Question

What are alcohols? State their sources.

Answer 1

Alcohols are the organic compounds with the general formula $\mathrm{R}-\mathrm{OH}$, where $\mathrm{R}$ is an alkyl group. They are the hydroxyl derivative of hydrocarbons where one or more $\mathrm{H}$-atoms are replaced by $-\mathrm{OH}$ group. They are classified on the basis of number of $-\mathrm{OH}$ group present. For example - ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$(ethanol/monohydric alcohol), ${\mathrm{HOCH}}_2-{\mathrm{CH}}_2\mathrm{OH}$ (Ethylene glycol/dihydric alcohol) and ${\mathrm{HOCH}}_2-\mathrm{CH}\left(\mathrm{OH}\right)-{\mathrm{CH}}_2\mathrm{OH}$ (Glycerol/trihydric).

Alcohols are obtained by synthesis. Following are the sources from which they can be obtained

1. Destructive distillation of wood
2. Fermentation of Sugar

$$\begin{gathered} \underset{\mathrm{Sugar}}{{\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\stackrel{\mathrm{Invertase}}{\to }\underset{\mathrm{Glucose}}{2{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\left(\mathrm{s}\right)} \\ \underset{\mathrm{Glucose}}{2{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\left(\mathrm{s}\right)}\stackrel{\mathrm{Zymase}}{\to }\underset{\mathrm{Ethanol}}{2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\left(\mathrm{l}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)} \end{gathered}$$

3. Hydrolysis of alkyl halides

$\underset{\mathrm{Bromomethane}}{{\mathrm{CH}}_3\mathrm{Br}}+\underset{\mathrm{Potassium}\mathrm{hydroxide}}{\mathrm{KOH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Methanol}}{{\mathrm{CH}}_3\mathrm{OH}\left(\mathrm{l}\right)}+\underset{\mathrm{Potassium}\mathrm{bromide}}{\mathrm{KBr}}$