In the Laboratory
Regioselective Hydrochlorination An Experiment for the Undergraduate Laboratory Philip Boudjouk,* Beon-Kyu Kim, and Byung-Hee Han Center for Main Group Chemistry, Department of Chemistry, North Dakota State University, Fargo, ND 58105 As pointed out by Kropp et al., hydrohalogenation is not a simple matter unless the double bond is activated by structural or electronic features (1). Using surface-mediated reactions, Kropp et al. developed greatly simplified hydrohalogenation procedures by using SiO2 or Al2O3 with a variety of active halides such as SOCl2, (COCl)2, Me3SiBr, and PI 3 , which feature higher yields and improved stereoselectivity over earlier methods (2). They postulated that the hydrogen halide is formed via hydrolysis of the active halides by surface-bound water on the alumina or silica gel. Some of these procedures have been modified for instructional purposes (3). Although these methods are simple, precaution should be exercised in using oxalyl chloride. Here we report a simple, convenient, and efficient procedure for the hydrochlorination of a variety of olefins using chlorotrimethylsilane and water: H
PCl3 produced hydrochlorinated products in acceptable yields but that chlorotrimethylsilane was the most generally useful reagent. In this procedure, these compounds evolve hydrogen chloride at rates much faster than chlorotrimethylsilane. Chemoselectivity and regioselectivity were investigated using (R)-carvone. (5R)-5-(1-Chloro-1-methylethyl)-2methylcyclohex-2-enone1 was obtained in 84% yield. Trace amounts of carvacrol are formed after 20 min. After 3 h, only carvacrol is detected in the product mixture. 1.71 (s) 6.71 (m) H
2.31 (s) 6.71 (m) CH3 H O
CH3 O
H H3C C CH 2 1.75 (s)
CH3 OH
Me3SiCl H2O, rt , 20min
3h Cl H3C C
4.75 (db)
CH(CH3)2
H CH3
1.31 (d)
(84%)
1.57 (d)
arom H'S at 7.5
Me3SiCl, H2O rt
Cl
Our results are summarized in Table 1. As shown in Table 1, regioselectivity is high. Markovnikov (electrophilic) addition (4) dominates for simple olefins and anti-Markovnikov (nucleophilic) addition (5) for α,β-unsaturated olefins. Our procedure calls for simple glassware and requires no solvent, and for most olefins, the reaction is complete within 5 h at room temperature. Product isolation is straightforward, requiring evaporation of unused chlorotrimethylsilane and hexamethyldisiloxane and, when necessary, distillation of the desired product. Heating the reaction mixture does not always lead to faster rates and often results in lower yields, presumably from increased vaporization of hydrogen chloride. We also found that active chlorides such as SiCl4 , Me2 SiCl2, SOCl2, SnCl4, and
The stereochemistry of the hydrochlorination can be studied using octalin. Formation of the trans product is easily followed by IR spectroscopy as the diagnostic band at 543 cm {1 increases (6). Experimental Procedure In a typical experiment, a 50-mL two-necked flask was charged with 5.00 mL (4.03 g, 75.9 mmol) of acrylonitrile and mixed with water (0.68 mL, 37.9 mmol) at room temperature. After stirring this two phase system for 5 min, chlorotrimethylsilane (11.45 mL, 9.90 g, 91.1 mmol) was added by syringe. After 2 h, the residual water was taken up by addition of anhydrous sodium sulfate. Fractional distillation removed excess chlorotrimethylsilane (bp 56 °C) and hexamethyldisiloxane (bp 99 °C). The remaining liquid was iden-
Table 1. Hydrochlorination of Olefins Using Chlorotrimethylsilane and Water Olefin
Time Product (h)
Yielda Mechanism (%)
CH3CH2C(CH3)=CHCH3
2
CH3CH2C(CH3)ClCH2CH3
98
Electrophilic addition
CH3CH2CH2C(CH3)=CH2
3
CH3CH2CH2C(CH3)2Cl
91
Electrophilic addition
CH3CH2CH=C(CH3)2
3
CH3CH2CH2C(CH3)2Cl
96
Electrophilic addition
CH2=CHOCOCH3
2
CH3CHClOCOCH3
93
Electrophilic addition
CH3CH=CHCOCH3
5
CH3CHClCH2COCH3
80
Nucleophilic addition
CH2=CHCN
3
ClCH2CH2CN
89
Nucleophilic addition
CH2=CHCOCH3
5
ClCH2CH2COCH3
98
Nucleophilic addition
CH2=CHCOOCH2CH3
2
ClCH2CH2COOCH2CH3
95
Nucleophilic addition
a
All yields are isolated yields.
*Corresponding author.
Vol. 74 No. 10 October 1997 • Journal of Chemical Education
1223
In the Laboratory tified as 3-chloropropionitrile (bp 174 °C [7] 174–176 °C, 89%). 1H-NMR (270 MHz, CDCl3) 2.87 (t, 2H), 3.72 (t, 2H). Acknowledgment Financial support from the National Science Foundation through grant OSR-9452892 is gratefully acknowledged. Note 1. 1H-NMR (CDCl 3, d): 1.57 (d, 6H), 1.81 (s, 3H), 2.1–2.8 (m, 5H), 6.7 (m, 1H).
Literature Cited 1. Kropp, P. J.; Daus, K. A.; Crawford, S. D.; Tubergen, M. W.; Kepher, K. D.; Craig, S. L.; Wilson, V. P. J. Am. Chem. Soc.
1224
1990, 112, 7433. 2. Kropp, P. J.; Daus, K. A.; Tubergen, M. W.; Kepher, K. D.; Craig, S. L.; Wilson, V. P.; Bailargeon, M. M.; Breton, G. W. J. Am. Chem. Soc. 1993, 115, 3071; Kropp, P. J.; Crawford, S. D. J. Org. Chem. 1994, 59, 3102. 3. Pienta, N. J.; Crawford, S. D.; Kropp, P. J. J. Chem. Educ. 1993, 70, 682; Berreth, C. L.; Miles, W. H.; Nutaitis, C. F. J. Chem. Educ. 1994, 71, 1097. 4. Marcuzzi, F.; Melloni, G.; Modena, G. Tetrahedron Lett. 1974, 5, 413; Fahey, R. C.; McPherson, C. A. J. Am. Chem. Soc. 1971, 93, 2445. 5. March, J. Advanced Organic Chemistry, 4th ed.; Wiley: New York, 1985; pp 664–666; Bernasconi, C. F.; Tetrahedron 1989, 45, 4017. 6. Becker, K. B.; Boschung, A. F.; Geisel, M.; Grob, C. A. Helv. Chim. Acta 1973, 56, 2747. 7. Stewart, R.; Clark, R. H. J. Am. Chem. Soc. 1947, 69, 713.
Journal of Chemical Education • Vol. 74 No. 10 October 1997
