Abstract:
The invention relates to esters of certain benzene polycarboxylic acids with 2-alkylalcohols, and their use as hydraulic fluid, as or in lubricant formulations or as an additive in cosmetics.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention concerns esters of benzenepolycarboxylic acids with branched aliphatic alcohols and their use as hydraulic fluid, lubricants or cosmetic additives. 
     2. Description of the Prior Art 
     Esters have long been known as lubricants. They are used on a large scale as lubricating oils and greases for aircraft engines, for example. Mainly the reaction products of simple monocarboxylic acids with C8 through C10 alcohol mixtures such as those obtained in oxo synthesis, hydrogenation or aldol condensation are used. Complex esters obtained by esterification with dicarboxylic acids and/or glycols are added to the simple ester oils to improve their viscosity, shear stability and lubricant behavior. Ester oils are also used in lubricant greases such as metal soaps or silicones. 
     The alcohols typically used for esterification are available by oxo synthesis, for example. These alcohols are not chemically uniform and are in the form of isomer mixtures. 
     Ester oils are characterized by low vapor pressures, a high oxidation stability, good temperature-viscosity characteristics and high aging stability. For certain applications, they must have good miscibility with the desired operating medium. The operating medium may be, for example, pure hydrocarbons, fluorochlorocarbons or fluorocarbons. The ester may also be optimized with regard to low temperature behavior (solubility, pour point) and with regard to heat stability (flash point). Additional requirements are necessitated for compatibility with contact materials such as plastics, metals or paint coatings as required for the application. Ester oils usually have a good high-pressure capacity and load-bearing capacity. 
     Ester oils of aromatic polycarboxylic acids are known per se. European Patent Application 0 157 583-A2 describes the use of trimellitic acid esters synthesized from linear and/or branched primary alcohols, especially C8 through C10 alcohols. According to European Patent Application 0 157 583-A2 exclusive use of branched alcohols leads to an undesirably high viscosity and a low oxidation stability. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to make available ester oils which meet special requirements with regard to viscosity, the viscosity-temperature characteristics and the high-temperature stability, especially with regard to oxidation stability as well as hydrolysis stability and especially with regard to load tolerance despite the excellent lubricant properties. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This invention concerns the esters of aromatic polycarboxylic acids with three or four carboxyl groups. The esters according to the present invention and the mixtures thereof can be described by the following structure:                           
     wherein 
     n denotes an integer from 3 to 4 and 
     R denotes a C12 through C40 hydrocarbon moiety 
     having the following structure:                           
      wherein 
     R′ denotes an unbranched C6 through C37 hydrocarbon residue and 
     R″ denotes a C1 through C20 hydrocarbon moiety, 
     where R, R′ and R″ may be different for each n. 
     These are preferably the esters of trimellitic acid, trimesic acid and/or pyromellitic acid. Trimellitic acid is also known as 1,2,4-benzenetricarboxylic acid and has the following structure:                           
     Trimesic acid is likewise an aromatic tricarboxylic acid and is also known as 1,3,5-tricarboxylic acid:                           
     Pyromellitic acid is also known as 1,2,4,5-benzenetetracarboxylic acid and has the following structure:                           
     The acids indicated above can be obtained by oxidation from suitably substituted polyalkylbenzenes, optionally in the presence of catalysts such as vanadium pentoxide or manganese catalysts. Trimellitic acid esters and pyromellitic acid esters are especially preferred. 
     The alcohol group has a 2-alkyl branch. The corresponding alkylalkan-1-ols are accessible by the Guerbet reaction, for example, or oxo synthesis.                           
     The alkyl group (R) of the alcohol group is preferably a C12 through C36 hydrocarbon residue, especially preferably a C12 through C28 hydrocarbon residue, where R′ is a C6 through C26 hydrocarbon residue, especially a C6 through C22 hydrocarbon residue, and R″ is a C1 through C18 hydrocarbon residue, especially a C3 through C16 hydrocarbon residue. Both hydrocarbon residues are preferably saturated residues, and R″ is preferably an unbranched (linear) hydrocarbon. 
     These esters should preferably have, independently of one another, a flash point (DIN ISO 2592) of more than 270° C., a solidification point of less than minus 40° C., preferably less than minus 45° C., and a viscosity index (DIN ISO 2909) of more than 100. 
     The esters according to this invention and compositions containing such esters are used as lubricants or lubricant additives, as cosmetic additives or as hydraulic fluid for transmission of forces. Use as lubricants for industrial gears, for metalworking (e.g., as a rolling oil), as a transmission fluid for processing plastics or textiles and/or as a cooling lubricant (refrigerator oil). 
     The esters according to this invention are accessible especially easily from the anhydrides or the aromatic polycarboxylic acids, but they can also be synthesized directly from the acids. Esterification is usually performed with the addition of a catalyst, such as an alkyl titanate, with dehydration. 
     The esters according to this invention can be used as lubricants in combination with other esters, especially neopentyl polyols or silicones for example. Likewise, the ester oils according to this invention can be used as the operating medium themselves or in combination with other operating media, e.g., in the sense of a hydraulic fluid. 
     Despite the good properties of the ester oils according to this invention, it may be expedient to add additives, such as agents to improve wear, agents to improve the viscosity index, antioxidants, high-pressure additives and corrosion inhibitors, dispersants or metal deactivators. 
    
    
     EXAMPLES 
     The following 2-alkylalkan-1-ols were used as educts: 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 2-Alkylalkan-1-ols 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Isofol ® 12 
                 &gt;95 mol% 
                 2-butyloctanol 
               
               
                   
                 Isofol ® 14T 
                 10-20 mol% 
                 2-butyloctanol 
               
               
                   
                   
                 45-55 mol% 
                 2-hexyloctanol/2-butyldecanol 
               
               
                   
                   
                 25-35 mol% 
                 2-hexyldecanol 
               
               
                   
                   
                 &gt;95 mol% 
                 (total) 
               
               
                   
                 Isofol ® 16 
                 &gt;97 mol% 
                 2-hexyldecanol 
               
               
                   
                 Isofol ® 20 
                 &gt;97 mol% 
                 2-octyldodecanol 
               
               
                   
                 Isofol ® 32 
                 &gt;90 mol% 
                 2-tetradecyloctadecanol 
               
               
                   
                   
               
             
          
         
       
     
     Isofol® is a registered trademark of RWE-DEA AG für Mineraloel und Chemie [RWE-DEA Mineral Oil and Chemistry Company]. The alcohols listed above are commercially available as products of Condea Chemie GmbH [Condea Chemical Co.]. 
     2-Alkylalkan-1-ol Trimellitates 
     Trimellitic anhydride was esterified in high yields with the corresponding alcohols in 10 mol % excess by adding 0.15 wt % isopropyl titanate as the catalyst at a temperature of 170° C. After isolation, colorless, odorless liquids were obtained. The products can be characterized as follows: 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Trimellitic acid esters 
               
             
          
           
               
                   
                 T12 
                 T14 
                 T16 
                 T20 
                 T32 
               
               
                   
                   
               
             
          
           
               
                 Carbon 
                   
                 45 
                 51 
                 57 
                 69 
                 105 
               
               
                 number 
               
               
                 Molecular 
                 g/mol 
                 714 
                 810 
                 882 
                 1050 
                 1566 
               
               
                 weight 
               
               
                 Acid value 
                 mg 
                 0.02 
                 0.03 
                 0.12 
                 0.06 
                 0.78 
               
               
                   
                 KOH/g 
               
               
                 Sapon- 
                 mg 
                 236 
                 209 
                 193 
                 150 
                 107 
               
               
                 ification 
               
               
                 value 
                 KOH/g 
               
               
                 Density 
                 g/cm 3   
                 0.946 
                 0.934 
                 0.927 
                 0.91 
                 0.865 
               
               
                 at 20° C. 
               
               
                 Dynamic 
                 mPas 
                 443 
                 429 
                 426 
                 453 
                 191 +   
               
               
                 viscosity 
               
               
                 at 20° C. 
               
               
                 Kinematic 
                 mm 2 /s 
                 395 
                 403 
                 403 
                 437 
                 — 
               
               
                 viscosity* 
               
               
                 at 20° C. 
               
               
                 Kinematic 
                 mm 2 /s 
                 122.6 
                 129.6 
                 133.3 
                 148.3 
                 226 
               
               
                 viscosity 
               
               
                 at 40° C. 
               
               
                 Kinematic 
                 mm 2 /s 
                 13.5 
                 14.9 
                 16 
                 18.4 
                 26.1 
               
               
                 viscosity* 
               
               
                 at 100° C. 
               
               
                 Viscosity 
                 — 
                 106 
                 117 
                 127 
                 139 
                 148 
               
               
                 index 
               
               
                 Melting 
                 ° C. 
                 −46 
                 −45 
                 −48 
                 −48 
                 +19 
               
               
                 range 
               
               
                 Solid- 
                 ° C. 
                 −47 
                 −46 
                 −48 
                 −48 
                 +16 
               
               
                 ification 
               
               
                 range 
               
               
                 Flash 
                 ° C. 
                 270 
                 280 
                 275 
                 280 
                 317 
               
               
                 point 
               
               
                 Smoke 
                 ° C. 
                 205 
                 205 
                 200 
                 200 
                 235 
               
               
                 point 
               
               
                 Hydrolysis 
                 %hyd- 
                 21.7 
                 20 
                 22.7 
                 23.8 
                 19.6 
               
               
                 stability 
                 rolyzed 
               
               
                 Acid value 
                 mg 
                 51.2 
                 41.5 
                 33.1 
                 29 
                 16.2 
               
               
                 after 7 
                 KOH/g 
               
               
                 days at 
               
               
                 150 ° C. 
               
               
                   
               
               
                 The number following the “T” denotes the number of the startinq Isofol ® and indicates the carbon number of the alcohol group. T stands for trimellitate.  
               
               
                 *according to Ubbelohde, + at 40° C.  
               
             
          
         
       
     
     2-Alkylalkan-1-ol Pyromellitates 
     Pyromellitic anhydride was esterified with the corresponding alcohols in 10 mol % excess with high yields by adding 0.15 wt % isopropyl titanate as the catalyst at a temperature of 170° C.-180° C. The products can be characterized as follows: 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Pyromellitic acid esters 
               
             
          
           
               
                   
                 P12 
                 P14 
                 P16 
                 P20 
                 P32 
               
               
                   
                   
               
             
          
           
               
                 Carbon number 
                   
                 58 
                 66 
                 74 
                 90 
                 138 
               
               
                 Molecular weight 
                 g/mol 
                 926 
                 1054 
                 1150 
                 1374 
                 2036 
               
               
                 Acid value 
                 mg KOH/g 
                 0.04 
                 0.04 
                 0.01 
                 0.03 
                 0.04 
               
               
                 Saponiflcation val 
                 mg KOH/g 
                 243 
                 221 
                 197 
                 165 
                 103 
               
               
                 Density at 20° C. 
                 g/cm 3   
                 0.947 
                 0.933 
                 0.926 
                 0.906 
                 0.872 
               
               
                 Dynamic Viscosity at 20 ° C. 
                 mPas 
                 771 
                 700 
                 657 
                 654 
                 250 +   
               
               
                 Kinematic viscosity* at 20 ° C. 
                 mm 2 /s 
                 709 
                 658 
                 625 
                 650 
                 — 
               
               
                 Kinematic viscosity* at 40 ° C. 
                 mm 2 /s 
                 210 
                 204 
                 201 
                 211 
                 253 
               
               
                 Kinematic viscosity* at 100 ° C. 
                 mm 2 /s 
                 20.3 
                 21.4 
                 22.4 
                 23.4 
                 29.1 
               
               
                 Viscosity index 
                 — 
                 112 
                 125 
                 135 
                 136 
                 153 
               
               
                 Melting range 
                 ° C. 
                 −43 
                 −43 
                 −47 
                 −44 
                 37 
               
               
                 Solidification range 
                 ° C. 
                 −43 
                 −44 
                 −47 
                 −44 
                 23 
               
               
                 Flash point 
                 ° C. 
                 265 
                 275 
                 273 
                 292 
                 315 
               
               
                 Smoke point 
                 ° C. 
                 195 
                 235 
                 235 
                 157 
                 170 
               
               
                 Hydrolysis stab. 
                 % hydrolyzed 
                 24.1 
                 23.8 
                 22.7 
                 23.8 
                 19.6 
               
               
                 Acid value after 7 days at 150 ° C. 
                 mg KOH/g 
                 43.8 
                 38.1 
                 33.1 
                 29.0 
                 16.2 
               
               
                   
               
               
                 The number following the “P” denotes the number of the starting Isofol ® and indicates the carbon number of the alcohol group. P stands for pyromellitate.  
               
               
                 *according to Ubbelohde, + at 40 ° C.