PROCESS FOR PREPARING SALTS OF POLYOLEFINIC SUBSTITUTED DICARBOXYLIC ACIDS

Abstract: This invention is a process for preparing Group I-B and II-B metal, preferably copper, salts of polyolefinic substituted dicarboxylic acids. The method involves the step of introducing substantially less than a stoichiometric amount of a short chain carboxylic acid (such as acetic or propionic acid), in a stagewise fashion, to a mixture of a source of the corresponding Group I-B or II-B metal (such as an oxide or hydroxide) with the polyolefinic substituted dicarboxylic acid. The product salt is then recovered.

Description: This invention is a process for preparing metal salts of polyolefinic substituted dicarboxylic acids. There are several known methods for preparing the Group I-B and II-B metal salts of polyolefinic substituted dicarboxylic acids. In US-A-4 552 677, a copper compound such as cupric acetate hydrate, basic cupric acetate, cuprous carbonate, basic cupric carbonate, and cuprous or cupric hydroxide is introduced into a reaction vessel containing a hydrocarbyl substituted succinic anhydride derivative. A variety of acidic, neutral and basic copper salts are shown as products. US-A-3 271 310 shows the production of a similar selection of salts, including Group I-B metal salts. It has been found that the yields of these prior art processes may be lower than is desired. The present invention is directed to a process for preparing Group I-B and II-B metal, particularly copper and/or zinc, salts of olefinic substituted dicarboxylic acids, being the products of a polyolefin having a numerical average molecular weight (M n ) of at least 600 which has been substituted with at least one dicarboxylic acid producing moiety per polyolefin molecule. The process involves the step of introducing a short chain carboxylic acid (such as acetic or propionic acid) preferably in an amount substantially less than that stoichiometrically required, to a mixture containing Group I-B or II-B metal sources (such as an oxide or hydroxide) with the polyolefinic substituted dicarboxylic acid. The product salt is then recovered. The process uses inexpensive metal-bearing reactants, notably the oxide or hydroxide or carbonate of copper or zinc. Short chain carboxylic acids are introduced into a liquid reaction mixture containing the metal-bearing reactant and a polyolefinic substituted dicarboxylic acid. The short chain carboxylic acids may be added in an amount which, in total, is substantially less than would be theoretically required to stoichiometrically react with, e.g., the copper-bearing reactants to produce the copper carboxylate. The reaction temperatures may be moderate, e.g., less than about 130°C, although higher temperatures may be used. Yields, on a metal-bearing reactant basis, are excellent and have been found to be superior to those of processes using the same metal reactant without the short chain carboxylic acid. The metal salts prepared by the invention have a variety of utilities as, for instance, compatabilizing agents or dispersants in lubricating oil formulations. The Reactants Polyolefinic-substituted Dicarboxylic Acids The polyolefinic-substituted dicarboxylic acids as reactants in this invention are long chain olefinic substituted dicarboxylic acid materials, i.e., acid anhydride, or ester, and include long chain hydrocarbons, generally olefin polymers which are substituted with alpha or beta unsaturated C₄ to C₁₀ dicarboxylic acids, (e.g., itaconic acid, maleic acid, maleic anhydride, chloromaleic acid, dimethyl fumarate, chloromaleic anhydride, etc.). Preferred olefin polymers from which the polyolefinic-substituted dicarboxylic acid reactants are derived are those polymers made up of a major molar amount of C₂ to C₁₀ monoolefin, e.g., C₂ to C₅, monoolefin. Such olefins include ethylene, propylene, butylene, isobutylene, pentene, octene-1, styrene, etc. The polymers may be homopolymers such as polyisobutylene or copolymers of two or more of such olefins. These include copolymers of: ethylene and propylene; butylene and isobutylene; propylene and isobutylene, etc. Other copolymers include those in which a minor molar amount of the copolymer monomers, e.g., 1 to 10 mole per cent, is a C₄ to C₁₈ diolefin, e.g., copolymers of isobutylene and butadiene; or copolymers of ethylene, propylene and 1,4-hexadiene, 5-ethylidene-2-norbonene, etc. In come cases the olefin polymer may be completely saturated, for example an ethylene-propylene copolymer made by a Ziegler-Natta synthesis using hydrogen as a moderator to control molecular weight. The olefin polymers will usually have number average molecular weights (M n ) above 600. Particularly useful olefin polymers have number average molecular weights within the range of from 900 to 5,000 with approximately one double bond per polymer chain. An especially suitable starting material for a dispersant additive is polyisobutylene. The number average molecular weight for such polymers can be determined by several known techniques. A convenient method for such determination is by gel permeation chromatography (GPC) which additionally provides molecular weight distribution information (see W W Yua, J J Kirkland and D D Bly, 'Modern Size Exclusion Liquid Chromatography', John Wiley & Sons, New York 1979). Processes for reacting the olefin polymer with the C 4-10 unsaturated dicarboxylic acid, anhydride or ester are known in the art. For example, the olefin polymer and the dicarboxylic acid material may be simply heated together as disclosed in US-A-3 361 673 and US-A-3 401 118 to cause a thermal 'ene' reaction to take place. Or, the olefin polymer can be first halogenated, for example, chlorinated or brominated to 1 to 8, preferably 3 to 7 weight per cent chlorine, or bromine, based on the weight of polymer, by passing the chlorine or bromine through the polyolefin at a temperature of 100° to 250°, e.g., 140° to 225° C for 0.5 to 10, e.g., 3 to 8 hours. Processes of this general type are taught in US-A-3 087 436; 3 172 892; 3 272 746, and others. Alternatively, the olefin polymer, and the unsaturated acid material are mixed and heated while adding chlorine to the hot material. Processes of this type are disclosed in US-A-3 215 707; 3 231 587; 3 912 764; 4 110 349; 4 234 435, and in GB-A-1 440 219. By the use of halogen, about 65 to 95 weight per cent of the polyolefin will normally react with the dicarboxylic acid material. Thermal reactions, those carried out without the use of halogen or a catalyst, cause only abut 50 to 75 weight per cent of the polyisobutylene to react. Chlorination obviously helps to increase the reactivity. Group I-B or II-B Metal-bearing Reactant The metal-bearing reactant may be any inorganic material which will react with the above described materials to produce the desired Group I-B or II-B salt using the minor amounts of short-chain carboxylic acids. The Group I-B and II-B metal-bearing reactants include, for example, the oxides, hydroxides and carbonates, such as a cupric carbonate, zinc oxide, cupric oxide, zinc hydroxide, zinc carbonate and the like. The preferred copper-bearing reactants are the copper oxides (CuO, Cu₂O), the copper hydroxides (CuOH, Cu(OH)₂), and the copper carbonates (Cu₂CO₃, CuCO₃, CuCO₃Cu(OH)₂. Especially preferred copper compounds, for economic reasons, are CuO and CuOH. The preferred zinc-bearing reactant is zinc oxide (ZnO). Short Chain Carboxylic Acids The short chain carboxylic acids which are used in this process are alkanoic acids of the formula: R COOH where R is a branched or straight chain alkyl group having from 1 to 6 carbon atoms. Especially preferred are those acids wherein R is alkyl of 1 to 2 carbon atoms, i.e., acetic and propionic acids. The function of the short chain mono-carboxylic acid material is not clear although it appears that the acid activates the Group I-B or II-B metal-bearing compound to form a metal carboxylate which, in turn, reacts with the polyolefinic-substituted dicarboxylic acid-producing material. The latter reaction would regenerate the short chain carboxylic acid and therefore catalyze the reaction. The Process The polyolefinic-substituted dicarboxylic acid is introduced into a reaction vessel in the desired amount. If the polyolefinic substituted dicarboxylic acid reactant is charged to the reaction vessel as the corresponding anhydride, water will generally be admixed with the anhydride (before, with or after charging the anhydride) in an amount and under conditions sufficient to hydrolyze the anhydride to the desired acid form, to facilitate the reaction of the acid groups with the selected Group I-B or II-B metal-bearing reactant. The amount of water added will generally be at least about that amount theoretically required to stoichiometrically hydrolyze the anhydride groups of the polyolefinic-substituted dicarboxylic acid anhydride, and preferably from 10 to 200 wt.% excess water above the stoichiometric amount. Typically, the reaction will be carried out in a liquid reaction solvent for this reactant, such as a hydrocarbon oil (such as a mineral oil, lubricating oil (including synthetic lubricating oil) and the like). Generally the mixture of the polyolefinic-substituted dicarboxylic acid and hydrocarbon solvent will have a kinematic viscosity of from 10 to 1500 cSt (at 100 o C), and preferably from 50 to 1000.10⁻⁶ m².s⁻¹ (cst) (at 100 o C). The Group I-B or II-B metal-bearing material may then be added in a single volume or in stages. It may be added dry, or in the form of an aqueous solution or slurry. Additional water may be added if desired. The short chain carboxylic acid will preferably be added in amounts up to a total of up to about 80%, more preferably 1 to 50%, and most preferably from 10 to 40%, of that amount which would be theoretically required to stoichiometrically react all of the metal-bearing material to the corresponding metal mono-carboxylate (e.g., the metal acetate when using acetic acid). The short chain carboxylic acid may be added in one or more amounts. Preferably, however, the short chain carboxylic acid is added continuously or intermittently, e.g., in a stagewise fashion, over the course of the reaction. For instance, when using acetic or propionic acid at a reaction temperature of about 100°C in a batch reactor, the carboxylic acid may be added in discrete steps over a period of up to, e.g., twelve hours. Substantially complete reactions may be had at four to five hours time at these temperatures. The temperatures of reaction may desirably be in the range of from 70° to 150°C. The reaction rate is higher at the upper end of the range but acceptable rates are found at the lower end. Preferably temperatures are not higher than about 150°C to minimise decomposition of the metal salt formed by the process of this invention. The reaction mixture may be stripped (with or without heating) with an unreactive gas e.g., nitrogen, to remove various light materials such as any unreacted mono-carboxylic acid (e.g., acetic acid) and then the stripped reaction mixture may be filtered if desired to remove insolubles, such as unreacted metal-bearing starting material solids (e.g., CuO or Cu(OH)₂) and by-products (e.g., metal salts of the monocarboxylic acid, such as Cu acetate). The resulting stripped, filtered liquid comprises a solution of a desired Group I-B or II-B metal salt of the polyolefinic-substituted dicarboxylic acid in the hydrocarbon oil, and will be generally characterised by a kinematic viscosity in the range of from 400 to 1500.10⁻⁶ m².s⁻¹ (cSt) (at 100 o C). This invention will be further understood by reference to the following examples, wherein all parts are parts by weight, unless otherwise noted. The examples are intended only to exemplify the invention and not limit it in any way. Examples Example 1 About 200 g (0.1927 mole) of a polyisobutenyl succinic anhydride (Sap.No.106.7, 80% active ingredient) derived from a 950 Mn polyisobutylene was charged to a stirred reaction flask equipped with a reflux condenser, and 23g of copper oxide powder (65.7% Cu), 75g of diluent oil solvent 150N and 50 ml of water were added. One gram of acetic acid was added and the reaction mixture was slowly heated to 100°C. Another 4g of acetic acid was added at a rate of 1g every hour for the following four hours. Thereafter the reaction mixture was heated to 120°C while nitrogen stripping and then filtered to remove any unreacted solids or solid by-products. The filtrate analysed for 2.23% copper. Examples 2-8; Comparative Example 9 The procedure of Example 1 was repeated several times with differing amounts of acetic acid (Examples 2-5), using propionic acid (Example 8), and with no carboxylic acid (Comparative Example 9). In the procedures of Examples 6 and 7, Example 1 was repeated except that the charged components did not initially include any acetic acid; rather the other components charged were heated to 100° C for 4 hours with stirring, and for an additional 1 hour at 120°C. At the end of this 5 hours, the indicated amounts of acetic acid (1g in Example 6 and 0.5g in Example 7) were added, after which the resulting liquid mixture was heated in each experiment for an additional 1 hour at 100°C. Comparison of the amounts of copper in the final products, as shown in the previous Table shows that the process of this invention is exceptionally well suited to producing high amounts of salts in the product. Example 10 About 103.7g (0.1 mole) of a polyisobutenyl succinic anhydride (Sap.No.106.7; 80% active ingredient) having a SA/PIB ratio of 1.04 and an average number molecular weight of 950 was mixed with 289.1g of mineral oil solvent 150 neutral, 8.1g of zinc oxide and heated to 90°C in the equipment described in Example 1. Thereafter, 0.75g of acetic acid was added every hour to a total of 3g. After the fourth hour the reaction mixture was heated to 130°C, then nitrogen for 2 hours and thereafer filtered. The filtered oil solution analysed for 1.61 wt.% Zn (theoretical 1.62%). Comparative Example 11 About 103.7g (0.1 mole) polyisobutenyl succinic anhydride (PIBSA) as used in Example 10 was mixed with 289g of mineral oil solvent 150 neutral. 8.1g ZnO, and 10ml water. The reaction mixture was then heated to 90°C and soaked at this temperature for four hours. Thereafter the reaction temperature was increased to 130°C, and the reaction mixture was nitrogen stripped for 2 hours, and filtered. The infrared analysis of the filtered oil solution showed the presence of unreacted PIBSA to a large extent. In addition, the product analysed for only 0.91 wt.% Zn (theory 1.62 wt.%).

Claims: A method of producing Group I-B and Group II-B metal salts of polyolefinic substituted dicarboxylic acids comprising the steps of: (i) Contacting an inorganic Group I-B or II-B metal-bearing material with a long chain olefinic substituted dicarboxylic acid substituted with at least one dicarboxylic acid producing moiety per polyolefin molecule, which is formed by reacting an olefin polymer of a C₂ to C₁₀ monoolefin having a number average molecular weight greater than 600 and a C₄ to C₁₀ monounsaturated acid material, and (ii) Recovering the Group I-B or II-B metal salt so formed, characterised in that a short chain carboxylic acid of the formula RCOOH (wherein R is a straight or branched alkyl group having from 1 to 6 carbon atoms) is added to Step (i). The process of Claim 1 wherein the short chain carboxylic acid is acetic acid or propionic acid. The process of Claim 1 or Claim 2 wherein the Group I-B metal-bearing material is CuO, Cu₂O, CuOH, Cu(OH)₂, Cu₂CO₃, CuCO₃ or CuCO₃Cu(OH)₂. The process of Claim 1 or Claim 2 wherein the Group II-B metal-bearing material is ZnO, Zn(OH)₂ or ZnCO₃. The process of any of Claims 1 to 4, wherein the olefin polymer is polyisobutylene. The process of any of Claims 1 to 5, in which the inorganic Group I-B or II-B metal-bearing material is contacted with the long chain olefinic substituted dicarboxylic acid in the presence of a liquid solvent for said long chain olefinic substituted dicarboxylic acid. The process as claimed in any of Claims 1 to 6, in which the short chain carboxylic acid is added in steps to said reaction mixture. The process as claimed in any of Claims 1 to 7, in which the short chain carboxylic acid is employed in an amount of up to 80 wt.% of that amount theoretically required to stoichiometrically react with all of said Group I-B or II-B metal-bearing material to form the corresponding carboxylate. The process of Claim 8, wherein said short chain carboxylic acid is employed in an amount of from 1 to 50 weight per cent of said stoichiometric amount. The use in a lubricating oil formulation of a Group I-B or Group II-B metal salt as prepared in any of Claims 1 to 9.

Inventors: COLCORD, LAURA JEAN, GUTIERREZ, ANTONIO, LUNDBERG, ROBERT DEAN
Applicants: EXXON CHEMICAL PATENTS INC.
Application year: 1987
Main classification: C08F8
IPC codes: C08F8, C10M129