Question

Draw structures of the product formed by oxidation of the following alcohols. Assume an excess of oxidizing agent is used in each case. (a) 2 -methyl-1-pentanol (b) 3-methyl-2-pentanol (c) \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (d) \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\)

Short answer

(a) 2-methylpentanoic acid; (b) 3-methyl-2-pentanone; (c) succinic acid; (d) 3-aminopropanoic acid.

Step-by-step solution

Identify the Alcohol Type for 2-methyl-1-pentanol

2-methyl-1-pentanol is a primary alcohol because the hydroxyl group (-OH) is attached to a carbon atom that is only bonded to one other alkyl group.

Determine Oxidation Product of Primary Alcohol

When a primary alcohol like 2-methyl-1-pentanol is oxidized with an excess oxidizing agent, it first forms an aldehyde and then further oxidizes to form a carboxylic acid. Therefore, 2-methyl-1-pentanol will oxidize to 2-methylpentanoic acid.

Identify the Alcohol Type for 3-methyl-2-pentanol

3-methyl-2-pentanol is a secondary alcohol because the hydroxyl group is attached to a carbon atom that is bonded to two other carbon atoms.

Determine Oxidation Product of Secondary Alcohol

A secondary alcohol such as 3-methyl-2-pentanol oxidizes to form a ketone. Thus, the product of oxidation will be 3-methyl-2-pentanone.

Identify the Alcohol Type for HOCH2CH2CH2CH2OH

HOCH2CH2CH2CH2OH is a diol, specifically a primary diol, since both hydroxyl groups are on primary carbons.

Determine Oxidation Product of Primary Diol

When a diol with two primary alcohol groups is oxidized, each group is converted to an aldehyde and further oxidized to form a carboxylic acid. Thus, HOCH2CH2CH2CH2OH oxidizes to form butanedioic acid (succinic acid).

Identify Alcohol Type for H2NCH2CH2CH2OH

In H2NCH2CH2CH2OH, the hydroxyl group is on a primary carbon, and it also has an amine group present.

Determine Oxidation Product for Alcohol with Amine

The primary alcohol in H2NCH2CH2CH2OH oxidizes to a carboxylic acid group, resulting in 3-aminopropanoic acid. The amine group does not oxidize but remains as is.

Key concepts

Primary Alcohol

Primary alcohols are characterized by the presence of the hydroxyl group (-OH) attached to a carbon atom that is only connected to one other carbon. This kind of setup makes primary alcohols susceptible to oxidation, especially when an excess of oxidizing agents is used. During the oxidation process, primary alcohols typically undergo two stages.

• First, they form an aldehyde. This occurs when the -OH group and its adjacent hydrogen are removed.
• Next, the aldehyde can be further oxidized to form a carboxylic acid, where the former carbonyl carbon now bonds to an -OH group and a double-bonded oxygen (O=).

For instance, 2-methyl-1-pentanol is a primary alcohol that first converts to an aldehyde and subsequently oxidizes further to yield 2-methylpentanoic acid upon the application of excess oxidizing agent.

Secondary Alcohol

Secondary alcohols have their hydroxyl group attached to a carbon atom that is bonded to two other carbon atoms. This particular structure leads primary and secondary alcohols to a different oxidative outcome. When secondary alcohols undergo oxidation, they typically form ketones. A ketone features a carbon-oxygen double bond (O=), with the carbon atom bonded to two other carbon groups, lacking the additional hydrogen required for further oxidation.
The reaction stops at the ketone stage because ketones are generally more stable and do not readily oxidize further under typical conditions. An example of this is 3-methyl-2-pentanol, a secondary alcohol. When it is oxidized, it forms 3-methyl-2-pentanone, a ketone.

Diol Oxidation

Diols are a special kind of alcohol that contain two hydroxyl (-OH) groups within their molecular structure. When both hydroxyl groups are found on primary carbons, we call it a primary diol. Upon oxidation, such as in the molecule HOCH2CH2CH2CH2OH, a dicarboxylic acid forms. The reason behind this result is that each primary alcohol group first converts to an aldehyde. Following this, each aldehyde can further oxidize into a carboxylic acid. Thus, HOCH2CH2CH2CH2OH is oxidized to produce butanedioic acid, also known as succinic acid.
It's important to note that diol oxidation often necessitates conditions strong enough to manage two simultaneous oxidation processes, making it slightly more complex than oxidizing single alcohol units.

Oxidation Products

The oxidation of alcohols results in different products depending largely on the starting alcohol's structure. We encounter wide-ranging products from aldehydes and ketones to carboxylic acids.

• Primary alcohols generally oxidize to form first an aldehyde, and with excess oxidizing agent, further to a carboxylic acid.
• Secondary alcohols convert into ketones, as they lack the structural context needed for further oxidation.
• In cases of diols, which can create diacids, each hydroxyl group transforms along primary alcohol oxidation patterns.

Such chemical behavior underpins significant industrial and biochemical processes, providing a foundation for synthesis in organic chemistry.