Question

Write chemical equations of the reactions of formation of $n$-hexane, pentaacetyl glucose, glucose cyanohydrin and gluconic acid from glucose.

Hint:

From glucose, remember: (a) strong \(\mathrm{HI/Red\ P}\) reduces to hydrocarbon; (b) \(\mathrm{Ac_2O}/\)pyridine protects all OH groups \(\Rightarrow\) pentaacetate; (c) \(\mathrm{HCN}\) adds to the aldehyde carbonyl \(\Rightarrow\) cyanohydrin; (d) mild oxidation with \(\mathrm{Br_2/H_2O}\) converts the \(-\mathrm{CHO}\) to \(-\mathrm{COOH}\) \(\Rightarrow\) gluconic acid.

Answer 1

(i) $n$-Hexane from glucose
\[ \mathrm{C_6H_{12}O_6} \xrightarrow[\text{Red P}]{\mathrm{HI},\,\Delta} \mathrm{n\!-\!C_6H_{14}} \] (Often shown via sorbitol: \(\mathrm{C_6H_{12}O_6 + H_2 \xrightarrow{Ni} C_6H_{14}O_6 \xrightarrow[\text{Red P}]{12\,HI,\ \Delta} n\!-\!C_6H_{14} + 6H_2O + 12I_2}\)).
(ii) Pentaacetyl glucose
\[ \mathrm{Glucose} \xrightarrow[\text{pyridine}]{\left(\mathrm{CH_3CO}\right)_2\mathrm{O}} \mathrm{Glucose\ penta\mbox{-}acetate} + 5\,\mathrm{CH_3COOH} \] (iii) Glucose cyanohydrin
\[ \mathrm{Glucose\ (open\!-\!chain)} \xrightarrow[\text{trace KCN}]{\mathrm{HCN}} \mathrm{Glucose\ cyanohydrin} \] (iv) Gluconic acid
\[ \mathrm{Glucose} \xrightarrow{\mathrm{Br_2/ H_2O}} \mathrm{Gluconic\ acid} \]