Olefin oxidative carboxylation

Carboxylation/Oxidation of Straight-Chain 1-Olefins. Selective carboxylation of a-olefins to predominately straight-chain aldehydes is realized through specific catalyst systems and by careful control of reaction conditions. The aldehyde produced is then air-oxidized to the acid using a Mn catalyst. Heptanoic acid [111-14-8] and pelargonic acid [112-05-0] are produced commercially in this manner. 

Lee and Chang (1978) have compared the ability of linear polyethers, crown ethers, and quaternary ammonium compounds to catalyse oxidations with KMn04 under liquid-liquid and liquid-solid conditions. In the presence of acetic acid as a scavenger for the KOH produced, the products of olefin oxidation were carboxylic acids, diones, diols and ketols. The three different classes of catalysts exhibited about the same activity in liquid-solid systems. 

Palladium (II)-Nucleophile Addition across Olefins. Adding palladium complexes to olefins, either in the presence of an external nucleophile or a ligand which is attached to palladium, produces a palladium-carbon sigma-bonded complex which is not usually isolated in the case of monoolefins. Instead it decomposes and in doing so oxidizes the olefin to an organic carbonyl compound or a vinyl compound, exchanges a substituent group on the olefin, isomerizes the double bond, arylates (alkylates) the olefin, or carboxylates the olefin (2, 3). 

While die above reactions will provide carboxylic acid products, each has problems associated with it. The cleavage of olefins to carboxylic acids [reaction (7.1)] can be carried out using potassium permanganate or by ozonolysis at low temperature followed by oxidative workup with hydrogen peroxide. Neither of diese mediods is very useful since only symmetric olefins provide a single carboxylic acid product. Unsymmetrical olefins give a mixture of two acids which must be separated. Furthermore the most useful synthetic processes are those which build up structures, whereas these reactions are degradative in nature. 

The oxidative carboxylation of olefins appears to be a very interesting synthetic methodology for synthesizing CCs, starting from cheap and easily available reagents such as C02 and 02 (Equation 7.16). 

The direct oxidative carboxylation of olefins has great potential, and many advantages. Notably, it does not require the C02 to be free of dioxygen this is an especially attractive feature, as the cost to purify C02 is extremely high, and may discourage its use. Moreover, the direct oxidative carboxylation of olefins can couple two processes-the epoxidation of olefins, and the carbonation of epoxides. Hence, the process makes direct use of those olefins that are available commercially at low price, and which represent an abundant feedstock. Such an approach also avoids having to isolate the epoxide. 

Work on the pyridine-modified ozonization of tetramethylethylene showed that pyridine oxide is not-a product of ozonization (8). Most of the pyridine (— 90% ) remains unchanged during double bond cleavage. Only one mole of acetone, rather than two, is formed for each mole of olefin oxidized. Other work with a disubstituted olefin, trans-4-octene, showed that ozonides are formed in the reaction so that the reaction of pyridine with ozonide to form acid and aldehyde cannot occur (9). An NMR study of trans-4-octene ozonolysis in the presence of pyridine using 1,2-dichloroethane as the solvent shows that aldehyde and hydroxyl-containing material (carboxylic acid, peracid, and other OH species) are formed directly during double bond cleavage. 

Another product of the reaction of an olefin with the O2/ CO2 mixture in the presence of Rh is the cyclic carbonate (VII) [3]. Only few reports can be found in the literature on the direct synthesis of carbonates from olefins, dioxygen and carbon dioxide, despite the usefulness of this reaction that avoids, with respect to the reaction of epoxides with carbon dioxide, the preliminary synthesis of epoxides. We have found that the product distribution in the oxidative carboxylation of styrene depends on the O2/ CO2 ratio and on the temperature (Scheme 3). As the epoxide is one of the oxidation products of styrene, it could be the origin of styrene carbonate. We have evidence that the formation of the... 

Barbier-Wieland degradation. Stepwise carboxylic acid degradation of aliphatic acids (particularly in sterol side chains) to the next lower homo log. The ester is converted to a tertiary alcohol that is dehydrated with acetic anhydride, and the olefin oxidized with chromic acid to a lower homologous carboxylic acid. 

Better yields are often obtained when ozone is used for oxidative cleavage of olefins to carboxylic acids or of cycloalkenes to dicarboxylic acids. Olefinic double bonds are very much more easily attacked by ozone than are aromatic systems, so that arylethylene derivatives can be successfully treated with ozone without appreciable effect on the ring. If the ozonide which is formed initially is decomposed with water, the aldehyde is obtained together with hydrogen peroxide and other products ... 

To convert olefins into carboxylic acids in this way it is preferable to oxidize the primary fission products of the ozonide in a subsidiary reaction. Particularly good results were obtained by Asinger using a hot suspension of silver oxide116 and by Wilms using peracetic acid 117 Wilms thus obtained adipic acid in yields of about 90% from cyclohexene ... 

Over the last decade, a considerable number of reactions has been studied (11,35) (i) olefins oxidation (38,39), hydroboration, and halogenation (40) (ii) amines silylation (41,42), amidation (43), and imine formation (44) (iii) hydroxyl groups reaction with anhydrides (45), isocyanates (46), epichloro-hydrin and chlorosilanes (47) (iv) carboxylic acids formation of acid chlorides (48), mixed anhydrides (49) and activated esters (50) (v) carboxylic esters reduction and hydrolysis (51) (vi) aldehydes imine formation (52) (vii) epoxides reactions with amines (55), glycols (54) and carboxyl-terminated polymers (55). A list of all the major classes of reactions on SAMs plus relevant examples are discussed comprehensively elsewhere (//). The following sections will provide a more detailed look at reactions with some of the common functional SAMs, i.e hydroxyl and carboxyl terminated SAMs. 

Kurth et al. 2002 Stigers and Tew 2003). One of them involves the oxidation of unsaturated PHAs i.e. poly[(/ )-3-hydroxyoctanoate-co-(/ )-3-hydroxyundecenoate] with KMnO in the presence of NaHCOj (Lee and Park 2000). Although it allowed the transformation of 50% of the olefins into carboxylic functions, this method involves a decrease in the molecular weight of the polymer. 

The oxidations of olefins with many oxygen nucleophiles other than water have also been reported. These reactions include the s5mthesis of vinylic and allylic ethers from reactions of olefins with alcohols and phenols, and vinylic and allylic esters from reactions of olefins with carboxylic acids. These reactions have been conducted with both monoenes and 1,3-dienes. Both intermolecular and intramolecular versions of each of these processes have been developed. Some discussion of these reactions was included in Chapter 11 because of their connection to the nucleophilic attack of oxygen nucleophiles on coordinated olefins and dienes. 

Intermolecular Additions of Alcohois and Carboxylates The intermolecular oxidations of olefins with alcohols as nucleophile typically generate ketals, whereas the palladium-catalyzed oxidations of olefins with carboxylic acids as nucleophile generates vinylic or allylic carboxylates. As a result, many of the oxidations with alcohols have been conducted with diols to generate stable cyclic acetal products. Both types of oxidations have been conducted on large industrial scale, and vinyl acetate is produced from the oxidative reaction of ethylene with acetic acid in the gas phase over a supported palladium catalyst. ... 

Examples of the oxidative reactions of olefins with carboxylic acids are shown in Equations 16.107-16.109. These examples illustrate the selectivities of the oxidations of ethylene, acylic alkenes, and cyclic alkenes. The reactions of alkenes with carboxylic adds generate either vinylic esters or allylic esters. 

The invention of the new methodology by White and coworkers was based on the hypothesis that site-selective oxidations of unactivated sp C—H bonds could be predictably controlled using a suitably reactive metal catalyst capable of discriminating subtle electronic and steric differences between C—H bonds in complex substrates much like Sharpless seminal work on site-selective olefin oxidations using electrophilic metal catalysts. White and coworkers demonstrated that the site of oxidation with the Fe(S, S-PDP) catalyst could be predicted in complex organic substrates on the basis of electronic and steric environments of the C—H bonds. Preexisting carboxyl-ate functionality could direct oxidation toward five-membered lactone formation. 

Antonelli, E., D Aloisio, R., Gambaro, M., et al. (1998). Efficient Oxidative Cleavage of Olefins to Carboxylic Acids with Hydrogen Peroxide Catalyzed by Methyltrioctylammonium Tetrakis(oxodiperoxotungsto)phosphate(3-) under Two-phase Conditions. Synthetic Aspects and Investigation of the Reaction Course, J. Org. Chem., 63, pp. 7190-7206. 

Oxidative Carboxylation of Olefins to Afford Cyclic Carbonates... 

The direct oxidative carboxylation of olefins [108-110] couples two processes, namely (1) the epoxidation of the olefins and (2) the carbonation of the epoxide, occurring in the same reactor. Interestingly, it has been shown that CO2 modulates the oxidant properties of O2 [111]. 

Aresta M, Dibenedetto A (2002) Carbon dioxide as building block for the synthesis of organic carbonates behavior of homogeneous and heterogeneous catalysts in the oxidative carboxylation of olefins. J Mol Catal 182-183 399-409... 

Aresta M, Dibenedetto A, Tommasi I (2000) Direct synthesis of organic carbonates by oxidative carboxylation of olefins catalyzed by metal oxides developing green chemistry based on carbon dioxide. Appl Organomet Chem 14 799-802... 

Therefore, the direct synthesis of cyclic carbonates from olefins instead of epoxides, a so-called one-pot "oxidative carboxylation" of olefins, would be appealing. The oxidative carboxylation synthesis from olefins can be roughly viewed as the coupling of two sequential processes of epoxidation of olefins and CO2 cycloaddition to epoxides formed (Scheme 18). The reaction uses easily available and low-priced chemicals of olefins as substrates and, moreover, preliminary synthesis and separation of epoxides would be avoided. So, the oxidative carboxylation would be a simpler and cheaper carbonate synthesis process with industrial potential from environmental and economic points of view. Although the three-component couplings have been known at least since 1%2 [66], up to date, only a few works have been made on these reactions in contrast to extensive studies on the addition reactions of CO2 to epoxides in ILs as catalyst/or solvent. 

The oxidative carboxylation of olefins to cyclic carbonates can proceed through the first step of epoxidation of olefins and the subsequent cycloaddtion of CO2 to epoxides formed (Scheme 18). Thus it is supposed that a system of combining catalysts effective for the first step and for the second one would be effective for the direct synthesis of cyclic carbonates via the oxidative carboxylation of olefins. Indeed the direct preparation of carbonates was successfully achieved with a few catalyst systems including ILs coupled with oxidation catalysts. One patent [66] reported that the cyclic carbonate was formed from an olefin, CO2, and oxygen in the presence of dual catalysts. The catalyst system includes a heavy metal compound and a quaternary ammonium hydroxide or haUde. However, the heavy metal compounds would easily induce the corrosion of equipments and result in the undesired reduction of activity and selectivity. 

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