Decomposition of organic peroxides

Depending on the peroxide class, the rates of decomposition of organic peroxides can be enhanced by specific promoters or activators, which significantly decrease the energy necessary to break the oxygen—oxygen bond. Such accelerated decompositions occur well below the peroxides normal appHcation temperatures and usually result in generation of only one usehil radical, instead of two. An example is the decomposition of hydroperoxides with multivalent metals (M), commonly iron, cobalt, or vanadium ... 

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). 

Aromatic amines and in particular, tertiary amines, catalyse the decomposition of organic peroxides in very small quantities. They are used to start the radical polymerisations of numerous monomers. 

Action of Aliphatic Amines on Slow Oxidation of Acetaldehyde and Ethyl Ether, and on Decomposition of Organic Peroxides in the Gas Phase... 

Detailed studies on the decomposition of organic peroxides are of fundamental interest and of high importance in polymerization reactions. The time-scales of intermediate radical formation and of their subsequent decomposition determine process parameters such as the initiator efficiency in radical polymerizations. An improved understanding of the mechanism and dynamics of photo-induced fragmentation is achieved by systematic investigations in which quantum-chemical calculations are carried out in conjunction with highly time-resolved experiments. 

A typical unimolecular reaction is the decomposition of organic peroxides for which always positive activation volumes of up to 15 cm3/mol have been observed. The decomposition of di(t-butyl)peroxide, an effective initiator for the high pressure polymerisation of ethylene, into two t-butoxyradicals, exhibits a positive activation volume of 13 cm3/mol (Table 3.2-1, a). When new bonds are formed as in the association... 

In this chapter, the application of the apparatus mentioned before to measure reaction rates under high pressure and to evaluate kinetic data, is described. As examples, the decomposition of organic peroxides, the radical polymerization of ethylene, and the synthesis of methanol are selected. 

The oxyl radicals resulting from the decomposition of organic peroxides are energy-rich intermediates and undergo a number of rapid reactions (Chap. 7). Here, it is briefly recalled that the tertiary oxyl radicals undergo facile (3-fragmentation [reaction (52)], and the primary and secondary oxyl radicals an equally fast water-assisted 1,2-H shift [reaction (53)]. 

Let us examine the different elementary steps of the mechanism. Initiators [In in Eq. (2)] can be chemical species of different origins. Very often they are peroxy (ROO ) and oxy (RO ) radicals produced by thermal homo-lytic decomposition of organic peroxides,... 

The entire complex situation is untypical of hydrogen peroxide. Decomposition of H202 starts from dissociation by O—O-bond to hydroxyl radicals, which then in gas-phase (refer to Chapter 4) and liquid-phase (refer to Chapter 6) decomposition lead to final products H20 and 02. Here one deals with a single complex reaction with a definite set of subsequently proceeding elementary reactions, but not with several sets as for decomposition of organic peroxides. 

Thus the induced H202 dissociation and auto-induced decomposition of organic peroxides (initiators) are accompanied by a change of, at least, one of three reaction parameters (a) stoichiometric equation of the reaction (decomposition products remain typical of the current substance) (b) reaction type and (c) reaction pathway (mechanism) with decomposition overall stoichiometric equation preserved. 

Decomposition of organic peroxides to free radicals follows first order kinetics. Half life (t ) is defined as the time required for half of the organic peroxide to decompose at a certain temperature. Half-life is an important parameter in... 

Cubbon RCP (1969) The kinetics of thennal decomposition of organic peroxides. In Porter G (ed) Progress in reaction kinetics, vol.5. Pergamon, Laporte Ind.Luton, p 31... 

When faujasites only exchanged with a transition metal are used as catalysts the oxidation of pinane at room temperature practically does not take place Transition metal ions are well known to catalyse the decomposition of organic peroxides [6]. Therefore, the low reactivity observed in those conditions is likely to be due to the decomposition of t-butyl-hydroperoxide before it can oxidise pinane... 

Another question to be considered is whether it is in principle possible to affect the course of radical polymerization catalytically. The ions of metals with a variable valence are well known to be capable of catalyzing the monomolecular decomposition of organic peroxides and hydroperoxides. 

Such free radicals can add to a carbon-carbon double bond and form a new reactive free radical that is capable of adding onto another monomer unit. Thus, the polymerization is catalyzed by free radicals such as those produced by the decomposition of organic peroxides like benzoyl peroxide. 

Most commercial grafting reactions are initiated by fiee radicals. The fiee radicals can be supplied by the themial decomposition of organic peroxides. 

The first commercial polymerizations of ethylene were initiated by radicals formed by thermal decomposition of organic peroxides, such as benzoyl peroxide. A radical is any molecule that contains one or more unpaired electrons. Radicals can be formed by the cleavage of a bond in such a way that each atom or fragment participating in the bond... 

One of the most important types of addition polymerization is free radical polymerization. This process is initiated by the action of free radicals (electrically neutral species with an unshared electron). Free radicals for the initiation of addition polymerization are usually generated by the thermal decomposition of organic peroxides or azo compounds. The polymerization of unsaturated polyesters with a peroxide catalyst is an example of a free radical polymerization process. 

Nakamura,H.R. (2007)Thermal decomposition of organic peroxides TATP and HMTD by T-jump/FTIR spectroscopy. Prop. Explos. Pyrotech., 32(2), 127-134. 

Allgrl-substituted phenols are the most widespread inhibitors. The phenoxyl radicals corresponding to them are readily produced by oxidizing the phenols with lead dioxide [3], in photolysis, y and /3 radiolysis, as well as in their reaction with active radicals produced in the thermal or catalytic decomposition of organic peroxides and hydroperoxides [4]. The stability of the radicals formed is determined by the structure of the initial phenol. The most stable radicals are strongly shielded phenols. Thus, 2,4,6-tri-tert-butylphenol (I), when oxidized by Pb02, forms phenoxyl radicals, the EPR spectmm of which is presented in Fig. 34a, in almost 100% yield ... 

Thermal decomposition of azo-compounds and organometallic compounds as weU as of peroxy compounds and alkyl iodides is a common source of free radicals. For instance, methyl radicals are generated by the decomposition of H3C—N—N—CH3 or Hg(CH3)2. Methylene is produced by thermal decomposition of diazomethane, H2CN2, or COCH2. Thermal decomposition of organic peroxides yields alkoxy radicals such as CH3O, C2H5O. 

Polyethylene can be crosslinked by decomposition of organic peroxides, hydrolysis of vinyl-silane grafted polyethylene or by high-energy (P or y) irradiation. Design a suitable experiment to determine the crosslink density and present the relevant equations. 

Vinyl acetate polymerizes by a free-radical mechanism. Free radicals generated by the decomposition of organic peroxides such as benzoyl or hydrogen peroxide or of inorganic per salts such as potassium or ammonium persulfate are commonly used to initiate polymerization. Reactions ordinarily are accomplished at temperatures above room temperature. Other techniques of polymerization have been used to make novel products low temperature redox polymerization, irradiation, and ionic catalysis. 

Free radicals for the initiation of addition polymerization are usually generated by the thermal decomposition of organic peroxides or azo compounds. Two common examples are... 

Recently, Morsi et al. [73] have studied the rate of charge transfer interactions in the decomposition of organic peroxides. O Driscoll and Ri-chezza [74] have also reported the ultraviolet absorbance study of the complex formation between benzoyl peroxide and dimethylaniline. According to Horner and Schwenk [45], the mechanism for the polymerization of vinyl monomers by benzoyl peroxide and dimethylaniline is as follows ... 

When crosslinking is carried out by irradiation or thermal decomposition of organic peroxides, silanes of the type CH2=CH—Si—(OR)3 or CH2=CH—CH2— Si—(0R)3 (i.e., vinyl or acrylyl silanes), can be reacted with fillers having surface... 

The rate at which initiator molecules decompose, and hence the rate of cross-linking, is a function of their chemical stability and the temperature to which they are subjected. The decomposition of organic peroxides is an approximately first-order reaction, its rate increasing exponentially as a function of temperature. The rate of spontaneous decomposition of an initiator at any temperature is typically characterized in terms of its half-life. The approximate half-lives of some commonly used peroxide intiators are listed in Table 1. Initiator molecules for cross-linking polyethylene are selected with respect to the temperature at which the resin must be processed. The goal is to homogenize and mold the resin into the desired shape below the temperature at which peroxide decomposition becomes significant premature decomposition of the peroxide is known as... 

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