Functional fluid compositions containing erosion inhibitors

A functional fluid composition comprising:

• (a) a base stock comprising a phosphate ester, and
• (b) an effective erosion inhibiting amount of at least one erosion inhibitor selected from compounds represented by the formulas
• or mixtures thereof;
• wherein said erosion inhibitor(s) used in said functional fluid composition at least partially ionize, and the effective amount of said erosion inhibitor(s) used in said functional fluid composition is essentially soluble in said functional fluid compositions;
• wherein Rf is selected from fluoroalkyl, fluoroaryl, fluoroaralkyl, fluoroalkaryl, fluorocycloalkyl, fluoroallcoxyalkyl, or fluoropolyalicoxyalkyl groups;
• Y and Y′ are independently selected from C, S, S(═A), P—Rf, P—OR, or P—NRR′;
• A and A′ are independently selected from O or NR;
• X is selected from N, or C—R″;
• Z is selected from Y′(═A′)—Rf, H, OC(═O)—Rf, or R1—NH—(SO2—Rf);
• R and R′ are independently selected from H, alkyl, fluoroalkyl, aryl, fluoroaryl, alkaryl, aralkyl, fluoroalkaryl, or fluoroaralkyl;
• R″ is selected from H, alkyl, fluoroalkyl, aryl, fluoroaryl, alkaryl, aralkyl, fluoroalkaryl, fluoroaralkyl, or —Y(═A)—R2;
• R2 is selected from alkyl, fluoroalkyl, aryl, fluoroaryl, alkaryl, aralkyl, fluoroalkaryl, or fluoroaralkyl;
• R1 is selected from unsubstituted or fluoro-substituted alkylene, cycloalkylene, alkarylene, aralkylene, or arylene groups;
• Rf3 is selected from fluoroalkylene, fluoroarylene, fluoroaralkylene, fluoroalkarylene, fluoroalkoxyalkylene, or fluoropolyalkoxyalkylene moieties;
• M is a cation of valence n;
• and n is 1, 2, 3 or 4;
• with the proviso that when both of Y and Y′ are S(═A), X is N, A is O and n is less than 2 then only one Rf is fluoroalkyl, fluoroalkaryl, fluorocycloalkyl, fluoroalicoxyalkyl, or fluoropolyalicoxyalkyl in Formula I.