Synthesis of Salicylic Acid from Wintergreen Oil Essay

EXPERIMENT 4: Synthesis of Salicylic Acid from Wintergreen Oil Abstract: The purpose of this experiment is to take methyl salicylate (wintergreen oil) and by heating it under reflux with NaOH as a solvent, and then cooling the mixture with H2SO4 as another solvent, synthesize salicylic acid. The final step involves purify the product to produce as pure a sample of salicylic acid as possible. This process allowed for the successful production of 1. 406g salicylic acid, an 82. 70% yield. The NMR and IR both produced images that correlate with the known spectrums indicating a pure product.

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The melting point range was slightly wider, though did encompass the accepted melting point values. Discussion: Reaction OH O OCH3 2) H2SO4 1) 2NaOH OH O OH 1. 595 ml methyl salicylate is reacted with sodium hydroxide by heating it under reflux. The sodium ions knock the methyl group from the methyl salicylate due to the greater attraction between the sodium cation and the slightly negative charge on the oxygen compared to the O-CH3 bond that had previously existed.

This reaction produces disodium salicylic acid, methyl hydroxide and water molecules.

The sodium crystals that form are visible as the white particulate matter seen as soon as the two chemicals are mixed. Heating of the substance under reflux increased the reaction rate as did the use of the solvent to increase the frequency of molecules being ripped off the original substance and sucking them into their new molecular formations. At this point the wintergreen smell has disappeared from the mixture indicating a rapid decline in the amount of methyl salicylate present in the reaction. When the sulfuric acid (pH ~. ) is added to the disodium salicylic acid (pH ~5-6), the two sodium atoms are replaced by hydrogen atoms creating salicylic acid and sodium sulfate and lower the pH of the solution to 2. The sodium cations are now more attracted to the slightly negative charge on the two oxygen anions on the SO42- ions than to the disodium salicylic acid and the hydrogens take their place. The ice bath kept the temperature low enough that the salicylic acid remained solid and the sulfuric acid components liquid, allowing for a final product with the most purity possible.

Determining limiting reagent: 1. 595 ???? ??????????? ???????????????????? ? 15. 0 ???? ???????????? ????????????????? ? Amount of methyl salicylate used: 1 ???? Amount of sodium hydroxide: 2. 13 g 1. 174 ?? Theoretical yield: Actual yield: 1. 406 g Percent yield = 1. 873 ?? ??????????? ???????????????????? ? 1. 406 ?? ? 1. 700 ?? Melting point range of purified product 150-162°C Mixed melting point range with salicylic acid: 153-160°C The melting point range of the synthetic salicylic acid includes the textbook value of 159°C.

Although a greater variance was seen with the synthetic salicylic acid melting point range (range=12°C) versus the provided salicylic acid (range=7°C), the full range of the provided salicylic acid fell within the range of the synthetic salicylic acid, indicating a relatively pure product. It should be noted that optimally the melting point range should be slightly narrower. Loss of product occurred due to loss at each transfer step including, crystals stuck to the vacuum filter, crystals sticking to the glass stir rod for pH testing as well as the metal spatula used for recrystallization.

While washing the crystals, some loss would also be seen due to the slight solubility of salicylic acid. I R: 10 0 = 8 2. 7 0% (138. 1 ?? /?????? ?????????????????? ???????? ) = 1. 700 ?? ?????????????????? ???????? (152. 1 ?? /?????? ??????????? ???????????????????? ) 1 ???? = 31. 95 ?? NaOH = 1. 873 ?? ***limiting reagent*** PE A K # 1 2 3 4 5 POSITION (cm-1) 748. 245 1204. 33 1654. 62 2850. 27 3235. 00 BOND (MODE) C-H bend (aromatic) C-O stretch C=O stretch O-H stretch (carboxylic) O-H stretch (on phenol) ASSIGNMENT 1 2 3 4 5 3 2 1 4 1 1 5 NMR Chemical Shift (ppm) 10. 5 8. 0 7. 5 6. 9 Integration 2 1 1 2 Multiplicity/splitting Singlet Doublet Triplet Triplet Assignment 1 2 3 4 3 4 1 4 2 1 NMR Discussion: Assignment 1: The singlet peak is located at 10. 5 ppm and is assigned to the hydrogens bonded to the two single bonded oxygens. These two can share this single peak because the hydrogens are constantly swapping places with each other due to their position within the molecular structure and if the NMR was magnified, two peaks could be seen.

Assignment 2: The peak located at 8. 0 ppm is a doublet peak assigned to the hydrogen bonded to carbon on the aromatic ring closest to the carboxylic group. It is shifted . 5-. 6 ppm downfield of where hydrogens on a benzene ring would normally appear due to de-shielding by the nearby carboxyl group. Assignment 3: The 7. 5 ppm triplet peak is indicative of the hydrogen bonded to carbon on the aromatic ring closest to the phenol group, again due to de-shielding by the nearby phenol group.

The extra peak is likely due to the interaction of the O-H bond with the C-H bond. Assignment 4: 6. 9 ppm has a triplet peak and is assigned to the two remaining C-H bonds on the aromatic ring. Conclusion: The final product was created by taking advantage of the electron affinity and nucleophilic properties of the chemicals and especially the solvents to create transition states to allow for a faster, more stable reaction. Heating of the substance under reflux also increased the reaction rate.

The melting point range contains the textbook value of salicylic acid and the IR and NMR matches the known IR/NMR for salicylic acid. This supports the purity of the substance created. The absence of the wintergreen scent indicates an absence of the methyl salicylate. After completion of this experimental process, 1. 406 g of salicylic acid was created from the initial 1. 595 g methyl salicylate which equates to an 82. 70% yield, a successful result.

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