Ethylidene diacetate formation

In the carbonylation of MeOAc to AC2O, little or no reaction corresponding to the vater gas shift takes place. Indeed it may be advantageous to feed small amounts of H2 to the process to increase catalyst activity [5]. This is also associated with the formation of ethylidene diacetate, CH3CH(OAc)2, (EDA) (Eq. (6)). 

Even with added iodide salt formation of the inactive [Rh(CO)2l4] can be a problem, since under anhydrous conditions this Rh(III) species cannot be reduced to the active [Rh(CO)2l2] by reaction with water. In the Eastman process, this problem is addressed by addition to the CO gas feed of some H2 which can reduce [Rh(CO)2l4] by the reverse of Equation 8. However, the added H2 does lead to some undesired by-products, particularly ethylidene diacetate (1,1-diacetoxyethane) which probably arises from the reaction of acetic anhydride with acetaldehyde (Equation 19 from hydrogenolysis of a rhodium acetyl) ... 

The next step in the reaction scheme—decomposition of the a-bonded alkylpalladium (XIV or XV)—has caused some controversy. To account for the results of several deuterium-labelling studies (15, 36, 54), a. palladium-assisted hydride transfer reaction (Reaction 4) has been proposed (36, 54). A number of inconsistencies in the studies using 2-deuteropro-pylene as substrate (54) have been discussed (i). In addition, the formation of a free carbonium ion such as VII [as proposed by Moiseev (36)], while accounting well for the formation of ethylidene diacetate, is much less satisfactory in accounting for the production of the unsaturated esters in an acetate-acetic acid medium. A simple elimination of -hydrogen (Reactions 13a and b) could also account for the products formed. While not necessary for the reaction, chloride assistance for proton removal is a possibility and has been postulated previously for a similar reaction (i, 37). 

Formation of 1,1-diacetates—e,g., ethylidene diacetate from ethylene or hexylidene diacetate from hexene—by simple acetate displacement of palladium (Reaction 16) is a much more satisfactory reaction scheme than any previously proposed. On the other hand, accounting for 1,2-diol type products is diflBcult by this scheme, necessitating a reverse hydrogen transfer to form a two-carbon insertion product intermediate. This type... 

An important aspect in the development of this process is the understanding of by-product formation, as a means of implementing specific ways to minimize side reactions. The important by-products are ethylidene diacetate, acetone, carbon dioxide, methane, and heavy ends. 

Acetals or ketals respectively are primary products since, quite analogously to the formation of ethylidene diacetate in the acetoxylation of ethylene with ROD, only deuterium-free acetals or ketals are obtained [3]. The mechanism ought to be analogous, too (cf. Section 3.3.14.3). 

In the liquid phase, this conversion takes place at low temperature (between 60 and 80°C), under low pressure (between Oil and 0J. 10 Pa absolute). Hence it requires a highly active catalyst, such as mercury salts (oxide, sulfate, phosphate, etc.), kept in suspension in an acid (preferably acetic add) at the rate of 1 to 5 per cent weight To prevent the formation oflarge amounts of ethylidene diacetate, the operating temperature must be kept as low as possible. The residence time of acetylene in the catalyst suspension can also be reduced, or a large excess employed. In this ca e. however, it is indispensable to use a polymerization inhibitor such as HF, BF3. etc. In these conditions, the molar yield is higher than 90 per cent... 

The reaction mechanism and rates of methyl acetate carbonylation are not fully understood. In the nickel-catalyzed reaction, rate constants for formation of methyl acetate from methanol, formation of dimethyl ether, and carbonylation of dimethyl ether have been reported, as well as their sensitivity to partial pressure of the reactants (32). For the rhodium chloride [10049-07-7] catalyzed reaction, methyl acetate carbonylation is considered to go through formation of ethylidene diacetate (33) ... 

Klatte s reaction is a liquid-phase reaction. In 1921, Baum et al. invented the gas-phase reaction [2]. With this process, it is possible to produce vinyl acetate practically without the formation of ethylidene diacetate. 

From acetylene and acetic acid. The direct addition of acetylene to acetic acid occurs in the liquid or the gas phase. The liquid-phase reaction is carried out at 75-80°C with HgS04 catalyst. The vinyl acetate must be removed from the reaction mixture as quickly as possible otherwise too much ethylidene diacetate will result. However, the formation of the diester can be inhibited by the addition of HgS04/BF3/HF. This method has the commercial disadvantage that the residual deposits of poly(vinyl acetate), metallic mercury, etc., produced can only be removed by burning. The gas-phase method proceeds at 180°C with zinc acetate as catalyst. Only 5-10% of vinyl acetate can be formed per cycle, since otherwise large amounts of by-products occur. The theoretically possible total yield... 

Ethylidene Diacetate. Hydrocarbonylation of methyl acetate leads to the formation of ethylidene diacetate and acetic acid via the following sequence of reactions ... 

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

Six-membered acetal rings fused to seven-membered rings are found in acetals formed directly from mannitol and certain of its derivatives. The 1,3 2,5 4,6-structure has been proved for the tri-O-methylene " and tri-0-ethylidene " derivatives of mannitol, and the 1,3 2,5-structure for the di-O-methylene derivative of 6-deoxy-L-mannitol. " These acetals are markedly more stable than the 2,4 3,5-diacetals discussed above. Their stability has been related to the probable mechanism of formation,"" but is also understandable on conformational grounds. " The ring junctions are trans, and the triacetals LXI have the trans-anti-trans configuration, which... 

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