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a somewhat less strained, non-planar structure,' there is little reason to doubt that the ring ketone will continue to be stabilized relative to the hydrocarbon by the reduction in the number of unfavorable conformations.j5 The parent cyclohexane structure is nicely staggered with no bond oppositions (XXXVIII). Introduction of a trigonal atom alters this nice symmetrical arrangement and introduces some nieaslire of unfavorable conformations (XXXTX) .sR
P
\
XXXVI II
XXXIX
According to this physical interpretation, the introduction of the carbonyl group stabilizes the cyclopentane ring and destabilizes the cyclohexane ring largely by altering the number and degree of unfavorable conformations involving the two alpha methylene groups. We have observed, however, that the effect is not restricted to carbon rings with alpha methylene groups. The lactones with but one alpha methylene group show the effect. Ethyl( 5 5 ) In this treatment it is assumed t h a t in t h e staggered arrangement t h e interaction of t h e doubly-bonded carbonyl group with t h e two alpha methylene groups will be quite small and not significantly greater t h a n t h e interactions which occur with a singly-bonded group in t h e same position. Justification for this view is o5ered by a comparison of t h e potential barrier in acetone, 1400 cal./mole with t h a t in propane, 3300 cal./mole. Thus replacement of t h e two hydrogen atoms in t h e methylene groups by a doubly-bonded oxygen a t o m has decreased t h e potential barrier by 1900 cal., o r 950 cal. per carhonhydrogen bond. This is practically identical with t h e estimated harrier per carhon-hydrogen bond in ethane. [For a summary of t h e available d a t a on potential barriers see J. A. McCouhrey and A . R . Uhbelohde, Qua?l. Reo., 5 , 364 (1051) I. (5n) For a recent discussion of t h e conformations of siibstituled cyclohexanones. see E. J. Corer, THISJ O U R N A L , 75, 2301 (195:3).
[CONTRIBUTIONFROM
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ene and trimethylene carbonates (XV, XVI), wilh no alpha methylene groups, exhibit the same effect of ring size on stability as that of the corresponding carbocyclic derivatives. This observation suggests that the two alpha methylene hydrogen atoms are not essential for the production of these strained conformational effects. I n the carbonates the two lone pairs of each oxygen atom must produce a conformational effect similar to that produced by the two carbon hydrogen bonds in the parent structure. X comparison of the potential barrier to rotatioil in dimethyl ether with that in propane should offer a suitable test of this proposal. The potential barrier in the oxygen derivative is reported to be 2700 ~ a l .not , ~ significantly ~ smaller than the value of 3400 cal. reported for p r ~ p a n e . ~ ~ . ~ ~ Conclusion.-In conclusion it may be stated that a large number of different experimental observations, with remarkably few exceptions, ale satisfactorily correlated with the aid of the proposed generalization. The generalization is in accord with the available thermochemical data. Moreover, it appears to have a sound theoretical basis. X systematic search for apparent exceptions and experimental study of the many predictions should provide a rigorous test of its adequacy and utility. Acknowledgment.-U-e wish to acknowledge the invaluable assistance of E. J. Prosen of the National Bureau of Standards in assembling and interpreting the thermochemical data. (S7) F. A . French and R. S. Rasmussen, J. C k e m . P h j s . , 1 4 , 389 (1946).
(58) K. S . Pitzer, ibid., 12,310 (1944). (59) A similar comparison of t h e potential barrier in methanol with t h a t in ethane appears t o involve difficultiesarisingfrom t h e highly ionic character of t h e hydrogen-oxygen bond and its resulting strong tendency t o form hydrogen bonds. See '8. Weltner, Jr. and K. S . Pitzer [THISJ O U R N A L , 73,2606 (195111 for a discussion of t h e barrier in methanol and pertinent literature references. I,AFAYETTE, ITDIANA COLCUBUS, OHIO
DEPARTMENT O F CHEMISTRY, PURDUE UNIVERSITY]
Preparation and Reactions of Perfluoroalkyllithiumsl BY 0. R. PIERCE,E. T. MCBEEAED G. F. JUDD RECEIVED SEPTEMBER 21, 1953
T h e conditions of formation of heptafluoropropyllithium and trifluoromethyllithium by interchange with butyl- or methyllithium have been studied and an over-all yield of the perfluoropropyllithium reagent of 77% was obtained as shown by hydrolysis to heptafluoropropane. Reaction of this reagent with carbonyl compounds having an active hydrogen led to aldol-type products as well as the expected addition product, the best yield occurring with propionaldehyde (5070)and the Iowest, benzophenone (0:C'c). T h e scope and limitations of the reactions are discussed.
Introduction Earlier attempts to prepare a lithium reagent directly from lithium and iodotrifluoromethane2 were unsuccessful. Studies involving the direct (1) This paper represents p a r t of t h e thesis submitted by G. F. Judd t o t h e Graduate School, Purdue University, in partial fulfillment of t h e requirements for t h e degree of Doctor of Philosophy. Presented before t h e Fluorine Symposium, 124th meeting of t h e American Chemical Society, Chicago, Illinois, September, 1953. ( 2 ) K. S . Haszeldirie, J . Chtiii. S o r . , 2052 (19.19).
formation of perfluoropropyl Grignard reagents,3-" however, have demonstrated the existence of a fluorine-containing organometallic compound and such materials as carbon dioxide, acetone, acetaldehyde and formaldehyde have reacted with (3) A. L. Henne and W. C. Francis, THIS J O U R N A L , 73, 3.518 (1951). (4) I b i d . , 75, 992 (1953). ( 5 ) R. X. Haszeldine, J . Chein. Soc., 3423 (1%2). i G ) 0. R. Pierce and A I . Levine. TRISJ O U R N A L , 76, 1254 (1953).
Jan. 20, 1954
PREPARATION AND REACTIONS OF PERFLUOROALKYLLITHIUMS 475
it in yields as high as 77%. Fainberg and Miller' methylanilinomagnesium bromide to effect mixed have inferred the existence of heptailuoropropylzinc and straight aldol condensations with good success iodide by isolating heptafluoropropane as an acid and Henne3 reported that heptafluoropropylhydrolysis product. In this Laboratory i t was found magnesium iodide converted acetone to mesityl that when heptafluoro-1-iodopropane was refluxed oxide. Other Grignard reagent-catalyzed condenwith zinc dust in a commercial grade of dioxane, sations of ketones and esters have recentlyg been reported and Levine and Hawelllo have used 42YGof i t was converted to heptafluoropropane. This paper demonstrates that a convenient and lithium salts of substituted amines for ester conpractical synthesis of fluorine-containing organo- densations. A study of the effect of mode of addition, reagent lithium compounds can be achieved by halogenmetal interchange. The conditions for formation concentration and dilution on the yield of 4,4,5,5,and use of peduoropropyllithium have been 6,6,6-heptafluoro-3-hexanoland by-products from studied extensively and are less troublesome to the reaction of heptafluoropropyllithium with achieve than those for direct formstion of per- propionaldehyde indicated that any condition fluoropropylmagnesium iodide. which promoted increased base concentration in When butyl-, phenyl- or methyllithium was the reaction mixture decreased the yield of addition added slowly to a rapidly stirred solution of hepta- product and increased aldolization and heptafluoro-1-iodopropane in ethyl ether, a vigorous fluoropropane formation. The yield of alcohol produced from propionreaction ensued, and the corresponding iodides were isolated from the respective interchanges. aldehyde and heptafluoropropyllithium was found When the solution from methyllithium inter- to be strongly influenced by temperature. Beconversion was warmed to reflux temperature a tween -40 and -50' an optimum value was ob9770 yield of hexafluoropropene was obtained and tained which fell sharply as the temperature was none of the heptafluoropropane noted by Haszel- raised to 3 O or lowered to - 74'. dine5 in preparation of the Grignard reagent. The scope of this reaction was studied with Depending on the alkyllithium used, the amount propionaldehyde, acetone, benzaldehyde, acetyl of hexafluoropropene obtained varied widely. chloride, ethyl benzoate, benzophenone and perMethyllithium was used in practically all of this fluorobutyraldehyde. Also diethylsilicon dichlowork, since i t can be stored for a considerable period ride has been converted to a mixture of fluoroof time without decomposition, and gives a smooth organosilanes. I n general, these reactions demoninterchange. An optimum yield value for the strate that the peduoropropyllithium reagent will reagent was obtained by hydrolyzing the reaction undergo both displacement and addition reactions mixture with 3 N sulfuric acid, and determining which are common to Grignard reagents and the amounts of heptafluoropropane produced and alkyllithiums. heptafluoro-1-iodopropane recovered. Since heptaThe reactions conducted thus far do not confirm fluoro-1-iodopropane underwent no change when the existence of trifluoromethyllithium although i t was refluxed in ether with 3 N sulfuric acid, the trifluoromethyl iodide reacted vigorously with heptafluoropropane must necessarily have arisen methyllithium a t -74'. When this reaction was from peduoropropyllithium. A study of the conducted in the presence of sulfuric acid, propionexperimental conditions affecting the over-all re- aldehyde, benzaldehyde, or ethyl heptafluoroaction has shown that the synthesis is best con- butyrate, only tetrafluoroethylene, recovered startducted by adding methyllithium simultaneously ing material and condensation products in the case with the other reactant to a solution of hepta- of the aldehydes, were obtained. These differfluoro-1-iodopropane in ether a t -40 to -50'. ences in properties of molecules containing the At O', decomposition of the reagent occurred to trifluoromethyl group and the peduoropropyl the complete exclusion of addition to benzophe- group have been observed in the chemical behavior none. With ethyl heptafluorobutyrate a t 4-6', of certain peduoro acid derivatives. l1 the reagent gave 35% hexafluoropropane and Heptafluoropropane was absent from all the pre28Y0 of 1,1,1,2,2,3,3,5,5,6,6,7,7,7-tetradecafluoro-4viously mentioned reactions if there were no reheptanone. These reactions demonstrate the lesser actants present having enolizable or strongly acidic reactivity of this fluorine-containing organometallic hydrogen atoms. It is unlikely, therefore, that in addition reactions compared to ordinary alkyl- homolytic fission of the heptafluoropropyllithium or aryllithiums and its instability with respect to occurred in any of these reactions or heptafluorodecomposition into hexafluoropropene and lithium propane would result from free-radical attack on fluoride. the solvent. Heptafluoropropyllithium reacted with propionExperimental aldehyde, acetone and benzaldehyde to give aldolThe physical properties and analyses of the compounds type products and heptafluoropropane as well as prepared from heptafluoropropyllithium and various rethe fluorine-containing alcohols. Methyllithium actants are summarized in Table I. Rectifications were performed with a Todd Precise Fracalso converted propionaldehyde to propion-trialdol tionation Assembly employing an 11 mm. i.d. barrel and at - 50°, as well as to 2-butanol. No case has been packed with ' / 8 in. stainless steel helices. reported where normal alkyllithiums cause such Preparation of Starting Materials .-Iodotrifluoromethane aldolizations, although Nielsen, et al., * have utilized and heptafluoro-1-iodopropanewere made as described pre(7) A. H. Fainberg a n d W. T.Miller, A. C. S. National Meeting, New York City, N. Y..Sept. 1951. (8) A. T.Nielsen, C . Gibbons a n d C. A. Zimmcrman, THIS JOURNAL, 78, 4606 (1951).
(Q)K. Sisido, H. Nozaki and 0. Kurihara, ibid., 74, 6254 (1952). (10) R. Levine and M . Hawell, J . Org. Chem., 15, 167 (1950). (11) D. (1953).
R. Husted a n d A. H . Ahlbrecht, TxIa
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TABLE I COMPOUNDS PREPARED FROM HEPTAFLUOROPROPYLLITHIUM REACTIONS Formula
'C.
B.p.
Mm.
M.P.,
"C.
nab
..
Carbon Calcd. Found
Analyses," Yo Hydrogen Calcd. Found
Fluorine Calcd. Found
CaFa -30 743 .... CaF7H -15 743 .... .. CaF7CHOHCtHs 115 743 1.3250 .. CaF?COH(CH;);! 107 743 1.3260 89 9.5 1.4141 C,FiCI-IOHC6Ho .. 43.50 43.63 2.53 2.65 C~F;COH(CHB)CHBCOCIF, 6 8 . 5 29 1.3194 .. 28.30 28.42 1.43 1.78 75 743 1.26985 (C87):CO (C3Fi)sCOIl 115 743 1.2890 10 22.34 22.99 0.18 0.84 74.40 73.25 95 3 1.4368 C~Hi80.9 .. 62.10 62.21 10.35 10.35 E~zS~(CJF~)Z 79 13 1.3380 .. 28.30 28.34 2.36 2.54 67.90 62.41 a Fluorine analyses were by I€. Clark, University of Illinois and the other elements by Galbraith Laboratories, Knoxville, Tennessee. TABLE I1 DERIVATIVES Formula
'C.
U.P. Mm.
h,l P . , nZOO
C.
Carbon Cdlcd. Found
Hydrogen Calcd. Found
Analyses," Bromine Calcd. Found
Nitrogen Calcd.
Found
CaF7CHCHCHg 62 743 1.3018 . . . 34.30 34.30 2.30 2.30 C8F7CHBrCHBrCH3 97.2 64 1.4009 . . . 19.45 19.61 1 . 3 5 1.46 43.95 43.68 nC&BrF1 10 743 1.3689 . . . 24.90 24.34 1 . 3 8 1.64 27.8 28.14 C~F7CHCsH~OzCNHC&I~. . .... .... 97.5 51.7 51.75 3.04 3 . 0 5 3 . 5 4 3.77 C~F~CHE~OZCNHC~H . .~ . . . . . . . . 106.5 45.00 45.04 3 . 4 6 3 . 5 8 4.03 4.96 .. .... .... 128 45.00 44.81 3 . 4 6 3 . 5 7 4.03 4 . 8 1 C.
