Dioxins, synthesis

Linear annulated dioxins synthesis were reported by analogy with that of the 1,4-benzodioxin series <2002T1533> or in a modification of the Ullmann ether synthesis <2004T8899>. 

Mason, G., M. A. Denomme, L. Safe, and S. Safe. 1987b. Polybrominated and chlorinated di-benzo-p-dioxins synthesis, biological and toxic effects and structure-activity relationships. Chemosphere 16 i-9) 1729-31. 

Although the absence of one of the five dioxin building conditions mentioned above hinders dioxin synthesis, it is currently not possible to precisely foresee dioxin emissions by considering known operational parameters. The building of a new furnace therefore needs the careful consideration of primary measures as well as the option to add secondary measures in case of unexpectedly high values. 

The proposed mechanism by which chlorinated dioxins and furans form has shifted from one of incomplete destmction of the waste to one of low temperature, downstream formation on fly ash particles (33). Two mechanisms are proposed, a de novo synthesis, in which PCDD and PCDF are formed from organic carbon sources and Cl in the presence of metal catalysts, and a more direct synthesis from chlorinated organic precursors, again involving heterogeneous catalysis. Bench-scale tests suggest that the optimum temperature for PCDD and PCDF formation in the presence of fly ash is roughly 300°C. 

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... 

Dichlorodibenzo-p-dioxin was prepared from isotopic potassium 2,4-dichlorophenate uniformly labeled with Ullman conditions gave a 20.5% yield. Small amounts of dichlorophenoxy chlorophenol were removed from the product by extraction with sodium hydroxide before purification by fractional sublimation and recrystallization from anisole. Chlorination of 2,7-dichlorodibenzo-p-dioxin in chloroform solution containing trace amounts of FeCls and 12 yielded a mixture of tri-, tetra-, and pentachloro substitution products. Purification by digestion in boiling chloroform, fractional sublimation, and recrystallization from anisole was effective in refining this product to 92% 2,3,7,8-tetrachloro isomer, which also contained 7% of the tri- and 1% of the penta-substituted dibenzo-p-dioxin. Mass spectroscopy was used exclusively to monitor the quality of the products during the synthesis. 

TAetection of the highly potent impurity, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), necessitated an environmental assessment of the impact of this contaminate. Information was rapidly needed on movement, persistence, and plant uptake to determine whether low concentrations reaching plants, soils, and water posed any threat to man and his environment. Because of the extreme toxicity of TCDD, utmost precautions were taken to reduce or minimize the risk of exposure to laboratory personnel. Synthesis of uniformly labeled C-TCDD by Muelder and Shadoff (I) greatly facilitated TCDD detection in soil and plant experiments. For unlabeled experiments it seemed wise to use only small quantities of diluted solutions in situations where decontamination was feasible and to rely on the sensitivity afforded by electron capture gas chromatography... 

Kuzuhara S, H Sato, N Tsubouchi, Y Ohtsuka, E Kasai (2005) Effect of nitrogen-containing compounds on polychlorinated dibenzo-p-dioxin/dibenzofuran formation through de novo synthesis. Environ Sci Technol 39 795-799. 

The complete elimination of functional groups is often an undesirable side reaction in organic synthesis, but on the other hand it is a possibility for the recycling of environmentally harmful compounds, for example phenols and haloarenes such as polychlorinated dibenzodioxins (PCDDs or dioxins ). For example, aryl chlorides can be effectively dechlorinated with Pd(0) NPs in tetra-butylammonium salts with almost quantitative conversions also after 19 runs (entry H, Table 1.4) [96]. On the other hand, a C-0 bond cleavage reaction also seems suitable for the fragmentation of sugar-based biomass such as cellulose or cello-biose in that way, sugar monomers and bioalcohol can be derived from renewable resources (entry F, Table 1.4) [164]. 

Miriyala and Williamson have described the synthesis of /i-kctocarboxam idcs from primary and secondary amines and 2,2-dimethyl-2H,4H-l,3-dioxin-4-ones as reactive a-oxoketene precursors (Scheme 6.158) [304], The experimental procedure involved heating a mixture of the dioxinone with 2-3 equivalents of the amine at ca. 180 °C for 1-3 min under solvent-free conditions in a sealed vessel by microwave irradiation. A small collection of 18 /3-ketocarboxamides was prepared in very high yields using this protocol. 

In Scheme 6.230, the multistep synthesis of 2,3-dihydro-4-pyridones is highlighted [411]. The pathway described by Panunzio and coworkers starts from a dioxin-4-one precursor, which is readed with 2 equivalents of benzyl alcohol under solvent-free microwave conditions to furnish the corresponding /1-diketo benzyl esters. Subsequent treatment with 1 equivalent of N,N-dimethylformamide dimethyl acetal (DMFDMA), again under solvent-free conditions, produces an enamine, which is then cyclized with an amine building block (1.1 equivalents) to produce the desired 4-pyridinone produds. All microwave protocols were conducted under open-vessel conditions using power control. 

I. M. Muslimova, F. F. Hizbullin.- Problem of Accumulation of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in Sludge Reservoirs of the Enterprises of Chlororganic Synthesis. Ecological Chemistry.-2001.-Vol. 10.- No. 04, p.269-274. 

Dioxin vinylogous esters derived from cyclic 1,3-diketones (e.g., 4) are valuable building blocks for the construction of natural and unnatural carbocyclic products.2 In connection with a synthesis of plant-growth regulators, Crow and... 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

The synthetic usefulness of dioxin vinylogous esters as p-keto vinyl cation equivalents was demonstrated by a variety of reductive and alkylative 1,3-carbonyl transpositions.5 7 Regioselective alkylation and hydroxylation at the a -position (and, in some cases, at the y-position)8 9 further extend the usefulness of 1,3-dioxin vinylogous ester templates in organic synthesis. 

As in the case of the 1,2-dioxins, the 1,2-dithiins exist in various states of saturation, oxidation, and benzoannelation (cf. Scheme 1, 17-27) and they have been studied in detail both theoretically and experimentally. Not only were the conformations of the ring and attached substituents investigated, but the valence isomerism of 1,2-dithiin by both NMR and high-level ab initio molecular orbital (MO) calculations and the dithiol/disulfide equilibrium by MP2 calculations were also examined. The latter equilibrium has been applied successfully as a luminescent molecular switch (cf. Section 8.10.2.1). Finally, as a very interesting 1,2-dithiin derivative, the synthesis, structure, and reactivity of the (-l-)-camphor-derived analog 25 and its sulfoxide 26 and sulfone 27 have been reported. Both the synthesis and the antimalarial activity of the 2,3-dioxabicyclo[3.3.1]nonane pharmacophore 28, which contains the 1,2-dioxane moiety, have been reviewed recently <2006BML2991>. 

Disubstituted-3,6-dihydro-l,2-dioxines can be dihydroxylated readily with OsOa to furnish the 4,5-diols 73 in yields of 33-98% and with de values not less than 90%. Subsequent reduction of the peroxy bond allowed the stereospecific synthesis of tetraols 74 without the use of protecting groups <2006JOC7236>. 

Disubstituted thiophenes 96 and 1,2,5-tri- and 2,5-disubstituted pyrrole derivatives 97 are available readily from m-3,6-disubstituted-3,6-dihydro-l,2-dioxins in a one-pot synthesis. The reaction proceeds by an initial Kornblum-de la Mare rearrangement of the 3,6-dihydro-l,2-dioxin to its isomeric 1,4-diketone followed by the condensation with Lawesson s reagent, ammonium carbonate, or a primary amine (Scheme 21) <2002TL3199>. 

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