Decomposition in reactions

Abstract The dirhodium(II) core is a template onto which both achiral and chiral ligands are placed so that four exist in a paddle wheel fashion around the core. The resulting structures are effective electrophilic catalysts for diazo decomposition in reactions that involve metal carbene intermediates. High selectivities are achieved in transformations ranging from addition to insertion and association. The syntheses of natural products and compounds of biological interest have employed these catalysts and methods with increasing frequency. 

The product is separated without the use of either heat or vacuum, conditions which might otherwise lead to loss of the weakly-bound ligand. In addition, the product is cooled somewhat by expansion of the SCF, thereby reducing the rate of decomposition. In reactions where the SCF is also a reactant (i.e. SCC2H4 in the preparation of C2H4 complexes) the product, once precipitated is held under a flow of the reactant gas, again minimizing the chances of decomposition [12]. 

Certain diquaternary ammonium compounds generate acetylenes on decomposition, in reactions closely analogous to the Hofmann degradation. One such is that of the ethylenediamine derivative on a laboratory scale the... 

In contrast to IR and NMR spectroscopy, the principle of mass spectrometry (MS) is based on decomposition and reactions of organic molecules on theii way from the ion source to the detector. Consequently, structure-MS correlation is basically a matter of relating reactions to the signals in a mass spectrum. The chemical structure information contained in mass spectra is difficult to extract because of the complicated relationships between MS data and chemical structures. The aim of spectra evaluation can be either the identification of a compound or the interpretation of spectral data in order to elucidate the chemical structure [78-80],... 

The concentration of nitromethane, CH3NO2, can be determined from the kinetics of its decomposition in basic solution. In the presence of excess base the reaction is pseudo-first-order in nitromethane. For a standard solution of 0.0100 M nitromethane, the concentration of nitromethane after 2.00 s was found to be 4.24 X 10 M. When a sample containing an unknown amount of nitromethane was analyzed, the concentration remaining after 2.00 s was found to be 5.35 X 10 M. What is the initial concentration of nitromethane in the sample ... 

More recent work reports the onset of thermal degradation at lower temperatures and provides a clearer picture of the role of oxygen (73—75). In the presence of oxygen, backbone oxidation and subsequent cleavage reactions initiate decomposition. In the absence of oxygen, dehydrofluorination eventually occurs, but at significantly higher temperatures. 

To extend the study of the apparent decomposition recombination reaction, and specifically to determine if the carbon atoms exchange with other atoms in other acetylene molecules, tests using carbon isotopes were conducted. A mixture of 50% regular acetylene, C2H2, and 50% heavy acetylene. 

Two secondary propagating reactions often accompany the initial peroxide decomposition radical-induced decompositions and -scission reactions. Both reactions affect the reactivity and efficiency of the initiation process. Peroxydicarbonates and hydroperoxides are particularly susceptible to radical-induced decompositions. In radical-induced decomposition, a radical in the system reacts with undecomposed peroxide, eg ... 

Decomposition and Decarboxylation. Maleic anhydride undergoes anaerobic thermal decomposition in the gas phase in a homogeneous unimolecular reaction to give carbon monoxide, carbon dioxide, and acetylene [74-86-2] in equimolar amounts. The endothermic... 

The iodine compound is more stable and separates as so-called nitrogen trHodide monoammoniate [14014-86-9], NI NH, an insoluble brownish-black soHd, which decomposes when exposed to light in the presence of ammonia. In reactions of the halogens with the respective ammonium salts, however, the action is different. Chlorine replaces hydrogen and nitrogen chloride [10025-85-1], NCl, separates as oily, yeUow droplets capable of spontaneous explosive decomposition. 

Decomposition of Thiols. Thiols decompose by two principal paths (i43— i45). These are the carbon—sulfur bond homolysis and the unimolecular decomposition to alkene and hydrogen sulfide. For methanethiol, the only available route is homolysis, as in reaction 29. For ethanethiol, the favored route is formation of ethylene and hydrogen sulfide via the unimolecular process, as in reaction 30. 

Cesium forms simple alkyl and aryl compounds that are similar to those of the other alkah metals (6). They are colorless, sohd, amorphous, nonvolatile, and insoluble, except by decomposition, in most solvents except diethylzinc. As a result of exceptional reactivity, cesium aryls should be effective in alkylations wherever other alkaline alkyls or Grignard reagents have failed (see Grignard reactions). Cesium reacts with hydrocarbons in which the activity of a C—H link is increased by attachment to the carbon atom of doubly linked or aromatic radicals. A brown, sohd addition product is formed when cesium reacts with ethylene, and a very reactive dark red powder, triphenylmethylcesium [76-83-5] (C H )2CCs, is formed by the reaction of cesium amalgam and a solution of triphenylmethyl chloride in anhydrous ether. 

Thermal Decomposition of GIO2. Chloiine dioxide decomposition in the gas phase is chaiacteiized by a slow induction period followed by a rapid autocatalytic phase that may be explosive if the initial concentration is above a partial pressure of 10.1 kPa (76 mm Hg) (27). Mechanistic investigations indicate that the intermediates formed include the unstable chlorine oxide, CI2O2. The presence of water vapor tends to extend the duration of the induction period, presumably by reaction with this intermediate. When water vapor concentration and temperature are both high, the decomposition of chlorine dioxide can proceed smoothly rather than explosively. Apparently under these conditions, all decomposition takes place in the induction period, and water vapor inhibits the autocatalytic phase altogether. The products of chlorine dioxide decomposition in the gas phase include chlorine, oxygen, HCl, HCIO, and HCIO. The ratios of products formed during decomposition depend on the concentration of water vapor and temperature (27). 

The temperature at which decarboxylation occurs is of particular interest in manufacturing processes based on polymerisation in the molten state where reaction temperatures may be near the point at which decomposition of the diacid occurs. Decarboxylation temperatures are tabulated in Table 2 along with molar heats of combustion. The diacids become more heat stable at carbon number four with even-numbered acids always more stable. Thermal decomposition is strongly influenced by trace constituents, surface effects, and other environmental factors actual stabiUties in reaction systems may therefore be lower. 

Double Decomposition. In the double decomposition reaction, an inorganic metal salt such as a sulfate, chloride, acetate, or nitrate reacts with the sodium salt of the carboxyUc acid ia a hot aqueous solution. The metal soap precipitate is filtered, washed, dried, and milled. 

A novel method for preparing amino heterocycles is illustrated by the preparation of 2-amino-5-methylthiophene (159). In this approach vinyl azides act as NH2 equivalents in reaction with aromatic or heteroaromatic lithium derivatives (82TL699). A further variant for the preparation of amino heterocycles is by azide reduction the latter compounds are obtained by reaction of lithio derivatives with p- toluenesulfonyl azide and decomposition of the resulting lithium salt with tetrasodium pyrophosphate (Scheme 66) (82JOC3177). 

Materials that on shor t exposure could cause death or major residual injury 4 Materials that will rapidly or completely vaporize at atmospheric pressure and normal ambient temperature, or that are readily dispersed in air and will burn readily 4 Materials that in themselves are readily capable of detonation or of explosive decomposition or reaction at normal temperatures and pressures... 

Hot spot develops in reaction medium. Temperature excursion outside the safe operating envelope, possibly resulting in a runaway reaction or decomposition. Potential mechanical failure of reactor wall. 

Electrostatic spark discharge and ignition during charging of solids resulting in possibility of fire/explo-sion. Potential for explosion to start a thermal decomposition of reaction mass. 

Quenching Rapid cooling from an elevated temperature, e.g., severe cooling of the reaction system in a short time (almost instantaneously), freezes the status of a reaction and prevents further decomposition or reaction. 

If the decomposition reaction follows the general rate law, the activation energy, heat of decomposition, rate constant and half-life for any given temperature can be obtained on a few milligrams using the ASTM method. Hazard indicators include heats of decomposition in excess of 0.3 kcal/g, short half-lives, low activation energies and low exotherm onset temperatures, especially if heat of decomposition is considerable. 

Cluster ions are also emitted from organic materials their identity and yield depend on the chemical structure of the materials. Molecular or quasi-molecular ions may be observed as well as other ions that are formed by fragmentation, rearrangement, decomposition, or reaction [52], Several typical ion formation processes are summarized in Table 3 [40]. 

Olefins may be obtained by elimination from the organoboron intermediates formed from enol derivatives and diborane. " As in the reaction with a,jS-unsaturated ketones (section IX), the conversion is carried out in two parts first formation of the diborane adduct and second, decomposition in refluxing acetic anhydride. 

An explosive decomposition in an ethylene oxide (EO) distillation column, similar in its results to that described in Section 7.3.2, may have been set off by polymerization of EO in a dead-end spot in the column base where rust, a polymerization catalyst, had accumulated. Such deadends should be avoided. However, it is more likely that a flange leaked the leaking gas ignited and heated an area of the column above the temperature at which spontaneous decomposition occurs. The source of ignition of the leak may have been reaction with the insulation, as described... 

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