Synthesis of a Fruity Ester Week 2

Synthesis and Characterization of a Novel Fruity Ester
Background
An ester is a chemical compound in which at least one hydroxyl group is replaced by O-alkyl group. Esters are formed from an interaction between carboxylic acid and alcohol. Esters are viable compounds which have different commercial and biological implications. Glycerides and triglycerides are important biological esters. These compounds are esters of fatty acids with glycerol. Glycerides and triglycerides are one of the main classes of lipids. Different animal fats and vegetable oils are comprised of glycerides and triglycerides. Phosphoesters forms the major structural backbone of nucleic acids. The molecular weights of these esters are usually high. The molecular weight of the ester depends on upon the alcohol from which it is formed. On the other hand, low molecular weight esters are commercially used for manufacturing fragrances and are also found in essential oils. Nitro-glycerin is an example of an ester that is used for manufacturing explosives. Polyesters are used in the production of clothes and fabrics. Volatile esters are acknowledged for their fruity odors. The typical fragrance and flavor of fruits/flowers are attributed to a mixture of esters. The mixture of esters present in a natural fruit/flower is difficult to duplicate. Hence, fruits and flowers are often recognized by their natural fragrance and flavor. The present article represented the process of synthesis of a fruity ester and its identification through infrared spectroscopy and its characteristic boiling point.

Review of Literature
Although the natural flavor of a mixture of esters is hard to duplicate, synthetic esters could mimic such flavors’. Hence, synthetic esters are routinely used in the food and beverage industry. Most esters are conveniently prepared by refluxing carboxylic acid with an appropriate alcohol in presence of string mineral acids (like sulphuric and hydrochloric acid). This reaction leads to an equilibrium condition. Although acid catalysis increases the rate of attaining equilibrium but it does not affect the position of the equilibrium. For shifting the equilibrium reaction to the right (that is to favor the formation of the desired ester) two strategies are usually deployed. Firstly, large amounts of alcohol may be added to shift the equilibrium towards right. Secondly, removing products (that is water or the desired ester) of the esterification reaction. The first process is usually deployed when the alcohol is relatively cheap. The process of shifting the equilibrium of the etherification reaction to the right (by using excess alcohol) is known as Fischer’s Esterification. Fischer’s Esterification is extensively used for the synthesis of synthetic esters. Hence, this process of esterification is viable for commercial production of synthetic flavors and fragrances.
Methodology
This two- week experiment represented the process of synthesizing an ester from alcohol and carboxylic acid. The synthesis was carried through distillation, reflux and liquid extraction. In week 1, the esterification reaction was carried out. In this reaction, acetic acid was mixed with isopentanol in presence of small amounts of sulphuric acid. The mixture was refluxed and the desired ester was isolated through liquid-liquid extraction. In week 2, the isolated ester was purified by simple distillation. The final product (isolated ester) was characterized by infrared spectroscopy and its characteristic boiling point. The characterization was done through a comparison with reference standards as reported in literature search. The IR-spectrum was also analyzed for the presence of impurities within the isolated ester.
In this reaction, 10.1 ml (density=1.05g/l) acetic acid was mixed with 5.07 ml (density=0.81g/ml) isopentanol in presence of 1ml of sulphuric acid in a 100ml round bottom flask. Hence, the mole of acetic acid and alcohol amounted to 0.175 moles and 0.038 moles respectively. The sulphuric acid was carefully added while swirling the flask. A magnetic stirrer bar was added to the conical flask and the apparatus was assembled for reflux. The reflux was carried out with stirring for 30 minutes. The flask was then allowed to cool at room temperature for 5 minutes and further cooled in an ice-bath.
The mixture was poured in a separator funnel and 10 ml cold water was added. The cold water was made from ice and distilled water which were chilled in an ice-bath). The layers were shaken and allowed to separate. The lower aqueous layer was discarded, while the upper organic layer was retained. 10 ml. Portion of cold water was further added to the organic layer. The layers were shaken and again separation was carried out. Once again, the lower aqueous layer was discarded, while the upper organic layer was retained. The organic layer was washed with 10 ml saturated sodium bicarbonate solution. The layers were separated and washed again with 10 ml saturated solution sodium chloride solution. The organic layer was transferred to a 125 ml- Erlenmeyer flask. The organic layer was dried for around 5 minutes over magnesium sulphate. The dried solution was filtered and the weight of the crude product (ester) was noted. The crude extract was subjected to simple distillation for purification. The purified extract was weighed again and the volume of the extract noted after condensation. The weight and volumes of the crude extract were compared at week 1 and week 2. The purified extract was then subjected to Infrared Spectroscopy.
Results
The theoretical moles of ester formed: 0.038 moles.
Theoretical weight (grams) of ester formed: 5.702 gram (Theoretical yield of the ester).
Volume of ester formed after week 1: 4.509 ml.
Actual weight of ester collected after week 1: 3.52 gram.
% yield of the ester (as a fraction of mass): 3.52 gram/5.7 gram= 61.88%.
Literature value of density of ester: 1.05g/l
Literature value of boiling point of acetic acid: 213 degree C.
Literature value of boiling point of isopentanol: 204 degree C.
Grams of ester formed after combined distillation: 1.413 gram.
Density of the ester after combined distillation: 0.696 g/ml
Literature value of density of ester: 1.05g/l
Characterization of the peak in IR spectra = between 1650 cm-1 and 1750-1.

Fig1: Comparison between the theoretical and actual yield of esters before and after purification with simple distillation.
Discussion and Conclusion
The results indicated that the percentage yield of the ester (as a function of crude extract) was quite low. The yield was only 61.88%. The density of the ester formed was much lower than its literature value (0.696 g/ml versus 1.05g/l). Hence, further purification through fractional distillation was desirable for the experimentation. However, the obtained ester showed characteristic peaks between 1650 cm-1 and 1750-1. This suggested that the extracted compound was an ester. Although there were other peaks too, suggesting the involvement of impurities in the collected extract. For increasing the yield of the ester the volume of isopentanol should be increased in the future experiments.