Which of the following reaction(s) do(es) NOT occur (i) [NPCl2]3 + 6 NaF \(\rm \xrightarrow[reflux]{MeCN}\) [NPF2]3 + 6 NaCl (ii) n PCl5 + n NH4Cl \(\rm \xrightarrow[reflux]{C_6H_5Cl}\) [NPCl2]n + 4 n HCl [n = 3, 4, 5] (iii) n PF 5 + n NH 4 F \(\rm \xrightarrow[reflux]{C_6H_5Cl}\) [NPF 2 ] n + 4 n HF [n = 3, 4, 5]
(iii) only
Phosphazene Reaction Analysis
Let's analyze each reaction provided to determine which one(s) do not typically occur under the given conditions. These reactions involve the chemistry of phosphazenes, which are inorganic polymers containing phosphorus and nitrogen atoms in the backbone.
Reaction (i): Halogen Exchange in Phosphazenes
The first reaction is:
[NPCl2]3 + 6 NaF ⎳ ⎳MeCN [NPF2]3 + 6 NaCl
This reaction represents the substitution of chlorine atoms by fluorine atoms in hexachlorocyclotriphosphazene ([NPCl2]3) using sodium fluoride (NaF). This type of halogen exchange reaction is a well-established method for synthesizing fluorophosphazenes from chlorophosphazenes. The reaction typically proceeds in polar solvents like acetonitrile (MeCN) under reflux conditions. Therefore, reaction (i) is expected to occur.
Reaction (ii): Synthesis of Chlorophosphazenes
The second reaction is:
n PCl5 + n NH4Cl ⎳ ⎳C6H5Cl [NPCl2]n + 4 n HCl [n = 3, 4, 5]
This is a classic method for the synthesis of chlorocyclophosphazenes, particularly the cyclic trimer ([NPCl2]3) and tetramer ([NPCl2]4), and to some extent, higher cyclic and linear oligomers. The reaction involves the condensation of phosphorus pentachloride (PCl5) and ammonium chloride (NH4Cl) in an inert solvent like chlorobenzene (C6H5Cl) under reflux conditions. This reaction is widely used in phosphazene chemistry. Therefore, reaction (ii) is expected to occur.
Reaction (iii): Synthesis of Fluorophosphazenes
The third reaction is:
n PF5 + n NH4F ⎳ ⎳C6H5Cl [NPF2]n + 4 n HF [n = 3, 4, 5]
This reaction proposes the synthesis of fluorophosphazenes directly from phosphorus pentafluoride (PF5) and ammonium fluoride (NH4F). While phosphorus-nitrogen compounds can be formed from phosphorus fluorides, the direct synthesis of stable cyclic or linear fluorophosphazenes of the form [NPF2]n from PF5 and NH4F is generally not a feasible or common synthetic route under these conditions. PF5 is a strong Lewis acid and reacts readily with various species, but its reaction with NH4F is unlikely to produce the stable N=P double bond framework of phosphazenes efficiently or in good yield under reflux conditions in chlorobenzene. Fluorophosphazenes are typically synthesized by the halogen exchange method from chlorophosphazenes (as shown in reaction i) or other specialized techniques, not by this direct condensation. Therefore, reaction (iii) is the one that is least likely to occur among the given options.
Summary of Reactions
- Reaction (i): Occurs (Halogen exchange).
- Reaction (ii): Occurs (Standard synthesis of chlorophosphazenes).
- Reaction (iii): Does NOT occur (Direct synthesis from PF5 and NH4F is not a viable method).
Based on the analysis, only reaction (iii) does NOT occur.
Important Questions from p - Block
- The correct statement for alkali metal is:
Consider the following pairs of compounds.
(i) NH4Cl and FeO
(ii) H3N∙BF3 and BCl3
(iii) HSO3F and HF
The more acidic species in (i), (ii) and (iii) are, respectively
Which of the following has the lowest boiling point?
Choose the equilibria from the following that are NOT favoured to go to right:
(A) As2S5 + 5HgO ⇌ As2O5 + 5 HgS
(B) La2(CO3)3 + Bi2S3 ⇌ La2S3 + Bi2(CO3)3
(C) CdSO4 + CaS ⇌ CdS + CaSO4
(D) BeF2 + HgI2 ⇌ BeI2 + HgF2
The reaction of XeF6 with a limited amount of quartz gives compound A. Then on reaction with an equivalent amount of XeO3, A gives B. The products A and B are, respectively
