METHOD FOR THE PREPARATION OF CARBAMATES

Abstract: Method for the preparation of carbamates by reaction of aromatic amines with organic carbonates in the presence of a metal based catalyst on an inert carrier support.

Description: METHOD FOR THE PREPARATION OF CARBAMATES DESCRIPTION The present invention relates to a method for the preparation of carbamates by reaction of aromatic amines with organic carbonates using a catalyst on an inert support. It is known to react amines with organic carbonates in order to obtain carbamates. US-A 5.347.034 discloses a process for producing poly(o-alkylurethanes) of the diphenylmethane series by reacting the corresponding amines with dialkyl carbonates in the presence of a catalyst, such that the formed poly(O-alkylurethanes) crystallize out in a highly pure form upon cooling. EP-A 391.473 describes a process for producing carbamates using reduced amounts of catalyst by first reacting an amine with a (cyclo)alkyl carbonate in the presence of a carbamation catalyst to produce a mixture of a carbamate and an urea, further reacting the urea with carbonate to produce the corresponding carbamate, and finally recovering the carbamate from the reaction mixture. In DE-A 3.202.690 a method for preparing aromatic urethanes is described by reacting aromatic amines and alkylcarbonates in the presence of an alcoholate of an alkali metal or an alkaline earth metal. US-A 4.268.684 discloses a method for the preparation of carbamates by reacting an organic carbonate with an aromatic amine in the presence of certain zinc, tin or cobalt salts which are only active at temperatures of at least 200° C whereas in US-A 4.268.683 zinc or tin salts are used which are soluble in the reaction mixture at the reaction conditions. EP-A 48.371 describes the preparation of N,O-disubstituted urethanes by reacting primary amines with dialkylcarbonates in the presence of neutral or basic inorganic or organic lead, titanium, zinc or zirconium compounds. In JP-A 07.328.435 a catalyst comprising an oxide composition containing Zr and Si is used for the production of carbamates from a diester carbonate and an aliphatic amine in the liquid phase. An improved method has now been found for the preparation of carbamates by reaction of aromatic amines with organic carbonates. The invention thus concerns a method for the preparation of carbamates by reaction of aromatic amines with organic carbonates in the presence of a metal based catalyst on an inert carrier support. The method allows easy recovery of the catalyst, thus improving the economics and environmental impact of the process. In a further aspect, the invention relates to a catalyst comprising an organic metal salt on an inert carrier support. Such catalysts show an improved processability in the conversion of aromatic amines to carbamates via reaction with an organic carbonate. 5 Aromatic amine compounds which can be used in the present method include mono-, di- or polyamines. Suitable amines according to the process of the invention include, for example, phenylamine, 4-chlorophenylamine, 2-fluorophenyl amine, 3,4-dichlorophenylamine, aniline, tolylamine, diisopropyl phenylamine, 102,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 2,2'-diaminodiphenylmethane and higher homologs (polyaminopolyphenylmethanes), 2,4-toluenediamine, 2,6-toluenediamine, m-phenyienediamine, 1 ,5-naphthylenediamine, and mixtures thereof. Preferred are aromatic di- or polyamines like toluenediamines, i5 diaminodiphenylmethanes or polyaminopolyphenylmethanes or any mixtures thereof. Suitable organic carbonates include cyclic or alicyclic carbonates such as, for example, ethylene carbonate, propylene carbonate, styrene carbonate, diphenyl 20 carbonate, methyl phenyl carbonate.dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, dihexyl carbonate, methyl ethyl carbonate, methyl butyl carbonate and the like. Organic or inorganic salts which may used include, for example, acetates, 25 chlorides, nitrates, sulfonates, propionates, isopropanoates, butanoates, 2-ethylhexanoates, n-octoates, isononanoates, benzoates, chlorobenzoates, naphthenates, stearates, itaconates, pivalates, phenolates, acetylacetonates, alkoxides, C 16 /C 18 -alkenylsuccinoates (ASA), C 12 -alkenylsuccinoates (DSA) and the like. 30 Preferred are alkanoates having from 1 to 15 carbons atoms. Suitable catalysts include, for example, zinc catalysts such as zinc chloride, zinc acetate, zinc propionate, zinc octoate, zinc benzoate, zinc p-chlorobenzoate, zinc naphthenate, zinc stearate, zinc itaconate, zinc pivalate, zinc phenolate, 35 zinc acetylacetonate, zinc methoxide, lead catalysts like lead acetate and lead octoate, and tin catalysts like stannous chloride, stannous octoate, and mixtures thereof. Preferably, the metal in the catalyst is selected from the group consisting of Ti, Zr, Zn, Sn and Pb. 40 The heterogeneous metal based catalyst on the carrier may be made by impregnating the catalyst with or precipitating it on the carrier. Suitable inert carrier supports include, for example, metal oxides such as alumina, silica, Ti0 2 , MgO and the like, clays, zeolites, polymer supports, resins, graphite and carbon. A preferred carrier comprises TiO 2 , alumina or silica. The supported catalyst is generally used in amounts between 10 "3 and 20 mole% 5 based on the amount of amines used. The polyamines and the organic carbonates may be reacted in stoichiometric quantities. The use of an excess of organic carbonates however is preferred. The reaction conditions largely depend on the type of reactants used. 10 The method may be carried out at atmospheric or superatmospheric pressures.The pressure is preferably not more than 20 bar. The reaction time is dependent on the temperature and on the type and quantity of the carbamate compound, but will normally be between 0.5 and 6 hours. Reaction times of less than 3 hours are common, and reaction times of less than 152.5 hours have been achieved without any problem. Generally, the reaction temperature will be between 50 and 300°C. Preferably, the method of the invention is carried out at temperatures between 100 and 250°C. The presence of a solvent is not required, but it may be added without adversely 20 affecting the reaction. Any solvent or mixture of solvents which is inert to the reactants under the reaction conditions may be employed. Suitable solvents which may be employed include, for example, aromatic hydrocarbons such as benzene, halogenated aromatic hydrocarbons such as 25 monochlorobenzene, ortho-dichlorobenzene, trichlorobenzene or 1-chloronaphthalene, alkylated aromatic hydrocarbons like toluene, xylene, ethylbenzene, cumene or tetrahydronaphthalene, other functionalised aromatic hydrocarbons such as anisole, diphenylether, ethoxybenzene, benzonitrile, 2-fluoroanisole, 2,3-dimethylanisole or trifluorotoluene, alkanes such as 30 n-pentane, n-hexane, n-heptane or higher or branched alkanes, cyclic alkanes like cyclopentane, cyclohexane or derivatives thereof, halogenated alkanes like chloroform, dichloromethane, carbontetrachloride, and alkanes with other functional groups like diethylether, acetonitrile, dioxane or mixtures thereof, and the like. Inert aromatic solvents are preferred. 35 The method can be conducted in any apparatus which can be equipped, if required, with agitation means and heating and/or cooling means to keep the temperature within the desired range. The method of the present invention may be conducted batchwise or as a semi-continuous or continuous process. 40 One type of continuous operation is in a fluidized bed reactor in which a catalyst is carried into the reactor as a slurry in one or more of the reactants. Still another way of operating continuously is in a moving bed reactor in which the catalyst bed and the reactants pass concurrently or countercurrently to each other. A preferred type of continuous operation however is in a fixed bed reactor in which the reactants are passed over the catalyst bed. During the reaction alcohols are formed as by-product. These can be removed from the reaction mixture either continuously during or after completion of the reaction by e.g. distillation. The present invention is illustrated by, but not limited to, the following examples. Examples Example 1 To a suspension of 2 g Ti0 2 in 100 ml acetone was added 0.308g zinc octoate (in mineral terpentine oil, 6wt% Zn), and the mixture was purged with Ar gas for 5 minutes. The flask was put in a sonication bath (frequency: 20 MHz), containing water at room temperature for 1 hour. After sonication, the solvent was removed under reduced pressure and the solid finally dried under reduced pressure at 70°C, for 1 hour. The solid thus obtained was used as such in the preparation of carbamates. Isolated yield: 2.2g. To a 100 ml steel autoclave was added 2.0g (10 mmol) 4,4' diamino diphenyl methane, 42.7g (0.47 mol) dimethyl carbonate and 0.18g Ti0 2 supported zinc octoate (20 wt% zinc salt of 2-ethyl hexanoic acid supported on TiO 2 ). The mixture was purged with nitrogen. The reaction mixture was then heated at 180°C for 2 hours. After reaction completion, the autoclave was cooled to room temperature and the crude product was evaporated to dryness, redissolved in dichloromethane and finally filtered to separate out the catalyst. The filtrate thus obtained was evaporated to dryness under reduced pressure to yield a crystalline solid. Conversion of amine was 100% based on starting material. Selectivity to urethane was 96.3% based on quantitative HPLC. Example 2 To a 100 ml steel autoclave was added 2.0g (10 mmol) 4,4' diamino diphenyl methane, 25.5g (0.28 mol) dimethyl carbonate, 16 ml toluene, and 0.18g TiO 2 supported zinc octoate (20 wt% zinc salt of 2-ethyl hexanoic acid supported on TiO 2 ). The mixture was purged with nitrogen. The reaction mixture was then heated at 180°C for 2 hours. After reaction completion, the autoclave was cooled to room temperature and the crude product was evaporated to dryness, redissolved in dichloromethane and finally filtered to separate out the catalyst. The filtrate thus obtained was evaporated to dryness under reduced pressure to yield a crystalline solid. Conversion of amine was 100% based on starting material. Selectivity to urethane was 98% based on quantitative HPLC. Example 3 To a 100 ml steel autoclave was added 2.0g (8 mmol) polymeric diamino diphenyl methane, 42.7g (0.47 mol) dimethyl carbonate and 0.18g (0.1 mmol active catalyst) TiO 2 supported zinc octoate (20 wt% zinc salt of 2-ethyl hexanoic acid supported on Ti0 2 ). The mixture was purged with nitrogen. The reaction mixture was then heated at 180°C for 2 hours. After reaction completion, the autoclave was cooled to room temperature and the catalyst was filtered off. The filtrate thus obtained was evaporated to dryness under reduced pressure to yield a solid. Conversion of amine was >98% based on starting material. Selectivity to urethane was estimated to be 89-92% based on lR and 13 C NMR. Example 4 A mixture of 1.22g (10 mmol) 2,4-diaminotoluene , 42.7g (0.47 mol) dimethyl carbonate and 0.18g (0.1 mmol active catalyst) TiO 2 supported zinc octoate (20 wt% zinc salt of 2-ethyl hexanoic acid supported on TiO 2 ) was charged in a 100 ml steel autoclave and purged with nitrogen. The reaction mixture was then heated at 180°C for 2h. After completion of the reaction the autoclave was cooled to room temperature and an equal volume of dichloromethane was added to dissolve partly precipitated 2,4-bis(methoxycarbonylamino)toluene. The mixture was then filtered off to separate out the catalyst. The filtrate thus obtained was evaporated to dryness under reduced pressure to obtain crystalline yellow 2,4-bis(methoxycarbonylamino)toluene solid. Conversion of amine and selectivity to urethane were found to be 100% and 92% respectively from quantitative HPLC technique. Example 5 To a suspension of 2 g AI 2 O 3 in 40 ml acetone was added 1.2g zinc octoate (in mineral terpentine oil, 6wt% Zn), and the mixture was purged with Ar gas for 5 minutes. The flask was put in a sonication bath (frequency: 20 MHz), containing water at room temperature for 1 hour. After sonication, the solvent was removed under reduced pressure and the solid finally dried under reduced pressure at 70°C, for 1 hour. The solid thus obtained was used as such in the preparation of carbamates. Isolated yield: 2.8g. To a 100 ml steel autoclave was added 2.0g (10 mmol) polymeric diamino diphenyl methane, 42.7g (0.47 mol) dimethyl carbonate and 0.212g (0.12 mmol active catalyst) AI 2 O 3 supported zinc octoate (20 wt% zinc salt of 2-ethyl hexanoic acid supported on AI 2 O 3 ). The mixture was purged with nitrogen. The reaction mixture was then heated at 180°C for 2 hours. After reaction completion, the autoclave was cooled to room temperature and the crude product was evaporated to dryness, redissolved in dichloromethane and finally filtered to separate out the catalyst. The filtrate thus obtained was evaporated to dryness under reduced pressure to yield a crystalline solid. Conversion of amine was 100% based on starting material. Selectivity to urethane was 91% based on HPLC. Example 6 To a 100 ml steel autoclave was added 2.0g (8 mmol) polymeric diamino diphenyl methane, 42.7g (0.47 mol) dimethyl carbonate and 0.212g (0.12 mmol active catalyst) AI 2 O 3 supported zinc octoate (20 wt% zinc salt of 2-ethyl hexanoic acid supported on AI 2 O 3 ). The mixture was purged with nitrogen. The reaction mixture was then heated at 180°C for 2 hours. After reaction completion, the autoclave was cooled to room temperature and the crude product was filtered to separate out the catalyst. The filtrate thus obtained was evaporated to dryness under reduced pressure to yield a crystalline solid. Conversion of amine was 98% based on starting material. Selectivity to urethane was 84-92% based on quantitative IR and 13 C NMR. Example 7 To a suspension of 2 g silica (silica gel for column chromatography, 200-300 mesh) in 40 ml acetone was added 1.2g zinc octoate (in mineral terpentine oil, 6wt% Zn), and the mixture was purged with Ar gas for 5 minutes. The flask was put in a sonication bath (frequency: 20 MHz), containing water at room temperature for 1 hour. After sonication, the solvent was removed under reduced pressure and the solid finally dried under reduced pressure at 70°C, for 1 hour. The solid thus obtained was used as such in the preparation of carbamates. Isolated yield: 2.4g. To a 100 ml steel autoclave was added 2.0g (10 mmol) 4,4' diamino diphenyl methane, 42.8g (0.47 mol) dimethyl carbonate and 0.216g silica supported zinc octoate (20 wt% zinc salt of 2-ethyl hexanoic acid supported on silicagel). The mixture was purged with nitrogen for 5-10 min. The reaction mixture was then heated at 180°C for 2 hours. After reaction completion, the autoclave was cooled to room temperature and the crude product was evaporated to dryness, redissolved in dichloromethane and finally filtered to separate out the catalyst. The filtrate thus obtained was evaporated to dryness under reduced pressure to yield a crystalline solid. Conversion of amine was 100% based on starting material. Selectivity to urethane was 81.8% based on quantitative HPLC. Example 8 To a 100 ml steel autoclave was added 2.0g (8 mmol) polymeric diamino diphenyl methane, 42.7g (0.47 mol) dimethyl carbonate and 0.216g (0.12 mmol active catalyst) acidic silica supported zinc octoate (20 wt% zinc salt of 2-ethyl hexanoic acid supported on silicagel). The mixture was purged with nitrogen. The reaction mixture was then heated at 180°C for 2 hours. After reaction completion, the autoclave was cooled to room temperature and the crude product was filtered to separate out the catalyst. The filtrate thus obtained was evaporated to dryness under reduced pressure to yield a solid. Conversion of amine was 97% based on starting material. Selectivity to urethane was 81-83% based on quantitative IR and 13 C NMR.

Claims: CLAIMS 1. Method for the preparation of carbamates by reaction of aromatic amines with organic carbonates in the presence of a metal based catalyst on an inert carrier support. 52. Method according to claim 1 wherein the catalyst comprises a metal selected from the group consisting of Ti, Zr, Zn, Sn and Pb. Method according to claim 1 or 2 wherein the catalyst comprises an alkanoate having from 1 to 15 carbons atoms. 4. Method according to any one of the preceding claims wherein the carrier 0 support comprises Ti0 2 , alumina or silica. Method according to any one of the preceding claims wherein the reaction is carried out at a temperature between 100 and 250°C. 6. Method according to any of the preceding claims wherein the aromatic amine is selected from the group consisting of toluenediamines, 5 diaminodiphenyimethanes or polyaminopolyphenylmethanes or mixtures thereof. 7. Method according to any one of the preceding claims wherein the reaction is carried out at a pressure of not more than 20 bar. 8. Method according to any of the preceding claims which is carried out in the 0 presence of an inert aromatic solvent. Method according to any of the preceding claims having a reaction time of less than 2.5 hours. 10. A catalyst comprising an organic metal salt on an inert carrier support. 11. A catalyst according to claim 10 wherein the metal is selected from the 5 group consisting of Ti, Zr, Zn, Sn and Pb. 12. A catalyst according to claim 10 or 11 wherein the organic salt is an alkanoate having from 1 to 15 carbons atoms. 13. A catalyst according to any one of claims 10-12 wherein the carrier support comprises Ti0 2 ,alumina or silica.

Inventors: SMITH RICHARD COLIN, SMITH, RICHARD, COLIN
Applicants: ICI LTD, IMPERIAL CHEMICAL INDUSTRIES
Application year: 1998
Main classification: C07C269
IPC codes: B01J21, B01J31, C07B61, C07C269, C07C271, C08G71