Background Art Preparation of arylalkylated p-phenylenediamines as effective anti- degradants for rubber vulcanizates from aromatic primary amines and aliphatic ketones belongs to their economically most favourable preparation techniques.

The synthesis proceeds first as acid catalysed condensation of amine with ketone, wherein this equilibrium reaction will be usually shifted in the direction of formation of the desired product by removing water, resulting from the condensation, by means of a removal of water, which may be constituted also by the ketone itself.

The ketimine, resulting from the reaction, is subsequently catalytically hydrogenated by hydrogen to an alkylaromatic p-phenylenediamine as the anti- degradant.

So, for example according to SK P 278 291 the nature of alkylarylamine production by reductive alkylation of aromatic amines by aliphatic ketones consists in that a mixture of the starting aromatic amine and ketone is first subjected to the action of a heterogeneous catalyst, and so obtained reaction mixture, containing ketimine, is later, also in the presence of a condensation catalyst, hydrogenated on a cupric hydrogenation catalyst. The reaction is performed without removing the reaction condensation water, this being the cause of slower process of

condensation. This problem of condensation of aromatic amines with aliphatic ketones is solved by further SK P 278 068, according to which from the starting mixture, containing aromatic amine, aliphatic ketone and acidic heterogeneous catalyst, there is water separated by distillation in an amount of 3 to 98 % of stoichiometric, and then the reaction mixture is hydrogenated. The mixture enters hydrogenation without previous ketimine separation, therefore an increased content of by-products after hydrogenation results.

Even more comprehensively is the condensation of aromatic amines, including 4-aminodiphenylamine, described in DE 2 901 863 A1 of the firm Bayer, according to which ketimines are prepared from aromatic amines, including 4- aminodiphenylamine, and ketones. According to SU P 183765 N- (1-phenylethyl)- N'-phenyl-1, 4-phenylenediamine has been prepared by reductive alkylation of 4- aminodiphenylamine or C-nitroso and 4-nitrodiphenylamine with acetophenone with removing water in one step under catalysis of zinc chloride and Raney nickel mixture in the presence of hydrogen. Catalysis by chlorides requires expensive catalyst separation related with high salt content in waste-waters.

The aim of the present invention is a preparation method which eliminates the disadvantages of the above solutions.

Disclosure of Invention The above disadvantages are eliminated by a method of preparation of N- (1-phenylethyl)-/V-phenyl-1, 4-phenylenediamine by condensation of acetophenone with 4-aminodiphenylamine in the presence of a catalyst at an elevated temperature with simultaneous removing water, resulting from the reaction, by means of water remover, whereby N- (1-phenylethylidene)-N'-phenyl-1, 4- phenylenediamine arises, which is without separation of the condensation catalyst or after its separation subjected to catalytic hydrogenation by hydrogen. The gist of this method consists in that the acid catalysed condensation reaction is performed to incomplete conversion of 4-aminodiphenylamine with the reaction velocity, as measured by velocity of distilling off the solvent, which solvent is the water

remover, from the condensation in the range of 0.8 to 3 I. h'1/kg of 4- aminodiphenylamine, while the N- (1-phenylethylidene)-N'-phenyl-1, 4- phenylenediamine, resulting from the reaction, is subsequently catalytically hydrogenated by hydrogen to N- (1-phenylethyl)-N'-phenyl-1, 4-phenylenediamine with purity of at least 96 %.

The reaction of acetophenone with 4-aminodiphenylamine is performed with molar ratio of 0.8 to 10, and the molar ratio of hydrogen to N- (1-phenylethylidene)- N'-phenyl-1, 4-phenylenediamine is 1 to 100. Instead of the starting raw materials it is also possible to use their precursors, i. e. organic or inorganic salts of the raw materials, or possibly substances, which allow the raw materials to arise by simple reaction, for example reduction, oxidation, hydration, dehydration, and the condensation reaction of acetophenone with 4-aminodiphenylamine and/or the subsequent hydrogenation reaction to take place. Conversion of the precursors to the raw materials can be performed also directly in the reaction mixture simultaneously with the progress of the main condensation or hydrogenation reaction.

As condensation catalysts, there will be used acidic, heterogeneous natural and/or synthetic aluminosilicates, natural and/or synthetic zeolites, montmorillonites, clinoptilolites or bentonites, or products made thereof and having acidic character, known under the name bleaching clay, Nobelin FF, where bentonite is activated by hydrochloric acid, Jeltar 100, Jeltar 200, Jeltar 300, prepared from bentonite activated by sulphuric acid in a similar way, as are prepared catalysts of the type Fulcate 22B, acidic inorganic salts and oxides, like, for example, acidic calcium phosphates and copper oxides or copper oxide- hydroxides, deposited on various carriers, or possibly mixtures of metal oxides, representing Adkins catalysts, consisting of copper, chrome and iron oxides in an amount of 0.01 to 20 % by weight, as referred to 4-aminodiphenylamine.

As hydrogenation catalyst, there will be used either cupric-chromic Adkins catalyst and/or hydrogenation catalyst copper on diatomaceous earth or Raney nickel, palladium or platinum, deposited on activated carbon, in an amount of 0.01

to 10 %, in a weight ratio of 0.001 to 1, as referred to N- (1-phenylethylidene)-N'- phenyl-1, 4-phenylenediamine.

It has been found that it is advantageous, when the condensation temperature is kept within an interval of 50 to 150 °C, and the hydrogenation temperature within 80 °C to 200 °C. The reactions may be performed within a pressure interval from moderate subatmospheric pressure to the pressure of 10 MPa, either discontinuously, continuously or semi-continuously.

Water removing is performed by azeotropic distillation in such a way that benzene, toluene, xylene, cyclohexane, n-hexane, n-heptane, n-octane and/or their mixture is used as the removal of water agent.

To obtain the required quality of N- (1-phenylethyl)-N'-phenyl-1, 4- phenylenediamine having the content of the active substance of at least 96 % by weight, it is necessary to prepare the N- (1-phenylethylidene)-N'-phenyl-1, 4- phenylenediamine (ketimine) intermediate product of good quality. Under the term "intermediate product of good quality"we understand an intermediate product having low content of the reactants, 4-aminodiphenylamine and acetophenone, but especially of by-products. The preparation method in question is able to achieve routinely ketimine of the purity of at least 99 % by weight. The ketimine quality during its preparation is influenced by several factors-flow of the toluene being distilled off, conversion degree, reaction time, temperature, intensity of stirring in the condensation reactor, and the amount of added recycled filtrate.

The above mentioned quality can be achieved by the method according to the present invention in such a way that the condensation is performed to 90 % at most, preferably to 50 to 90 %, of the conversion of 4-aminodiphenylamine, ensuring minimum formation of by-products. In this way high purity of ketimine after crystallization is ensured also if recycled mother liquors from the preceding condensation are used, so that the amount of by-products in the dry matter of the reaction mixture does not exceed the value of 0.5 % by weight, while 50 to 85 % of the filtrate from the N- (1-phenylethylidene)-N'-phenyl-1, 4-phenylenediamine crystallization are used in a new condensation.

It has been found that N- (1-phenylethyl)-N'-phenyl-1, 4-phenylenediamine prepared by the method according to the present invention may be used as anti- degradant with long-lasting persistent efficiency either alone or as a component of anti-degradation systems for antioxidant, antiozonant and anti-fatigue protection of rubber vulcanizates in combination with faster migrating anti-degradants.

The invention is more detailed described by examples of its embodiments, but these do not limit the invention in any way.

Examples of invention embodiments Example 1 A three-neck sulfonation flask, equipped with a stirrer, thermometer and reflux condenser with a water phase separator, was charged with 120 g of acetophenone, 184 g of 4-aminodiphenylamine (4-ADFA), 10 g of a catalyst prepared from bentonite activated by hydrochloric acid (bleaching clay), and 150 mi of toluene. The reaction mixture was tempered to a temperature of 125 °C, the arising condensation water was separated by means of a distillation head, and toluene was returned back with the velocity of 1.21 I/h/kg 4-ADFA. After 4 hours of the reaction 14 ml of water have been separated, representing about 80% conversion of 4-aminodiphenylamine to N- (1-phenylethylidene)-N'-phenyl-1, 4- phenylenediamine. After the reaction had been completed the catalyst was left to settle, the reactants were decanted and left to crystallize by cooling. N- (1- phenylethylidene)-N'-phenyl-1, 4-phenylenediamine was separated by filtration.

Crystals of the product were analysed by gas chromatography and they contained 99.7 % by weight of N- (1-phenylethylidene)-N'-phenyl-1, 4-phenylenediamine.

Subsequently, the product was diluted with toluene in a weight ratio of 1: 1, 1.5 % by weight of batch of hydrogenation catalyst Pd/C (containing 3 % by weight of Pd) were added, and the reaction mixture was hydrogenated by hydrogen at a temperature of 160 °C and a pressure of 5 MPa. After the intake of hydrogen had been stopped, the catalyst was filtered off, solvent was separated and the product melt was formed to pastilles.

The product contained 96.3 % by weight of N- (1-phenylethyl)-N'-phenyl-1, 4- phenylenediamine.

Example 2 50 ml of toluene and 100 mi of filtrate from the condensation from Example 1 and 5 g of bleaching clay were added into the apparatus from Example 1 to the starting reactants and the used condensation catalyst from Example 1. After 14.2 ml of water had been separated from the condensation with the velocity of 0.5 I/h/kg 4-ADFA, the reaction mixture was decanted and N- (1-phenylethylidene)-N'- phenyl-1, 4-phenylenediamine was left to crystallize. It contained 99.8 % by weight of the active substance.

The crystals were dissolved in toluene and charged in the hydrogenation reactor with 1.0 % by weight of hydrogenation Adkins cupric-chromic catalyst containing iron added. After the intake of hydrogen had been stopped, and toluene had been separated by distillation, the product in the form of lumps contained 97.8 % by weight of N- (1-phenylethyl)-N'-phenyl-1, 4-phenylenediamine.

Example 3 Product from Example 2 was milled and used as anti-degradant in rubber mixtures based on natural rubber and synthetic rubber, and its protecting effects were compared with the effects of classical anti-degradants based on p- phenylenediamine, like N- (1, 3-dimethylbuthyl)-N'-phenyl-1, 4-phenylenediamine (6PPD) or N-isopropyl-N'-phenyl-1, 4-phenylenediamine (IPPD).

Besides the intrinsic effect of N- (1-phenylethyl)-N'-phenyl-1, 4- phenylenediamine substantial increase of the protective effect (antiozonant, antioxidant and anti-fatigue) has been achieved especially in mixtures with the above derivatives of p-phenylenediamine, particularly after pre-ageing of vulcanizates at elevated temperatures, as well as after washing them out in acidified water.

Vulcanizates of natural rubber, protected by 6PPD in the amount of 2 weight parts of 6PPD to 100 parts of the natural rubber, together with non- protected vulcanizate of this rubber and vulcanizates, protected by two weight parts of N- (1-phenylethyl)-N'-phenyl-1, 4-phenylenediamine or a mixture of one weight part of 6PPD with one weight part of N- (1-phenylethyl)-N'-phenyl-1, 4- phenylenediamine (SPPD), were subjected to accelerated thermal ageing on air in a drier according to STN 621 522 for a period of 72 hours at a temperature of 100 °C. The anti-degradation activity was monitored by comparing selected physico- mechanical properties. Sample Sample 0 2.0 1.0 : 1.0 2.0 [weight parts/100 parts of rubber] 6PPD 6PPD/SPPD SPPD Parameter monitored Tensile strength [MPa] 25 °C 6. 94 12. 34 13. 63 12. 88 Coefficient of residual tens. strength 27.37 48.38 54. 50 49.74 [%] Elongation [%] 25duc 241.5 276.0 295.0 299.5 coefficient of residual elongation [%] 48.47 53.68 58.76 56.71 M200 [Mpa] 25 °C 6.89 7.83 7.58 7. 70 Legend: 0-vulcanizate of natural rubber without anti-degradant 6PPD-N-(1, 3-dimethylbuthyl)-M-phenyl-1, 4-phenylenediamine SPPD-N- (1-phenylethyl)-N'-phenyl-1, 4-phenylenediamine From the coefficients of residual tensile strength and elongation it is obvious that SPPD is effective also alone, but in a mixture with 6PPD its protective effect has manifested itself by an increase of activity.

Product from Example 2, together with compared anti-degradants, was admixed to styrene-butadiene rubber and subsequently subjected to determination of the resistance of SBR vulcanizates against ozone using the method of trapezoids after leaching in Linitest during ten days at a temperature of 40 °C and at the leaching water pH of 4. The ozone concentration was 50 pphm, temperature 20 °C, deformation time before treating by ozone 68 hours, deformation 31 %.

Components SPPD SPPD : IPPD 0 Components 2 0. 5: 1. 5 1 : 1 1. 5 : 0. 5 0 : 2 ratio PD 15. 8 12.8 10.9 9.4 10.4 8.4 ED 7h PD 12. 6 12.0 10.2 6.3 10.2 5.6 ED24h Legend: PD-threshold deformation ED-exposition time SPPD-N- (1-phenylethyl)-N'-phenyl-1, 4-phenylenediamine IPPD-N-isopropyl-N'-phenyl-1, 4-phenylenediamine 0-SBR vulcanizate without anti-degradant From the results, there is obvious antiozonant effect of N- (1-phenylethyl)-N'- phenyl-1, 4-phenylenediamine alone, as well as in combination with IPPD.

Example 4 1200 ml of acetophenone and 35.0 g of iron containing cupric-chromic catalyst, as well as 100 mi of toluene and 500 ml of filtrate of the composition as that of the filtrate from the condensation from Example 1 were added to the starting 4-aminodiphenylamine in the apparatus from Example 1 with the volume of the sulfonation flask of 4 litres. After tempering to the condensation temperature 14.8 mi of water have been distilled off with the velocity of 3 I/h/kg 4-ADFA.

Subsequently the unreacted acetophenone was distilled off and after cooling down

to a temperature of 30 °C the N- (1-phenylethylidene)-N'-phenyl-1, 4- phenylenediamine has been left to crystallize. It contained 99.5 % by weight of N- (1-phenylethylidene)-N'-phenyl-1, 4-phenylenediamine.

Hydrogenation was further performed in n-heptane at a temperature of 150 °C and a pressure of 3 MPa with the hydrogenation catalyst Raney nickel in an amount of 25 % by weight, as referred to the charged N- (1-phenylethylidene)-N'- phenyl-1, 4-phenylenediamine. After separation of the catalyst and n-heptane, melt was obtained which contained 96.1 % by weight of N- (l-phenylethyl)-N'-phenyl- 1, 4-phenylenediamine.

Example 5 6 g of catalyst Jeltar 300, prepared from bentonite activated by sulphuric acid, were added to the starting reactants, toluene and used condensation catalyst from Example 2, in the apparatus from Example 1. After tempering to the working temperature of 120 °C and separating off 11.5 ml of water from condensation with velocity of 2.1 1 of toluene/h/kg 4-ADFA, the reaction mixture was decanted and N- (1-phenylethylidene)-N'-phenyl-1, 4-phenylenediamine was left to crystallize.

The condensation product, containing 99.4 % by weight of N- (l- phenylethylidene)-N'-phenyl-1, 4-phenylenediamine, was subsequently dissolved in toluene and hydrogenated to N- (1-phenylethyl)-N'-phenyl-1, 4-phenylenediamine using 1.5 % by weight of catalyst, containing 25 % by weight of copper, deposited on hydrotalcite. The product of hydrogenation and finalization consisted of pastilles, containing 97.1 % by weight of N- (1-phenylethyl)-N'-phenyl-1, 4- phenylenediamine.

Example 6 8 g of catalyst, which consisted of natural powder zeolite (Zeocem Bystre) were added to the starting reactants, toluene and the used condensation catalyst from Example 4, in the apparatus from Example 1. After tempering to the working

temperature of 120 °C and separating off 13.0 ml of water from condensation with velocity of 2. 1 1 of toluene/h/kg 4-ADFA, the reaction mixture was decanted and N- (1-phenylethylidene)-N'-phenyl-1, 4-phenylenediamine was left to crystallize.

It contained 99.6 % by weight of N-(1-phenylethylidene)-N'-phenyl-1, 4- phenylenediamine. The condensation product was subsequently dissolved in toluene and hydrogenated to N- (1-phenylethyl)-N'-phenyl-1, 4-phenylenediamine using copper on diatomaceous earth (Cherox 4611) as hydrogenation catalyst.