Chlorine elimination

A five-membered methanide auracycle [Au(C6F5)2(SPPli2CFl2PPh2)]C104 (25) is described with the monosulfonated dppm, obtained after chlorine elimination of [Au (C6F5)2Cl(SPPh2CH2PPh2)j with a silver salt. After deprotonation of the methylene group (26) and later coordination of additional metal centers affords dinuclear and trinuclear methanide derivatives (27, 28) [210]. 

During slow thermal chlorination, elimination of HC1 from the monochloride with the resultant formation of an alkene followed by chlorine addition may be the dominant route to yield dichloroalkanes. This mechanism, however, is negligible in rapid thermal or photochemical reactions. 

However, using a chlorinated version of a related ester compound 36 (Scheme 5.17) required only one silver equivalent to prepare pyrrolofuranone 37, since chlorine elimination directly provided the final product without the need of a silver-mediated oxidation. 

Ranzi et al. [13] demonstrated that the radical generation by initiation is by far more important than by chlorine elimination or C-C bond breaking. 

The identification of isomers i and ii is made on the basis of NMR data (170). Only isomer i undergoes further chlorine elimination in the presence of mercury to afford the desired product in 10% yield. Isomer ii under similar conditions decomposes to give SOF4 and C1CN. The IR and 14N NMR spectra (170, 172) are used to differentiate between SF5 cyanate and SF5 isocyanate. 

When the chlorine elimination pathway prevails, one observes mainly products from intramolecular cyclization (10, 33, 34). Although no inserted SiCl2 group is involved in the products, the reaction mechanism [Eq. (30)] is related to the insertion reactions described above. 

Treatment with chlorine eliminates a cycZohcxyl group, forming cycZohexylphenylchloroarsine. 

Structure (33) has been assigned to the product obtained when PC15 reacts with the sodium salt of methane tricarbonitrile, NaC(CN)3 similar reactions occur when the PC15 is replaced by PhnPCl5 , where n = 1 or 3.330 However, if the silver salt of the nitrile is used, a cyclic compound (34) is obtained in addition to (33). Chlorine elimination occurs when N-l-cyano-alkyl-P-phenylphosphonimidic chlorides are prepared according to equa-... 

We have pictured in Scheme 25 the whole mechanism we could expect for monosubstitutions on 69 and 70. Fortunately all those reactions have not the same probability. Indeed, according to hydrogen acidities of halogenobenzenes7 48, and chlorine elimination probabilities49 arynes are formed following the decreasing order ... 

Whether the intense CT loss from i/9120 yields species of the structure 120 or 121 is not yet clarified. The chlorine elimination, however, has among all other competing decompositions from 119 the lowest activation energy. 

Lewis-acid catalyzed acetalization with enantiomerically pure alcohol 37 afford crystalline trans-aceXdX 63 in high yield (85% from oxazinone 61) and diastereoselectivity (96 4 trans/cis). Hydrogenolysis gave secondary amine 64 that was cleanly converted to imine ether 65 by a chlorination/elimination procedure. The diastereoselectivity of the subsequent imine hydrogenation was >99 1 (cis/trans). The resulting penultimate amine 5 was isolated as either the HCl or TsOH salt in 81% yield (Scheme 19). 

The El mass spectra of PCBs are characterized by the cluster of the chlorine isotopic distribution (i.e., 75.8% Cl and 24.2% CI), which is very useful for the identification of chlorinated species. The most abundant fragments are obtained by chlorine elimination the odd-electron species are favored (i.e., [M], [M — CI2], [M — Cl4]. Asymmetrically substituted ortfio-chloro PCBs only exhibit the [M — 35] fragment ion. For less chlorinated isomers, the loss of HCl is also observed. 

Another possibility is that, as in polycondensation, the formation of per-chloro-p-methylbenzyl radical is also brought about by iodide ion, but its subsequent reaction with iodide ion occurs so fast that its dimerization to perchloro-p,/7 -dimethylbibenzyl or subsequent vicinal chlorine elimination is prevented. Accordingly, when the reaction is carried out in the presence of toluene as hydrogen-atom donor (see preceding section) the yield of per-chloro-p-xylylene diminishes (72%), the rest being a, a //-octachloro-p-xylene, benzyl acetate, and, according to H-nmr spectroscopy, a mixture of cis- and tra 5-a/7,a //-tetradecachlorostilbene (46) (Diaz-Alzamora, 1968). 

Thermal dimerization of perchlorotolane cannot be carried out at moderate temperatures. At about 250°C, an excellent conversion to a mixture of the dimers perchloro-1,2,3-triphenylnaphthalene and perchloro-(Z)-2,3,8-triphenylbenzofulvene is obtained. Perchloro-5,10-diphenyldibenzo[a,e]-pentalene (perchloro-5,10-diphenylindeno[2,l-a]indene) is also formed this has been shown to originate from the fulvene by thermal chlorine-elimination (Ballester et al., 1986a). 

The other product could come from chlorination, elimination to give a benzyne, addition of amide anion to put the anion ortho to MeO (p. 524 in the textbook) and protonation. 

Statistical analysis of chlorine loss via route (a) indicates that only 86.4% of the chlorine will react due to the fact that, as elimination is a random process, about 13.6% of the chlorine atoms become isolated during the reaction and will rranain in the chain. Elimination by mechanism (b) results in total removal of chlorine. Analysis of poly(vinyl chloride) after treatment with zinc dust showed 84 to 86% chlorine elimination, and this figure rranained constant even after prolonged heating of the reaction mixture. This leads one to the conclusion that the polymer is almost entirely in the head-to-tail orientation. 

The availability of chemisorbed chlorine for substitution by other groups was examined by Puri et al. and Boehm. by refluxing the chlorinated carbons with 2.5 M sodium hydroxide and by treatment with ammonia, which indicated the substitution of chlorine by amino groups. The presence of amino groups imparted a basic character to the carbon surface, and there was a noticeable increase in the acid adsorption capacity (Table 1.18). Equivalence in chlorine eliminated, nitrogen... 

The rate of oxidation of some a-amino acids to the corresponding aldehydes, ammonia, and carbon dioxide by A-chloronicotinamide (NCN) in acidic medium is first-order in both oxidant and HCl and fractional order in amino acid nicotinamide, the reduction product of NCN, has a retarding effect on the rate. Molecular chlorine has been postulated as the reactive oxidizing species in the reaction. " Deuterium solvent isotope effects suggest decomposition through two processes in the oxidation of Ala-Gly and Pro-Gly by aqueous chlorine elimination then imine hydrolysis in alkaline medium and in acidic medium the chloramine dipeptide disproportionates to N, A-dichloramine dipeptide. 

It should be noticed that all possible reactions do not always take place Thus chlorine elimination (reaction 23) from c-CgHi CCl2CClF and C-C6H11C2CI3 radicals is so fast that reaction 24 cannot compete with it. Also, cyclohexyl radicals add only to the less substituted end in trichloroethylene. When reaction 24 does occur, it is of minor importance, as is indicated by the fact that G(RECl) G(RECl2H). 

Chlorine elimination reactions. Chloroethyl radicals CClEt) formed by Cl or Br transfer reactions in cyclohexane can subsequently eliminate a Cl atom by reaction 34 or abstract a H atom from the solvent by reaction 35. The rate constant ratio 34/ 35 el/ H related Arrhenius parameters can be... 

---