A CONSTANT-TEMPERATURE HEATER S. H O R W W D TUCKER The University, Glasgow, Scotland
INWORK on the Ullmann reaction, difficulty was experienced in maintaining reaction mixtures a t a constant temperature of 200°, 220°, or 240°, over periods of several hours. Oil baths are messy, and they, as well as metal baths, render it difficult to observe what is proceeding in the reaction mixture: furthermore, the temperature cannot be kept constant. These drawbacks have been overcome by use of the apparatus diagrammed. A liquid of the desired boiling point is boiled in the 50-ml. conical (or spherical) flask, A. The burner under A is adjusted so that the vapor of the liquid jackets the inner reaction tube, BD, but does not enter the side arm, C, of the jacketing tube; however, as a precaution, the side arm has an air condenser attached a t C. The reaction mixture, a t D, is stirred (thermometer removed) by means of a spiral of tantalum wire attached by rubber tubing to the motor spindle. Boiling of the liquid in A is kept regular by use of a bubbler, E.I Different flasks (A) were used for different liquids, and these, when out of use, were stoppered. The same sample was used repeatedly. Following is a lit of readily available liquids which provide convenient heating temperatures above 100". Heating-bath Liquids
. .. 130' 150'
Cblorobeneene (1323') Cumene (isopropylbenzene) (152-3'), bromobenzene
,-"-,
/l**DI
p-Cymene (176') o-Dichloroben~ene(180m),aniline (184') trans) 1185-195"). monomethvl diDecalin (cis
+
The author has also used the simplified version of the above heating apparatus, in which the inner tube, BD, is inserted through the middle neck of a 3-necked flask; but this modification has been recently de~cribed.~
The ahove-described apparatus, with a still head fitted a t C,can function as a Hahna condenser.
ACKNOWLEDGMENT
J. CHEM.EDUC.,26, 546 (1949). 'HAEN, A,, Ber., 43, 420 (1910). See a180 ARNDT, F.,Org. A. L., 019.Reactions, 2, 197 Syntheses, 20, 27 (1940); WILDS, (1944).
My thanks are due to Mr. J. Leslie for constructing the apparatus, and to Mr. J. Findlay for the drawing. LINKE,W. F.,J . CHEM.EDUC.~ 29,492 (1952).
