DE2105682A1 - Platinum-on-carbon catalyst - useful for reduction of halonitroaromatic cpds - Google Patents

Abstract

Sulphite Pt-on-Carbon catalyst are produced by suspending a particulate Pt-on-carbon catalyst with an effective surface of >=800 m2/g. in an aq. acid medium (pref. at a pH of 0-4), saturating the catalyst with H2 at normal or elevated pressure, then saturating with a sulphiting agent (esp. Na2SO3) such that 0.30-7, esp. 0.5-0.63, equivs. of sulphiting agent are used per mol. H2 taken up, after which the catalyst is recovered from the suspension. Catalysts are esp. useful for hydrogenative reduction of nitrohalo-aromatic cpds. to the corresp. amines with little loss of halogen.

Description

Process for the preparation of halogen-containing aromatic amines The invention relates to a process for the production of halogenated aromatic Amino compounds by catalytic reduction of the nitro compounds with hydrogen using a sulfited platinum-on-carbon catalyst.

The catalytic reduction of halogenated nitroaromatics with hydrogen and nickel, platinum, palladium or other noble metals to the corresponding amines is known, but it depends on the constitution of the respective Compound a sometimes considerable dehalogenation. Except for the losses of halogenated aromatics and the increased stress on ateriae are for extraction of the pure products, additional cleaning measures are required, which increases the profitability question the procedures.

Various methods have been worked out to circumvent these disadvantages been. According to British patent specification 859251, in catalytic reduction of halogenated nitroaromatics in the presence of a platinum-on-carbon catalyst Magnesium oxide or hydroxide added to suppress dehalogenation. A similar procedure is followed according to DBP 1 187 243, only that there is cycloaliphatic Nitrogen bases, such as morpholine, can be used for the same reasons.

But it is also possible to work completely without additives and the carry out catalytic reduction with a modified platinum-on-carbon catalyst. In J.Am.Chem.Soc. 87 (1965) 2767 a method for catalytic reduction of 2,5-dichloronitrobenzene with hydrogen and a sulfided platinum-on-carbon catalyst described, this catalyst showing a pronounced selectivity and to 2,5-dichloroaniline of high quality leads Iu in practice it has been shown that such contacts often lose their activity after a single use, To the technical application of the working methods described so far, however, it is necessary that, given the high price of platinum, the catalyst repeated and without Weakening of the activity can be used.

In accordance with the present invention, these requirements are surprisingly met met when one halogen-substituted aromatic nitro compounds with 1, 2 or 3 halogen atoms in the core or, for example, with 3 fluorine atoms in the side chain, catalytic in the presence of sulfited platinum-on-carbon catalysts at temperatures from about emergency to about 1200C and hydrogen pressures from about 5 to about 50 atmospheres reduced.

In particular, those nitro compounds are those of the general formula where X is a halogen atom, Y is a hydrogen atom, an alkyl or a hydroxyalkyl group having 1 - 4 carbon atoms or a trifluoromethyl group and n and Z are integers from 1 to 3, the sum of which is 5.

The sulfited platinum-on-carbon catalysts are after the German patent application P 21 +) obtained in a simple way in such a way that one commercial platinum-on-carbon catalysts in an acidic aqueous suspension at about 250C saturates with hydrogen and then the suspension with a aqueous solution of sulfiting agents, such as Na2S03 added, the molar ratio H2: Na2S03 should preferably be 1: 0.55. After brief stirring, filtration and washing, the moist, sulfited catalyst is ready for use because of its additives for suppressing dehalogenation are excellent selectivity not mandatory.

The reduction method according to the invention is in normal pressure equipment easy to do. If solvents are used, water, lower Alcohols as well as usual aro - +) IIOE 71 / FO44 from matic solvents such as benzene, toluene, chlorobenzene and the like can be used.

In general, you fill the nitro compound, optionally with one Solvent, and the catalyst in the reactor, the mixture heated to 500 - 800C and the supply of hydrogen begins while the catalyst is suspended negative pressure. The desired reduction temperature is reached by the heat of reaction and appropriately kept constant by cooling. The reduction is finished when no more H2 pressure drop is registered to complete the reduction the measures mentioned can be maintained for another 15-20 minutes.

To recover the catalyst, the cooled reaction mixture is expediently by filtration, separated off, the contact is fed to the next batch and the organic filtrate is worked up in a known manner. The one in the reduction applied pressures and temperatures can be varied within wide ranges. A temperature range from about 500 to about 1200.degree. C. is particularly favorable and work at a pressure interval of e, about 5 to about 50 atm. The temperature and optionally the solvent must be chosen so that the reduction process can be done in the liquid phase.

The great advantage of the catalyst used over the known is particularly in the fact that it depends on the type of nitro compound to be reduced to can be used up to 50 times or more without intermediate cleaning or regeneration.

The weight ratio of nitro compound to platinum can be between 10000: 1 and 1000: 1 can be selected; to achieve a favorable reaction rate with a high return rate (number of uses without regeneration) of the A ratio of about 4000: 1 is preferably used for the catalyst.

The method according to the invention can be used to transfer a large Range of halogenated, aromatic nitro compounds in the corresponding halogen-containing aromatic amines are used. It will in most cases less than 0.1% of the halogen is split off, in no case caused by more than 0.2%. The process with sulfited platinum-on-carbon catalysts is therefore particularly suitable for converting the technically interesting halogen-substituted ones Nitrobenzenes and nitroalkylbenzenes into the corresponding amines.

Example 1 In a stainless steel autoclave with a magnetic lifting device, Heating mantle and cooling are provided: 2.16 mol of o-chloronitrobenzene 355 g of methanol 0.15 g of platinum, in the form of 6 g of moist 5% platinum-on-carbon catalyst, sulfited After displacing the air in the reactor with nitrogen and after purging with hydrogen the starting mixture is heated to 600-700C, then becomes hydrogen with stirring of an average of 25 atmospheres. The reduction immediately begins to generate heat and under H2 pressure drop. The temperature is then allowed to rise to an average of 950.degree and then keeps this constant with cooling. The H2 pressure is reduced after one Drop of 10 atm is set back to the initial value. If no hydrogen waste If more takes place, the reduction mixture is stirred for a further 20 minutes at 25 atm and 950 ° C. The total reduction time is 60 - 70 minutes. At 500C and after relaxing is filtered and the catalyst is returned to the next batch. In organic In the filtrate, the elimination of chlorine is determined by titration with 1 N NaOH. Afterward worked up by distillation in the customary manner.

Yield of o-chloroaniline: 97% of theory, EP .: -1.90C, diazo value: 99.8%, elimination of halogen: (0.1 Z, minimum number of catalyst recirculations: 50 times, examples 2-13 according to The following halogen-containing amines were prepared using the procedure described in Example 1: Yield . EP. Diazo Halogen Minimum At amine value split number of Sp.% Tion contact return d.Th. ° C%% struggles 2 m-chloroaniline 97. -10.0 99.8 «0.1 30 3 p-chloroaniline 96.5 69.7 99.9 «0.1 30 # 4 | 2,4-chlorotoluidine | 98 | 23.3 | 99.6 | <0.1 | 40 5 | 4,2-chlorotoluidine 97.5 22.7 99.8 «0.1 25 6 6,2-chlorotoluidine 98.8 3.7 99.8 0.02 25 7 3,4-dichloroaniline 96.2 71.6 99.9 @ 0.1 30 8 2,5-dichloroaniline 97 48.5 99.8 0.1 30 9 2-chloro-p-anisidine 98.5 60.4 98.3 0.2 20 10 3-aminobenzotri- 94 5.6 99.6 <0.1 30 fluoride 11 4-chloro-3-amino-95 10.9 99.7 0.1 20 benzotrif luoride 12 p-fluoroaniline 95 -1.6 99.6 <0.1 15 13. o-bromoaniline 95 29.5 99.6 0.2 12

Claims (3)

Claim 10 A process for the preparation of halogen-containing aromatic amines of the general formula wherein X is a halogen atom, Y is a hydrogen atom, an alkyl or a hydroxyalkyl group with 1-4 carbon atoms, or a trifluoromethyl group and n and Z are integers of 1 w 3, the sum of which is 5, by catalytic reduction of nitro compounds of the general formula wherein X, Y, n and Z have the abovementioned meanings, in the liquid phase at elevated pressure and elevated temperature, characterized in that catalysts are used which are obtained by treating a particulate platinum-on-carbon catalyst in acidic aqueous suspension after prior saturation with hydrogen under normal pressure or slightly increased pressure with a sulfiting agent. 2. The method according to claim 1, characterized in that the reduction at temperatures from about 500 to about 1200C and pressures from about 5 to about 50 atü takes place. 3. The method nac) i claim 1 and 2, characterized in that 0.01 up to 0.1% contact, based on the platinum content, can be used.