William B. Smith
I
Student Preparation of Butyl Ether
The variety of reactions possible between an alcohol and sulfuric acid makes up one of the most intriguing portions of any elementary organic chemistry course. The role of structure and reaction conditions on the formation of alkyl hydrogen sulfates, dialkyl sulfates, alkenes, and ethers is often best brought out in the laboratory by the preparation of an ether by the sulfuric acid process. Many professors find the preparation of ethyl ether, as described in several laboratory texts, too frought with hazards to make the experiment attractive. Various authors have done away with the ethyl ether preparation experiment altogether or have replaced it with the safer preparation of butyl ether. In the preparation of hutyl ether, water is formed; and in order to reach the desired reaction temperature (125°-1450) some provision must be made to remove this from the reaction mixture. One technique is to run the reaction in a conventional fractional distillation apparatus. As the butyl alcohol and water mixture codistill, the heating period must be interrupted several times while the water is separated from the distillate and the unreacted butyl alcohol returned to the reaction flask. The disadvantages of the method are obvious.
Butyl ether appordus.
A more attractive method of preparation utilizes a Dean-Stark tube to separate the water from the reaction mixture as it is formed. Since Dean-Stark tubes are rather expensive and little used in other experiments, feT,, to carry laboratories are out the experiment by this method. The accompanying figure shows a simple form of apparatus which fulfills the same function as a Dean-Stark tube and which has the advantage of being constructed from apparatus readily available in most undergraduate laboratories. A procedure for preparing- butyl ether using this aPparatus is given &re. 21 2
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Journal o f Chemicul Educution
A mixture of 50 g (62 ml) of n-butyl alcohol and 6 ml of concentrated sulfuric acid is prepared in a 150ml extraction flask. The acid is added slowly to the alcohol with continual swirling to give a homogeneous mixture. A boiling stone is added to the flask, and the flask is stoppered with a cork containing a thermometer which extends into the reaction mixture and a short piece of 10-mm tubing bent as shown in the figure. The bent tube is connected by a very short sleeve of rubber tubing to an 18-mm X 150-mm side arm test tube. Before connecting the side arm tube the latter should he calibrated as follows: At a point two-thirds of the height of the tube a mark is made with a wax pencil or gummed tape. The tube is filled with water up to this point. An additional volume of water equal to that produced during the above reaction is added to the tube (6.08 ml from 50 g of alcohol) and a second mark is made.' The water level in the tube is then adjusted back to the first mark. The open end of the test tube is connected to a vertical reflux condenser. The reaction mixture is now gently heated until refluxing occurs. The temperature of the reaction mixture will be in the range of 120-125°C. Over the course of the first hour a small amount of reaction water collects in the test tube. The heat is then increased and after an additional 30 min the reaction temperature will rise to about 135"C, while the rest of the reaction water (about 6 ml total) is collected. During the course of the reflux period, a 50% sulfuric acid wash is prepared. Slowly add 20 ml of concentrated sulfuric acid to 35 ml of water and cool in an ice bath. Pour the crude reaction product plus the material in the water trap into a separatory funnel and wash as follows: (1) 50 ml of water; (2) two 20-ml portions of cold 50% sulfuric acid; and (3) 30 ml of water. Dry the product over 2-3 g of calcium chloride. Filter the product into a 125-ml distilling flask and distill. Collect the portion boiling between 136' and 14.7' as pure butyl ether. The yield is about 20 g. 1 Butyl alcohol has a slight solubility (ea. 6%) in water, and it ~houldbe pointed out to the student that if the alcohol dissolves in the water in the trap 8 slightly larger volume change might be noted. However, with no mechanical miring between the two layers it is douhtful that saturation of the aqueous layer with alcohol will occur. Practice has indicated that the reaction is essentially over when the theoretical amount has been collected in the water layer. It might be well also to point form out that bubnol-water and butanol-butyl .,,,t,,~es. The former boils at about 92" and contains about
