CA2117735A1 - Process for preparing 1-bromo-3,5-difluorobenzene - Google Patents
Process for preparing 1-bromo-3,5-difluorobenzeneInfo
- Publication number
- CA2117735A1 CA2117735A1 CA002117735A CA2117735A CA2117735A1 CA 2117735 A1 CA2117735 A1 CA 2117735A1 CA 002117735 A CA002117735 A CA 002117735A CA 2117735 A CA2117735 A CA 2117735A CA 2117735 A1 CA2117735 A1 CA 2117735A1
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- bromo
- difluorobenzene
- reaction
- preparing
- zeolites
- Prior art date
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-
- 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
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- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
- Catalysts (AREA)
Abstract
Abstract of the disclosure:
Process for preparing 1-bromo-3,5-difluorobenzene Process for preparing 1-bromo-3,5-difluorobenzene, which comprises isomerizing 1-bromo-2,4-difluorobenzene or a mixture of 1-bromo-2,4-difluorobenzene and 1-bromo-2,6-difluorobenzene over acid zeolites of the pentasil type.
Process for preparing 1-bromo-3,5-difluorobenzene Process for preparing 1-bromo-3,5-difluorobenzene, which comprises isomerizing 1-bromo-2,4-difluorobenzene or a mixture of 1-bromo-2,4-difluorobenzene and 1-bromo-2,6-difluorobenzene over acid zeolites of the pentasil type.
Description
-~ 21~77~
HOECHST AKTIENGESELLSCHAFT HOE 93/F 314 Dr.MU/wo Description Proce~s for prepar~ng 1-bromo-3,5-difluorobenzene The present invention relates to a proce~ for preparing 5 1-bromo-3,5-difluorobenzene. -~
1-Bromo-3,5-difluorobenzsne is a precur~or for prepar~ng pharmacoutical~
According to the prior art, 1-bromo-3,5-difluorobenzene can be prepared by the following methode:
1. By brominating 2,4-difluoroaniline, followed by diazotization with NaNO2 and deamination with hypo-pho~phorous acid in acid ~olution.
Using this method, A. Roe and W.F. Little, J. Org.
Chem. 20 (1955) 1577/1590 obtain 1-bromo-3,5-difluorobenzene in a yield of 60%. -L.I. gruse et al., J. Org. Med., 29 (19B6) 887/889 and J. Org. Med., 30 (1987) 486/494 achieve an overall yield of 57% o$ l-bromo-3,5-difluorobenzene.
US 5,157,169 de~cribe~ a yield of 70% of l-bromo-3,5-difluorobenzene.
The yield~ obtained by thie process are low and expensiYe ~tarting material~ get loat. The proces~
consi~ts of many step~ and producea, in particular in the diazotization and deamination proce~s steps, acid~ and salt~ a~ coupled product~. Accordingly, this proce~s i~ not very suitable for preparing 1-bromo-3,5-difluorobenzene on a larger scale.
1 1773~
HOECHST AKTIENGESELLSCHAFT HOE 93/F 314 Dr.MU/wo Description Proce~s for prepar~ng 1-bromo-3,5-difluorobenzene The present invention relates to a proce~ for preparing 5 1-bromo-3,5-difluorobenzene. -~
1-Bromo-3,5-difluorobenzsne is a precur~or for prepar~ng pharmacoutical~
According to the prior art, 1-bromo-3,5-difluorobenzene can be prepared by the following methode:
1. By brominating 2,4-difluoroaniline, followed by diazotization with NaNO2 and deamination with hypo-pho~phorous acid in acid ~olution.
Using this method, A. Roe and W.F. Little, J. Org.
Chem. 20 (1955) 1577/1590 obtain 1-bromo-3,5-difluorobenzene in a yield of 60%. -L.I. gruse et al., J. Org. Med., 29 (19B6) 887/889 and J. Org. Med., 30 (1987) 486/494 achieve an overall yield of 57% o$ l-bromo-3,5-difluorobenzene.
US 5,157,169 de~cribe~ a yield of 70% of l-bromo-3,5-difluorobenzene.
The yield~ obtained by thie process are low and expensiYe ~tarting material~ get loat. The proces~
consi~ts of many step~ and producea, in particular in the diazotization and deamination proce~s steps, acid~ and salt~ a~ coupled product~. Accordingly, this proce~s i~ not very suitable for preparing 1-bromo-3,5-difluorobenzene on a larger scale.
1 1773~
2. ~y photochamical bromination of m-difluorobenzene R. Bolton and E.S.E. Owen, J. Fluor. Chem. 46 (1990) 393/406 describe that thi~ method gives 19% of 1-bromo-3,5-difluorobonz~n- in addltion to 10% of other bromodifluorobenzene i~omer~ and 43% of moro highly brominated difluorobenzenes. In thl~ proces~, the formation of l-bromo-3,5-difluorobenzeno has low selectivity.
l-Bromo-3,5-difluorobenzene cannot be obtained by direct bromination o m-difluorobenzene. This reaction selectively produces 1-bromo-2,4-difluoro-benzene .
l-Bromo-3,5-difluorobenzene cannot be obtained by direct bromination o m-difluorobenzene. This reaction selectively produces 1-bromo-2,4-difluoro-benzene .
3. By isomerization of l-bromo-2,4-difluorobenzene In EP 63,066, 1-bromo-2,4-di$1uorobenzsne i8 isomer-ized in the presence of alkali metal bases, prefer-ably alkali metal amides, and macrocyclic compounds, such as, for exEmple, polyethers.
This proce~s ha~ a number o~ disadvantages. The macrocyclic compou~d~ have a complicated structure and are therefore very expensive. They are not recovered after the reaction. To work up the pro-duct, the ba~ic reaction mixture must be neutral-ized, resulting in the formation of salts. Owing to the low yields of 63% of 1-bromo-3,5-di~luorobe~zene and the high CoEt of material~, this proce~ is not very economic.
~P 04 182 440 (CA 117: 170951n) describes the isomerization o$ 1-bromo-2,4-difluorobenzene in the presence o~ alkali metal t-butoxi.d2s or aluminum halides. This procesR too requires an additional, ~alt-forming neutralization ~tep. The yield of 1-bromo-3,5-difluorobenzene is only 41.4%.
~'','.`'.,~,.`...... ,'',.. '`'. ' ;
''` ,,'. ,~. '' .. ',.,.', , : ,'; , ; ' . . ` ' ` '2~ 1773~) . I .`~
; - 3 -Other materials used for preparing 1-bromo-3,5-difluoro-benzene have not been described in the literature.
Accordingly, there wa~ a need for a procea~ whlch avold~
the dl~advantage~ de~cribed and provide~ 1-bromo-3,5-difluorobenzene by a ~lmplo indu~trial proce~, avoid~by-products and leads to low environmental pollution.
This ob~ect is achieved by a proce~ for preparing 1-bromo-3,5-difluorobenzeno which comprisos isomorizing 1-bromo-2,4-difluorobenzene or a mixture of 1-bromo-2,4-difluorobonzene and 1-bromo-2,6-difluorobonzene on acid zeolites of the pentasil type. ~ -JP 58/144,330 describes isomerization of di- and tri-chlorobenzene over acid zeolites. The process i8 said to be generally applicable to polyhalogenated monocyclic -~
aromatics, the claimed halogens being fluorine, chlorine, bromine and iodine. Any acid zeolites into the pores of which educts and products can diffuee are said to be suitable zeolites according to the invention.
Surprisingly, it has now been found that in contrast to the teaching of ~P 58/144i330 acid zeolitos are not generally suitable for catalyzing the isomorization of polyhalogenatod monocyclic aromatic compounds. Whil- JP
58/144,330 claims that zeolites of the mordenite typo are also suitable for effecting isomerization of polyhalo-genated monocyclic aromatics, which, however, is only documented for di- and trichlorobenzenes, it has however been ~hown that zeolites of tha mordenite type are not suitable at all for isomerizing 1-bromo-2,4-difluoro-- benzene~ Acid mordenites preferentially lead to undesir-able ~ide reactions, such a~ elimination of HBr and transbromination. Thus, the use of an acid mordenite gives m-difluorobenzene and difluorodibromobenzenes at a conversion of as low as 10% with a selectivity of 75~. -Furthermore, the teaching of JP 58/144,330 does not apply to all halogenated aromatics. Since a fluorine atom on an aromatic ring i8 immobile, compound~ exclusivoly sub0ti-tuted by fluorine, ~uch ao m-difluorobenzene, cannot bo isomerlzed (~. Pardillo~ et al., J. Am. Chem. Soc., 112 (1990) 1313/131B).
Against this baakground, it could not be expected that an acid zeolite would bo suitable at all for i~omerizing 1-bromo-2,4-difluorobenzene to 1-bromo-3,5-difluoro-benzene~ It is all the more surprislng that zeolites of the penta~il type are highly ~uitable for this type of isomerization. It i~ particularly ~urpris~ng that l-bromo-2,6-difluorobenzene can bo l~omerized to l-bromo-3,5-difluorobenzene since the intramole¢ular mochanism described for the isomerization of halogonated aromatics (J. Pardillos et al., J. Am. Chem. Soc., 112 ~1990) 1313/
1318) cannot take place. In the ca~e of acid mordenite~, the result iB as expected in that bromine i8 eliminated from 1-bromo-2,6-difluorobenzene a~ ~r or tran~ferred to another bromodifluorobenzene molecule. Thus, when a mixture of 1-bromo-2,4-difluorobenzene and 1-bromo-2,6-difluorobenzene i~ used for the reaction, the selectivityof the formation of m-difluorobenzene and dibromodi-fluorobenzenes l~ 93% at a conver~ion of 6%.
Zeolite~ of the pentasil type usable as catalysts for the proces~ according to the invention belong to the medium-pore zeolites whose pore opening~ are formed by 10tetrahedral atoms. Tetrahedral atoms are Al ~nd Si atoms 3urrounded tetrahedrally by oxygen atom~. These tetra-hedra are linked via common oxygen atoms and ~orm a cry~tal structure which is a network of pore~ and void~.
The characteri~tic feature of the pentasils is a ~truc-ture which can be built up from the ~o-called penta~il unit~. The two la~t members o$ all pentasil structures are ZSM-5 (MFI ~tructure) and ZSM-11 (NEL structure). The crystal structure~ of the penta~ are described, for example, in P.A. Jacobs and J.A. Marten~, "Synthesi~ of High-Silica Zeolites", El~evier Science Publishers, 1989.
` ~17735 ., .` -In many case~, the uRe of zeolites hav~ng the ZSM-5 crystal structure ha~ given good re~ults ln the ~somer-ization of bromodifluorobenzene~.
It ha~ also prov~n favorablo lf tho S~O2/A12O3 ratlo of the zeollte~ according to the invention is botwoen 22 and 200, preferably botween 24 and 100.
The zeolites mentioned can be prepared by hydrothermal synthesis using procedur0~ from the literature. After crystall$zation, the zeolite~ are filterod off and dr~ed.
If synthe~i~ was carried out ln the pre~ence of an organic template, it mu~t be followed by calcining ln an oxidizing atmo~phere, preferably in air, in order to remove the organic compound from the pores. (The template-free form i~ free of alkylammonium or -phosphon-ium ions of amines).
Any alkali metal ions present are then exchanged for di-or trivalent metal cations or for ammonium ions or protons. Of these, ion exchange with NH4' or H~ iB very particularly preferred. This acid modification is neces-sary since otherwise the zeolite doe~ not exhibit anycatalytic effect. It i~ advantageous to exchange at least 50%, ~referably at least 90%, of the alkali metal ion~
for the other ion~ mentioned. At 200 to 800C, preferably 400 to 500C, the zeolitos are converted into the cata~
lytically form by dehydration (and elimination of ammonia in the case of NH4t forms).
For the use according to the invention, the zeolites can either be compacted in the ab~ence of binders or brought into a suitable application form using binders, for exa~ple into the form of extrudates. Suitable binder~ are in particular oxide~, hydroxides or hydroxychlorides of aluminum and the oxides of ~ilicon, titanium and zircon-ium and clay materials.
The i~omerization temperature can be between about 250 ~1~ 7735 . .
; .--- 6and 550C, preferably between 275 and 450C.
The process according to the lnvontlon can be carried out either batchwi~e or cont~nuou~ly.
Batchwise isomorizatlon can bo effected most ~imply in an autoclave. Since the reaction tempsrature is higher than the boiling point temperature~ of the reactants and products, the reaotion i~ carried out at A correspond-ingly increased reaction pres~ure.
The catalyst which is in the form of a powder or has been compaoted to give pellets can be suspended in the feed mixture. The feed mixture/cataly~t weight ratio can range from 1:1 to 1000:1, preferably from 5:1 to 50:1. The reaction can be carried out in the presence of a ~olvent which is inert to the catalyst, or in the absence of a solvent, i~omerization in the absence of a solvent being preferred. The reaction time can be between about 1 hour and 12 hours, depending on the reaction temperature and the degree of conversion to be achieved.
Continuous ieomerization can take place in any apparatu-ses suitable for thi~ purpose, such as, for example, ina fixed bed or in a fluidized bed. A fixed bed reactor is the ~implest in tRrms of technical operation. The cata-lyat is introduced into the reactor in the form of pellets, and l-bromo-2,4-difluorobenzene or mixtures of bromodifluorobenzene isomer~ are passed over it.
The reaction can be carried out in the presence of gases, such as, for example, nitrogen or hydrogen. The presence of hydrogen may have the effect of reducing the formation of higher-boiling products, ~uch as dibromodifluoro-benzene, and increasing the service life of the catalyst.
The catalyst treatment, which i~ oharacterized by theLHSV (= liquid hourly space velocity, 9 feed per hour per 1 of catalyet), can be varied in the range between 0.1 ;à~ ", '~117735 . ~
.;.
and 5 h-1, preferably betwe~n 0.2 and 2 h-1.
The product mixture obtained ~n tho roa¢tlon cun be separated by dl~tlllatlon. H~r and HF, whlch are formed during the reactlon ln trace~, can be removed prior to the di~tillat~on by wa~hing wlth water or alkallne solu~ions or el~e separated off directly together wlth m-difluorobenzene a~ low-boiling fraction. m-Difluoro-benzene can bo reused for bromination. Of the 3 lsomeric difluorobenzenes, 1-bromo-3,5-difluorobenzsne can be ~eparated off as the lowost bo~ling $somer. After 1-bromo-3,5-difluorobenzene ha~ boen eeparated off, l-bromo-2,6-difluorobonzene and h~gher-boillng products and po~sibly ~mall amount~ of 1-bromo-3,5-difluorobenzene remain, apart from 1-bromo-2,4-difluorobenzene. This fraction can elther be directly recycled into the isomer-ization or be ~eparated off from the higher-boiling products by further distlllatlon. Recycling the uncon-verted l-bromo-2,4-difluorobenzene and the by-products formed during isomerization makes it possible to achieve a high yieid of 1-bromo-3,5-difluorobenzene.
The examplee which follow serve to illustrate the process according to the invention in more detail without limit-ing it thereto.
, ~ ~
; Examples:
Example~ 1 to 6 and C1 and C2 are carried out in a fixed-bed flow reactor at a~mospheric pressure. 25 ml of catalyst (zeolite content 80%, Al203 binder 20%, particle size 1 to 2 mm) are introduced into a quartz glass reactor (internal dia~eter 20 ), which can be heated by an electrio furnace, 1-bromo-2,4-difluorobenzene i8 metered in at the top, and the reaction products are condensed at the reactor exit. The L~SV is 0.5 h-1. If a carrier gas i~ u~edl ~he flow rate is 3 l/h. Prior to the reaction, the zeolites are dried at 500C in nitrogen.
~ ~'~
. ~. .?~
The reaction product~ are analyzed by ga~ chromatography.
The re~ult~ from i~omerlzation over variou~ cataly~t~ are ~ummarized ln Table 1.
Table 1:
Ex. Zeolite SiO2/ ~ar- Temp. Time Con- S3 5 s2 6 SDP~ S~B
Al23 rier C h ver- mo~ mo~ mol mol gao ion % % % %
_ ,,,, .o , _ _ ~ ' 10 1 HZSM-5 27 300 0.3 1 82 9 9 ~ 1 _ _ :
2 HZSM-5 27 350 0.3 6 72 7 17 4 _ _ 2 63 85 8 5 2 15 4 HZSM-5 27H2 300 1.3 4 74 7 14 4 315 6.8 8 88 8 3 1 345 29.5 1 89 9 2 0 - _ 435 55.8 25 84 12 4 0 HZSM-530 ~2300 3.3 8 82 6 12 1 335 27. 26 88 6 5 0 , _. .
6 XZSM-ll 80 H2355 5.8 16 87 9 3 0 390 14. 22 86 11 3 0 _ _ ,-~ , .
Cl H mor-34 350 0.3 44 15 8 5522 denite _ 2.5 12 14 1150 24 C2 ~ beta 24 _ 350 2 27 14 6 53 28 ' S3, 5 Selecti~ity of the formation of l-bromo-3,5-difluorobenzene S2, 6 Selectivity of the formation of l-bromo-2,6-difluorobenzene ~'-',',i,,,,,,,,,~",'~,:;~i,'"~"',,`.,"~ ",,~ :' " ~, `~ 7 7 ~ ~
..
g SDFB Selectivity of the formation of m-difluoro-benzene SHB Selectivity of the high-bolling component~, v.o. dibromodifluorobenzenes Example~ 7 and C3:
The exp~riment~ were carried out as de~cribed ~n Example~
1 to 6. A mixture ~ontaining 87% of 1-bromo-2,4-d~fluoro-benzene, 12~ o~ br~mo-2,6-difluorobenzene and 1% of dibromodifluorobenzenes ie used.
The re~3ult~ are summarized in Table 2.
Table 2:
Ex. Zeolite SiO2/ Car- Temp. Time Con- S3 5 SDFB SHB
Al23 rier C h ver- moi mol mol gas moln % % %
.. __ __ % ., ~ -7 HZSM-5 27 H2 320 1.538 86 10 4 C3 H mor- 34 H2 320 1.5 6 7 58 35 denite l l Conver~ion: Conversion of 1-bromo-2,4-difluorobenzene and l-bromo-2,6-difluorobenzene Example 8:
170 g of 1-,romo-2,4-difluorobsnzene are heated in the presence of 5% by weight of catalyat ~80% of ~ZSM-5 (SiO2/Al203 = 27), 20% of Al203 binder, particle 8iZ~7 1 to 2 mm, predried at 400C) in a stirred laboratory auto-clave at 320C for 1 hour. The pre~sure is about 25 bar.
The conver~ion obtained i~ 29~, and the selectivities of the ~'ormation of l-bromo-3,5-difluorob~,nzene, l-bromo-2,6-difluorobenzene, m-difluorobenzene and dibromofluoro~
benzene are 73 mol %, 7 mol %, 17 mol % and 4 mol %, re3pecti~ely.
` ~ 7 7 3 .~
After the cataly~t has been filtered off, 170 g of 1-bromo-2,4-difluorobenzene are again hoatod togother with the used catalyst at 320C for 1 hour. Tho con-version drops to 21%, and tho seloctlvitios of tho formatlon of 1-bromo-3,5-difluorobenzons, 1-bromo-2,6-difluorobenzene, m-dlfluorobenzeno and dibromofluoro-benzene are found to be 80 mol %, 8 mol %, 9 mol % and 3 mol %, respoctively.
This proce~s ha~ a number o~ disadvantages. The macrocyclic compou~d~ have a complicated structure and are therefore very expensive. They are not recovered after the reaction. To work up the pro-duct, the ba~ic reaction mixture must be neutral-ized, resulting in the formation of salts. Owing to the low yields of 63% of 1-bromo-3,5-di~luorobe~zene and the high CoEt of material~, this proce~ is not very economic.
~P 04 182 440 (CA 117: 170951n) describes the isomerization o$ 1-bromo-2,4-difluorobenzene in the presence o~ alkali metal t-butoxi.d2s or aluminum halides. This procesR too requires an additional, ~alt-forming neutralization ~tep. The yield of 1-bromo-3,5-difluorobenzene is only 41.4%.
~'','.`'.,~,.`...... ,'',.. '`'. ' ;
''` ,,'. ,~. '' .. ',.,.', , : ,'; , ; ' . . ` ' ` '2~ 1773~) . I .`~
; - 3 -Other materials used for preparing 1-bromo-3,5-difluoro-benzene have not been described in the literature.
Accordingly, there wa~ a need for a procea~ whlch avold~
the dl~advantage~ de~cribed and provide~ 1-bromo-3,5-difluorobenzene by a ~lmplo indu~trial proce~, avoid~by-products and leads to low environmental pollution.
This ob~ect is achieved by a proce~ for preparing 1-bromo-3,5-difluorobenzeno which comprisos isomorizing 1-bromo-2,4-difluorobenzene or a mixture of 1-bromo-2,4-difluorobonzene and 1-bromo-2,6-difluorobonzene on acid zeolites of the pentasil type. ~ -JP 58/144,330 describes isomerization of di- and tri-chlorobenzene over acid zeolites. The process i8 said to be generally applicable to polyhalogenated monocyclic -~
aromatics, the claimed halogens being fluorine, chlorine, bromine and iodine. Any acid zeolites into the pores of which educts and products can diffuee are said to be suitable zeolites according to the invention.
Surprisingly, it has now been found that in contrast to the teaching of ~P 58/144i330 acid zeolitos are not generally suitable for catalyzing the isomorization of polyhalogenatod monocyclic aromatic compounds. Whil- JP
58/144,330 claims that zeolites of the mordenite typo are also suitable for effecting isomerization of polyhalo-genated monocyclic aromatics, which, however, is only documented for di- and trichlorobenzenes, it has however been ~hown that zeolites of tha mordenite type are not suitable at all for isomerizing 1-bromo-2,4-difluoro-- benzene~ Acid mordenites preferentially lead to undesir-able ~ide reactions, such a~ elimination of HBr and transbromination. Thus, the use of an acid mordenite gives m-difluorobenzene and difluorodibromobenzenes at a conversion of as low as 10% with a selectivity of 75~. -Furthermore, the teaching of JP 58/144,330 does not apply to all halogenated aromatics. Since a fluorine atom on an aromatic ring i8 immobile, compound~ exclusivoly sub0ti-tuted by fluorine, ~uch ao m-difluorobenzene, cannot bo isomerlzed (~. Pardillo~ et al., J. Am. Chem. Soc., 112 (1990) 1313/131B).
Against this baakground, it could not be expected that an acid zeolite would bo suitable at all for i~omerizing 1-bromo-2,4-difluorobenzene to 1-bromo-3,5-difluoro-benzene~ It is all the more surprislng that zeolites of the penta~il type are highly ~uitable for this type of isomerization. It i~ particularly ~urpris~ng that l-bromo-2,6-difluorobenzene can bo l~omerized to l-bromo-3,5-difluorobenzene since the intramole¢ular mochanism described for the isomerization of halogonated aromatics (J. Pardillos et al., J. Am. Chem. Soc., 112 ~1990) 1313/
1318) cannot take place. In the ca~e of acid mordenite~, the result iB as expected in that bromine i8 eliminated from 1-bromo-2,6-difluorobenzene a~ ~r or tran~ferred to another bromodifluorobenzene molecule. Thus, when a mixture of 1-bromo-2,4-difluorobenzene and 1-bromo-2,6-difluorobenzene i~ used for the reaction, the selectivityof the formation of m-difluorobenzene and dibromodi-fluorobenzenes l~ 93% at a conver~ion of 6%.
Zeolite~ of the pentasil type usable as catalysts for the proces~ according to the invention belong to the medium-pore zeolites whose pore opening~ are formed by 10tetrahedral atoms. Tetrahedral atoms are Al ~nd Si atoms 3urrounded tetrahedrally by oxygen atom~. These tetra-hedra are linked via common oxygen atoms and ~orm a cry~tal structure which is a network of pore~ and void~.
The characteri~tic feature of the pentasils is a ~truc-ture which can be built up from the ~o-called penta~il unit~. The two la~t members o$ all pentasil structures are ZSM-5 (MFI ~tructure) and ZSM-11 (NEL structure). The crystal structure~ of the penta~ are described, for example, in P.A. Jacobs and J.A. Marten~, "Synthesi~ of High-Silica Zeolites", El~evier Science Publishers, 1989.
` ~17735 ., .` -In many case~, the uRe of zeolites hav~ng the ZSM-5 crystal structure ha~ given good re~ults ln the ~somer-ization of bromodifluorobenzene~.
It ha~ also prov~n favorablo lf tho S~O2/A12O3 ratlo of the zeollte~ according to the invention is botwoen 22 and 200, preferably botween 24 and 100.
The zeolites mentioned can be prepared by hydrothermal synthesis using procedur0~ from the literature. After crystall$zation, the zeolite~ are filterod off and dr~ed.
If synthe~i~ was carried out ln the pre~ence of an organic template, it mu~t be followed by calcining ln an oxidizing atmo~phere, preferably in air, in order to remove the organic compound from the pores. (The template-free form i~ free of alkylammonium or -phosphon-ium ions of amines).
Any alkali metal ions present are then exchanged for di-or trivalent metal cations or for ammonium ions or protons. Of these, ion exchange with NH4' or H~ iB very particularly preferred. This acid modification is neces-sary since otherwise the zeolite doe~ not exhibit anycatalytic effect. It i~ advantageous to exchange at least 50%, ~referably at least 90%, of the alkali metal ion~
for the other ion~ mentioned. At 200 to 800C, preferably 400 to 500C, the zeolitos are converted into the cata~
lytically form by dehydration (and elimination of ammonia in the case of NH4t forms).
For the use according to the invention, the zeolites can either be compacted in the ab~ence of binders or brought into a suitable application form using binders, for exa~ple into the form of extrudates. Suitable binder~ are in particular oxide~, hydroxides or hydroxychlorides of aluminum and the oxides of ~ilicon, titanium and zircon-ium and clay materials.
The i~omerization temperature can be between about 250 ~1~ 7735 . .
; .--- 6and 550C, preferably between 275 and 450C.
The process according to the lnvontlon can be carried out either batchwi~e or cont~nuou~ly.
Batchwise isomorizatlon can bo effected most ~imply in an autoclave. Since the reaction tempsrature is higher than the boiling point temperature~ of the reactants and products, the reaotion i~ carried out at A correspond-ingly increased reaction pres~ure.
The catalyst which is in the form of a powder or has been compaoted to give pellets can be suspended in the feed mixture. The feed mixture/cataly~t weight ratio can range from 1:1 to 1000:1, preferably from 5:1 to 50:1. The reaction can be carried out in the presence of a ~olvent which is inert to the catalyst, or in the absence of a solvent, i~omerization in the absence of a solvent being preferred. The reaction time can be between about 1 hour and 12 hours, depending on the reaction temperature and the degree of conversion to be achieved.
Continuous ieomerization can take place in any apparatu-ses suitable for thi~ purpose, such as, for example, ina fixed bed or in a fluidized bed. A fixed bed reactor is the ~implest in tRrms of technical operation. The cata-lyat is introduced into the reactor in the form of pellets, and l-bromo-2,4-difluorobenzene or mixtures of bromodifluorobenzene isomer~ are passed over it.
The reaction can be carried out in the presence of gases, such as, for example, nitrogen or hydrogen. The presence of hydrogen may have the effect of reducing the formation of higher-boiling products, ~uch as dibromodifluoro-benzene, and increasing the service life of the catalyst.
The catalyst treatment, which i~ oharacterized by theLHSV (= liquid hourly space velocity, 9 feed per hour per 1 of catalyet), can be varied in the range between 0.1 ;à~ ", '~117735 . ~
.;.
and 5 h-1, preferably betwe~n 0.2 and 2 h-1.
The product mixture obtained ~n tho roa¢tlon cun be separated by dl~tlllatlon. H~r and HF, whlch are formed during the reactlon ln trace~, can be removed prior to the di~tillat~on by wa~hing wlth water or alkallne solu~ions or el~e separated off directly together wlth m-difluorobenzene a~ low-boiling fraction. m-Difluoro-benzene can bo reused for bromination. Of the 3 lsomeric difluorobenzenes, 1-bromo-3,5-difluorobenzsne can be ~eparated off as the lowost bo~ling $somer. After 1-bromo-3,5-difluorobenzene ha~ boen eeparated off, l-bromo-2,6-difluorobonzene and h~gher-boillng products and po~sibly ~mall amount~ of 1-bromo-3,5-difluorobenzene remain, apart from 1-bromo-2,4-difluorobenzene. This fraction can elther be directly recycled into the isomer-ization or be ~eparated off from the higher-boiling products by further distlllatlon. Recycling the uncon-verted l-bromo-2,4-difluorobenzene and the by-products formed during isomerization makes it possible to achieve a high yieid of 1-bromo-3,5-difluorobenzene.
The examplee which follow serve to illustrate the process according to the invention in more detail without limit-ing it thereto.
, ~ ~
; Examples:
Example~ 1 to 6 and C1 and C2 are carried out in a fixed-bed flow reactor at a~mospheric pressure. 25 ml of catalyst (zeolite content 80%, Al203 binder 20%, particle size 1 to 2 mm) are introduced into a quartz glass reactor (internal dia~eter 20 ), which can be heated by an electrio furnace, 1-bromo-2,4-difluorobenzene i8 metered in at the top, and the reaction products are condensed at the reactor exit. The L~SV is 0.5 h-1. If a carrier gas i~ u~edl ~he flow rate is 3 l/h. Prior to the reaction, the zeolites are dried at 500C in nitrogen.
~ ~'~
. ~. .?~
The reaction product~ are analyzed by ga~ chromatography.
The re~ult~ from i~omerlzation over variou~ cataly~t~ are ~ummarized ln Table 1.
Table 1:
Ex. Zeolite SiO2/ ~ar- Temp. Time Con- S3 5 s2 6 SDP~ S~B
Al23 rier C h ver- mo~ mo~ mol mol gao ion % % % %
_ ,,,, .o , _ _ ~ ' 10 1 HZSM-5 27 300 0.3 1 82 9 9 ~ 1 _ _ :
2 HZSM-5 27 350 0.3 6 72 7 17 4 _ _ 2 63 85 8 5 2 15 4 HZSM-5 27H2 300 1.3 4 74 7 14 4 315 6.8 8 88 8 3 1 345 29.5 1 89 9 2 0 - _ 435 55.8 25 84 12 4 0 HZSM-530 ~2300 3.3 8 82 6 12 1 335 27. 26 88 6 5 0 , _. .
6 XZSM-ll 80 H2355 5.8 16 87 9 3 0 390 14. 22 86 11 3 0 _ _ ,-~ , .
Cl H mor-34 350 0.3 44 15 8 5522 denite _ 2.5 12 14 1150 24 C2 ~ beta 24 _ 350 2 27 14 6 53 28 ' S3, 5 Selecti~ity of the formation of l-bromo-3,5-difluorobenzene S2, 6 Selectivity of the formation of l-bromo-2,6-difluorobenzene ~'-',',i,,,,,,,,,~",'~,:;~i,'"~"',,`.,"~ ",,~ :' " ~, `~ 7 7 ~ ~
..
g SDFB Selectivity of the formation of m-difluoro-benzene SHB Selectivity of the high-bolling component~, v.o. dibromodifluorobenzenes Example~ 7 and C3:
The exp~riment~ were carried out as de~cribed ~n Example~
1 to 6. A mixture ~ontaining 87% of 1-bromo-2,4-d~fluoro-benzene, 12~ o~ br~mo-2,6-difluorobenzene and 1% of dibromodifluorobenzenes ie used.
The re~3ult~ are summarized in Table 2.
Table 2:
Ex. Zeolite SiO2/ Car- Temp. Time Con- S3 5 SDFB SHB
Al23 rier C h ver- moi mol mol gas moln % % %
.. __ __ % ., ~ -7 HZSM-5 27 H2 320 1.538 86 10 4 C3 H mor- 34 H2 320 1.5 6 7 58 35 denite l l Conver~ion: Conversion of 1-bromo-2,4-difluorobenzene and l-bromo-2,6-difluorobenzene Example 8:
170 g of 1-,romo-2,4-difluorobsnzene are heated in the presence of 5% by weight of catalyat ~80% of ~ZSM-5 (SiO2/Al203 = 27), 20% of Al203 binder, particle 8iZ~7 1 to 2 mm, predried at 400C) in a stirred laboratory auto-clave at 320C for 1 hour. The pre~sure is about 25 bar.
The conver~ion obtained i~ 29~, and the selectivities of the ~'ormation of l-bromo-3,5-difluorob~,nzene, l-bromo-2,6-difluorobenzene, m-difluorobenzene and dibromofluoro~
benzene are 73 mol %, 7 mol %, 17 mol % and 4 mol %, re3pecti~ely.
` ~ 7 7 3 .~
After the cataly~t has been filtered off, 170 g of 1-bromo-2,4-difluorobenzene are again hoatod togother with the used catalyst at 320C for 1 hour. Tho con-version drops to 21%, and tho seloctlvitios of tho formatlon of 1-bromo-3,5-difluorobenzons, 1-bromo-2,6-difluorobenzene, m-dlfluorobenzeno and dibromofluoro-benzene are found to be 80 mol %, 8 mol %, 9 mol % and 3 mol %, respoctively.
Claims (10)
1. A process for preparing 1-bromo-3,5-difluorbenzene, which comprises isomerizing 1-bromo-2,4-difluoro-benzene or a mixture of 1-bromo-2,4-difluorobenzene and 1-bromo-2,6-difluorobenzene over acid zeolites of the pentasil type.
2. The process as claimed in claim 1, wherein the zeolite used has the crystal structure of ZSM-5.
3. The process as claimed in claims 1 and 2, wherein the SiO2/Al2O3 ratio of the zeolite used is between 22 and 200, in particular between 24 and 100.
4. The process as claimed in at least one of claims 1 to 3, wherein at least 90% of the cations are protons or ammonium ions.
5. The process as claimed in at least one of claims 1 to 4, wherein the reaction temperature is between 250 and 500°C, in particular between 275 and 450°C.
6. The process as claimed in at least one of claims to 5, wherein the reaction is carried out continu-ously in a fixed-bed flow reactor.
7. The process as claimed in at least one of claims 1 to 6, wherein the process is carried out in the presence of gases, preferably hydrogen.
8. The process as claimed in at least one of claims 1 to 7, wherein the space velocity is 0.1 to 5, in particular 0.2 to 2, 1 of feed per 1 of catalyst per hour.
9. The process as claimed in at least one of claims 1 to 8, wherein the reaction pressure equals atmospheric pressure.
10. The process as claimed in at least one of claims 1 to 5, wherein the feed mixture/catalyst weight ratio in the batchwise isomerization is between 1:1 to 1000:1, in particular from between 5:1 and 50:1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4334437A DE4334437A1 (en) | 1993-10-08 | 1993-10-08 | Process for the preparation of 1-bromo-3,5-difluorobenzene |
| DEP4334437.2 | 1993-10-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2117735A1 true CA2117735A1 (en) | 1995-04-09 |
Family
ID=6499765
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002117735A Abandoned CA2117735A1 (en) | 1993-10-08 | 1994-10-07 | Process for preparing 1-bromo-3,5-difluorobenzene |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0648724B1 (en) |
| JP (1) | JPH07165637A (en) |
| CA (1) | CA2117735A1 (en) |
| DE (2) | DE4334437A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19544870C2 (en) | 1995-12-01 | 1997-09-11 | Hoechst Ag | Process for the preparation of 1-bromo-3,5-difluorobenzene |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5740428A (en) * | 1980-08-25 | 1982-03-06 | Toray Ind Inc | Isomerization of halogenated toluene |
| JPS58144330A (en) * | 1982-02-24 | 1983-08-27 | Toray Ind Inc | Isomerization of polyhalogenated aromatic compound |
| JPH04182440A (en) * | 1990-11-16 | 1992-06-30 | Ishihara Sangyo Kaisha Ltd | Production of 3,5-difluoro-1-bromobenzene |
-
1993
- 1993-10-08 DE DE4334437A patent/DE4334437A1/en not_active Withdrawn
-
1994
- 1994-09-22 EP EP94114937A patent/EP0648724B1/en not_active Expired - Lifetime
- 1994-09-22 DE DE59403537T patent/DE59403537D1/en not_active Expired - Fee Related
- 1994-10-06 JP JP6243093A patent/JPH07165637A/en active Pending
- 1994-10-07 CA CA002117735A patent/CA2117735A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| EP0648724A1 (en) | 1995-04-19 |
| DE4334437A1 (en) | 1995-04-13 |
| DE59403537D1 (en) | 1997-09-04 |
| EP0648724B1 (en) | 1997-07-30 |
| JPH07165637A (en) | 1995-06-27 |
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