Dehydrochlorination confirmation

Normally, p,p -DDT occurs together with its metabolite p,p -DDE, which can interfere with dehydrochlorination confirmation unless it has been previously removed, for example, by TLC (Table I). One chemical... 

Dehydrochlorination of a 1-chlorosilanamine by vacuum gas solid reaction (VGSR). The presence of the iminosilane was confirmed by direct analysis of the gaseous flow.7... 

In all cases, the generation of a true nitrile imine was confirmed by the formation of the expected cycloadducts (e.g., 139) with the expected regioselectivity. However, in several cases, carbonyl derivatives (e.g., 137) were also formed in relatively low yield. These compounds were not formed when triethylamine was used as the base. From these data, it was suggested that the dehydrochlorination is a two-step process, involving first silver-ion promoted dehalogenation to give the carbocation... 

The dehydrochlorination rate increases substantially in a wet oxidation environment and this acceleration is believed to be due to peroxy radicals, which are formed by the straight oxidation of a hydrocarbon or a fraction of polymer. However, this also is yet to be confirmed experimentally. 

The chemistry of nonaromatic condensed 1,3-dithiolanes has received considerable interest due to the reported interesting conductivity properties. Some of this chemistry has been recently reviewed <1995S215>. The chlorination of 188 was efficiently performed with 1 equiv of SO2CI2 in refluxing carbon tetrachloride to afford racemic 189 with 2 equiv of sulfuryl chloride, /ra r-5,6-dihydro-5,6-dichloro-l,3-dithiolo[4,5-3][l,4]dithiene-2-one 73 was obtained as a racemic mixture of (R,R)- and (3, 31-enantiomers without any (R,31-diastereoisomer, as confirmed by the presence of a single H NMR signal. Dehydrochlorination of 189 and 73 into 190 and 191, respectively, could be effected as shown in Scheme 9 <2000CC1117>. 

Raman microspectroscopy [3] allows the observation of the transformation of a polyene structure to a carbon one. The formation of conjugate polyene units under the conditions of chemical dehydrochlorination of the polymer was confirmed by the presence of characteristic narrow peaks at 1,107 and 1,490 cm in the Raman spectra. The products obtained by thermal treatment at elevated temperatures are highly disordered sp -carbon materials, in which the porous structure has developed upon subsequent gasification (Fig. 4.3). 

TGA data confirm transformation of the polyene structure into the carbon one. Thus isothermal heating at 200°C resulted in almost complete dehydrochlorination of the polymer, and intense weight loss occurs only at 300°C (Fig. 4.2, curve 2). 

The catalysts which operate by means of an E2 mechanism give a high proportion of reaction products which are formed by the anti-elimination. This fact has been discussed in Sect. 2.1 and only few remarks need to be added here. Quantum chemical calculations [73] on the transition state of the dehydrochlorination of chloroethane, initiated by an attack of a basic species, confirmed the preference of the anti-elimination over the syn-mode. On the contrary, calculations on the transition state for non-catalytic (homogeneous) thermal elimination [201,202] confirmed the syn-elimination path. 

This hypothesis has been confirmed by the greatly improved thermal stability of PVC as a result of the formation of a graft copolymer of d -l,4-polybutadiene onto poly (vinyl chloride). The improved thermal stability is demonstrated by the almost total absence of discoloration on molding the graft copolymer into a film at 200°C in air, the reduced rate of dehydrochlorination on heating in an inert atmosphere at 180°C, and higher onset and peak temperatures for hydrogen chloride evolution as determined by differential thermal analysis. 

Confirmation of the identity of the gas chromatographic components has been accomplished by thin layer chromatography, relative retention times on different gas chromatographic columns, "p" values, and most recently by mass spectrometry. Dicofol can be separated from its phenone by using a Florisil column (17) or TLC. Dehydrochlorination of dicofol to DBP can be used as a confirmatory test for the parent compound. Gajan and Lisk (23) used cathode ray polarography to analyze vegetables for dicofol residues. 

The OH group of organic acid is characterised by an absorption band at 3400 cm 1, corresponding to the stretching vibration. The best heat stability and gelation effects are obtained with ESO for long heating times, which are confirmed by dehydrochlorination rate constants. 

In connection with the methoxy participation, the gas-phase pyrolytic elimination of 4-chloro-1 -butanol was investigated177. The products are tetrahydrofuran, propene, formaldehyde and HCl. It is implied that the OH group provides anchimeric assistance from the fact that, besides formation of the normal unstable dehydrochlorinated intermediate 3-buten-l-ol, a ring-closed product, tetrahydrofuran, was also obtained. The higher rate of chlorobutanol pyrolysis with respect to chlorethanol and ethyl chloride (Table 27) confirmed the participation of the OH group through a five-membered ring in the transition state. 

Thus, cement-containing systems provide the conversion of dichloroethane to be increased to more than 70% even at 673K. An important positive factor is that vinyl chloride molecule is stable at this temperature. At 673K, the side reaction of vinyl chloride dehydrochlorination with forming acetylene proceeds slowly, acetylene does not form, and the reaction is not complicated by the formation of a number of by-products, for example, of perchloroethylene. Thus, the above-made supposition about bifunctional character of copper—cement catalytic systems was confirmed in the investigations of their activity in the above-mentioned reactions. 

These values probably have little meaning in absolute magnitude but in a relative sense they show that the X2 Catalyzed chain reaction should be much faster than the unimolecular thermal decomposition. This prediction is confirmed by the observed catalytic effect of chlorine in promoting dehydrochlorination. Mugdan and Barton reported dehydrochlorination of ethylene dichloride to vinyl chloride and HCl in the presence of per cent chlorine as 30 per cent at 300 C, 50 per cent at 350" C, and 70 per cent at 370 C for a flow rate of 38 g per hr through a 600-mm length of hot zone. In the absence of chlorine, there was only 2 per cent dehydrochlorination at 400 C and 30 per cent at 500" C with the same experimental setup. The mechanism used by Sherman, Quimby, and Sutherland for this catalyzed chain reaction was as follows ... 

At the same time, we confirmed that ZnCl2 catalyses the dehydrochlorination of polychloroprene at temperatures below 200°C, but the reaction is very slow, and also accelerates on the evolution of hydrogen chloride by thermal degradation. The effect of ZnO has been observed in other chlorine - containing polymers including polyvinylidene chloride, chlorinated polyethylene and polyepichlorohydrin. The phenomenon thus seems unlikely to be a function of polymer structure. 

The addition of chalk increases thermal stabihty of the filled PVC sample, indicated by a longer induction period of dehydrochlorination. Also, the rate of HCl-elimination is lower in the presence of calcium carbonate. Other investigations with unstabihzed PVC samples have shown that the filler acts as a trap for the split-off hydrogen chloride, but it has no influence on the decomposition of PVC. This is confirmed by the UV-spectra of PVC which was heat-treated in the absence and in the presence of chalk. Under both conditions, the same unsaturated sequences in PVC are formed, as shown in Figure 8 (curve a and b). On the contrary, in the presence of stabilizers (curve c) practically no polyene sequences are formed during the induction period. 

The specific ion current decreased with increasing molecular weight as would be expected. There was some evidence of the evolution of aliphatic hydrocarbons, but they were not characterised. The evolution profiles for some of the aromatic hydrocarbon fragments were bimodal and the first evolution maximum occurred concomitantly with the dehydrochlorination step. These results confirm that the ion (PhCHCl) was formed in secondary gas-phase reactions since it was not observed in the positive ion spectra. It is interesting to note that not all the ions have this bimodal evolution profile. 

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