Question

Show how to prepare pentanoic acid from each compound. (a) 1-Pentanol (b) Pentanal (c) 1-Pentene (d) 1-Butanol (e) 1-Bromopropane (f) 1-Hexene

Short answer

Answer: (a) Oxidize 1-Pentanol using PCC to form Pentanal, which is then oxidized with KMnO4 to form Pentanoic acid. (b) Oxidize Pentanal with KMnO4 to form Pentanoic acid. (c) Perform an oxidative cleavage of 1-Pentene using O3 and (CH3)2S to directly form Pentanoic acid. (d) Convert 1-Butanol to 1-Bromobutane with PBr3, react it with Mg to form a Grignard reagent, and then react it with CO2 to form the pentanoate ester. Hydrolyze the ester to obtain Pentanoic acid. (e) Convert 1-Bromopropane to a Grignard reagent with Mg and then react with ethyl formate to form a pentanoate ester. Hydrolyze the ester to form Pentanoic acid. (f) Perform an oxidative cleavage of 1-Hexene using O3 and (CH3)2S to form Hexanoic acid, which is then subjected to decarboxylation with soda lime to obtain Pentanoic acid.

Step-by-step solution

(a) Conversion of 1-Pentanol to Pentanoic Acid

: 1-Pentanol is an alcohol with the chemical formula CH3(CH2)4OH. To convert it to pentanoic acid (CH3(CH2)4COOH), we need to oxidize it using the following reactions: Step 1: Oxidation to form Pentanal React 1-Pentanol with an oxidizing agent such as PCC (Pyridinium Chlorochromate) in dichloromethane: CH3(CH2)4OH --(PCC)--> CH3(CH2)3CHO Step 2: Oxidation to form Pentanoic Acid React Pentanal with an oxidizing agent such as KMnO4 in a basic aqueous solution or CrO3 in an acidic solution: CH3(CH2)3CHO --(KMnO4)--> CH3(CH2)4COOH

(b) Conversion of Pentanal to Pentanoic Acid

: Pentanal is an aldehyde with the formula CH3(CH2)3CHO. Converting it to pentanoic acid (CH3(CH2)4COOH) requires the oxidation of the aldehyde group to the carboxylic acid group. Step 1: Oxidation to form Pentanoic Acid React Pentanal with an oxidizing agent such as KMnO4 in a basic aqueous solution or CrO3 in an acidic solution: CH3(CH2)3CHO --(KMnO4)--> CH3(CH2)4COOH

(c) Conversion of 1-Pentene to Pentanoic Acid

: 1-Pentene is an alkene with the formula CH3(CH2)3CH=CH2. Converting it to pentanoic acid (CH3(CH2)4COOH) requires the addition of a carboxylic acid group and oxidizing the double bond. Step 1: Oxidative Cleavage to form Pentanoic Acid React 1-Pentene with ozone (O3) in the presence of a reducing agent like Zn/H2O or (CH3)2S to achieve oxidative cleavage: CH3(CH2)3CH=CH2 --(O3, (CH3)2S)--> CH3(CH2)4COOH

(d) Conversion of 1-Butanol to Pentanoic Acid

: 1-Butanol is an alcohol with the formula CH3(CH2)3OH. Since it has 4 carbons, we need to add an extra carbon to obtain pentanoic acid (CH3(CH2)4COOH). The conversion of 1-butanol to pentanoic acid is as follows: Step 1: Conversion to 1-Bromobutane Treat 1-Butanol with PBr3 to convert it to the alkyl halide 1-bromobutane: CH3(CH2)3OH --(PBr3)--> CH3(CH2)3Br Step 2: Grignard Reaction with Carbon Dioxide Convert 1-bromobutane into a Grignard reagent by reacting it with magnesium (Mg) in a dry ether solvent: CH3(CH2)3Br + Mg --(Dry Ether)--> CH3(CH2)3MgBr Then, react the Grignard reagent with carbon dioxide (CO2) to add a carboxylic acid group and form pentanoate: CH3(CH2)3MgBr + CO2 --(Dry Ether)--> CH3(CH2)4COOMgBr Step 3: Hydrolyze to form Pentanoic Acid Hydrolyze the pentanoate to form a free pentanoic acid: CH3(CH2)4COOMgBr + H2O --> CH3(CH2)4COOH + MgBr(OH)

(e) Conversion of 1-Bromopropane to Pentanoic Acid

: 1-Bromopropane is an alkyl halide with the formula CH3CH2CH2Br. Since it has 3 carbons, we need to add two extra carbons to obtain pentanoic acid (CH3(CH2)4COOH). Step 1: Grignard Reaction with Ethyl Formate Convert 1-bromopropane into a Grignard reagent by reacting it with magnesium (Mg) in a dry ether solvent: CH3CH2CH2Br + Mg --(Dry Ether)--> CH3CH2CH2MgBr Then, react the Grignard reagent with ethyl formate (HCOOEt) to form the pentanoate ester: CH3CH2CH2MgBr + HCOOEt --(Dry Ether)--> CH3(CH2)4COOEt + MgBrOH Step 2: Hydrolyze the ester to form Pentanoic Acid Hydrolyze the pentanoate ester to form a free pentanoic acid: CH3(CH2)4COOEt + H2O --(H+)--> CH3(CH2)4COOH + EtOH

(f) Conversion of 1-Hexene to Pentanoic Acid

: 1-Hexene is an alkene with the formula CH3(CH2)4CH=CH2. Converting it to pentanoic acid (CH3(CH2)4COOH) requires oxidation of the double bond and the removal of one carbon. Step 1: Oxidative Cleavage to form Hexanoic Acid React 1-Hexene with ozone (O3) in the presence of a reducing agent like Zn/H2O or (CH3)2S: CH3(CH2)4CH=CH2 --(O3, (CH3)2S)--> CH3(CH2)5COOH Step 2: Decarboxylation to form Pentanoic Acid Heat Hexanoic Acid with soda lime (NaOH + CaO) to perform a decarboxylation reaction: \[ CH_{3}(CH_{2})_{5}COOH --(soda\ lime)--> CH_{3}(CH_{2})_{4}COOH + CO_{2} \]