Succinic acid esters and hydraulic fluids therefrom

#This invention relates to new hydrocarbyl succinic esters and more particularly to aqueous based hydraulic fluids which contain hydrocarbyl succinic acid esters, which hydraulic fluids have improved characteristics in being stable and possessing excellent hard water stability.

#Aqueous based hydraulic fluids are well known in the art as exemplified, for example, by U.S. Pat. Nos. 3,580,847, 4,151,099, 3,657,123, 3,005,776, 2,944,976, and 4,257,902. These aqueous based hydraulic fluids are used in various areas as mechanical power or pressure transmitting media in situations where lubricating and wear preventing characteristics are necessary. In the technology of hydraulic power transmission, mechanical power is imparted to a fluid called a hydraulic fluid in the form of pressure by means of a hydraulic pump. Power is utilized where desired by tapping a source of the hydraulic fluid and transforming the power as pressure back to mechanical motion by a hydraulic motor. The hydraulic fluid is utilized as a pressure and volume transmitting medium and any non-compressible fluid can perform the function. Water is the oldest fluid used for this purpose and is still sometimes used without additives. In the prior art, however, there has been heavy emphasis on the development of aqueous based fluids which contain various types of additives and which are designed and manufactured specifically for specialty used.

#Within any hydraulic system there are found such metals as iron, brass, solder, bronze, aluminum, zinc, cadmium and other commonly used metals and the presence of several metals in a hydraulic system provides the possibility for the formation of various corrosion problems. Therefore, such fluids traditionally contain corrosion inhibitors.

#The present invention relates to a novel group of succinic acid esters which are useful as dispersants in a series of aqueous based hydraulic fluids. The succinic acid esters are produced in general by a series of reactions starting with the reaction of a hydrocarbyl substituted succinic anhydride with at least one equivalent, preferably 1-3 equivalents, of maleic anhydride to produce a succinic anhydride of the following formula: ##STR1##

#In the above formula, R is a hydrocarbyl or hydrocarbon substituent which contains at least about 10 carbon atoms. Preferably R contains olefinic unsaturation and branch chained configurations and provides the starting succinic anhydride with a molecular weight in the range of about about 700.

#The reaction between the hydrocarbon substituted succinic anhydride and the maleic anhydride to produce the compound of Formula (I) is conducted by heating the succinic anhydride reactant to a temperature of about 150.degree.-200.degree. C. and thereafter adding at least one equivalent of the maleic anhydride to the succinic anhydride over a period of time such as 1 to 3 hours. After the addition is complete, the reaction mixture is then agitated for 2 to 4 hours to complete the reaction.