Preheat oven grease and flour a 10 inch Bundt pan. In a large measuring cup dissolve baking soda in water, then add coffee, 1/2 cup of the coffee liqueur, and vanilla.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the cocoa, then the egg yolks one at a time. Alternately beat in the flour and the coffee mixture just until incorporated.
In a large glass or metal mixing bowl, beat egg whites until stiff peaks form. Fold 1/3 of the whites into the batter, then quickly but carefully fold in remaining whites until no streaks remain.
Pour batter into a 10 inch Bundt pan. Bake until a toothpick inserted into the center of the cake comes out clean. Let cool for 10 minutes in the pan, then turn out onto a wire rack. Pierce warm cake all over with a fork and drizzle glaze a spoonful at a time over cake until it is absorbed. Wrap cake tightly with plastic wrap to preserve moisture.

To make the glaze: In a small bowl combine confectioner’s sugar and remaining 1/2 cup of coffee liqueur.