Thermal or catalytic decompositions

The decomposition of diphosgene is catalysed in the presence of various nitrogen-containing derivatives, such as pyridine, quinoline, or tertiary amines, to give complete 

Cl3CC(0)0Na 170 C Cl3C(0)Cl - major COClj - trace 476,943a 

CljCOCCOICl 100 C Pressure Heat under reflux 2COClj 867,946 947 

Phosgene generation can be too rapid to constitute a convenient synthesis. For example, careful heating of the peroxide CCl jCOOOH can result in the formation of phosgene, as indicated in Table 5.6. This reaction, however, can proceed violently and may 

Other materials can generate phosgene by decomposition at room temperature. Thus, Cl2C=NOH, commonly known as phosgene oxime, decomposes on standing at room 

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Mass spectra can only be obtained from compounds which are in the vapor-phase. The vapor pressure required to obtain a spectrum depends on the kind of sample introduction system if the sample is first evaporated in the gas container of the spectrometer and from there introduced into the ion source, a vapor pressure of about 10-2 mm Hg is necessary, while for direct introduction of the substance into the ion source a vapor pressure of only 10-6 mm is needed,2 usually sufficient to obtain spectra of very polar and nearly nonvolatile compounds, e.g., amino acids. Therefore, direct introduction systems2-9 (see also Biemann,10 p. 33) available since the pioneering work of Reed2 in all commercial instruments should be used in spite of experimental difficulties, if thermal or catalytic decomposition of the sample is to be expected. If the vapor pressure is so low that the sample cannot be vaporized sufficiently in the ion source, protecting of polar OH and NH groups by methylation or acetylation may produce a derivative of volatility enough to obtain a spectrum. 

Derivation (1) Reaction of steam with natural gas (steam reforming) and subsequent purification (2) partial oxidation of hydrocarbons to carbon monoxide and interaction of carbon monoxide and steam (3) gasification of coal (see Note 1) (4) dissociation of ammonia (5) thermal or catalytic decomposition of hydrocarbon gases (6) catalytic reforming of naphtha (7) reaction of iron and steam (8) catalytic reaction of methanol and steam (9) electrolysis of water (see Note 2). In view of the importance of hydrogen as a major energy source of the future, development of the most promising of these methods may be expected. 

The results of the survey runs may show that, irrespective of the type of column used or of the operational parameters, not all of the components of the mixture are eluted. It may also be found that, as a result of strong interaction between the stationary phase and the solute, tailing of certain bands is prevalent or that the resultant extended retention time on the column has caused excessive thermal or catalytic decomposition of the solute. These undersirable effects can often be obviated by the conversion of the components into more volatile and usually less polar derivatives. Some examples of such conversions are given below in Table 13.2. 

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 ... 

Despite the interest of such energetic IL-based hybrid engine, the current development replaced EIL by hydrogen peroxide this is most probably due to the formation of major nitric acid (kinetic product) instead of expected oxygen (thermodynamic product) during thermal or catalytic decomposition of HAN ... 

We have seen that different ionic liquids are proposed for the different propulsion systems (monopropellants, hypergolic bipropellants, ion electrospray, hydrid engines). The current and future challenges that can be drawn from this review are summarized as follows (i) to find new and safe EILs whose thermal or catalytic decomposition avoid the formation of nitric acid as a primary product (ii) to develop new catalysts able to decompose EILs at low temperature and stable at high temperature (iii) to find new fuels associated to IL oxidizers but with no inhibiting properties for the catalysts and (iv) to develop cheaper and safer synthetic method to prepare ILs. 

Because of the longer residence times in the injector, with the splitless technique, there is an increased risk of thermal or catalytic decomposition of labile components. There are losses through adsorption on the surface of the insert, which can usually be counteracted by suitable deactivation. Much more frequently there is an (often intended) deposit of involatile sample residues in the insert or septum particles get collected at the bottom of the liner. This makes it necessary to regularly check and clean the insert according to a preventive maintenance procedure. 

Reactions that have led to other deoxyhalogeno sugars do not necessarily lead to deoxyfluoro sugars, as, for example, in the attempted decomposition of fluoroformates, the treatment of diazoketones and of 2-deoxy-2-diazohexonates with hydrogen fluoride, and the reaction of benzoxonium ions with halide ions. The reaction2281229 by which fluoroformates are thermally or catalytically decarbonylated to give alkyl fluorides has been applied to carbohydrates. Both thermal and catalytic treatment of 6-0-(fluoroformyl)-l,2 3,4-di-0-isopropylidene-... 

Functionalized cyclopropenes are viable synthetic intermediates whose applications [99.100] extend to a wide variety of carbocyclic and heterocyclic systems. However, advances in the synthesis of cyclopropenes, particularly through Rh(II) carboxylate—catalyzed decomposition of diazo esters in the presence of alkynes [100-102], has made available an array of stable 3-cyclopropenecarboxylate esters. Previously, copper catalysts provided low to moderate yields of cyclopropenes in reactions of diazo esters with disubstituted acetylenes [103], but the higher temperatures required for these carbenoid reactions often led to thermal or catalytic ring opening and products derived from vinylcarbene intermediates (104-107). 

The primary pyrolysis products relate directly to the chemical structure and composition of the resin, and also to the mechanism of its decomposition (purely thermal or catalytic)... 

Some kinetic models for thermal or catalytic polymer degradation have been proposed. The commonly used approach is first-order kinetics to investigate the characteristics of degradation (Equation 9.1). In this approach at first the weight loss curve of polymers during the decomposition is determined, and overall rate constants are calculated... 

The reverse trend was found for intramolecular cyclopropanation of a-(alkenyloxysilyl)diazo-acetic esters. For the synthesis of methyl 2,2-diisopropyl-3-oxa-2-silabicyclo[4.1.0]heptane-l-carboxylate (7) from methyl diazo[(but-3-enyloxy)diisopropylsilyl]acetate, the thermal procedure gave the best result. In contrast, the lower homologs, 3-oxo-2-silabicyclo[3.1.0]hexanes, were only obtained by photochemical or catalytic decomposition of the corresponding diazo esters (see also Section 1.2.1.10.). 

Three events are involved with chain-growth polymerization catalytic initiation, propagation, and termination [3], Monomers with double bonds (—C=C—R1R2—) or sometimes triple bonds, and Rj and R2 additive groups, initiate propagation. The sites can be anionic or cationic active, free-radical. Free-radical catalysts allow the chain to grow when the double (or triple) bonds break. Types of free-radical polymerization are solution free-radical polymerization, emulsion free-radical polymerization, bulk free-radical polymerization, and free-radical copolymerization. Free-radical polymerization consists of initiation, termination, and chain transfer. Polymerization is initiated by the attack of free radicals that are formed by thermal or photochemical decomposition by initiators. When an organic peroxide or azo compound free-radical initiator is used, such as i-butyl peroxide, benzoyl peroxide, azo(bis)isobutylonitrile, or diazo- compounds, the monomer s double bonds break and form reactive free-radical sites with free electrons. Free radicals are also created by UV exposure, irradiation, or redox initiation in aqueous solution, which break the double bonds [3]. 

The influence of the fuel (methanol and glycerol) added in stoichiometric proportions, or in excess, to HAN, ADN, or HNF was evaluated (Amariei et al., 2005). Fig. 5 displays the thermogravimetiic results obtained for binary (no fuel) and ternary HAN-based propellants. Obviously, the presence of the fuel increases the ignition temperature for both thermal and catalytic decomposition, disdosing an inhibiting behavior. 

Avoidance of thermal and/or catalytic decomposition or chemical reaction of sample components. 

An a-diazo ketone 1 can decompose to give a ketocarbene, which further reacts by migration of a group R to yield a ketene 2. Reaction of ketene 2 with water results in formation of a carboxylic acid 3. The Woljf re arrangement is one step of the Arndt-Eistert reaction. Decomposition of diazo ketone 1 can be accomplished thermally, photochemically or catalytically as catalyst amorphous silver oxide is commonly used ... 

The positive hole (C204) migrated rapidly to a surface where subsequent decomposition may proceed either by the thermal or the catalytic path. The adsorbed species C02 has been identified [1057] by ESR in the decomposition of MgC204. 

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