Amide chemical structure. Image credit: Flickr
Amide chemical structure. Image credit: Flickr

Amide represents a functional group type that comprises a nitrogen atom attached to the carbonyl group and the nitrogen atom attached to R groups. Amides come from carboxylic acid (-COOH) wherein the hydroxyl group is replaced by ammonia or amine. Ammonium carboxylate salt forms when carboxylic acid and amine react with each other. Amide is formed when this salt gets heated at a temperature above 100 degrees Celsius.

Amide’s chemical structure is -CONH2, which is basically substituting the OH part of –COOH with NH2. There are three common amides: methanamide, ethanamide, and propanamide. Paracetamol is a popular over-the-counter medication that helps reduce fever or relieve pain. The medicine’s chemical structure comprises synthetic amide. Different amides have different physical traits. For example, methanamide at room temperature is a liquid; its melting point is 3 degree Celsius. However, other amides remain solid at room temperature.

Structure 

A carbonyl group is an integral part of the amide structure. A carbonyl group is basically a carbon atom and oxygen atom double bonded to each other, with two R groups having separate single bonds with the carbon atom. The R group could be a bunch of carbon or hydrogen atoms, or any other element. Unless it’s clearly specified what an R group comprises, it’s hard to tell what the R group is representing. The amine is attached to two R groups, which are distinguished as R1 and R2. If there are more R groups, they would be named R3, R4, and so on.

One of the R groups in case of amide is the amine group, which comprises a nitrogen atom having a single bond with a couple of R groups. The three amide types do not have the same bonding structure for the nitrogen atom. The primary amide, as aforementioned, has the nitrogen atom bonded to a carbon atom. However, in case of the secondary amide, nitrogen bonds individually bond with two carbon atoms. And it’s three carbon atoms in the case of a tertiary amide. The drug paracetamol comprises a secondary amide.  

Amides Formation and Reaction

Besides the aforementioned common amide formation method, amides can also be made courtesy the Willgerodt-Kindler reaction comprising the chemicals sulfur, alkyl aryl ketones, and morpholine. The Ugi reaction and Passerini reaction are two other amide-forming reactions. Amide hydrolysis can help break down amide. Amide can be converted into a functional group called imine courtesy the Vilsmeier-Haack reaction.  

An amide is an extremely weak base, especially when compared to amines. However, amides are stronger (bases) than esters, carboxylic acids, ketones, and aldehydes. A weak base partially ionizes in water-based solutions, unlike a strong base that ionizes in solutions completely. The pH value of a substance indicates how strong or weak the substance is as a base. Compared to strong bases, a weak base has a lower value on the pH scale

Amide Types

Amides can be primary, secondary, or tertiary. These differ from each other based on the nitrogen atom’s location in the molecular chain, and also the number of carbon atoms the nitrogen is attached to. In a primary amide, there’s just one carbon atom attached to nitrogen. Secondary amides have two carbon atoms bonded to nitrogen. And tertiary amides have three carbon atoms. Of these carbons, one carbon belongs to the carbonyl group.

A primary amide basically drops the ‘-oic acid’ ending and replaces it with ‘-amide’. For example, methanamide, ethanamide, and propanamide are basically derived from the acids methanoic acid, ethanoic acid, and propanoic acid. The name of secondary amides begin with the capital letter N – for instance, N-methylpropanamide. The letter “N” indicates the nitrogen atom is attached to an alkyl group (an alkane or substituent that has one hydrogen missing). Tertiary amides have two N’s, such as in the case of N,N-dimethylformamide.

High Boiling Point

Amides are known for their extremely high boiling points; other acid derivatives don’t record such high boiling points. Primary amides and secondary amides have higher melting/boiling points compared to tertiary amides. This is not just because the molecules in an amide comprise negative and positive charges of the same level, but also due to the hydrogen bonding in amides (primary and secondary).

Thanks to the hydrogen bonding, greater amount of energy is required to break that bond, which explains the higher boiling point. This hydrogen bonding strength is higher in primary and secondary amides compared to tertiary amides. Primary amide’s boiling point figure is the highest. A secondary amide has the second highest boiling point of the three, and tertiary amides falling in at third.

The carbonyl group also lends to amides’ boiling points, thanks to the carbon’s partial positive charge and oxygen’s partial negative charge. The bond between nitrogen and hydrogen leaves the carbonyl group exposed further, which makes it easier for the carbonyl group to interact with other molecules’ carbonyl groups, causing more number of dipole-dipole attractions.

Generally, the mass of a molecule or atom has a major say in boiling point numbers. In the case of amides, however, the type of amide is more important and there’s a higher correlation with boiling points. In other words, the more number of hydrogen atoms bonded to nitrogen, the higher the hydrogen bonding strength. 

Amide Uses

Amides can be used for a variety of purposes. Sodium amide, also called sodamide, is used to make sodium cyanide (a highly toxic, but low-hazard chemical), hydrazine (oily, colorless liquid that serves as a reducing agent and reactive base in several medical and industrial applications), and indigo. Sodamide helps dry gaseous or liquid ammonia.   

Dimethylformamide (DMF) is used to make plastics and acrylic fibers, along with several other materials. It has a role to play in the pesticide development and production, and manufacturing of synthetic leathers, adhesives, films, fibers, and surface coatings.

Potassium amide helps destroy, repel, or prevent pest formation. Amide chains help hold together the repeating carbon chains found in nylon, and benzene chains in Kevlar.