Question 14.9: Design the synthesis of ethyl propanoate from organic alcoho...
Design the synthesis of ethyl propanoate from organic alcohols.
The ease with which alcohols are oxidized to aldehydes, ketones, or carboxylic acids (depending on the alcohol that you start with and the conditions that you employ), coupled with the ready availability of alcohols, provides the pathway necessary to many successful synthetic transformations. For example, let’s develop a method for synthesizing ethyl propanoate, using any inorganic reagent you wish but limiting yourself to organic alcohols that contain three or fewer carbon atoms:
\underset{\begin{matrix} Ethyl \; propanoate \\ (ethyl \; propionate) \end{matrix} }{\begin{array}{r c}\underset{||}{O} \qquad \qquad \qquad \quad \; \\ CH_3CH_2C-O-CH_2CH_3 \end{array}}Ethyl propanoate can be made from propanoic acid and ethanol:
\begin{matrix} \begin{array}{r c}\underset{||}{O} \qquad \; \; \; \\ CH_3CH_2C-OH \\ \\ \end{array} & + & CH_3CH_2OH & \xrightleftharpoons[]{H^+ \; , heat} & \begin{array}{r c}\underset{||}{O} \quad \qquad \qquad \qquad \; \\ CH_3CH_2C-O-CH_2CH_3 \\ \\ \end{array} & + & H_2O \\ \begin{array}{l} Propanoic \; acid \\ (propionic \; acid) \end{array} & & \begin{array}{l} Ethanol \\ (ethyl \; alcohol) \end{array} & & \begin{array}{l} Ethyl \; propanoate \\ (ethyl \; propionate) \end{array} \end{matrix}Ethanol is a two-carbon alcohol that is an allowed starting material, but propanoic acid is not. Can we now make propanoic acid from an alcohol of three or fewer carbons? Yes!
\begin{matrix} CH_3CH_2CH_2OH & \xrightarrow[]{[O]} & \begin{array}{r c}\underset{||}{O} \qquad \\ CH_3CH_2C—H \\ \\ \\ \end{array} & \xrightarrow[]{[O]} & \begin{array}{r c}\underset{||}{O} \qquad \; \; \> \\ CH_3CH_2C—OH \\ \\ \\ \end{array} \\ \begin{array}{l} Propanol \\ (propyl \; alcohol) \end{array} & & \begin{array}{l} Propanal \\ (propionaldehyde) \end{array} & & \begin{array}{l} Propanoic \; acid \\ (propionic \; acid) \end{array} \end{matrix}Propanol is a three-carbon alcohol, an allowed starting material. The synthesis is now complete. By beginning with ethanol and propanol, ethyl propanoate can be synthesized easily.