Preparation of Banana Flavors
2 Bio 6 Ramon Asturiano, Justine Baquiran, Nathan Batungbacal*, Carmela Bulang Bs Biology, Department of Science, University of Sto. Tomas, Sampaloc Manila
Abstract This experiment was conducted to exhibit the sythesis of banana flavoring in the laboratory through the esterification of isoamyl alcohol and acetic anhydride with the use of the Fischer-Speier reaction. The set-up used was the reflux modified with a water bath at the constant temperature between 75-80o Celsius. The actual yield that was attained was 0.6005 grams of banana essence (Isoacetate). The theorecial yield, on the other hand, was computed to be 2.99 grams. The percent yield was dertermined to be 20.08%.
Introduction Food chemistry plays an important role in culinary enterprises nowadays. It deals with the biological and non-biological components of food and its chemical processes. As businesses heighten in the food industry, there is a need to develop newer and cheaper ways of incorporating flavoring in snacks or beverages without decreasing the quality of flavor of the food. Using artificial flavoring may bring many benefits such as prolonging the shelf life or simply enhancing the tastiness of food. [4]Esters are organic compounds that have a distinct scent or flavor to them. They can easily be synthesized in the laboratory through the utilization of the Fischer-Speier reaction. Any compound that has the functional group ester would include the structure
H O H | || | . H-C— H-C—C—O—C-H | | H H
This would then enable the compound to
have a certain aroma or flavor that could then be added to food after it has been well or properly purified. The [3] Fischer-Speier reaction is a type of esterification technique that requires refluxing a carboxylic acid and an alcohol with the aid of an acid catalyst. In the reaction, the carboxylic acid and the alcohol reactants are in equilibrium with the ester product. The Fischer-Speier reaction is also considered as an example of a nucleophilic acyl stubstitution when based on the electrophilicity of the carbonyl carbons and the nucleophilicity of the alcohol reagents within the chemical equation and the experiment. Despite to its simplicity, the Fischer-Speier reaction also holds some disadvantages in esterification. One example of its disadvantage is the in the thermodynamic flow in the aspect that it is reversible. Another disadvantage would be its slow reaction rates. This could pose as a problem especially when the reactants that are being used are compounds that are sensitive to strong acids. Coupling the Fischer-Speier reaction would be the use of the reflux set-up. The reflux set-up allow for reactions that require heat to take place with minimal loss of reactants that have high volatility such as alcohol. The reflux set-up set -up has several crucial components that allow it to be efficient. The distilling flask is the container where the reactants of the Fischer-Speier reaction will usually be placed. The flask is attached to the condenser that has a constant flow of cooling water flowing through it. This cools the interior of the tube of the condenser condensing and hindering the alcohol or highly volatile liquids from escaping. The condenser has an incurrent passage and an excurrent passage to expel the water. Another aspect the experiment has aimed to tackle is to display a specific filtration method called extraction. This method is only efficient for liquid-liquid isolation. It is usually done with the help of a separation funnel. The funnel funnel is shaped like a water droplet with the topside globular and the bottom side funnel shaped. The top end has a small opening for the entry of reagents or liquids with different densities while the opposite end has a valve to allow and segregate the liquids.
Results and Discussion
The chemical formula in preparing a banana essence ester is: Isoamyl Alcohol (Ialc*) + Acetic Anhydride (AA*) => Isoacetate (Ia*) + Acetic Acid (Aa*)
* For convenience’s convenience’s sake, we will use these abbreviations abbreviations in parentheses parentheses () in computations
Being that this reaction is a sythesis of esters, the reagents are in equilibrium witht the products. The chemical formula formula therefore, depicts 1:1 ratios among the reagents and the products. Given that there is an availability of 2.5 ml isoamyl alcohol and 2.6 ml of acetic ac etic anhydride, it is possible to determine the limiting reagent and the theoretical yield. Once the theoretical yield is known and the experiment has been conducted with the weighed product, the percent yield can then be computed for. The given densities and molecular weight for: Isoamyl alcohol is: 0.8092 g/ml
88.2 g/mol
Acetic anhydride is: 2.8132 g/ml
102.1 g/mol
With the desities given, the mass of the reactants can now be calculated as follows: 2.5 ml isoamyl alcohol x 0.8092 g/ml = 2.023 g 2.6 ml acetic anhydride x 1.0820 g/ml = 2.8132 g
These values are the grams of isoamyl alcohol and acetic anhydride given for the experiment. With these, we can now find out the limiting reagent. 2.8132 g AA x 1 mol AA x 1 mol Ialc x 88.2 g Ialc = 102.1 g AA
1 mol AA
2.430 g Ialc
1 mol Ialc
Because only 2.023 grams of isoamyl alcohol is given when the equation requires 2.430 g, isoamyl alcohol is therefore the limiting reagent as 2.430 g (theoretical computation) > 2.023 g (amount given).
2.023 g Ialc x 1 mol Ialc x 1 mol AA x 102.1 g AA
=
2.34 g AA
88.2 g Ialc 1 mol Ialc 1 mol AA
The required amount for acetic anhydrate is only 2.34 grams when 2. 8132 grams is available. This means that acetic anhydrate is the excess reagent. To find the theoretical yield, one must use the mass of the limiting reagent because the amount of product produced is directly proportional to the limiting reagent available. In an analogy, no matter how may tires a car company has, if only three chassis are available then only three cars can be produced. 2.023 g Ialc x 1 mol Ialc x 1 mol Ia 88.2 g Ialc
1 mol Ialc
x 130.2 g Ia = 1 mol Ia
2.99 g Ia
Now that the theoretical yield has been determined, the percent yield can be accounted for. The formula is as follows:
% yield =
(0.6005) actual yield (2.99) theoretical yield
x 100 = 20.08%
Actual Yield = (pre-weighed (pre-weighed vial + banana essence) - pre-weighed vial vial = (31.8318) – 31.2313 = 0.06005 grams Naturally, the percent yield was computed for to determine dete rmine mathematically how efficient the set-up worked or how much flaw was present in conducting the experiment. As for the rationalization of the chemicals used in the experiment and the techniques used, it will be explained further in this section of the discussion. Based on the procedures, five drops of acid were added to the anhydride. This may lead to the question as a s to why the acid was not dropped into the alcohol. The reason for this is for safety precautions. It would be lessen the possibility of an exothermic reaction if the acid was added to the anhydride because the anhydride is a type of acid too. It is imperative that the test tubes be submerged in ice water because the reaction is highly exothermic and is more likely to have faster moving molecules thus is also likely to splatter and burn causing injury. Ice even when melting and the water puddle it makes around it will maintain a constant temperature of 100 degrees Celsius until the ice is completely melted which is why ice water is preferred over just chunks of ice with air in between. It would be more difficult for the ice to cool the air in between the chunks of ice as the molecules are farther from each other as compared to water. The set-up was also partial submerged in a water bath to evenly distribute the heat and it is standard operating procedures for safety to apply water baths to
flammable, reactive and highly volatile liquids such as the alcohol used in the experiment. The HCO3 was then added to the mixture. This helps by creating an aqueous layer and organic layer contributing in purifying the mixture. The bubbles and the fizz are the byproduct of the HCO3 which is CO2. After the fizz has dissipated, the funnel must be swirled carefully to avoid the formation of emulsion of the organic layer. Formation of these fine dispersions of minute miscible droplets, may cause error when segregating the fluids. Then a half spatula of Na2SO4 was used to
dry the organic product. [2] The chemistry term ‘drying’ refers to the absorption of excess or unnecessary water.
Experimental
Preparation of banana essence. The test tubes were labeled ‘A’ and ‘B‘. The test tube
labeled ‘A’ was filled with the reactant isoamyl alcohol (2.5 ml) while the test tube ‘B’ was filled with the reactant acetic anhydride (2.6 ml). Bo th test tubes were both placed in an ice-water bath. Concentrated H 2SO4 was slowly added mixed in test tube B. After, the contents of test tube B were cautiously mixed drop-by-drop using a dropper with the isoamyl alcohol in test tube A while it was being swirled constantly. A [1] reflux set-up was assembled with and a nd modified with the distillation flask partial submerged in a water bath. The mixture in test tube A was then poured in a reflux set-up at 80° with a few boiling chips for thirty minutes. Then the mixture was cooled for one minute and poured in a beaker with a crushed ice cube. Next, the concoction was then transferred to a separatory funnel where 15 ml of o f saturated NaHCO3 was added. Bubbles from the solution were allowed to escape and cease forming before the funnel was secured with a cap. The separatory funnel was gently swirled and allowed to separate before the top, less dense organic layer was isolated. The denser aqueous layer was discarded. The process was repeated with another 15 ml of HCO3 then extracted with 15 ml of saturated NaCl solution,
discarding the aqueous layer. The organic layer was then added with one half spatula of and decanted to be placed in a pre-weighed vial.
Separating Funnel Set-up
Reflux Set-up
[1]http://www.chem.ucla.edu/~bacher/Specialtopics/reflux.html [1]http://www.chem.ucla.edu/~bacher/Specialtopics/reflux.html [2]http://orgchem.colorado.edu/hn [2]http://orgchem.colorado.edu/hndbksupport/dry dbksupport/drying/drying.html ing/drying.html [3]http://www.organic-chemistry.org/namedreactions/fischer-esterification.shtm [3]http://www.organic-chemistry.org/namedreactions/fischer-esterification.shtm [4]http://www.chemg [4]http://www.chemguide.co.uk/organicprops/esters/ uide.co.uk/organicprops/esters/background.html background.html Fundamentals of Analytical Chemistry. [5] Skoog, W. H. Fundamentals
