Synthesis, Purification and Identification of an Ester free essay sample

An ester was synthesized from the conversion of acetic acid and isopentyl alcohol. A mixture of isopentyl alcohol and sulfuric acid was separated and distilled to purify the ester. Physical properties were compared to known standards for identification. Purification through steam distillation was determined comparing a range of boiling points of a known compound and the mixture, which was observed at 134Â ° C. Steam distillation produced 12. 969g of ester. Theoretical yield was calculated at 19. 138g, resulting in 67. 77% recovery. It was detected that the ester smelled similar to bananas. Various methods of spectroscopy were then performed, including IR and spectras from HNMR, CNMR, COSY, and HQMC were analyzed to predict bond formations and structure of the ester. GS-MS was run to predict the percent of the product synthesized and its molecular formula. Molecular mass of the ester was 130. 19 g/mol. It was concluded that the ester formed was isopentyl acetate, C5H11O2. INTRODUCTION Esters are found in nearly aspect of life. Naturally occurring in animals as fats and in plants, esters are what give the flavor and fragrance of many fruits and flowers. They also make up a form of textile known as polyester. Esters are commonly used as solvents, added to foods and candies as artificial flavorings and included in perfumes and soaps as artificial scents. Essential oils are distilled from the leaves, flowers, stems, roots or other parts of a plant. They are highly concentrated and contain the pure essence of the plant. Essential oils are used most often in aromatherapy. They can be used as an inhalation treatment, as well as applied to the body. They can also be used as fresheners or as a natural pest repellant. Additionally, hydrosols, which are the aromatic waters that remain as a byproduct from producing essential oils by way of steam distillation, are also used commercially. 5 Esters are organic compounds formed from a reaction between an organic acid and an alcohol. Esters are synthesized through esterification. The process, also known as Fisher esterification, is a substitution reaction that uses an acid catalyst to produce an ester. Esters are isolated and purified by way of steam distillation. The steam vaporizes the volatile compounds of a natural product, which when condensed produces a liquid that can be collected and the ester purified. Further isolation is done by separation extraction. Steam distillation is an optimal way to separate volatile compounds from nonvolatile contaminants in high yield and is used extensively in the isolation of natural products. 3 Figure 1 shows the set-up of a steam distillation apparatus. 4 Figure 1 Esters can be identified based on structure and bond formations, in addition to physical properties. Spectroscopy is used to determine what ester has been produced. Infrared spectroscopy (IR) is used to detect vibrational energies of functional groups of atoms present. IR spectra show each functional group vibrates at different wavelengths and frequencies of light. A database of IR spectra from a vast collection of compounds is used for comparisons when trying to identify an ester. The spectra will show characteristic peaks for specific bond types present. Another form of spectroscopy is known as nuclear magnetic resonance, NMR. It can determine the location of atoms such as carbon and hydrogen within a molecule using strong magnetic fields. The nuclei of some atoms act as a small magnet and can be aligned when in the presence of a stronger magnet. Radio waves are then presented to a sample in order to cause the nuclei to flip direction. Different atoms require unique wavelengths in order to be flipped. The peaks of these wavelengths can be analyzed to determine chemical shift, giving atom numbers and functional group information. Carbon NMR gives the number of unique carbons as a single peak on a spectrum, while functional groups appear based on what is attached. Electron density is the main factor when determining chemical shift. Atoms with fewer electrons appear downfield, such as carbon attached to a high electronegative atom. As more electrons shield the atom from the effects of the magnetic field, decreasing the energy required to flip the nuclei, the peak appears upfield. A reference point using TMS is always given. Hydrogen NMR, also called proton NMR, gives the number of unique hydrogens present. It also gives functional group information, in addition to giving the relative number of hydrogens using integration and the number of hydrogens on adjacent carbons. Peaks can appear split on a spectrum. This is due to the magnetic influence they have on nearby atoms. This splitting occurs only when there are hydrogens located on the adjacent carbon, but not when hydrogen is attached to other atoms. Peak splitting has specific names for the number of peaks present. One peak in a singlet, two peaks is a doublet, three peaks is a triplet, four peaks is a quartet and peaks with five or more splits is known as a multiplet with the number of peaks present given as part of the name. 2D NMR, known as COSY and HMQC GC-MS The following experiment was conducted to synthesize an ester through esterification, separate and purify the ester through distillation and identify the ester through spectroscopy to determine chemical structure and according to physical properties. The process of distillation is an ideal way to isolate useful compounds, such as esters, in a manner that will purify the compound and produce a high yield of product. This is an important step when attempting to synthesize esters for commercial use. Natural product extraction requires purity whether the sample is being used merely for testing purposes or if intended for public use. Separation of the product helps in maintaining its purity and presents the greatest likelihood of proper identification. Highly accurate testing through IR, NMR, GS-MS with a pure sample will determine the correct structure based on comparisons with known compounds and issue definitive results. RESULTS and DISCUSSION Synthesis is the process of combining separate substances to make a complete compound through chemical reactions. Formation of esters using Fisher esterification occurs by refluxing carboxylic acid and an alcohol using an acid catalyst. Fisher esterification is a nucleophilic substitution reaction where the reaction mechanism occurs in several steps. First, a proton is transferred from the catalyst to the carbonyl oxygen. The nucleophilic oxygen of the alcohol attacks the carbonyl carbon. There is an additional proton transfer to a second molecule of the alcohol. Water leaves and deprotonation forms the ester. The reaction is shown in the figure below. 2 Reaction mechanism IR spectrum C NMR H NMR COSY HMQC HQMC Expansion GC-MS GC-MS Theoretical yield was calculated using the molar ratio of the limiting reagent, which was 0. The amount recovered of 12. 969g was then divided by the theoretical yield of 19. 138g and multiplied by 100 to give percent yield of 67. 77%. The calculations below indicate the results. (reagent in excess) (limiting reagent) (theoretical yield) (percent yield) SUMMARY In conclusion, EXPERIMENTAL General Procedures Acetic acid and isopentyl alcohol were used to in the synthesis of an ester of isopentyl acetate by way of Fisher esterification. These were reagent grade products purchased for the experiment and used without need for additional purification. Analysis of the ester was performed using a GC-MS model 6890 N Agilent with 5975 inert mass selection detector. The oven temperature runs at 30Â ° C for 3 minutes, ramps up 20Â ° C every minute until temperature reaches 140Â ° C, which holds for 2 minutes. Injector temperature is 250Â ° C with an auxiliary temperature of 280Â ° C. The column used was HP-5ms capillary size 30m by 0. 25mm coated with 0. 25 microns of 5% phenyl-95% methylsiloxane based stationary phase. 10Additional analysis was run using a JEOL 400 SS NMR spectrometer. It contains a 400 MHz magnet and automates various NMR measurements such as two-dimensional NMR measurement and one-dimensional measurement of 1H and 13C or other nuclei. 11 The sample containing a small amount of ester and deuterated chloroform, Chloroform-d, was added to an NMR tube and adjusted into place in a spinner. The tube was wiped to prevent issues with spinning or incorrect data being processed with the sample. The spinner was inserted into the NMR and data acquired through processing software. The experiment was carried out according to procedures of Mohring, et al. from experiment 4 of the Organic Chem Lab textbook.