[hzy]

Hi juz need some clarification on some Q

1) After SOCl2 reacts with water and a few drops of K2Cr2O7 is added. What is observed?

2) When dil HNO3 is added to an ester. Can Acid hydrolysis take place?

[shelanachium]

SOCl2 is the acid chloride of sulfurous acid, which exists in equilibrium with sulfur dioxide and water. Consequently SOCl2 reacts with water thus:

SOCl2 + 2H2O -> H2SO3 + 2HCl

H2SO3 <-> H2O + SO2

SO2 and H2SO3 are reducing agents, easily oxidised to sulfuric acid by the oxidising agent dichromate thus:

3 H2SO3 + [Cr2O7]2- + 8H+-> 2Cr3+ + 3 H2SO4 + 4 H2O

Therefore the orange dichromate solution changes to the green of Cr3+(aq).

Any dilute acid, especially a strong one like nitric acid, will catalyse ester hydrolysis, but nitric acid is not a good choice as it may oxidise the products - especially the alcohol; also some nitrite ester may be formed as one of the reduction products of HNO3 is nitrous acid HNO2, which in acid solution produces some NO+. This itself can react with alcohols to give nitrite esters:

HNO2 + H+ <-> NO+ + H2O

NO+ +ROH -> RONO + H+

[hzy]

oh is it possible for cl- ion (also a reducing agent) to react with Cr2O7 too?

[shelanachium]

Not usually.  In very strongly acid conditions Cr(VI) tends to yield a volatile compound, chromyl chloride CrO2Cl2, with chloride, rather than oxidising it. In less acid conditions there is no reaction. Chloride is rather a weak reducing agent, as the powerfully oxidising powers of its oxidation product Cl2 suggest!