Question

How do aldehydes and ketones react with alcohol.

Answer 1

Addition of alcohol on aldehyde: In the presence of dry HCl, aldehyde and monohydric alcohol react to produce hemiacetal, an alkoxy alcohol. Acetal, a geminaldialkoxy molecule, is then produced by the additional reaction between hemiacetal and monohydric alcohol.

\[\begin{array}{cc}
\phantom{.................}\ce{H}\\
\phantom{.................}|\\
\ce{R - C = O + \underset{(Alcohol)}{R' - OH}<=>[dry HCl][dil. HCI] R - C - OR' + R - OH}\\
\phantom{}|\phantom{.............................}|\phantom{.............}\\
\ce{\underset{(Aldehyde)}{H}\phantom{......................}\underset{(Hemiacetal)}{OH}}\phantom{............}
\end{array}\]

\[\begin{array}{cc}
\phantom{}\ce{H\phantom{.............................}H}\phantom{.........}\\
\phantom{..}|\phantom{..............................}|\phantom{...........}\\
\ce{R - C - OR' +  \underset{(Alcohol)}{R' - OH}<=>[dry HCl][dil. HCI] R - C - OR' + H2O}\\
\phantom{....}|\phantom{...............................}|\phantom{.............}\\
\ce{\underset{(Hemiacetal)}{OH}\phantom{.........................}\underset{(Acetal)}{OR'}}\phantom{.........}
\end{array}\]

Addition of alcohol on ketone: Ketones react with 1, 2 or 1, 3 dials in presence of d ry HCl to give five or six membered cyclic ketals.