1220 Journal of Chemical Education • Vol. 74 No. 10 October 1997 In the Laboratory Ozonolysis Experiments Using Gas Chromatography– Mass Spectrometry An Undergraduate Organic Chemistry Laboratory Experiment Charlene M. Rhoads, George R. Farquar, and William F. Wood* Department of Chemistry, Humboldt State University, Arcata, CA 95521 Reaction of ozone with organic compounds was first described by Schönbein in 1855 from a reaction of ethylene with ozone to produce carbonic acid, formic acid, and form- aldehyde (1). Ozonolysis has been used in the synthesis of aldehydes, ketones, and carboxylic acids (2), but its most important application has been in determining the position of carbon–carbon double bonds in a compound (3). This tech- nique has rarely been introduced into the organic chemis- try laboratory curriculum due to the specialized apparatus needed to generate ozone and to identify the products. We developed several ozonolysis experiments using an easily constructed ozone generator and analysis with a gas chro- matograph–mass spectrometer (GC-MS). Ozone reacts with carbon–carbon double bonds by a 1,3-dipolar addition mechanism (4) to give a 1,2,3-trioxolane or molozonide product (eq 1). This trioxolane is thermally unstable and quickly rearranges to a 1,2,4-trioxolane, C C O O O R R H R O 3 R C R C H R (1) better known as an ozonide (eq 2). Because ozonides fre- quently detonate on purification attempts, they are rarely isolated. Instead they are usually reduced to aldehydes O O C O C H R R R C C O O O R R H R (2) and/or ketones with a variety of reagents (eq 3). Examina- tion of these fragments can be used to locate the position of a carbon–carbon double bond in the original molecule. The new carbonyl groups indicate where the –C=C– bond ex- isted in the original molecule. + C O H R R C R O [H] O O C O C H R R R (3) Discussion of Chemistry Ozone was produced in an apparatus described by Beroza and Bierl (5 ), which can be constructed from material found in most chemistry laboratories (Fig. 1). This generator was reported to produce about 0.5 mg of O 3 per minute (6), but our apparatus produced about half this value. Frequently ozonolysis is done at dry-ice temperature to minimize reaction at sites other than the double bond; however, in our experiments we found few side products at room temperature. Many reagents reduce the ozonide; we found triphenylphosphine to be efficient and not to interfere with the GC-MS analysis. Ozonolysis products were identi- fied by comparison of retention times and mass spectra with those of known compounds. Methyl oleate was used to illustrate this technique on a straight-chain compound. A solution of this compound was analyzed by GC-MS as a reference. After ozonolysis, the compound in the initial analysis was absent and two new compounds were observed. Comparison of the retention time and mass spectra of these with a homologous series of *Corresponding author. Figure 1. Ozone generator. A: Tesla coil (vacuum leak detector); B: stainless steel needle; C: injectable septum; D: test tube; E: solution of compound; F: moistened KI-starch test paper; G: Teflon tubing; H: rubber stopper (also GC septum or Teflon plug): I, glass tubing; J: aluminum foil; K: rubber tubing; L: ground; M: copper wire.