DECEMBER, 1941 THE REACTIVE PARAFFINS-AN ADDITION HERBERT C. BROWN and'^. S. KHARASCH Uniuersity of Chicago, Chicago, Illinois
IN A recent article in this journal ( I ) , the statement was made that the "paraffins are neither inert nor uninteresting." With this thesis, we are in complete agreement. However, the experimental evidence advanced in support of the proposition leaves much to he desired. The types of reactions listed in the paper under the headings of (a) thermal conversion, (b) alkylation, (c) oxidation, and (d) nitration are those which require high temperatures (300' to 110O0C.). Although the reactions cited may demonstrate that the paraffin hydrocarbons are not uninteresting, they do not furnish, in our estimation, very satisfactory evidence of the "reactivity"' of these substances. In the last three years it has been shown that the paraffin hydrocarbons participate in a number of reactions under surprisingly mild conditions. Thus, they may be chlorinated smoothly and rapidly by snlfuryl chloride in the presence of small quantities (0.1 mol per cent) of organic peroxides (Z), RH
+ S02C12peroxide a RCl + HCl + SO1 40"-80
and they can be sulfonated photochemically under equally mild conditions (3).
Furthermore, direct introduction of the chloroformyl group (--COCl) may be accomplished by the action of oxalyl chloride on the hydrocarbon, either with the aid of actinic radiation, or of small quantities of organic peroxides (4), RH
RH
+ (COCI)*&
+ (COCl),
+ CO + HC1 RCOCl + CO + HCI
RCOCl
:e
Most interesting to the student of organic chemistry are the observations that, by means of these reactions, the paraffin hydrocarbons may be made to react selectively in the presence of so-called "reactive" aromatic hydrocarbons (such as benzene) (2,3,4), and that even in the presence of the "reactive" olefins the inert paraffins may be selectively chlorinated (5). It is submitted that the concepts presented in elementary organic texts concerning the relative reactivities of the various classes of hydrocarbons are badly in need of revision. LITERATURE CITED
(1) GILBERT,"The reactive paraffins," J. CHEM.EDUC.,18, 435 (1941). AND BROWN."Chlorinations with sulfurvl chic(2) . . KRARA~CH ride. I. The peroxide+atalyzed chlorination -of hyhu, pyridine t RS0,Cl HCl RH SOnClz 50 s-60 droca~hons,"J. Am. C h m . Soc., 61,2142 (1939). (3) KHARASCE AN? READ, "Sulfanation reactions with snlfuryl AND BROWN, The significance of the term "reactivity" for the classification chloride," ibad.. 61, 3089 (1939); KKARAS~A "Chlorinations with sulfnwl chloride. 111. (a)The of m u ~ ofs substances is fully discussed in a forthcoming ~ u h licition from this laboratory.. I t is pertinent to indicate, howperoxide-catalyzed chlorination of aliphatic a d d i and ever, that the term "reactivity" has no real meaning unless the acid chlorides.,, (6) The photochemical snlfonation of aliphatic acids, rbid., 62, 925 (1940). reaction which is used as the criterion of reactivity is carefully (4) suecified. The hallowed belief of the oreanic chemist in the inert. . KHARASCH AND BROWN."The uhotochemiral reactions of &s of the paraffin hydrocarbons is probHbly t o he ascribed t o the oxalyl chloride and phosaen< with cyclohexane." ibid.. fact that these subitances undergo reaction mast readily by 62, 454 (1940)., &RAS&, KANE, *ND BROWN,forth: comlng puhhcatlons. means of mechanisms involving atomic and free radical inter"The hi&-temnerature chlorination of mediates. and the studv of reactions of this t m e is a recent de- (51 RUSTAND VAUGHAN.
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