2. PREPARATION OF SALICYLIC ACID FROM METHYL SALICYLATE (Two students together)
In a round bottom 250 ml Quick lit flask, mix 5g of methyl salicylate with 50 ml of 10% sodium hydroxide solution. The sodium salt of the phenolic group in the methyl salicylatc, which usually separates at this point, dissolves when the mixture is warmed Set the flask up for reflux (condenser) on a 250 ml heating mantel for 15 minutes. Pour the solution into a beaker (rinse the flask with a little RO water) and cool the reaction mixture in an ice bath. Acidify the mixture with dilute sulphuric acid and collect the precipitated salicylic acid in a Buchner funnel and dry your sample in a desiccators. The melting point of the dried crystals should be 157°C.
THEORETICAL YIELD CALCULATIONS We started with 5 g of methyl salicylate No of mol n = ni/M
59
152 OA
= XXXXXXXXXXM which = n (number of salicylic acid form) So the theoretical yield of salicylic acid = 0.0329M X 138 g/M = 4.54 g
ASSESSMENT A report must be written up in full for both parts of this experiment using the headings: introduction, experimental, results and conclusions. Both experimental and literature melting points must be quoted and percentage yields calculated. Your dried samples (salicylic acid and aspirin) should be placed in the plastic bags provided and these should be labelled with the name of the sample, your name, locker number and practical session time and passed up for marking.
QUESTIONS I. Give the structure of the sodium salt of methyl salicylate? 2. In the second part of the experiment, what is the structure of the anionic form of salicylic acid before it is acidified with the dilute sulphuric acid? 3. As you can see from this experiment, aspirin is not.very soluble in water, how do you think you could make it more soluble in tablet form? 4. What is the equation for the decomposition reaction of aspirin with water?