Download Hyd methyl sal and more Study Guides, Projects, Research Analytical Chemistry in PDF only on Docsity!
PURPOSE^ HYDROLYSIS OF METHYL SALICYLATE
Hydrolyze the ester known as methyl salicylate under base conditions in order to synthesize salicylic acid, a carboxylic acid.
TECHNIQUES • Hydrolysis of an ester
- • Heating under refluxFiltration
- • CrystallizatioMelting pointn
THEORY Methyl salicylate is an ester easily recognized by its odor and is known as oil of wintergreen because of its natural source. This ester will be treated with aqueous base. The hydrolysis reaction that occurs will form methanol, water, and the sodium salt of salicylic acid. Salts of organic compounds usually are soluble in water or will dissolve in water with a bit of heating. Later in the work-up, the salt is acidified with sulfuric acid to convert the organic salt into the protona products of this reaction are methanol and salicylic acid. The salicylic acid is a solid thatted carboxylic acid. Therefore, the major organic can be isolated and purified by crystallization. The chemical equations that describe this experiment are:
C-O-CH 3 OH
O O
C-O-^ Na+
O-Na+
OH
O
C-OH
CH 3 OH + H 2 O
H (d (^2) iSluOte (^4) )
2 NaOH
methyl salicylate
salicylic acid
Be sodium salt during the basic hydrolysis. In the subsequent acidification, this group alsocause the phenolic hydroxyl group is acidic, it is also converted to the corresponding becomes reprotonated. (continued on other side)
PROCEDURE
APPARATUS 1) Assemble a reflux apparatus, using a 250 mL round-bottom flask and your water- cooled condenser with the wide bore inside tube (Fig. 23.1, p. 204, Survival Manual). Be sure to use a small amount of stopcock grease to seal the glass joint between the round bo can be dropped down when cooling is desired.ttom and condenser. Use a heating mantle to heat, setting its height so that the mantle
REACTION MIXTURE 2) Dissolve 10 g sodium hydroxide into 50 mL of deionized water in a 250 mL Erlenmeyer flask. While this your reflux set up. Weigh 5.0 g of the methyl salicylate liquid into a small beaker, then solution cools a bit, remove the round-bottom flask from pour this liquid into your round bottom. Finally, add the sodium hydroxide solution to this same round-bottom. Add one or two small boiling stones to the round-bottom. Reassemble the apparatus for reflux. REFLUX 3) Start water flowing through the condenser, turn on the mantle, and bring the mixture to boil. Continue heating under vigorous reflux for 30 minutes. be about ½ to 2/3 the way up your condenser. After the thirty minutes of reflux, stop Your "reflux ring" should heating, lower the heating mantle if possible, and shut down the water flow. CRYSTALLIZATION AND FILTRATION 4) When the solution has cooled for about five minutes, transfer it to a 250 mL beaker. Try to leave the boiling stones "behind" when you decant the reaction mixture from the round-bottom to the beaker.
litmus paper (blue litmus turns red). It may be necessary to add as much as 150 mL of the Carefully add enough 1 M sulfuric acid to make the solution acidic when tested with acid, so you can pour in large quantities before checking with litmus each time. When the litmus turns pink, add an additional 15 mL of 1 M sulfuric acid to guarantee an acidic environment. The acid addition should cause the salicylic acid to precipitate from the solution.
using a Buchner funnel and filter paper (Fig. 13.5, p. Cool the mixture in an ice bath to a temperature of 5 110, Survival Manual). Start the °C. Set up a vacuum filtration vacuum on the Buchner system, swirl the beaker containing the precipitate to loosen it, then carry out the filtration. Use a stirring rod or spatula to transfer as much solid as possible to the filter. Since you will be re next step, you need not get it very dry at this time.crystallizing the product "from water" in the
QUESTIONS
What is the white solid that formed introduced to the aqueous solution of sodium hydroxide? immediately when the methyl salicylate was
Suppose a student forgot to turn on the reflux condenser water and proceeded to heat the reaction mixture for a long period of time. This student ended up with a disappointing yield of product. What could have happened?
What do you think the purpose was to filter the hot product solution through the filter paper? fluted
Write a good definition for what a catalyst is. Is the sodium hydroxide a catalyst in this experiment? Explain.
You could say that the reaction you have completed is a "reverse esterification." Research how esters are typically prepared, look at the chemical equations for this lab, then identify which two substances would be required to prepare the methyl salicy ester that we used as a starting material. late
reflux apparatus hot filtration set-up
