Beat egg in a large mixing bowl until foamy. Gradually add 1 1/2 cups sugar and butter, beating constantly.
Dissolve soda in buttermilk; add to creamed mixture, beating well. Stir in flour and coconut. Cover and chill dough at least 1 hour.
Shape dough into 1-inch balls; roll in additional sugar. Place 2 inches apart on greased cookie sheets. Bake at 350° for 10 to 12 minutes. Remove from cookie sheets, and cool on wire racks.