Thermal dehalogenation

Thus, it was shown that the tautomerization may be of importance in the thermal dehalogenation of chloroaromatics14. The formation of diarylamines in this reaction can be also explained by the presence of aniline tautomers in the reaction mixtures14. One of the well-known types of aniline tautomerism is the enol-imine-keto-amine equilibrium. In effect, it is a reversible conversion of Schiff bases into enamines that is frequently employed for the synthesis of photochromic compounds, as well as of mesomorphic... 

Preparation. Thermal elimination of HCl from l-chloro-l,l-difluoroethane (HCFC-142b) [75-68-3] is the principal industrial route to VDF covered by numerous patents (8—19). Dehydrohalogenation of l-bromo-l,l-difluoroethane (20), or 1,1,1-trifluoroethane (HFC-143a) (21—25), or dehalogenation of l,2-dichloro-l,l-difluoroethane (26—28) are investigated alternative routes (see Fluorine compounds, organic-fluorinated aliphatic compounds). 

Under the experimental conditions dehalogenation proved to be extremely rapid and was complete within 1 min. This contrasts with the 90-270 min at 100 °C required for thermal debromination of 2-bromonapthalene. No dehalogenation takes place in the absence of the formate donor and when the deuterium is located in the cosolvent rather than the donor (i. e. HCOOK + D20) hardly any deuterium incorporation takes place. Another interesting observation was that the amount (%) deuterium incorporation was always lower when protic solvents such as alcohols were used than aprotic solvents such as dimethyl sulfoxide (DMSO). These are both interesting and useful findings which are valuable for proposed tritiation studies. 

Iron carbonyls also mediate the cycloaddition reaction of allyl equivalents and dienes. In the presence of nonacarbonyldiiron a,a -dihaloketones and 1,3-dienes provide cycloheptenes (Scheme 1.5) [14,15]. Two initial dehalogenation steps afford a reactive oxoallyliron complex which undergoes a thermally allowed concerted [4 + 31-cycloaddition with 1,3-dienes. The 1,3-diene system can be incorporated in cyclic or heterocyclic systems (furans, cyclopentadienes and, less frequently, pyrroles). Noyori and coworkers applied this strategy to natural product synthesis, e.g. a-thujaplicin and P-thujaplicin [14, 16]. 

The radical anion of pentachlorobenzene has been generated thermally by electron transfer from lithium / ,//-di-ter -butylbiphenyl radical anion (LiDBB)424. The relative ratios of the three dehalogenation products were in excellent agreement with the product ratios obtained photochemically in the presence of triethylamine. 

The compounds are characterized by 19F and H NMR, IR, and Raman spectral studies. Compounds of the type SF5ORf are thermally very stable. They do not yield the perfluorovinyl derivative, SF5OCF=CF2, on dehalogenation as is the case when CF3OCF=CF2 is formed from CF30CFC1CF2C1 (94). 

A thermally induced, intramolecular dehalogenation of a (chloro)(diethylamino)-carbene ligand affords a diethylaminocarbyne complex quantitatively in aliphatic, olefinic, aromatic or ether solvents ... 

The depolymerization catalyst possesses cations that make it act as an ion exchanger. Before the hydrocarbon plastics begin to thermally crack, they are dechlorinated and dehalogenated by neutralization by the ion exchanger. 

A. Homung, S. Donner, A. Balabanovich and H. Seifert, Dehalogenation of electronic waste and corresponding pyrolysis residues, 22nd International Conference on Incineration and Thermal Treatment Technologies (ITS), Orlando, Florida., 12-16, (2003). 

For the cyclooctatetraene (COT)-bicyclo[4.2.0]octa-2,4,7-triene system (125)-(126), earlier studies using an indirect method afforded an equilibrium composition at 100 C containing 0.01% of the bicyclic form (126) (AG = 6.8 kcal mol" less stable). The bicyclic form (126) has been prepared, however, by low-temperature dehalogenation of dibromide (127) and found to rearrange to COT at 0 °C ( a = 18.7 kcal mol" ). " Recently, a high-temperature thermal trapping technique has been utilized to assess more completely the transformation between (126) and (125) in a quantitative manner. ... 

Although silylenes have been known for a long time as transient intermediates in thermal, photochemical or dehalogenation reactions, stable species have become available only recently. Si(II) compounds with coordination number larger than two have already been isolated in the late eighties, i.e., decamethylsilicocene prepared by Jutzi et al [1] and the tetracoordinated phosphine derivative obtained by Karsch et al [2]. 

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