Acetaldehyde methyl acetate reductive

B. Acetaldehyde From Methyl Acetate Reductive Carbonylation. A... 

The Pd-catalyzed reductive carbonylation of methyl acetate with CO and H2 affords acetaldehyde. The net reaction is the formation of acetaldehyde from MeOH, CO, and H2P4]. Methyl formate (109) is converted into AcOH under CO pressure in the presence of Lil and Pd(OAc)2[95],... 

X-ray structure analyses of Rh(COCH3)(I)2(dppp) (14) and [Rh(I I)(I)(//-I)(dppp)]2 (15), where dppp l,3-bis(diphenylphosphino) propane, were reported. Unsaturated complex (14) possesses a distorted five-coordinate geometry that is intermediate between sbp and tbp structures.69 Under CO pressure, the rhodium/ionic-iodide system catalyzes either the reductive carbonylation of methyl formate into acetaldehyde or its homologation into methyl acetate. By using labeled methyl formate (H13C02CH3) it was shown that the carbonyl group of acetaldehyde or methyl acetate does not result from that of methyl formate.70... 

By adjusting the C0 H2 ratio, catalytic systems for the reductive carbonylation of methyl acetate can be tuned to the production of acetic anhydride, ethylidene diacetate or acetaldehyde. 

Methyl acetate probably originates from the reaction of methanol with the intermediate cobalt-acyl complex. The reaction leading to the formation of acetaldehyde is not well understood. In Equation 8, is shown as the reducing agent however, metal carbonyl hydrides are known to react with metal acyl complexes (20-22). For example, Marko et al. has recently reported on the reaction of ri-butyryl- and isobutyrylcobalt tetracarbonyl complexes with HCo(CO) and ( ). They found that at 25 °C rate constants for the reactions with HCo(CO) are about 30 times larger than those with however, they observed that under hydroformylation conditions, reaction with H is the predominant pathway because of the greater concentration of H and the stronger temperature dependence of its rate constant. The same considerations apply in the case of reductive carbonylation. Additionally, we have found that CH C(0)Co(C0) L (L r PBu, ... 

The single step conversion of methyl acetate to ethylidene diacetate is catalyzed by either a palladium or rhodium compound, a source of iodide, and a promoter. The mechanism is described as involving the concurrent generation of acetaldehyde and acetic anhydride which subsequently react to form ethylidene diacetate. An alternative to this scheme involves independent generation of acetaldehyde by reductive carbonylation of methanol or methyl acetate, or by acetic anhydride reduction. The acetaldehyde is then reacted with anhydride in a separate step. 

Alternatively, the transformation of methyl acetate to ethylidene diacetate may also be achieved in a multistep process. Either conversion of methyl acetate to acetic anhydride, followed by reduction to ethylidene diacetate plus acetic acid, or production of acetaldehyde directly and subsequent reaction with acetic anhydride to form ethylidene diacetate are successful. This will be examined in greater detail. 

Concurrent with acetic anhydride formation is the reduction of the metal-acyl species selectively to acetaldehyde. Unlike many other soluble metal catalysts (e.g. Co, Ru), no further reduction of the aldehyde to ethanol occurs. The mechanism of acetaldehyde formation in this process is likely identical to the conversion of alkyl halides to aldehydes with one additional carbon catalyzed by palladium (equation 14) (18). This reaction occurs with CO/H2 utilizing Pd(PPh )2Cl2 as a catalyst precursor. The suggested catalytic species is (PPh3)2 Pd(CO) (18). This reaction is likely occurring in the reductive carbonylation of methyl acetate, with methyl iodide (i.e. RX) being continuously generated. 

An alternative scheme to simultaneous formation of acetaldehyde and acetic anhydride could entail the carbonylation of methyl acetate to acetic anhydride which is subsequently reduced to acetaldehyde and acetic acid. The reaction of acetaldehyde with excess anhydride would form EDA. In fact, Fenton has described production of EDA by the reduction of acetic anhydride using both rhodium and palladium salts as catalysts when modified with triphenylphosphine (26). Two possible mechanisms for the reduction are postulated in equation 16. 

When the anhydride was placed under the reductive carbonylation conditions, EDA was produced along with methyl acetate and acetic acid. However, the rate of EDA formation was substantially lower than usual methyl acetate conversions. Also, a mechanism incorporating Fenton s reduction cannot account for excess acetaldehyde along with EDA formation. This cannot be the major path to EDA. 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

Hydroxybenzo[6]thiophene has been isolated from coal tar.42 It may be prepared from 6-aminobenzo[fr]thiophene by standard procedures.241 6-Methoxybenzo[h]thiophene may be prepared by decarboxylation of the corresponding 2-carboxylic acid,341 and 6-ethoxybenzo[6]thiophene is obtained by reduction of 6-(ethoxy)-thioindoxyl (Section VI, 1,2). 6-Methoxy-5-methylbenzo[6]thiophene is obtained by cyclization of (3-methoxy-4-methylphenylthio)-acetaldehyde dimethyl acetal (Section IV,B).617 The product previously described542 as 6-hydroxy-3-phenylbenzo[6]thiophene has now been shown to be the 2-phenyl isomer.307 6-Methoxy-818 and 6-methoxy-5-methyl-benzo[6]thiophene617 are demethylated by pyridine hydrochloride. 

With methyl acetate at 200 C and 34.5 MPa and a Co-LiI-NPh3 catalyst the acetaldehyde yield is nearly quantitative. In the reductive carbonyiation of CH3OH, the product mixture contains a wide variety of compounds including methyl acetate, acetic acid, 1,1-dime-thoxyethane and copious amounts of H2O. Separating acetaldehyde from this mixture is difficult. In contrast, with a methyl ester feedstock, the product mixture is anhydrous and acetaldehyde is readily distilled from RC(0)OH. RC(0)OH is esterified in a separate step and recycled. The simplified reaction mechanism for methyl acetate is ... 

Ethyl acetate is obtained from methyl acetate if the reductive carbonyiation is carried out with a catalyst capable of in situ hydrogenation of acetaldehyde to ethanol. The reaction sequence is ... 

Carbonylation of Alcohols and Esters. The mechanism of ttie Rh/I" catalysed alcohol carbonylation has been studied in detail. Rates decrease sharply from methanol to n-propanol. Formation of isobutyric acid as a by-product points to a p-H elimination-reinsertion sequence.This sequence has also been demonstrated for ethanol carbonylation by selective C labelling (eqn.l8). The reductive carbonylation of methanol in the presence of Col2 and PPhg generates acetaldehyde, ethanol and methyl acetate. Only diphenylether and alkanes as solvents did not decompose under the reaction conditions (17CPC,... 

Two processes of direct methanol carbonylation are well established already The direct carbonylation of methanol yielding acetic acid, the Monsanto process and carbonylation of methyl acetate giving acetic anhydride, a technology commercialized by Tennessee Eastman Kodak. By adjusting the CO H2 ratio, catalytic systems for the reductive carbonylation of methyl acetate can be tuned to the production of acetic anhydride, ethylidene diacetate or acetaldehyde. 

Carbonylation acetic acid, acetic anhydride, methyl acetate, methyl formate Reductive carbonylation acetaldehyde, ethanol, ethyl acetate, ethylidene diacetate Oxidative carbonylation dimethyl carbonate, dimethyl oxalate... 

As part of the Megacity Initiative Local and Global Research Observations (MILAGRO) project, a comprehensive airborne study by Yokelson et al. reported the first detailed field measurements of biomass emissions in the Northern Hemisphere tropics [169]. Volatile emissions were measured from 20 deforestation and crop residue fires on the Yucatan peninsula. This included two trace gases which are often considered to be useful as indicators of biomass burning. One we have discussed before, namely acetonitrile, and the other is hydrogen cyanide. A variety of instrumentation was co-deployed for this investigation (FTIR spectroscopy, GD-FID, a GC-Trace Analytical Reduction Gas Detector, fluorescence and chemiluminescence instruments and various other spectrometers). PTR-MS was used to monitor methanol, acetonitrile, acetaldehyde, acetone, methyl ethyl ketone, methyl propanal, hydroxyacetone plus methyl acetate, benzene and 13 other volatile species. 

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