- Novel method for continuous production of fluroxypyr intermediate 3,5-dichloro-2,4,6-trifluoropyridine
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The invention discloses a novel method for continuous production of fluroxypyr intermediate 3,5-dichloro-2,4,6-trifluoropyridine. The method comprises the steps as follows: N-stage reactors are used,compound pentachloropyridine and a catalyst are added to each stage of reactor, and hydrogen fluoride is introduced into the first-stage reactor after heating, melting and dehydration; unreacted hydrogen fluoride and produced hydrogen chloride tail gas in each stage of reactor are introduced into a condenser in each stage for condensing, the uncondensed tail gas is introduced into the next stage of reactor, the tail gas of the last stage of reactor is condensed by two condensers, hydrogen fluoride is separated, discharged, absorbed by a tail gas recovery device and used as by-product hydrochloric acid, and hydrogen fluoride condensed and recovered by the condenser in each stage is returned to each stage of reactor. With adoption of the synthesis method, hydrogen fluoride use rate is high,purity of by-product hydrochloric acid is high, and the content of hydrogen fluoride is lower than 1%; the method has the advantages of being high in product yield and reaction selectivity, solvent-free, low in production cost, simple in process, green and environmentally friendly, and is very suitable for industrial production.
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Paragraph 0053-0060
(2018/05/30)
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- Computational and Experimental Studies of Regioselective SNAr Halide Exchange (Halex) Reactions of Pentachloropyridine
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The Halex reaction of pentachloropyridine with fluoride ion was studied experimentally and computationally with a modified ab initio G3MP2B3 method. The G3 procedure was altered, as the anionic transition state optimizations failed due to the lack of diffuse functions in the small 6-31G? basis set. Experimental Halex regioselectivities were consistent with kinetic control at the 4-position. The reverse Halex reaction of fluoropyridines with chloride sources was demonstrated using precipitation of LiF in DMSO as a driving force. Reverse Halex regioselectivity at the 4-position was predicted by computations and was consistent with kinetic control. Scrambling of halide ions between chlorofluoropyridines was catalyzed by n-Bu4PCl, and the products of these reactions were shown to result from a combination of kinetic and thermodynamic control. Comparison of the C-F and C-Cl homolytic bond dissociation energies suggests that an important thermodynamic factor which controls regioselectivity in this system is the weak C2-Cl bond. The differences between ΔH° values of chlorofluoropyridines can be explained by a combination of three factors: (1) the number of fluorine atoms in the molecule, (2) the number of fluorine atoms at the C2 and C6 positions, and (3) the number of pairs of fluorine atoms which are ortho to one another.
- Froese, Robert D.J.,Whiteker, Gregory T.,Peterson, Thomas H.,Arriola, Daniel J.,Renga, James M.,Shearer, Justin W.
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supporting information
p. 10672 - 10682
(2016/11/29)
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- POLYHALOAROMATIC EQUILIBRATIONS
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Chromium oxide is a good catalyst for scrambling halogens among polyhaloaromatic compounds.Chloropentafluorobenzene and bromopentafluorobenzene disproportionate to hexafluorobenzene and the respective tetrafluorodihalobenzenes.Pentachloro- and pentafluoropyridines produce pyridines with intermediate numbers of both types of halogens.Cyano, trifluoromethyl and a single hydrogen can be present on the aromatic rings without interfering with the chemistry.
- Weigert, F. J.
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- Preparation of 2-cyano-6-chloropyridine compounds
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Novel methods for preparing 2-cyano-6-chloropyridines are disclosed. The compounds are useful as intermediates in preparing other intermediates or as intermediates directly used in making pesticides, especially herbicides.
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