What is the Hell, Bohard, Zelensky (HVZ) reaction primarily used for?

How does phosphorus tribromide function as a catalyst in the HVZ reaction?

What type of reaction mechanism is involved when bromine displaces the alpha hydrogen in the HVZ reaction?

What is the key feature of ammonia's attack on the alpha carbon in the HVZ reaction?

What is a potential limitation of the HVZ reaction in the synthesis of amino acids?