1 ,2,4-Trichlorobenzene, thermal

Chlorinated dibenzo-ip-dioxins were prepared on the gram scale for use as toxicological standards, 2,7-Dichlorodi-henzo-p-dioxin was prepared by catalytic condensation of potassium 2-bromo-4-chlorophenate in 70% yield. Thermal condensation of the potassium salt of 2,4,4 -trichloro-2 -hydroxy diphenyl ether gave a mixture of the 2,8- and 2,7-dichlorodibenzo-p-dioxins which were separated by fractional recrystallization. 2,3,7,8-T etrachlorodibenzo-p-dioxin of 99.9- -% purity was prepared by catalytic condensation of potassium 2,4,5-trichlorophenate. An isomeric mixture of hexachlorodibenzo-p-dioxins was prepared by pyrolytic condensation of sodium 2,3,4,6-tetrachlorophenate. Chlorination of pentachlorophenol (containing < 0.07% tetrachlorophenol) in trichlorobenzene gave octachlorodi-benzo-p-dioxin in 80% yield contaminated by 5-15% heptachlorodibenzo-p-dioxin. Oxidative methods were used to produce octachlorodibenzo-p-dioxin at 99.9% purity. 

A reliable procedure for determination of molecular parameters number, weight and z-averages of the molecular weight (Mj, i = n, w and z respectively) for polyethylenes, PE, by means of Size Exclusion Chromatography, SEC, has been developed. The Waters Sci. Ltd. GPC/LC Model 150C was used at 135 C with trichlorobenzene, TCB, as a solvent. The standard samples as well as commercial stabilized and not stabilized PE-resins were evaluated. The effects of sampling, method of solution preparation, addition of antioxidant(s), thermal and shear degradation were studied. The adopted procedure allows reproducible determination of and M , with a random error of 4% and M2, with 9%, within 2 to 72 hrs from the initial moment of preparation of solutions. 

An enantioselective synthesis of (+)-estradiol has been accomplished from 1,3-dihy-drobenzo[c]thiophene 2,2-dioxide (306) by successive thermal S02-extrusion and cycloaddition (80HCA1703). Treatment of the optically active iodide (307) with two mole equivalents of the masked quinodimethane (306) in the presence of two mole equivalents of sodium hydride gave (308) as a 1 1 mixture of diastereoisomers. Thermolysis of this alkenic sulfone in 1,2,4-trichlorobenzene furnished the trans-anti-trans steroid (309) in 80% yield. Treatment of (309) with methyllithium gave the methyl ketone, which was subjected to a Baeyer-Villiger oxidation and then silyl ether-acetate cleavage to afford (-l-)-estradiol (310 Scheme 66). 

When cyclization of the acrylamide (167) was attempted in refluxing 1,2,4-trichlorobenzene, 6-chloro-3-dichloromethylene-3//-imidazo[l,2-6]pyridazin-2-one (35) was formed instead of the expected pyrimido[1,2-6]pyridazin-4-one (34). The latter compound could be obtained by conducting the cyclization in refluxing xylene. Since (34) and (35) are in practice not thermally interconvertible (at 210 °C), it can be assumed that (34) is not a precursor in the formation of (35) (71JOC3506). 

The possibility of using porphyrins as dienophiles in DA reactions emerged in 1997 when Cavaleiro and coworkers <97CC1199> found that meio-tetraarylporphyrins la-d can behave as dienophiles in the presence of o-benzoquinodimethane, a highly reactive diene generated in situ by the thermal extrusion of SO2 from a sulfone by refluxing in 1,2,4-trichlorobenzene, TCB, giving chlorins 2a-d in moderate yields (Scheme 1). 

The effect of dialkyltin maleates and laurates on the thermal dehydrochlorination of PVC has been compared in 1,2,4-trichlorobenzene solution by IR analysis, and showed that tin laurates are superior to tin maleates in replacing the labile chloride atoms in PVC. Attempts to trace intermediate monochlorotin derivatives in the case of maleates by polarography and Mossbauer spectroscopy were not conclusive. 

In 1953, recycling efforts for these waste isomers began, and thermal decomposition of these residues led to integration of several process steps (see figure). Thermal decomposition of the HCH isomers led to a 75% yield of 1,2,4-trichlorobenzene, which opened the process for production of 2,5-dichlorophenol and the corresponding bro-mination product. In addition to 2,5-dichloro-4-bromo-phenol production, the recycled trichlorobenzene was converted to 1,2,4,5-tetrachlorobenzene which could then be converted to 2,4,5-trichlorophenoxyacetic acid. 

Effects of a series of transition metal stearates, the concentration of the copper stearate, the solvent, various additives, and other factors on the thermal oxidation of polypropylene were studied in trichlorobenzene solution. The mechanism of copper catalysis is discussed. The order of decreasing catalytic activity of the metal stearates was Cu > Mn > Fe > Cr > Al Ni Co control Ti >> Zn >> V. The addition of propionic acid to the solvent accelerated the oxidation of the polymer. The presence of the copper leveled off oxygen uptake of the polymer after a certain time. The amount of oxygen absorbed decreased with increasing concentration of the copper, and at higher concentration (7.9 X 10 3M) the polymer oxidation was inhibited. 

Effect of Metal Stearates. The oxygen uptake curves of isotactic and atactic polypropylene in the presence of transition metal stearates in trichlorobenzene are shown in Figures 1 and 2, respectively. The order of decreasing catalytic effect of the metal stearates at the early stage of the oxidation of the polymers is for isotactic PP, Cu > Mn > Fe > Cr > Co > Ni > Ti > control > A1 > > Zn > > V and for atactic PP, Cu > Mn> Fe > Cr > Ah Ni Co control Ti >> Zn >> V. The order of the catalytic effect of the metals is quite different from that in bulk reported previously (16). In particular, V-stearate inhibits the thermal oxidation, and Co-stearate is not as effective as in bulk. In the presence of effective metal stearates such as Cu and Fe, the oxygen uptake levels off after a certain time. However, the amount of oxygen absorbed in the isotactic polypropylene is higher than that in the atactic polypropylene. 

One of the main functions of a metallic catalyst during autoxidation is believed to be promoting the breakdown of hydroperoxides to free radicals, thus continuing chain reactions (8). Thus, thermal decomposition of tert-butyl hydroperoxide was carried out in trichlorobenzene in the presence of the metal stearates. The results obtained are shown in Figure 3. It is difficult to correlate the catalytic activity of the metal stearates in the polymer oxidation with that of the decomposition of tert-butyl hydroperoxide in solution. 

Effect of Propionic Acid in Solvent. The thermal oxidation of the polypropylene in mixed solvent of trichlorobenzene and propionic acid was carried out, and the oxygen uptake curves obtained are shown in... 

Effect of Various Additives. From the results mentioned above, it is evident that the copper stearate is converted to inhibitors by the interactions of oxidation products, and the oxygen uptake appears to level oflF after a certain time. Thus, the effects of model compounds of oxidation products (n-octylaldehyde, n-octanoic acid, 2-octanone, n-octanol, and n-octanoic aCid methyl ester), tert-hutyl hydroperoxide, and di-ter -butyl peroxide on the thermal oxidation of the polypropylene in trichlorobenzene were examined. 

The isomers formed in either case are predominantely 1,2,4-trichlorobenzene and about 10-20 per cent of the 1,2,3-isomer. In the thermal dehydrochlorination, some disproportionation occurs with the formation of dichlorides and tetrachlorides and shifts to the stable 1,3,5-trichloro-berizene isomer can be produced in the presence of catalysts. 

Thiazolo- and benzothiazolopyrimidines are generally prepared by thermal cyclization of the enaminones prepared from 2-aminothiazoles and 2-aminobenzothiazoles with diethyl ethoxymethylenemalonate (Table IX). Two methods have been employed. Method A is a one-pot reaction of aminothiazoles with malonate in refluxing 1,2,4-trichlorobenzene without isolation of the enaminone intermediates. In method B. isolation of the enaminone intermediates prior to cyclization in trichlorobenzene usually provides purer products (72JMC1203). 

This reaction is quantitative in the presence of an excess of the amine and is the basic reaction for most of the methods by which the isocyanate content of a sample is determined. After completion of the reaction the excess amine is determined by back-titration with an acid. Since this involves acid-base reactions, the results must be corrected for any free acid in the sample. The most widely used amine is dibutylamine and this is the method that will now be described. Although for most isocyanates, toluene can be used as the solvent, for undistilled or modified isocyanates where thermal treatment is employed, better reproducibility is obtained using dry trichlorobenzene. 

In addition, again because of their well known thermal stability, PCBs are liable to oxidize into polychlorobenzofurans Instead of decomposing when exposed to air. Meanwhile, the trichlorobenzenes often found together with PCBs may form polychlorodibenzodioxins, which are well-known to be toxic, carcinogenic and teratogenic. However, this is not the reason for the prohibition of PCBs, as such reactions produce only small quantities of the more toxic substances. ... 

The unique phenomenon in the pyrolysis of vinylidene chloride/vinyl chloride copolymer is the trimer formation. Under pyrolysis conditions, the polymer will directly undergo the thermal dehydrochlorination to form a conjugated polyene [205]. The polymer will then unzip, followed by a radical cyclisation to form benzene, chlorobenzene, dichlorobenzene, and trichlorobenzene. The mechanism can be expressed as ... 

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