# Why can NCl3 be hydrolyzed but CCl4 cannot?

While explaining why $\ce{CCl4}$ cannot be hydrolyzed, we say carbon atom doesn't have any d-orbitals and therefore a water molecule (lone pair electrons of $\ce{O}$ atom) cannot form coordinate bond with carbon. So, $\ce{CCl4}$ cannot be hydrolyzed. In $\ce{NCl3}$, nitrogen also does not have any d-orbital.

Why it can be hydrolyzed?

Is hydrolysis mechanism for $\ce{CCl4}$ and $\ce{NCl3}$ different? If so how they are different?

Again, in some sources I have found, in the case of $\ce{NCl3}$ water forms coordinate bonds with the $\ce{Cl}$ atom and hence the molecule gets hydrolyzed. Why does the same thing thing not happen in $\ce{CCl4}$ which also has a $\ce{Cl}$ atom?

• Related question: chemistry.stackexchange.com/questions/37073/… – Ivan Neretin Oct 2 '15 at 6:26
• $\ce{CCl4}$ can be hydrolysed. Also, welcome to chemistry.stackexchange.com. Feel free to take a tour of the site and visit the help center if questions about using it arise. Also note that you can improve your posts with MathJax; see this meta page for more information. I'll do it to this post of your's right away. – Jan Oct 2 '15 at 7:10

There are a few (mis-) conceptions in the question that require addressing other than giving the simple (yet correct) answer that permeakra gave.

# $\ce{NCl3}$

The hydrolysis of this compound is different from the hydrolysis of the other two. This is because the $\ce{N-Cl}$ bonds are polarised towards nitrogen, not towards chlorine as they would be for $\ce{SiCl4}$ and $\ce{CCl4}$. Since the oxygen in water usually attacks nucleophilicly, the attack happens on the chlorine; it can proceed nicely with an $\mathrm{S_N2}$ mechanism (the rear side of all three chlorines are pointing into the solution). Note that another water molecule or the same will likely protonate the nitrogen either before or concertedly, so the leaving group won’t be $\ce{NCl2-}$ but rather $\ce{NHCl2}$. The other reaction product is $\ce{HOCl}$.

Other concerted mechanisms including only one water molecule might be possible, but sound less likely.

# $\ce{SiCl4}$

Silicon atoms are rather large compared to both carbon and nitrogen: They have an additional electron shell. (Layman’s simplification, but it works.) As such, even in crowded cases like tri-iso-propylsilyl chloride $\ce{((CH3)2CH)3-SiCl}$ with three bulky iso-propyl groups, the silicon atom can be rear-side attacked by water (or catalysts such as 4-(N,N-dimethylamino)pyridine) liberating a chloride atom in a traditional $\mathrm{S_N2}$ mechanism.

No d-orbital contribution is required to explain it. In fact, silicon does not have ‘low-lying’ or ‘accessable’ d-orbitals; that is an old, superceded explanation.

The hydrolysis products of $\ce{SiCl4}$ are $\ce{Si(OH)4}$ (which will likely condensate to some polysilicate or $\ce{SiO2}$) and $\ce{HCl}$.

# $\ce{CCl4}$

Technically, this could also proceed via an $\mathrm{S_N2}$ mechanism. However, carbon is much smaller and the chlorine atoms much larger in relation, so the rear-side attack is disfavoured sterically.

Instead, this molecule has access to the $\mathrm{S_N1}$ pathway, which can be described as follows:

$$\ce{CCl4 -> CCl3+ + Cl-} \\ \ce{CCl3+ + H2O -> Cl3C-OH2+} \\ \ce{Cl3C-OH2+ + Cl- -> CCl3-OH + HCl}$$

And so on, displacing the remaining chlorine atoms, ultimately liberating $\ce{H2CO3}$. (After the second chlorine displacement, phosgene will form which can be attacked directly by water with the $\ce{C=O}$ bond acting as an electrophile.)

Note that here again we gain $\ce{HCl}$, an indirect proof of chlorine being the more electronegative element.

# Conclusion

The three molecules we considered are so different in their steric and electronic properties, that we need to consider three different mechanisms that lead us to two different sets of products (depending on which side gains the hydrogens and which formally gains hydroxides). Nowhere do we need d-orbitals.

• Nice. I didn't have time to write a proper answer, thank you for the job well done. – permeakra Oct 2 '15 at 12:15
• Great response, thanks for putting the effort in on this one – Aaron Oct 2 '15 at 17:28

$\ce{CCl4}$ can be hydrolysed under pressure at elevated temperature. Seems the reaction proceeds via $S_N1$ mechanism. See the source.

• I stand corrected – Aaron Oct 2 '15 at 8:20