Application of the Olefin Oxidation to Organic Syntheses

Glycol derivatives, e.g., 2-chloroethanol (eq. (31)) are to a small extent byproducts in the technical olefin oxidation. With a very high concentration (ca. 5 mol/L) of cupric chloride and high pressure, 2-chloroethanol is the main product of ethylene oxidations, besides some acetaldehyde [33]. Cupric chloride is essential. In its absence, in spite of a high chloride ion concentration absolutely no 2-chloroethanol is obtained. It is assumed that analogously to acetaldehyde formation a y9-hydroxyethyl species bonded to a bi- or oligo-Pd-Cu cluster is an intermediate from which 2-chloroethanol is liberated by reductive elimination. 

2-Chloroethanol is also formed from ethylene in the presence of pyridine and necessarily cupric chloride even with low chloride ion concentration [55], whereas in the absence of CUCI2 acetaldehyde is the sole product. With chiral amines and phosphines as ligands instead of pyridine, optically active chlorohydrins can be obtained from higher a-oleftns [56, 57]. 

A heterogenized PdS04-VOS04-H2S04-on-coal catalyst has been described 

Quite a surprising reaction has recently been reported [74]. With a catalyst of palladium metal on carbon in aqueous phase, propene is oxidized with oxygen to give acrylic acid, probably via allyl alcohol in a allylic-type oxidation (for allylic oxidation see Section 3.3.14). In the presence of chloride or oxidants the normal Wacker-type reaction product acetone arises. 

Palladium reagents have been proved most variable and useful in organic synthesis and it may be expected that this progress has not yet come to an end. Among the different synthetic reaction types, acetoxylation has gained particular importance in preparative as well as in technical application (see Section 3.3.14). 

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