2023 Volume 14 Issue 2

Organic Compounds Containing Aromatic Structure Used in Pharmaceutical Production

 

Mevlüt Seyfullah Doğan, Hülya Çelik*

Department of Basic Pharmaceutical Sciences, Faculty of Pharmacy, Agri Ibrahim Cecen University, Agri, Turkey.

 

 

 

 

 

*E-mail: [email protected]


Abstract

Aromatic compounds are a large group of organic compounds that differ from aliphatic compounds with their cyclic molecular structure and different properties. Many ingredients in this group are called "aromatic" because they have a pleasant smell. Aromatic compounds and their derivatives are used in many areas of industry, especially in the pharmaceutical industry. Aromatic substances have a very important place not only in pharmaceutical product but also in many industrial areas such as cosmetics, dyes, textiles, pharmaceuticals, agriculture, cosmetics, perfumery, preservatives, sweeteners. With our study, we examined the properties, history, source, and place of aromatic substances in the pharmaceutical industry and wanted to draw attention to the awareness of the privilege of aromatic substances for the pharmaceutical industry. Drugs are classified according to their pharmacological properties as analgesics, antibiotics, antihistamines, antiallergics, antipyretics, anti inflammatories, analeptics, anesthetics, and antidepressants. It is seen that drugs containing aromatic structures have one or more of these classes. We believe that the design of new and original aromatic drugs will carry the pharmaceutical industry to a higher level.

Keywords: Aromatic, Analgesic, Antibiotic, Pharmaceutical industry


Introduction

What are Aromatic Compounds?

Aromatic compounds are a class of organic compounds that contain one or more aromatic rings or benzene rings in their molecular structure. Aromatic rings are cyclic structures made up of carbon atoms, with alternating single and double bonds. The most common and well-known aromatic compound is benzene (C6H6), which has a ring of six carbon atoms with alternating single and double bonds. The term "aromatic" originated from the observation that many of these compounds were found to have a pleasant aroma. However, it was later discovered that the presence of an aromatic ring is the defining characteristic, rather than the smell. Not all aromatic compounds have a noticeable aroma; some may even have strong and unpleasant odors. Aromatic compounds are widely found in nature and have numerous applications in various industries. They are important in organic chemistry and serve as the backbone for many organic molecules, such as pharmaceuticals, dyes, plastics, fragrances, and more. The stability and reactivity of aromatic compounds have made them crucial in the development of synthetic methods and in the production of various commercial products (Schleyer, 2001).

History of Aromatic Compounds

August Willhelm Hoffman used the word aromatic as a chemical term for the first time in an article he wrote in 1856 and introduced a new concept to the chemical literature. In the early 20th century, Kekule-Couper-Butlelerov's theory known as the valence bond principle divided organic compounds into two main classes: aliphatic and aromatic hydrocarbons. Many of the first aromatic compounds known in history were derived from balsams, resins and essential oils, all of which are odorous compounds (Smith, 2012). The most important aromatic hydrocarbon is benzene, the organic compound that forms the basis of aromatic substances. This highly stable molecule is represented by the formula C6H6. It would not be wrong to define aromatic compounds as compounds that resemble benzene in terms of chemical behavior and have aromatic properties. By replacing one of the hydrogens in the benzene molecule with fluorine, chlorine, bromine, iodine and many functional groups, many aromatic compounds are derived and many aromatic substances are formed. If the atoms forming the ring are all carbon atoms, such compounds are called homoaromatic compounds, and if there are different atoms, these compounds are called heteroaromatic compounds (von Schleyer & Jiao, 1996). Benzene was first isolated in 1825 by Michael Faraday in the early 1800s from the oily part remaining from the gas obtained as a result of the heat decomposition of whale oil used for lighting. Eilhart Mitscherlich is a German chemist who used the name benzene for the first time in history and made a great contribution to the field of chemistry. It was determined in 1834 that the benzene molecule discovered and revealed by Faraday in 1825 had a C6H6 structure, and various structures were proposed to indicate its open structure. The closest to reality is the structure proposed and recommended by Kekule in 1865.

Figure 1.  Kekule structure of benzene and the various representations (https://commons.wikimedia.org)

In 1825, benzene was first isolated from condensed liquid by Michael Faraday by compressing petroleum gas, and later benzoic acid was obtained by heating with quicklime.  Interestingly, benzene itself is not an odorous compound, but its origin is based on a pleasant and fragrant substance found in plant extracts, which has led to benzene and benzene-like compounds being called aromatic hydrocarbons (Lloyd, 1996).

Properties of Aromatic Compounds

At the beginning of chemical research, many hydrocarbons with pleasant and impressive odors were classified as aromatic. As the number of studies increased, it was concluded that aromatic compounds are not fragrant and fragrant compounds are not always aromatic. For a molecule to be considered aromatic, it must have certain properties.  The most well-known property of aromatic compounds is that they are more stable than other organic compounds. This stability was modeled by Hückel in 1931 and described as Hückel's Rules. According to this model, for a molecule to be an aromatic compound, it must have the following properties;

  • The compound must be circular and planar.
  • The bonds in the ring structure of the compound must be conjugated
  • The compound should contain (4n+2) several delocalized π bonds. (n=0, 1, 2.3...).

Sources of Aromatic Compounds

Coal tar distillation is a method of historical importance that is no longer relevant today. Distillation of coal tar, an industrial source of aromatic compounds, yields aromatic compounds such as benzene, toluene, naphthalene, anthracene, xylenes, aniline, pyridine derivatives, phenol and derivatives. Of these, naphthalene is the most abundant hydrocarbon in tar. The most important source of aromatic compounds is petroleum (Smith, 2012).

Aromatic Substances Used in the Pharmaceutical Industry

Aromatic substances are of great importance in the pharmaceutical industry. By being used in the chemical structure of drugs, aromatic substances can increase the effectiveness of drugs, improve their pharmacokinetic properties and sometimes even improve the smell or taste of drugs (Lee, 2012).