A MICROREACTION BLOCK MICRO

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A MICROREACTION BLOCK HARRY P. SCHULTZ University of Miami, Coral Gahles, Florida

MICRO and semimicro techniques in organic chemistry are becoming increasingly popular for both instructional and research purposes. Cheronis' and S t ~ c kwith , ~ coworkers, have published much material on this subject. The author has developed an electrically heated reaction block for executing numerous laboratory operations of analytical samples, and determination of melting points up to 360°. The block is machined from a lilrin. X 2-in. X 7411. piece of ST 37 aluminum alloy. The photographs illustrate the cuts and holes, none of which is of critical dimension. Drilled endwise through the block are three holes for 7-mm. sealed glass tubes; in the right end is one hole for a 76-mm. immersion, 360' thermometer; on top of the block are two seats for 6-in. test tubes; also on top is a viewing chamber, in. diameter, drilled throueh to the bottom of the block: and in the rear of the brock are two holes for meltingrpoint capillaries, projecting into the viewing chamber. The block is heated with a Briskeat standard insulated heating tape in. X 2 ft., 93 ohms, 115 watts, woven into 1/16-in.X =/*-in.grooves cut into the bottom of the block. Holes 3/1e in. diameter a t intersections of the grooves facilitated turning the corner into the next groove with the tape. Burrs were removed from the grooves and corners with emery tape before the Briskeat tape was pressed into the bottom of the block. The block was then mounted on a '/rin. transite platform, surrounded by a transite top, in a wooden cabinet. One end of the cabinet is equipped with two electric plugs; to one outlet, for Variac use, are connected the leads from the Briskeat tape; to the other, leads for n 7.5-watt, 110-volt night light (Fig. 1). The light is positioned in the cabinet with the bulb directly beneath the viewing chamber in the aluminum block for observing samples in tips of melting point capillaries. A short piece of hard glass rod supported by the light bulb is placed in the bottom of the viewing chamber; the top of the viewing chamber is counterbored and sealed with a mica disc. Although the use of the block for most unit operations is obvious, a few comments may prove of interest and value. Reaction mixtures may be reflnxed virtually at constant temperature in either 3- or 6-in. test tubes for long periods of time. Because the heat input can be very closely controlled, a l-ft. length of 7-mm. glass

' CHERONIS,N. D., "Technique of Organic Chemistry, Volume VI: Micro and Semimicro Methods," Interscience Publishers, Inc., New York, 1954. STOCK,J. T., J. CHEM.EDUC..34, 358 (1957), and references cited.

tubing serves as an adequate air cooled condenser for even such volatile solvents as ethyl ether (Fig. 2). Again, because of precise heat cont,rol, fractional distillations are efficiently executed. ,

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Figure 1

Components of microreantion a p p r r a t ~ sshowing thermometer, aluminum bloek (bottom view) with heating tape in prooues, transite phiform and top, and cabinet with Light and eleotriesl outlets. When sssemhled. the viewing ohamber of the blook is above the light in the cabinet.

Front v i e r of miororeaction apparatus showing a reflux assembly on the blaok. On top of the blaok note empty test tube seat and top of viewing chamber corered with a mica disc.

JOURNAL OF CHEMICAL EDUCATION

Sealed tubes 7 mrn. X 150 mm. holding approximately 1.2 ml. of reactant volume when half full, can be heated in the three 7-in. holes drilled endwise through the block. Water has been heated to 300'-315" in soft glass sealed tubes before they burst; this amounts to approximately 1200 psi internal pressure. However, in typical sealed tube reactions using Pyrex tubes, temperatures have not been taken above 180°, caustic solutions have not been placed in the tubes, and all usual precautions necessary to such work have been observed. Sublimations may be carried out either in a vacuum in glass tubes placed within the block, or from beakers placed upon the top of the block.

VOLUME 35. NO. 10, NOVEMBER, 1958

Because the block is designed for illumination of the melting point tubes from below, on the same axis as the tubes are viewed, it is advantageous when determining melting points to place above the viewing chamber a tripod magnifying glass (metal frame, not plastic) focused directly upon the samples in the melting point capillaries. ACKNOWLEDGMENT

The author is grateful to Mr. William Ishman, Engineering School, University of Miami, for aid in machining the block; and to Dr. Jackson Sickels, Chemistry Department, University of Miami, for photographs of the microreaction block.