PROCESS FOR PREPARING 3,5-DIHYDROCARBYL-4-HYDROXYBENZYLMALONIC ACID ESTERS

Abstract: Esters of 3,5-dihydrocarbyl-4-hydroxybenzyl malonic acid are prepared by reacting an N,N-dihydro-carbyl-2,6-dihydrocarbyl-4-aminomethylphenol with an ester of a 1,3-dicarboxylic acid in the presence of a basic substance selected from the group consisting of alkali metal hydroxides, alkali metal salts of a weak acid, alkaline earth metal hydroxides, alkaline earth metal salts of a weak acid, amine bases and mixtures of the same. The products are useful as antioxidants.

Description: PROCESS FOR PREPARING 3,5-DIHYDROCARBYL-4- HYDROXYBENZYLMALONIC ACID ESTERS This invention relates to 3,5-dihydrocarbyl-4- hydroxy-benzylmalonic acid esters and the preparation and uses thereof as antioxidants for oxidizable organic materials when such materials are exposed to oxidative dag adative conditions-, The materials of the invention are prepared by reacting an N,N-dihydrocarbyl-2,6-dihydrocarbyl- 4-aminomethylphenol with an ester of a 1, 3-dicarboxylic acid in the presence of an alkali or an alkaline earth metal hydroxide, an alkali or an alkaline earth metal salt of a weak acid, an a ine base or mixtures of the same. Thus, in one embodiment of the invention there is provided a novel process for the preparation of 3, 5-dihydrocarbyl-4-hydroxybenzylmalonic acid esters which comprises reacting an N,N-dihydrocarbyl-2,6- dihydrocarbyl-4-aminomethylphenol with an ester of a 1,3-dicarboxylic acid in the presence of an alkali metal hydroxide, an alkali metal salt of a weak acid, an alkaline earth metal hydroxide, an alkaline earth metal salt of a weak acid, an amine base or mixtures of the same. Thus, in the present invention there is provided a process for the preparation of 3,5-dihydro-carbyl-4- hydroxybenzylmalonic acid esters having the general formula: which comprises reacting an N,N-dihydrocarbyl,2,6-di- hydrocarbyl-4-aminomethylphenol of the general formula: with an ester of a 1,3-dicarboxylic acid of the general formula: 0 0 R 5 0CCH 2 C0R 6 (II) in the presence of an alkali metal hydroxide, an alkali metal salt of a weak acid, an alkaline earth metal hydroxide, an alkaline earth metal salt of a weak acid, an amine base or mixtures of the same wherein in the structural formulas above R, and R2 are the same or different and are hydrogen or hydrocarbyl radicals having " up to at least 40 carbon atoms with the provision that at least one of R, or R 2 must be other than hydrogen; R3 and R4, are the same or different and are linear, branched or unbranched alkyl, aralkyl or cycloalkyl radicals having up to at least 20 carbon atoms; Re and R β are the same or different and are linear or branched alkyl radicals having up to at least 20 carbon atoms with the provision that at least one of Rr or Rg must be other than hydrogen. Representative examples of radicals described above are secondary radicals such as secondary butyl, secondary • amyl, secondary octyl; tertiary radicals such as tertiary butyl, tertiaryhexyl and tertiary decyl; alkyl radicals such as methyl, ethyl, propyl, butyl, nonyl, decyl, tetradecyl, hexadecyl, nonadecyl; aralkyl radicals such as methyl phenyl and pentyl phenyl, and cycloalkyl radicals such as cyclo- pentyl, cyclohexyl and cycloheptyl radicals. Representative examples of the Group I compounds are N,N-dimethyl,2,6-di-t-butyl-4-aminomethyl- phenol, •5 N,N-dimethyl,2-methyl-*6-isopropyl-4-amino- methylphenol, N,N-dimethyl,2-methyl-6-t-butyl-4-aminomethyl- phenol, N,N-dimethyl,2,6-diisopropyl-4-aminometbyl- 0 phenol, N,N-dimethyl,2-sec-butyl-4-aminomethylphenol, N,N-dimethyl,2-isopropyl-4-aminomethylphenol, N,I.-dimethyl,2-t-butyl-4-aminomethylphenol, N,N-diethyl,2,6-di-t-butyl-4-aminomethylphenol, *5 N,N-dioctyl,2,6-di-t-butyl-4-aminomethylphenol, N,N-dioctyl,2-ethyl-6-t-butyl-4-aminomethyl- phenol, N,N-dioctyl,2,6-diheptyl-4-aminomethylphenol, N,N-dioctyl,2-ethyl-6-methyl-4-aminomethyl 0 phenol, N,N-dioctyl,2-t-butyl-6-heptyl-4-aminomethyl- phenol, N-ethyl,N-methyl,2,6-di-t-butyl-4-amino- meth lphenol, N-octyl,N-methyl,2-methyl-6-ethyl-4-amino- methylphenol, 3,5-di-t-but l-4-hydroxybenzylpiperidine, 3, 5-di-t-butyl-4-hydroxybenzylmorpholine, 3,5-di-t-butyl-4-hydroxybenzylpyrrolidine, and the like. Representative examples of Group II esters of 1,3-dicarboxylic acid compounds are malonic acid, dimethyl ester, malonic acid, diethyl ester, malonic acid, diisopropyl ester, malonic acid, di-n-hexyl ester, malonic acid, dioctyl ester, malonic acid, didodecyl ester, malonic acid, ethyl, methyl diester, malonic acid, ethyl, isopropyl diester, malonic acid, n-butyl, ethyl diester, malonic acid, n-butyl, dodecyl diester, malonic acid, octyl, ethyl diester, malonic acid, ethyl monoester, malonic acid, n-propyl monoester, malonic acid, n-butyl monoester, malonic acid, n-hexyl monoester, malonic acid, octyl monoester, malonic acid, dodecyl monoester, and the like. Representative examples of Group III benzylated malonic acid esters, functioning as antioxidants, are 3 , 5-d i-t-butyl-4-hydroxybenzylmalonic acid , _ dimethyl ester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, diethyl ester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, diisopropyl ester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, di-n-hexyl ester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, dioctyl ester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, didodecyl ester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, ethyl, methyl diester, 3,5-di-t-butyl-4-hydroxybenzylmalonic acid, ethyl, isopropyl diester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, n-butyl, ethyl diester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, n-butyl, dodecyl diester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, octyl, methyl diester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, octyl, ethyl diester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, ethyl monoester, 3, 5-di-t-butyl-4.-hydroxybenzylmalonic acid, n-propyl monoester, 3,5-di-t-butyl-4-hydroxybenzylmalonic acid, n-butyl monoester, 3,5-di-t-butyl-4-hydroxybenzylmalonic acid, n-hexyl monoester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, octyl monoester, 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, dodecyl monoester, 3-ethyl-5-methyl-4-hydroxybenzylmalonic acid, dioctyl ester, 3-n-butyl-5-octyl-4-hydroxybenzylmalonic acid, ethyl, methyl diester, 3-ethyl-5-methyl-4-hydroxybenzylmalonic acid, ethyl monoester, 3, 5-dioctyl-4-hydroxybenzylmalonic acid, octyl monoester, and the like. An essential component of the reaction mixture is a basic substance selected from the group consisting of alkali metal hydroxides, alkali metal salts of a weak acid, alkaline earth metal hydroxides, alkaline earth metal salts of a weak acid, amine bases or mixtures of the same. Specific examples of these include sodium hydroxide, potassium hydroxide, barium hydroxide, rubidium hydroxide, cesium hydroxide, potassium car- bonate, sodium carbonate, cesium carbonate, rubidium carbonate, potassium sulfite, sodium borate, potassium acetate, diazabicyclonone, pyridine, tetra ethyl- quanidine and l,4-diazabicyclo(2,2,2)-octene. Potassium carbonate is preferred. The process of the invention is carried out by reacting the benzylamine starting material with at least 1 molar equivalent of the malonic acid ester reactant although an excess of ester reactant can be used. A preferred range of malonic acid ester reactant to benzylamine reactant is from about 1 to 10 moles of ester per mole of benzylamine. At least 1 mole of basic substance per mole of benzylamine reactant should be used in the process of the invention, although an amount of base up to about 50 moles of base per mole of benzylamine reactant can be used, if desired.. The reaction is advantageously conducted at a tem- perature of from 50°C. to 500°C. While lower tempera¬ tures can be used, the reaction rates are generally correspondingly lower. Temperatures above 500 C. can be used, but excessive decomposition of the reaction components can occur. Reflux temperature at atmospheric pressure is effective and preferred. Typically, the reaction can be conducted at atmospheric pressure. However, higher pressures up to about 1000 psig may be used, if desired. The use of a solvent for the reaction mixture is not generally required, especially if an excess of malonic acid ester reactant is used. However, if de¬ sired, a solvent which is inert under the reaction con¬ ditions, i.e., those solvents which do not enter into the reaction, may be added to the reaction vessel. Useful solvents comprise aprotic solvents which include ethers such as diethyl ether, dibutyl ether, 1-ethoxy- hexane, tetrahydrofuran, 1,4-dioxane, 1, 3-dioxolane, digly e, 1,2-diethoxyethane, and tertiary amines such as pyridine, N-ethylpiperidine, triethylamine, tributyl- amine, N,N-diphenyl-N-methylamine, N,N-dimethylalanine, etc. Especially useful solvents are dipolar aprotic solvents such as dimethyl sulfoxide, N,N-dimethyl- forαiamide, N.N-dimethylacetamide, dimethyl sulfone, tetramethylene sulfone, N-methylpyrrolidinone, aceto- nitrile and like materials. Other solvents which are inert under the reaction conditions may be used: for example, low boiling hydrocarbons, halogenated hydro¬ carbons, examples of which are benzene, toluene, tetrachloroethane, the chlorinated benzenes, the chlori- nated toluenes, etc., and lower alkanols having up to about 6 carbon atoms. These include, methanol, ethanol, n-propanol , isopropyl alcohol , n-butanol , sec-butyl _ alcohol, t-butyl alcohol, n-pentanol, isopentyl alcohol, n-hexanol and isohexyl alcohol. The amount of solvent can be expressed as a volume ratio of solvent to benzylamine reactant. Suit¬ able volume ratios of solvent to benzylamine reactant can be from 0/1 to 500/1 and preferably from 1/1 to 300/1. The mode of addition in the process is not particularly critical. Accordingly, it is convenient to add the benzylamine reactant to a mixture of the other materials, add the malonic acid ester compound to a mixture of the other materials, add the reactants to a mixture of the benzylamine and solvent, introduce all ingredients simultaneously into the reaction zone, or the like. The process should be carried out for the time sufficient to convert substantially all of the benzylamine reactant to the corresponding benzylated malonic acid ester. The length of time for optimum yield will depend primarily upon the reaction tempera¬ ture and the particular solvent, if any, used in the reaction. In general, excellent yields of the benzylated malonic acid ester are obtained in from two to twenty-four hours. Although not required, the process can be . conducted in a substantially anhydrous reaction system, and accordingly, the components of the reaction system are brought together and maintained under a substan- tially dry, inert atmosphere. By "substantially anhydrous" is meant a reaction system wherein the total amount of water present is no more than about 5 percent by weight, based on the reaction mixture. When the amount of waterin the system exceeds this, both reaction rate and yield of product decrease. The process may readily be conducted in a batch- wise, semi-batch or continuous manner and in conventional equipment. The process of the invention when run continously can be illustrated schematically by the equation shown below. R,, R«, RΛ, R , and Rg are the same radicals as described and exemplified above. Under the reaction conditions, the benzylamine reactant is fragmented to yield a quinone methide inter¬ mediate which undergoes nucleophilic attack by the malonic acid ester reactant to form the desired benzylated malonic acid ester product. Some bis(hydroxyphenyl)methane by-product may be formed by the process. The benzylated malonic acid ester product is easily separated from the reaction mixture by such means as distillation, extraction, crystallization and other methods obvious to those skilled in the chemical processing art. The benzylated malonic acid ester products prepared by the process of this invention have antioxidant properties and are capable of stabilizing polymers normally subject to oxidative degradation when incorporated into the polymers using conven- tional techniques such as by addition to polymer lattices ; or by addition to solid polymers on a mill or in a Banbury. Further, the novel compounds of this invention are effective antioxidants in both unleaded and leaded gasolines made from a wide variety of base stocks and for engine and industrial oils which are derived from crude petroleum or produced synthetically. The practice of this invention will be still further apparent by the following illustrative example. O PI Example I To a dimethylformamide solution (20 mLs) of N,N-dimethyl-2,6-di-t-butyl-4-aminomethylphenol (1.31 g; 5 m ols) and diethyl malonate (0.95 g, 6 mmols) , solid potassium carbonate (0.95 g, 7 mmols) was added with stirring under a nitrogen at- mosphere, thus generating the potassium salt of diethyl malonate. The reaction mixture was heated to a temperature of 110 C and held at that temperature for 3 hours and then poured into cold 2N hydrochloric acid (60 mLs). The aqueous reaction slurry was extracted with diethyl ether (2 x 50 mLs) . The combined organic extract was dried (MgSO,) and concentrated to give 1.80 g; 867. by VPC of 3, 5-di-t-butyl-4-hydroxybenzylmalonic acid, diethyl ester as a yellow-orange oil.

Claims: CLAIMS : 1. A process for the preparation of 3,5-dihydrocarbyl-4-hydroxybenzylmalonic acid esters which comprises reacting an N,N-dihydrocarbyl-2,6- dihydrocarbyl-4-aminomethylphenol with an ester of a 1,3-dicarboxylic acid in the presence of a basic sub¬ stance selected from the group consisting of an alkali metal hydroxide, an alkali metal salt of a weak acid, an alkaline earth metal hydroxide, an alkaline earth metal salt of a weak acid, an amine base or mixtures of the same. 2. A process as claimed in Claim 1 in which said 3,5-dihydrocarbyl-4-hydroxybenzylmalonic acid esters having the general structural formula OMPI and said N,N-dihydrocarbyl., 2,6-dihydrocrbyl-4-amino- methylphenol has the general structural formula and said 1,3-dicarboxylic acid has the general structural formula 0 0 II II R c 0CCH o C0R, (ID in which in said general formula R-, and R 2 are the same or different and are hydrogen or hydrocarbyl radicals having up to at least 40 carbon atoms with the provision that at least one of R, or R 2 must be other than hydrogen, R« and R, are the same or different and are linear, branched or unbranched alkyl, aralkyl or cyclo¬ alkyl radicals having up to at least 20 carbon atoms and Re and Rg are the same or different and are linear or branched alkyl radicals having up to at least 20 carbon atoms with the provision that at least one of Re or Rg must be other than hydrogen. ΓOR Λ. , OMPI 3. The process as claimed in Claim 2 in which said basic substance is selected from sodium hydroxide, potassium hydroxide, barium hydroxide, rubidium hydroxide, cesium hydroxide, potassium carbonate, sodium carbonate, cesium carbo- nate, rubidium carbonate, potas¬ sium sulfite, sodium borate, potassium acetate, diazabi- cyclonone, pyridine, tetramethylquanidine and 1,4-diazabicyclo-(2,2,2)-octene. 4. The process as claimed in Claim 2 in which said reaction is carried out at a temperature of from 50°C to 500°C. 5. The process as claimed in Claim 2 in which said reaction is carried out under pressure in the range of from atmospheric up to 1000 psig. 6. The process as claimed in Claim 2 in which said reaction is carried out in the presence of a solvent which is inert under the reaction conditions. 7. The process as claimed in Claim 6 in which said solvent is a dipolar aprotic solvent selected from dimethyl sulfoxide, N,N-dimethylformamide, N,N- dimethylacetamide, dimethyl sulfone, tetrameth lene sulfone, N-methylpyrrolidinone and acetonitrile. 8. The process as claimed in Claim 6 in which said solvent is selected from the group consisting of low boiling hydrocarbons, halogenated hydrocarbons and lower alkanols having from 1 to about 6 carbon atoms. OMPI - IPO

Inventors: EVERLY CHARLES RAY, ROPER JERRY MONROE, EVERLY, CHARLES, RAY, ROPER, JERRY, MONROE
Applicants: ETHYL CORP, ETHYL CORPORATION
Application year: 1983
Main classification: C07C69
IPC codes: C07C69