Preparation of Aspirin and Determination of the Melting Point

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PREPARATION OF ASPIRIN AND
DETERMINATION OF THE MELTING POINT
Ferrer, Lara Melissa V.
Faculty of Engineering
University of Santo Tomas
Manila, Philippines

ABSTRACT
This experiment involved three steps: synthesis of aspirin, isolation and purification, and the estimation of purity of the final product. The synthesis involved the reaction of salicylic acid and acetic anhydride in the presence of a catalyst, phosphoric acid, H3PO4. When the aspirin was prepared, it was isolated and filtered. The percentage yield of the synthesis was calculated to be 78.42%. The experimental melting point range of aspirin was determined to be 122 -132°C. Due to its wide range, and lower value than that of the theoretical melting point of 136°C, it was assessed that the prepared aspirin was impure.

INTRODUCTION

Aspirin is a most widely sold over-the-counter drug. It has the ability to reduce fever (an antipyretic), to reduce pain (an analgesic), and to reduce swelling, soreness, and redness (an anti-inflammatory agent). One of the first recorded accounts for the discovery of aspirin appeared in England, in 1763, crediting the bark of willow trees with a beneficial effect in alleviating distress due to fevers, aches, and pains. Later, the compound salicylic acid (named for the Latin word for willow, salix) was isolated from willow bark; it proved to be the active ingredient. By 1860, organic chemists were able to synthesize salicylic acid from basic starting materials, this furthered the therapeutic use of the substance, but there were problems. Salicylic acid proved to be irritating to the membranes of the throat, mouth, and stomach. These problems are directly associated with the high acidity of the compound, but a simple remedy was discovered, namely, replacement of the acidic phenolic hydrogen atom with an acetyl group.
A useful synthesis of acetylsalicylic acid was developed in 1893, patented in 1899, marketed under the trade name of “aspirin” by the Bayer Company in



Bibliography: “Synthesis and Analysis of Aspirin”. (n.d.). Retrieved 23 April 2011: “Preparation of Aspirin from Salicylic Acid”. 1999-2011. Retrieved 23 April 2011: Theoretical Yield and Useful Nomenclature. (n.d.). Retrieved March 1, 2010, from CU Boulder Organic Chemistry Undergraduate Courses : “Determination of Melting Point”. (n.d.). Retrieved 23 April 2011: “The Synthesis of Aspirin”. (n.d.). Retrieved 23 April 2011: APPENDIX Calculations: "wt.of aspirin fr.SA = 3g × " (1 mole C7H6O3)/(138 g C7H6O3)×(1 mole C9H8O4)/(1 mole C7H6O3)×(180 g C9H8O4)/(1 mole C9H8O4)=3.9130 "wt.of aspirin fr.AA = 3ml × " (1.082 g)/ml×(1 mole C4H6O3)/(102 g C4H6O3)×(1 mole C9H8O4)/(1 mole C4H6O3)×(180G C9H8O4)/(1 mole C9H8O4)=5.7282

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