Question

Chemists have found that chromium (VI) in a chromium trioxide dipyridine complex (CrO3-2Py) can be used to selectively oxidize a primary alcohol to an aldehyde without further oxidizing the aldehyde to an acid. An additional benefit is that double bonds are not oxidized either. 6. Write a balanced half reaction for the oxidation of cinnamyl alcohol, C6H5CH-CHCH2OH to cinnamaldehyde, C6H5CH=CHCHO Write a balanced half reaction for the reduction of chromium trioxide to chromium (III) Write the overall balanced reaction for the oxidation of cinnamyl alcohol to cinnamaldehyde with chromium trioxide a b. c.

Answer 1

a) Cinnamyl alcohol, C₆H₅CH=CHCH₂OH is oxidized to cinnamaldehyde, C₆H₅CH=CHCHO.

The oxidation states of the carbon atoms in cinnamyl alcohol and cinnamaldehyde are -1 and + 1 respectively.

Therefore, the oxidation half reaction is given as

C₆H₅CH=CHCH₂OH ---------> C₆H₅CH=CHCHO + 2 H⁺ + 2 e^-

b) CrO₃ is reduced to Cr (III).

CrO₃ + 6 H⁺ + 3 e^- --------> Cr³⁺ + 3 H₂O

c) The balanced redox equation is obtained by equating the number of electrons on both the sides.

3 C₆H₅CH=CHCH₂OH + 2 CrO₃ + 6 H⁺ --------> 3 C₆H₅CH=CHCHO + 2 Cr³⁺ + 6 H₂O