NON-DUTCHED COCOA

The big chemistry difference is that regular cocoa is acidic and dutched is not. If your recipe calls for baking soda, it's not going to work well with the dutched cocoa. If there is baking soda in the recipe you can use baking powder instead - use 3 to 4 times as much baking powder as soda. You could also add cream of tartar at 5/8 teaspoon per 1/4 teaspoon of baking soda called for.

In a brownie recipe, I don't think the dutched cocoa will make that much of an impact in final product. The flavor will be different (you won't have that nice bitterness of the natural cocoa) and there might not be any leavening. You'll probably get a fudgier brownie. Which isn't necessarily a bad thing.