Alkenes to carboxylic acids

Esters can be formed when the hydrocarbonylation reaction is carried out in an alcohol.242 Although hydrocarbonylation is the basis for conversion of alkenes to carboxylic acids on an industrial scale, it has seen only limited application in laboratory synthesis. 

The reaction of alcohols with CO was catalyzed by Pd compounds, iodides and/or bromides, and amides (or thioamides). Thus, MeOH was carbonylated in the presence of Pd acetate, NiCl2, tV-methylpyrrolidone, Mel, and Lil to give HOAc. AcOH is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a Pd compound, an ionic Br or I compound other than HBr or HI, a sulfone or sulfoxide, and, in some cases, a Ni compound and a phosphine oxide or a phosphinic acid.60 Palladium(II) salts catalyze the carbonylation of methyl iodide in methanol to methyl acetate in the presence of an excess of iodide, even without amine or phosphine co-ligands platinum(II) salts are less effective.61 A novel Pd11 complex (13) is a highly efficient catalyst for the carbonylation of organic alcohols and alkenes to carboxylic acids/esters.62... 

Non-oxidative hydrocarboxylation of alkenes to carboxylic acids with CO and H20 is catalyzed by palladium complexes such as PdCl2(PhCN)2 or PdCl2(PPh3)2, and a-methyl acids predominate in the presence of HC1.374,443 A recent improvement of this reaction consisted of the use of a PdCl2/CuCl2/HCl catalyst under oxidative conditions.377 Almost quantitative yields of a-methyl carboxylic acids and dicarboxylic acids were obtained from terminal alkenes and terminal dialkenes respectively, at room temperature and atmospheric pressure (equation 174).377... 

This system is highly efficient for cleavage of alkenes to carboxylic acids (75-95% yield). Examples are given of some other oxidations now possible with Ru04.2... 

Oxidative cleavage of alkenes to carboxylic acids.1 Alkenes are oxidized to carboxylic acids by H202 (35%) catalyzed by H2W04 in a weakly acidic medium (pH 4-5) maintained by addition of KOH. The oxidation probably involves initial oxidation to a 1,2-diol followed by dehydrogenation to an a-ketol, which is then cleaved to a mono- or dicarboxylic acid. 

The direct conversion of alkenes to carboxylic acids using dirhenium heptoxide in a solution of acetic anhydride and dioxane is illustrated below for the oxidative cleavage of 1-octene to form n-heptanoic acid (2) ... 

Sodium permanganate monohydrate, NaMn04 H20, which is commercially available, is used for the oxidation of alkenes to carboxylic acids [834] and of alcohols to carbonyl compounds [SJ5], the conversion of sul-finic acids into sulfonic acids [836], and the selective oxidation of sulfoxides to sulfones (sulfides are not oxidized with sodium permanganate in dioxane solutions) 837. ... 

Oxidations of halogenated alkenes to carboxylic acids are discussed in a previous section, Oxidative Cleavage of Double Bonds (equations 118-120). 

Addition of carbon monoxide and water to an alkene, i.e. hydrocarboxylation, is catalyzed by a variety of transition metal complexes, including [Ni(CO)4], [Co2(CO)s] and [HaPtClg]. Unfortunately this reaction usually leads to mixtures of products due to both metal-catalyzed alkene isomerization and the occurrence of Irath Markownikov and anti-Markownikov addition of the metal hydride intermediate to the alkene. The commercially available zirconium hydride [(C5Hs)2Zr(H)Cl] can be used as a stoichiometric reagent for conversion of alkenes to carboxylic acids under mild conditions (equation 23). In this case the reaction with linear alkenes gives exclusively terminal alkyl complexes even if the alkene double bond is internal. Insertion of CO followed by oxidative hydrolysis then leads to linear carboxylic acids in very good yield. 

This species, completely characterized also by X-ray diffraction studies as its tetrahexylammonium salt (Figure 1)5 was responsible for the epoxidation of a series of structurally diversified olefins with typical selectivities of ca. 95% and chemical yields in the range 85-95%. These catalysts have found industrial applications in the epoxidation of alkenes and in the oxidative cleavage of alkenes to carboxylic acids. The favourable characteristics of these catalysts are thermal stability, ease of synthesis, stability to oxidation, solubility- in both water and organic solvents, effectiveness as phase transfer catalysts. 

The following modifications of substituents without alteration of the pyrido[3,4-r]pyridazine system have been performed oxidation alkenes to carboxylic acids (ArCH=CHPh - ArC02H) 104 condensation methyl groups with carbaldehydes (ArMe- ArCH = CHPh) Ar = pyridolT -elpyridazinyl.104... 

Standard oxidation of alkyldibromoboranes with alkaline hydrogen peroxide affords alcohols. Conversion of terminal alkenes to carboxylic acids using alkyldibromoboranes works well, although hydrolysis prior to oxidation is needed." Chiral alkyldibromoboranes have been used as catalysts for the asymmetric Diels-Alder reaction. 

Nonoxidative hydrocarboxylation of alkenes to carboxylic acids with CO and water catalyzed by Pd catalysts is greatly improved in the presence of oxygen (Scheme 16). Almost quantitative yields of mono- and dicarboxylic adds were obtained from the corresponding terminal alkenes and terminal dialkenes, respectively, under atmospheric pressure at room temperature. ... 

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