Question

Primary, secondary and tertiary alcohols may be distinguished by converting them to the corresponding nitroalkanes and then treating with (a) \(\mathrm{NaNO}_{2}\) and dilute \(\mathrm{HCl}\) (b) \(\mathrm{con} \cdot \mathrm{H}_{2} \mathrm{SO}_{4}\) (c) Sn and hydrochloric acid (d) Ammonium hydroxide

Short answer

Short Answer: To distinguish between primary, secondary, and tertiary alcohols after converting them into nitroalkanes, treat them with ammonium hydroxide. This reaction forms hydroxamic acids, which create different colored complexes upon treatment with ferric chloride, allowing us to differentiate between the different types of alcohols.

Step-by-step solution

Identifying Primary, Secondary, and Tertiary Alcohols

To distinguish between primary, secondary, and tertiary alcohols, one must first understand their structure. Primary alcohols have the hydroxyl group attached to a carbon atom that is only bonded to one other carbon atom. Secondary alcohols have the hydroxyl group attached to a carbon atom that is bonded to two other carbon atoms. Tertiary alcohols have the hydroxyl group attached to a carbon atom that is bonded to three other carbon atoms.

Reaction with Nitroalkanes

Primary, secondary, and tertiary alcohols can be converted into their corresponding nitroalkanes by reacting with an inorganic nitrite such as \(\mathrm{NaNO}_{2}\) and dilute \(\mathrm{HCl}\).

Treatment with the given reagents

Now let's analyze the reactions of nitroalkanes with the given reagents: (a) \(\mathrm{NaNO}_{2}\) and dilute \(\mathrm{HCl}\): Nitroalkanes would react with \(\mathrm{NaNO}_{2}\) and dilute \(\mathrm{HCl}\) to form alkyl halides. However, this will not show any distinct results as the alkyl halides formed from primary, secondary, and tertiary alcohols would be similar. (b) \(\mathrm{con} \cdot \mathrm{H}_{2} \mathrm{SO}_{4}\): Nitroalkanes do not show any distinguishing reaction with concentrated sulfuric acid and will not result in identifying primary, secondary, and tertiary alcohols. (c) Sn and hydrochloric acid: Nitroalkanes will react with Sn and hydrochloric acid, resulting in the formation of primary, secondary, and tertiary amines. This reaction will also not differentiate between primary, secondary, and tertiary alcohols since the corresponding amines are similar in structure. (d) Ammonium hydroxide: Nitroalkanes will react with ammonium hydroxide to form hydroxamic acids, which can form colored complexes upon treatment with ferric chloride (FeCl3). Primary, secondary, and tertiary alcohols will give rise to hydroxamic acids with different appearances, which can help differentiate between them. Based on the above analysis, the correct answer is:

Answer

(d) Ammonium hydroxide

Key concepts

Primary Alcohols

Primary alcohols are a type of alcohol distinguished by the presence of a hydroxyl group (-OH) attached to a primary carbon. This primary carbon is bonded to only one other carbon atom. It is this simple structural characteristic that makes primary alcohols unique.

For example, ethanol ( (CH₃CH₂OH) ) is a classic example of a primary alcohol. Here, the hydroxyl group is bonded to a carbon which in turn is bonded to just one other carbon atom.

Primary alcohols undergo a range of chemical reactions, such as oxidation, where they can be converted into aldehydes, and further into carboxylic acids. Their reactions are generally distinctive and make them easily identifiable in laboratory settings.

Their properties and reactivity play a significant role in distinguishing them from secondary and tertiary alcohols. In analyses such as the conversion into nitroalkanes followed by treatment with specific reagents, understanding the primary structure is key to correctly interpreting the results.

Nitroalkanes

Nitroalkanes are organic compounds containing one or more nitro groups (-NO₂) attached to an alkane chain. These compounds are quite significant in organic chemistry due to their reactivity and ability to participate in various chemical transformations.

When alcohols are converted to nitroalkanes, it allows for further exploration of their structural differences through subsequent reactions. This process is particularly useful in distinguishing primary, secondary, and tertiary alcohols when treated with specific reagents.

For instance, nitroalkanes can react with ammonium hydroxide to form hydroxamic acids, which can then form colored complexes with ferric chloride. This step is crucial in the identification process, providing a visual cue that aids the differentiation among the types of alcohols.

Understanding nitroalkanes enhances one's grasp of how various functional groups can be manipulated to achieve desired chemical transformations.

Hydroxamic Acids

Hydroxamic acids are a special class of organic compounds characterized by the presence of a distinct functional group: the -C(=O)NHOH group. These compounds are notable for their ability to form stable complexes with metal ions, such as iron (Fe³⁺).

In the context of distinguishing alcohols, converting nitroalkanes into hydroxamic acids using ammonium hydroxide is a critical step. When treated with ferric chloride, these hydroxamic acids give rise to colored complexes. The colors produced can vary based on the type of alcohol from which the nitroalkane was derived, thus enabling the differentiation among primary, secondary, and tertiary alcohols.

The color-forming ability of hydroxamic acids in the presence of metal ions is an essential feature that is applied in various qualitative analyses in chemistry, making them an invaluable tool in laboratory-based studies and experiments.