Oxidation of alcohols by strong oxidants in acid medium

Exercise 5

    

Butanone can be obtained from an alcohol $A$ oxidation by using potassium dichromate in acidified aqueous solution. 1) Give the semi-structural formula and the name of this alcohol $A$ 2) Establish the half-equations and the redox equation of the oxidation of $A$ 3) Assuming a yield of $100\;\%$, calculate what volume of alcohol $A$ with density $0.810$ is to be used to obtain a mass of $14.4\;g$ butanone. What amount of oxidant is needed?

1) $CH_3CH_2CHOHCH_3$ butan-2-one 2) $CH_3CH_2CHOHCH_3$ $-$ $2e^-$ $\rightarrow$ $CH_3CH_2COCH_3$ $+$ $2H^+$ $Cr_2O_7^{2-}$ $+$ $6e^-$ $+$ $14H^+$ $\rightarrow$ $2Cr^{3+}$ $+$ $7H_2O$ $3CH_3CH_2CHOHCH_3$ $+$ $Cr_2O_7^{2-}$ $+$ $8H^+$ $\rightarrow$ $3CH_3CH_2COCH_3$ $ +$ $2Cr^{3+}$ $+$ $7H_2O$ 3) $n_{butanone}$ $=$ $\frac{14.4}{72.0}=0.200$ $n_{butanol}$ $=$ $0.200$ $m_{butanol}$ $=$ $0.200\cdot 74.0$ $=$ $14.8\; g$ $V_{butanol}$ $=$ $\frac{14.8}{0.810}$ $=$ $18.3 \; mL$ One mole dichromate needs 3 moles butanol: $n_{dichromate}$ $=$ $\frac{0.200}{3}$ $=$ $0.0666$