Synthesis of Esters

Synthesis of Esters

Introduction

Esters are often characteristic of a pleasant aroma and are responsible for the lovely odor present in fruits and flowers. Esters can now be synthesized on an industrial basis and have a wide application in the making of perfumes and food aromas (Rajabi, Abdollahi & Luque, 2016). This can be achieved by using single esters or even combining esters to develop various classes of flavors and aromas. The most common method for synthesis of any ester is the reaction between a carboxylic acid and alcohol while using an acid as a catalyst to speed up the reaction rate. In most cases, these reactions can be reversible, producing back the reactants (Haibiao & Shaoxiao, 2006). It, therefore, requires the reactant to be added in excess or for continued removal of water, which is formed as an end product in addition to the ester so that the reaction can go into completion.

Esters can also be synthesized in the lab artificially through the combination of alcohols and organic acids using sulfuric acid as the catalyst. Carboxylic acids and alcohols are characteristic of a carboxyl group at their terminal end of the hydrocarbon chain. The carboxyl group is derived from the combination of a (C=O) carboxyl group and a (^–OH) hydroxyl group. The combination of the two gives an ester in addition to water, as shown by the reaction below.

The produced esters can be distinguished by way of smell. However, several safety precautions need to be taken while handling the highly corrosive sulfuric acid. It is also essential to use wafting as the technique for detecting the odor of the synthetic esters rather than smelling them directly in addition to wearing protective hand gloves while handling chemicals throughout the experimental procedure.

Purpose of the Study

• To familiarize with esterification reactions
• To use different carboxylic acids and alcohols to produce a variety of esters
• To identify esters produced in the lab by comparing them with known esters.

Materials and Methods

Materials

50 ml dropper bottle for:

• Acetic acid 6 test tubes (14mm x 100mm)
• Ethyl alcohol Pasteur pipets
• Methyl alcohol       100 ml beaker
• Sulfuric acid hot plate
• Salicylic acid thermometer
• Ice water bath

Procedure

A 100ml beaker and an approximate of 50 ml water were obtained. A warm water bath was created by placing the beaker on the hot plate, and the water warmed until it attained a temperature of 60 degrees Celsius. Care was taken to ensure the temperature never exceeded 70 degrees and that the thermometer was never left to set at the bottom of the beaker. Three clean test tubes were then obtained and adequately number and labeled in accordance with the table below.

Five drops of concentrated sulfuric acid were then added to each of the test tubes, and the contents mixed thoroughly by carefully tapping the bottom of each tube. The test tubes were then placed in a water bath, and the mixtures allowed about 15 minutes to react. They were then removed from the water bath and allowed to cool for about two minutes on a test tube rack.  An ice bath was then prepared using about 20 ml of water and a few ice cubes. 2 ml of the cold water was then placed in each of the test tubes. The test tubes were then brought out of the fume hood, and their respective order noted using a wafting technique. The odors were then matched with the provided odor, which was banana, nail polish remover, and wintergreen.  This was done for all the tubes. The results were recorded in the table below.

Results

Condensed chemical reactions of the carboxylic acids and the organic alcohols

• Acetic acid + iso-methyl alcohol

• Acetic acid + ethyl alcohol

• Salicylic acid + methyl alcohol

Discussion

All the esters that we prepared in the lab had flavors as those that we provided in the lab. The reaction between Acetic acid and iso-methyl alcohol in the presence of sulfuric acid resulted in an ester with a noticeable banana-like scent. The reaction between acetic acid and ethyl alcohol, on the other hand, resulted in a nail polish like scent which was accompanied by an overwhelming vinegar-like odor. Acetic acid is an organic molecule characteristic of vinegar-like odor that is always present in vinegar, which has a wide range of applications at home. The strong vinegar-like odor observed when acetic acid was reacted with ethyl alcohol was due to the presence of the acetic acid in the reaction mixture. Given that the reaction is highly reversible, the ester is more likely to change to their corresponding reactants after a short period. The reaction between salicylic acid and methyl alcohol resulted in a wintergreen flavor, which was among the reference flavors provided in the lab.

Esters have wide applications in our day to day life, especially in the food industries. For instance, esters have been used in the manufacture of fats and lipids. The reaction of fatty acids and glycerol result in triglyceride esters (Haibiao & Shaoxiao, 2006). Fats and lipids have a very wide domestic application, especially in preparing foods. Esters have also been used for the industrial preparation of washing detergents and soaps in a reaction known as hydrolysis. In this case, fats and oils, with the help of strong alkalis in the process of saponification, are reacted to produce glycerol (Theodorou, 2007). The sweat odor in soaps can also be derived through esterification processes. Esters are also used to make many of the food flavors and sweet-smelling odor in most perfumes that people use daily. It is due to their ability to produce sweet and pleasing odor, which are very attractive and also increase food flavor. Esters also have an application in the pharmaceutical and cosmetic industry in the production of drugs and skincare products.

Conclusion

The reaction between carboxylic acids and alcohol results in the production of esters in the process of esterification. Different carboxylic acids and alcohols can be used to produce a variety of floors and odor as each reaction give their distinct flavor or order. Knowledge of the esterification process has a wide application in our day to day life and the industrial standpoint. All the lab objectives were reached, and the entire project was, therefore, a success. It is, however, important to observe lab safety measures when doing an esterification reaction since they require the use of concentrated sulfuric acid, which is very corrosive.

References

Haibiao, C. H. L. Q. Y., & Shaoxiao, P. (2006). Synthesis and Application of Esters with Fatty Acid and Pentaerythritol [J]. Modern Plastics Processing and Applications, 3.

Rajabi, F., Abdollahi, M., & Luque, R. (2016). Solvent-free esterification of carboxylic acids using supported iron oxide nanoparticles as an efficient and recoverable catalyst. Materials, 9(7), 557.

Theodorou, V., Skobridis, K., Tzakos, A. G., & Ragoussis, V. (2007). A simple method for the alkaline hydrolysis of esters. Tetrahedron Letters, 48(46), 8230-8233.