What is the indication that the conversion of alcohol to halide is taking place?

Question

What is the indication that the conversion of alcohol to halide is taking place? Why does this occur? Once the reaction is completed, sodium bicarbonate is added to the reaction mixture. Why is bicarbonate added to the reaction mixture? Why is anhydrous calcium chloride added to the crude t-butyl chloride? What would be the theoretical yield in this reaction if 12.5 g of t-butyl alcohol were reacted with 12.5 g of hydrochloric acid? If 10.2 g of pure halide is produced in the reaction, what is the percent yield?

Explanation / Answer

Alcohols has -OH group, hence is a poor leaving group. As a result of this direct substituion of the -OH by halide is impossible..that is why we use protonation...when the alcohol is protonated ....O+H2 is formed ..whic potentially is a good leaving group...

Luca's reagent is used as the test to distinguish alcohols....inpresence of ZnCl2

ROH + HCl -----> RCl + H2O

ROH + H+ ----> RO+H2

RO+H2 + Cl- -----> RCl + H2O

for primary alcohols

genarally no visible reaction at room temperature and forming an oily layer.

for secondary alcohols

solution forms oily layer in 3–5 minutes

for tertiary alcohols

solution forms oily layer immediately.

6) the HCl is traken in excess ...and to neutralise the excess acid we add sodium bicarbonate.

7) (you have already answered it) ... but i will add H2O formed has to be removed ... either by distillation or by usinig anhydrous CaCl2 .

8) 1 mole of alcohol should give ....1 mole of alkyl halide

hence when

12.5 gram of alcohol is used ....hence moles of alcohol used = 12.5 / 74

= 0.169 mol

hence same moles of alkyl halide must be formed ...(as the moles of acid used is high..leaving alcohol to be the limiting reagent)

hence amount of alkyl chloride formed = 92.5 X 0.169

= 15.62 g

henc etheoretical yield = 15.62 g

% yield = (practical yield /theoretical yield ) X 100

=(10.2 /15.62) X 100

= 65.3 %

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