Question

To accomplish the oxidation of cinnamyl alcohol to cinnamaldehyde, CCOCC=Cc1ccccc1 Which of the following reagents should not be employed? (A) \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{NH}^{+} \mathrm{ClCrO}_{3}^{-}(\mathrm{PCC})\) (B) \(\left(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{NH}^{+}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{PDC})\) (C) \(\mathrm{MnO}_{2}\) (D) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) and \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

Short answer

The reagent that should not be employed for the oxidation of cinnamyl alcohol to cinnamaldehyde is (D) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) and \(\mathrm{H}_{2} \mathrm{SO}_{4}\).

Step-by-step solution

Identify the Cinnamyl Alcohol and Cinnamaldehyde Molecules

Cinnamyl Alcohol is an organic molecule containing an alcohol group (-OH) and has the SMILES representation: CCOCC=Cc1ccccc1. Cinnamaldehyde is the product of oxidizing cinnamyl alcohol and features an aldehyde group (-CHO) at the end of the molecule.

Analyze Each Reagent

We will analyze each reagent and determine if it is appropriate for the oxidation of cinnamyl alcohol to cinnamaldehyde. (A) \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{NH}^{+} \mathrm{ClCrO}_{3}^{-}(\mathrm{PCC})\) - Pyridinium Chlorochromate (PCC) is a mild oxidizing agent commonly used for transforming primary alcohols into aldehydes and secondary alcohols into ketones. It can be used for this oxidation process. (B) \(\left(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{NH}^{+}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{PDC})\) - Pyridinium Dichromate (PDC) is another mild oxidizing agent that is also used for the selective oxidation of primary alcohols to aldehydes and secondary alcohols to ketones. This reagent is suitable for the required oxidation process. (C) \(\mathrm{MnO}_{2}\) - Manganese Dioxide (MnO2) is an oxidizing agent that is mainly used for the oxidation of allylic and benzylic alcohols to their corresponding aldehydes or ketones. It is not very effective for non-allylic or non-benzylic alcohols, so it can be used for this specific oxidation, as cinnamyl alcohol is an allylic alcohol. (D) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) and \(\mathrm{H}_{2} \mathrm{SO}_{4}\) - Potassium Dichromate (K2Cr2O7) and Sulfuric Acid (H2SO4) are strong oxidizing agents. When combined, they will oxidize primary alcohols to carboxylic acids, bypassing the aldehyde stage. Thus, this reagent combination should not be used for the desired oxidation process.

Choose the Incorrect Reagent

Based on the analysis in Step 2, the reagent that should not be employed for the oxidation of cinnamyl alcohol to cinnamaldehyde is: (D) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) and \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

Key concepts

Cinnamyl Alcohol

Cinnamyl alcohol is an organic compound recognized for its characteristic fragrant scent. It forms part of the family of compounds known as allylic alcohols. This means it has a hydroxyl group (-OH) connected to a carbon atom that is adjacent to a double-bonded carbon. Its chemical structure can be represented as CCOCC=Cc1ccccc1 in SMILES notation, where the double bonds and alcoholic group are evident. This placement affects its chemical reactivity, making it easier to oxidize compared to ordinary alcohols.
Cinnamyl alcohol is primarily found in the bark of cinnamon trees, as well as in storax, a natural resin. Its use extends to various industries, including the perfume sector, thanks to its pleasant aroma. When considering chemical transformations, particularly oxidation, cinnamyl alcohol's structure allows it to undergo specific reactions, turning into valuable products like cinnamaldehyde.

Cinnamaldehyde

Cinnamaldehyde is a naturally occurring organic compound that gives cinnamon its flavor and odor. It's an aldehyde, which means it carries a -CHO group. This structural group is crucial for its unique chemical behavior. In the context of oxidation, cinnamaldehyde arises as the oxidized form of cinnamyl alcohol.
Converting cinnamyl alcohol into cinnamaldehyde involves removing electrons and hydrogen from the hydroxyl group to form a carbonyl group. This transformation is highly valuable because cinnamaldehyde serves multiple purposes beyond flavor, such as in pharmaceuticals and as a precursor for synthetic organic compounds. Its reactivity, including being able to undergo further oxidation to carboxylic acids, dictates its use in various chemical applications. However, specific oxidizing agents need to be selected to ensure only the desired aldehyde stage is reached instead of being oxidized further to carboxylic acids.

Oxidizing Agents

Oxidizing agents are substances that facilitate the oxidation of other compounds by accepting electrons. In the transformation of cinnamyl alcohol to cinnamaldehyde, selecting the appropriate oxidizing agent is crucial for achieving the desired reaction. Several options are available, each with specific characteristics and suitability:

• Pyridinium Chlorochromate (PCC) - Known for its mild nature, PCC is a prime choice for converting primary alcohols to aldehydes while preventing over-oxidation.
• Pyridinium Dichromate (PDC) - Similar to PCC, this reagent is also mild and ensures selective oxidation without pushing the reaction to carboxylic acids.
• Manganese Dioxide ( MnO_{2} ) - Effective for oxidizing allylic alcohols like cinnamyl alcohol to aldehydes, thanks to its selectivity for such structures.
• Potassium Dichromate ( K_{2}Cr_{2}O_{7} ) with Sulfuric Acid ( H_{2}SO_{4} ) - A strong oxidizing pair, tending to over-oxidize alcohols to carboxylic acids, which is not desired when targeting aldehydes.

Understanding the nature and strength of these oxidizing agents allows chemists to control reactions precisely, aiming for desired outcomes without unwanted side products.

Organic Chemistry Reactions

Organic chemistry is centered around the reactivity and transformation of carbon-containing molecules. Reactions such as the oxidation of alcohols to carbonyl compounds are fundamental examples. These reactions highlight the interplay between structure and reactivity.
For example, the oxidation of cinnamyl alcohol to cinnamaldehyde involves losing hydrogen from the alcohol and forming a carbon-oxygen double bond. This kind of reaction illustrates the concept of functional group transformation, where molecules change one group for another while largely retaining their carbon framework.
Such transformations are vital in organic synthesis, allowing for the creation of a wealth of useful compounds. They follow predictable patterns depending on the reagent used, the type of carbon skeleton, and the desired end product. Chemists leverage this predictability when designing synthesis pathways to construct complex molecules from simpler ones. This is why understanding these reactions, along with correct reagent selection, is essential for efficient organic synthesis.