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1.
S. Koritala R. O. Butterfield H. J. Dutton 《Journal of the American Oil Chemists' Society》1973,50(8):317-320
A mixture of methyl linoleate and alkali-conjugated methyl linoleate was reduced with nickel, palladium, platinum and copper-chromite
catalysts. The course of hydrogenation was followed by gas liquid chromatography of samples withdrawn at intervals. Relative
rate constants of reactants and inermediates were calculated by a computer. Conjugated linoleate was 10–18 times more reactive
than methyl linoleate with all catalysts except platinum, which showed no selectivity at 60 C. At 150 C conjugated diene reacted
four times faster than methyl linoleate with platinum catalyst. A conjugated diene-to-stearate shunt was observed with palladium
and platinum catalysts. When β-eleostearate was hydrogenated with the same catalysts, 50–97% of the triene was reduced directly
to monoene with all catalysts except copper chromite, which selectively reduced conjugated triene to conjugated diene. On
the basis of present kinetic data and previous knowledge about the mode of hydrogen addition to conjugated systems, a scheme
has been proposed to account for the products formed during hydrogenation of methyl linolenate.
ARS, USDA. 相似文献
2.
The isomerization reaction of methyl linoleate and methyl linolenate with potassiumt-butoxide has been investigated. The compositions of the reaction products formed at three temperatures have been determined
and the relationships between these analyses and observed differences in absorptivities by UV spectrometry are discussed.
Conclusions concerning the reaction mechanisms are based on compositional analysis and results of experiments using radioactive
or stable isotope labeled reagent. Double bonds in molecules which are not conjugated during the reaction retain the originalcis configuration. The double bond in the Δ12 position is the most susceptible to positional isomerization to form the conjugated
system. With the diene, this selectivity is small, while with the triene, the shifting of the Δ12 bond is the preponderant
initial reaction. Isotopic experiments yielded direct evidence for the postulated carbanion mechanism of reaction. An activated
methylene group is generally required for the formation of the carbanion. While the UV spectra of the reaction products formed
from methyl linolenate at 140 C showed no peak in the diene region, 34% conjugated diene-triene was present. The intact conjugated
systems can migrate when the reaction is sufficiently energentic to produce conjugated trienes with double bonds other than
the 10, 12, 14 system. The conjugation of triene is a stepwise reaction through the conjugated dienetriene.
This paper reports in part research submitted to satisfy thesis requirements for a Master’s Degree at Bradley University.
Bond Award paper. Award presented at the 43rd AOCS Fall Meeting, Minneapolis, October 1969.
No. Utiliz. Res. Dev. Div., ARS, USDA. 相似文献
3.
The structures of maleic anhydride adducts of essentially pure oleic, linoleic and linolenic methyl esters have been determined. The cleavage of the methyl oleate adduct yields a product with a succinyl structure, with or without shift of the double bond; four isomeric structures are possible. The first adduct of maleic anhydride with methyl linoleate is a succinyl derivative followed by a shift into the conjugated isomer with which the second maleic anhydride reacts via a 1–4 Diels Alder addition to yield a second adduct having a cyclohexene structure. The first two moles of maleic anhydride add to methyl linolenate to form di-succinyl derivatives followed by a shift into conjugated diene and triene. The third maleic anhydride adds via a 1–4 addition to yield a disuccinyl and one 1–4 adduct. A number of isomers are possible for the linoleate and linolenate adduct. 相似文献
4.
Sambasivarao Koritala 《Journal of the American Oil Chemists' Society》1970,47(12):463-466
Hydrogenation of linolenate with copper chromite produced a large amount of conjugated diene and minor amounts of nonconjugatable
dienes. The double bonds in conjugated dienes and monoenes were scrambled all along the chain. This product distribution can
be explained if it is assumed that conjugation of the double bonds is followed by hydrogenation. In competitive hydrogenation,
fatty esters with conjugated double bonds were reduced preferentially over fatty esters with methylene-interrupted double
bonds. Isomerization of conjugated double bonds (geometric and positional) occurred more rapidly than reduction. Reduction
of conjugated double bonds in the presence of deuterium resulted in a majority of the products containing no deuterium. Most
of the added deuterium was incorporated into the unreacted material. Mechanisms are proposed to account for the products formed
during the hydrogenation of linolenate, linoleate and their isomers.
One of 10 papers to be published from the Symposium “Hydrogenation,” presented at the AOCS Meeting, New Orleans, April 1970.
No. Utiliz. Res. Dev. Div., ARS, USDA. 相似文献
5.
E. N. Frankel E. P. Jones V. L. Davison E. Emken H. J. Dutton 《Journal of the American Oil Chemists' Society》1965,42(2):130-134
Homogeneous hydrogenation of unsaturated fats by cobalt carbonyl has been compared with the previously reported catalysis
by iron carbonyl. Soybean methyl esters, methyl linoleate and linolenate have been hydrogenated at 75–180C, 250–3,000 psi
H2 and 0.02 molar concn of catalyst. The cobalt carbonyl catalyst is more active at lower temp than iron carbonyl. The partially
reduced products are similar to those observed with iron carbonyl, but the reaction differs in showing much less accumulation
of conjugated dienes, no selectivity toward linolenate, almost complete absence of monoene hydrogenation to saturates, less
double bond migration and moretrans isomerization. No evidence was found for a stable complex between cobalt carbonyl and unsaturated fats as previously observed
with iron carbonyl. The rates of hydrogenation/double bond were the same for linoleate and linolenate on one hand, and for
alkali-conjugated linoleate and nonconjugated linoleate on the other.
Presented at AOCS Meeting in Minneapolis, 1963.
A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, USDA. 相似文献
6.
Summary The isomerization that takes place during the catalytic hydrogenation of linoleic acid and methyl linoleate producescis andtrans 9, 10, 11, and 12 monoenes. The double bond at the 12 position appears to hydrogenate slightly faster than that in the 9
position. More octadecenoic acids with double bonds at the 10 or 11 positions are produced during a selective (high temperature,
low pressure) hydrogenation than during a non-selective process.
Although the degree of selectivity of the hydrogenation is determined by the amount of isomerization of the original pentadiene
system to a conjugated diene, only part of the methylene-interrupted diene goes through this type of isomerization even during
a highly selective hydrogenation.
The half hydrogenation-dehydrogenation reaction mechanism is applied to explain the simultaneous positional and geometrical
isomerizations. 相似文献
7.
Polyunsaturated fatty acid methyl esters of soybean oil (MeSBO) were selectively conjugated as a means of increasing the linolenate
selectivity of various homogeneous and heterogeneous hydrogenation catalysts. Kinetics of the conjugation reaction in various
solvents indicated that linolenate conjugated 5–8 times faster than linoleate. Selective conjugation of MeSBO with potassiumt-butoxide in dipolar solvents resulted in an increase in linolenate hydrogenation selectivity to 7–8 with Ni and Pd heterogeneous
catalysts, and to 7–10 with homogeneous and heterogeneous chromium carbonyl catalysts.Trans-unsaturation in the hydrogenated products was only 1–3% with the chromium carbonyl catalysts, in contrast to 30–39% with
the heterogeneous metal catalysts. Triglycerides were readily converted to partial glycerides andt-butyl esters with the potassiumt-butoxide reagent.
Presented at the AOCS North Central Section Symposium, March 1980. 相似文献
8.
Carbonyl complexes of Cr, Mo and W have been studied as soluble catalysts for the hydrogenation of methyl sorbate and of methyl
esters from soybean oil. With methyl sorbate, relative catalytic activity decreased in the approximate order: mesitylene-Mo(CO)3, cycloheptatriene-Mo(CO)3, cycloheptatriene-Cr(CO)3, bicyclo (2,2,1) hepta-2,5-diene-Mo(CO)4, chlorobenzene-Cr(CO)3, methyl benzoate-Cr(CO)3, mesitylene-W(CO)3, benzene-Cr(CO)3, toluene-Cr(CO)3, mesitylene-Cr(CO)3, and hexamethylbenzene-Cr(CO)3. Order of catalytic activity was related to thermal stability of the complexes during hydrogenation. With mesitylene-M(CO)3 complexes, selectivity varied in the order Cr>Mo>W. Under certain conditions the mesitylene complexes of W, Cr and Mo reduced
methyl sorbate respectively to methyl 2-, 3-, and 4-hexenoates as main products.
The more active and thermally stable Cr(CO)3 complexes catalyzed effectively the hydrogenation of linoleate and linolenate in soybean oil esters with little or no stearate
formation. The hydrogenated products formed with the benzoate complex at 165–175 C contained 50–67% monoene, 18–30% diene,
2–7% conjugated diene, and only 3–7%trans unsaturation. Linolenate-linoleate selectivity values varied from 3 to 5 and linoleate-oleate selectivity from 7 to 80. Monoene
fractions had 40–50% of the double bond in the C-9 position; the rest of the unsaturation was distributed mainly between the
C-10 and C-12 positions. Conjugation is apparently an intermediate step in the hydrogenation of linoleate and linolenate.
The Cr(CO)3 complexes are unique in catalyzing the hydrogenation of polyunsaturated fatty esters to monounsaturated fatty esters of lowtrans content.
Presented at AOCS-AACC Joint Meeting, Washington, D.C. April, 1968.
No. Utiliz. Res. Dev. Div., ARS, USDA. 相似文献
9.
S. Koritala J. P. Friedrich T. L. Mounts 《Journal of the American Oil Chemists' Society》1980,57(1):1-5
Soybean oil was partially hydrogenated with copper-chromite catalyst at 170 C and up to 30,000 psig hydrogen pressure. Catalyst
activity increased with increase in pressure up to 15,000 psig. The linolenate selectivity (SLn) of the reaction remained essentially unchanged over 50–1000 psig pressure range. A SLn of 5.5 to 5.6 was achieved at 15,000 to 30,000 psig pressure range. This value is somewhat lower than the selectivity at
50–1000 psig, but much higher than that obtained with nickel catalysts. Geometric isomerization increased as pressure increased
up to 200 psig; above this pressure, the percenttrans remained the same up to 500 psig.trans Isomer content decreased when the pressure was increased to 30,000 psig. cis,trans Isomerization of linoleate was greater at 1000 psig and 15,000 psig than at 50 psig. At 15,000 psig, part of the linoleate
in soybean oil was hydrogenated directly without prior conjugation, whereas at low pressures, all of the double bonds first
conjugate prior to hydrogenation. This difference in mechanism might explain the lower selectivities obtained at high pressures.
Conjugated diene isomers were found in the products up to 200 psig. Above this pressure conjugated diene was not measurable.
No significant differences were found in the double bond distribution oftrans monoenes even though the amount oftrans monoene formed decreased as pressure was increased to 30,000 psig.
1 Presented at the AOCS meeting, San Francisco, May 1979. 相似文献
10.
E. N. Frankel J. P. Friedrich T. R. Bessler W. F. Kwolek N. L. Holy 《Journal of the American Oil Chemists' Society》1980,57(10):349-354
New polymer-bound hydrogenation catalysts were made by complexing PdCl2, RhCl3·3H2O, or NiCl2 with anthranilic acid anchored to chloromethylated polystyrene. The Pd(II) and Ni(II) polymers were reduced to the corresponding
Pd(O) and Ni(O) catalysts with NaBH4. In the hydrogenation of methyl sorbate, these polymer catalysts were highly selective for the formation of methyl 2-hexenoate.
The diene to monoene selectivity decreased in the order: Pd(II), Pd(O), Rh(I), Ni(II), Ni(O). Kinetic studies support 1,2-reduction
of the Δ4 double bond of sorbate as the main path of hydrogenation. In the hydrogenation of soybean esters, the Pd(II) polymer
catalysts proved superior because they were more active than the Ni(II) polymers and produced lesstrans unsaturation than the Rh(I) polymers. Hydrogenation with Pd(II) polymers at 50~100 C and 50 to 100 psi H2 decreased the linolenate content below 3% and increasedtrans unsaturation to 10~26%. The linolenate to linoleate selectivity ranged from 1.6 to 3.2. Reaction parameters were analyzed
statistically to optimize hydrogenation. Recycling through 2 or 3 hydrogenations of soybean esters was demonstrated with the
Pd(II) polymers. In comparison with commercial Pd-on-alumina, the Pd(II) polymers were less active and as selective in the
hydrogenation of soybean esters but more selective in the hydrogenation of methyl sorbate.
Presented at ISF-AOCS Meeting, New York, April 1980. 相似文献
11.
Asmbasivarao Koritala C. R. Scholfield E. Selke H. J. Dutton 《Journal of the American Oil Chemists' Society》1973,50(1):11-15
Conjugated isomers of methyl linoleate and linolenate were reduced with palladium, platinum, nickel and Lindlar catalysts
at atmospheric hydrogen or deuterium pressure. After the products were separated, positions of their double bonds were determined
by ozonolysis. Palladium and platinum catalysts reduced β-eleostearate directly to monoene. Nickel reduced β-eleostearate
to dienes chiefly by 1,2-addition and to a lesser extent by 1,4- and 1,6-addition, whereas Lindlar catalyst reduced by 1,2-and
1,6-addition only. All catalysts reduced conjugated linoleate isomers by both 1,2- and 1,4-addition, with nickel being somewhat
preferential for 1,2-addition. Selectivity for the catalytic reduction of dienes to monoenes decreased in the order: nickel,
palladium and platinum. Lindlar catalyst did not isomerize or reduce monoenes that formed during reduction. Palladium and
platinum did not isomerize conjugated dienes and trienes during their reduction, whereas nickel and Lindlar catalysts isomerized
them slightly. Some deuterium was found in unreacted conjugated diene and triene with nickel and Lindlar catalysts, but none
with palladium or platinum. Deuterated products contained a wide range of isotopic isomers with some products having up to
31 deuterium atoms. This wide deuterium distribution resulted from (a) exchange followed by addition, (b) addition followed
by exchange and (c) exchange-addition-exchange reactions.
Presented at the AOCS Meeting, Atlantic City, October 1971.
ARS, USDA. 相似文献
12.
Photosensitized oxidation of unsaturated fatty acid methyl ester was carried out using methylene blue as a sensitizer. Oxidation
products, monohydro-peroxides, were identified as trimethylsilyl derivatives. Methyl oleate gave the 9- and 10-isomers; methyl
linoleate, the 9-, 10-, 12-, and 13-isomers; and methyl linolenate, the 9-, 10-, 12-, 13-, 15-, and 16-isomers, respectively.
The double bond to which the hydroperoxide group attached was shifted to the adjacent position in each isomer. Thus, both
conjugated and nonconjugated isomers were present in methyl linoleate monohydroperoxides and methyl linolenate monohydroperoxides.
By the inhibition experiment, it was ascertained that the above reaction proceeded via singlet oxygen. The relative rates
of methyl oleate, methyl linoleate, and methyl linolenate were 1.0∶1.7∶2.3, respectively. These results obtained from the
methyl esters were applied to the photosensitized oxidation of triglycerides purified from vegetable oils, and the reaction
mechanism on triglycerides was proposed. 相似文献
13.
Selective Hydrogenation of Fats and Derivatives Using Ziegler-Type Organometallic Catalysts IV: Distribution of Isomers during Hydrogenation of Polyunsaturated Fatty Acid Methylesters Hydrogenation of methyl linoleate using a Ziegler-type catalyst, containing nickel stearate and triethyl aluminium, proceeds mainly without previous conjugation or trans-isomerization. Both olefinic double bonds are hydrogenated with equal probability. As long as the reaction mixture contains double unsaturated esters, these compounds are inhibiting hydrogenation and isomerization of single unsaturated esters. During hydrogenation of methyl linolenate there is only less selectivity to formation of methyl linoleate. Intermediate product is a mixture of single and double unsaturated fatty acid methylesters. In the latter compounds after consumption of triple unsaturated esters both double bonds are separated by two or more methylene groups. Polyenic compounds with 1,4-position of olefinic double bonds are preferably hydrogenated than polyenic compounds with greater distance between the double bonds. 相似文献
14.
C. R. Scholfield E. P. Jones Janina Nowakowska E. Selke B. Sreenivasan H. J. Dutton 《Journal of the American Oil Chemists' Society》1960,37(11):579-582
Methyl linolenate hydrogenated at 140°C, with 0.5% Ni catalyst and 1.1 mole of hydrogen at atmospheric pressure was separated
into octadecenoate, octadecadienoate, and octadecatrienoate fractions by countercurrent distribution. Gas chromatography on
a 200-ft. capillary Apiezon L column revealed one component in the triene fraction, four in the diene fraction, and nine in
the monoene fraction. These components were partially fractionated by low-temperature crystallization, and their solubilities
were correlated with alkali conjugation results, with infrared data forcis andtrans configuration of bonds and with dibasic acids isolated from the fractions after oxidative cleavage. Approximately 45% oftrans acids were present in both the monoene and diene fractions. Considerable migration of double bonds from the original 9, 12,
and 15 positions occurred.Cis,cis dienes which could not be conjugated by alkali were formed. Little alteration of the residual methyl linolenate was observed.
The results demonstrate the applicability and utility of new techniques of fractionation and analysis to the study of the
hydrogenation mechanism.
Presented at 51st annual meeting, American Oil Chemists' Society, Dallas, Tex., April 4–6, 1960.
This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department
of Agriculture. 相似文献
15.
E. N. Frankel Helen M. Peters E. P. Jones H. J. Dutton 《Journal of the American Oil Chemists' Society》1964,41(3):186-191
Iron pentacarbonyl is an effective homogeneous catalyst for the reduction of polyunsaturated fats. Hydrogenation of soybean oil and its methyl esters has been achieved at 180C, hydrogen pressures of 100-1,000 psi, and 0.05–0.5 molar concentrations of catalyst. Analyses of partially reduced products show considerable isomerization of double bonds, reduction of linolenate and linoleate with little or no increase in stearate, and accumulation ofcis,trans- andtrans, trans-conjugated dienes, and isolatedtrans monoenes. The unreduced trienes include diene conjugated fatty esters. The nonconjugated dienes contain large amounts oftrans and nonalkali conjugatable unsaturation. Considerable scattering of double bonds is evident in different fractions between the C4 and C16 positions. Complex formation between iron carbonyl and unsaturated fats is also indicated. The course of the homogeneous hydrogenation catalyzed by iron pentacarbonyl appears similar to the heterogeneous catalytic reaction. Metal carbonyls are well known for their isomerizing effects and their ability to form stable complexes with olefins. These homogeneous complexes provide suitable model systems to study the mechanism of catalytic hydrogenation of fats. 相似文献
16.
Sambasivarao Koritala 《Journal of the American Oil Chemists' Society》1970,47(8):269-272
β-Eleostearate was found to be reduced by 1,6 addition of hydrogen. Because of the extensive isomerization of conjugated trienes
during hydrogenation, the occurrence of 1,2 and 1,4 addition reactions could not be proven. Conjugated dienes were reduced
by both 1,2 and 1,4 addition of hydrogen. The double bond distribution in the products formed from linoleate, linolenate and
their isomers was consistent with the assumption that the double bonds in polyunsaturated fatty esters conjugate and then
add hydrogen. Extensive isomerization (positional and geometric) of the conjugated double bond systems occurred during hydrogenation.
Monoenes were not isomerized under similar conditions of hydrogenation. Since double bond distribution in monoenes formed
from linoleate and alkali-isomerized linoleate was identical, indications are that conjugation precedes hydrogenation.
Presented in part at the symposium “Hydrogenation Process,” Division of Industrial Engineering Chemistry, 157th American Chemical
Society Meeting, Minneapolis, April 1968.
No. Utiliz. Res. Dev. Div., ARS, USDA. 相似文献
17.
E. N. Frankel D. G. McConnell C. D. Evans 《Journal of the American Oil Chemists' Society》1962,39(6):297-301
A liquid-partition chromatographic procedure was used to separate hydroxy fatty acids, their methyl esters, and reduced fatty
ester hydroperoxides. Mixtures of methyl stearate, mono- and dihydroxystearate, and mixtures of the corresponding free fatty
acids were easily separated. Chromatographic determinations for ricinoleate in castor oils compared favorably with the chemical
and infrared analyses.
The chromatographic procedure was used to separate hydroxy fatty acids inDimorphotheca andStrophanthus seed oils. The methyl ester of dimorphecolic acid, the principal hydroxy fatty ester ofDimorphotheca oil, behaved like reduced methyl linoleate hydroperoxide and showed a polarity intermediate between methyl 12-hydroxystearate
and methyl 9,10-dihydroxystearate. The 9-hydroxy-12-octadecenoic ester ofStrophanthus oil had a larger retention volume than methyl ous hydroxy fatty esters isolated chromatographically. The diene content of
the reduced hydroperoxides agrees well with values reported in the literature (1,5,16). The diene content of the chromatographed
methyl dimorphecolate is higher than reported by Smithet al. (20) for their preparations but agrees well with the value reported by Chipault and Hawkins (6) for puretrans-trans conjugated methyl linoleate. The extinction coefficient of methyl 12-hydroxystearate at 2.8 μ is higher than that reported
for ricinoleate and the absorption band is much sharper. Because of these two conditions no association of the hydroxyl groups
is indicated. These results also confirm the purity of the hydroxy fatty esters obtained by LPC. This method has been a valuable
adjunct to the study of various oxygen-containing fatty acid and esters and was used to characterize the hydroxy esters obtained
from the hydrogenation of methyl linolenate hydroperoxides (9). This work offers a basis for the development of analytical
methods to determine the hydroxy and other polar acid content of fatty glycerides and their derivatives. 相似文献
18.
A previous study of autoxidation products by high pressure liquid chromatography (HPLC) of methyl oleate and linoleate was
extended to methyl linolenate. Autoxidized methyl linolenate was fractionated by HPLC either after reduction to allylic alcohols
on a reverse phase system, or directly on a micro silica column. Isolated oxidation products were characterized by thin layer
and gas liquid chromatography and by ultraviolet, infrared, nuclear magnetic resonance and mass spectrometry. Secondary products
from the autoxidation mixtures (containing 3.5–8.5% monohydroperoxides) included epoxy unsaturated compounds (0.2–0.3%), hydroxy
or hydroperoxy-cyclic peroxides (3.8–7.7%), epoxy-hydroxy dienes (<0.1%), dihydroxy or dihydroperoxides with conjugated diene-triene
and conjugated triene systems (0.9–2.9%). Cyclization of the 12- and 13-hydroperoxides of linolenate would account for their
lower relative concentration than the 9- and 16-hydroperoxides. Dihydroperoxides may be derived from the 9- and 16-linolenate
hydroperoxides. Cyclic peroxides and dihydroperoxides are suggested as important flavor precursors in oxidized fats. 相似文献
19.
Summary 1. Kinetic studies showed that concurrent oxidation of preformed hydroperoxides may be expected to take place at all stages
of the autoxidation of methyl linoleate. The rate of oxidation relative to the rate of autoxidation of unoxidized ester is
determined chiefly by the extent of the accumulation of hydroperoxides.
2. Infrared spectral analysis of hydroperoxides oxidized to various degrees indicated thattrans, trans diene conjugation and isolatedtrans double bonds produced in the autoxidation of methyl linoleate are related to the concurrent oxidation of the accumulated
hydroperoxides.
3. The low absorptivity observed for diene conjugation, compared to that which may be expected for the exclusive production
ofcis, trans diene conjugated hydroperoxide isomers during the autoxidation of methyl linoleate is attributed to the concurrent oxidation
of accumulated hydroperoxides.
4. The effect of antioxidants in giving a well-defined induction period in the oxidation of hydroperoxides isolated from autoxidized
methyl linoleate indicated that the oxidation proceeds by a chain reaction.
5. The primary reaction products of the oxidation of hydroperoxides isolated from autoxidized methyl linoleate were found
to be polymers formed in a sequence of reaction involving the diene conjugation.
6. Studies on the autoxidation of methylcis-9,trans-11-linoleate showed thatcis, trans isomerization of the conjugated diene took place with the concurrent production of isolatedtrans double bonds and loss of diene conjugation.
Hormel Institute publication no. 138. Presented before the American Oil Chemists’ Society, Philadelphia, Pa., Oct. 10–12,
1955.
This work was supported by a grant from the Hormel Foundation. 相似文献
20.
Mechanistic and kinetic studies of Pd-catalyzed hydrogenation at atmospheric pressure and 30–100 C were carried out with methyl
sorbate, methyl linoleate and conjugated linoleate. Homogeneous Pd catalysts and particularly Pd-acetylacetonate [Pd(acac)2] were significantly more selective than Pd/C in the hydrogenation of sorbate to hexanoates, mainlytrans-2-hexenoate. Relative rate constants for the different parallel and consecutive reactions, determined by computer simulation,
indicated that the low diene selectivity of Pd/C can be dattributed to a significant direct reduction of sorbate to hexanoate.
The similar behavior of PdCl2 to that of Pd/C suggests that Pd(II) was initially reduced to Pd(O). Valence stabilization of PbCl2 by adding DMF or a mixture of Ph3P and SnCl2 increased the diene selectivity but decreased the activity. Stabilization of Pd(acac)2 with triethylaluminum (Ziegler catalyst) resulted in increased activity but decreased selectivity. The kinetics of methyl
linoleate hydrogenation showed that although Pd(acac)2 was only half as active as Pd/C, their respective diene selectivity was similar (10.4 and 9.6). The much greater reactivity
of conjugated compared with unconjugated linoleate toward Pd(acac)2 suggests the possible formation of conjugated dienes as intermediates that are rapidly reduced and not detected in the lipid
phase during hydrogenation. 相似文献