Question

Show how to synthesize 5-nonanone from 1-bromobutane as the only organic starting material.

Short answer

Question: Synthesize 5-nonanone from 1-bromobutane as the only organic starting material by describing the necessary steps. Answer: To synthesize 5-nonanone from 1-bromobutane, follow these steps: 1. Form a Grignard reagent (butylmagnesium bromide) by treating 1-bromobutane with magnesium metal in anhydrous diethyl ether. 2. React the Grignard reagent with carbon dioxide (CO2) to form a carboxylate salt. 3. Convert the carboxylate salt into a carboxylic acid (pentanoic acid) by treating it with aqueous hydrochloric acid (HCl). 4. Perform Claisen condensation by making an ester (pentyl methanoate) from pentanoic acid and methanol, then treating it with ethoxide ion to form a β-keto ester. 5. Hydrolyze and decarboxylate the β-keto ester using an aqueous solution containing an acid catalyst under reflux to obtain the desired ketone, 5-nonanone.

Step-by-step solution

Form a Grignard reagent from 1-bromobutane

Firstly, treat 1-bromobutane with magnesium metal in anhydrous diethyl ether. This reaction will form a Grignard reagent, butylmagnesium bromide (BuMgBr). The reaction proceeds as follows: R-Br + Mg → R-MgBr In our case: CH3CH2CH2CH2-Br + Mg → CH3CH2CH2CH2-MgBr

Perform a Grignard reaction with carbon dioxide

Next, react the butylmagnesium bromide with carbon dioxide (CO2). This reaction will form a magnesium alkoxide, specifically a carboxylate salt, by creating a carbon-carbon bond. The reaction proceeds as follows: R-MgBr + CO2 → R-COO-MgBr In our case: CH3CH2CH2CH2-MgBr + CO2 → CH3CH2CH2CH2COO-MgBr

Convert the carboxylate salt into a carboxylic acid

Treat the carboxylate salt (CH3CH2CH2CH2COO-MgBr) with aqueous hydrochloric acid (HCl) to protonate the alkoxide and convert it into a carboxylic acid. The reaction proceeds as follows: R-COO-MgBr + HCl → R-COOH + MgBrCl In our case: CH3CH2CH2CH2COO-MgBr + HCl → CH3CH2CH2CH2COOH + MgBrCl This gives us pentanoic acid (CH3CH2CH2CH2COOH).

Perform Claisen condensation

Make an ester by reacting pentanoic acid with an alcohol (e.g., methanol) and an acid catalyst (e.g., H2SO4) under reflux. In our case, we use methanol (CH3OH) as the alcohol, and the ester formed will be pentyl methanoate (CH3CH2CH2CH2COOCH3). Now, perform a Claisen condensation by treating pentyl methanoate with ethoxide ion (CH3CH2O-) to form a β-keto ester. The reaction proceeds as follows: 2 RCOOR' + CH3CH2O- → RCO-CH2-COOR + R'OH + CH3CH2OH In our case: 2 CH3CH2CH2CH2COOCH3 + CH3CH2O- → CH3CH2CH2CH2CO-CH2-COOCH3 + CH3OH + CH3CH2OH

Convert the β-keto ester into a ketone

Finally, hydrolyze and decarboxylate the β-keto ester (CH3CH2CH2CH2CO-CH2-COOCH3) using an aqueous solution containing an acid catalyst (e.g., H2SO4) under reflux. This reaction will convert the β-keto ester into the desired ketone, 5-nonanone. The hydrolysis and decarboxylation proceed as follows: RCO-CH2-COOR → RCO-CH2-COOH (hydrolysis) RCO-CH2-COOH → R-CO-CH3 + CO2 (decarboxylation) In our case: CH3CH2CH2CH2CO-CH2-COOCH3 → CH3CH2CH2CH2CO-CH2-COOH (hydrolysis) CH3CH2CH2CH2CO-CH2-COOH → CH3CH2CH2CH2CO-CH3 + CO2 (decarboxylation) The final product is 5-nonanone (CH3CH2CH2CH2CO-CH3).