Francis 1. Williams, Jr. and s. Charles Baber'
Antioch College Yellow Springs, Ohio
Cyclobutane Chemistry A student laboratory experiment
Two articles on cyclobutane chemistry have appeared recently in THIS JOURNAL.^ We would like to suggest a sequence of experiments for pursuit of this topic in the student laboratory. The experiments involve the use of tetramethyl-1,3-cyclobutanedione (I),athe %ormal" dimer of dimethylketene. This dione possesses a number of distinctive properties. F i s t , it sublimes readily to give well defined needles. Second, it undergoes facile basic hydrolysis to the salt (11) of 2,2,4-trimethyl-3-oxovaleric acid (111). Acidification of I1 gives the p-keto acid, 111, which decarboxylates to give diisopropyl ketone in high yield.
Another unusual property of the dione is its ability to simulate an ester. Hydrolysis of the dione with excess sodium hydroxide in aqueous alcohol followed by back titration to the phenolphthaleiu end-point indicates that each mole of the dione consumes one mole of base. The dione thus gives an accurate saponification equivalent. The dione itself can be prepared from triethylamine
'Student research assistant on Grant No. 1101-B of the Petroleum Resewch Fund for which grateful achowledgment is made. 1 WII~ON, A,, AND GOLHAMER, D., J. CHEM.EDUC., 40, 504 (1963); 40, 599 (1963). Tetnrmethyl-1,3-cyclobutanedianeis available from the Aldrich Chemical Company, Milwsukee, Wisconsin at $4.00 per 500 g.
and isobutyryl chloride.' We suggest that students desiring additional laboratory work be given the reference, chemicals, and equipment, and left to themselves to translate and carry out the procedure. Procedure
Sublimation. Make a hole the size of a lead pencil in the center of a piece of ll-cm filter paper. Spread about 5 g of the dione (I) on the bottom of a 100-mm crystalliing dish. Cover the dish with the filter paper and invert a 100-mm funnel over it. Place the assembly on a heat source atabout 80°Corless. A steam bath turned low and covered with an asbestos board serves nicely. Crystals soon begin to form in the upper part of the funnel. Preparation of Diisopropyl Ketae. Place 10 g of the dione in a 500-ml flask with 16 g of NaOH and 200 ml of water. Attach a condenser and reflux the mixture until no solid is evident (about 45-60 min). After coolmg, acidify the mixture with 6 M HC1. The mixture is then steam distilled (direct) until the head temperature is that of boiling water. Saturate the distillate with K&Oa and extract with two 75-ml portions of ethyl ether. Combine the extracts and wash them once with water and once with saturated NaCl solution. After drying over drierite, remove the ether by evaporation. The residue (about 7.4 g, 90%) may be distilled; excepting a little ether, it is fairly pure diisopropyl ketone as evidenced by gas chromatography. Titration. Place about 1 g (to zb0.01 g) of the subl i e d dione from sublimation process in a 25-ml flask. Add 3 ml (to rt0.01 ml) of standard 3 N NaOH and enough ethyl alcohol to effect solution (1-2 ml). Stopper the flask and leave it at room temperature for a day. (Note: This must be completed by the end of the first laboratory session if the sequence of experiments is to be completed in two periods.) Quantitatively transfer the flask contents with more water and titrate to the phenolphthalein end point with standard 0.1 N HCI. Care must be taken not to heat the flask contents during the titration since COz is easily lost. Calculate the moles of base consumed by the dione. STAUDINQE~, H., Ber., 39, 1631 (1906).
Volume 41, Number 10, Odober 1964
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