Reppe-Type Chemistry

After discussing in detail the specific aspects of Reppe s chemistry and of hydroformylation and related reactions, it is quite interesting to examine the general mechanistic implications of these two types of reactions. 

Ni-organic chemistry of butadiene started in the early 1950 s when this substrate could be slowly dimerized to cis, cis-cycloocta-l,5-diene in relatively low yields ( 40%) by using so-called Reppe catalysts of the type L2Ni (CO)2. Carbonyl-free low-valent Ni-complexes and catalysts on the basis of Cr and Ti were more effective and also led to further ring-syntheses (Scheme 1-1)... 

The term carbonylation was first used by W.Reppe while working with syngas and carbon monoxide chemistry at BASF during the 1930s and 1940s. Carbonylations are catalytic reactions in which carbon monoxide, alone or with other compounds, is incorporated in an organic substrate. There are three general types of carbonylation reactions Reppe reactions, hydroformylations, and Koch carbonylations. 

Hydroformylation is the reaction of carbon monoxide and hydrogen with olefins to produce aldehydes and derivative alcohols. It is also known as 0X0 chemistry and the alcohol products produced by this method are known as 0X0 alcohols. Of all three types of carbon monoxide reactions, Reppe reactions, Koch carbonylations, and hydroformylations, oxo chemistry currently has the greatest commercial importance. An extremely broad range of products and end use markets are served by the aldehydes, alcohols, and derivatives produced by hydroformylation. The list of products shown in Table 6 illustrates the range of oxo chemical products. 

Similar reactions are possible with acetylenic and alcoholic substrates, but the former (an industrial component of Reppe chemistry which held sway for a number of years) are no longer of any practical importance. These specific types of carbonylation are referred to as hydroxycarboxylation. We shall very briefly consider some important reactions belonging to these classes. 

Like many carbonylation processes, the hydrocarboxylation and hydroesterification reactions were first reported by Reppe. These first reactions involved the hydrocarboxylation of alkynes. These reactions were conducted with nickel carbonyl as catalyst and occurred with very low turnover numbers. Hydrocarboxylation and hydroesterification have now been studied extensively in both academic and industrial laboratories. As a result of these investigations, commercialization of this chemistry as part of new industrial processes has occurred, and the mechanism of these processes is now generally accepted. This section of Chapter 17 presents the scope and industrial applications of hydrocarboxylation and hydroesterification, the types of catalysts that have been used for these processes, and the elementary steps that constitute the catalytic cycle for olefin and alkyne hydroesterification. 

---