Question

Show how to convert trans-3-phenyl-2-propenoic acid (cinnamic acid) to each compound. (a) OCC=Cc1ccccc1 (b) O=C(O)CCc1ccccc1 (c) OCCCc1ccccc1

Short answer

Question: Describe the synthesis steps for the conversion of cinnamic acid to allyl phenyl ether, undecanoic acid, and phenethyl alcohol. Answer: 1. Conversion to Allyl Phenyl Ether: a) Reduction of the carboxylic acid to an alcohol using lithium aluminum hydride (LiAlH4). b) Williamson ether synthesis using 3-phenylprop-2-en-1-ol and allyl bromide in the presence of sodium hydride (NaH). 2. Conversion to Undecanoic Acid: a) Hydrogenation of trans-3-phenyl-2-propenoic acid with hydrogen gas (H2) and palladium on carbon (Pd/C) catalyst. b) Extension of the carbon chain by first converting hexanoic acid into hexanoyl chloride using thionyl chloride (SOCl2) and then reacting it with n-butyl magnesium bromide. 3. Conversion to Phenethyl Alcohol: a) Reduction of the carboxylic acid and the alkene using diisobutylaluminum hydride (DIBAL-H) followed by catalytic hydrogenation with hydrogen gas (H2) and a palladium on carbon (Pd/C) catalyst. b) Isomerization to phenethyl alcohol using a base-catalyzed reaction with potassium tert-butoxide (KOtBu).

Step-by-step solution

Conversion to Allyl Phenyl Ether (a)

To convert cinnamic acid to allyl phenyl ether, follow these steps: 1. Reduction of the carboxylic acid to an alcohol: Add a reducing agent such as lithium aluminum hydride (LiAlH4) to convert the carboxylic acid group (-COOH) of cinnamic acid to an alcohol group (-OH), forming 3-phenylprop-2-en-1-ol. 2. Williamson ether synthesis: Perform the Williamson ether synthesis by reacting 3-phenylprop-2-en-1-ol with allyl bromide in the presence of a base such as sodium hydride (NaH). This reaction results in the formation of allyl phenyl ether.

Conversion to Undecanoic Acid (b)

To convert cinnamic acid to undecanoic acid, follow these steps: 1. Hydrogenation of trans-3-phenyl-2-propenoic acid: Treat cinnamic acid with hydrogen gas (H2) in the presence of a catalyst, such as palladium on carbon (Pd/C), to fully hydrogenate the alkene and the aromatic ring. This reaction results in the formation of hexanoic acid. 2. Extension of the carbon chain: Perform a two-step reaction to extend the carbon chain. First, convert hexanoic acid into hexanoyl chloride using thionyl chloride (SOCl2). Then, react hexanoyl chloride with n-butyl magnesium bromide in a Grignard reaction to append four carbons, forming undecanoic acid.

Conversion to Phenethyl Alcohol (c)

To convert cinnamic acid to phenethyl alcohol, follow these steps: 1. Reduction of the carboxylic acid and the alkene: Use a reducing agent such as diisobutylaluminum hydride (DIBAL-H) to selectively reduce the carboxylic acid group (-COOH) to an aldehyde group (-CHO). Then, perform a catalytic hydrogenation using hydrogen gas (H2) and a palladium on carbon (Pd/C) catalyst to reduce the alkene, forming (E)-phenethyl alcohol as the major product. 2. Isomerization to phenethyl alcohol: To fully convert the E-isomer to the desired phenethyl alcohol, perform a base-catalyzed isomerization using a mild base, such as potassium tert-butoxide (KOtBu), in a suitable solvent. This step will provide the target compound, phenethyl alcohol.