[keepinawut]

Pyrrolidine (2 mole) is slowly added to 164 ml conc. HCl  in 400 g ice water to adjust the pH to 3-4. When it is mixed, the pH is 14, how do I lower the pH to 3-4? I cannot add more HCl  because it only calls for 164 ml.

[TheUnassuming]

Without knowing more, you would slowly add the base to your acid while monitoring the pH and stop at ~3-4 (which in the authors case was 2mol).  Since you added too much, add some HCl to the solution to get back to the desired pH. 

What are you trying to do?

[keepinawut]

Thank you for your reply , to answer your question, peptide coupling. Yes I understand you what you say makes since.
but the literature I am reading calls for Pyrrolidine (2 mole) is slowly added to 164 ml conc. HCl  in 400 g ice water and the pH was adjusted to 3-4.
The literature has no more details than this. So do you think maybe the author adjusted the pH with more HCL? Sorry for my English but it is not my native tongue. 

[keepinawut]

Because it seems to me the author is slowly adding 2 moles of Pyrrolidine  to 164 ml conc. HCl  in 400 g ice water and then adjusting the pH to 3-4.

[Borek]

When it is mixed, the pH is 14

No way. Pyrrolidine is not a base strong enough to produce that high pH.

Besides, I have problems reproducing the pH claimed. What you produce is a buffer (2 moles of pyrrolidine with about 1.9 moles of HCl, assuming "concentrated" to mean 36%). Wikipedia lists pKa of pyrrolidine as 11.3, so the pH should be around 10. make it ±1 because of the very high ionic strength of the solution - still no way of getting even close to 14, but also no way of getting close to 3-4. For that you will need more acid.

[Borek]

and then adjusting the pH to 3-4.

So perhaps they use more acid, they just start with 164 mL?