Methyl formate, isomerization

The production of methyl formate by carbonylation of methanol with basic catalysts [134] can be used to separate carbon monoxide from by-product synthesis gas streams, e.g., steel-mill off-gases [135], to generate clean sources of CO for production of acetic acid by methyl formate isomerization. Therefore methyl formate could be produced near cheap CO sources and then transported to an appropriate site for conversion to acetic acid. This route to acetic acid is potentially competitive with a classic grass-roots methanol carbonylation process. Though the process has not been commercialized, numerous companies have patented the isomerization of methyl formate [136]. 

An interesting reaction of methyl formate is its isomerization to give acetic acid. Based on patent literature, a number of companies have recently reinvestigated this isomerization which has been known for over 30 years ( ). It is unlikely that it can compete with the Monsanto process however, since it doesn t need pure CO and may be operable at milder reaction conditions, some potential may be seen. Combining isomerization to acetic acid and decarbonylation to methanol and CO, could provide a direct synthesis for acetic anhydride starting directly from methyl formate (Equation 13). 

Photolysis of the four examples of 2,3-dihydro-6f/-l,3-thiazines 101-104 resulted in the formation of different products which is dependent on R and R (Scheme 3). When both groups are methyl (101), isomeric thiazolines 105 and 106 are isolated, the thiazoline 106 being the major isomer. The ethyl analogue 102 reacts differently and the thioamide 107 is formed. All four thioamide isomers are formed when the benzyl analogue 103 is photolyzed and the... 

As a comparison of the enthalpies of formation of isomeric aldehydes and ketones shows, the disubstituted carbonyl compounds (ketones) are more stable than the monosubstituted carbonyl compounds (aldehydes), analogous to the stability order for the corresponding 1,1-disubstituted ethenes and the 1-n-alkenes. For the three aldehyde/methyl ketone isomeric pairs (nc = 3-5), initially it seems that the enthalpies of isomerization are fairly constant. However, if the interpolated value for pentanal is used, the trend is clearly that of more negative enthalpy of isomerization with increasing c(g) —31.7, —33.9, —34.5 kJmol-1. The non-constant enthalpies are expected because the slopes, ag, in Table 4 are quite different for aldehydes and ketones. The greater contribution to the isomerization enthalpy differences comes from the methyl ketone which is more stabilized than the aldehyde by an additional —CH2— group. The enthalpies of isomerization of the corresponding alkenes are much less exothermic (—6.1 0.8 kJmol-1) than those of the carbonyl compounds. 

In this part, we will summarize some of our results on the investigation of the toluene intramolecular isomerization pathways." " Both cluster approach and periodic approach methods have been employed which allow giving an illustration of the consequence of the simplistic model in the cluster approach. H-Mordenite (H-MOR) zeolite is used for the periodic calculations. The toluene molecule does not have a problem to fit within the large 12-membered ring channels of this zeolite. Furthermore, the intramolecular transition states do not suffer from steric constraints. It is known that intramolecular aromatics isomerization can proceed via two different reaction pathways (see Figure 7). The first route proceeds through a methyl shift isomerization, whereas the second route involves a dealkylation or disproportionation reaction which results in the formation of a methoxy species and benzene as intermediate. 

Acetic acid. Various catalysts (h e. Co, Nt, Rh) upon heating under CO pressure can isomerize methyl formate to acetic acid [49. Again iodine Is needed. An economic advantage of producing acetic acid through isomerization may he given in comparison with the methanol-acetic acid process. 

It is known that formic acid is synthesized from H2/CO2 as ester in alcohol solvent using metal complex catalysts such as HM(CO)5 (M W,Cr,Ru) in batch reactor system.[61] However, specific activity (TOF) of these system are relatively low. Recently, Noyori et al. found a significant increase of formic acid in a supercritical mixture of H2/CO2 with N(C2H5)3 using RuH2 P(CH3)3)4 complex at the condition of 20.5 Mpa, 5013 and H2/C02=l/1.4.[62] TOF increased one order of magnitude over that of conventional process because of high miscibdity of H2 with supercritical CO2. It is also noted that methyl formate produced from H2/CO2 is easdy converted to acetic acid by isomerization reaction. 

Alkyl Formate Production. In the past few years, formate esters have become an important class of organic compounds mainly because of their versatility as chemical feedstock (16,36-42), and as raw materials for the perfume and fragrance industry (43-46). Specifically, formate esters (methyl, ethyl, pentyl, etc.) have been used as starting material for the production of aldehydes (36), ketones ( ), carboxylic acids (37-40), and amides ( ). For example, methyl formate can be hydrolyzed to formic acid (39,40) or catalytically isomerized to acetic acid ( ). On the other hand, alkyl formates have been employed in the perfume and fragrance industry in amounts of approximately 1000 to 3000 Ib/year (43—46). Among the formates that have been commonly used for these purposes are octyl ( ), heptyl ( ), ethyl ( ), and amyl ( ) formates. 

As part of a study of the isomerizations, pyrazole to imidazole and 1-methyl- to 4-methyl-imidazole, isomerization enthalpies have been determined from the experimental heats of formation. For the former rearrangement A/7 was calculated as —42.7 kJ mol" (cf. experimental value, —40.2 kJ mol ), whereas 4-methylimidazole was calculated to be more stable by 27.6 kJ mol than its 1-methyl isomer <86JOC1105>. In view of the known thermal rearrangement of 1- to 2-methylimidazole it would be of interest to apply similar measurements of isomerization enthalpy to the species in this transformation. 

Isomerization of methyl formate to acetic acid is a well-known reports in the patent literature date back to 1929. With a Co-iodide catalyst the reaction is carried out at 160° and 10.5 MPa CO . The selectivity to acetic acid is >95%. The best reported productivities are obtained with a Rh-Lil catalyst. In this case, the reaction is carried out at 180°C and 2.75 MPa with 99% conversion and near quantitative yield of acetic acid. The mechanism of the reaction involves initial cleavage of methyl formate by Lil. CH3I, obtained in the cleavage reaction, is carbonylated to acetyl iodide via the same catalytic chemistry observed in CH3OH carbonylation. The key to making acetic acid is that the mixed anhydride CHjCfOlOCfOlH is unstable and thermally decomposes to acetic acid and CO at the reaction conditions. 

Ir(Cl)3] catalyzes the isomerization of methyl formate at 473-508 K/33-250 bar CO in the presence of an Mel promoter. The major product is acetic acid, with methyl acetate as a byproduct. The synthesis of PhNCO via carbonylation of PhN02 at 398 K under 80 atm CO pressure can be catalyzed by [ (COjjCPPhjjj] . ... 

Methylation of nickelacycle 30, obtained in the reaction between Ni(COD)(py)2 and 2-cyclopentencarboxylic acid, unexpectedly leads to the formation of cw-2-methylcyclopentanecarboxylic acid (Scheme 29) 33(0 pjijs product probably arises by methylation of isomeric nickelacycle 56, formed by 3-hydride elimination and insertion with the opposite regiochemistry. When the same reaction is carried out with a large excess of iodomethane, d.y-3-methylcyclopentanecarboxylic acid is obtained. Methylation reactions of related azanickelacycles have also been reported. ... 

This procedure does not liberate HCl, however methyl chloride and methyl formate are formed as by-products. Thus, no catalyst is produced to affect the isomerization of the product, and no water is formed preventing siloxane formation and condensation. 

In a carboxylic acid solvent, [Ir(cod)Cl]2 with a Mel promotor effects the isomerization of methyl formate to acetic acid. Kinetic and chemical studies indicate that the reaction proceeds in the carboxylic acid by transesterification to give formic acid which then reacts with iridium (Scheme 9). " ... 

Bromination of isoprene using Br2 at —5 ° C in chloroform yields only /n j -l,4-dibromo-2-methyl-2-butene (59). Dry hydrogen chloride reacts with one-third excess of isoprene at —15 ° C to form the 1,2-addition product, 2-chloro-2-methyl-3-butene (60). When an equimolar amount of HCl is used, the principal product is the 1,4-addition product, l-chloro-3-methyl-2-butene (61). The mechanism of addition is essentially all 1,2 with a subsequent isomerization step which is catalyzed by HCl and is responsible for the formation of the 1,4-product (60). The 3,4-product, 3-bromo-2-methyl-1-butene, is obtained by the reaction of isoprene with 50% HBr in the presence of cuprous bromide (59). Isoprene reacts with the reactive halogen of 3-chlorocyclopentene (62). 

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