What is the optimum range of pH for the formation of Schiff Bases by the addition of hydroxylamine to an aldehyde or a ketone?
According to Peter Sykes' A Guidebook to Mechanisms in Organic Chemistry,
"The initial addition step or the dehydration step can be made rate limiting at will, depending on the pH of the solution. At neutral and alkaline pHs it is generally dehydration, that is the slow and rate limiting step while at acidic pHs it is the initial addition which is slow and rate limiting. This clearly has significance in preparatory terms, and formation of such derivatives of carbonyl compounds tends to exhibit pH optima."
My doubts are :
How does the pH change the rate limiting step? That is, why is dehydration the rate limiting step at neutral and alkaline pHs and why is addition the rate limiting step at acidic pHs?
What is the significance in preparative terms that Sykes is taking about?
How will this significance determine the pH and what is that pH (or the range of pHs)?