Carbonylation methyl benzoate

Carter, O. L., McPhail, A. T. Sim, G. A. (1967) Metal-carbonyl and metal-nitrosyl complexes. Part V. The crystal and molecular structure of the tricarbonylchromium derivative of methyl benzoate, J. Chem. Soc. A, 1619-1626. 

The carbonyl group of methyl benzoate condenses with Na-HMDS 486 to give methoxytrimethylsilane 13a and 51% yield of N,0-bis(trimethylsilyl)benzamide 296 [99], which is also accessible by silylation of benzamide with TCS 14/triethyla-mine. Benzamide or N-silylated benzamide, however, are converted by Na-HMDS 486 in benzene and subsequent quenching with MesSiCl 14 into 34% N,0-bis(trimethylsilyl)benzamide 296, 24% crystalline N-silylated benzamidine 524, and HMDSO 7 [99] (Scheme 5.32). 

These authors also reported that /V-acyloxy-/V-alkoxyamides did not undergo methanolysis under the same conditions but treatment of /V-acctoxy-/V-ethoxybenz-amide 25a in more forcing conditions with NaOMe in DME afforded a mixture of ethyl and methylbenzoate, 97 and 98 (Scheme 20). They attributed the formation of the former to a HERON reaction and methyl benzoate to the direct attack of methoxide at the amide carbonyl. 

There is one report of competitive nucleophilic attack at the amide carbonyl in an Ai-acyloxy-A-aUtoxyamide. Shtamburg and coworkers have reported that MeONa reacted with Ai-acetoxy-A-ethoxybenzamide (159) in DME giving methyl and ethyl benzoate (160 and 161) (Scheme 26) . They attributed the formation of methyl benzoate to the direct attack of methoxide ion at the amide carbonyl rather than at nitrogen. The formation of 161 was attributed to a HERON reaction. Though not mentioned by the authors, it seems likely that under these aprotic conditions, 162 could also have been formed by methoxide attack at the acetate carbonyl leading to an anion-induced HERON reaction, by analogy with the reaction of Ai-acyloxy-Ai-alkoxyamides and aqueous hydroxide discussed above (Section IV.C.3.c)... 

When CF3 is allowed to react with methyl benzoate, a new reaction channel appears along with the formation of the carbonyl addition product (Eq. 25). The nucleophile attacks at the methyl group to give an Sn2 substitution with the formation of the benzoate ion. In this case, proton transfer is not possible (no ot hydrogens), but benzoate is a better leaving group than acetate and substitution at the methyl group becomes viable. 

Comisarow (1977) has shown that, in the gas phase, methoxide ions react readily with methyl trifluoroacetate and methyl benzoate by an SN2 mechanism, while no reaction is observed as a result of nucleophilic displacement at the carbonyl centre. As for the case above, the SN2 reaction is highly exothermic, while the same is not true for the equivalent of reaction (64b). There is at present no satisfactory explanation of why (64a) apparently proceeds very slowly in the gas phase. 

Methyl benzoate gives88 no carbonyl-containing products over potassium tetrafluoro-cobaltate(III) at 300 °C very low yields of perfluorocyclohexane and perfluorocyclohexene are obtained. 

This was very early work, and not enough data for meta- and para-substituted compounds were obtained for an accurate determination of p, but the plot of log k versus pKa of ArCOOH (both at 100°C) for o- and p-substituted methyl benzoates gave a good straight line of slope 0.67. This result, together with that of Eschenmoser et al. 77, emphasizes that steric hindrance at the carbonyl group has little or no effect on the displacement of the ether oxygen of the ester. 

The effects of polar substituents on the alkaline hydrolysis of esters are well-established. Since the rate of the reaction is determined largely by the rate of addition of hydroxide ion to the carbonyl group of the ester, any substituent which withdraws electrons from the carbonyl group will increase the reactivity of the ester. The most accessible quantitative measure of the effect is the Hammett or Taft reaction constant, and a large number of measurements are available. Taft et al.2i0 found p = 2.53 for the base-catalyzed methanolysis of meta- and para-substituted (/)-menthyl benzoates, closely similar to the known value of p = 2.37 for the alkaline hydrolysis of substituted ethyl benzoates. Jones and Sloane s value239, obtained with five esters, of p = 2.41 for the methoxyl exchange reaction of substituted methyl benzoates in methanol, is almost identical. 

Carboxy carbons of methyl benzoates are shielded by electron-withdrawing substituents in the oposition of the benzene ring [320] (Table 4.38). Carbonyl shifts of phthalic acid diesters and phthalimide are larger than those of phthalic anhydride [321]. fi effects of the O-alkyl group in the esters and hydrogen bonding of the imide are the obvious reasons. 

The photolysis of hexachloroacetone or tribromoacetaldehyde in methanol does not yield any alcoholysis product253. The major reaction is reduction. On the other hand, a,a,a-tribromoacetophenone yields the alcoholysis product methyl benzoylformate in good yield (equation 56)254. The initial photomethanolysis product is a,a-dibromo-a-methoxy-acetophenone, which in a dark reaction is converted into the benzoylformate. The methyl benzoate is formed by nucleophilic attack on the carbonyl carbon. 

Reaction of methyl benzoate (144) with a palladium acetate/heteropolyacid mixture has been studied by Lee and coworkers [98]. They showed that aryl-aryl coupling occurs mainly at the 2-2 positions in the presence of various heteropolyacids (HPA e.g. H3PM012O40, H5PM09V3O40, H5PM010V2O40, etc.) (Scheme 34). The selectivity in favor of the 2-2 coupling product is between 53 and 84 %, but the conversions are low (0.48 to 6.93) due to deactivation of the catalyst. The observed selectivity can be rationalized in terms of formation of the (T-palladium complex 146 with stabilization by the carbonyl group (Figure 3). 

The carbonylations also proceed with palladium(II) acetate instead of palladium(II) chloride2. When the carbonylation reactions are carried out with methanol as the reaction medium methyl benzoates are obtained4. 

EXAMPLE Acid-catalyzed formation of methyl benzoate from methanol and benzoic acid. Part 1 Acid-catalyzed addition of methanol to the carbonyl group. 

Infrared spectra of (a) ethyl octanoate and (b) methyl benzoate. The carbonyl stretching frequency of simple esters is around 1735 cm-1 and that of conjugated esters is around 1710-1725 cm-1. 

A. Bagno, V. Lucchini and G. Scorrano, unpublished results cited in A. Bagno, G. Scorrano and R. A. More O Ferrall, Rev. Chem. Intermed., 7, 313 (1987). These authors list p H+ (acidity constants of carbonyl-oxygen-protonated conjugate acids) values for acetone, acetophenone, pinacolone and methyl benzoate. For the first three, the values were combined with keto-enol equilibrium constants to give the pK values shown in the Table. 

The photochemical reactions of arenecarboxylic acid esters with alkenes has received recent attention by Cantrell. - For example, irradiation of 2,3-dimethyl-2-butene and methyl benzoate gave a mixture of alkoxyoxetane (56), carbonyl-alkene metathesis product (57) and ketone (58), resulting from alkoxy radical allylic hydrogen abstraction and radical recombination. Such alkoxyoxetane photoproducts are... 

Decomposition of methanesulphonyl azide in aromatic solvents (methyl benzoate or benzotrifluoride), in the presence of transition metal compounds (e.g. copper(ri) acetylacetonate, manganese(ii) acetylacetonate, di-cobalt octacarbonyl, tri-iron dodecacarbonyl, and iron pentacarbonyl) led to a marked decrease in the aromatic substitution product compared with thermolysis, and, with the iron carbonyls, to an increased yield of methanesulphonamide . In addition, the aromatic substitution products shifted from mainly ortAo-substitution with no additives to mainly w ia-substitution in the presence of the additives mentioned above. 

Use SpartanView to display the vibrations of acetone, methyl benzoate, and dimethylformamide, and identify the C=0 stretching frequency in each. What fea tures of the C=0 stretching motion and the vibrational frequency make this a go diagnostic tool for identifying the carbonyl group ... 

Palladium(II) acetate micro-encapsulated in polyurea is an economical and versatile heterogeneous catalyst for a range of phosphine-free cross-coupling reactions in both conventional solvents and supercritical carbon dioxide. The catalyst can be recovered by simple filtration and recycled up to four times [93]. The potential of these materials has been demonstrated by their efficacy in Suzuld-type couplings. Investigations have centered upon carbonylation reactions to prepare aryl esters from commercially available aryl iodides. Treatment of iodo-methyl benzene tvith 3 mol% of catalyst in butanol and triethylamine at 90 °C under an atmosphere of carbon monoxide afforded butyl-methyl benzoate in an excellent yield of 89% in 16 h. 

---