CA2099108A1 - Method for the continuous nitration of nitrable aromatic compounds - Google Patents
Method for the continuous nitration of nitrable aromatic compoundsInfo
- Publication number
- CA2099108A1 CA2099108A1 CA002099108A CA2099108A CA2099108A1 CA 2099108 A1 CA2099108 A1 CA 2099108A1 CA 002099108 A CA002099108 A CA 002099108A CA 2099108 A CA2099108 A CA 2099108A CA 2099108 A1 CA2099108 A1 CA 2099108A1
- Authority
- CA
- Canada
- Prior art keywords
- reaction
- acid
- nitrating
- water
- aromatic compound
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07B—GENERAL METHODS OF ORGANIC CHEMISTRY; APPARATUS THEREFOR
- C07B43/00—Formation or introduction of functional groups containing nitrogen
- C07B43/02—Formation or introduction of functional groups containing nitrogen of nitro or nitroso groups
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C201/00—Preparation of esters of nitric or nitrous acid or of compounds containing nitro or nitroso groups bound to a carbon skeleton
- C07C201/06—Preparation of nitro compounds
- C07C201/08—Preparation of nitro compounds by substitution of hydrogen atoms by nitro groups
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
Abstract Process for the continuous nitration of nitratable aromatic compounds A process for the continuous nitration of a nitratable aromatic compound, which forms an azeotrope with water, by treatment with nitric acid in the presence of nitrating acids, which comprises carrying out the reaction using a molar ratio of nitric acid to the aromatic compound of at least 1.1, the temperature and the pressure being coordinated with one another in such a way that the reaction mixture boils, recycling the nitrating acid in the circulation without further intermediate treatment, extracting the product mixture with water and recycling the eluate, to return nitrating acid. to the reaction.
Description
~ ~ ~ e~
HOECHST AKTIENGESELLSCHAFT HOE 90/F 390 Dr.MM/je De~cription Process for the continuous nitration of nitratable aromatic compounds The present invention relates to a process for the continuous nitration of nitratable aromatic compounds with nitrating acids using nitric acid in excess.
Nitrohaloben2enes are useful intermediates for the synthesis of dyes, photographic developers, antioxidants and inhibitors in the rubber industry.
The nitration of aromatic compounds, for example the nitration of chlorobenzene to give a mixture of o- and p-nitrochlorobenzene, i~ known. Thus, according to US
Patent 4,453,027, monochlorobenzene is reacted with nitric acid and a further acid, such as sulfuric acid or phosphoric acid, which is added in excess. The excess of nitrating acid serves as a heat transfer medium for the strongly exothermic nitration reaction. As stoichiometric amounts of water are formed in the nitration, the nitrating acid has to be concentrated again in separate equipmsnt. Thi~ expenditure of energy i8 further incressed by the u~e of nitrating acid in excess. In addition, the concentration require~ large amounts of energy and is only po~sible in equipment made of expensive materials, wh~ch must be resi~tant to acids.
~he nitration of chlorobenzene with nitric acid in the presence of strong acids, such as phosphoric acid, is described in DE Patent 2,422,306. In order to avoid the decrease in the yield of nitrated haloaromatic compounds owing to the shift in the equilibrium due to the formation of water during the reaction, this process is carried out in the presence of polyvalent metals or their soluble compounds. ~he used nitrating acid i8 also concentrated again.
Such nitrated product mixtures are in general worked up in several stages, unreacted nitrating acid first being extracted with water or alkaline solutions (NaHCO3, NaOH) The resulting stream of waste water must be biologically clarified.
A proces~ for the continuous nitration of aromatic compounds is described in EP Patent 39,556, in which the water formed during the reaction i2 removed by stripping with inert ga~es at 120 to 140C. This process require~
large amounts of inert gas in order to be able to control the heat of reaction of the strongly exothermic nitration in a technically safe manner.
DE Patent 3,244,293 de~cribe~ a process for thQ nitration of chlorobenzene using at mo~t stoichiometric amounts of nitric acid to chlorobenzen~ in the presence of con-centrated phosphoric acid. By means of thi~ mea~ure and the u~e of a reaction temperature, of, as 8 rule, below 100C. The formation of undesired dinitrated products should be reduced. However, this process requires rela-tively long reaction times.
It wa~ an ob~ect of the present invention to make avail-able a continuous process for the nitration of aromatic compounds which form an azeotrope with water, which doe~
not have the disadvantages of the prior art and which leads, in particular at h$gh conversions of aromatic compound, to a8 few undesired by-products, such as dinitrated product~, as possible. Moreover, the heat of reaction occurring in the ~trongly exothermic reactlon should be removed in a technically ~afe manner, the working up of the nitrating acid should be avoided and the waste water pollution should be reduced.
It has now been found that this ob~ect can be achieved by carrying out the reaction using a molar ratio of nitric acid to the aromatic compound of at least 1.1. The temperature and the pressure are in this ca9e coordinated with one another in such a way that the reaction mixture boils. The nitrating acid in the circulation i~ recycled to the reaction without further intermediate treatment, the product mixture is extracted with water and, to return nitrating acid, the eluate is also recycled to the reaction.
The molar ratio of nitric acid to the aromatic compound is in general 1.1 to 4.0, preferably 1.2 to 2.5, particularly preferably 1.3 to 2Ø It was not to be expected from the prior art that dinitration would hardly occur even u~ing thi~ high excess of nitric acid.
Chlorobenzene, benzene or toluene are in particular employed as the nitratable aromatic compound which form an azeotrope with water. However, in general all compounds which form an azeotropic mixture with water are suitable.
Nitration i~ advantageously carried out at temperature~
from 60 to 120C, preferably 75 to 105C, and at a pres~ure from 100 to 900 mbar, preferably 200 to 400 mbar. The nitration i9 carried out with vapor cooling, i.e. the heat of reaction i9 removed by means of the component~ of the boiling reaction mixture passing over and tho organic condensate i8 recycled to the reactor. During the cour~e of this, tho water formed in the reaction a~ an azeotrope with tho nitratable aromatic compound and the unreacted nitric acid are romoved from the reaction mixture.
A suitable nitrating acid i9 in particular sulfuric acid and/or phosphoric acid. When using mixtures of phosphoric acid and sulfuric acid, the conversion i8 increa~ed by an increase in the content of sulfuric acid in proportion to the phosphoric acid.
The process according to the invention is illustrated in , greater detail u~ing the enclosed proceqs scheme.
The nitrating acid (water and phosphoric acid and/or sulfuric acid) and the aromatic compound are introduced into the reactor 1. The water content in the nitrating acid introduced is in general 10 to 30 ~ ~y weight. The desired pressure is establi~hed and the introduced mixture is heated to boiling point. The aromatic compound A and nitric acid B (expediently 100 % strength) are then metered in continuously in the de~ired ratio. In order to maintain boiling of the reaction mixture, heat can be supplied to the reac~or.
The di~tillate of the reactor 1 i9 fractionated in the column 2 and then liquefied in the condenser 3~ The organic pha~e is returned to the column 2 from the 2-phase condensate (container 4) and the aqueous phase is purged.
The reaction product of the reactor 1 is, as the specifically lighter pha~e, continuously removed as overflow and returned to the phase separator 5. The specifically heavier phase (nitrating acid) is returned to the reactor and the specifically lighter organic phase i~ transferred to the extr~ction unit 6. In addition to the nitrated products, the product mixture which i~
extracted still contains dis~olved portions of sulfuric acid, pho~phoric acid and nitric acid. Suitable extraction units are the known extraction equipment, for exsmple a mixer-sQttler. Water is added a8 the extracting agent. The ~mount of water can be chosen such that either a specifically lighter (as described) or a specifically heavier eluate is formed. Tho aqueous phase is removed and returned to the reactor 1.
The organic phase is fed to the column 7 in which unreacted chlorobenzene i8 distilled off over the top, condensed in the conden~er 8 and returned to the reactor 1. The product mixture i3 obtained as the bottom of the .
HOECHST AKTIENGESELLSCHAFT HOE 90/F 390 Dr.MM/je De~cription Process for the continuous nitration of nitratable aromatic compounds The present invention relates to a process for the continuous nitration of nitratable aromatic compounds with nitrating acids using nitric acid in excess.
Nitrohaloben2enes are useful intermediates for the synthesis of dyes, photographic developers, antioxidants and inhibitors in the rubber industry.
The nitration of aromatic compounds, for example the nitration of chlorobenzene to give a mixture of o- and p-nitrochlorobenzene, i~ known. Thus, according to US
Patent 4,453,027, monochlorobenzene is reacted with nitric acid and a further acid, such as sulfuric acid or phosphoric acid, which is added in excess. The excess of nitrating acid serves as a heat transfer medium for the strongly exothermic nitration reaction. As stoichiometric amounts of water are formed in the nitration, the nitrating acid has to be concentrated again in separate equipmsnt. Thi~ expenditure of energy i8 further incressed by the u~e of nitrating acid in excess. In addition, the concentration require~ large amounts of energy and is only po~sible in equipment made of expensive materials, wh~ch must be resi~tant to acids.
~he nitration of chlorobenzene with nitric acid in the presence of strong acids, such as phosphoric acid, is described in DE Patent 2,422,306. In order to avoid the decrease in the yield of nitrated haloaromatic compounds owing to the shift in the equilibrium due to the formation of water during the reaction, this process is carried out in the presence of polyvalent metals or their soluble compounds. ~he used nitrating acid i8 also concentrated again.
Such nitrated product mixtures are in general worked up in several stages, unreacted nitrating acid first being extracted with water or alkaline solutions (NaHCO3, NaOH) The resulting stream of waste water must be biologically clarified.
A proces~ for the continuous nitration of aromatic compounds is described in EP Patent 39,556, in which the water formed during the reaction i2 removed by stripping with inert ga~es at 120 to 140C. This process require~
large amounts of inert gas in order to be able to control the heat of reaction of the strongly exothermic nitration in a technically safe manner.
DE Patent 3,244,293 de~cribe~ a process for thQ nitration of chlorobenzene using at mo~t stoichiometric amounts of nitric acid to chlorobenzen~ in the presence of con-centrated phosphoric acid. By means of thi~ mea~ure and the u~e of a reaction temperature, of, as 8 rule, below 100C. The formation of undesired dinitrated products should be reduced. However, this process requires rela-tively long reaction times.
It wa~ an ob~ect of the present invention to make avail-able a continuous process for the nitration of aromatic compounds which form an azeotrope with water, which doe~
not have the disadvantages of the prior art and which leads, in particular at h$gh conversions of aromatic compound, to a8 few undesired by-products, such as dinitrated product~, as possible. Moreover, the heat of reaction occurring in the ~trongly exothermic reactlon should be removed in a technically ~afe manner, the working up of the nitrating acid should be avoided and the waste water pollution should be reduced.
It has now been found that this ob~ect can be achieved by carrying out the reaction using a molar ratio of nitric acid to the aromatic compound of at least 1.1. The temperature and the pressure are in this ca9e coordinated with one another in such a way that the reaction mixture boils. The nitrating acid in the circulation i~ recycled to the reaction without further intermediate treatment, the product mixture is extracted with water and, to return nitrating acid, the eluate is also recycled to the reaction.
The molar ratio of nitric acid to the aromatic compound is in general 1.1 to 4.0, preferably 1.2 to 2.5, particularly preferably 1.3 to 2Ø It was not to be expected from the prior art that dinitration would hardly occur even u~ing thi~ high excess of nitric acid.
Chlorobenzene, benzene or toluene are in particular employed as the nitratable aromatic compound which form an azeotrope with water. However, in general all compounds which form an azeotropic mixture with water are suitable.
Nitration i~ advantageously carried out at temperature~
from 60 to 120C, preferably 75 to 105C, and at a pres~ure from 100 to 900 mbar, preferably 200 to 400 mbar. The nitration i9 carried out with vapor cooling, i.e. the heat of reaction i9 removed by means of the component~ of the boiling reaction mixture passing over and tho organic condensate i8 recycled to the reactor. During the cour~e of this, tho water formed in the reaction a~ an azeotrope with tho nitratable aromatic compound and the unreacted nitric acid are romoved from the reaction mixture.
A suitable nitrating acid i9 in particular sulfuric acid and/or phosphoric acid. When using mixtures of phosphoric acid and sulfuric acid, the conversion i8 increa~ed by an increase in the content of sulfuric acid in proportion to the phosphoric acid.
The process according to the invention is illustrated in , greater detail u~ing the enclosed proceqs scheme.
The nitrating acid (water and phosphoric acid and/or sulfuric acid) and the aromatic compound are introduced into the reactor 1. The water content in the nitrating acid introduced is in general 10 to 30 ~ ~y weight. The desired pressure is establi~hed and the introduced mixture is heated to boiling point. The aromatic compound A and nitric acid B (expediently 100 % strength) are then metered in continuously in the de~ired ratio. In order to maintain boiling of the reaction mixture, heat can be supplied to the reac~or.
The di~tillate of the reactor 1 i9 fractionated in the column 2 and then liquefied in the condenser 3~ The organic pha~e is returned to the column 2 from the 2-phase condensate (container 4) and the aqueous phase is purged.
The reaction product of the reactor 1 is, as the specifically lighter pha~e, continuously removed as overflow and returned to the phase separator 5. The specifically heavier phase (nitrating acid) is returned to the reactor and the specifically lighter organic phase i~ transferred to the extr~ction unit 6. In addition to the nitrated products, the product mixture which i~
extracted still contains dis~olved portions of sulfuric acid, pho~phoric acid and nitric acid. Suitable extraction units are the known extraction equipment, for exsmple a mixer-sQttler. Water is added a8 the extracting agent. The ~mount of water can be chosen such that either a specifically lighter (as described) or a specifically heavier eluate is formed. Tho aqueous phase is removed and returned to the reactor 1.
The organic phase is fed to the column 7 in which unreacted chlorobenzene i8 distilled off over the top, condensed in the conden~er 8 and returned to the reactor 1. The product mixture i3 obtained as the bottom of the .
column, and i9 worked up by customary methods (cf., for example, Ullmanns Enzyklopadie der Techn. Chemie, (Ullmann's Encyclopedia of Industrial Chemistry), 4th edition, vol. 17 (1979), p. 396).
The para/ortho isomer distribution in the process according to the invention ean be influenced by variation of the excess of nitrie aeid and the ratio of phosphorie acid to sulfuric aeid without an increase in the formation of the meta-isomer or the formation of dinitrated products being observed. Aecording to the invention, the conve sion of the aromatie eompound ean also be increased by the excess of nitric aeid without increased dinitration being caused at the same time.
A further advantage of the process according to the invention is that hardly any waste water iB produced whieh then has to be purified, as the product mixture is extraeted with water and the aqueous eluate can be returned to the nitration reaetor without impairment of the eonversion. Moreover, the heat of reaetion ean be removed in a teehnieally safe manner, the spaee-time yields are very high and eoneentration of the nitrating aeid iB avoided.
In the following examples, the ~ data are without exeeption % by weight.
Examples 1. Chlorobenzene was nitrated in the apparatus deseribed above. 1067 g of a mixture of 753 g of H3P0~, 182 g of H2S0~ and 132 g of H20 were introdueed into the reaetor 1.
A boiling temperature of 105C at 270 mbar was ~0 established. 604 g/h of ehlorobenzene and 503 g/h of HN03 were added dropwise eontinuously in 6 hours. 798 g/h of crude product and 342 g/h of distillate were produeed.
The crude produet was washed with 33 g/h of water in the extraetor F6. The eluate was returned to the reaetor. The effect of washing ean be seen from Table 1:
The para/ortho isomer distribution in the process according to the invention ean be influenced by variation of the excess of nitrie aeid and the ratio of phosphorie acid to sulfuric aeid without an increase in the formation of the meta-isomer or the formation of dinitrated products being observed. Aecording to the invention, the conve sion of the aromatie eompound ean also be increased by the excess of nitric aeid without increased dinitration being caused at the same time.
A further advantage of the process according to the invention is that hardly any waste water iB produced whieh then has to be purified, as the product mixture is extraeted with water and the aqueous eluate can be returned to the nitration reaetor without impairment of the eonversion. Moreover, the heat of reaetion ean be removed in a teehnieally safe manner, the spaee-time yields are very high and eoneentration of the nitrating aeid iB avoided.
In the following examples, the ~ data are without exeeption % by weight.
Examples 1. Chlorobenzene was nitrated in the apparatus deseribed above. 1067 g of a mixture of 753 g of H3P0~, 182 g of H2S0~ and 132 g of H20 were introdueed into the reaetor 1.
A boiling temperature of 105C at 270 mbar was ~0 established. 604 g/h of ehlorobenzene and 503 g/h of HN03 were added dropwise eontinuously in 6 hours. 798 g/h of crude product and 342 g/h of distillate were produeed.
The crude produet was washed with 33 g/h of water in the extraetor F6. The eluate was returned to the reaetor. The effect of washing ean be seen from Table 1:
Table l HNO3, ~ H2SO4, % H3PO4, %
Crude product 2.0 0.2 0.1 washed product 0.1 under 0.01 under 0.1 A conversion of chlorobenzene of 75 % and a p/o ratio of 1.4 was achieved. The content of dinitrochlorobenzene was les~ than 0.1 %. The space-time efficiency wa~ 980 g/l h.
2. Example 1 wa~ repeated, the reaction time, however, being 60 hours. After stopping the reaction, the amount of acid (H3PO4, H2SO4 and H2O) in the reactor was weighed and gave 1089 g (cf. with initial charge of 1067 g in Ex.1), so that within the limits of analytical accuracy it is to be a~sumed that the amount of H3PO4 and H2SO4 and the ratio of these two acids to one another have also remained constant in the continuous experiment.
3. to 6. The procedure was as in Example 1, 650 g of nitrating acid being introduced in each case with different H3PO4/H2SO4 ratios. Nitration wa~ carried out at 105C/270 mbar. 1158 g of chlorobenzene per hour and 910 g/h of HNO3 were continuously added. The results are reproduced in Table 2.
Table 2 Ex. ~2SO~, % H3PO~, % ~2~ % Conversion, % Dinitrochloro-benzene, %
3 10 80 10 63 under 0.1 4 50 40 10 64 under 0.1 under 0.1 6 70 - 30 68 under 0.1 The Table show~ that, in spite of the high reaction temperature, dinitration does not occur even with nitrating acid mixture~ of variou~ strengths.
. ' , .: .
-, - 7 - ~ Q~
7. to 9. 1400 g of H2SO4 (70 % strength) were introduced into the apparatus described. The nitration was carried out at a reaction temperature of 90C and a reaction pressure of 190 to 160 mbar using different stoichiometric amounts of HNO3. The results are compiled in Table 3.
Table 3 Ex. HNO3 excessConversion pto ratio Dinitrochlorobenzene (%) (%) (%) 107 1.4 63 1.68 0.1 8 1.7 70 1.72 0.1 9 2.0 83 1.73 0.1 The experiments show that an excess of HNO3 increases the conversion, but does not increase dinitration.
, .. . .
Crude product 2.0 0.2 0.1 washed product 0.1 under 0.01 under 0.1 A conversion of chlorobenzene of 75 % and a p/o ratio of 1.4 was achieved. The content of dinitrochlorobenzene was les~ than 0.1 %. The space-time efficiency wa~ 980 g/l h.
2. Example 1 wa~ repeated, the reaction time, however, being 60 hours. After stopping the reaction, the amount of acid (H3PO4, H2SO4 and H2O) in the reactor was weighed and gave 1089 g (cf. with initial charge of 1067 g in Ex.1), so that within the limits of analytical accuracy it is to be a~sumed that the amount of H3PO4 and H2SO4 and the ratio of these two acids to one another have also remained constant in the continuous experiment.
3. to 6. The procedure was as in Example 1, 650 g of nitrating acid being introduced in each case with different H3PO4/H2SO4 ratios. Nitration wa~ carried out at 105C/270 mbar. 1158 g of chlorobenzene per hour and 910 g/h of HNO3 were continuously added. The results are reproduced in Table 2.
Table 2 Ex. ~2SO~, % H3PO~, % ~2~ % Conversion, % Dinitrochloro-benzene, %
3 10 80 10 63 under 0.1 4 50 40 10 64 under 0.1 under 0.1 6 70 - 30 68 under 0.1 The Table show~ that, in spite of the high reaction temperature, dinitration does not occur even with nitrating acid mixture~ of variou~ strengths.
. ' , .: .
-, - 7 - ~ Q~
7. to 9. 1400 g of H2SO4 (70 % strength) were introduced into the apparatus described. The nitration was carried out at a reaction temperature of 90C and a reaction pressure of 190 to 160 mbar using different stoichiometric amounts of HNO3. The results are compiled in Table 3.
Table 3 Ex. HNO3 excessConversion pto ratio Dinitrochlorobenzene (%) (%) (%) 107 1.4 63 1.68 0.1 8 1.7 70 1.72 0.1 9 2.0 83 1.73 0.1 The experiments show that an excess of HNO3 increases the conversion, but does not increase dinitration.
, .. . .
Claims (5)
1. A process for the continuous nitration of a nitratable aromatic compound, which forms an azeotrope with water, by treatment with nitric acid in the presence of nitrating acids, which comprises carrying out the reaction using a molar ratio of nitric acid to the aromatic compound of at least 1.1, the temperature and the pressure being coordinated with one another in such a way that the reaction mixture boils, recycling the nitrating acid in the circulation without further intermediate treatment, extracting the product mixture with water and recycling the eluate, to return nitrating acid, to the reaction.
2. The process as claimed in claim 1, wherein the molar ratio of nitric acid to the aromatic compound is 1.1 to 4.0, preferably 1.2 to 2.5, particularly preferably 1.3 to 2Ø
3. The process as claimed in claim 1 or 2, wherein the reaction is carried out at a temperature from 60 to 120°C, preferably from 75 to 105°C.
4. The process as claimed in one or more of claims 1 to 3, wherein the reaction is carried out at a pressure of 100 to 900 mbar, preferably from 200 to 400 mbar.
5. The process as claimed in one or more of claims 1 to 4, wherein the nitratable aromatic compound is chlorobenzene.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4041775 | 1990-12-24 | ||
| DEP4041775.1 | 1990-12-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2099108A1 true CA2099108A1 (en) | 1992-06-25 |
Family
ID=6421438
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002099108A Abandoned CA2099108A1 (en) | 1990-12-24 | 1991-12-10 | Method for the continuous nitration of nitrable aromatic compounds |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0564478A1 (en) |
| JP (1) | JPH05508865A (en) |
| KR (1) | KR960009567B1 (en) |
| CN (1) | CN1062899A (en) |
| BR (1) | BR9107188A (en) |
| CA (1) | CA2099108A1 (en) |
| MX (1) | MX9102783A (en) |
| WO (1) | WO1992011227A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4225023A1 (en) * | 1992-07-29 | 1994-02-03 | Bayer Ag | Process for the preparation of 2,3-dichloro-nitrobenzene |
| DE19512114C2 (en) | 1995-04-04 | 2000-04-27 | Meissner Gmbh & Co Kg Josef | Recovery of nitric acid from nitriding processes |
| KR101585704B1 (en) * | 2008-11-14 | 2016-01-14 | 노람 인터내셔널 리미티드 | Method for reducing the formation of by-product dinitrobenzene in the production of mononitrobenzene |
| US9139509B2 (en) | 2011-02-17 | 2015-09-22 | Noram International Limited | Removal of non-aromatic impurities from a nitration process |
| CN104649910B (en) * | 2013-11-25 | 2017-01-11 | 江苏扬农化工集团有限公司 | Method capable of recycling acids for preparing 2,5-dichloronitrobenzene (DCNB) through continuous nitration |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL277560A (en) * | 1962-04-30 | |||
| US3780116A (en) * | 1972-06-15 | 1973-12-18 | Zaverchand & Co | Method for nitration of aromatic hydrocarbon compounds |
| DE3705091A1 (en) * | 1987-02-18 | 1988-09-01 | Bayer Ag | METHOD FOR SEPARATING SULFURIC ACID AND Nitric Acid FROM DINITROTOLUOLIC MIXTURES OBTAINED FROM THE NITRATION OF TOLUOL |
-
1991
- 1991-12-10 BR BR9107188A patent/BR9107188A/en unknown
- 1991-12-10 WO PCT/EP1991/002357 patent/WO1992011227A1/en not_active Application Discontinuation
- 1991-12-10 CA CA002099108A patent/CA2099108A1/en not_active Abandoned
- 1991-12-10 JP JP92500376A patent/JPH05508865A/en active Pending
- 1991-12-10 EP EP92900191A patent/EP0564478A1/en not_active Withdrawn
- 1991-12-23 CN CN91111847A patent/CN1062899A/en active Pending
- 1991-12-23 MX MX9102783A patent/MX9102783A/en unknown
-
1993
- 1993-06-23 KR KR93701935A patent/KR960009567B1/en active IP Right Grant
Also Published As
| Publication number | Publication date |
|---|---|
| WO1992011227A1 (en) | 1992-07-09 |
| JPH05508865A (en) | 1993-12-09 |
| CN1062899A (en) | 1992-07-22 |
| EP0564478A1 (en) | 1993-10-13 |
| KR960009567B1 (en) | 1996-07-20 |
| BR9107188A (en) | 1994-09-27 |
| MX9102783A (en) | 1992-06-01 |
| KR930703237A (en) | 1993-11-29 |
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