This experiment was conducted to synthesise methyl benzoate signifier benzoic acid and methyl alcohol by utilizing the Fischer esterification method. The Fischer exterification technique is utilized in the academic and industrial scenes due to the simplified synthesis and safety parametric quantities of the overall reaction. Both benzoic acid and methyl alcohol are comparatively inexpensive to obtain from a commercial beginning every bit good as being easy to hive away with a comparatively long shelf life. The Fischer esterification method is a cardinal and of import synthesis procedure in developing our hereafter chemists in both commercial and academic employment and rules. By using this method of synthesis. the chemist has the cognition to use certain chemicals to ease farther reactions and derive pertinent informations of said reactions by using differing laboratory equipment. i. e. . atomic magnetic resonance ( NMR ) . mass spectrometry ( MS ) . infrared ( IR ) . and gas chromatography ( GC ) for analysis. These techniques allow the chemist to deduce functional groups and insulate unknown compounds that can verify and place unknown compounds frequently obtained through academic and commercial research lab research undertakings.
The existent transition of carboxylic acid to esters utilizing an acerb accelerator and an intoxicant was given the name Fischer esterification after the German chemist. Emil Fischer ( 1 ) . The basic mechanism for this reaction is shown below in Fig. 1 ( 5 ) . The reaction begins with the transportation of a proton from an acerb accelerator to an intoxicant molecule. A proton transportation follows from the protonated intoxicant and eventually to the carboxylic acid. The protonated carbonyl of the acid is attacked by the lone brace of negatrons on the H atom of the intoxicant for the oxonium ion. A proton transportation follows from the oxonium ion to an intoxicant molecule. bring forthing a tetrahedral carbonyl add-on intermediate. One of the OH groups I the intermediate abstracts a proton from the protonated methyl alcohol molecule to organize a really good go forthing group. which is H2O. In the concluding measure. the methyl alcohol molecule abstracts a proton signifier the protonated carbonyl to renew the carbonyl and whether molecule is displaced. The concluding merchandise is the ester.
Fig. 1 Mechanism of Reaction ( 5 )
Fischer esterification is an equilibrium reaction ( 2 ) . The rate or equilibrium changeless K is dependent upon the simple expression of merchandises over the reactants and can be manipulated by the basic rules of Le Chatlier ( 2 ) . One can increase or diminish the rate of the reaction by utilizing these basic rules. One can increase the cheaper reactant such as an intoxicant ( methyl alcohol in our reaction ) . take a merchandise. such as H2O. utilizing the Dean Stark setup. or one can pull strings the force per unit area or temperature. Most organic chemists do non acquire involved with force per unit area use ; the consequences can frequently be unsafe when carry oning experiments using high force per unit areas. Manipulating the reaction utilizing these different rules will let the chemist to give more of the ester compound by maximising the reaction potency. The fact that the reaction is an equilibrium reaction opens the door for side merchandise such as reactants being isolated in the concluding merchandise every bit good. The reaction has the ability to travel both ways.
MATERIALS AND METHODS
Topographic point 2. 0 g of benzoic acid and 5. 0 milliliter of methyl alcohol in a 10. 0 ml conelike phial ( 2 ) . Cool this mixture in an ice bath for about 10 proceedingss ; so add 0. 6 milliliter of concentrated sulphuric acid. Twirl the vial to blend the constituents of the mixture ( 2 ) . Following. add a boiling rock and piece a reflux setup utilizing a water-cooled capacitor.
Procure a hot home base and sand bath to convey the mixture to a furuncle. Make certain to reflux the mixture for at least one hr. Remove from sand bath and let chilling to room temperature. Decant the mixture into a little separatory funnel incorporating 10 milliliter of H2O and rinse the phial with 10 milliliters diethyl ether ( 2 ) . Add to the separatory funnel and mix smartly. Drain off underside ( H2O ) bed. This bed will incorporate the sulphuric acid and extra methyl alcohol. Wash the staying quintessence bed in the funnel with 6. 0 milliliter of H2O followed by 6. 0 milliliter of 0. 5 M Na hydrogen carbonate to take all the unreacted carboxylic acid ( 2 ) . Shake good and vent often to let go of force per unit area. Repeat the hydrogen carbonate rinsing procedure until the solution is basic when proving with pH paper. Drain the hydrogen carbonate bed into a 50. 0 ml beaker. so wash the quintessence bed with a few millilitres of concentrated Na chloride solution. so dry the solution over Ca chloride pellets. Make certain to add calcium chloride pellets until no clip-clop is observed.
After about 10 proceedingss. pour the quintessence into a 125. 0 ml vacuity flask. Add about 3 – 4 milliliter of fresh quintessence to rinse the drying agent ( 2 ) . After reassigning the merchandise to the flask. cap it by utilizing an adapter and vaporize the dissolver utilizing an aspirator. Once the dissolver is evaporated. oil will stay. This oil will necessitate to be purified by distillment. Set up the Hickman Still apparatus and air capacitor and topographic point the setup in a sand bath to heat the oil until it boils ( 2 ) . The boiling point of ester is about 199 grades Celsius ; roll up all stuff boiling above that temperature ( 2 ) . Pre-weigh a conelike phial and reassign the distillation. After weighing the merchandise. cipher the per centum output and take the merchandise to the IR to obtain a spectrum of the pure merchandise ( 2 ) .
DATA AND RESULTS
As a consequence of the Fischer esterification procedure. 0. 344 g of methyl benzoate was recovered for the concluding merchandise. The computation for the output obtained by the synthesis is provided below ( 3 ) :
% Output =
% Output =
The synthesizing of methyl benzoate from benzoic acid and methyl alcohol was a successful enterprise. This reaction really produced the merchandise better than anticipated in a research lab puting. Based on the I. R. spectra obtained ; we can reason that we had formed the merchandise. The first extremum was in the 3066 cm-1 scope being the C=C-H. and the C-H at the 2953 cm-1 extremum ( 1 ) . We besides have the C=O extremum at 1725 cm-1 along with the C=C at 1602 and C-O-C at the 1279 cm-1 scope ( 2 ) . This construction verifies our concluding merchandise of methyl benzoate. We recovered 0. 344 g of the concluding merchandise ( methyl benzoate ) for a 15. 46 % concluding output. Methyl benzoate has a boiling point of 199. 5 grades Celsius and a molecular weight of 136. 15 gms per mole ( 3 ) . With a boiling point this high. it was of import to reflux for the full hr. We refluxed for merely over one hr and so allowed it to chill to room temperature. At this point we used the separatory funnel to divide our merchandises and wash. so dry by vaporizing the liquid on the hot home base.
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4. Synthesis of methyl benzoate. Available at hypertext transfer protocol: //www. mccfl. edu/Faculty/GambinoA/CHM % 202211/Labs % 20in % 20Word/Synthesis % 20of % 20Methyl % 20Benzoate. DOC. Downloaded 28 Wednesday 2004.
5. Mechanism of reaction. Available at hypertext transfer protocol: //www. chem. ubc. ca/courseware/260/Reactions_Acids_and_amides. pdf. Downloaded 28 Wednesday 2004.