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FRANKEL, EMKEN, PETERS, DAVISON, AND BUTTERFIELD
VOL. 29
Homogeneous Hydrogenation of Methyl Linoleate Catalyzed by Iron Pentacarbonyl. Characterization of Methyl Octadecadienoate-Iron Tricarbonyl Complexes' E. N. FRAXKEL, E. A. EMKEN, HELENAI. PETERS, V. L. DAVISON, AND R. 0. BUTTERFIELD .Vorthern Regional Research Laboratory, Peoria, Illinois Received J u n e 4, 1964 Iron pentacarbonyl is an effective, soluble catalyst for the hydrogenation of methyl linoleate. Monoenoic fatty esters, the niajor products, show considerable geometric and positional isomerization. Intermediates important in the reduction include conjugated dienes and their complexes with iron carbonyl. Distribution of double bonds in the monoenes can be accounted for by a nonselective reduction of either double bond of the intermediate conjugated dienes. Stable iron carbonyl complexes of conjugated dienes are formed by reacting methyl linoleate and Fe( CO)5a t 180" under either hydrogen or nitrogen pressure. Pure complexes are separated by either countercurrent distribution or alumina chromatography. Elemental and spectral analyses, n.m.r., and degradation studies characterize the complexes as mixtures of isomeric, conjugated methyl octadecadienoateiron tricarbonyl. Structure I is proposed for the complexes that involves overlapping of iron orbitals and conjugated diene a-orbitals. The pure conjugated diene-iron tricarbonyl complexes undergo rapid hydrogenation a t 180" under hydrogen pressure and yield monoenes and methyl stearate. The complexes also catalyze the hydrogenation of methyl linoleate under conditions milder than required for the F e ( C 0 h catalysis. They are probably important catalytic intermediates in homogeneous hydrogenation and provide suitable model systems for basic studies in catalytic hydrogenation.
Advances in the chemistry of organometallic complexes have stimulated further research on their function in homogeneous catalysis. 3-5 Reduction of olefinic bonds, frequently observed under conditions of the hydroformylation or oxo r e a ~ t i o n ,led ~ ' ~us to an investigation of metal carbonyls as catalysts in the homogeneous hydrogenation of unsaturated fats. Iron and cobalt carbonyls catalyze the reduction and the isomerization of polyunsaturated fats.Bs9 With Fe(C0)5 the formation of a stable, fat-iron carbonyl complex during hydrogenation was indicated.8 Metal carbonyls are known to form stable complexes directly with conjugated dienes'O and with unconjugated dienes after they become conjugated."-13 Metal carbonyl complexes of ~yclopentadiene~ and conjugated ketones14 also reportedly catalyze hydrogenation. In the present investigation we isolated and characterized a complex of iron carbonyl and methyl linoleate in pure form, and we compared the catalytic activity of this complex with that of the parent Fe(CO),. Results Hydrogenation.-Methyl linoleate was effectively reduced with Fe(CO), under moderate hydrogen pres(1) Presented before the Division of Organic Chemistry, 147th National lleeting of the American Chemical Society, Philadelphia, Pa.. April, 1964. Article is not copyrighted. (2) One of the laboratories of the Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture. (3) .J. Halpern. Quart. Reo. (London). 10, 463 (1956); Advan. Catalysis, 9 , 301 (19.59); J . P h ~ s Chem., . 63, 398 (1959). (4) J . Ralpern, J. F. Harrod, and I3. R. James, J . A m . Chen. Soc., 83, 753 (1961). (5) H. W. Sternberg and I. Wender, International Conference of Coordination Chemistry, London, April 6-11, 1969; Special Publication No. 13, The Chemical Society, London, 1959, p. 35. (6) .If. Orchin. A d ~ . a n Catalysis, . 6, 385 (1953). (7) I. \Tender and H. W. Sternberg. i b i d . . 9 , 594 (1957). ( 8 ) E. N. Frankel, €1. M. Peters, E. P. Jones, and H. J. Dutton. J . A m . O d Chemzsts' Soc., 41, 186 (1964). (9) E. N. Frankel. E. P. Jones, V. L. Davison, E. Emken, and H. J. Dutton. thzd.. in press. (10) h l . A . Bennett, Chem. R e v . . 62, 611 (1962). ( 1 1 ) K . R. Kine. T. A. Alanuel, and F. G. 4 . Stone, J . Inorg. .Vucl. Chem.. 16,233 (1961). (12) R. Pettit. G. Emerson, and J. Mahler, J . C h e m . Educ., 40, 175 (1963). (13) J. E. &net and R. Pettit. J . A m . C h e m . , Soc., 83, 2954 (1961). (14) 11. ?L. Brown. .J. P. Hargaden, C. M. McMullin, S . Cogan, and XI. Sloan. J . Chem. Soc., 4914 (1963).
sure (400 p.s.i.). Rates of hydrogenation were estimated by the decrease in dienes, which followed firstorder kinetics within a tenfold range in catalyst concentration. Hydrogenation and composition data are summarized in Table I. The rate of hydrogenation was negligible at 150'; at 180" it increased with catalyst concentration. Monoenoic fatty esters, the major products, showed considerable conversion of cis to trans isomers. Other products detected by gas chromatography included conjugated dienes and methyl stearate. The reduction products were yellow and showed strong absorption in the carbonyl stretching region (4.88 and 5.05 K), previously ascribed to a fatiron carbonyl complex.8 Concentration of this complex in the reduced products, estimated by the intensity of the carbonyl stretching bands, was directly related to the initial concentration of catalyst. The pure iron carbonyl complex of linoleate, described below, was a much more efficient catalyst than Fe(C0)6. With this complex, reduction occurred under conditions milder than necessary with Fe(C0)s. Product composition was generally the same with either catalyst. Rate curves in a typical hydrogenation catalyzed by Fe(CO), are shown in Fig. 1. Conjugated dienes and the iron carbonyl complex reach constant levels a t about 50y0 reduction of linoleate. At higher levels of catalyst (runs 3 and 4, Table I) the Conjugated dienes and complex follow the same rate curves, but a decrease in concentration occurs after 70% conversion of linoleate. Hydrogenations catalyzed with the iron carbonyl complex of linoleate show similar rate curves as with Fe(CO), catalysis. During the first 50% conversion conjugated dienes and complex remain constant and then decrease a t higher levels of reduction. Hydrogenated products of linoleate were fractionated by countercurrent distribution between hexane and acetonitrile (Fig. 2). The diene was further separated into nonconjugated and conjugated isomers by preparative gas chromatography. The double bond distribution in these fractions was determined by analysis of the mono- and dicarboxylic acids produced by permanganate-periodate oxidation (Table 11). The calculated distribution that best reproduces the experimental data is reasonably consistent with a reduction of conjugated dienes by 1,2-addition with no selectivity
METHYLOCTADECADIENOATE-IRON TRICARBON YL COMPLEXES
NOVEMBER, 1964
3293
TABLEI HYDROQENATION OF METHYL LINOLEATE Runsa
Catalyst, M b
Temp., OC.
ki,' hr. -1
Time ( t ) , hr.
Stearate,
Monoene,
Diene,
%
%
%
-Composition a t t Conjd. diene, % am mp
7
Complex,*
%
%
1 Fe(CO)&, 0 . 1 150 0.01 5 0 1.6 95.0 3.4 0 0 0 2 0.12 180 41.3 45.2 7 5.0 Fe(CO)s, 0 . 1 8.5 10.35 34.0 10.2 3 0.22 180 10.0 Fe(CO)5, 0 . 5 61.2 22.9 6 5.9 11.01 40.2 14.9 4 13.4 0.31 180 5 65.5 12.3 Fe(C0)6, 1.O 8.8 10.67 42.0 18.1 150 Complex,* 0 . 1 5 0.07 7 5.1 33.5 49.0 5.2 6.13 24.8 9.9 2 180 Complex,' 0 . 1 0.60 12.9 61.2 23.3 6 2.7 6.42 43.9 11.0 180 Complex,. 0 . 2 -1.3 39.9 3 7 53.6 6.5 0 0 36.3 3.8 a Initial hydrogen pressure of 400 p.s.i., and cyclohexane used as solvent in all runs. * Per mole of methyl linoleate. c Decrease of diene. Expressed as methyl elaidate. e Methyl octadecadienoate-iron tricarbonyl, a4.88II 4.54 and a 5 . 0 6 ~7.95 ( a is absorptivity).
TABLEI1 DOUBLE BONDDISTRIBUTION IN FRACTIONS OF HYDROQENATED METHYL LINOLEATE Run 8 ' Nonconjugated dienes Bond Mole positionsd %
8,ll9,1210,1311,14
5.4 87.8 5.1 1.7
-Free--Bond positionsE
6,87,98,lO9,ll10,1211,1312,14 13,15-
Conjugated deine-Complex-Mon0ene-Y Mole Undecomposed, Decomposed Bond Found, Calculated,d % mole % (FeClr), mole % positionsE mole % Sf mole %
*
0.8 2.9 12.9 34.4 33.5 12.3 1.7 1.5
1.0 3.9 13.6 34.4 32.1 12.0 3.0
...
4-
4.6 13.7 35.6 32.8 11.0 2.3
...
...
567891011121314 1516-
1.9f 0 . 2 1.6f0.1 2.5f0.1 4.5f0.5 8.410.5 15.9f0.3 20.6 1 0 . 6 18.9f0.3 15.8f1.2 5.4 i 0 . 4 2.5f0.1 2.2f0.1
...
+Sf ... ... 0.4 1.4 6.9 18.6 23.2 23.4 17.5 7.0 0.9 0.8
...
Run 9* -7 -Monoenesc-cis, trans, mole % mole %
I
... 1.0 1.9 3.0 6.1 18.9 20.8 21.0 14.9 5.1 2.7 1.8 2.7
2.3 1.3 2.1 3.4 9.6 17.8 21.0 18.9 12.7 6.4 2.2 1.5 0.8
a Reaction conditions: 0.5 M Fe(CO)s, B O 0 , 400 p.s.i. H2, 2 hr; fractions (%)-monoenes, 44.4; nonconjugated dienes, 20.1; Reaction conditions: 0.1 M Fe(CO)s, 180", 400 p.s.i., conjugated dienes (free), 13.5; complex (I), 20.0. 3 hr; fractions (distilled product %)--stearate, 11.0; e&-monoenes,18.8; trans-monoenes, 33.7; nonconjugated dienes, 29.9; conjugated dienes, 6.6. c Data baaed on analyses of dibasic acids only. Assuming that they are derived from conjugated dienes exclusively and that either double bond is hydrogenated _with equal probability. e Dibasic acids with no matching monobasic acids were considered spurious and neglected; they totaled 9.6% in the nonconjugated dienes, 2.670 in the free conjugated dienes, 3.5% in the complex, and 1.37, in the monoenes. f S = standard deviations from five determinations.
'
toward either double bond. Based on reduction of either nonconjugated dienes by l,&addition or conjugated dienes by 1,4-addition, calculated values do not agree with the experimental data. The monoene fraction was also separated into cis and trans isomers by argentation chromatography. l b Oxidative cleavage analysis showed similar scattering of double bonds in the cis and trans isomers as in the original unfractionated monoenes. Iron Carbonyl Complex.-The diene-iron carbonyl complex1Bwas separated from hydrogenated linoleate by countercurrent distribution (Fig. 2) and isolated in 227" yield. When methyl linoleate was heated a t 180" with an equimolar quantity of Fe(C0)6 under nitrogen, the same complex was obtained and separated by alumina chromatography in 10% yield. Appreciable conjugated dienes were also formed under such conditions. The iron carbonyl complex behaved as one component with the same retention as methyl stearate on argentation by chromatography with either thin layer plates of silica gel or columns of cation exchange resin treated with AgN03. The double bonds of these (15) E. A. Emken, C. R. Scbolfield, and H. J. Dutton, J . Am. OiZChemO t s ' Soc., 41,388 (1964).
(16) A preliminary report is given by E. N. Frankel, E. P. Jones, and C . A. Glass, i b i d . , 41, 392 (1964).
-1
0
1
2
3 1 5 6 7 lime, hr. Fig. 1.-Rate of hydrogenation of methyl linoleate catalyzed by Fe(CO)&(run 2, Table I). Concentration of individual components was normalized to take into account the concentration of complex not detectable by gas chromatography.
complexes, therefore, are not free to complex with silver. Analytical data are consistent with the empirical formula lor methyl octadecadienoate-iron
3294
FRANKEL, EMKEN, PETERS, DAVISON, AND BUTTERFIELD
VOL.29
I
HA _-
A:$
C D2
8:3 2.0
3.0
4.0
5.0
6.0
7.0
8.0
E k3
9.0
10.0
7
Transfer Number Fig. 2.-Countercurrent distribution of hydrogenated methyl linoleate (run 8, Table 11) between hexane and acetonitrile in a 200-tube instrument. Fractions were removed by simple withdrawal. Shaded area shows presence of diene-Fe(CO)a complex by thin layer chromatography.
tricarbonyl, CZ2Ha4FeO5.The infrared spectrum shows intense absorption bands a t 4.88 and 5.05 p , characteristic of diene-iron carbonyl complexes. l2r1' The ultraviolet spectrum shows strong end absorption a t 215 mp, corresponding to that reported for (1,3butadiene) -iron tricarbonyl. The 60-Mc. n.m.r. spectrum of the iron carbonyl complex is compared with that of methyl linoleate in Fig. 3. Peak assignments are based on previous studies with natural fats.lg Signal A ( T 5.01) is equivalent to two olefinic protons in the complex compared with four in linoleate. The apparent "doublet" structure, with outer shoulders, of A is consistent with its being the partially resolved spectrum of one-half of an AzX2 4-spin system. 2o Furthermore, a more detailed analysisZ1of this portion of the spectrum indicates that it comes from the central pair of olefinic protons (HA)in the conjugated diene system. This interpretation agrees with that made by Wilkinson, et al.,22-24for various metal carbonyl complexes of conjugated diene systems. The terminal olefinic proton resonance (Hx) apparently shifts upfield into region E, broader (17) K. Xoack, Helu. Chim. Acta, 46, 1847 (1962). (18) R. T. Lundquist and M. Csis, J . O w . Chem., I T , 1167 (1962). (19) L. F. Johnson and J. N. Shoolery, Anal. Chem.. 34, 1136 (1962). (20) H. S. Gutowsky and C. J u a n , J . Chem. Phye., 3 7 , 120 (1962): D. M. Grant, R. C. Hirst, and H. S. Gutowsky. ibid., 38, 470 (1963). (21) We are indebted t o Professors R. T. Gutowsky. University of Illinois, and R. B. Bates. University of Arizona. for aid in this interpretation. (22) M. L. H. Green, L. P r a t t , and G. Wilkinson, J . Chem. Soc., 3753 (1959); 989 (1960). (23) R. Burton, L. P r a t t , and G . Wilkinson. idid.. 594 (1961). (24) G. Wilkinson, "Advances in the Chemistry of the Coordination Compounds," S. Kirschner, Ed., The Macmillan Co., New York, N. Y., 1961, p. 50.
Fig. 3.--?J.m.r. spectra (60 Mc.) of methyl linoleate and dieneiron tricarbonyl complex, in r using tetramethylsilane (SiMer) and benzene (Bz) as references. Peaks are identified by letters followed by relative proton intensity.
than in linoleate, owing to normal aliphatic proton resonance. Such a shift characterizes conjugated olefins bound to metals.25 Treating the olefinic protons as an A2X2 system, Bates26aevaluated the following = 4.3, JAX = 8.5, and J I A X = coupling constants: JAA -1.7 C.P.S. These constants are consistent with the view that the iron is bonded to some extent to four carbon atoms, but inconsistent with the structures in which the iron is strongly bonded only to carbons 1 and 4 of the diene system. I n the latter case, JAA would be larger and J,AX would be smaller. Peak C, due to methylenic protons adjacent to two double bonds ( T 7.2), is eliminated in the complex as expected of conjugated dienes. The signal in region D, due to resonance of allylic protons ( T 7.71), is also absent' and apparently shifts into region E. 26b The methyl octadecadienoate-iron tricarbonyl complex was decomposed by treating with either potassium hydroxide, ferric chloride, or triphenylphosphine. Conjugated methyl octadecadienoates were obtained with maximum absorptivity a t 231 mp of the same order of magnitude as given by alkali-conjugated methyl linoleate. These dienes have a trans,trans configuration (A,, 10.1 p ) as expected if the conjugated system (25) G. Wilkinson, Proc. I n t e r n . Cong. Pure A p p l . Chem. (London). 1, 127 (1960). (26) (a) R. B. Bates, personal communication. (b) T. A. Manuel observed a similar shift of peaks assigned t o allylic protons in 1,l'-bicycloalkenyls toward the position corresponding t o methylenic protons in the iron tricarbonyl complex. I n his presentation a t the 147th National Meeting of the American Chemical Society, Philadelphia, Pa., April. 1964 [ I n o w . Chem., 3, 510 (1964)], he favored the following specific structure involving spa hybridization of C-1 and C-4 instead of sp2 which is consistent with n.m.r. data.
METHYLOCTADECADIENOATE-IRON TRICARBONYL COMPLEXES
SOVEMBER, 1964
assumes a cisoid conformation in the complex.I2 Also, the complex was decomposed by permanganateperiodate oxidation. Cleavage mono- and dicarboxylic acids were obtained from the complex either directly or after decomposition with ferric chloride. The double bond distribution of the conjugated methyl octadecadienoate ligands corresponds to that of the free conjugated dienes in hydrogenated linoleate (Table 11). The results characterize the complex as a mixture of* isomeric conjugated dienoic fatty esters attached to iron tricarbonyl. The proposed structure I for the complex is similar to that given for the well-known complexes of metal carbonyls and conjugated dienes'O, l 2 involving overlapping of atomic orbitals of iron and x-orbitals of the diene.
produced, followed by complex formation with iron carbonyl. This complex is then hydrogenated according to Mechanism I. MECHANISM I CH3-( CHz)a-CH=CH-CHrCH=CH-( methyl linoleate Fe(CO)s (1)
I
Fe(CO)a (2)
4
4t
(3)
complex I CHa-( CHz)m-CH=CH-(
L----. ---.y. CH-(CH2),-COOCH~
CHz),-COOCH3 monoenes (5)
(7)
~
4
CH3-( CHZ)~B-COOCHS methyl stearate
Fe
06 1 'co
s,y
CO
V,W
=
=
I x , y = 4 , 8 ; 5 , 7 ; 6,6; 7 , 5 ; 8 , 4 ; 9 , 3 ; 1 0 , 2
Complex I does not absorb hydrogen in the presence of a heterogeneous catalyst (palladium-alumina, acetic acid). This resistance to hydrogenation is analogous to that observed for iron carbonyl complexes of butadiene*' and of other conjugated polyene^,^^,^^ and has been regarded as evidence for n-complex formation involving all double bonds of the conjugated systems. Independent experiments, however, revealed that complex I effectively poisons the heterogeneous catalytic hydrogenation of methyl linoleate, which becomes highly selective. This poisoning is most likely attributable to adsorption on the catalyst surface of the complex through its carbonyl moieties. Resistance to heterogeneous hydrogenation, therefore, may have no bearing on the nature of the bonding involved in the complex. When heated with methyl linoleate under nitrogen, complex I was stable at 150°, but at 180" it decomposed and the carbonyl stretching absorption at 4.88 and 5.05 p was completely eliminated within 4 hr. This decomposition yielded a mixture of conjugated dienes. Under hydrogen pressure (400 p.s.j.) the dieneiron carbonyl complex was more easily decomposed at 150 " to conjugated dienes with some hydrogenation. At 180" the complex was rapidly hydrogenated to a mixture of approximately equal amounts of monoenes and methyl stearate within 2 hr. and with almost complete loss of the carbonyl stretching absorption bands.
Discussion The rate data and isomeric composition of the reduction products clearly implicate conjugated dienoic fatty esters and their complexes with iron carbonyl as important intermediates in the homogeneous catalytic hydrogenation of methyl linoleate. It may be postulated that conjugated dienes are initially (27) B. F. Hallam and P. L. Pauson. J . Chem. Soc.. 642 (1958). (28) M. D. Rausoh and G. N. Schrauzer, Chem. I n d . (London), 957 (1959). (29) T. A . Manuel and F. G. A. Stone,
CHz)rCOOCHs-
CHs-( CHz)y-CH=CH-CH=CH-( CHz)z-COOCHaconjugated dienes
CH-CH
CHJ-(CH~),-CH
3295
J. A m . Chem. Soc., 82, 366 (1960).
same as in I 2,12; 3 , l l ; 4,lO; 5,9; 6,8; 7 , 7 ; 8 , 6 ; 9,5; 10,4; 11,3; 12, 2; 13, 1; 14, 0
Decomposition of complex I by step 3 gives conjugated dienes and Fe(C0)B. Iron tricarbonyl has been reported as a product of the decomposition of iron hydrocarbonyl, H2Fe(C0)4.30 If monoenes can be reduced to stearate to a small extent by reaction 5, then it seems likely that linoleate and conjugated dienes would also reduce directly by reactions 6 and 7. The homogeneous catalysis by Fe(C0)6 could be explained by formation of H2Fe(C0)4,which is a strong reducing agent15,30either directly or through the intermediacy of the diene-iron tricarbonyl complex I according to reactions 8 and 9.
+ H? +HZFe(CO)r + CO 2monoene + HtFe(C0)4+ 2CO + Fe
Fe(CO)a 21
+ 3Hz -+
(8)
(9 )
Reduction could also be catalyzed by the hydride form of complex I by intramolecular hydrogen transfer. The hydride of cyclopentadienyl-iron carbonyl, (C6H6)Fe(C0)2H,has been invoked by Sternberg and Wenders in the hydrogenation of cyclopentadiene with iron carbonyls. Since then, Brown, et a1.,I4 have suggested that reduction of certain conjugated ketones with moist chromium hexacarbonyl proceeds either by hydrogen transfer through an unstable, protonated n-complex or through the stable arene-chromium tricarbonyl complex in acid solution. Pettit, et al. , l a also proposed that the rearrangement of nonconjugat ed l14-dienes into conjugated l13-diene-iron tricarbonyl complexes proceeds by hydrogen transfer through a n-allyl-hydroiron tricarbonyl complex. The observation that complex I catalyzes the homogeneous hydrogenation without initial change in concentration strongly suggests that I constitutes a catalytic intermediate. The mechanism involving steps 1 to 7 receives further support by simulation of the rate curves with an analog computer.31 Reasonably good fits are obtained with the relative first-order constants in Table 111. (30) I. Wender, H. W. Sternberg, R. A. Frledel, S. J. Metlm, and R. E. Markley, c'. S . Bur. Mznea Bull., 600 (1962). (31) R. 0. Butterfield, E. D. Bitner, C. R. Scholfield, and H. J. D u t t o n , J . A m . 0 1 1 Chemists' SOC.,41, 29 (1964).
FRANKEL, EMKEN, PETERS, DAVISON, AND BUTTERFIELD
3296
TABLE I11 Run 2 Run 3 Run 4
ki
ka
ka
kk
ka
ks
0.1 0.1 0.1
1.0 1.0 1.0
0.6 0.4 0.4
0.6 0.4 0.3
0.03 0.03 0.02
0.01 0.01 0.03
In 0.03 0.01 0.04
Although a reasonable fit could be obtained by ignoring steps 6 and 7, a better fit resulted when they were made small and of the same order of magnitude as step 5 . This reaction scheme is, of course, not proved, and more definitive evidence is now being sought with radioactively labeled intermediates. Another mechanism considered involves initial formation of complex I which either decomposes to conjugated dienes or hydrogenates directly to monoenes and stearate. Conjugated dienes also in turn hydrogenate to monoenes and stearate. However, analog simulation of this scheme is not as good as the initial mechanism.
Experimental Materials.-Iron pentacarbonyl was a gift of Antara Chemicals, General Aniline and Film Corp.32 Methyl linoleate was obtained from the Hormel Institute, Austin, Minn., and analyzed 100% by gaa chromatography. Hydrogenation.-All hydrogenations were carried out in cyclohexane solution (200/, w./v.) stirred in Magna-Dash, high-pressure autoclaves adapted with sampling tubes. In a typical run (no. 2, Table I) 10.76 g. (37 mmolea) of methyl linoleate waa charged into a 150-ml. autoclave together with 0.7 g. (3.6 mmolea) of Fe(CO)s and 40 ml. of cyclohexane. The autoclave was purged with nitrogen, charged to 250 p.8.i. with hydrogen, and heated to 180'. At this temperature the hydrogen pressure waa raised to 400 p.s.i. just before sampling, which was done every hour for 7 hr. The products, which were homogeneous during hydrogenation, were dissolved in petroleum ether (b.p. 39-52'). The catalyst was decomposed by repeated washing with dilute HC1 (2: l ) , then with dilute KOH ( l O ~ o and ) , finally with distilled water to neutrality. After drying (NanS04)and removal of solvent, the products were a deep yellow. For characterization of products, nonkinetic runs were made at two times the scale given above. In run 9 (Table 11) 20.73 g. (70 mmoles) of methyl linoleate waa hydrogenated in a 500-ml. autoclave with 1.4 g. (7.1 mmoles) of Fe(COh and 80 ml. of cyclohexane. The reduced products (20.8 g.) were isolated as described and then distilled through a short Vigreux column (120140" at 0.02 mm.) yielding 18.1 g. of clear methyl esters and a deep reddish brown residue. The yellow color of the nondistilled products was associated with the iron carbonyl complex I , which showed intense absorption at 4.88 and 5.05 p (carbonyl stretching). This absorption was absent in the distilled fatty esters and increased in the distillation residue. Fatty acid composition of the products was determined by gas chromatography with a Hy-Fi flame ionization aerograph and a 6 ft. X l / g in. column packed with Chromosorb W (60-80 mesh) coated with 15-2070 diethylene glycol succinate. Optimum separations were obtained at 180-185" and a nitrogen flow rate of 30 to 40 ml./min. Peak-area measurements were made by a diskmechanical integrator. Infrared and ultraviolet analyses of geometric and conjugated isomers were made by procedures described previously.33 Measurements of the complex by infrared in the carbonyl stretching region (4-6 M ) were made in carbon tetrachloride solutions. Fractionations.-For detailed characterization, a nondistilled and a distilled product (runs 8 and 9, Table 11) were fractionated by countercurrent distribution between n-hexane and acetonitrile according to the degree of unsaturation by the procedure of Scholfield, et a1.34 Individual fractions were monitored by gm chromatography and thin layer chromatography with methyl stea(32) Companies are named to provide full information on experimental conditions. Naming them does not constitute an endorsement by the U. S. Department of Agriculture of their products over those of other manufacturers. (33) C. R. Scholfield, E. P. Jones, J. Nowakowska, E. Selke, B. Sreenivasan. and H. J. Dutton, J . Am. Oil Chemists' Soc., 37,579 (1960). (34) C. R. Scholfield,' J. Nowakowska. and H. J. Dutton. ibid., 37, 27 ( 1960).
VOL. 29
rate, oleate, elaidate, linoleate, linolenate, and alkali-conjugated linoleate being used as reference standards. Fractions were then combined into monoenes, dienes, and complex (Fig. 2). Thin layer chromatography was carried out on glass plates coated with silica gel and AgNOB according to the procedure of Barrett, et a1.,3S substituting benzene as developing solvent. Complex I had the same migration as methyl stearate and was characterized by a black spot showing after the plates were developed and evidently caused by metallic silver. The other organic components were detected by charring with sulfuric acid (50%). The diene fraction (run 8, Table 11) was separated into nonconjugated and conjugated isomers by preparative gas chromatography in an Autoprep aerograph instrument. The column (20 ft. X 3/g in.) was packed with Chromosorb P (60-80 mesh) and coated with 30y0 diethylene glycol succinate. The conjugated dienes separated well from the nonconjugated dienes at 198" and a helium flow rate of 300 ml./min. Repeated injections of 70 mg. of sample were made, and the fractions were collected at room temperature (collector temperature 208") into bottles with inlet tubes tightly packed with glass wool. Total recovery was 83 wt. %. The products showed one component by gas chromatography. Infrared analyses showed 23.0% trans (as methyl elaidate) in the nonconjugated diene fraction and &,trans and trans,trans conjugation (at 10.15 and 10.6 p , e 94.2 and 28.9) in the conjugated diene fraction. Ultraviolet analysis of the conjugated diene fraction at 231 mp gave e 21,800. The monoene (run 9, Table 11) was separated chromatographically into cis and trans isomers by argentation with a silversaturated ion-exchange resin column.15 The sample (0.357 g.) was passed through a column (225 X 1.3 cm.) packed with Amberlyst XN-1005 previously saturated with Ag?lTOa, and then it was washed with water and methanol. The separations were followed by a differential refractometer. Elution with methanol yielded 0.224 g. of trans monoene followed by 0.093 g. of cis monoene. The trans fraction contained 92.7y0 trans (as methyl elaidate) by infrared analysis. Position of double bonds in the fractions waa determined by the KMn04-KI04 oxidative cleavage technique of Jones and Stolp .as This procedure was improved by analysis of butyl esters of monocarboxylic acids, as well aa methyl esters of dicarboxylic acids, by programmed temperature gas chr~matography.~'The analyses of these two acids were in good agreement and averaged in the determination of positional isomers. Diene-Iron Tricarbonyl Complex 1.-In separating hydrogenated linoleate by countercurrent distribution a fraction, isolated in 22% yield (transfer 480 to 600, Fig. 2), waa shown to be a pure diene-iron tricarbonyl complex. Argentation by chromatography either on thin layer plates (silica gel-AgNO,) or in silversaturated resin columns yielded one component of the same retention aa methyl stearate. The infrared spectrum showed bands at 4.88 and 5.05 p ( e 1970 and 3450). Ultraviolet analysis showed strong end absorption at 215 mp ( e 23,100), but it may have doubtful validity because of instrument limitations. A n d . Calcd. for I, CZ2H34Fe05: C, 60.9; H , 7.8; Fe, 12.9; mol. wt., 434. Found: C, 61.6; H, 8.0; Fe, 12.5; mol. wt., 430 (osmometric, benzene). The same complex was obtained by heating at 180" equimolar quantities of methyl linoleate (14.71 g., 50 mmoles) and Fe(C0)b (9.8 g., 50 mmoles) with nitrogen bubbling in a round-bottom flask provided with a reflux condenser. After 4 hr. the unreacted iron carbonyl waa distilled off and the reaction product contained conjugated dienes (a230m,, 38.3). Chromatography of a sample (0.510 g.) on a column of alumina (35 X 1.5 cm., 50 g. of Al&, Brockman activity I ) yielded, on elution with n-hexane, the noncomplexed fatty esters (0.350 9.) followed by the pure complex (0.053 g.) moving aa a sharp yellow band. Infrared analysis at 4.88 M gave e 2250 and a t 5.05 p gave c 3700. Anal. Found: C, 61.8; H, 8.0; Fe, 12.0. Analyses by n.m.r. were made in carbon tetrachloride solutions with a Varian A60 spectrometer. The following r-values (Fig. 3) were obtained: 5.01 (A, olefinic protons), 6.37 (B, methoxy protons), 7.71 (D, methylene a to C=O), 8.71 (E, insulated methylene), and 9.1 ( F , terminal methyl). The relative inten(35) C. B. Barrett, M. S. J. Dallas, and F. B. Padley, Chem. I n d . (London), 1050 (1962). (36) E. P. Jones and J. A. Stolp, J . A m . Oil Chemists' Soc., 36,71 (1958). (37) E. P. Jones and V. L. Davison. 55th Meeting, American Oil Chemists' Society, New Orleans, La., April 19-22, 1964, Paper 77.
NOVEMBER, 1964
SYNTHESIS AND OZONOLYSIS OF BENZO [c]PHENANTHRENE
sity of the signals shown in Fig. 3 was estimated by assuming that there were 34 protons in the methyl octadecadienoate ligand. Complex I (30 mg.) was decomposed by heating with alkali under conditions used for isomerization (6.6% KOH in ethylene glycol, 180', 45 mi^^.).^* A finely divided black precipitate was filtered and identified as iron. The resulting conjug'ated diene had a230mp 71.2 compared with 85.6 for methyl linoleate conjugated under the same conditions. Decomposition with FeCl3I* &'as carried out by dissolving 0.194 g. of complex I in 10 ml. of 95'30 ethanol solution saturated with FeC13 and by stirring occasionally for 30 min. Water was added, and the mixture was extracted with petroleum ether yielding 0.128 g. of conjugated diene (recovery 97%; at 231 mp gave e 25,400 and at 10.14 p gave e 218, due to trans,trans conjugation). Decomposition of 0.213 g. of complex I with triphenylphosphine" (0.265 9.) was carried out by heating a t 150' in an evacuated tube for 12 hr. A solid yellow precipitate formed and was extracted with petroleum ether. Infrared of the fatty extract (run as a smear) showed a decrease in carbonyl bands at 4.88 and 5.05 p and a strong band at 10.14 p due to trans,trans conjugation. Complex I was also decomposed by KMn04-KI04 oxidation. A mixture of mono- and dicarboxylic acids was obtained and analyzed to determine the position of double bonds in the dienoic ligand. Oxidation with KMn04KIOa was also carried out on the conjugated dienes obtained after decomposition of the complex with FeC13(Table 11). Complex I (0.20 g.) was stirred in a manometric system under 1 atm. of hydrogen with a reduced palladium catalyst (5% on (38) B. A. Brice, M. L. Swain, S. F. Herb, P. L. Nichols, Jr., and R. W. Riemenschneider, J . A m . Oil Chemiats' s o c . , 29, 279 (1952).
3297
alumina, 0.16 g.) in 4 ml. of acetic acid. N o hydrogen waa absorbed after 1 hr. at 30". Under the same conditions 1.9 mmoles of methyl linoleate absorbed 1.7 mmoles of hydrogen. Analysis of the hydrogenated product showed complete conversion to methyl stearate. When complex I(0.030 9.) was added to methyl linoleate (0.12 g.), hydrogenation proceeded slowly and after 5 hr. reached 60% of theory. Analysis of the product showed 97.3% monoene, 2.3% conjugated dienes, and 0.4% methyl stearate. Complex I (0.127 g., 0.29 mmoles) was heated with methyl linoleate (0.871 g., 2.96 mmoles) in a tube with nitrogen bubbling. The mixture was analyzed after 2 hr. at 150" (diene 77.2, conjugated dienes 13.3, and complex 9.5y0); after 3 hr. at 160' (diene 78.2, conjugated dienes 16.1, and complex 5.7'3,); and after 4 hr. at 180" (diene 82.1, conjugated diene 17.9, and complex 0 % ) . In another experiment, a solution of complex I(0.213 g.) in 40 ml. of cyclohexane was heated under 400-p.8.i. hydrogen pressure in a 150-ml. autoclave with agitation for 1 hr. a t 150' ( A n a l . Found: stearate, 7.0; monoene, 6.3; diene, 1.4; conjugated diene, 49.3; complex, 36.0), and for 2 hr. at 180' ( A n a l . Found: stearate, 53.6; monoene, 44.0; complex, 2.4).
Acknowledgment.-We are grateful to C. A. Glass for the n.m.r. analyses, Mrs. Clara E. McGrew and Mrs. Bonita Heaton for elemental analyses, Drs. J. C. Cowan, H. J. Dutton, and R. B. Bates (University of Arizona) for helpful discussions, and Dr. W. F. Kwolek (ARS Biometrical Services) for the statistical analysis.
Synthesis and Ozonolysis of Ben~o[c]phenanthrene'-~ EMILJ. MORICONI, LUDWIG SALCE, AND LUBOMYR B. TARANKO Contribution N o . 738 f r o m Fordham University, Department of Chemistry, N e w York, N e w York Received A p r i l 27, 1964 Gram quantities of benzo[c]phenanthrene (1) were prepared by a modification of the Szmuszkovicz and Modest procedure. Predictably, on the basis of our published oxidation-reduction potential hypothesis, ozonization of 1 in methylene chloride proceeded slowly to yield an initial peroxidic solid (2). Alkaline hydrogen peroxide oxidation of 2 led to the 5,6-bond-cleavage product, l-(o-carboxyphenyl)-2-naphthoic acid ,(3), in 30Q/, crude yield; 40% of unreacted 1 was recovered. Compound 3 was identified as its dimethyl ester (4).
A number of reliable, multistep syntheses of berizo [ c ] phenanthrene (1) are available in the l i t e r a t ~ r e . ~Com-
produce 2-5-g. quantities of 1 were successful only with an experimental modification of the Szmuszkovicz and Modest procedure. 4g,5
a
11
Ozonolysis Results
1
mon to all is the last-step production of milligram (or unspecified) 4b quantities of 1 by either dehydrogenation4b-f or decarb~xylative~~,g techniques. In our hands attempts to scale up each of these syntheses to (1) Paper XI11 in the series entitled "Ozonolysis of Polycyclic Aromatics." Paper X I I : E. J. Moriconi and F. A. Spano, J . A m . Chem. Soc., 88, 38 (1964). Presented in part at the Symposium on Ozone Chemistry, 135th National Meeting of the American Chemical Society, Atlantic City, N. J., Sept., 1959. (2) Thia research was supported by Public Health Service Research Grant No. CA-03325-06 from the National Cancer Institute. (3) Ozonization of five (triphenylene, chrysene, naphthacene, pyrene, and benz [alanthracene) of the six possible quadricyclic benz-fused aromatics has been reported to date. This paper completes the sextet. (4) (a) J. W. Cook, J . Chem. Soc.. 2524 (1931); (b) C. L. Hewett, abid., 596 (1936); (c) M. S. Nowman and L. M . Joshel, J . A m . Chem. Soc., SO, 485 (1938); (d) W. E. Bachman and R . 0. Edgerton, i b i d . , 62, 2970 (1940): (e) E . D. Bergmann and 2. Pelchowicz, J . Org. Chem., 19, 1383 (1954); ( f ) W. Davies and Q. N. Porter, J . Chem. Yoc., 4967 (1957); (9) J . Szmuszkovicz and E. J. Modest, J . A m . Chem. S o c . , 70, 2542 (1948); i b i d . , 72, 566 (1950).
Compound 1 showed expected resistance toward ozone oxidation. It was only after a large excess of ozone (10 mole equiv.) had been passed through a solution of 1 in methylene chloride that 0.6 mole equiv. of ozone reacted. The white, gelatinous, peroxidic product 2, on further oxidation with alkaline hydrogen peroxide, ultimately led to a 30% yield of crude 1-(o-carboxyphenyl)-2-naphthoic acid (3). Some 40% of unreacted 1 was recovered. Compound 3 adhered tenaciously to other organic acid impurities which caused erratic elemental analyses and neutralization equivalents, and which could not be removed by recrystallization and chroniatographic techniques. Ultimately 3 was converted to its known dimethyl ester (4) which was purified by liquid-solid chromatography. Compound 4 was independently prepared (a) via peracetic acid oxidation of benzo [c]phenanthrene-5,6-dione (5) to 3, followed by esterification to 4, and (b) directly, by a mixed Ullinann condensation of methyl 1-bromo-2-naphthoate ( 6 ) and methyl o-iodobenzoate ( 7 ) . 4 e (5) See Experimental
