6967 and, with vigorous stirring, 0.01 mol of acyl chloride dissolved in 3 g of solvent was added at a constant rate over a period of 5 min. The reaction was allowed to proceed an additional 10 min after the additions were complete. The solution was then washed with ice water and extracted with ether. The organic layer was separated, dried (Na2S04), condensed on a water bath, and analyzed by gas-liquid chromatography. The data obtained are summarized in Tables I and 11. (b) Without Solvent. To a solution of 0.1 mol each of benzene and toluene in a reaction flask fitted with a thermometer, reflux condenser, and gas inlet tube, was introduced 0.04 mol of formyl (or acetyl) fluoride at -30". Stirring was begun and 0.04 mol of boron trifluoride gas was introduced into the solution at -30" over a period of 3 min. The reaction system was then allowed to warm to 25" and stirring was continued for another 10 min. The solution was then washed three times with water. The organic layer was extracted with ether, separated, dried (Na2S04),and analyzed by gas-liquid chromatography. The data obtained are shown in Table I. Determination of Kinetic Hydrogen Isotope Effect. Benzene4 ~ (0.02 mol) and toluene (0.02 mol) were used to obtain k H : k values for formylation and acetylation. The reaction conditions, work-up procedures, and gas-liquid chromatographic analyses were followed as described above (b). For formylation, k T : kB-ds was found to be 92.7. Calculations gave a k ~ : value k ~ for benzene of 2.68 (92.7/ 34.6). For acetylation, kT:kB-dswas found to be 318; calculation gave a k ~ : value k ~ for benzene of 2.45 (318/130). Conversion of Nitro-Substituted Benzophenones to Benzophenones (Replacement of NO*,by H). Competitive reaction products of p-nitrobenzoyl, 3,5-dinitrobenzoyl, and 2,4-dinitrobenzoyl chlorides were converted to the corresponding benzophenones and analyzed as such by gas-liquid chromatography. A typical experiment was as follows. A mixture of 0.005 mol of competitive reaction products, 0.03 mol of stannous chloride crystals," and 10 g of concentrated hydrochloric acid was placed at 0" in a flask equipped
with a thermometer and reflux condenser, then warmed up to 80" and kept for 30 min. The solution was cooled in an ice water bath, neutralized with 3 0 z sodium hydroxide solution, and extracted three times with ether. Evaporation of ether gave the corresponding anilines whose analysis by ir and nmr spectroscopy confirmed the conversion of the nitro groups to amino groups. The aminobenzophenones were diazotized at 5-10' by treating a mixture of 0.003 mol of amines, 0.9 g of concentrated hydrochloric acid, and 10 g of water with 0.009 mol of sodium nitrite in 2 g of water. The solution was then added to 30 g of 3 0 z hypophosphorous acid solution12 and placed in a refrigerator overnight. The reaction mixture was extracted with ether, dried over Na2S04, concentrated, and analyzed by gas-liquid chromatography. Gas-Liquid Chromatographic Analysis. The analyses of all products were carried out by gas-liquid chromatography on a Perkin-Elmer Model 226 gas chromatograph equipped with a hydrogen flame ionization detector system and open tubular capillary columns. Characteristic retention time of benzaldehyde, acetophenone, and benzophenone derivatives along with Golaytype capillary columns employed and column temperatures are listed in Table 111. Peak areas were determined with an Infotronics Model CRS-1 electronic integrator. Products were identilied by comparison with authentic samples.
Acknowledgment. Partial support of our work by the Petroleum Research Fund, administered by the American Chemical Society, and the C. F. M a b e r y Fund of Case Western Reserve University is gratefully acknowledged. Esso Research and Engineering Company is also thanked for their help. (11) J. S. Buck and W. S. Ide, "Organic Syntheses," Collect. Vol. 11, Wiley, New York, N. Y., 1943, p 130. (12) N. Kornblum, "Organic Syntheses," Collect. Vol. 111, Wiley, New York, N. Y., 1955, p 295.
Participation of Acetylenic Bonds in Pericyclic Reactions. Thermal Cleavage of ,E!-Hydroxyacetylenes Alfred Viola,* la John H. MacMillan,'" Robert J. Proverb," and Brian L. Yates* lb Contribution from the Department of Chemistry, Northeastern University, Boston, Massachusetts 02115, and the Department of Chemistry, Universidad del Valle, Cali, Colombia. Received December 8, 1970 Abstract: The ability of acetylenic systems to participate in intramolecular reactions proceeding oia six-membered cyclic transition states has been established by thermolyses of a number of substituted P-hydroxyacetylenes, in both the vapor and the liquid states. Thermolyses products consisted solely of those allenes and carbonyl compounds derivable from a 1,5-hydrogen transfer. The homogeneous reactions followed the first-order rate law. Activation energies with a variety of alkyl substituents were essentially within experimental error. The activation parameters, E, 40 kcal/mol and AS N - 10 eu, a r e indicative of a cyclic transition state and closely parallel the parameters for the cleavages of those analogous olefins whose data a r e available. However, the acetylenic compounds utilized reacted a t rates varying from 1.3 t o 7 times as fast as those of their olefinic analogs. The effects of alkyl, phenyl, and vinyl substituents, and relative rate comparisons with the reaction of analogous olefins, a r e in accord with a planar transition state for the participation of the triple bond.
-
*
T
he i n v e s t i g a t i o n reported herein concerns the part i c i p a t i o n of acetylenes in r e a c t i o n s whose olefinic a n a l o g s n o r m a l l y p r o c e e d via s i x - m e m b e r e d cyclic t r a n s i t i o n states. A l t h o u g h the acetylenic bond is c o n s i d e r e d to b e l i n e a r in the ground state in acyclic molecules, t h e existence of c y c l o o c t y n e and t h e trans i t o r y f o r m a t i o n of s m a l l e r cycloalkynes, down to c y c l o p e n t y n e , * s u g g e s t that d e v i a t i o n f r o m l i n e a r i t y is not improbable.3 (1) (a) Northeastern University; (b) Universidad del Valle.
A m o n g the recent r e p o r t s of r e a c t i o n s of acetylenes which fall into the a b o v e category are the following: t h e r m o l y s e s of vinyl p r o p a r g y l e t h e r s to yield 3,4p e n t a d i e n a l s 4 i n t h e v a p o r as well as in the l i q u i d p h a s e (2) L. K. Montgomery and L. E. Applegate, J . Amer. Chem. Soc., 89, 5305 (1967), and references cited therein. (3) There is a low energy bending mode for propyne at 336 cm-1. G. Herzberg, "Infrared and Raman Spectra of Polyatomic Molecules," D. Van Nostrand Co., Inc., New York, N. Y., 1951. (4) D. K. Black and S . R. Landor, J . Chem. SOC.,6784 (1965); J. K. Crandall and G. L. Tindell, Chem. Commun., 1411 (1970). For arecent review of triple bond participation in Claisen rearrangements, see A.
Viola, et al. j Thermal Cleavage of P-Hydroxyacetyienes
6968
including one example of stereospecificity ; 5 the aromatic Claisen rearrangement of substituted phenyl propargyl ethers;6 ,the thio-Ciaisen rearrangement in aromatic' as well as acyclic* systems; a nitrogen analog of the acyclic Claisen rearrangement ;9 an enolyne rearrangement ;lo a stereospecific SNi' reaction; 11 the rearrangement of a propargylic to an allenic acetate with migration of the acetoxy group;12 Cope rearrangements; 4,13 and oxy-Cope rearrangements. 14-17 There have also been several reports of Cope-type rearrangements of various 1,5-hexadiynes in which both acetylenic systems appear to participate in the same sixmembered transition state, although the mechanism of these reactions is still uncertain. 16,18-20 Finally, there have been several reports of thermal cleavages of 0hydroxyacetylenes. I 4 - l 6 Despite the analogy to the corresponding olefinic reactions, only in a few of the above examples is there evidence for the participation of cyclic transition states. Only a few involve vapor state rearrangements and most of the reactions cited occurred in the liquid state, accompanied by extensive polymerization, under conditions favoring intermolecular reactions. Only in two cases does the observation of stereospecificity implicate a concerted intramolecular rearrangement.5~11 However, in all of the few instances where activation parameters have been determined,7bJ7JBthe low Arrhenius energy implicates energetic assistance of bondforming steps in the bond-breaking process and the large negative entropies of activation imply rigid transition states, Thermal cleavage of 0-hydroxy olefins has been shown to be a homogeneous, unimolecular, first-order reaction, which apparently proceeds through a sixmembered cyclic transition state. 2 2 This process constitutes a competing reaction in the oxy-Cope re-
arrangement. Similarly, the acetylenic oxy-Cope rearrangement of 1-hexen-5-yn-3-01'~ and its 3-methyl derivativel6V16appears to be a process competing with P-hydroxyacetylene cleavage. Although activation
-
Hop " 7 Cope
Ill cleavage
-0
+ ==
parameters for either competitive process could not be determined, both processes occurred at a faster rate than the corresponding reactions of their olefinic analogs in 1,5-hexadien-3-01.24 In addition, we have reported that the P-hydroxyacetylene cleavage is not restricted to the oxy-Cope systems, in that 5-hexyn-3-01 is quantitatively converted to propionaldehyde and allene at 350°.25 Therefore, thermal cleavage of P-hydroxyacetylenes appeared to represent an ideal system for a study of the participation of acetylenes in cyclic six-membered transition states.
Results Thermolyses of all 0-hydroxyacetylenes, which were found or have been reported to undergo a thermal cleavage reaction, result in the formation of the carbonyl and allenic compounds expected on the basis of a 1,5 sigmatropic hydrogen shift. In no case has there been any evidence for the formation of acetylenic products.
Jefferson and F. Scheinmann, Quart. Rea., Chem. Soc., 22, 411 (1968). (5) E. R. H. Jones, J. D. Loder, and M. C. Whiting, Proc. Chem. Soc., 180 (1960). (6) I. Iwai and J. Ide, Chem. Pharm. Bull. Jap., 10, 926 (1962); 11, 1042 (1963); J. Zsindely and H. Schmid, Helu. Chim. Acta, 51, 1510 ( 1968). (7) (a) Y. Makisumi and A. Murabayashi, Tetrahedron Lett., 1971 (1969); H. Kwart and T. J. George, Chem. Commun., 433 (1970); (b) B. W. Bycroft and W. Landon, ibid., 168 (1970). (8) P. J . W. Schuijl, H. J. T. Bos, and L. Brandsma, Recl. Trao. Chim. Pays-Bas, 88, 597 (1969); L. Brandsma and P. J. W. Schuijl, ibid., 88, 30 (1969). (9) P. Cresson and J. Corbier, C. R . Acad. Sci., Ser. C, 1614 (1969). (10) R. Bloch, P. Le Perchec, F. Rouessac, and J. M. Conia, Tetrahedron, 24, 5971 (1968). (11) R. J. D. Evans, S. R. Landor, and R. Taylor-Smith, J . Chem. Soc., 1506 (1963). (12) P. D. Landor and S. R. Landor, ibid., 1015 (1956); HoffmanLaRoche and Co., Akt.-Ges., Belgian Patent 617,174; Chem. Abstr., 59, 1540 (1963). (13) W. D. Huntsman, J. A. DeBoer, and M. H. Woosley, J . Amer. Chem. Soc., 88, 5846 (1966). (14) A. Viola and J. H. MacMillan, ibid., 90, 6141 (1968). (15) (a) J. W. Wilson and S . A. Sherrod, Chem. Commun., 143 (1968); (b) A. Viola and J. H. MacMillan, ibid., 301 (1970). (16) J. Chuche and N. Manisse, C. R . Acad. Sci., Ser. C, 267, 78 ( 1968). (17) A. Viola and J. H. MacMillan, J . Amer. Chem. Soc., 92, 2404 (1970). (18) W. D. Huntsman and H. J. Wristers, ibid., 89, 342 (1967). (19) B. A. W. Coller, M. L. Hefferman, and A. J. Jones, Aust. J . Chem., 21, 1807 (1968); M. B. D'Amore and R. G. Bergman, J . Amer. Chem. Soc., 91, 5694 (1969). (20) A. Viola and J. H. MacMillan, Abstracts, 159th National Meeting of the American Chemical Society, Houston, Texas, Feb 1970, ORGN 50. (21) G . G. Smith and B. L. Yates, J . Chem. Soc., 7242 (1965). (22) R. T. Arnold and G. Smolinsky, J . Amer. Chem. Soc., 81, 6443, (1959); J . Org. Chem., 25, 129 (1960).
The nine 0-hydroxyacetylenes, 1-9, listed in Chart I, were thermolyzed in static systems which permitted the determination of reaction kinetics, In addition, most of these compounds were also thermolyzed in a vapor state flow system, on a preparative scale. In all cases the reaction appeared homogeneous and no other primary products were detectable. As indicated in Chart I, the strutures of a sufficient number of the products were verified to establish the generality of the reaction. Included in Chart I are the three previously reported examples of 0-hydroxyacetylene cleavage in oxy-Cope systems 10-12. Rates of the vapor phase thermolytic cleavage of acetylenic compounds 1-9 and of l-phenyl-3-buten-301, 13, were determined in static system A and are Iisted in the Experimental Section, Table V. Visual observation of the hot tubes confirmed that the sample was completely vaporized, except in the case of the 1-phenyl 3-buten-1-01, 13, and I-phenyl-3-butyn-1-01, 9. These latter compounds pyrolyzed at too low a temperature (23) A. Viola, E. J. Iorio, K. I
