1.2- Dioxines, reactions

Six-membered heterocycles with two heteroatoms are prepared by reaction of diketene with a substrate containing a C—O or C—N multiple bond. With carbonyl compounds diketene reacts in the presence of acids to give l,3-dioxin-4-ones. The best known is 2,2,6-trimethyl-4H-l,3-dioxin-4-one [5394-63-8] (15), the so-called diketene—acetone adduct, often used as a diketene replacement that is safer to handle and to transport, albeit somewhat less reactive than diketene itself (103,104), forming acetylketene upon heating. 

A shippable but somewhat less reactive form of diketene is its acetone adduct, 2,2,6-trimethyl-4JT-l,3-dioxin-4-one (15) (103,104). Thermolysis of this safer to handle compound provides acetylketene, a reactive intermediate that can be used for acetoacetylation and cycloaddition reactions. The diketene—acetone adduct as weH as / fZ-butylaceto acetate [1694-31 -1] (also used for aceto acetylations by the trans aceto acetylation reaction) (130), are offered commercially. 

Anhydrous aluminum chloride, AIQ, is manufactured primarily by reaction of chlorine [7782-50-5] vapor with molten aluminum and used mainly as a catalyst in organic chemistry ie, in Friedel-Crafts reactions (qv) and in proprietary steps in the production of titanium dioxine [13463-67-7] Ti02, pigment. Its manufacture by carbochlorination of alumina or clay is less energy-intensive and is the preferred route for a few producers (19). 

Dibenzo[6,e][l,4]dioxin, 2-nitro-bromination, 3, 974 cleavage reactions, 3, 973 Dibenzo[b,e][l,4]dioxin, 2,3,7,8-tetrachloro-synthesis, 3, 985 toxicity, 3, 992 Dibenzodioxins... 

Dioxins aromaticity, 3, 945 deprotonation, 3, 972 electronic energy levels, 3, 946 electrophilic reactions, 3, 965 half-wave potential, 3, 968... 

When the steam was shut off and, 15 minutes later, the agitator was switched off, heat transferred from the hot wall above the liquid level to the top part of the liquid, which became hot enough for a runaway reaction to start. This resulted in a release of TCDD (dioxin), which killed a number of nearby animals, caused dermatitis (chloracne) in about 250 people, damaged vegetation near the site, and required the evacuation of about 600 people (Kletz 1994). 

In cleaning up the site, dioxin-contaminated waste from the reaction ve.ssel were pac ked i ri turty-oric barrels that went astray in May 1983. They were eventually found in 1985 in the luirdicrn french town of Anguilcourt-le-Sart at an abattoir. Their contents were burned in t d i liigh-temperature incinerator. 

The use of an unnecessarily hot heating medium led to the runaway reaction at Seveso, Italy, in 1976, which caused a fallout of dioxin over the sun ounding countryside, making it unfit for habitation. Although no one was killed, it became one of the best-known chemical accidents, exceeded only by Bhopal, and had far-reaching effects on the laws of many countries. 

Cycloaddition reactions of o-benzoquinones with formation of bi- and tetracyclic systems including 2,3-dihydrobenzo[d]dioxine fragment 96SL1143. 

Thermal fragmentation of l,3-dioxin-4-ones or acylated Meldrum acids with generation of a-oxoketenes, hetero Diels-Alder reactions of the latter, and their transformations into lactones and lactams, among them macrocyclic 99YGK76. 

OOMIl, 01 Mil). Similar reactions of 1,2-dihydroxybenzene derivatives 237 with various less activated 2,6-dinitrochlorobenzene derivatives provided usually low yields of the corresponding dioxins (59JCS1899, 84JHC1073). To improve the yields, especially with less activated chloronitro compounds, a two-step... 

Trifluoromethyl-l,3-dioxin-4-ones can act as the enone component in [2 + 2] or as dienophiles in Diels-Alder reactions and are potential synthons for enantiomerically pure trifluoromethyl aliphatics [92JCS-(Pl)1393). 

Mere destruction of the original hazardous material is not, however, an adequate measure of the performance of an incinerator. Products of incomplete combustion can be as toxic as, or even more toxic than, the materials from which they evolve. Indeed, highly mutagenic PAHs are readily generated along with soot in fuel-rich regions of most hydrocarbon flames. Formation of dioxins in the combustion of chlorinated hydrocarbons has also been reported. We need to understand the entire sequence of reactions involved in incineration in order to assess the effectiveness and risks of hazardous waste incineration. 

The process needs input of lime and water next to the PVC waste. No energy input is needed since the organic condensate provides for the energy needed in the process. Energy needed for pretreatment can be up to 25-35 kWh/tonne. Downstream separation of the coke products needs another 30-40 kWh/toime. The process does not emit dioxins, metals or plasticisers. Due to internal recycling there are no aqueous waste streams. The reaction of lime with HCl forms some CO2. The coke product provides a calorific value. 

Uniformly labeled 2,4-dichlorophenol- C (purchased from New England Nuclear Corp, Boston, Mass.) was used in the tracer preparation. This provided a label at all carbon positions in the dibenzo-dioxin structure. 2,7-Dichlorodibenzo-p-dioxin- C after initial cleanup by fractional sublimation, contained approximately 5% of an impurity, detected by thin layer chromatography (TLC) which gave mass peaks at 288, 290, 292, and 294 in the mass spectrometer, consistent with a trichloro-hydroxydiphenyl oxide. This is probably the initial condensation product of the Ullman reaction and is most likely 2-(2,4-dichlorophenoxy)-4-chlorophenol. It was removed easily by extractions with aqueous... 

Muelder and Shadoff (3) prepared C-2,3,7,8-Cl4-DBpD (0.9 mCi/ mmole) by chlorination of C-2,7-dichlorodibenzo-p-dioxin made from potassium C-2,4-dichlorophenate. The preparation of tritium-labeled 2,3,7,8-Cl4-DBpD is justified because the radiolabeled intermediates are less expensive and more accessible and because a higher specific activity is potentially attainable. Here, we consider the optimal conditions for the reaction sequence designed to obtain products of high chemical and radiochemical purity shown at the top of p. 8. 

Several cases have been encountered that show the utility of x-ray powder diffraction as an analytical method for identifying dioxins. An attempt was made to synthesize 2,8-dichlorodibenzo-p-dioxin by heating the potassium salt of a trichlorinated 2-hydroxydiphenyl ether (3). Surprisingly, the major crystalline product under the initial reaction condi-... 

Thermal properties of several chlorinated phenols and derivatives were studied by differential thermal analysis and mass spectrometry and in bulk reactions. Conditions which might facilitate the formation of stable dioxins were emphasized. No two chlorinated phenols behaved alike. For a given compound the decomposition temperature and rate as well as the product distribution varied considerably with reaction conditions. The phenols themselves seem to pyro-lyze under equilibrium conditions slowly above 250°C. For their alkali salts the onset of decomposition is sharp and around 350°C. The reaction itself is exothermic. Preliminary results indicate that heavy ions such as cupric ion may decrease the decomposition temperature. 

For lower chlorinated phenates the reactions become even more complicated. The phenols vaporize without decomposition, and the sodium salts react in the melt (Figure 5), as shown for sodium 2,4-dichlorophenate. The relative amount of dioxins produced is lower in favor of more highly condensed material. 

In summary thermal decomposition of chlorinated phenols does not generally lead to dioxins. There are, however, several conditions which by themselves or combined would favor dioxin formation. First, of all chlorinated phenols either in bulk or in solution, only pentachlorophenol produced measurable amounts of dioxin. Secondly (Table II), only sodium salts in salid state reactions produced dioxins in reasonable yields. In contrast, the silver salt of pentachlorophenol (Figure 8) undergoes an exothermic decomposition at considerably lower temperatures and produced only higher condensed materials. No dioxin was detected. 

Thus, it seems that dioxins are only formed if the intermediate phenoxyphenol can be forced and held in a special molecular configuration to avoid the various competitive reactions leading to diflEerent products. 

Light can effect the coupling of phenols. For example, Joschek and Miller (22) found that phenoxyphenols could be produced in the flash photolysis of phenol, but although sought, no dioxin was detected in the reaction products. 

Oevere toxicological responses have been associated with certain chloro- dibenzodioxins. One of these responses is chloracne, a folliculosis first associated with skin contamination by chlorohydrocarbons in 1899 (3). Serious outbreaks of chloracne-like lesions associated with runaway reactions in the production of 2,4,5-trichlorophenol occurred in Germany in the early 1950 s (5). 2,4,5-Trichlorophenol itself does not cause acne (S), but the contaminants which may be formed in the uncontrolled production of 2,4,5-trichlorophenol are extremely potent acnegens (5). 2,3,7,8-Tetrachlorodibenzo-p-dioxin and tri- and tetra-... 

---