Ketones alkene oxidations, palladium chloride

PdCl2/CuCl2/02 (Wacker oxidation) (palladium chloride/cupric chloride/oxygen) Sulpholane/water RT to 100 terminal alkenes-> methyl ketones... 

Lead tetraacetate initiates a similar type of oxidation with terminal alkenes, in the presence of acid, to give an aldehyde hy selective oxidation of the terminal carhon. l Ajj example is the conversion of styrene to phenylacetaldehyde in 98% yield. Palladium chloride (PdCl2) reacts with terminal alkenes, in the presence of oxygen and copper salts, to give a methyl ketone (this reaction is called the Wacker process and is discussed in sec. 12.6.A). It is more useful than the LTA oxidation. Oxidation of terminal alkenes with LTA leads to the aldehyde, whereas oxidation with PdCl2 leads to the methyl ketone. The PdCl2 oxidation is illustrated hy conversion of 402 to 403 in 77% yield, in Ikegami s synthesis of coriolin. ... 

The oxidation of ethylene to acetaldehyde employing palladium chloride and cupric chloride as catalysts and molecular oxygen as oxidant. The reaction has been extensively developed for the oxidation of terminal alkenes to methyl ketones ... 

Oxidation. The use of l,4-ben2oquinone in combination with paHadium(Il) chloride converts terminal alkenes such as 1-hexene to alkyl methyl ketones in high yield (81%) (32). The quinone appears to reoxidi2e the palladium. 

The metal-catalysed autoxidation of alkenes to produce ketones (Wacker reaction) is promoted by the presence of quaternary ammonium salts [14]. For example, using copper(II) chloride and palladium(II) chloride in benzene in the presence of cetyltrimethylammonium bromide, 1-decene is converted into 2-decanone (73%), 1,7-octadiene into 2,7-octadione (77%) and vinylcyclohexane into cyclo-hexylethanone (22%). Benzyltriethylammonium chloride and tetra-n-butylammo-nium hydrogen sulphate are ineffective catalysts. It has been suggested that the process is not micellar, although the catalysts have the characteristics of those which produce micelles. The Wacker reaction is also catalysed by rhodium and ruthenium salts in the presence of a quaternary ammonium salt. Generally, however, the yields are lower than those obtained using the palladium catalyst and, frequently, several oxidation products are obtained from each reaction [15]. 

In new studies heteropoly acids as cocatalysts were found to be very effective in combination with oxygen in the oxidation of ethylene.1311 Addition of phosphomo-lybdic acid to a chloride ion-free Pd(II)-Cu(II) catalyst system results in a great increase in catalytic activity and selectivity.1312 Aerobic oxidation of terminal alkenes to methy ketones can be performed with Pd(OAc)21313 or soluble palladium complexes. Modified cyclodextrins accelerates reaction rates and enhance selectivities in two-phase systems under mild conditions.1315 1316... 

One of the earliest uses of palladium(II) salts to activate alkenes towards additions with oxygen nucleophiles is the industrially important Wacker process, wherein ethylene is oxidized to acetaldehyde using a palladium(II) chloride catalyst system in aqueous solution under an oxygen atmosphere with cop-per(II) chloride as a co-oxidant.1,2 The key step in this process is nucleophilic addition of water to the palladium(II)-complexed ethylene. As expected from the regioselectivity of palladium(II)-assisted addition of nucleophiles to alkenes, simple terminal alkenes are efficiently converted to methyl ketones rather than aldehydes under Wacker conditions. 

The combination of silicon hydrides and a Pd° catalyst is essentially useless for reduction of electron-deficient alkenes. However, addition of catalytic amounts of zinc chloride creates a new three-component mixture that enables rapid conjugate reduction of a,p-unsaturated ketones and aldehydes. In fact, soluble palladium complexes of various oxidation states were equally efficient catalysts, an obvious practical advantage of this approach. The generality of the method with respect to the substrate, its experimental simplicity, and its easy applicability to large-scale work make it a method of choice for conjugate reduction of unsaturated ketones and aldehydes. 

Cuprous chloride CuCl (mp 430 °C), when complexed with amines such as pyridine or phenanthroline, catalyzes the oxidation of alcohols to aldehydes and ketones by air [347]. In the presence of palladium dichloride, l dCl2, in aqueous dimethylformamide, terminal alkenes are converted by oxygen into methyl ketones [348],... 

The Wacker oxidation of ethene to ethanal is an important industrial process for the oxygenation of a hydrocarbon feedstock. Essentially, the same process may be used to convert 1-alkenes to methyl ketones. The stoichiometry of the process is shown in Figure 23.23. The reaction is catalytic in both palladium and copper the ultimate oxidant is (inexpensive) molecular oxygen. A proposed mechanism is shown in Figure 23.24 the main controversy has been as to whether the attack of water on the coordinated alkene is external or via prior coordination of the water to palladium. Current thinking is that external attack predominates in high concentrations of chloride ion and internal attack when [CT] is low. Different details of mechanisms under the two conditions are supported by different reaction kinetics. 

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