Title of Invention

AN IMPROVED PROCESS FOR THE SELECTIVE HYDROGENATION OF NITRO AROMATICS.

Abstract The present invention describes an improved process for the selective hydrogenation of nitrogen containing aromatics. In the process nitro aromatics, nitrosoaromatics and aromatic hydroxyl amines gets converted to their corresponding amines using gaseous hydrogen, in the presence of soluble iron compounds as a catalyst and optionally other reducible groups. The soluble catalyst can be operated in homogeneous or in biphasic conditions. An advantage of the biphasic mode of operation is the facile recovery and recycle of the catalyst system
Full Text Technical Field:
The present invention relates to an improved process for the selective hydrogenation of nitro aromatics. The homogeneous iron catalysts of the present invention catalyze the selective hydrogenation of substituted and unsubstituted nitro aromatics, nitrosoaromatics and aromatic hydroxylamines to aromatic amines with gaseous hydrogen in the presence of other substituent functional groups that are reducible or susceptible to hydrogenolysis. Background and the Prior Art of the Invention:
A large variety of aromatic amines are widely used for the production of polymers, dyes, pharmaceuticals, agrochemicals and photographic chemicals (P.F. Vogt, J. J. Gerulis, 'Aromatic Amines' in Ullmann's Encyclopedia, 5th Ed Vol A2, Verlag Chemie, Weinheim (1885) 37-55). In earlier days the reduction of nitro aromatics using iron/acid discovered by Bechamp (Bechamp A. J. , Ann. Chim. Phys, 1854, [3],42,186), was extensively used, though, nowadays, this process has lost relevance for products such as aniline due to availability of efficient heterogeneous catalysts. The Bechamp process, despite being corrosive and polluting still remains a method of choice for reduction of specialty nitro aromatics due to its remarkable selectivity against other reducible functional groups. References may be made to U. Siegrist, P. Baumeister, H. U. Blaser, M. Studer, Chem. Ind. (Dekker 75 (1998) 207, and Blaser H. U. and Studer M. , Appl. Catal. 1999, Vol 189, pages 191-204, wherein the controlled poisoning of heterogeneous noble metal catalyst has also been used to achieve selective hydrogenation of nitro functional group as described. Although these catalysts selectively reduce nitro aromatics they suffer from a drawback, which is that the catalyst preparation process often remains critical and amount of poison needs to be precisely controlled.
In US Patent No. 3832,401 (1974), the hydrogenation of nitroaromatics has been claimed using the specific Fe complexes Fe(CO)3(PPh3)2, Fe(acac)3 and Fe(CO)3(AsPh3)2, however the advantage of the present invention over US 3832,401 is that the catalysts and process employing these can be carried out in organic, aqueous and combination of organic-aqueous media. In contrast it is specifically mentioned in US 3832,401 that non-aqueous solvent medium is necessary for reaction.

The use of iron doped Raney Nickel catalysts for the hydrogenation of organic
compounds has been proposed in US 4287365, and a similar iron doped Raney nickel
catalyst has been used for the selective hydrogenation of halo nitro aromatic
compounds in US 5801284. Iron doped Raney nickel catalysts have also been
proposed for hydrogenation of numerous organic functionalities in US 6368996 and
US 6395934. In all the above patents the iron catalyst is used as a metal in a
heterogeneous form, and as an additive to the well known Raney nickel. US 5126485
claims the selective hydrogenation of halo nitro compounds in the presence of
heterogeneous raney nickel, cobalt and iron catalysts.
Iron in combination with iridium, supported on carbon has been used as a catalyst for
the hydrogenation of nitro compounds in US 6316381. Here the main catalyst is the
iridium with iron as an additive.
Iron hexacyano cobaltate complex and hexacyanoferrate compounds have been
claimed for the hydrogenation of organic compounds including nitro compounds in
US 4503249 and US 4401640. Here the metal complexes are supported on any
suitable support like alumina etc and used in a heterogeneous form.
A combination of iron and a noble metal catalyst selected from palladium, platinum,
and rhodium, supported on a suitable support is active for hydrogenation of dinitro
aromatics and substituted dinitro aromatic compounds as mentioned in US 5105012.
A similar hydrogenation is feasible using iron in combination with platinum
forselective hydrogenation as claimed in US 4212824.
The use of iron carbonyl complexes in stoichiometric quantity for the reduction of
nitrobenzene to aniline has been discussed by Vancheesan et al [J. Mol Catal 1989,
52(2), 297 -300], however the reaction mentioned therein is undertaken in the
absence of hydrogen and the iron compound is employed in stoichiometric quantities
and not used as a catalyst.
In all the examples mentioned above iron has never been used as a unique component
of the catalyst, and also not in the soluble form. The only report where soluble iron
compound is used pertains to its use for stoichiometric hydrogenation conducted in
the absence of hydrogen.
Need therefore continues to exist for the catalytic equivalent of the stoichiometric
nitro-reduction processes with high chemoselectivity. It is further desired that the
needed catalyst should compliment catalytic performance with exclusive selectivity
towards nitro group and physically the nature of the catalyst system should be such
that it is easily recoverable preferably by simple phase separation. Thus, in view of
the many possible applications involving the selective hydrogenation of nitro group
to corresponding amines a new catalyst is a definite need.
Object of the invention
The main object of the present invention is to provide an improved process for the
selective hydrogenation of nitro aromatics, which obviates the draw backs associated
with existing catalytic processes regarding chemoselectivity and ease of catalyst
product separation and recycle.
Still another object of the present invention is to develop a catalytic process for the
selective catalytic conversion of nitro functional group into amine in presence of other
reducible functional groups such as aldehyde, ketone, olefm , nitrile etc
Yet another object of this invention is to use a soluble catalyst that can be operated in
homogeneous or in biphasic conditions. An advantage of the biphasic mode of
operation is the facile recovery and recycle of the catalyst system
Summary of the Invention:
Accordingly, the present invention provides an improved process for the selective
hydrogenation of nitro aromatics using homogeneous iron catalysts, wherein said
catalyst is operated such that the catalyst is restricted to the one of the liquid phase
existing in the reaction mixture while the starting materials and products
predominantly exist in the other phase thereby facilitating recovery of the catalyst.
Detailed description of the invention
In order to achieve the above objectives, the present invention provides an improved
process for selective hydrogenation of nitrogen containing aromatics, said process
comprising the steps:
(a) mixing the nitrogen containing aromatics with a soluble iron compound /
complex as a catalyst, optionally in presence of a solvent and a co-solvent;
(b) contacting the mixture of step (a) with gaseous hydrogen at a temperature
ranging between 25° to 250°C under hydrogen pressure in the range of 15 to
2000 psi for a time period greater than 2 hours to obtain a hydrogenated
product, and
(c) separating the hydrogenated product thus obtained from the soluble iron
catalyst.
In an embodiment of the present invention, wherein the nitrogen containing aromatics
are selected from substituted or unsubstituted nitroaromatics, nitrosoaromatics and/or
aromatic hydroxylamines.
In another embodiment of the present invention, wherein substituted or unsubstituted
nitroaromatics, nitrosoaromatics and/or aromatic hydroxylamines have general
formula Ar-Y, wherein Y is NOz, NO or NHOH and Ar is an aromatic ring fragment
selected from aryl fragments with or without one or more substitutions selected from
the group consisting of Cl to C8 alkyl group, Cl to C4 aliphatic or aromatic vinyl
group, Cl to C4 aliphatic or aromatic vinyloxy group, Cl to C8 alkoxy group, CeH5 to
CioHg aryloxy, fluro group, chloro group, bromo group, iodo group, hydroxy group,
OCOalkyl group, OCOaryl group, COOH group, OH group, SH group, CN group,
SOs" group, SO2alkyl group, NHb group, Nhalkyl group, SO2NH2 group, SO2N(alkyl)2
group, SO2Nhalkyl group, Cl to C4 aliphatic or aromatic aldehyde group, aliphatic or
aromatic ketone group, Cl to C6 imino group, Cl to C6 ether group, thioester and
sulfide.
In yet another embodiment of the present invention, wherein the catalyst used
contains one or more soluble iron salts or one or more soluble iron organometallic
complexes or mixture of one or more soluble iron salts and one or more soluble iron
organometallic complexes.
In still another embodiment of the present invention, wherein the catalyst used is a
soluble iron compound selected from iron salts of halogen acids, salts of oxo acids,
iron organometallic complexes consisting of iron and a cordinating additive, wherein
oxidation state of the iron atom ranges from 0 to 3.
In one more embodiment of the present invention, wherein the coordinating additives
used is selected from the family of phosphines, bipyridyines, phenanthrolines,
pentanediones and secondary or tertiary amines.
In one another embodiment of the present invention, wherein the coordinating
additives used is selected from salts of water soluble derivatives of phosphines,
bipyridyines, pentanediones, secondary or tertiary amine and ethylene diamine
tetracetic acid.
In a further embodiment of the present invention, wherein the coordinating additive to
iron ratio is in the range of 1:1 to 1:10.
In a further more embodiment of the present invention, wherein the catalyst is soluble
in the reaction medium prior to commencement of the reaction or is solubilized under
reaction conditions.
In an embodiment of the present invention, wherein catalyst is a unique iron
compound or is formed as a mixture of entities containing as a constituent such that
the entire mixture is soluble in intended liquid media prior to or during reaction
conditions.
In another embodiment of the present invention, wherein the catalyst is soluble in
organic medium or in aqueous medium and operates in homogeneous conditions or in
biphasic conditions.
In yet another embodiment of the present invention, wherein when the catalyst
operates in homogeneous conditions, the catalyst and the nitroaromatics,
nitrosoaromatics and/or aromatic hydroxylamines are simultaneously soluble in
organic medium or aqueous medium.
In still another embodiment of the present invention, wherein when the catalyst
operates in biphasic conditions, the catalyst is soluble in organic medium and the
nitroaromatics, nitrosoaromatics and/or aromatic hydroxylamines are soluble in
aqueous medium or vice versa.
In one more embodiment of the present invention, wherein under biphasic operating
conditions, the nitroaromatics, nitrosoaromatics and/or aromatic hydroxylamines are
soluble in aqueous medium and the catalyst is soluble in organic medium.
In one another embodiment of the present invention, wherein the solvent used is
selected from the group consisting of petroleum liquids such as crude oils, condensate
and natural gases, aromatic liquids, alcohols, aliphatic or aromatic ethers, aliphatic or
aromatic esters, nitriles, aliphatic or aromatic ketones, water or combinations thereof,
wherein the solvent serves as a medium for dilution or facilitation of processing or
separation.
In a further embodiment of the present invention, wherein the co-solvent used is
selected from the group consisting of ethanol, acetone and acetonitrile, while facilitate
the solubilization of the reactants into the catalyst phase.
In a further more embodiment of the present invention, wherein the concentration of
the soluble iron catalyst is in the range of 10-4 to 10 mole % of the nitroaromatics,
nitrosoaromatics and/or aromatic hydroxylamines.
In yet another embodiment of the present invention, the catalyst is selected from
FeSo4.7H20, Fe(No3)3.9H2O, Fe11 (acac)3 or Fe" / EDTANa2.
In a feature of the of the present invention is also possible to carry out hydrogenation
reaction with aqueous soluble nitroaromatic substrate such that catalyst is dissolved in
organic medium while substrate and products can exist in aqueous phase.
In another feature the substituted and unsubstituted nitro aromatics, nitrosoaromatics
and aromatic hydroxylamines may exist as a suspended solid in the liquid phase
containing catalyst. The resulting aromatic amine can either phase separate from the
catalyst containing liquid phase or remain as a solution.
In another feature the present invention may be performed in a batch or a continuous
mode, wherein the catalyst recovered from these processing can be recycled after
correction of volume without requiring any further operation of catalyst regeneration.
In yet another feature in biphasic operations of the present invention the catalyst
containing phase can be directly recycled for subsequent reaction.
In another feature the catalyst of the present invention may be prepared by any known
method for complexation of coordinating additive with iron atom or prepared in situ
by addition of catalyst components to the reaction mixture.
In another embodiment the co-ordinating additive to iron ratio may be in the range of
1:1 to 1:10.
The process of the present invention is described hereinbelow with reference to the
examples which are illustrative only and should not be construed to limit the scope of
the present invention in any manner whatsoever.
The catalyst is generally prepared in situ by addition of the iron compound to the
solvent/solvents and substrate mixture, followed by the coordinating additive in the
requisite molar ratio desired. The catalyst is formed in-situ under the reaction
conditions. Alternately the complex may also be formed separately by interaction of
the iron compound with the coordinating additive taken in excess of the
stoichiometric requirement, in a solvent like ethanol or acetonitrile such that both the
metal compound and the coordinating additive are dissolved. The mixture is refluxed
for a period of 4 hours to yield the iron complex which is then filtered and separated.
Example-1
This example demonstrates the hydrogenation of nitrobenzene carried out using different iorn catalysts and different solvents as mentioned in table-1. The
hydrogenation of nitro benzene was carried out using Nitrobenzene: 9.6xlO"2 mol, solvent: 9x10~5 m3, catalyst 7.2x10"5 mol,. The reaction mixture was charged in the 300 ml Parr autoclave and air in the autoclave was displaced with nitrogen and subsequently with hydrogen. Contents of the autoclave were heated to 150 °C and pressurized with 400 psi of hydrogen. The reaction was followed by absorption of gas and analysis of liquid phase, In all cases conversion was complete and selectivity to aniline was found to exceed 98%. Except example no 6 where in absence of iron compound no conversion was observed Apart from aniline other compounds were found to be azoxybenzene, azobenzene and hydrazobenzene.
Table 1
(Table 1 Removed)
Example-2
The example illustrates the Biphasic hydrogenation of nitrobenzene using different
catalysts as mentioned in table-2.
The hydrogenation of nitro benzene was carried out under following conditions: Nitrobenzene: 9.6xlO"2 mol, toluene: 5xlO"5 m3, water 5xlO"5 m3' catalyst FeSO4.7H2O: 7.2xlO"5 mol. The reaction mixture was charged in the 300 ml Pan-autoclave and air in the autoclave was displaced with nitrogen and subsequently with hydrogen. Contents of the autoclave were heated to 150 °C and pressurized with 400 psi of hydrogen. The reaction was followed by absorption of gas and analysis of liquid phase. In all cases conversion was complete and no iron was detected in organic phase except for reaction no 7 where in absence ligand total iron was found in organic phase. In reaction no 10, hydrogenation was carried out with 50 ml (0.483 mols) nitrobenzene.
Table 2
(Table 2 Removed)
Example-3
The example illustrates the recycle of the catalyst in hydrogenation of nitrobenzene as
mentioned in Table 3.
General procedure for recycle of aqueous biphasic catalyst: The reaction mixture discharged from reaction 9 [ Table 2] was phase separated to remove aqueous phase. The aqueous phase was transferred to reactor to which was added 10 ml nitro benzene and hydrogenation was carried out as described earlier. In subsequent runs this procedure was repeated.
Table 3
(Table 3 Removed)
Example-4
The following example illustrates toe hydrogenation of various nitroaromatics as mentioned in Table 4.
The hydrogenation of exemplary nitroaromatics was conducted under the following conditions. The procedure was similar to that for biphasic reactions [ reaction numbers 7-10, Table 2] Reaction conditions: Pressure: 400 psi; Temperature: 423K; Aqueous phase: 9xlO"5 m3; Organic phase consists of neat substrate; catalyst FeS04.7H2O: 7.2xlO"5 mol; Fe: EDTANa21:5; conversion in all cases was complete; TOP calculated as mols of nitro compound converted per mol of Fe, § based on GC analysis.
Table 4(Table 4 Removed)
Advantages of the present invention
The present invention provides an improved catalyst and process for the selective hydrogenation of substituted nitro aromatics, nitrosoaromatics and aromatic hydroxyl amines with gaseous hydrogen to the corresponding amines in the presence of soluble iron compound as a catalyst. The present invention uses a soluble iron compound or complex as a catalyst, which is not disclosed in any prior art and is a new discovery. The present invention provides a highly chemoselective route for the manufacture of substituted aromatic amines using a homogeneous catalyst. The catalysts in the prior art are normally heterogeneous supported metal catalysts wherein iron is used as an additive, and are generally less selective hydrogenation catalysts. The use of two phase solvent systems has manifold advantages pertaining to catalyst -product separation, catalyst recycle and recovery, and prevention of deactivation of catalyst by interaction with products or byproducts. In the present invention the product being more soluble in the non catalyst phase is swept out leaving no possibility of interaction of catalyst and product thereby decreasing the risk of deactivation of catalyst. Additionally the present invention being applied in a solution form the advantages of temperature control and processing are evident.






We claim:
1. An improved process for selective hydrogenation of nitrogen containing
aromatics, said process comprising the steps:
(a) mixing the nitrogen containing aromatics with a soluble iron compound / complex as a catalyst, optionally in presence of a solvent and a co-solvent;
(b) contacting the mixture of step (a) with gaseous hydrogen at a temperature ranging between 25° to 250°C under hydrogen pressure in the range of 15 to 2000 psi for a time period greater than 2 hours to obtain a hydrogenated product, and
(c) separating the hydrogenated product thus obtained from the soluble iron catalyst.

2. A process as claimed in claim 1, wherein the nitrogen containing aromatics are selected from substituted or unsubstituted nitroaromatics, nitrosoaromatics and/or aromatic hydroxylamines.
3. A process as claimed in claim 2, wherein substituted or unsubstituted nitroaromatics, nitrosoaromatics and/or aromatic hydroxylamines have general formula Ar-Y, wherein Y is NO2, NO or NHOH and Ar is an aromatic ring fragment selected from aryl fragments with or without one or more substitutions selected from the group consisting of CI to C8 alkyl group, C1 to C4 aliphatic or aromatic vinyl group, C1 to C4 aliphatic or aromatic vinyloxy group, C1 to C8 alkoxy group, C6H5 to QoHg aryloxy, fluro group, chloro group, bromo group, iodo group, hydroxy group, OCOalkyl group, OCOaryl group, COOH group, OH group, SH group, CN group, SO3" group, SO2alkyl group, NH2 group, Nhalkyl group, SO2NH2 group, SO2N(alkyl)2 group, SO2Nhalkyl group, C1to C4 aliphatic or aromatic aldehyde group, aliphatic or aromatic ketone group, C1 to C6 imino group, C1 to C6 ether group, thioester and sulfide.
4. A process as claimed in claim 1, wherein the catalyst used contains one or more soluble iron salts or one or more soluble iron organometallic complexes or mixture of one or more soluble iron salts and one or more soluble iron organometallic complexes.
5. A process as claimed in claim 1, wherein the catalyst used is a soluble iron compound selected from iron salts of halogen acids, salts of oxo acids, iron

organometallic complexes consisting of iron and a cordinating additive, wherein oxidation state of the iron atom ranges from 0 to 3.
6. A process as claimed in claim 5, wherein the coordinating additives used is selected from the family of phosphines, bipyridyines, phenanthrolines, pentanediones and secondary or tertiary amines.
7. A process as claimed in claim 5, wherein the coordinating additives used is selected from salts of water soluble derivatives of phosphines, bipyridyines, pentanediones, secondary or tertiary amine and ethylene diamine tetra acetic acid.
8. A process as claimed in claim 5, wherein the coordinating additive to iron ratio is in the range of 1:1 to 1:10.
9. A process as claimed in claim 1, wherein the catalyst is soluble in the reaction medium prior to commencement of the reaction or is solubilized under reaction conditions.
10. A process as claimed in claim 1, wherein catalyst is a unique iron compound or is formed as a mixture of entities containing as a constituent such that the entire mixture is soluble in organic media selected from toluene and methanol or aqueous media-water prior to or during reaction conditions.
11. A process as claimed in claim 1, wherein the catalyst is soluble in organic medium or in aqueous medium and operates in homogeneous conditions or in biphasic conditions.
12. A process as claimed in claim 10, wherein wherein the catalyst operates in homogeneous conditions, the catalyst and the nitroaromatics, nitrosoaromatics and/or aromatic hydroxylamines are simultaneously soluble in organic medium or aqueous medium.
13. A process as claimed in claim 10, wherein when the catalyst operates in biphasic conditions, the catalyst is soluble in organic medium and the nitroaromatics, nitrosoaromatics and/or aromatic hydroxylamines are soluble in aqueous medium or vice versa.
14. A process as claimed in claim 13, wherein under biphasic operating conditions, the nitroaromatics, nitrosoaromatics and/or aromatic hydroxylamines are soluble in aqueous medium and the catalyst is soluble in organic medium.

15. A process as claimed in claim 1, wherein the solvent used is selected from the group consisting of petroleum liquids such as crude oils, condensate and natural gases, aromatic liquids, alcohols, aliphatic or aromatic ethers, aliphatic or aromatic esters, nitriles, aliphatic or aromatic ketones, water or combinations thereof, wherein the solvent serves as a medium for dilution or facilitation of processing or separation.
16. A process as claimed in claim 1, wherein the co-solvent used is selected from the group consisting of ethanol, acetone and acetonitrile, while facilitate the solubilization of the reactants into the catalyst phase.
17. A process as claimed in claim 1, wherein the concentration of the soluble iron catalyst is in the range of 10-4 to 10 mole % of the nitroaromatics, nitrosoaromatics and/or aromatic hydroxylamines.
18. A process as claimed in claim 1, wherein the catalyst is selected from FeSo4.7H2O, Fe(No3)3.9H20, Fe11 (acac)3 or Fe11 / EDTANa2.
19. An improved process for selective hydrogenation of nitrogen containing aromatics substantially as herein describe with reference to examples accompanying this specification.


Documents:

0547-delnp-2004-abstract.pdf

0547-delnp-2004-claims.pdf

0547-delnp-2004-correspondence-others.pdf

0547-delnp-2004-description (complete).pdf

0547-delnp-2004-form-1.pdf

0547-delnp-2004-form-18.pdf

0547-delnp-2004-form-2.pdf

0547-delnp-2004-form-3.pdf

0547-delnp-2004-form-5.pdf

0547-delnp-2004-gpa.pdf

0547-delnp-2004-pct-304.pdf

547-DELNP-2004-Abstract-(12-05-2009).pdf

547-DELNP-2004-Claims-(12-05-2009).pdf

547-DELNP-2004-Corresponence-Others-(12-05-2009).pdf

547-DELNP-2004-Description (Complete)-(12-05-2009).pdf

547-DELNP-2004-Form-2-(12-05-2009).pdf

547-DELNP-2004-Form-3-(12-05-2009).pdf


Patent Number 235913
Indian Patent Application Number 547/DELNP/2004
PG Journal Number 37/2009
Publication Date 11-Sep-2009
Grant Date 03-Sep-2009
Date of Filing 05-Mar-2004
Name of Patentee COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH
Applicant Address Rafi Marg, NEW DELHI-110001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 AVINASH NARENDRA MAHAJAN NATIONAL CHEMICAL LABORATORY.
2 PRAKASH SHIVANAND OZARDE NATIONAL CHEMICAL LABORATORY.
3 RAJ MADHUKAR DESHPANDE NATIONAL CHEMICAL LABORATORY.
4 RAGHUNATH VITTHAL CHAUDHARI NATIONAL CHEMICAL LABORATORY.
PCT International Classification Number C07C 5/00
PCT International Application Number PCT/IB03/06185
PCT International Filing date 2003-12-24
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 PCT/IB03/06185 2003-12-24 PCT