The Chemistry of Smells
By: Stephanie Ng
For many materials, the chemical makeup of the components can help determine the smell that is given off, with slight altercations to the formula causing changes. As a result, a compounds’ structure can determine whether it can be used in a variety of industries, such as food or perfume.
One common group that possesses a distinct odor is esters that have a lower molecular weight. Many of these esters have a fruit-like or sweet smell, and therefore, they can be found in common natural foods. In addition, they can be utilized in synthetic foods or drinks or other products. Some examples include orange, banana, or spearmint, which odors are composed of octyl acetate, isoamyl acetate, and benzyl ethanoate, respectively. These esters can generally be formed through the process of a Fischer esterification, making them especially useful products for synthetic foods.
In the process of a Fischer esterification, a carboxylic acid and an alcohol will react in the presence of a strong acid catalyst, generally sulfuric acid. For example, with octyl acetate, the ester can be formed using acetic acid and 1-octanol as starting materials. Since the reaction is reversible through reaction of the ester with the acid and water, the water is usually removed or an excess of reagent is used in order to form the desired amount of product. The simplicity of the reagents, combined with the easily shifted equilibrium, allows a Fischer esterification to be reliable on a larger industrial scale. By using a large excess of the cheaper starting material, it can be assured that the reaction is the most productive. In this manner, the large scale production of low weight esters can be used for things such as artificial flavors. For example, pear oil is a commonly found artificial flavor that is formed from a solution of isoamyl acetate in ethanol.
Another industry that heavily utilizes chemistry in combination with smells is the perfume industry. For perfumes, the smells are carefully layered and engineered, such that different smells unfold as time goes on. To create these layers, it is determined how fast certain chemicals evaporate from the skin, with stronger smells lasting the shortest time and baser smells lasting longer. Many places will resort to using gas chromatography mass spectrometry (GC-MS) in order to break down the many different components of a smell. After distinguishing individual parts, chemists may try and synthesize the fragrance from scratch.
In exploring organic chemistry, there are many different areas that the knowledge can be applied, and smell is one of the most interesting areas since humans innately link smells to memories and experiences. By researching different compounds, newer combinations can be created, allowing production of a bigger variety of products such as candles, perfumes, soaps or foods.
