Peroxide-amine mechanism

The diacyl peroxide-amine system, especially BPO-DMT or BPO-DMA, has been used and studied for a long time but still no sound initiation mechanism was proposed. Some controversy existed in the first step, i.e., whether there is formation of a charge-transfer complex of a rate-controlling step of nucleophilic displacement as Walling 1] suggested ... 

Volume 17 covers gas-phase combustion, which includes probably the most complex processes investigated by chemists. Chapter 1, about half the book, deals with the oxidation of hydrogen and carbon monoxide, with extensive consideration of all the individual reactions occurring. In Chapter 2, the combustion of hydrocarbons is discussed, with emphasis on the general mechanisms which have been suggested to account for the numerous products of partial oxidation. In Chapter 3, the oxidation of aldehydes, which are important intermediates in combustion of other compounds, is considered, and in Chapter 4, the oxidation of alcohols, ketones, oxirans, ethers, esters, peroxides, amines and halocarbons. 

Heikkila R and Cohen G Inhibition of Biogenic Amine Uptake by Hydrogen Peroxide A Mechanism for Toxic Effects of 6-Hydroxydopamine. Science 1971 172 1257-58. 

The crosslinking is very rapid at first with the benzoyl peroxide-amine system, unless the concentration of tertiary amine (N,N-dimethyl aniline or N,N-dimethyl para-toluidine) is very low. But the reaction fades early, probably because of the retarding effect of the benzoic acid. The mechanical properties of the finished product tend not to match those obtained with the cobalt system. Also there is a yellowing of the resin as cure proceeds. Consequently, the hydroxide-cobalt(n) system is more widely used. One proposed mechanism is ... 

Decomposition Hazards. The main causes of unintended decompositions of organic peroxides are heat energy from heating sources and mechanical shock, eg, impact or friction. In addition, certain contaminants, ie, metal salts, amines, acids, and bases, initiate or accelerate organic peroxide decompositions at temperatures at which the peroxide is normally stable. These reactions also Hberate heat, thus further accelerating the decomposition. Commercial products often contain diluents that desensitize neat peroxides to these hazards. Commercial organic peroxide decompositions are low order deflagrations rather than detonations (279). 

Materials that promote the decomposition of organic hydroperoxide to form stable products rather than chain-initiating free radicals are known as peroxide decomposers. Amongst the materials that function in this way may be included a number of mercaptans, sulphonic acids, zinc dialkylthiophosphate and zinc dimethyldithiocarbamate. There is also evidence that some of the phenol and aryl amine chain-breaking antioxidants may function in addition by this mechanism. In saturated hydrocarbon polymers diauryl thiodipropionate has achieved a preeminent position as a peroxide decomposer. 

Organic peroxide-aromatic tertiary amine system is a well-known organic redox system 1]. The typical examples are benzoyl peroxide(BPO)-N,N-dimethylani-line(DMA) and BPO-DMT(N,N-dimethyl-p-toluidine) systems. The binary initiation system has been used in vinyl polymerization in dental acrylic resins and composite resins [2] and in bone cement [3]. Many papers have reported the initiation reaction of these systems for several decades, but the initiation mechanism is still not unified and in controversy [4,5]. Another kind of organic redox system consists of organic hydroperoxide and an aromatic tertiary amine system such as cumene hydroperoxide(CHP)-DMT is used in anaerobic adhesives [6]. Much less attention has been paid to this redox system and its initiation mechanism. A water-soluble peroxide such as persulfate and amine systems have been used in industrial aqueous solution and emulsion polymerization [7-10], yet the initiation mechanism has not been proposed in detail until recently [5]. In order to clarify the structural effect of peroxides and amines including functional monomers containing an amino group, a polymerizable amine, on the redox-initiated polymerization of vinyl monomers and its initiation mechanism, a series of studies have been carried out in our laboratory. 

Initiation Mechanism and Structural Effects of Amine and Peroxide... 

The chemistry of the di-/-butyl and cumyl peroxides is relatively uncomplicated by induced or ionic decomposition mechanisms. However, induced decomposition of di-/-butyl peroxide has been observed in primary or secondary alcohols31" "14 (Scheme 3.37) and primary or secondary amines.312 The reaction... 

A family of 3-aminosteroids reportedly inhibit lipid peroxidation while acting as anti-inflammatories. These activities were attributed to the combination of the steroid and the amine as neither component was, by itself, efiective (Spyriounis et /., 1993). In this sense, they resemble the 21-aminosteroid lazaroids. These 3-aminosteroids most probably inhibit lipid peroxidation through a physicochemical mechanism. 

The mechanism of H02 formation from peroxyl radicals of primary and secondary amines is clear (see the kinetic scheme). The problem of H02 formation in oxidized tertiary amines is not yet solved. The analysis of peroxides formed during amine oxidation using catalase, Ti(TV) and by water extraction gave controversial results [17], The formed hydroperoxide appeared to be labile and is hydrolyzed with H202 formation. The analysis of hydroperoxides formed in co-oxidation of cumene and 2-propaneamine, 7V-bis(ethyl methyl) showed the formation of two peroxides, namely H202 and (Me2CH)2NC(OOH)Me2 [16]. There is no doubt that the two peroxyl radicals are acting H02 and a-aminoalkylperoxyl. The difficulty is to find experimentally the real proportion between them in oxidized amine and to clarify the way of hydroperoxyl radical formation. 

The oxidation of primary and secondary alcohols in the presence of 1-naphthylamine, 2-naphthylamine, or phenyl-1-naphthylamine is characterized by the high values of the inhibition coefficient / > 10 [1-7], Alkylperoxyl, a-ketoperoxyl radicals, and (3-hydroxyperoxyl radicals, like the peroxyl radicals derived from tertiary alcohols, appeared to be incapable of reducing the aminyl radicals formed from aromatic amines. For example, when the oxidation of tert-butanol is inhibited by 1-naphthylamine, the coefficient /is equal to 2, which coincides with the value found in the inhibited oxidation of alkanes [3], However, the addition of hydrogen peroxide to the tert-butanol getting oxidized helps to perform the cyclic chain termination mechanism (1-naphthylamine as the inhibitor, T = 393 K, cumyl peroxide as initiator, p02 = 98 kPa [8]). This is due to the participation of the formed hydroperoxyl radical in the chain termination ... 

Some times even catalysts can include initiators to decompose into free radicals. In such type of reaction, an electron transfer mechanism is involved. Peroxides and hydroperoxides are decomposed in this way. For example, the decomposition of benzoyl peroxide by an aromatic tertiary amine at room temperature. 

Many different pathways, mechanisms, and enzymes are associated with activation. These include dehalogenation, AT-nitrosation of secondary amines, epoxidation, conversion of phosphothionates to phosphate, metabolism of phen-oxyalkanoic acids, oxidation of thioethers, hydrolysis of esters and peroxides. The following is a summary. 

It was postulated [152, 153] that the aryl amine is oxidized by direct oxygen transfer from Compound I to the substrate. In contrast, for the oxidation of alkaloids, e.g. morphine, codeine and thebaine (Eq. 12), to the corresponding N-oxi-des by hydrogen peroxide in the presence of HRP or crude enzyme preparation from poppy seedlings, a radical mechanism was proposed [154]. 

There are demethylases which act like amine oxidases that are dependent in their mechanism on their cosubstrate flavine adenine dinucleotide (FAD). So far, lysine-specific demethylase 1 (LSDl) is the only representative of this class [62]. LSDl, as an amine oxidase leads to oxidation of the methylated lysine residue, generating an imine intermediate, while the protein-bound cosubstrate FAD is reduced to FAD H2. In a second step, the imine intermediate is hydrolyzed to produce the demethylated histone lysine residue and formaldehyde. Importantly the reduced cosubstrate is regenerated to its oxidized form by molecular oxygen, producing hydrogen peroxide (Figure 5.7) [62, 63]. 

While it is well established that HO—ONO can be involved in such two-electron processes as alkene epoxidation and the oxidation of amines, sulfides and phosphines, the controversy remains concerning the mechanism of HO-ONO oxidation of saturated hydrocarbons. Rank and coworkers advanced the hypothesis that the reactive species in hydrocarbon oxidations by peroxynitrous acid, and in lipid peroxidation in the presence of air, is the discrete hydroxyl radical formed in the homolysis of HO—ONO. The HO—ONO oxidation of methane (equation 7) on the restricted surface with the B3LYP and QCISD methods gave about the same activation energy (31 3 kcalmol" ) irrespective of basis set size . ... 

The same catalytic system as described for the CDC of amines and ni-troalkanes, complemented with C0CI2 as a co-catalyst, also proved efficient for the allylic alkylation via cross-dehydrogenative coupling between various cycloalkenes and diketones (Eq. 9). Again, the exact mechanism or role of the organic peroxide are not known to date, but the formation of water probably provides the thermodynamic driving force for these reactions [121,122]. 

Mechanism III. Amines may interact with important molecule intermediates formed during the oxidation of the fuel—e.g., peroxides. If this occurred by a nonchain process, degenerate chain branching would be stopped, and there would be effective inhibition, provided that the initiation reaction between the fuel and oxygen was slow. 

The results given in this paper show that aliphatic amines do not catalyze the decomposition of peroxides, and compared with their effect at the start of reaction, they have much less effect on the later stages of oxidation, although they appear to retard the decomposition of peracetic acid. The reactions of radicals with aliphatic amines indicate that an important mode of inhibition is most probably by stabilization of free radicals by amine molecules early in the chain mechanism, possibly radicals formed from the initiation reaction between the fuel and oxygen. For inhibition to be effective, the amine radical must not take any further part in the chain reaction set up in the fuel-oxygen system. The fate of the inhibitor molecules is being elucidated at present. 

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