1.4- Dioxan, chlorination

In 1991, Krespan reported the preparation of 111 using the sequence, including photochemical chlorination of 1,4-dioxane, chlorine-fluorine exchange, and dechlorination of 1,2-dichlorohexafluoro-1,4-dioxane. ° Compound 114 was prepared using similar procedure. 

Phenols, m-cresol, concentrated mineral acids, formic acid Ethanolamine, dioxane, chlorinated hydrocarbons, cyclohexanone Dichlorobenzene, pentachloroethylene, dichloroethylene, tetralin Cresol, concentrated sulfuric acid, chlorophenol, trichloroacetic acid Dichlorobenzene, DMF, chlorophenol, benzyl alcohol Aromatic and chlorinated hydrocarbons, pyridine, ethyl acetate, dioxane, chloroform, acetone Fluorocarbon oil... 

The N-trif1uoroacetylated derivative of PCL is quickly soluble in many solvents (such as acetone, THF, dioxane, chlorinated hydrocarbons, etc.) and can easily be analyzed by conventional GPC apparatus. 

As an example, the self-ignition of gas phase mixtures of dioxane and chlorine was thoroughly investigated by F. Battin-Leclerc (refs. 10, 11). Dioxane is sometimes mentioned as a solvent for chlorination processes (ref. 12) whereas selfignitions of dioxane + chlorine mixtures is easily obtained near the ambient temperature. 

Alkane/alcohols Alkane / tetrahydrofuran Alkane/dioxan Chlorinated solvents... 

Chlorination of the azobenzene complex 463 with chlorine produces mono-chloroazobenzene with regeneration of PdCN. Then complex formation takes place again with the chlorinated azobenzene. By this sequence, finally tetra-chloroazobenzene (503) is obtained using a catalytic amount of PdCT. The reaction, carried out by passing chlorine gas into an aqueous dioxane solution of azobenzene and PdCf for 16 h, gives a mixture of polychlorinated azoben-zenes[455]. 

Methylene chloride is one of the more stable of the chlorinated hydrocarbon solvents. Its initial thermal degradation temperature is 120°C in dry air (1). This temperature decreases as the moisture content increases. The reaction produces mainly HCl with trace amounts of phosgene. Decomposition under these conditions can be inhibited by the addition of small quantities (0.0001—1.0%) of phenoHc compounds, eg, phenol, hydroquinone, -cresol, resorcinol, thymol, and 1-naphthol (2). Stabilization may also be effected by the addition of small amounts of amines (3) or a mixture of nitromethane and 1,4-dioxane. The latter diminishes attack on aluminum and inhibits kon-catalyzed reactions of methylene chloride (4). The addition of small amounts of epoxides can also inhibit aluminum reactions catalyzed by iron (5). On prolonged contact with water, methylene chloride hydrolyzes very slowly, forming HCl as the primary product. On prolonged heating with water in a sealed vessel at 140—170°C, methylene chloride yields formaldehyde and hydrochloric acid as shown by the following equation (6). 

Furan reacts vigorously with chlorine and bromine at room temperature to give poly-halogenated products. Low temperature (-40 °C) reaction of furan with chlorine in dichloromethane yields mainly 2-chlorofuran and reaction of furan with dioxane dibromide at 0 °C affords 2-bromofuran in good yield. 2-Iodofuran is obtained by treatment of 2-furoic acid with iodine and potassium iodide in aqueous sodium hydroxide. 

Compounds in which conformational, rather than configurational, equilibria are influenced by the anomeric effect are depicted in entries 4—6. Single-crystal X-ray dilfiaction studies have unambiguously established that all the chlorine atoms of trans, cis, ira j-2,3,5,6-tetrachloro-l,4-dioxane occupy axial sites in the crystal. Each chlorine in die molecule is bonded to an anomeric carbon and is subject to the anomeric effect. Equally striking is the observation that all the substituents of the tri-0-acetyl-/ -D-xylopyranosyl chloride shown in entry 5 are in the axial orientation in solution. Here, no special crystal packing forces can be invoked to rationalize the preferred conformation. The anomeric effect of a single chlorine is sufficient to drive the equilibrium in favor of the conformation that puts the three acetoxy groups in axial positions. 

Oxidations usually proceed in the dark at or below room temperature in a variety of solvents ranging from aqueous bicarbonate to anhydrous benzene-pyridine. Base is quite commonly used to consume the hydrogen halide produced in the reaction, as this prevents the formation of high concentrations of bromine (or chlorine) by a secondary process. The reaction time varies from a few minutes to 24 hours or more depending on the nature of the reagent and the substrate. Thus one finds that NBS or NBA when used in aqueous acetone or dioxane are very mild, selective reagents. The rate of these oxidations is noticeably enhanced when Fbutyl alcohol is used as a solvent. In general, saturated, primary alcohols are inert and methanol is often used as a solvent. 

However, when the chlorine atoms are more dispersed through a polychlorofluorocarbon, both chlorine and fluorine may be removed by zinc. In these cases, triphenylphosphine in dioxane can be used to prepare dechlonnated products in high purity and good yield [6S](equations 36 and 37)... 

Chloramine-B (CAB, PhS02NClNa) and chloramine-T (CAT, p-Me-C6H4S02NClNa) have also been used for the oxidation of sulphoxides107-115. The required sulphone is produced after initial attack by the sulphoxide sulphur atom on the electrophilic chlorine-containing species, forming a chlorosulphonium intermediate as shown in equation (34). These reactions take place at room temperature, in water and aqueous polar solvents such as alcohols and dioxane, in both acidic and basic media. In alkaline solution the reaction is slow and the rate is considerably enhanced by the use of osmium tetroxide as a catalyst115. 

Amorphous bisphenol-A polyarylates are soluble in dioxane and in chlorinated solvents such as CH2C12, 1,2-dichlororethane, 1,1,2-trichloroethane, and 1,1,2,2-tetrachloroethane while semicrystalline and liquid crystalline wholly aromatic polyesters are only sparingly soluble in solvents such as tetrachloroethane-phenol mixtures or pentafluorophenol, which is often used for inherent viscosity determinations. 

PVC has been shown to have a head-to-tail structure. Typical experimental evidence for this is that when dissolved in dioxan and treated with zinc dust, it undergoes a Wurtz-type reaction to yield a product containing a small amount of chlorine and no detectable unsaturation. The alternative possible structure, the head-to-head arrangement, would yield unsaturated sites where adjacent chlorine atoms had been removed (Reaction 1.4). 

TLC Analysis. Samples were examined by TLC using standard procedures. Rf values were determined and compared with those of authentic reference materials. Radioactive components were located by scanning (Vanguard Instrument Corp., North Haven, Conn., Model 885) or by autoradiography (Eastman Kodak, Rochester, N. Y., type AA film). The relative Rf value of DCDD on silica gel plates (Brinkmann Instruments, Inc., Westbury, N. Y., type For,4) when developed with n-hexane dioxane acetic acid, 90 10 4, V/V/V, was 0.90. The observed impurity had a relative Rf value of 0.40. On Brinkmann alumina plates, developed with n-hexane, DCDD had a relative Rf of 0.32. Neither system separated the chlorinated dibenzodioxin isomers. 

Marvel, Sample, and Roy concluded that cyclopropane rings were formed when a dilute solution of poly-(vinyl chloride) in dioxane was treated with zinc, which removes halogen atoms from alternate carbon atoms. Only 84 to 86 percent of the chlorine could be removed, however, a result which was attributed to the occasional isolation of a lone substituent between reacted neighbors. The structure of the product was presumed to be... 

Chlorine-enhancement may offer a partial solution. The addition of the chlorinated olefin TCE, PCE, or TCP to air/contaminant mixtures has recently been demonstrated to increase quantum yields substantially [1, 2, 6]. We recently have extended this achievement [3], to demonstrate TCE-driven high quantmn efficiency conversions at a reference feed concentration of 50 mg contaminant/m air not only for toluene but also for other aromatics such as ethylbenzene and m-xylene, as well as the volatile oxygenates 2-butanone, acetaldehyde, butsraldehyde, 1-butanol, methyl acrylate, methyl-ter-butyl-ether (MTBE), 1,4 dioxane, and an alkane, hexane. Not 1 prospective contaminants respond positively to TCE addition a conventional, mutual competitive inhibition was observed for acetone, methanol, methylene chloride, chloroform, and 1,1,1 trichloroethane, and the benzene rate was altogether unaffected. 

Aromatics, chlorinated hydrocarbons, lower alcohols, ketones, esters Alcohol, benzene, chlorinated hydrocarbons, esters, ether Alcohol, esters, ketones, dioxane... 

The only reported X-ray structure of a it-bonded diiodine exists in the 12/coronene associate [75], which shows the I2 to be located symmetrically between the aromatic planes and to form infinite donor/acceptor chains. -Coordination of diiodine over the outer ring in this associate is similar to that observed in the bromine/arene complexes (vide supra), and the I - C separation of 3.20 A is also significantly contracted relative to the stun of their van der Waals radii [75]. For the highly reactive dichlorine, only X-ray structures of its associates are observed with the n-type coordination to oxygen of 1,4-dioxane [76], and to the chlorinated fullerene [77]. 

It is believed that equatorial substituents such as chlorine or bromine would increase the guest diameter beyond the allowed values (assuming that the guest molecules stack roughly parallel to the canal68)). Support for this comes from the study of fluorocyclohexane where the population of the axial conformer is not enhanced to any major extent70. Nitro-71) and cyano-cyclohexane, trans-l,2-dichloro-, trans-1,2-dibromo-, tram-1,4-dichloro-, trans-1,4-dibromo-, and trans-l-bromo-4-chloro-cyclohexane all pack most efficiently in the thiourea canals as the axial or diaxial conformer 68,72. Tram-2,3-dichloro-1,4-dioxane behaves similarly73. In contrast isocyanato-, tram-1,4-diiodo-, trans-1 -bromo-4-iodo-, and tram-1 -chloro-4-iodo-cyclohexane are present as mixtures of the axial/equatorial or diaxial/diequatorial conformations as appropriate 68,72). The reason for this anomalous behaviour of the iodosubstituted cyclohexanes is not clear. 

A study of autoignition of dioxan vapour and chlorine, in the gas phase at rather below 1 atm. Ignition was once observed at 25°C in daylight. In the dark it occurred from 100°C. The maximum pressure rise observed was 26 MPa per sec [1]. Detonation properties of gaseous mixtures of chlorine and dioxane, sometimes diluted with argon, are studied in detail [2], The combination is more sensitive than most fuel/air mixtures. 

Dinitrobenzenes Dinitrotoluenes 1,4-Dioxane Esters Ethylamine Ethers Ethylene Nitric acid Nitric acid Silver perchlorate Nitrates Cellulose, oxidizers Oxidizing materials, boron triiodide Aluminum trichloride, carbon tetrachloride, chlorine, nitrogen oxides, tetrafluo-roethylene... 

When poly (vinyl chloride) in dioxane solution is made to treat with zinc dust the resulting polymer gets saturated and is having a small chlorine content. This reveals that it is having a head-to-tail structure. 

Mass chromatography of mlz 146 and 148 and mlz 180 and 182 is shown to be highly selective for di- and trichlorobenzenes. These components are only present in relatively minor amounts. A mass chromatogram at mlz 88 showed the presence of the rather volatile compound dioxane. This sediment sample obviously is heavily polluted with non-biodegraded mineral oil fractions and a number of other components (i.e. stearic acid, chlorinated benzenes), which point to spills of numerous bulk chemicals. 

The molecules of trans-2,3- and -2,5-dichloro-l, 4-dioxanes in the crystal are in the chair conformation with both chlorine atoms occupying axial positions (29). In solution, too, there is a preference for this conformation however, the dipole moment for the former molecule in solution is higher than expected for the purely diaxial conformation (30). 

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