General decomposition routes

The most general treatment of possible decomposition routes on elemental and (A-B) semiconductors has been provided by Gerischer and Mindt 

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Scheme 1 A generalized decomposition route for aryl calcium halide complexes. The acidic proton from the THE co-ligand is abstracted, yielding benzene, followed by liberation of ethene and formation of an aryl calcium ethenolate. The above mechanism is proposed based on observations from NMR experiments [71] and is in agreement with other estabhshed ether cleavage decomposition routes [99, 100]...

Nitration of benzofuroxans (Section VII, A) and decomposition of polynitrophenyl azides, provide generally satisfactory routes to nitrobenzofuroxans. The nitro groups render the ring susceptible to nucleophilic attack (see Section VII,B). 4,6-Dinitrobenzofuroxan, 5,6-dinitrobenzofuroxan, and nitrobenzodifuroxan (34) act as acceptors in change-transfer complex formation with aromatic hydrocarbons. Nitrobenzofuroxans have not been reduced to the... 

Carbenes from Diazo Compounds. Decomposition of diazo compounds to form carbenes is a quite general reaction that is applicable to diazomethane and other diazoalkanes, diazoalkenes, and diazo compounds with aryl and acyl substituents. The main restrictions on this method are the limitations on synthesis and limited stability of the diazo compounds. The smaller diazoalkanes are toxic and potentially explosive, and they are usually prepared immediately before use. The most general synthetic routes involve base-catalyzed decomposition of V-nitroso derivatives of amides, ureas, or sulfonamides, as illustrated by several reactions used for the preparation of diazomethane. 

The most generally applicable route to nuclear substituted aromatic halogen compounds involves decomposition of a diazonium salt under suitable conditions. These reactions are discussed in Section 6.7.1, p. 922. 

Attachment of substituents incompatible to ozone required a different general synthetic route. For example, allyl acid 59 displayed poor chemoselectivity on exposure to ozone. Contrary to reports of alkaline decomposition of the lactone-acetal-peroxide functionality,16 the enolate of the prefabricated tetracycle 42 could be generated at low temperature and alkylated. As a notable example, this methodology produced a single allylated tetracycle, the a-epimer 59. This initial alkylation product was unchanged after prolonged acid treatment, and structure 57 was... 

These are generally limited to what are termed kinetically stabilized alkyls, i.e. those devoid of protons p to the metal (Figure 4.5). These also include norbornyl and adamantyl examples since decomposition via p-metal hydride elimination (see below) would require the installation of an alkenic bond between the a and p carbons of the precursor alkyl. This is precluded for these two alkyls because of the prohibitive strain associated with forming a double bond to a bridgehead atom within a small cage structure (Brendt s rules). The tetrakis(norbornyl) complexes are also remarkable because some uncharacteristic oxidations states can be attained, e.g. Cr(IV), Co(IV) (low-spin e4t2°). The second factor which may confer stability is steric bulk bimolecular decomposition routes are thereby discouraged. 

Alkyl compounds of transition metals are often kinetically instable, since they generally display lower activation energies for the decomposition routes, i.e., reduetion-elimination and/or / -H elimination, than the alkyl compounds of main group metals. With transition metal anodes, decomposition of the intermediary formed alkyl-metal complex therefore leads to the swift generation of disproportion and/or recombination products of the alkyl groups [121]. A diagram of these reactions is shown in Scheme 6, exemplified by the electrolysis of ethylaluminum compounds. Since the deeomposition reactions resulting from alkyl-metal interaction proceed at different rates for different transition metals, the dependence of the anodic reaction products on the type of metal is easy to understand. 

Subsequent loss of carbon dioxide from the alkyl acyl carbonate may occur. It was estimated, in the decomposition of Ira 5-4-I-butylcyclohexanecarbonyl peroxide in carbon tetrachloride, that two-thirds of the reaction occurs via the inversion process and one-third by the homolytic process It is suspected that inversion may be major decomposition route for other secondary aliphatic diacyl peroxides as well as for some bridgehead peroxides . Confirmation that the inversion process does contribute to the decomposition of i-butyryl peroxide is given . Further evidence for the inversion process is found in the volumes of activation for the decomposition of i-butyryl peroxide in isooctane at 50° and ram-4-r-butylcyclohexanecarbonyl peroxide in -butane at 40 °C. The AF values are —5.1 and —4.1 cm. mole , respectively. These values may be compared to the positive values of A F for benzoyl peroxide (Table 77) where there is no inversion. While the transition states for homolytic decomposition and inversion for secondary and tertiary diacyl peroxides are both polar, it is felt that the transition state for inversion is more polar . The extent of contribution of structure (V) to the transition state in the homolytic decomposition must be held with considerable reservation. In general much of the reported data for the decomposition of secondary and tertiary alkyl diacyl peroxides should be viewed with some scepticism unless efforts were made to assess the importance of the inversion process. One clue that may be used to evaluate the importance of this process is the yield of ester, which is a product of this reaction. 

The generally accepted route of formation of LAL is through the formation of dehydroalanine from cysteine, cystine, serine or phosphoserine through e-elimination reaction followed by Michael addition between the dehydroalanine and the e-amino group of lysine. The formation of LAL from the oxidized derivatives of cystine has been reported by Finley et al. (13). It was suggested that oxidation of cystine to cystine monoxide may accelerate dehydroalanine formation and subsequent LAL formation. It was also observed that very little LAL was formed through the 6-elimination of cysteine. Mel let (14) proposed that the elimination reaction in serine residues was responsible for the formation of dehydroalanine in peptides. Whitaker and Feeney (15) have reviewed the alkaline decomposition of phosphoserine and glycosylated serine or threonine residues in proteins. 

The most general synthetic route involves base-catalyzed decomposition of N-nitroso derivatives of amides or sulfonamides. The reaction of N-nitrosoureas with base generates diazoalkanes, which can then eliminate nitrogen upon heating to... 

The most stable oxidation state for all lanthanide elements is the +3 state. This primarily arises as a result of the lack of covalent overlap, which stabilizes low and high oxidation states in the d-block metals by the formation of Ji bonds. While some zero-valent complexes are known, only the +2 and -1-4 oxidation states have an extensive chemistry and even this is restricted to a few of the elements. The reasons for the existence of compounds in the -1-4 and -j-2 oxidations states can be found in an analysis of the thermodynamics of their formation and decomposition reactions. For example, while the formation of all LnF4 and LnX2 is favorable with respect to the elements, there are favorable decomposition routes to Ln for the majority of them. As a result, relatively few are known as stable compounds. Thus L11X4 decomposition to L11X3 and X2 is generally favorable, while most UnX2 are unstable with respect to disproportionation to LnXs and Ln. 

Coal can be converted to gas by several routes (2,6—11), but often a particular process is a combination of options chosen on the basis of the product desired, ie, low, medium, or high heat-value gas. In a very general sense, coal gas is the term appHed to the mixture of gaseous constituents that are produced during the thermal decomposition of coal at temperatures in excess of 500°C (>930°F), often in the absence of oxygen (air) (see Coal CONVERSION PROCESSES, gasification) (3). A soHd residue (coke, char), tars, and other Hquids are also produced in the process ... 

As with the simple boranes, the closo carboranes are generally more thermally stable than the corresponding nido and arachno species. Thermal decomposition of nido and arachno carboranes often leads to one or more closo carborane. For example, pyrolysis of 2,3-C2B4Hg is another route to 2,3-C2B3H2 [30347-95-6], l,2-C2B4Hg [20693-68-9] and l,6-C2B4Hg [20693-67-8], and 1,5-C2B3H3 [20693-66-7] (123). 

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