Aldox reaction

The described reactions have been carried to technical production (Esso) under the name Aldox reaction, utilizing a condensation catalyst. Compounds of Zn, Sn, Ti, Zr, Hf, Th, Pb, Cd, Hg, A1 and Cu may also be used for this purpose [709, 715-717, 757, 758, 782-785]. Shell also produces these alcohols in a similar reaction and uses KOH as a condensation catalyst [707]. 

The same front-end Oxo process is used to make the butyraldehyde feed for 2-EH manufacture, but then the butyraldehyde is dimerized in a reaction called aldol condensation. Some plants even combine the Oxo process and the Aldol process and then refer to it as the Aldox process. 

Ethylhexanol is usually produced by subsequent aldolization of butyraldehyde produced in the oxo reaction followed by hydrogenation of the intermediate unsaturated aldehyde.89 In Esso s Aldox process, however, in situ aldol condensation is effected by suitable promoters.11 Magnesium ethoxide and soluble zinc compounds are recommended to promote controlled aldolization during the oxo reaction. The Shell variant uses potassium hydroxide. Serious disadvantages (mixed aldolization with the branched aldehyde, problems associated with recycling of the additives), however, prevented wider use of the Aldox process. 

Alcohols from an aldol reaction may be linear if acetaldehyde is a reactant, but usually aldol alcohols are branched primary alcohols. An aldol condensation sometimes is done with an OXO reaction. The combined process is called the ALDOX process. 

This so-called Aldox process, commercially performed by Shell as well as by Exxon [4, 35], is realized in a one-pot reaction by adding Ni and KOH as co-catalysts to the medium of the Co -catalyzed oxo reaction (cf. Section 2.1.1). 

Major intermediates include a hydroxyl amino acid, aldox-ime, nitrile, and an a-hydroxynitrile (Fig. 16.4) (Halkier and Mpller, 1990 Halkier et al., 1988). These mtermediates are observed only at extremely low levels in the plants which contain them. In the course of the biosynthetic studies, it was observed that the proposed intermediates were incorporated at very different and inconsistent rates. These differences in rate were inconsistent with the order of incorporation of the different intermediates. A channeled process has been proposed in which the compounds are not liberated from the enzyme surface (Conn, 1981). Channeling provides for the rapid and efficient flow of carbon and nitrogen atoms and at the same time perhaps protects labile intermediates from wasteful side reactions (( onn, 1981). 

The Aldox (aldolization-Hoxo reaction) process of Esso and Shell describes a one-pot transformation (Scheme 5.127) running with a phosphine-modified cobalt catalyst in the presence of additives such as Zn decanoate [13]. High yields... 

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