Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
  • C07C209/30—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of nitrogen-to-oxygen or nitrogen-to-nitrogen bonds
  • C07C209/32—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of nitrogen-to-oxygen or nitrogen-to-nitrogen bonds by reduction of nitro groups
  • C07C209/36—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of nitrogen-to-oxygen or nitrogen-to-nitrogen bonds by reduction of nitro groups by reduction of nitro groups bound to carbon atoms of six-membered aromatic rings in presence of hydrogen-containing gases and a catalyst
  • C07C209/365—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of nitrogen-to-oxygen or nitrogen-to-nitrogen bonds by reduction of nitro groups by reduction of nitro groups bound to carbon atoms of six-membered aromatic rings in presence of hydrogen-containing gases and a catalyst by reduction with preservation of halogen-atoms in compounds containing nitro groups and halogen atoms bound to the same carbon skeleton

Definitions

• the present invention relates to the production of chlorinated aromatic amines.
• Chlorinated aromatic amines are important starting materials for the manufacture of dyestuffs and pigments by diazotisation followed by coupling with various coupling components. It is known that chlorinated aromatic amines can be prepared by catalytic hydrogenation of the corresponding nitro compound. However, in the normal course of this reaction, some dechlorination also occurs. Attempts have been made to reduce this dechlorination using deactivated catalysts, such as sulphided platinum on carbon, or by deliberately adding a catalyst poison, such as a thioether in suitable amounts. All these reactions have been performed in solution in various solvents.
• deactivated catalysts such as sulphided platinum on carbon
• a catalyst poison such as a thioether
• the present invention provides a process for the manufacture of chlorinated aromatic amines which comprises catalytically hydrogenating the corresponding molten nitro compound in the presence of thiophene as dechlorination inhibitor.
• the catalyst may be any that is known for carrying out catalytic hydrogenation reactions, such as nickel, platinum, palladium, ruthenium and rhodium.
• platinum on charcoal we prefer to use platinum on charcoal as the catalyst, in suitable catalytic amounts. It is possible to use already deactivated catalysts as well, if desired, such as sulphided platinum on charcoal.
• the amount of catalyst may be varied over a wide range and may be from 0.005% to 0.1%, based on the weight of the nitro compound. We prefer to use about 0.01%.
• the amount of thiophene used may be from 25% to 300% by weight of the catalyst (pure 100% metal), but preferably from 100 to 250%. If too much thiophene is used, it will poison the catalyst too much, and this has the effect of slowing or even stopping the hydrogenation. If too little thiophene is used, there is insufficient inhibition of the dechlorination.
• a hydrochloric acid acceptor to the reactants so as to maintain a reaction pH of 7.0 - 9.0.
• a carbonate or bicarbonate of an alkali metal may be added in amounts of up to 5% by weight. Preferably, about 0.1 - 1.0% of sodium carbonate or bicarbonate is added.
• the reaction is carried out at a temperature above the melting point of the nitro compound being reduced. Once the nitro compound has been melted it is not necessary to heat to a higher temperature, although this may be done if desired.
• the reaction may be carried out under elevated pressure which may be from 15 to 1400 psi, preferably from 70 to 420 psi.
• the reaction is continued until consumption of hydrogen ceases, which may take from 1 to 10 hours.
• the time taken is dependent on the temperature and pressure used in the reaction and on the efficiency of the mixing during the reaction. For example, reaction times may be reduced by carrying out the hydrogenation in a spray nozzle high circulation reactor, such as a Buss loop reactor.
• a spray nozzle high circulation reactor such as a Buss loop reactor.
• Such a loop reactor normally renders an enhanced selectivity to the catalyst through more efficient mixing and cooling of the exothermic reaction.
• the reactor Before the hydrogenation is started, the reactor should be purged to remove oxygen.
• the purging can be carried out using an inert gass, such as nitrogen or, preferably, hydrogen.
• the process of the invention can be applied to various chlorinated nitro aromatic compounds.
• these include, for example, 2-chloro-4-nitro-aniline, 2-chloro-4-nitrotoluane, 2,5-diehlornitrobenzene, 2,4-dichlornitrobenzenep 2,3-dichlornitrobenzene, o-, m- and p-chloro-nitrobenzene and 2,4,5-trichlornitrobenzene.
• a shaking autoclave was charged with 258.6 parts by weight of 2-chloro-4-nitroaniline. To this was added 0.51 parts by weight of catalyst comprising 5% sulphided platinum on charcoal, as a 50% paste, 0.5 parts by weight sodium carbonate and 0.06 parts by weight of thiophene. The reactor was then closed, purged twice with hydrogen and then heated to 120°C. to melt the educt. With agitation, hydrogen was introduced at 140 psi and the conditions were maintained for 10 hours when consumption of hydrogen ceased.
• a shaking autoclave was charged with 150 parts by weight 2-chloro-4-nitrotoluene (containing 0.5% p-nitrotoluene as impurity)and a mixture of 1.5 parts by weight of catalyst comprising 1% platinum on charcoal, as a 50% paste, 1.5 parts by weight of sodium bicarbonate, 5 parts by volume water (to mix the catalyst) and 0.025 parts by volume thiophene.
• the mixture was hydrogenated at a pressure of 140 psi and a temperature of 85 - 90°C. Reduction was completed in 2 hours and the product was obtained in 95.8% yield.
• the product contained 0.5% p-toluidine as impurity formed entirely from the 0.5% nitrotoluene present in the starting material, i.e. no p-toluidine formed during the reduction by dechlorination of 2-chloro-4-nitrotoluene.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)

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Cited By (7)

Citations (1)

• 1978
  • 1978-07-12 EP EP78300142A patent/EP0000805A1/de not_active Withdrawn
  • 1978-08-08 IT IT7826592A patent/IT1206624B/it active

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