PROCESS FOR THE PREPARATION OF UREA DERIVATIVES AND CATALYST SYSTEM

Abstract: The invention relates to a process for the preparation of urea derivatives of the general formula wherein R is an alkyl group and X is a halogen atom, an alkyl-, alkoxy-, aryloxy-, cyano-, ester- or trifluoromethyl group and n is from 0 to 5, which comprises reacting an aromatic nitro compound of the general formula wherein X and n are as defined above with carbon monoxide and an amine HNR₂ wherein R is an alkyl group, in the presence of a catalyst system comprising (a) a group VIII noble metal or a compound thereof, (b) a bidentate ligand and (c) an acid having a pKa of more than 2 or a transition metal salt of said acid.

Description: The invention relates to a process for the preparation of urea derivatives, to the urea derivatives prepared and to a catalyst system, used in the preparation of the urea derivatives. The invention particularly relates to the preparation of urea derivatives of the general formula: wherein R is an alkyl group and X is a halogen atom, an alkyl-, alkoxy-, aryloxy-, cyano-, ester- or trifluoromethyl group and n is from 0 to 5. It is generally known that the urea derivatives may be prepared by reaction of isocyanates with amines. Isocyanates may be prepared via the well-known phosgen route. Isocyanates and phosgen are known as very poisonous. Applicant has now found a one-step process, in which the use of the poisonous phosgen is avoided and isocyanates do not need to be isolated. The invention relates to a process for the preparation of urea derivatives of the general formula wherein R is an alkyl group and X is a halogen atom, an alkyl-, alkoxy-, aryloxy-, cyano-, ester- or trifluoromethyl group and n is from 0 to 5, which comprises reacting an aromatic nitro compound of the general formula wherein X and n are as defined above with carbon monoxide and an amine HNR₂ wherein R is an alkyl group, in the presence of a catalyst system comprising (a) a group VIII noble metal or a compound thereof, (b) a bidentate ligand of the formula R¹R²-M-A-M-R³R⁴ in which M is P, As or Sb, A is a divalent organic bridging group having at least 2 carbon atoms in the bridge, none of these carbon atoms carrying substituents that may cause steric hindrance, and R¹ ,R² ,R³ and R⁴ represent similar or dissimilar optionally substituted hydrocarbon groups, and (c) an acid having a pKa of more than 2 or a transition metal salt of said acid. In the US patent specifications 3,523,962; 3,903,125 and 3,914,268 is disclosed the preparation of an aromatic isocyanate by reacting an aromatic nitro compound with carbon monoxide with the aid of a noble metal catalyst, but mention of urea compounds has not been made. A process for preparing carbamates is disclosed by EP-A-86281, wherein an organic nitrogenous compound, an organic hydroxyl containing compound, and carbon monoxide are reacted in the presence of a catalyst system based on palladium and a bifunctional Group VA ligand. The catalyst system may further comprise an acid. Symmetric urea derivatives may be initially formed or be added as reactant in advance, but appear to be converted to carbamates in this known process. WO-A-85/01285 discloses a process for converting a nitrogen-containing compound into the corresponding urethane in the presence of a catalyst system comprising a halide-free ruthenium compound. No mention of any use of an acid is made. Again, symmetric urea derivatives may be initially formed, but are ultimately converted in other product in this known process. The urea derivatives prepared by the process according to the invention may be substituted or unsubstituted in the phenyl group in formula (I). X may be an alkyl group, preferably having from 1 to 10 carbon atoms, more preferably having from 1 to 4 carbon atoms. When X is halogen, chlorine and bromine are preferred. Preferably the alkoxy and aryloxy groups comprise not more then 10 carbon atoms and are preferably bound to the phenyl nucleus via the oxygen atom. The ester group preferably has not more then 10 carbon atoms, more preferably not more then 6 carbon atoms. The most preferred substituents are chlorine atoms and methyl groups. In formula (I) the groups R are preferably alkyl groups having from 1 to 10 carbon atoms, more preferably having from 1 to 4 carbon atoms, such as methyl or ethyl groups. As already indicated the substituents X in formula I and II correspond with each other. Preferred aromatic nitro compounds are nitrobenzene, 2-chloro-4-nitro toluene and para-isopropyl nitrobenzene. The amines used as starting materials in the process according to the invention are preferably dialkylamines with alkyl groups having from 1 to 10 carbon atoms, more preferably having from 1 to 4 carbon atoms, such as dimethylamine and diethylamine. The reaction is presumed to occur according to the following equation The reaction temperature may range from 50 °C to 200 °C, preferably from 70 °C to 150 °C. Pressures may range from atmospheric pressure to 200 bar. The invention further relates to a catalyst system comprising (a) a group VIII noble metal or a compound thereof, (b) a bidentate ligand of the formula R¹R²-M-A-M-R³R⁴ in which M is P, As or Sb, A is a divalent organic bridging group having at least 2 carbon atoms in the bridge, none of these carbon atoms carrying substituents that may cause steric hindrance, and R¹,R²,R³ and R⁴ represent similar or dissimilar optionally substituted hydrocarbon groups, and (c) an acid having a pKa of more than 2 or a transition metal salt of said acid. The noble metals of group VIII are palladium, ruthenium, rhodium, platinum, iridium and osmium. Palladium, platinum and rhodium are preferred, palladium being the most preferred. It is with reference to palladium compounds that hereinafter the process according to the invention is described in more detail. Both homogeneous and heterogeneous palladium compounds can be used. Homogeneous systems are preferred. Suitable palladium compounds are salts of palladium with, for example, nitric acid, sulphuric acid or alkanoic acids containing not more than 12 carbon atoms per molecule. Salts of hydrohalogenic acids can in principle be used as well. Palladium carboxylates are the preferred catalyst compounds, in particular palladium acetate. Further, palladium acetylacetonate can also be used. Palladium on carbon and palladium combined with an ion exchanger are examples of suitable heterogeneous palladium compounds. The quantity of palladium, or other noble metal or compound thereof is not critical. Preference is given to the use of quantities in the range of from 10⁻⁴ to 10⁻¹ mol per mol of aromatic nitro compound. In the bidentate ligand substituents offering steric hindrance should be absent, which means that no substituents may be present that are able to hinder the formation of complex compounds having the general formula In that formula, Q represents Pd or other noble metal, Y represents a non-coordinating anion, whilst Q²⁺ can also be written as in which the ligands L₁ and L₂ are weakly coordinated solvent ligands, e.g. acetonitrile, methanol, acetone, or acetylacetone, or correspond with those employed in the palladium compounds described in the preceding paragraph. In the bidentate ligand, M is preferably phosphorus. Hydrocarbon groups R¹, R², R³ and R⁴ will as a rule contain 2 to 18 carbon atoms, preferably 6 to 14 carbon atoms. Aryl groups are the most suitable, in particular the phenyl groups. Preferred bridging groups -R- are those having the formula (CR⁵R⁶) in which R⁵ and R⁶ are hydrogen atoms or hydrocarbon groups offering no steric hindrance and n is 3 or 4. Substituents R⁵ and R⁶ are preferably hydrogen atoms. The bridging groups R may also make part of cyclic structure, e.g. an aromatic or cycloaliphatic group, the carbon to carbon bond or bonds in the bridge may be saturated or unsaturated and in the bridge or in the cyclic or non-cyclic groups attached to the bridge one or more hetero atoms, e.g. sulphur, oxygen, iron or nitrogen, may have been substituted for carbon atoms, other than the two carbon atoms which must be present in the bridge linking both atoms M. Examples of suitable bidentate ligands are 1,3-di(diphenylphosphino)propane, 1,4-di(diphenylphosphino)butane, 2,3-dimethyl-1,4-di(diphenylphosphino)butane, 1,4-di(dicyclohexylphosphino)butane, 1,3-di(di-p-tolylphosphino)propane, 1,4-di(di-p-methoxyphenylphosphino)butane, 2,3-di(diphenylphosphino)-2-butene, 1,3-di(diphenylphosphino)-2-oxopropane, 2-methyl-2-(methyldiphenylphosphino)-1,3-di(diphenylphosphino)propane, 0,0′-di(diphenylphosphino)biphenyl, 1,2-di(diphenylphosphino)benzene, 2,3-di(diphenylphosphino)naphthalene, 1,2-di(diphenylphosphino)cyclohexane, 2,2-dimethyl-4,5-di(diphenylphosphino)dioxolane and It is observed that compounds having a structure like 2-methyl-2-(methyldiphenylphosphino)-1,3-di(diphenylphosphino)-propane, CH₃-C-(CH₂-P(C₆H₅)₂)₃, although being trifunctional, are nevertheless considered bidentate ligands in the terms of this invention since only two of the three phosphorous atoms can coordinate with the palladium atom in the complex. The bidentate ligand can be employed in quantities which may vary within wide limits, e.g. of from 0.1 to 10 mol per mol of palladium or other noble metal. The acid having a pKa of more than 2 is preferably a carboxylic acid having 2 to 14 carbon atoms, e.g. acetic acid, 9-anthracene carboxylic acid and 2,4,6-trimethylbenzoic acid. The transition metal which may form a salt with the carboxylic acid, may be defined as a metal of group I B , II B , III B , IV B , V B , VI B and VIII, the lanthanides and actinides of the Periodic System. Preferred are copper, iron and nickel. Iron and nickel salts give about the same conversion and selectivity as those with copper salts. It is observed that with a potassium salt no conversion at all is achieved. The process according to the invention can be carried out conveniently in the presence of a solvent. A variety of solvents can be applied such as ketones, e.g. acetone, methyl ethyl ketone, methyl isobutyl ketone, acethophenone and cyclohexanone; ethers, such as diethylene glycol dimethylether (also referred to as "diglyme"), anisole, diphenyl ether; aromatic compounds, such as benzene, toluene and the three xylenes; halogenated aromatic compounds, such as chlorobenzene and ortho-dichlorobenzene; halogenated paraffinic hydrocarbons, such as methylene chloride and carbon tetrachloride; paraffins such as hexane, heptane, cyclohexane, methylcyclohexane and iso-octane; nitriles, such as benzonitrile and acetonitrile and esters such as methyl benzoate. The reaction may be carried out batch-wise; semi-continuous or continuously. The urea derivatives may be useful as herbicides, plant growth regulators or as intermediates in the preparation of urethanes. Examples In a Hastelloy C autoclave provided with magnetic stirrer were introduced 0.1 mol of an aromatic nitro compound, 0.075 mol of an amine, 50 ml diethylene glycol dimethylether as reaction solvent and the catalyst system. The autoclave was pressurized with CO at 60 bar and the temperature was raised to the required reaction temperature by electrical means. After the required reaction time the pressure was dropped, the autoclave was gradually cooled and the reaction mixture was analyzed by NMR and GLC/MS to determine the amount of urea derivative. In the following table all examples are given with the amounts of catalyst components in millimoles, the reaction times (t), the reaction temperatures (T), the conversion (calculated on the amine) and the selectivity to urea derivative, the amine and the aromatic nitro compound as starting compounds.

Claims: A process for the preparation of urea derivatives of the general formula wherein R is an alkyl group and X is a halogen atom, an alkyl-, alkoxy-, aryloxy-, cyano-, ester- or trifluoromethyl group and n is from 0 to 5, which comprises reacting an aromatic nitro compound of the general formula wherein X and n are as defined above with carbon monoxide and an amine HNR₂ wherein R is an alkyl group, in the presence of a catalyst system comprising (a) a group VIII noble metal or a compound thereof, (b) a bidentate ligand of the formula R¹R²-M-A-M-R³R⁴ in which M is P, As or Sb, A is a divalent organic bridging group having at least 2 carbon atoms in the bridge, none of these carbon atoms carrying substituents that may cause steric hindrance, and R¹,R²,R³ and R⁴ represent similar or dissimilar optionally substituted hydrocarbon groups, and (c) an acid having a pKa of more than 2 or a transition metal salt of said acid. A process according to claim 1 wherein the amine HNR₂ has R groups having from 1 to 4 carbon atoms. A process according to claim 2 wherein the amine is dimethylamine or diethylamine. A process according to one or more of the claims 1-3 wherein the aromatic nitro compound has at least one alkyl group of 1 to 4 carbon atoms or a chlorine atom. A process according to claim 4 wherein the aromatic nitro compound is p-isopropyl nitrobenzene; 3,4-dichloro nitrobenzene; 3-chloro-4-methyl nitrobenzene. A process according to claim 1 wherein the aromatic nitro compound is nitrobenzene. A process according to one or more of the claims 1-6 wherein the group VIII noble metal is palladium, ruthenium, rhodium, platinum or iridium. A process according to one or more of the claims 1-7 wherein a bidentate phosphine is used. A process according to claim 8 wherein the bidentate phosphine is 1,3-di(diphenylphosphino)propane. A process according to one or more of the claims 1 and 7-9 wherein the acid is a carboxylic acid, having 2 to 10 carbon atoms. A process according to claim 10, wherein the carboxylic acid is acetic acid. A process according to claim 1, 10 or 11, wherein the salt of the transition metal is a copper salt, an iron salt or a nickel salt. A process according to any one of the preceding claims wherein the reaction takes place in the presence of a solvent. A process according to claim 13 wherein the solvent is diethylene glycol dimethylether or nitrobenzene. A process according to any one of the preceding claims wherein the reaction temperature is between 50 °C and 200 °C, preferably between 70 °C and 150 °C. A catalyst system comprising (a) a group VIII noble metal or a compound thereof, (b) a bidentate ligand of the formula R¹R²-M-A-M-R³R⁴ in which M is P, As or Sb, A is a divalent organic bridging group having at least 2 carbon atoms in the bridge, none of these carbon atoms carrying substituents that may cause steric hindrance, and R¹,R² ,R³ and R⁴ represent similar or dissimilar optionally substituted hydrocarbon groups, and (c) a copper, nickel or iron salt of an acid having a pKa of more than 2. A catalyst system according to claim 16, wherein the group VIII noble metal is palladium, ruthenium, rhodium, platinum or iridium. A catalyst system according to claim 16 or 17 wherein in the formula of the bidentate ligand R¹ ,R² ,R³ and R⁴ are phenyl groups and M is a phosphorus atom, and A is a divalent straight alkyl chain. A catalyst system according to one or more of the claims 16 to 18 wherein the acid is a carboxylic acid having 2 to 10 carbon atoms.

Inventors: DRENT, EIT
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1987
Main classification: C07C273
IPC codes: B01J31, C07C273, C07C275, C07B61