Metals, activated anhydrides

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

In addition to these principal commercial uses of molybdenum catalysts, there is great research interest in molybdenum oxides, often supported on siHca, ie, MoO —Si02, as partial oxidation catalysts for such processes as methane-to-methanol or methane-to-formaldehyde (80). Both O2 and N2O have been used as oxidants, and photochemical activation of the MoO catalyst has been reported (81). The research is driven by the increased use of natural gas as a feedstock for Hquid fuels and chemicals (82). Various heteropolymolybdates (83), MoO.-containing ultrastable Y-zeoHtes (84), and certain mixed metal molybdates, eg, MnMoO Ee2(MoO)2, photoactivated CuMoO, and ZnMoO, have also been studied as partial oxidation catalysts for methane conversion to methanol or formaldehyde (80) and for the oxidation of C-4-hydrocarbons to maleic anhydride (85). Heteropolymolybdates have also been shown to effect ethylene (qv) conversion to acetaldehyde (qv) in a possible replacement for the Wacker process. 

The introduction of tritium into molecules is most commonly achieved by reductive methods, including catalytic reduction by tritium gas, PH2], of olefins, catalytic reductive replacement of halogen (Cl, Br, or I) by H2, and metal pH] hydride reduction of carbonyl compounds, eg, ketones (qv) and some esters, to tritium-labeled alcohols (5). The use of tritium-labeled building blocks, eg, pH] methyl iodide and pH]-acetic anhydride, is an alternative route to the preparation of high specific activity, tritium-labeled compounds. The use of these techniques for the synthesis of radiolabeled receptor ligands, ie, dmgs and dmg analogues, has been described ia detail ia the Hterature (6,7). 

These anionic surfactants are based on the petrochemically gained maleic acid anhydride. Sulfosuccinates are surface-active metal (mostly sodium) salts of either monoester or diesters of sulfosuccinic acid. 

Poly(methyl 3-(l-oxypyridinyl)siloxane) was synthesized and shown to have catalytic activity in transacylation reactions of carboxylic and phosphoric acid derivatives. 3-(Methyldichlorosilyl)pyridine (1) was made by metallation of 3-bromopyridine with n-BuLi followed by reaction with excess MeSiCl3. 1 was hydrolyzed in aqueous ammonia to give hydroxyl terminated poly(methyl 3-pyridinylsiloxane) (2) which was end-blocked to polymer 3 with (Me3Si)2NH and Me3SiCl. Polymer 3 was N-oxidized with m-ClC6H4C03H to give 4. Species 1-4 were characterized by IR and H NMR spectra. MS of 1 and thermal analysis (DSC and TGA) of 2-4 are discussed. 3-(Trimethylsilyl)-pyridine 1-oxide (6), l,3-dimethyl-l,3-bis-3-(l-oxypyridinyl) disiloxane (7) and 4 were effective catalysts for conversion of benzoyl chloride to benzoic anhydride in CH2Cl2/aqueous NaHCC>3 suspensions and for hydrolysis of diphenyl phosphorochloridate in aqueous NaHCC>3. The latter had a ti/2 of less than 10 min at 23°C. 

Alternative paths for decomposition of the metal carboxylate can lead to ketones, acid anhydrides, esters, acid fluorides (1,11,22,68,77,78), and various coupling products (21,77,78), and aspects of these reactions have been reviewed (1,11). Competition from these routes is often substantial when thermal decomposition is carried out in the absence of a solvent (Section III,D), and their formation is attributable to homolytic pathways (11,21,77,78). Other alternative paths are reductive elimination rather than metal-carbon bond formation [Eq. (36)] (Section III,B) and formation of metal-oxygen rather than metal-carbon bonded compounds [e.g., Eqs. (107) (119) and (108) (120). Reactions (36) and (108) are reversible, and C02 activation (116) is involved in the reverse reactions (48,120). 

The first examples of transition metal-catalyzed [5 + 2]-cycloadditions between vinylcyclopropanes (VCPs) and 7r-systems were reported in 1995 by Wender and co-workers.10 This [5 + 2]-reaction was based conceptually on the Diels-Alder reaction, replacing the four-carbon, four-7r-electron diene with a five-carbon, four-electron VCP (Scheme 1). Although the [5 + 2]-reaction of VCPs and 7r-systems can be thought of as a homolog of the Diels-Alder [4 +21-reaction, the kinetic stability of VCPs (activation barrier for the thermal isomerization of VCP to cyclopentene has been reported as 51.7 kcal mol-1)11 makes the thermal [5 + 2]-reactions involving VCPs and 7r-systems very difficult to achieve. A report of a thermal [5 + 2]-cycloaddition between maleic anhydride and a VCP has been published,12 but this reaction has not been reproduced by others.13 14 Based on the metal-catalyzed isomerization of VCPs to cyclopentenes and dienes,15-20 Wender and co-workers hypothesized that a metal might be used to convert a VCP to a metallocyclohexene which in turn might be trapped by a 7r-system to produce a [5 + 2]-cycloadduct. Based on its previous effectiveness in catalyzed [4 + 2]-21 and [4 + 4]-cycloadditions (Section 10.13.2.4), nickel(0) was initially selected to explore the potential of VCPs as four-electron, five-carbon components in [5 + 2]-cycloadditions. 

In 1990, Choudary [139] reported that titanium-pillared montmorillonites modified with tartrates are very selective solid catalysts for the Sharpless epoxidation, as well as for the oxidation of aromatic sulfides [140], Unfortunately, this research has not been reproduced by other authors. Therefore, a more classical strategy to modify different metal oxides with histidine was used by Moriguchi et al. [141], The catalyst showed a modest e.s. for the solvolysis of activated amino acid esters. Starting from these discoveries, Morihara et al. [142] created in 1993 the so-called molecular footprints on the surface of an Al-doped silica gel using an amino acid derivative as chiral template molecule. After removal of the template, the catalyst showed low but significant e.s. for the hydrolysis of a structurally related anhydride. On the same fines, Cativiela and coworkers [143] treated silica or alumina with diethylaluminum chloride and menthol. The resulting modified material catalyzed Diels-Alder reaction between cyclopentadiene and methacrolein with modest e.s. (30% e.e.). As mentioned in the Introduction, all these catalysts are not yet practically important but rather they demonstrate that amorphous metal oxides can be modified successfully. 

Even more than [6 + 4] and [8 + 2] cycloaddition reactions, the [2 + 2 + 2] cycloaddition reactions require a very well preorganized orientation of the three multiple bonds with respect to each other. In most cases, this kind of cycloaddition reaction is catalyzed by transition metal complexes which preorientate and activate the reacting multiple bonds111,324. The rarity of thermal [2 + 2 + 2] cycloadditions, which are symmetry allowed and usually strongly exothermic, is due to unfavorable entropic factors. High temperatures are required to induce a reaction, as was demonstrated by Berthelot, who described the synthesis of benzene from acetylene in 1866325, and Ullman, who described the reaction between nor-bomadiene and maleic anhydride in 1958326. As a consequence of the limiting scope of this chapter, this section only describes those reactions in which two of the participating multiple bonds are within the same molecule. 

The use of ethylene adduct lb is particularly important when the species added to activate catalyst la is incompatible with one of the reaction components. Iridium-catalyzed monoallylation of ammonia requires high concentrations of ammonia, but these conditions are not compatible with the additive [Ir(COD)Cl]2 because this complex reacts with ammonia [102]. Thus, a reaction between ammonia and ethyl ciimamyl carbonate catalyzed by ethylene adduct lb produces the monoallylation product in higher yield than the same reaction catalyzed by la and [Ir(COD)Cl]2 (Scheme 27). Ammonia reacts with a range of allylic carbonates in the presence of lb to form branched primary allylic amines in good yield and high enantioselectivity (Scheme 28). Quenching these reactions with acyl chlorides or anhydrides leads to a one-pot synthesis of branched allylic amides that are not yet directly accessible by metal-catalyzed allylation of amides. 

Solutions of alkali metal or ammonium nitrates in trifiuoroacetic anhydride are useful nitrating agents for a range of activated to moderately deactivated substrates and particularly... 

Metal triflate Lewis acids can also be dispersed in ionic liquids for catalytic applications. Acetylation of alcohols with acetic anhydride and acetic acid has been reported with Cu(OTf)2, Yb(OTf)3, Sc(OTf)3, In(OTf)3, HfClq. (THF)2, and InCl3 in ionic liquids that consist of [BMIM] and the anions BF4, PF, or SbF 166). With lmol% acid, all the catalysts in [BMIMJPF showed >99% acetylation products in acetyl anhydride acetylation of benzyl alcohol. Sc(OTf)3 showed the best yield with recycling, with a 25% drop in yield after two cycles. A relatively long reaction period was needed to obtain a high yield (95-98%) for the acetylation of benzyl alcohol with acetic acid, indicating that the activities of the catalysts were... 

Bi salts proved to be as active as RET or other metallic triflates in the FC acylation of aromatic compounds using acyl chlorides or anhydrides [13, 66]. While... 

Carbonylation of Methyl Acetate on Ni/A.C. Catalysts. Table II shows the catalytic activities of nickel and platinum group metals supported on activated carbon for the carbonylation of methyl acetate. Ruthenium, palladium, or iridium catalysts showed much lower activity for the synthesis of acetic anhydride than the nickel catalyst. In contrast, the rhodium catalyst, which has been known to exhibit an excellent carbonylation activity in the homogeneous system (1-13), showed nearly the same activity as the nickel catalyst but gave a large amount of acetic acid. 

Rh > Ir > Ni > Pd > Co > Ru > Fe A plot of the relation between the catalytic activity and the affinity of the metals for halide ion resulted in a volcano shape. The rate determining step of the reaction was discussed on the basis of this affinity and the reaction order with respect to methyl iodide. Methanol was first carbonylated to methyl acetate directly or via dimethyl ether, then carbonylated again to acetic anhydride and finally quickly hydrolyzed to acetic acid. Overall kinetics were explored to simulate variable product profiles based on the reaction network mentioned above. Carbon monoxide was adsorbed weakly and associatively on nickel-activated-carbon catalysts. Carbon monoxide was adsorbed on nickel-y-alumina or nickel-silica gel catalysts more strongly and, in part, dissociatively,... 

Arylzinc species prepared via the sacrificial anode process and from aryl halides in the presence of a nickel 2,2 -bipyridine, as already reported in Section . .1, were found totally unreactive towards common electrophiles such as aldehydes, carboxylic anhydrides or activated alkyl halides. However, they react with some electrophiles when they are activated by the presence of a catalytic amount of copper salts (10 mol% Cul) together with tetramethylethylene diamine (1MEDA) as described by Knochel and Singer on the ArZnX—CuCN metal exchange47 or when the reaction is catalyzed by palladium complex. 

Many such activated acyl derivatives have been developed, and the field has been reviewed [7-9]. The most commonly used irreversible acyl donors are various types of vinyl esters. During the acylation of the enzyme, vinyl alcohols are liberated, which rapidly tautomerize to non-nucleophilic carbonyl compounds (Scheme 4.5). The acyl-enzyme then reacts with the racemic nucleophile (e.g., an alcohol or amine). Many vinyl esters and isopropenyl acetate are commercially available, and others can be made from vinyl and isopropenyl acetate by Lewis acid- or palladium-catalyzed reactions with acids [10-12] or from transition metal-catalyzed additions to acetylenes [13-15]. If ethoxyacetylene is used in such reactions, R1 in the resulting acyl donor will be OEt (Scheme 4.5), and hence the end product from the acyl donor leaving group will be the innocuous ethyl acetate [16]. Other frequently used acylation agents that act as more or less irreversible acyl donors are the easily prepared 2,2,2-trifluoro- and 2,2,2-trichloro-ethyl esters [17-23]. Less frequently used are oxime esters and cyanomethyl ester [7]. S-ethyl thioesters such as the thiooctanoate has also been used, and here the ethanethiol formed is allowed to evaporate to displace the equilibrium [24, 25]. Some anhydrides can also serve as irreversible acyl donors. 

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