Oxidation carbonyl derivatives, release

Free cyclobutadiene has been detected in solution using an insoluble polymer-bound precursor, with trapping of the cyclobutadiene by a second polymer-bound reagent. As only a negligible fraction of the active polymer sites are at the surface of the solid, any reaction between the two solid phases requires the existence of an unbound intermediate. The cyclobutadiene precursor, a polymer-bound < -phenan-throline derivative of cyclobutadieneiron carbonyl (580) was oxidized in presence of a polymer-bound maleimide (581). The imide was then released from the polymer by treatment with methylamine. The reaction proceeds with 96% transfer of cyclobutadiene between the two polymers. 

In reaction with benzaldehyde or its dimethyl acetal, or benzylidene dibromide, sucrose undergoes conversion into its 4,6-acetal in moderate yield (28-35%).160,161 The transacetalation reaction of dialkyl acetals prepared from unsaturated or aromatic aldehydes can take place under very mild acidic conditions. For example, sucrose-derived monomers or surfactants (variously substituted 4,6-(9-methylidenesucroses) have been prepared146,162 and 4,6-monoacetals incorporating masked aromas or fragrances derived from p-citral or a- or p-ionone were prepared directly from sucrose in high yields.163,164 These latter molecules, whose unsaturated carbonyl system is very susceptible to oxidation, are thus temporarily protected and are readily released under very mild conditions (Scheme 13). 

Other studies also give an extensive analysis of by-product identification. The work of Dowideit and Von Sonntag [187] is a good example. These authors studied the ozonation of ethylene and some methyl- and chlorine-substituted derivatives. They showed that these compounds are practically removed via Criegge mechanism (see Fig. 3) to yield a carbonyl compound and a hydroxyhydroperoxide, which, in the case of chlorine-substituted derivatives, rapidly releases HC1. It should be remembered that in the case of saturated VOCs, hydroxyl radical is the main route of oxidation regardless of the presence of ozone. 

The structure of the food matrix is also known to affect the release of volatile compounds having an impact on flavors and aroma. Changes in flavor result from the interactions of lipid-derived carbonyl compounds by aldolization with the amino groups of proteins. Undesirable flavors are produced when beef or chicken are fried in oxidized fats by the interaction of secondary lipid oxidation... 

The reactions between the Group VI metal hexacarbonyls, representing relatively simple binary carbonyl complexes, and a variety of oxides is illustrative and also derives interest from the active alkene metathesis catalysts provided [20,21]. The initial interaction of Mo(C0)5 with silica has been monitored by infrared [22] and Raman [23] spectroscopies. The complex has been shown to be physisorbed in a similar environment to that adopted in a polar solvent and to have its symmetry lowered. At 44°C, in vacuo, this species is converted to a chemically bound carbonyl which itself is apparently decarbonylated. This is complete by 100 C, giving rise to an active propene metathesis catalyst [22]. Although no C-0 infrared absorptions are evident, only 3 CO groups per metal atom have been released [21], but the nature of the molybdentam in this yellow material is unclear. Some of the metal is EPR active, and this signal indicates a Mo site in an axially symmetric site, possibly square pyramidal [24]. The proportion of Mo increases to a maximum with an activation temperature of 200°C [25]. At that... 

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