Free Radical Chlorination composition of Monochlorides Formed in Chlorination of 2,4-Dimethylpentane
The reaction of 2,4dimethylpentane(I) with sulfuryl c h b ride or N-ohlorosuccinimide is used to demonstrate free radical reactions and the relative readivities of primary, sewndary, and Method I1 111 1" tertiary earhon-hydrogen bonds. The experimental procedure SO~C~Z, CCL, Although used is similar to one described in THIS JOURNAL.> Peroxide, 80°C 56.6 22.9 21.5 msny hydrocarbons are suitable for this type of experiment, the NCS, CCL, hv, hydrocarbon selected, 2,4-dimethylpentane, hes all three typesof 80°C 20'2 37'2 42.6 carbon-hydrogen bonds. Its reaction with sulfuryl chloride or N-chlorosuccinimide gives all three isomers, 1-ehloro-2,4dimethylpentane(II), 3-chlaro-2,4-dimethyIpentme(III),and 2-chloro-2,4-dimethylpentane(1V)corresponding to the abstraction of a primary, secondary, snd tertiary hydrogen atom, respectively. The percentages of the isomers formed were established by glc analysi~.~To substantiate their existence in the reaction mixture, all three isomers were synthesized independently and used for identification. The results are summarized in the table. The experiments are simple and nonhaaardous and are well suited far the beginning organic student. The student can determine the relative amounts of the three isomers formed, compare these values with those found in a photochemical chl~rination,~ with predicted values, and calculate the relative reactivities of hydrogen a t primrtry, secondary, and tertiary sites. Even though the observed values do not entirely agree with those predicted, they do demonstrate that the relative rates of hydrogen abstraction are in the usual order. Differences between observed and predicted values could serve as s. topic for a clsss discussion or the laboratory writeup. Acknowledgment is made for support given by the Division of Chemical EducationduPont Small Grants and the technical assistance of J. E. Betts and M. Brewer.
J. H., J. CEEM.Ennc., 46,610 (1969). 'MARKGRAF, Approximate retention times (in min) were observed far the following compounds: 2,4dimethylpentane(I), 0.8; CCL, 1.6; 2-ehloro-2,4-dimethyIpentttne(IV), 2.2; 3-chloro-2,4dimethylpentane(lII), 2.9; 1-chloro-2,4dimethylpentane(II), 3.3. Conditions: Perkin-Elmer 800 Gas Chromatograph; sample, 0.2 ~ 1 ;column, 12-ft 10yo Carbowsx 20M on Chromosorh W; column temperature, 80°C; injection port and hydrogen flame detector temperature, 200°C; attenuation, 2K; helium flow rate, 30 ml/min. a RUSSELL, G. A., AND HAFFLEY,P. G., J . Org. Chem., 31,1869 (1966).
Volume 48, Number 5, May
1971
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