Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/35—Preparation of halogenated hydrocarbons by reactions not affecting the number of carbon or of halogen atoms in the reaction
  • C07C17/358—Preparation of halogenated hydrocarbons by reactions not affecting the number of carbon or of halogen atoms in the reaction by isomerisation

Definitions

• the invention relates to a process for the isomerization of substituted aromatic compounds in the presence of special molten salts.
• Poly-substituted aromatic compounds have a high industrial importance.
• Aromatic compounds having halogen substituents can be isomerized to the thermodynamic equilibrium with the aid of acidic catalysts.
• Aromatic compounds having halogen substituents may be, for example, dichlorobenzene mixtures.
• Suitable catalysts include acidic zeolites (Russ, Chem. Bull., 1994, 43 (11), 1809-1811) or aluminum chloride, which contains acidic protons by partial hydrolysis or by addition of acid.
• DE 1020323 A describes the continuous isomerization of dichlorobenzene mixtures containing para and ortho-dichlorobenzene with the aid of aluminum chloride in combination with support materials and in the presence of a hydrogen chloride gas stream. This is formed meta-dichlorobenzene over a with the
• DE 4430950 A describes an improved isomerization process in which the activity of the aluminum chloride catalyst is increased by the addition of special water-donating activators.
• common to the prior art processes is that the separation of the catalyst and the maintenance of the catalytic activity are problematic. This means that a significant proportion of the catalyst must be hydrolyzed and replaced. The resulting costs for wastewater and catalyst are significant disadvantages of the described method.
• the object was to provide a particularly economical process that allows the efficient isomerization and product workup.
• the invention now provides a process for the isomerization of compounds of the formula (I) or mixtures of compounds of the formula (I)
• Ar is an n-valent aromatic radical
• n represents a natural number of 2 or more, preferably 2 or 3 and more preferably 2 and
• R each independently is halogen, alkyl, fluoroalkyl, aryl, alkylaryl or amino, which is characterized in that the isomerization is carried out in the presence of a molten salt which comprises:
• M 1 for aluminum, gallium, indium, copper, iron, cobalt, nickel or copper,
• X 1 is a halogen, preferably chlorine or bromine, more preferably chlorine, and ml is aluminum, gallium, indium, iron is 3, cobalt, nickel and copper is 2
• M 2 is an alkali metal, preferably lithium, sodium or potassium, with lithium being even more preferred,
• X 2 is a halogen, preferably chlorine or bromine, more preferably chlorine and m2 for alkali metals is 1.
• Ar is preferred for carbocyclic aromatic radicals having 6 to 24 skeleton carbon atoms or for heteroaromatic radicals having 5 to 24 skeletal atoms, in which none, one, two or three skeletal atoms per cycle, in the entire molecule at least one skeleton atom are heteroatoms selected from the group Nitrogen, sulfur or
• Ar is particularly preferably aromatic radicals derived from benzene, naphthalene,
• Ar is most preferably aromatic radicals derived from benzene or
• derivative is meant here that it is an n-valent radical of the otherwise unsubstituted aromatic compound.
• the trivalent aromatic radical for example in the case of trichlorobenzene, is derived from benzene.
• each alkyl is independently a straight-chain, cyclic, branched or unbranched alkyl radical.
• alkyl is methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, cyclohexyl, n-hexyl, n-heptyl, n-octyl, iso-octyl, n-decyl or n- dodecyl.
• fluoroalkyl each independently represents a straight-chain, cyclic, branched or unbranched alkyl radical which is substituted by at least one fluorine atom.
• fluoroalkyl is fluoromethyl, difluoromethyl, trifluoromethyl, 2,2,2-trifluoroethyl, pentafluoroethyl, heptafluoroisopropyl or nonafluoro-n-butyl.
• Particularly preferred compounds are the respective isomers of dichlorobenzene, preferably p-dichlorobenzene and o-dichlorobenzene, trichlorobenzene, chlorotoluene, dibromobenzene and bromochlorobenzene.
• Particularly preferred are the isomers of dichlorobenzene.
• a molten salt is to be understood as meaning a liquid which is at least 90% by weight or more, preferably up to 95% by weight or more, particularly preferably up to 98% by weight or more, of the compounds of the formula (II) and ( III).
• the deviating from 100% share may result, for example, from the imperfect purity of the compounds used, which may for example have technical quality. This brings economic benefits.
• Double salts of the formula [M ⁇ M ⁇ L 'L 2 ] ⁇ ) such as L1AICI 4 or triplet salts such as NaAl 2 Cl 7 or even higher complex salts can form.
• Such compounds are subsumed under the term molten salt containing at least one compound of formula (II) and at least one compound of formula (III) or such compounds meet the feature "containing at least one compound of formula (II) and at least one compound of formula
• the melting point may vary depending on the composition of these molten salts.
• the molar ratio of compounds of the formula (II) to compounds of the formula (III) is preferably 1: 1 to 10: 1, preferably 1: 1 to 3: 1 and particularly preferably 1.8: 1 to 2.2: 1 with 2: 1 being even more preferred.
• Preferred compounds of formula (II) are aluminum chloride (AICI 3 ), aluminum bromide (AICI 3 ) and gallium chloride (GaCL), with aluminum chloride being preferred.
• Preferred compounds of formula (III) are lithium chloride (LiCl), lithium bromide (LiBr), potassium chloride (KCl), sodium chloride (NaCl) and cesium chloride (CsCl), with lithium chloride being preferred.
• the Lewis acidity introduced via the compounds of the formula (II) is high and the melting point of the molten salt is so low that the isomerization can be carried out at temperatures which affect the compounds of the formula (I) at least largely undecomposed.
• Table 1 shows examples of low-melting salt melts which are particularly suitable as catalyst systems for isomerization.
• Table 1 Melting points of binary and ternary molten salts
• the content of protons is, for example, from 1 mol ppm to 50,000 mol ppm, based on compounds of the formula (II), preferably 10 to 1,000 mol ppm. Higher levels are likely to interfere with isomerization by decreasing Lewis acidity.
• Protons here are to be understood as meaning those protons which originate from compounds which are precisely these protons having a pKa of 5 or less, preferably 2 or less and more preferably 1 or less at 25 ° C., based on an aqueous system or aqueous reference system , can release.
• the separate addition of corresponding compounds that provide these protons is not required since the compounds of formulas (II) and (III) used are typically never absolutely free of water.
• Water typically reacts with compounds of formula (II) to form corresponding acidic compounds.
• aluminum chloride by partial hydrolysis with minimal amounts of water typically always contains traces of hydrogen chloride, which provides protons due to its low pK value of -6.
• the molar ratio of compounds of the formula (I) to compounds of the formula (II) is preferably 1: 1000 to 100: 1, preferably 1: 1 to 10: 1, more preferably 20: 1 to 3: 1, and very particularly preferably 2: 1 to 5: 1.
• the reaction temperature in the isomerization is, for example, between 100 ° C and 220 ° C are selected, with a lower temperature leads to an unfavorable slowing down of the reaction and too high a temperature sublimation of some compounds of formula (II) such as aluminum chloride and depending Type of compound of formula (I) promotes decomposition of the same.
• the reaction temperature during the isomerization is preferably 120 to 200 ° C., more preferably 140 to 180 ° C.
• a temperature of 160 to 180 ° C. and, for methyl halobenzenes a temperature of 140 to 160 ° C. are particularly advantageous.
• the isomerization is due to the different nature of the compounds of the formulas (I) to (III) typically and preferably two liquid phases, wherein the first phase of the compounds of formula (I) is formed and the second phase of the compounds of Formulas (II) and (III).
• the two phases are mixed together by introducing mixing energy to increase the phase interfaces.
• mixing energy to increase the phase interfaces. The more intense this happens, the faster the reaction typically proceeds.
• the reaction time of the isomerization is usually between 10 minutes and 168 hours, preferably between 30 minutes and 24 hours.
• the product mixture obtained from the compounds of the formula (I) can be separated off from the compounds of the formulas (II) and (III), preferably as long as they still form a melt and are not solidified.
• protons are, as above, those protons which originate from compounds which contain precisely these protons having a pKa of 5 or less, preferably 2 or less and more preferably 1 or less at 25 ° C. relative to an aqueous system or Aqueous reference system, can release.
• the compounds of the formula (II) and (III) are therefore preferably brought into contact with hydrogen chloride or hydrogen bromide gas before or during their renewed or repeated use, the partial pressure of these gases being, for example, 50 hPa to 1 MPa, preferably 500 hPa to 2500 hPa can.
• Advantage of the invention is that a complex extraction of the product phase or workup with water is eliminated and the isomerization catalyst can be used multiple times without loss of activity.
• a sample is taken directly from the reaction mixture, dissolved in dichloromethane and extracted with water. To determine the isomer ratio, the sample is analyzed by gas chromatography (GC). All data are based on GC area percent. The following data with mol% refer to the salt components with respect to the particular substrate used, which was isomerized.
• Example la Isomerization of para-dichlorobenzene with AICI 3 / L1CI in a glass autoclave
• Aluminum was typically less than 1%> with respect to the aluminum chloride used. A discharge of lithium could not be observed.
• Example lb Recycling of the molten salt
• the product phase was separated.
• the discharged aluminum chloride was replaced and 250 g of new para-dichlorobenzene was added.
• a reaction temperature of 170 ° C was set.
• a hydrogen chloride pressure of about 1.0 bar was applied.
• the activity of the molten salt remained constant over at least 5 recycles.
• Table 2 Product composition after recycling meta-dichlorobenzene para-dichlorobenzene ortho-dichlorobenzene
• the product mixture consisted essentially of the three isomers of dichlorobenzene, small amounts of discharged aluminum chloride and small amounts of by-products.
• the dichlorobenzene was quantitatively separated by flash distillation. Both the aluminum chloride and the by-products remained in the sump. The proportion of by-products was less than 1 wt .-%.
• Example 4 Temperature dependence of the isomerization of para-dichlorobenzene with AlCl 3 / NaCl / LiCl
• Example 6b Recycling of the molten salt in the isomerization of ortho-dichlorobenzene
• Example 11 Isomerization of para-dibromobenzene with AlCVLiCl and AlBr 3 / LiBr
• Example 12 Isomerization of para-xylene with AlC / NaCl / LiCl

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• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
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• 2012
  • 2012-06-18 EP EP12172384.5A patent/EP2676947A1/de not_active Withdrawn
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