I was reading Jan's answer to the following question-:
Why can NCl3 be hydrolyzed but CCl4 cannot?.
Since nitrogen is less electronegative than fluorine in $\ce{NF3}$, the electrophilic site is the Nitrogen atom. That means the water molecule should attack nitrogen atom in an $\mathrm{S_N2}$ manner. The stearic crowding around the atom is also less. Then why is the reaction not taking place? Is it only because fluoride ion is a poor leaving group due to its high basic strength?
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3$\begingroup$ I would assume that thermodynamic factors need consideration here too, NF3 is relatively stable and has a negative enthalpy of formation. $\endgroup$– AS_1000Aug 22, 2017 at 11:00
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2$\begingroup$ Bonds of other second period elements to fluorine are relatively strong. So in addition to the other factors already mentioned, there is an inherent high activation energy. Fluoroalkanes are not good substrates for nucleophilic substitution either, same reason. $\endgroup$– Oscar LanziAug 22, 2017 at 12:51
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$\begingroup$ Can anyone summarise everything into an answer with data and examples if possible? $\endgroup$– Kartikeya BadolaAug 22, 2017 at 14:30
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$\begingroup$ @KartikeyaBadola They aren't related. $\endgroup$– MithoronAug 22, 2017 at 15:31
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1 Answer
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Nitrogen trifluoride is extremely inert to hydrolysis, attack by base or acids or oxidation because of the fact that there is no d-orbitals in Nitrogen trifluoride and fluorine is far more electronegative than nitrogen. However, in the presence of base or acids, nitrogen trifluoride can however undergo hydrolysis because there is now excess of nucleophile which can attack nitrogen trifluoride.
There is a old paper which discuss the hydrolysis of nitrogen trifluoride in presence of acids and base.
In the presence of aqueous base, however, slow hydrolysis occurs at 100°C yielding nitrite and fluoride.
$$\ce{NF3 + 4 OH- ->[100℃] NO2- + 3F- + 2H2O}$$
It further says:
This behavior differs sharply from that of nitrogen trichloride, which is known to give ammonia and hypochlorite under similar con- ditions. The latter products are readily explained in terms of nucleophilic attack directed at the chlorine atoms, a mechanism which appears reasonable in view of the fact that the electronegativities of $\ce{N}$ and $\ce{Cl}$ are very nearly the same and that the halogen may easily expand its valence shell. Obviously, these considerations cannot be applied to the nitrogen trifluoride molecule since fluorine is considerably more electronegative than nitrogen and it has no available d orbitals. Although the nitrogen atom also has no free orbitals, the relatively low electron density would at least offer less resistance to the approach of a nucleophile .
The proposed intermediate $\ce{HONF2}$ would be expected to be unstable with respect to the loss of $\ce{HF}$, as is apparently the case with the unknown perfluoro alcohols .
Two other reaction modes worth considering include the formation of an intermediate activated complex with water.
answered Aug 24, 2017 at 13:39
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2$\begingroup$ @Mithoron At least that paper tells us that $\ce{NF3}$ hydrolyses at $\pu{100 ^\circ C}$ in highly basic conditions. In reverse, that means hydrolysis is probably kinetically inhibited at room temperate. And it also states that it does indeed follow the expected $\mathrm{S_N2}$ mechanism with nucleophilic attack on nitrogen followed by displacement of the fluoride. (I reserve the right to be skeptical about the $\ce{HF}$ dissociation but it’s not entirely unlikely.) $\endgroup$– JanAug 24, 2017 at 15:39
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10$\begingroup$ @Mithoron Why? Did chemistry changed from the 40s ? $\endgroup$ Aug 24, 2017 at 17:19
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5$\begingroup$ @permeakra Any explanation with "having d-orbitals" is outdated. $\endgroup$– MithoronOct 7, 2017 at 23:53
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$\begingroup$ My book says NF3 undergoes hydrolysis through Sn1 mechanism under drastic conditions $\endgroup$ Mar 15 at 2:15