously require many operations such as refluxing, mechanical stirring, bubbling a gas through the reaction mixture, and continuous addition of reactants are very common. These reactions are usually carried out in multineck flasks. But attaching multiple necks to small-volume flasks and their use in such reactions are fraught with problems due to obvious geometrical constraints. Recently, Eisenbraun and Denton (1) published the design of an apparatus to substitute a three-neck flask. In this article, the simple design of a glass reactor in which all the above-mentioned operations can be carried out with reaction mixture volumes as low as 5–8 mL is described. The most innovative aspect of the design is that an ordinary glass hypodermic syringe has been modified to function simultaneously as a mechanical stirrer-cum-gas-bubbler. Ace Glass Co. of U.S.A. supplies a hollow stirrer and bearing assembly that functions similarly (2). But the novel use of a readily available syringe in the present design makes the fabrication much easier and is expected to bring down the cost substantially.
The three components of the reactor and their parts are shown in Figure 1. An ordinary glass syringe of 10-mL Figure 2. The capacity was used for fabricaassembled tion. The outer cylinder and reactor. Comthe hollow piston of the syponents 1, 2, ringe were modified. A length and 3 correof ca. 1.5 cm of the middle porspond to the tion of the outer cylinder (a) components was softened in a flame and illustrated in bulged slightly. An inlet tube Figure 1. (b) was attached to it. A short glass tube (d) of larger diameter was attached to the bottom of the cylinder and a joint (e) was fixed at the end. To the side of the short tube (d), another joint (c) was attached. Exactly at the middle of the piston (g), three to four holes (h) of about 1-mm diameter were drilled. A capillary (i) of 0.5 mm bore was fixed to the bottom end of the piston. Stirrer fins (j) were attached to the end of the capillary without closing the capillary bore. A glass rod (f) was fused to the top end of the piston. These modifications were done without affecting the coaxiality of the outer cylinder and the piston. The dimensions of the components 1, 2, and 3 may be fixed to suit specific requirements. The reactor was assembled as shown in Figure 2. The outer cylinder and the flask (l) are to be clamped. The rod should be connected to the motor through a strong but flexible coupling. The gas entering the inlet enters the rotating hollow piston through the holes and bubbles into the reaction mixture through the capillary. The neck can act as the condenser port and as the gas outlet. Additional side necks can be easily added (onto the part d, Fig. 1) if necessary. Heating of the flask can be done by heating tape, mantle, or oil bath. Acknowledgment I wish to thank the staff of the Glass Blowing Unit of NCL, Pune, for the fabrication work. Note
Figure 1. The components 1, 2, and 3 of the reactor. Parts: a, outer cylinder of the syringe; b, gas inlet; c, outer joint, S/T 14/15; d, short glass tube; e, inner joint, S/T 24/25; f, glass rod; g, piston of the syringe; h, 1-mm-diameter holes; i, 0.5-mm capillary; j, stirrer fins; k, outer joint, S/T 24/25; l, reaction flask.
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1. NCL communication No. 6326.
Literature Cited 1. Eisenbraun, E. J.; Denton, T. T. J. Chem. Educ. 1995, 72, 459. 2. Product Catalog; Ace Glass Co., U.S.A.; Cat. Nos. 9525 and 9535, pp 368, 370.
Journal of Chemical Education • Vol. 74 No. 4 April 1997
