Methyl acetate, viii

Reaction 10 is not limited to methyl acetate but can be generally applied. Table VIII shows some results with various starting esters and alkanoic acid solvents. In Experiments I and II the parent acid of the ester is different from the acid solvent. Transesterification reactions lead to two different starting esters and acids. Homologa-... 

Activities of Group VIII Metal Catalysts. Methanol conversions to methyl acetate and acetic acid on group VIII metals supported upon activated carbon are illustrated in Figure 1, The yield was calculated as methanol conversion to acetyl group. For each catalyst, acetic acid formation is predominant at high temperature while methyl acetate has a point of maximum yield. 

Fig. 97. Solvent retained by nitrocellulose films (50/i thickness) after exposure to air at 25°C (Baelz [48]). I—Cyclohexenyl acetate, II—methyl cyclohexanone, III—diacetone alcohol, IV—cyclohexanone, V—cellosolve acetate, VI—amyl acetate-ethyl alcohol I 1, VII—amyl acetate, VIII— methyl cellosolve acetate, IX—amyl acetate-toluene 1 1, X—butyl acetate-ethyl alcohol 1 1, XI—butyl acetate, XII—cellosolve, XIII—methyl-ethyl ketone, XIV—cellosolve-toluene 1 1, XV—methyl cellosolve, XVI—ethyl acetate, XVII—acetone.

To quantitatively understand the preference for the chairlike and boathke transition states of the Claisen rearrangement, Houk et al. carried out a computational study12 (Scheme l.VIII). In the theoretical treatment two methyl acetals, 7Z(OMe) and 7/ (()Me), were used as a model system instead of the fert-butyl-dimethylsilyl (TBS) ketene acetal. Calculations locate four transition states for the rearrangement of 7Z(OMe), among which boathke transition state A is of the lowest energy that leads to the formation of the major isomer observed experimentally. Chairlike transition state B is disfavored, due to steric repulsion between the axial hydrogen of the cyclohexenyl unit and the methoxy substituent of the alkene. 

Finally, methyl acetate could be made directly from methanol via carbonyla-tion [33]. Preferentially, the catalyst system is based on rhodium, but other metals of Group VIII or Zr, Hf have also been patented. The addition of iodine seems necessary for good selectivities and conversions. Intermediates similar to those discussed for the acetic acid synthesis have been proposed [34] and Scheme 10 shows some species. 

The vinylation of methyl acetate and methyl propionate took place in the presence of oxygen over Ti -TSM (35,39). The results are briefly summarized in Thble VIII, where the values of conversion and selectivity are calculated on the ester basis. Because of the acidity of Ti -TSM and the presence of water formed by the reaction, the esters fed and produced undergo... 

On the basis of the carbonylation of methyl acetate using Co, Ni or Fe catalysts by BASF [48] in the 1950s and of the initial results from the Rh catalyzed carbonylation of methanol by Monsanto [21, 49] in the early 1970s, Halcon [49, 50], Eastman [41b, 51], Ajinamoto [52], Showa Denko [53], BP [2, 20, 54, 55], and Hoechst [56] worked on substantial developments for the Group VIII metal-catalyzed manufacture of acetic anhydride. Promising catalyst metals are Rh, Pd, Ni, and Co among these, Rh has an essential position due to its exceptional carbonylation activity [20]. 

Of the group VIII metal catalysts, Co has received the most attention. With CojfCOlg, at 180-185 C and CO H2 pressures of 35 MPa, CH3OH gives a product distribution of 38.8% ethanol, 4.7% n-propanol, 9.0% methyl acetate, 6.3% ethyl acetate, 8.5% methane and traces of acetaldehyde, methyl formate, propyl acetate and butanol. At 160-180° and 21 MPa of CO H2, tert-butanol gives a 63% yield of iso-amyl alcohol, and iso-propanol gives 11% of a mixture of n- and iso-butanol. n-Propanol reacts slowly at 180°C. 

Liquid-liquid equilibrium data of polystyrene in methyl acetate and methyl acetate-d6 Data extract from Landolt-Bornstein VIII/6D3 Polymers, Polymer Solutions, Physical Properties and their Relations I (Thermodynamic Properties Equilibria of Ternary Polymer Solutions) ... 

Methanol Carbonylation. Metal-ion exchanged heteropoly acids (HPAs) of the general formula M[PWi204o] (M = a Group VIII metal) supported on Si02 have been found to be excellent catalysts for the vapor-phase carbonylation of methanol or DME to methyl acetate at 225°C and 1 atm total operating pressure (84). Experiments witii H3PM12O40 (M = Mo,W) carried out in a conventional flow reactor at 1 atm CO and 200-275°C have shown that methanol is converted into DME and small amount of C1-C5 saturated hydrocarbons (HCs) and C2-C4 olefins. No carbonylation products are detected under these... 

Kinetic studies have allowed the optimum conditions to be defined for the synthesis of acetic anhydride by the carbonylation of methyl acetate using a variety of Group VIII metal catalysts. Such studies, complemented by IR and UV spectroscopic studies, have helped to elucidate the main catalytic pathways for the rhodium- and iridium-catalyzed reactions in the presence of iodide. Although complex, both mechanisms essentially involve oxidative addition of Mel to [M(CO)2l2] (M = Rh or Ir) followed by CO insertion into the metal-methyl bond and subsequent reductive elimination of MeCOI the latter reacts with acetate ion to give acetic anhydride and regenerate iodide. ... 

This synthesis came shortly after one by Prelog, Kohlberg, Cerkovnikov, Rezek and Piantanida (1937) based on a series of reactions which, with modifications and extensions. Prelog and his colleagues have applied to the syntheses of bridged heterocyclic nuclei, of which this is an example. 4-Hydroxymethyltetrahydropyran (VI R =. OH) is converted via the bromo-compound (VI R = Br) and the nitrile (VI R = CN) into tetrahydropyran-4-acetic acid of which the ethyl ester (VII) is reduced to 4-()3-hydroxyethyl)-tetrahydropyTan (VIII). This is converted by fuming hydrobromic acid into 3-(2-bromoethyl)-l 5-dibromopentane (IX) which with ammonia in methyl alcohol yields quinuclidine (V). 

Note TLC was performed on silica gel, and the solvents were (1) -bntanol/glacial acetic acid/water (2 1 1, v/v), (IV) isoamyl alcohol/ethy methyl ketone/glacial acetic acid/water (40 40 7 13, v/v), (VII) n-bntanol/2-propanol/water/glacial acetic acid (30 50 10 2, v/v), (VIII) ethyl methyl ketone/acetic acid/methanol (3 1 1, v/v), and (IX) n-bntanol/benzyl alcohol/glacial acetic acid (8 4 3, v/v). 

The reaction is catalyzed by a group VIII metal species, particularly that of rhodium or palladium. The initial metal species may be any variety of complexes (e.g., PdCl2 Pd acetate, etc.). A source of halide is necessary iodide is especially effective. The most convenient source is methyl iodide, since it is likely a reaction intermediate. In addition, an organic promoter must be included for catalytic activity. These promoters are generally tertiary phosphines or amines. Also, chromium complexes were found to have an important promotional effect. 

The remarkable feature of Woodward s procedure was the facile way in which the five adjacent stereochemical centers in ring E were built into the critical intermediate, the aldehyde acid (XLII) (Chart VIII). Parenthetically, the preparation of this compound has opened up the possibility of a general synthesis of all the yohimbines and their isomers, although this has not yet been done. Condensation of the aldehyde acid with 6-methoxytryptamine gave a Schiff base which was reduced in situ with sodium borohydride to furnish the amide (XLIII) which was ring-closed to the A3 compound XLIV and subsequently transformed into the methyl dl-isoreserpate-O-acetate (XLVIII). 

When p-nitro-N,N-dimethylaniline (IVc) was ozonized at 0°C in ethyl acetate, methylene chloride, or methanol, a mixture of products resulted. In addition to the expected side-chain oxidation products— p-nitro-N-methylaniline (Vc), p-nitro-N-methyl formanilide (Vic)—a peroxide compound was formed. This peroxide, which is not formed until the solvents are removed, was shown by a series of experiments (described below) to be identical with di-[(N-methyl-p-nitrophenyl)-aminomethyl] peroxide (VII). Deoxygenation of VII with triethyl phosphite (7) yielded the ether VIII, which in turn decomposed at its melting point to the amine IX. 

A few comments on the values of r and (r+ - - r ) (cf. Table VIII) are necessary. Increasing hydrocarbon content decreases the hydrophilic property of the anion (cf. formic, acitic, propanoic, butanoic, 3-methyl-butanoic, and benzoic acids) resulting in the decrease of hydration the trend eventually levels off. Hydrophilic substitution increases hydration (cf. acetic, chloroacetic, cyanoacetic, glycolic acids cf. glutaric, succinic, and malonic acids cf. benzoic and salicyclic acids). Also note that r is smallest for benzoic acid and largest for malonic acid. These trends cannot be fortuitous. 

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