The portal has been deactivated. Please contact your portal admin.

Question Video: Determining the Product of the Oxidation of a Primary Alcohol under Different Reaction Conditions Chemistry

Two different experiments were performed under different reaction conditions with propan-1-ol. Details on each experiment are shown in the scheme. What are the names of products A and B? [A] A: propanone, B: propanal [B] A: propanal, B: propanone [C] A: propanone, B: propanoic acid [D] A: propanoic acid, B: propanal [E] A: propanal, B: propanoic acid

05:45

Video Transcript

Two different experiments were performed under different reaction conditions with propan-1-ol. Details on each experiment are shown in the scheme below. What are the names of products A and B? (A) A is propanone; B is propanal. (B) A is propanal; B is propanone. (C) A is propanone; B is propanoic acid. (D) A is propanoic acid; B is propanal. Or (E) A is propanal; B is propanoic acid.

To answer this question, we need to determine the names of products A and B. A and B are both made from the same starting material, propan-1-ol. Looking at the structure of propan-1-ol, we see a hydroxy group bonded to a carbon atom that has one alkyl substituent. So propan-1-ol is a primary alcohol. Both A and B are produced when propan-1-ol reacts with potassium dichromate, an oxidizing agent. Let’s clear some space for now to take a closer look at these reactions.

When a primary alcohol is reacted with an oxidizing agent, represented here by a capital O in brackets, the hydrogen of the hydroxy group and one of the hydrogen atoms bonded to the same carbon as the hydroxy group will be removed. To make up for this loss of bonds, a new carbon-oxygen double bond will form between the two atoms that each lost a hydrogen atom. This produces an aldehyde and water. Aldehydes are easily oxidized. If there’s still oxidizing agent and water present in the reaction vessel, the newly formed aldehyde will be oxidized in a series of complex steps to produce a carboxylic acid.

By closely monitoring the reaction conditions, we can attempt to control which product is ultimately formed, an aldehyde or a carboxylic acid. If an aldehyde is the desired product, then the reaction should be run with excess alcohol and the aldehyde should be distilled as it is produced to prevent it from oxidizing further. If a carboxylic acid is the preferred product, then the reaction should be run with excess oxidizing agent under reflux to ensure that any aldehyde produced is further oxidized to the carboxylic acid.

If we look at the reaction conditions provided in the scheme, we can see that the first set of reaction conditions indicates that product A is an aldehyde. And the second set of reaction conditions indicates that product B is a carboxylic acid. We can use the general equations to help us draw the structures of A and B. Looking at the first equation, we can see that the R group and the carbon atom bonded to the hydroxy group in the primary alcohol are in the same position in the product aldehyde. So, we can start drawing structure A by redrawing the R group and the carbon atom that is bonded to the hydroxy group.

In the primary alcohol, we see that the carbon atom that is not a part of the R group is single bonded to a hydroxy group and two hydrogen atoms. When the aldehyde is formed, this carbon atom becomes double bonded to an oxygen atom and single bonded to one hydrogen atom. So, to complete our structure, we need to replace the hydroxy group and two hydrogen atoms of the primary alcohol with one double-bonded oxygen atom and one single-bonded hydrogen atom.

Now that we know the structure of A, we can determine the structure of B. Looking at the second reaction equation, we can see that the aldehyde and carboxylic acid have the same basic structure except the position occupied by a hydrogen atom in the aldehyde is occupied by a hydroxy group in the carboxylic acid. So, to draw structure B, we can redraw the structure of A, then replace the hydrogen atom with a hydroxy group.

Now that we have identified the structures of A and B, let’s take another look at the answer choices. We can see that each name provided in the answer choices starts with “propan,” prop- meaning three carbon atoms and A-N indicating that the carbon atoms are single bonded together. We can see that the structures of A and B both contain three carbon atoms that are joined by single bonds.

While the beginning of each name provided in the answer choices is the same, the endings are different, with the names ending in either -one, -al, or -oic acid. Each ending indicates a different functional group. -one indicates that the structure contains a ketone, -al is used to indicate the presence of an aldehyde, and -oic acid indicates that the molecule is a carboxylic acid. Since product A is an aldehyde, we should expect the name to end in A-L. Thus, the name of product A is propanal. As product B is a carboxylic acid, we should expect the name to end in -oic acid. Thus, the name of product B is propanoic acid.

Therefore, the answer choice which correctly names the products of the oxidation of propan-1-ol is answer choice (E). A is propanal; B is propanoic acid.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.