[dane502]

Hi guys!

This is my first post here, so I hope I am doing this right..

We have recently done an experiment called "Reaction between Tert-Butyl chloride and water" as part of our "Reactions kinetics"-course. In the experiment we dissolved 99 mL of water into a 0,1 M solution of Tert-Butyl chloride (the solvent was acetone). We then meassured the electrical conductivity every 15th second in 3 min. I have done all calculations, gotten good results and basically made a good report 

However, I don't feel that I have understood the underlying ideas of the expirement. For instance why is Tert-Butyl chloride dissolved in acetone? - I've read the Chloride isn't soluble in acetone, that water and acetone are miscible and that Tert-Butyl chloride isn't very soluble in water.

So my question are:
1)
If Tert-Butyl chloride isn't very soluble in water, how come the chloride is carried away, when dissolved in water?

2)
If chloride isn't soluble in acetone, it must be dissolved in the water. If so, the reaction must look like so:
Cl^- + H₂O --> HCl (aq) + OH^-. But then the hydroxide ion is conductive as well. So then how should I calculate from conductivity to concentration of HCl?

3)
How can I be sure that the reaction only is one way:
C₄H₉Cl + H₂O --> C₄H₉OH + HCl and not
C₄H₉Cl + H₂O <-- C₄H₉OH + HCl ?


Thank you so much for helping me!
dane502

[Yggdrasil]

1)
If Tert-Butyl chloride isn't very soluble in water, how come the chloride is carried away, when dissolved in water?

tert-butyl chloride is a covalent compound with the structure shown here.  The chlorine is covalently bonded to the carbon atom, so it cannot dissociate from the rest of the molecule unless a chemical reaction occurs.  This is in contrast to an ionic compound such as NaCl.  In NaCl, the Na and Cl molecules are held together by ionic bonds which can easily be broken up by water molecules.  This leads to NaCl dissolving in water.  It is considerably harder for water to break apart covalent bonds.

2)
If chloride isn't soluble in acetone, it must be dissolved in the water. If so, the reaction must look like so:
Cl^- + H₂O --> HCl (aq) + OH^-. But then the hydroxide ion is conductive as well. So then how should I calculate from conductivity to concentration of HCl?

HCl is a strong acid, meaning that it will always be deprotonated in aqueous solution.  So, the reaction will always go toward production of Cl^-.  The reaction that you're observing in this experiment is a substitution reaction where the OH from water replaces the chlorine:

tBu-Cl + H₂O --> tBu-OH + H⁺ + Cl^-

where tBu represents the tert-Butyl group.  This reaction shows how the chloride gets carried away.  The chloride enters solution not because tBuCl dissolves, but because tBuCl reacts with water.

3)
How can I be sure that the reaction only is one way:
C₄H₉Cl + H₂O --> C₄H₉OH + HCl and not
C₄H₉Cl + H₂O <-- C₄H₉OH + HCl ?

The reaction can go both ways.  Typically in kinetics experiments, however, we measure the initial rate of reaction when very few products are present.  We do this because when few product molecules are present, then the rate of the backward reaction is negligible compared to the rate of the forward reaction.


I hope these help clear some of these issues up for you.

[dane502]

I hope these help clear some of these issues up for you.

It certainly did! Looks like I got some ideas wrong 

Thank you so much
dane502

[dane502]

Hi everybody!

I was just thinking: The reaction between Tert-Butyl chloride and water, can be split into:

1) C₄H₉Cl --> C₄H₉⁺ + Cl^-

2) C₄H₉⁺ + H₂O --> C₄H₉OH₂⁺

3) C₄H₉H₂O⁺ --> C₄H₉OH + H⁺

Which overall gives:

4) C₄H₉Cl + H₂O --> C₄H₉OH + HCl

Which one of these reaction, am I actually calculating the rate of, when calculating from conductivity to concentration of HCl, and then looking at changes in HCl contration pr. time?

[Kryolith]

The rate-determining step is 1)