Homologation methyl acetate

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... 

Wender and coworkers conclude that cobalt-catalyzed benzyl alcohol homologation involves the intermediate formation of car-bonium ions (8). However, since the methyl cation (CH3+) is unstable and difficult to form (9), it is more likely that methanol homologation to ethanol proceeds via nucleophilic attack on a protonated methyl alcohol molecule. Protonated dimethyl ether and methyl acetate forms have been invoked also by Braca (10), along with the subsequent formation of methyl-ruthenium moieties, to describe ruthenium catalyzed homologation to ethyl acetate. 

Syngas Homologation of Acetic Acid. To a N2-flushed liquid mix of acetic acid (50.0 gm) and methyl iodide (5.67 gm, 40 mmole), set in a glass liner is added 0.763 gm of ruthenium(IV) oxide, hydrate (4.0 mmole). The mixture is stirred to partially dissolve the ruthenium and the glass liner plus contents charged to a 450 ml rocking autoclave. The reactor is sealed, flushed... 

While the direct carbonylation is well accepted by industry, the reductive and oxidative carbonylations are still in the research and development stage. Using Texaco technology (j, 7/ ) the combined synthesis of ethene and ethanol is feasible via homologation of acids according to Figure 3. Ethene can also be obtained from the reductive carbonylation of methyl acetate to ethyl acetate followed by pyrolysis (2 ). Both routes, so far, lack selectivity. 

Thus, the overall acetaldehyde selectivity approaches 98%. The utility of methyl acetate as an alternative feedstock has been previously illustrated by the reported carbonylation to acetic anhydride ( ) and homologation ( ) to ethyl acetate via reaction with synthesis gas. 

Table I shows the unique results obtained when a combination of RUCI3 and RhCl3, in the presence of an iodide, is used in the homologation of methyl acetate. In particular experiments VI-IX demonstrate that the theoretical stoichiometry ...

Table III. Homologation of Methyl Acetate to Ethyl Acetate Effect of Iodide Source...

For both reactions a RhCl3/CH3l/TPO catalyst in acetic acid as reaction solvent affords propionic acid in more than 80 % yield according to the respective stoichiometries of Equations 12 and 13. Although acetic acid is present in excess in the reaction medium, it does not participate in the homologation as reactant. Only traces of propionic acid are produced in the absence of methyl acetate, ethyli-dene diacetate or acetic anhydride under our reaction conditions. Homologation of carboxylic acids has been reported by Knifton (10) to require more severe reaction conditions (220 °C, > 100 bar). 

Reaction 15 also plays a minor role in the homologation of methyl acetate to ethyl acetate (Reaction 4). However, when acetic acid is used as a reaction solvent, C2H5I never builds up to a significant concentration because of the equilibrium ... 

These species show different promoting effects on the activity and selectivity of the homologation of methyl acetate with CO + H2 (carbonylation to acetic acid, homologation to ethyl acetate and hydrogenation to methane) (5). 

The predominance of the ruthenium iodocarbonyl over the cobalt carbonyl species in the bimetallic Co-Ru systems is evidenced by the I.R. spectra of the catalytic solutions of the methyl acetate homologation with cobalt and ruthenium catalysts used in about the same concentration or with an excess of ruthenium. The latter compositions actually show the highest activity for the homologation... 

Carbonylation and homologation of ethers - The carbonylation and homologation of dimethyl ether to methyl and ethyl acetate (eqs. 4 and 5) in methyl acetate-acetic acid solution are considerably affected by the acidity of the reaction medium and by the nature of the iodide promoter which determines the concentration of HRu(CO)3l3. 

Methyl acetate homologation - Our recent work on the effect of formation of ion-pairs in the homologation of methyl acetate to ethyl acetate (eq. 6) has clarified the role played by HRu(00)3X3 and M [Ru(CO)3l3] salts (M = alkali metal) (5,10). 

Performances of different promoters of the[Ru(CO)313] species in the homologation of methyl acetate to ethyl acetate... 

Industrial development of homologation processes for dimethyl ether, methyl formate, methyl acetate and acetic acid is likely only if they are integrated into a comprehensive plant for the production of C2 derivatives from syn-gas (Scheme 5). 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

A further reaction of the above type is ester homologation. The production of ethyl acetate from methyl acetate (equation 71) using similar catalytic systems to the above has been studied.382... 

In the future, there is no doubt that alcohols will play a major role not only as fuel components (70,71) but also as feed stocks for the syntheses of more complicated organic compounds (72). A great amount of research effort is presently directed to the economic conversion of CO and to methanol (73), and on homologation of methanol to higher alcohols (74). Conversion of synthesis gas from coal to acetic anhydride (75) through the intermediacy of methyl acetate (from methanol) will soon be a commercial reality. 

Ester homologation. The anion of 1 reacts with carbonyl compounds to form ketene-0,S-acetals (2), which are converted into homologated methyl esters (3) by reaction with methanol in the presence of HgCl2. 

Propionic acid is also formed as a co-product when methyl acetate is treated with carbon monoxide in the presence of hydrogen [28]. Rhodium-based homogeneous catalyst systems have been described which permit the homologation of esters according to two alternative stoichiometries. The reactions proceed under mild conditions according to eqs. (17) and (18) [31] ... 

Thus the homologation reaction can be used, for example, for the synthesis of acetaldehyde from methanol [48], propionic acid from acetic acid [47], or ethyl acetate from methyl acetate [50]. Styrene may be produced from toluene by oxidation to benzyl alcohol [51] and homologation to 2-phenylethanol, which in turn can be dehydrated to styrene. From the chemical point of view, the applications of homologation reactions are broad and useful. But, as mentioned before, low selec-... 

---