Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

Hyd methyl sal, Study Guides, Projects, Research of Analytical Chemistry

Its about hydrolysis of methyl salicylate.

Typology: Study Guides, Projects, Research

2014/2015

Uploaded on 08/29/2015

aman2781
aman2781 🇮🇳

2 documents

1 / 4

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
S '08 M. Hauser (Survival Manual 7e)
HYDROLYSIS OF METHYL SALICYLATE
PURPOSE
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 reflux
Filtration
Crystallization
Melting point
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 protonated carboxylic acid. Therefore, the major organic
products of this reaction are methanol and salicylic acid. The salicylic acid is a solid that
can be isolated and purified by crystallization. The chemical equations that describe this
experiment are:
C-O-CH3
OH
OO
C-O- Na+
O-Na+
OH
O
C-OH
+CH3OH H2O
H2SO4
(dilute)
2 NaOH
methyl salicylate
salicylic acid
++
Because the phenolic hydroxyl group is acidic, it is also converted to the corresponding
sodium salt during the basic hydrolysis. In the subsequent acidification, this group also
becomes reprotonated. (continued on other side)
pf3
pf4

Partial preview of the text

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.

  1. 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.

  2. 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

  1. What is the white solid that formed introduced to the aqueous solution of sodium hydroxide? immediately when the methyl salicylate was

  2. 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?

  3. What do you think the purpose was to filter the hot product solution through the filter paper? fluted

  4. Write a good definition for what a catalyst is. Is the sodium hydroxide a catalyst in this experiment? Explain.

  5. 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