Hydroperoxides cleavage

There are many variations of the basic process and the patent Hterature is extensive. Several key patents describe the technology (16). The process steps are oxidation of cumene to a concentrated hydroperoxide, cleavage of the hydroperoxide, neutralization of the cleaved products, and distillation to recover acetone. 

As this acid cleavage releases considerable heat, the apparatus used needs efficient heat exchange units [64]. Selectivity of the hydroperoxide cleavage is affected if temperature rises in an undesired manner. For this reason, not the technical 65-90 wt.-% solutions, but rather strongly diluted ones (e.g. below 10%) are employed. In the first case, a sudden loss of the heat exchange function could result in an temperature increase from 50 to 500 °C within seconds. 

A third possible fate of the alkoxy radical is shown in Scheme 18.3 (lower reaction) and was postulated by Grossetete et al. [11], In this reaction, the hydroxy radical in the cage from hydroperoxide cleavage yields an anhydride by extraction of the a-hydrogen to the radical. These workers cite IR evidence in support of this reaction which seems quite reasonable. In addition, the report by Valk et al. [21] of glycolic acid would seem to confirm this path as well. 

Figure 10-20 Lipoxygenase Catalyzed Formation of Aroma Compounds in Cucumber. Source Reprinted from Biochim. Biophys. Acta., Vol. 441, T. Galliard, D.R. Phillips, and J. Reynolds, The Formation of cw-3-nonenal, mwu-2-nonenal and Hexanol from Linoleic Acid Hydroperoxide Isomers by a Hydroperoxide Cleavage Enzyme System in Cucumber (Cucumis Sativus) Fruits, p. 184, Copyright 1976, with permission from Elsevier Science.

Galliard, T., et al. 1976. The formation of cw-3-none-nal, frarw-2-nonenal and hexanal from linoleic acid hydroperoxide isomers by a hydroperoxide cleavage enzyme system in cucumber (Cucumis sativus) fruits. Biochim. Biophys. Acta 441 181-192. 

Yeast-derived saturated short-medium chain and branched-chain aldehydes are formed from sugar metabolism, fatty acid metabolism and branched-chain amino acid metabolism (Fig 8D.7). In addition, hexanal, as well as hexenal isomers, are formed during the pre-fermentative stages of winemaking by the sequential action of grape lipoxygenase and hydroperoxide cleavage enzyme on linoleic and linolenic acid, respectively (Crouzet 1986). 

Formation of 2-Ethyl-2(5H) Furanone. The presence of artifacts with increased retention times suggests the formation of components of increased polarity and/or the formation of higher molecular weight constituents from condensation or addition reactions. The acids, aldehydes and alcohols present can undergo oxidation to form y- and 6-lactones (14, 15). The formation of the lactone, 5-ethyl-2(5H)-furanone, probably occurs by the steps outlined in Figure 4. A plausible sequence would be reaction of 2-hexenoic acid to form a peroxy radical at the y-position followed by production of the hydroperoxide. Cleavage of the 0-0 bond with the subsequent addition of H could lead to 4-hydroxy-2-hexenoic acid. Intramolecular esterification would then produce the identified lactone. 

When the desired product is an alkyl or aralkyl hydroperoxide or peracid, careful control of metal concentration is required to minimize hydroperoxide cleavage. When the reactant is an alcohol, the hydroperoxide is the hydrogen peroxide adduct of an aldehyde or ketone, i.e. 

The hydroperoxide cleavage enzyme from cucumber fruit is optimally active at pH 6.5, is very heat-labile, and attacks both 9- and 13-hydroperoxide isomers with equal facility. Subcellular localization studies have shown that the enzyme is associated mainly with the plasmalemma, Golgi body, and endoplasmic reticulum membranes (Wardale et al., 1978). 

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