Hydroperoxides aldehydes

It provides the fast transformation of intermediate products (hydroperoxide, aldehydes) into the final product, viz., acid. 

The health impairing and toxic elfects of oxidation of lipids are due to loss of vitamins, polyenoic fatty acids, and other nutritionally essential components formation of radicals, hydroperoxides, aldehydes, epoxides, dimers, and polymers and participation of the secondary products in initiation of oxidation of proteins and in the Maillard reaction. Dilferent oxysterols have been shown in vitro and in vivo to have atherogenic, mutagenic, carcinogenic, angiotoxic, and cytotoxic properties, as well as the ability to inhibit cholesterol synthesis (Tai et ah, 1999 Wpsowicz, 2002). 

The oxygen atom reacts with 02 to produce ozone. Both O and 03 react with organic materials to produce peroxides, hydroperoxides, aldehydes, and other toxic substances. An excellent review of the photochemistry of air pollution has been given by Leighton.278... 

In summary, the main products derived from these photochemical reactions are O3, peroxides (e.g., PAN, PBN, and H202), hydroperoxides, aldehydes, ketones, alcohols, nitro compounds (alkyl and benzyl nitrates and nitrites), and acids such as sulfuric, nitric, and nitrous acid. 

The large number of precursors of volatile decomposition products affecting the flavor of oils has been discussed in Chapter 4. Only qualitative information is available on the relative oxidative stability of hydroperoxides, aldehydes and secondary oxidation products. As observed with the unsaturated fatty ester precursors, the stability of hydroperoxides and unsaturated aldehydes decreases with higher unsaturation. Different hydroperoxides of unsaturated lipids, acting as precursors of volatile flavor compounds, decompose at different temperatures. Hydroperoxides of linolenate and long-chain n-3 PUFA decompose more readily and at lower temperatures than hydroperoxides of linoleate and oleate. Similarly, the alkadienals are less stable than alkenals, which in turn are less stable than alkanals. The short-chain fatty acids produced by oxidation of unsaturated aldehydes will further decrease the oxidative stability of polyunsaturated oils. For secondary products, dimers are less stable than dihydroperoxides, which are less stable than cyclic peroxides. 

In contrast to oxidation in water, it has been found that 1-alkenes are directly oxidized with molecular oxygen in anhydrous, aprotic solvents, when a catalyst system of PdCl2(MeCN)2 and CuCl is used together with HMPA. In the absence of HMPA, no reaction takes place(100]. In the oxidation of 1-decene, the Oj uptake correlates with the amount of 2-decanone formed, and up to 0.5 mol of O2 is consumed for the production of 1 mol of the ketone. This result shows that both O atoms of molecular oxygen are incorporated into the product, and a bimetallic Pd(II) hydroperoxide coupled with a Cu salt is involved in oxidation of this type, and that the well known redox catalysis of PdXi and CuX is not always operalive[10 ]. The oxidation under anhydrous conditions is unique in terms of the regioselective formation of aldehyde 59 from X-allyl-A -methylbenzamide (58), whereas the use of aqueous DME results in the predominant formation of the methyl ketone 60. Similar results are obtained with allylic acetates and allylic carbonates[102]. The complete reversal of the regioselectivity in PdCli-catalyzed oxidation of alkenes is remarkable. 

Oxidation begins with the breakdown of hydroperoxides and the formation of free radicals. These reactive peroxy radicals initiate a chain reaction that propagates the breakdown of hydroperoxides into aldehydes (qv), ketones (qv), alcohols, and hydrocarbons (qv). These breakdown products make an oxidized product organoleptically unacceptable. Antioxidants work by donating a hydrogen atom to the reactive peroxide radical, ending the chain reaction (17). 

Usually, organoboranes are sensitive to oxygen. Simple trialkylboranes are spontaneously flammable in contact with air. Nevertheless, under carefully controlled conditions the reaction of organoboranes with oxygen can be used for the preparation of alcohols or alkyl hydroperoxides (228,229). Aldehydes are produced by oxidation of primary alkylboranes with pyridinium chi orochrom ate (188). Chromic acid at pH < 3 transforms secondary alkyl and cycloalkylboranes into ketones pyridinium chi orochrom ate can also be used (230,231). A convenient procedure for the direct conversion of terminal alkenes into carboxyUc acids employs hydroboration with dibromoborane—dimethyl sulfide and oxidation of the intermediate alkyldibromoborane with chromium trioxide in 90% aqueous acetic acid (232,233). 

The simple hydroperoxide mechanism so far discussed is incomplete for representing reactions with significant products other than hydroperoxides. It can be adequate for oxidations of certain unsaturates, aldehydes, and alkylaromatics where the yield of the corresponding hydroperoxide can exceed 90%. 

Browning Reactions. The fluorescent components formed in the browning reaction (8) of peroxidized phosphatidylethanolamine are produced mainly by interaction of the amine group of PE and saturated aldehydes produced through the decomposition of fatty acid hydroperoxides. 

Oxidation. Olefins in general can be oxidized by a variety of reagents ranging from oxygen itself to ozone (qv), hydroperoxides, nitric acid (qv), etc. In some sequences, oxidation is carried out to create a stable product such as 1,2-diols or glycols, aldehydes, ketones, or carboxyUc acids. In other... 

Bases, such as potassium or sodium hydroxide, piperidine, and pyridine, react with primary and secondary hydroperoxides to form aldehydes or ketones (28). In some cases, this reaction is slow or fails unless heating is employed. 

Hydroxyall l Hydroperoxides. These compounds, represented by (1, X = OH, R = H), may be isolated as discreet compounds only with certain stmctural restrictions, eg, that one or both of R and R are hydrogen, ie, they are derived from aldehydes, or that R or R contain electron-withdrawing substituents, ie, they are derived from ketones bearing a-halogen substituents. Other hydroxyalkyl hydroperoxides may exist in equihbrium mixtures of ketone and hydrogen peroxide. 

Hydroxyalkyl hydroperoxides having at least one a-hydrogen ie, (7, X = OH, R = alkyll, R = R = H), ie, those derived from aldehydes, lose hydrogen peroxide and form dialkyl peroxides (2, X = Y = OH), especially in the presence of water ... 

Acidic hydrolysis of these hydroxyaLkyl hydroperoxides yields carboxyUc acids, whereas basic hydrolysis regenerates the parent aldehyde, hydrogen peroxide, and often other products. When derived from either aldehydes or cycHc ketones, peroxides (1, X = OH, = H, R, = alkylene or... 

In the presence of strong acid catalysts such as sulfuric acid, aUphatic (R CHO) aldehydes react with alkyl hydroperoxides, eg, tert-55ky hydroperoxides, to form hydroxyalkyl alkyl peroxides (1), where X = OH R, = hydrogen, alkyl and = tert — alkyl. 

Polymeric OC-Oxygen-Substituted Peroxides. Polymeric peroxides (3) are formed from the following reactions ketone and aldehydes with hydrogen peroxide, ozonization of unsaturated compounds, and dehydration of a-hydroxyalkyl hydroperoxides consequendy, a variety of polymeric peroxides of this type exist. Polymeric peroxides are generally viscous Hquids or amorphous soHds, are difficult to characterize, and are prone to explosive decomp o sition. 

Physical and Chemical Properties. The (F)- and (Z)-isomers of cinnamaldehyde are both known. (F)-Cinnamaldehyde [14371-10-9] is generally produced commercially and its properties are given in Table 2. Cinnamaldehyde undergoes reactions that are typical of an a,P-unsaturated aromatic aldehyde. Slow oxidation to cinnamic acid is observed upon exposure to air. This process can be accelerated in the presence of transition-metal catalysts such as cobalt acetate (28). Under more vigorous conditions with either nitric or chromic acid, cleavage at the double bond occurs to afford benzoic acid. Epoxidation of cinnamaldehyde via a conjugate addition mechanism is observed upon treatment with a salt of /-butyl hydroperoxide (29). 

Aromatic aldehydes and cyclic perfluoroketones are oxidized to a-hydroxy hydroperoxides or bis(a-hydroxy) peroxides, aliphatic ketones are converted to esters, and ketenes are converted to a-lactones... 

The a-hydroxy hydroperoxides obtained by the above reacbon (equation 61) can oxidize highly fluonnated aliphatic aldehydes [70] (equation 62)... 

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