Homogeneous hydrogenation of dienes with rhodium complexes

Different Rh complex catalysts were compared for the hydrogenation of methyl sorbate and linoleate in the absence of solvents. At 100 C and 1 atm H₂ the following complexes, RhCl(Ph₃ P)₃ (Ph= phenyl), [RhClNBD]₂ (NBD=norbornadiene) and RhH(CO)(Ph₃P)₃, produced mainly methyltrans-2-hexenoate (34 to 56%). Their diene selectivity was not particularly high as they produced 14 to 41% methyl hexanoate. With RhCl(Ph₃ P)₃ constant ratios between rates of methyl sorbate disappearance and formation of methyltrans-2- andtrans-3-hexenoate indicate approximately the same activation energy for 1,2-addition of H₂ on the Δ4 double bond of methyl sorbate and for 1,4-addition to this substrate. In the hydrogenation of methyl linoleate with RhCl(Ph₃ P)₃, the kinetic curves were simulated by a scheme in which 1,2-reduction was more than twice as important as 1,4-addition of H₂ via conjugated diene intermediates. Although the complexes RhCl(CO)(Ph₃ P)₃ and [Rh(NBD)(diphos)]⁺PF₆ (diphos=diphosphine) were inactive in the hydrogenation of methyl sorbate, they catalyzed the hydrogenation of methyl linoleate at 100 C and 1 atm. Catalyst inhibition apparently was caused by stronger complex formation with methyl sorbate than with the conjugated dienes formed from methyl linoleate.     

Biodiesel production by the transesterification of cottonseed oil by solid acid catalysts

Methyl esters (biodiesel) were produced by the transesterification of cottonseed oil with methanol in the presence of solid acids as heterogeneous catalysts. The solid acids were prepared by mounting H₂SO₄ on TiO₂ · nH₂O and Zr(OH)₄, respectively, followed by calcining at 823K. TiO₂-SO₄ ²⁻ and ZrO₂-SO₄ ²⁻ showed high activity for the transesterification. The yield of methyl esters was over 90% under the conditions of 230°C, methanol/oil mole ratio of 12:1, reaction time 8 h and catalyst amount (catalyst/oil) of 2% (w). The solid acid catalysts showed more better adaptability than solid base catalysts when the oil has high acidity. IR spectral analysis of absorbed pyridine on the samples showed that there were Lewis and Br?nsted acid sites on the catalysts. Translated from The Chinese Journal of Process Engineering, 2006, 6(4): 571–575 [译自: 过程工程学报]     

Homogenous catalytic conjugation of polyunsaturated fats by chromium carbonyls

Various arene-Cr (CO)₃ complexes and Cr(CO)₆ are effective soluble catalysts for the conjugation of polyunsaturated fats. Methyl benzoate-Cr(CO)₃ is one of the most active catalysts. The following conjugation levels were obtained: methyl linoleate, 65%; methyl linolenate, 45%; the polyunsaturates in soybean and safflower oils, 73%; and in linseed oil 48%. Conjugated dienes from linoleate were predominantlycis,trans in configuration. Their double bonds were distributed between C₅ and C₁₆ of the fatty acid chain. Hydrogenation and dehydrogenation are side reactions, which seem to limit the yield of conjugated dienes from methyl linoleate. A conjugation mechanism is proposed that involves allyl-HCr(CO)₃ complexes as intermediates undergoing 1,3- and 1,5-hydrogen shifts. Presented at the AOCS Meeting, San Francisco, April 1969. No, Utiliz. Res. Dev. Div., ARS, USDA.     

Peroxide value determination—Comparison of some methods

A comparison between the determination of the peroxide value by the methods of Wheeler and Sully (iodometric titration) and that of Stine, et al. (ferric thiocyanate method) was made. Some oxidized vegetable oils, H₂O₂, t-butyl hydroperoxide, cumene hydroperoxide, methyl oleate hydroperoxides, and methyl linoleate hydroperoxides were used as substrates. One-hundred percent of the methyl linoleate hydroperoxides were recovered by the Wheeler reduction, 85% by the Sully method. The Wheeler method was used to reduce the methyl linoleate hydroperoxides to the corresponding hydroxy acids. In the Sully procedure, the hydroxy acids are only intermediates which are dehydrated to octadecatrienoic acids. One equivalent methyl linoleate hydroperoxide oxidized two equivalents of I⁻ (Wheeler) and four equivalents of Fe²⁺ (Stine, et al.). By way of contrast, H₂O₂ needs only two equivalents I⁻ or Fe²⁺ for reduction. The excess consumption of reduction equivalents in the ferric thiocyanate method probably is caused by secondary reactions of the methyl linoleate hydroperoxide acyl residue.     

Homogeneous catalytic hydrogenation of unsaturated fats: Group VIB metal carbonyl complexes

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.     

Catalytic epoxidation of methyl linoleate

The epoxidation of methyl linoleate was examined using transition metal complexes as catalysts. With a catalytic amount of methyltrioxorhenium (4 mol%) and pyridine, methyl linoleate was completely epoxidized by aqueous H₂O₂ within 4 h. Longer reaction times (6 h) were needed with 1 mol% catalyst loading. Manganese tetraphenylporphyrin chloride was found to catalyze the partial epoxidation of methyl linoleate. A monoepoxidized species was obtained as the major product (63%) after 20 h.     

Stereoselective hydrogenation of model compounds and preparation of tailor-made glycerides with chromium tricarbonyl complexes

Studies on the mechanism of stereoselectivity of chromium tricarbonyl catalysts with model compounds provided the basis for the preparation of simulated fats. These synthetic fats were prepared by taking advantage of the unique property of chromium carbonyl complexes to catalyze hydrogenation of polyunsaturates tocis-monounsaturates. Oils simulating the composition of peanut oil were produced by hydrogenating soybean oil stereoselectively to an IV of 94. Simulated olive oil was made the same way from either soybean or safflower oil hydrogenated to an IV of 82–84. Stereoselective 1,4-reduction of eleostearate in tung oil produced oils that had a high proportion of linoleate and that simulated safflower oil. The oleo-disaturated glyceride structure of cocoa butter was also simulated by selectively hydrogenating linoleate in cottonseed oil stearines and in fractionated high-palmitate stearines. Dilatometric and chromatographic studies showed that thecis-monoene-disaturated glyceride is the major component (60–70%) in the synthetic cocoa butter. 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.     

Hydrogenation of soybean oil with cationic Rh(I)-Phosphine complexes as catalysts — Para-toluene sulfonate and sulfonated styrene resins as counterions

A cationic rhodium(I) complex, viz. Rh NBD diphos⁺ 4-CH₃-C₆H₅SO ₃ ⁻ [NBD = norbornadiene, diphos = (C₆H₅)₂ P-CH₂-CH₂-P(C₆H₅)₂], has been used as a homogeneous catalyst for the hydrogenation of soybean oil in acetone solution. This complex acts almost in the same way as the corresponding ones with ClO ₄ ⁻ or PF ₆ ⁻ as conuterions, i.e., it gives high polyene selectivity and low formation oftrans isomers. Because of the somewhat stronger basic character of the p-toluene-sulfonate ion compared with the perchlorate and hexafluorphosphate ions, the relative proportion of reaction via the so-called monohydride path is larger in the present case. When the ionic complex, Rh NBD diphos⁺, is bound to a solid support, e.g., to the anionic sites of sulfonated polystyrene resins, a nearly total lack of catalytic activity is observed. Possible reasons for these effects are discussed-in terms of π-arene-metal binding and covalent coordination of the sulfonate group.     

Comparison of homogeneous and heterogeneous palladium hydrogenation catalysts

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.     

Kinetic study of the prooxidant effect of tocopherol. Hydrogen abstraction from lipid hydroperoxides by tocopheroxyls in solution

A kinetic study of the prooxidant effect of vitamin E (tocopherol, TocH) has been carried out. The rates of hydrogen abstraction (k₋₁) from methyl linoleate hydroperoxide (ML-OOH) by α-tocopheroxyl (α-Toc^.) (1) and eight types of alkyl substituted Toc^. radicals, (2–9) in benzene solution have been determined spectrophotometrically. The results show that the rate constants decrease as the total electron-donating capacity of the alkyl substituents on the aromatic ring of Toc^. increases. The k₋₁ value (5.0×10⁻¹M⁻¹s⁻¹) obtained for α-Toc^. (1) was found to be about seven orders of magnitude lower than the k₁ value (3.2×10⁶M⁻¹s⁻¹) for the reaction of α-TocH with peroxyl radical, which is well known as the usual radical-scavenging reaction of α-TocH. The above reaction rates (k₋₁) obtained were compared with those (k₃) of methyl linoleate with Toc^. (1–9) in benzene solution. The rates (k₋₁) were found to be about six times larger than those (k₃) of the corresponding Toc^.. The results suggest that both reactions may relate, to the prooxidant effect of α-TocH at high concentrations in foods and oils. The effect of the phytyl side chain on the reaction rate, of Toc^. in micellar dispersions has also been studied. We have measured the rate constant, k₋₁, for the reaction of phosphatidylcholine hydroperoxide with a Toc^. radical in benzene,tert-butanol and in Triton X-100 micellar dispersions, and compared the observed k₋₁ values with the corresponding values for ML-OOH.     

Catalytic hydrogenation of soybean oil with Rh(l) dihydride complexes as catalysts

Cationic rhodium(I) complexes of the type [NBD Rh L₂]⁺[C1O₄]⁻ (NBD = norbornadiene and L = diphenylphosphinoethane or triphenylphosphine) have been studied as catalysts for the hydrogenation of soybean oil. These catalysts give a good yield of products with cis-configuration. Indeed, hydrogenation could be performed under mild conditions (30 C, 1 atm hydrogen pressure) to an iodine value of 80 with not more than 12% oftrans monoenes and only 5% conjugated isomers formed. The results obtained are interpreted on the basis of the equilibrium H₂RhL _n ⁺ ⇌HRhL_n+H⁺. By the addition of acid (HClO₄ ) the bishydrido form of the catalyst could be studied. With this system only small amounts of trans monoenes were formed and no othertrans isomers could be detected. By the addition of a base such as triethylamine, the monohydridic form of the catalyst could be studied. In contrast to the bishydrido complex, this system gave large amounts oftrans monoenes, together withcis-trans andtrans-trans forms of the 18:2 acid. With both forms of the catalyst system, conjugated isomers were formed.     

Photo-initiated peroxidation of lipids in micelles by azaaromatics

The monoazaaromatics, pyridine (1), hexyl nicotinate (2), and quinoline (3) and diazaaromatics pyrimidine (4) and purine (5), readily act as photo-initiators for the peroxidation of methyl linoleate in 0.50 M SDS at 37°C giving free radical chain oxidations of linoleate. Quantitative kinetic runs on the order in substrate, RH, and in the rate of chain initiation, R_i, showed that the classical rate law for autoxidation,-d[O₂]/dt=(k _p/(2 k _t ^1/2))[RH]xR _i ^1/2, is applicable to these photo-initiated oxidations. The oxidizability of methyl linoleate under these conditions is 2.92×10⁻² M^−1/2 s^−1/2. These peroxidations were inhibited by chromanol phenolic antioxidants of the vitamin E class, such as lipid-soluble 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC) and water-soluble 2-carboxy-2,5,7,8-tetramethyl-6-hydroxychroman (Trolox) and derived rate constants for inhibition of peroxidation were k _inh (PMHC)=4.35×10⁴ M⁻¹ s⁻¹ and k _inh (Trolox)=2.81×10⁴ M⁻¹ s⁻¹ during inhibited oxidation of methyl linoleate photo-initiated by 4. The products from photo-initiated peroxidation of methyl linoleate by 1 through 5 were determined by reduction and high-performance liquid chromatography analyses to be the 9-and 13-positional hydroperoxides of the four geometrical isomers: cis-9, trans-11 (6), trans-10, cis-12 (7), trans-9, trans-11 (8), and trans-10, trans-12 (9)-octadecadienoates typical of the free radical chain mechanism of lipid peroxidation. Products from dye-sensitized oxidation by Methylene Blue or Rose Bengal of methyl linoleate gave a product distribution of six hydroperoxides typical of oxidation by singlet oxygen. Thermal or photo-initiated peroxidation of methyl linoleate in SDS gave some selectivity of oxidation at the 13-position of the linoleate chain. The ratio of 13-to 9-oxidation varied in the range 1.23 to 1.14 as the cis/trans to trans/trans ratio of geometric isomers varied from 0.44 to 1.25 during photooxidation of increased amounts of linoleate in SDS. This selectivity is attributed to loss of the pseudo symmetry around the pentadienyl system in the lipid chain in the SDS system during the peroxidation.     

Selective conjugation of soybean esters to increase hydrogenation selectivity

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.     

Synthesis of Biodiesel from Canola Oil Using Heterogeneous Base Catalyst

A series of alkali metal (Li, Na, K) promoted alkali earth oxides (CaO, BaO, MgO), as well as K₂CO₃ supported on alumina (Al₂O₃), were prepared and used as catalysts for transesterification of canola oil with methanol. Four catalysts such as K₂CO₃/Al₂O₃ and alkali metal (Li, Na, K) promoted BaO were effective for transesterification with >85 wt% of methyl esters. ICP-MS analysis revealed that leaching of barium in ester phase was too high (~1,000 ppm) when BaO based catalysts were used. As barium is highly toxic, these catalysts were not used further for transesterification of canola oil. Optimization of reaction conditions such as molar ratio of alcohol to oil (6:1–12:1), reaction temperature (40–60 °C) and catalyst loading (1–3 wt%) was performed for most efficient and environmentally friendly K₂CO₃/Al₂O₃ catalyst to maximize ester yield using response surface methodology (RSM). The RSM suggested that a molar ratio of alcohol to oil 11.48:1, a reaction temperature of 60 °C, and catalyst loading 3.16 wt% were optimum for the production of ester from canola oil. The predicted value of ester yield was 96.3 wt% in 2 h, which was in agreement with the experimental results within 1.28%.     

Hydrogenation of canola oil in the presence of nickel and the methyl benzoate-chrome carbonyl complex

Canola oil was hydrogenated using a mixture of homogeneous methyl benzoate-Cr(CO)₃ and heterogeneous nickel catalysts. The effect of the methyl benzoate-Cr(CO)₃_to-nickel ratio on the activity, specific isomerization index, linoleate and linolenate selectivities, and fatty acid composition was evaluated, and the results compared with those obtained with commercial nickel catalyst and methyl benzoate-Cr(CO)₃ used individually. At higher chromium-to-nickel ratios the activity of nickel was inhibited and the system behaved essentially like the pure chrome complex, while at low chromium-to-nickel ratios the characteristics of the nickel predominated. In a short transition zone relatively high reaction rates were obtained with significantly reducedtrans-isomer levels in the product. In a broader sense, it may be possible to combine a homogeneous and heterogeneous catalyst while retaining the advantages of both. We may thus be able to design catalyst systems for specific applications.     

Establishment of a model substrate oil for antioxidant activity assessment by oil stability index method

A model substrate oil using methyl linoleate was established for the determination of the antioxidant activity by Oil Stability Index (OSI) method. OSI values for methyl linoleate with different concentrations (5–100%) in silicone oil were measured at different temperatures (70–120°C). As the temperature increased, the OSI value decreased in each concentration of methyl linoleate. Optimal temperature and concentration of antioxidants, α-tocopherol, and butylated hydroxytoluene on OSI values for 10% methyl linoleate model oil was measured at 90, 100, 110, and 120°C. The logarithmic relationship between temperature and OSI using model substrate oil was similar to that of soybean oil. Furthermore, application of some spice extracts to this model oil system was carried out to give results thhat compared well with those available in the literature. Thus, the procedure using methyl linoleate-silicone oil as a model substrate oil is available for evaluating the antioxidant activity by the OSI method.     

Stimulation of hepatic lipogenesis by eicosa-5,8,11,14-tetraynoic acid in mice fed a high linoleate diet

Liver slices, from mice fasted for one day and then refed for three days either a 15% corn oil diet or a 15% corn oil diet containing eicosa-5,8,11,14-tetraynoic acid (TYA), were incubated with [1-¹⁴C] acetate or [³H]H₂O to determine lipogenic capacity. Dietary TYA produced a twofold stimulation in fatty acid and cholesterol synthesis. TYA also caused an increase in the relative proportion of linoleate (C_18∶2) and a decrease in that of arachidonate (C_20∶4) in liver. Thus, (a) despite high levels of C_18∶2, hepatic lipogenesis can be increased, and (b) even short term feeding of TYA can alter the hepatic fatty acid composition presumably by inhibition of arachidonate synthesis from linoleate.     

Hydrogenation of cyclopropenoid fatty acids occurring in cottonseed oil

The hydrogenation of cyclopropenoid acids and their relative reactivities during hydrogenation as compared to linoleic and oleic acids were examined. Pure methyl sterculate and purifiedSterculia foetida oil and its methyl esters, which have a cyclopropene content more than 60 times that of cottonseed oil, were used for the hydrogenation experiments. Nickel, palladium and platinum catalysts were used. The effect of temperature and type of catalyst were demonstrated in a series of hydrogenation experiments of safflower andS. foetida oil mixtures, and methyl oleate and methyl dihydrosterculate mixtures. Partial hydrogenation of methyl sterculate formed as many as twenty compounds in addition to the cyclopropenoid derivatives. Most of these compounds were monounsaturated. The cyclopropene group hydrogenated very readily compared to the 9,12-diene system in linoleate. The cyclopropane group obtained by hydrogenating the cyclopropenoid acids group was quite resistant to further attack by hydrogen and nickel catalyst had little effect. With palladium catalyst, a temperature of 180 C was necessary for the reaction to go to completion. Platinum in acetic acid was a good system for hydrogenolysis of the cyclopropane group at 80 C. Retired.     

Deactivation of MoS2 catalysts during the HDS of thiophene

Catalytic properties of unsupported MoS₂ catalysts in the thiophene hydrodesulfurization reaction were determined in the temperature range 623–653 K. The catalysts were prepared by ex situ decomposition of ammonium thiomolybdate (ATM) crystals in a mixture of 15% H₂S in H₂ at 673 K. Activity of catalysts decreased very rapidly before reaching a steady state after 15 h on‐stream. The thiophene conversion went down from 10–12 to 3–4% in that time. The surface area of the catalysts also decreased during the catalytic reaction from 40–50 to 8–10 m²/g. Selectivity for hydrodesulfurization, hydrogenation and isomerization reactions was affected distinctly by the deactivation process. By increasing the reaction time, double‐bond isomerization increased, hydrogenation of butenes decreased and hydrodesulfurization remained constant. Results indicate that the main cause of activity decay was surface area loss that was due to sintering of MoS₂ crystallites. Selectivity variation indicates that different active sites are involved for the three reactions. A deactivation model involving diminution of active sites located in edge and rim sites of small MoS₂ particles is proposed to explain the variation of product distribution. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of the catalytic esterification of castor oil with lauric acid using <Emphasis Type="Italic">n</Emphasis>-butyl benzene as a water entrainer

The esterification of castor oil with lauric acid was investigated using tetra n-butyl titanate (TBT), SnCl₂·2H₂O (stannous chloride), CoCl₂·6H₂O (cobalt chloride), and (CH₃COO)₂Zn·2H₂O (zinc acetate dihydrate) as catalysts. Effects of catalyst concentration and reaction temperature on the progress of the reaction were investigated. TBT was the best catalyst for the esterification of castor oil with lauric acid at temperatures lower than 200°C. The reaction was first order with respect to each reactant. The activation energy for the esterification reaction of castor oil with lauric acid using TBT was 26.69 kcal/mol. The rate constants obtained for the esterification of castor oil with decanoic, lauric, palmitic, and stearic acids were nearly the same (15.80, 15.44, 15.06, and 14.67 mL mol⁻¹ min⁻¹), as were the rate constants obtained for the reaction of castor oil and hydrogenated castor oil.