Method for preparation of hydrophobic precipitated silica

A method for the preparation of hydrophobic precipitated silica comprising contacting an aqueous suspension of a hydrophilic precipitated silica with (1) a catalytic amount of an acid and (2) an organosilicon compound selected from the group consisting of organosilanes described by formula

• R1aHbSiX4-a-b,
• organosiloxanes described by formula
• R2nSiO(4-n)/2,
• and organodisilazanes described by formula
• (R33Si)2NH,
• in the presence of (3) a water-miscible organic solvent in an amount sufficient to facilitate reaction of the hydrophilic precipitated silica with the organosilicon compound to form a hydrophobic precipitated silica;
• where each R1 is an independently selected hydrocarbon radical comprising 1 to about 12 carbon atoms, each R2 is independently selected from the group consisting of hydrogen, chlorine, hydroxy, and hydrocarbon radicals comprising 1 to about 12 carbon atoms with the proviso that at least 50 mole percent of the R2 substituents are hydrocarbon radicals, each R3 is an independently selected hydrocarbon radical comprising 1 to about 12 carbon atoms, each X is an independently selected hydrolyzable group bonded to silicon, a=1, 2, or 3;
• b=0 or 1;
• a+b=1, 2, or 3 with the proviso that when b=1 then a+b=2 or 3;
• and n is an integer from 2 to 3 inclusive.