Hydrochlorination of (4-Carvone William H. Miles, Charles F. Nutaitis, and Christina L. 6erreth1 Lafayette College, Easton, PA 18042 Hydrohalogenation enjoys extensive coverage i n introductory organic textbooks ( I ) . However, we a r e n o t aware of anv hvdrohaloaenation e x ~ e r i m e n t isn current ~ndrr~~>~du~t(!~lat,orato~y textbook;, presumably due to ~ nnd the ~ r o b l e m sassoc~atedwith h a n d l i n ~~ I W O U .IICI H B (2). ~ A recently described procedu~eusinghydrogen bromide i n acetic acid (3) alleviates some of the experimental difficulties inherent i n the hydrobromination of alkenes a n d is clearly suitable for t h e undergraduate laboratory. Kropp (4) h a s reported a n improved procedure for the hydrohalogenation of alkenes and alkynes that offers practical advantages and improved stereoselectively over standard experimental procedures. Pienta. Crawford. and Kronn ( 5 )have develooed a n exneriment based on this procedure t h a t demonstrates kinetic and thermodynamic control i n the addition of HC1 to 1propynylbenzene. The two salient features of the Kropp ~ r o c e d u r eare the catalvsis of the addition reaction bv silica gel or alumina and the i n situ generation of t h i hydrogen halide. We have found t h a t Kropp's procedure i s readily adaptable to the sophomore organic chemistry laboratory. I n this paper we describe t h e hydrochlorination of (R)-carvone (6) t h a t illustrates the concepts of regioselectivity (Markovnikov addition) and chemoselectivity (electron-rich double bond versus electron-poor double bond). The addition of hydrogen chloride to (R)-carvone (1) gives (5R)-5-(l-chloro-l-methylethyl)-2-methylcyclohex-2enone (2) a s t h e maior ~ r o d u c talone w i t h variable amount's of carvacrol(i) (eq 1).solutiono of oxalyl chloride (1.0 M in C H X L ) was used for the in situ generation of IlCl that is b2ie;ed to be formed by the hyd;olysis of oxiilyl chloride by surface-bound water on the: alumina (4,51. The addition of HC1 is presumably surface-mediated because the HCl is strongly absorbed by the alumina (4).The minor uroduct (3) and traces of acid were readilv removed by a n 'aqueous base extraction. The product (2) was isolated a s a n oil and identified bv 'H NMR s ~ e c t r o s c o ~The v. reaction proceeds to completibn with the'addition'of two molar equivalents of oxalyl chloride if water is excluded. Despite the lack of special equipment for insuring the exclusion of water (e. g., syringes and Nz lines), greater than 75% of our students obtained pure chloride (2) in 40-75% yields. The rest of the students had some starting material in their final product. The hydrochlorination of (R)-carvone illustrates many important concepts in the electrophilic reactions of alkenes and i s accomplished readily within a three-hour lab period. Kropp's procedure should
be readily adaptable for the hydrochlorination, hydrobromination, and hydroiodination of various alkenes and alkynes in a n undergraduate laboratory (4). Experimental Procedure The reaction should be conducted i n a well-ventilated fume hood and gloves should be worn when handling the oxalyl chloride solution. (R)-Carvone (0.075 g, 0.50 mmol; (S)-carvone i s also appropriate) was weighed directly into a dry 10-mL round-bottomed flask equipped with a magnetic stirrer and dissolved i n CH2C12 (3 mL). Alumina (1.0 g; neutral Brockmann I, 150 mesh; dried a t 110 O C for a t least two days) was then added with stirring. Oxalyl chloride (1.0 mL of a 1.0 M solution i n CH2C12,1.0 mmol) was added dropwise over one to two minutes with a graduated pipet. Caution: Gas is evolved vigorously.
An air condenser was placed on the flask, and the reaction mixture was stirred a t room temperature for 20 min. The reaction mixture was filtered directly into a 25-mL separatory funnel using a Pasteur pipet with a plug of cotton i n order to remove the alumina, and the alumina was washed with CH2C1, (2 x 2 mL). The combined organic phases were washe cautiously with aqueous NaOH (5 mL of a 0.5 M soluti ) and then dried over Na2S04. The solution was trans rred into a tared beaker a n d t h e solvent was evap ated gently with a warm sand bath i n the hood. The resulting oil was weighed, dissolved i n CDC13 , and a 'H NMR spectrum was obtained. 'H NMR (60 MHz, CDC13) 6.7 (m, l H ) , 2.1-2.8 (m, 5H), 1.8 (s, 3H), 1.6 (s, 6H).
if
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Acknowledament The authors gratefully acknowledge Lafayette's Committee of Advanced Studv and Research for their financial support in the fonn of a summer stipend to CLB. We would like to thank the organic chemistry students a t Lafayette who conducted this experiment, and Paul Kropp for his helpful comments and a preprint of the paper cited in reference 5. Literature Cited 1. For example see Carey, E A. Organic ChemiBq. 2nd ed.: MeGrsw-Hill,
Inc: New Ymk. 1992;Chapter 7. 2. W , A . J. J. Chsm. Edue 1087,M,366. Thomas,N. C. J . Chem. Edve 1940. 67.431. Maurya, M.R. J Chem Educ 1990,67,974. 3. Bmwn,T. M.;Dmnsfleld, A T.;Ellis, R. J. Chem. E d u 1990.67.518, BTOM, T M.; Dronsfield. A.T.:Hifehcock, I. J Chern. Educ. 1991,68,785. 4. Kmpp, P. J.;Daua,K.A.;Crawford, S. D.:lhbergen.M. W.: Kepler, K D.:Crsig,S.L.: W ~ l r o n , V PJAm.Chern. Soc. 1940,112,7433 Kropp,P. J.;Daus.KA.;Tubergen, M. W : Keoier K. D.: Wilson. V P.: Craic. S. L.: Baillareeon. M. M: Breton. G. W. J.
1991,32,3705.
'Dana Scholar, 1991-1992.
5. P1enta.N. J.; Crawf3rd.S.D.; Kmpp, P J. J. Chrm. Edue 1953.70.682. 6. For the hydrohalogenation of raeemic carvone see Wolinsks J.; Hamahel J. J.: Hutchins.R. 0.J. Org. Chem 1970.33.207.
Volume 71
Number 12 December 1994
1097
