2016 YJC JC2 Block test
https://www.dropbox.com/s/68y2bmpevqboy3g/20160913_203034-1.jpg?dl=0
is this plausible?
gaseous SOCl2 bubbled into a soln containing molecules with
hydroxy group. the pH of resulting soln no doubt will be lower,
with or without any molecule ,as long as one bubble socl2 into any
soln
but is this reaction viable? does Vit A(in this qn) , gets its
hydroxy group substituted with a Cl?
if we want to cause nucleophillic sub of a halogen onto Vit A
containing the OH group, we would carry out in anhydrous condition
, with Vit A as a solid right?
no doubt only a very small percentage of Vit A , will dissolve
in water, as the molecule is majority Non-polar and hydrophobic
so perhaps it does undergoes nu sub for the halogen when Vit A
is put in water and SOCl2 in bubbled into this soln of water
containing Vit A , after substituting for halogen most likely still
Solid, as molecule is largely non polar
Both u and YJC teacher made an error here (urs way more coconaden
and unforgivable!).
U coconaden, anhydrous doesn't mean no solvent! The reactant is
solvated (not solid) and thus can exists in a solution, just not
with water (ie. not aqueous solution, a non-aqueous solution
lah)!
The solvent has to be inert (ie. no protic OH or NH groups), so
that it won't use up the PCl5 or SOCl2 reagent.
The YJC teacher's error : if it's an aprotic solvent which won't
react with PCl5 or SOCl2, then neither will [H+] in solution
increase, and hence there'll be no change in pH.
But for A level purposes, Cambridge may willingly commit the
same 'error' as ur YJC teacher (ie. they may set this same qn), coz
they don't expect A level H2 students to think deeply enough to
recognize this as an error.