Preheat the oven to 350 degrees. Grease and flour two 8 or 9 inch loaf pans. Line the bottoms with parchment paper.Place the butter and 2 cups of sugar in a large bowl. Beat the mixture about 5 minutes or until light and fluffy. Beat the eggs into the butter mixture one at a time, then add the orange zest to the bowl and mix until incorporated.Sift the flour, baking powder, baking soda and salt together in a large bowl.In a medium bowl combine 1/4 cup orange juice, the buttermilk and vanilla. Add the flour and buttermilk mixtures alternately to the batter, beginning and ending with the flour mixture.Divide the batter evenly between the 2 prepared loaf pans. Smooth the tops and bake for 45 minutes to 1 hour or until toothpick inserted comes out clean.Orange Syrup:While the cake bakes, place 1/2 cup white sugar with the remaining 1/2 cup orange juice in a small saucepan. Cook over low heat until the sugar dissolves. When the cakes are done, let them cool 10 minutes on a wire rack. Remove the cakes from the pans onto a wire rack. Spoon the orange syrup over both loaves evenly. Allow the cakes to cool completely.Orange Glaze: Glazes one loafCombine the confectioners sugar and orange juice in a medium bowl, whisk until smooth. If necessary add a few drops of juice to make it a pouring consistency. Pour the glaze over one loaf and allow it to dry.