Oxidative fragmentation

The reactions with IF are more amenable to control giving good yields of identifiable products and lower losses from oxidative fragmentation. The reaction of IF and iodine with tetrafluoroethylene produces the telomer perfluoroethyl iodide [354-64-3] ia yields that exceed 98% based on... 

Figure 20, a magnitude schematic view of zone 1 in Fig. 19, depicts this effect. These exothermic oxidative reactions in zone 1 can release sufficient heat to expel partially combusted products, pyrolysis products, and fuel and oxidizer fragments into the gas phase, where they can intermix and burn completely. The maximum flame temperature will then be reached in the luminous zone, where the largest portion of the heat is released. However, a relatively... 

Several procedures that intercept the intermediates have been developed. When ozonolysis is done in alcoholic solvents, the carbonyl oxide fragmentation product can be trapped as an a-hydroperoxy ether.202 Recombination to the ozonide is then prevented, and the carbonyl compound formed in the fragmentation step can also be... 

Figure 5 1,2,4-Oxadiazoles that undergo fragmentation by loss of a nitrile oxide fragment.

For analysis of dienes and polyenes via oxidations one has to distinguish between the formation of an oxidized product of the target molecule (epoxide, peroxide, ozonide etc.) and the oxidative fragmentation of the molecule as in the case of ozonolysis30. Both... 

The use of both ozonation and ozonolysis is reviewed32. Ozonation leads to ozonide and ozonolysis leads to oxidized fragments, showing the use of both oxidative (AgN03) or reductive [(CH3)2S or PI13P] methods to produce the FAME (fatty acids methyl esters) that by subsequent GC analysis enabled determination of the position of the double bonds in the original molecule (equations 2-4). 

Cycloreversion with nitrile oxide formation is known not only in furoxans but also in isoxazolines, 1,2,4-oxadiazoles, furazans, and some other live-membered heterocycles (76). Such process, eliminating nitrile oxide fragment 3-R CeHiC N+Cr ", was observed mass spectrometrically in 3a,4,5,6-tetrahydro-[ 1,2,4 oxadiazolo[4,5-a J [ 1,5 benzodiazepine derivatives 11 (83). 

Nitronates, in which the /V -oxide fragment is absent, are characterized by strong paramagnetic shifts of the signals of the a-C atom and the proton bound to this atom (see, e.g., entry 5 in Table 3.10 and entries 2 and 9 in Table 3.11). 

FUNCTION RUBISCO CATALYSES TWO REACTIONS THE CARBOXYLATION OF D-RIBULOSE 1,5-BISPHOSPHATE, THE PRIMARY EVENT IN PHOTOSYNTHETIC CARBON DIOXIDE FIXATION, AS WELL AS THE OXIDATIVE FRAGMENTATION OF THE PENTOSE SUBSTRATE IN THE PHOTORESPIRATION PROCESS. BOTH REACTIONS OCCUR SIMULTANEOUSLY AND IN COMPETITION AT THE SAME ACTIVE SITE. 

Smiley, P.L., Stremler, K.E., Prescott, S.M., Zimmerman, G.A., and McIntyre, T.M., 1991, Oxidatively fragmented phosphatidylcholines activate human neutrophils trough the receptor for platelet-activating factor,/. Sioi. Chem. 266 11104-11110. 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

Results of ab initio studies lend support to a mechanism, involving initial formation of Me3C+, CO2 and Me3C0C(0)N=N, proposed to account for oxidative fragmentation of di-tert-butyl azodicarboxylate promoted by thianthrenium perchlorate. ... 

An useful alternative to the already known retropinacol reactions is presented by Liu and co-workers [7], This works demonstrates that pinacols bearing (dimethylamino)phenyl substiments can be subjected to fast oxidative fragmentation via photoinduced electron transfer with chloroform as the electron acceptor in yields up to 80%. The extremely fast dechlorination of the chloroform radical anion inhibits back-electron transfer and thus leads to effective fragmentation of the pinacol radical cation (Scheme 8). 

Stable rhenium tricarbonyls bonded to the surface of MgO have been prepared and characterized by EXAFS. Heating under He, O2 or vacuum of a sample obtained by impregnation of Re2(CO)io produced the oxidative fragmentation of the initial surface organometallic species [39-41]. These types of supported well-characterized species can be used as models in the study of reaction mechanisms [42]. 

Similarly, the adsorption of Rli4(CO)i2 on y-Al203 followed by an oxidative fragmentation produced dicarbonyl rhodium (1) species that have been characterized by EXAFS [100]. 

In contrast to other crystaUine nitrates, pentaerythrol tetranitrate (PETN C Hg(0N02)4) is a crystalline nitrate ester similar to NG and NC. Though PETN is one of the most powerful energetic materials used in explosives, no excess oxidizer fragments are formed when it decomposes. Thus, PETN is not used as an oxidizer of propellants. 

Polymeric materials that act as fuels and oxidizers are composed of nitrogen, oxygen, carbon, and hydrogen atoms. The hydrocarbon structures act as fuel components, and the oxidizer fragments, such as -C-NOj, -O-NOj, -O-NO, or -N-NO2, are attached to the hydrocarbon structures through covalent chemical bonds. 

NC is an energetic nitropolymer consisting of a hydrocarbon structure with -O-NO2 bonds as oxidizer fragments. In general, NC is produced from the cellulose, C6H702(0H)3 j of cotton or wood, which is nitrated using nitric acid (HNO3) to introduce -O-NO2 bonds into its structure. 

Molecules in which fuel and oxidizer components are chemically bonded within the same structure are suitably predisposed for the formulation of energetic materials. Nitropolymers are composed of O-NO2 groups and a hydrocarbon structure. The bond breakage of O-NO2 produces gaseous NO2, which acts as an oxidizer fragment, and the remaining hydrocarbon structure acts as a fuel fragment. NC is a typical nitropolymer used as a major component of propellants. The propellants composed of NC are termed nitropolymer propellants . 

Crystalline particles that produce gaseous oxidizer fragments are used as oxidizer components and hydrocarbon polymers that produce gaseous fuel fragments are used as fuel components. Mixtures of these crystalline particles and hydrocarbon polymers form energetic materials that are termed composite propellants . The oxidizer and fuel components produced at the burning surface of each component mix together to form a stoichiometrically balanced reactive gas in the gas phase. 

Ammonium nitrate contains a relatively high concentration of oxidizer fragments, as shown in Table 2.6. In order to maximize the binder mixed with AN is GAP. The maximum of 238 s and the maximum Tjof 2400 K are obtained at (AN) = 0.85, as shown in Fig. 4.16. However, since AN crystal particles are not wholly compatible with GAP, the practical (AN) is less than 0.8, at which Isp drops to 225 s and drops to 2220 K. 

Hydrazinium nitroformate (HNF) contains a relatively high concentration of oxidizer fragments, as shown in Table 2.6. When GAP is used as a binder of HNF particles, HNF-GAP composite propellants are made. The maximum of 285 s and the maximum Tf of 3280 K are obtained at (HNF) = 0.90 with an optimum expansion from 10 MPa to 0.1 MPa, as shown in Figs. 4.20 and 4.21, respectively. Since a... 

Since the energetics of nitropolymer propellants composed of NC-NG or NC-TMETN are limited due to the limited concentration of oxidizer fragments, some crystalline particles are mixed within these propellants in order to increase the thermodynamic energy or specific impulse. The resulting class of propellants is termed composite-modified double-base (CMDB) propellants . The physicochemical properhes of CMDB propellants are intermediate between those of composite and double-base propellants, and these systems are widely used because of their great potential to produce a high specific impulse and their flexibility of burning rate. 

The oxidizer fragment (HNO3) of TAGN is attached by an ionic bond in the molecular structure and the physicochemical processes of TAGN combustion are different from those of HMX and RDX, the oxidizer fragment of which (-N-NO2) is attached by a covalent bond in their molecular structures. Though the flame temperature of TAGN is lower than that of HMX by 1200 K, the value of the thermodynamic parameter (Tf/M y appears to be approximately the same for both materials. The... 

When some portion of the AP particles contained within an AP composite propellant is replaced with nitramine particles, an AP-nitramine composite propellan-tis formulated. However, the specific impulse is reduced because there is an insufficient supply of oxidizer to the fuel components, i. e., the composition becomes fuel-rich. The adiabatic flame temperature is also reduced as the mass fraction of nitramine is increased. Fig. 7.49 shows the results of theoretical calculations of and Tf for AP-RDX composite propellants as a function of Irdx- Th propellants are composed of jjxpb(0-13) and the chamber pressure is 7.0 MPa with an optimum expansion to 0.1 MPa. Both I p and T)-decrease with increasing Irdx- The molecular mass of the combustion products also decreases with increasing Irdx due to the production of Hj by the decomposition of RDX. It is evident that no excess oxidizer fragments are available to oxidize this H2. 

Fig. 10.1 shows part of the Periodic Table of the elements, highlighting the fact that some pure solid elements are used as fuel components of pyrolants. For example, magnesium (Mg) is oxidized by oxidizer fragments to produce magnesium oxides... 

As shown in Table 10.5, non-metaUic fuels used as ingredients of pyrolants are boron, carbon, silicon, phosphorus, and sulfur. Similarly to metal particles, non-metal particles are oxidized at their surfaces. The processes of diffusion of oxidizer fragments to the surface of a particle and the removal of oxidized fragments therefrom are the rate-controlling steps for combustion. 

The heat produced by the reaction of a pyrolant is dependent on various physicochemical properties, such as the chemical nature of the fuel and oxidizer, the fractions in which they are mixed, and their physical shapes and sizes. Metal particles are commonly used as fuel components of pyrolants. When a metal particle is oxidized by gaseous oxidizer fragments, an oxide layer is formed that coats the particle. If the melting point of the oxide layer is higher than that of the metal particle, the metal oxide layer prevents further supply of the oxidizer fragments to the metal, and so the oxidation remains incomplete. If, however, the melting point of the oxide layer is lower than that of the metal particle, the oxide layer is easily removed and the oxidation reaction can continue. 

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