NELISWA DLAMINI
ID: 202102918
CHE 301
EXPERIMENT 8: ACETYLATION OF α-D-GLUCOSE
INTRODUCTION
Carbohydrates such as D-glucose are essential biomolecules that play important roles in
metabolism. They are also organic molecules that feature alcohol functional groups and, as
such, undergo many of the reactions of simple alcohols such as ester formation [1]. Acetylation
is one of the most essential transformations in organic synthesis. Protection of the hydroxyl
functionality by an acetyl group has advantages over various protecting groups in view of its
easy introduction, stability towards acidic reaction conditions, and mild removal by alkaline
hydrolysis. Acetic anhydride2 is the most commonly used acetyl source [2]. The product Dglucose pentaacetate is an important intermediate in synthetic carbohydrate chemistry.
Acetylation is a chemical reaction that involves the addition of an acetyl group to a molecule.
D-glucose is a type of sugar that is commonly found in nature. The iodine catalyzed acetylation
of D- glucose involves the addition of an acetyl group to one of the hydroxyl groups on the
glucose molecule [3]. The reaction is carried out by dissolving the D glucose in a solvent, acetic
anhydride. Iodine is added to facilitate the acetylation reaction. The acetic acid anhydride reacts
with the iodine to form iodine acetate, which is the active species that acetylates the glucose.
The iodine catalysed acetylation of D glucose is an important reaction in carbohydrate
chemistry, as it allow for the modification and functionalization of glucose.
Iodine is used as a catalyst in the acetylation of glucose because it can promote the reaction by
increasing the rate without being consumed. In this experiment, iodine helps in the removal of
hydroxyl group from the glucose molecule to make it more reactive and ready to undergo
acetylation. Iodine also selectively react with any unreacted acetic acid anhydride present [4].
During acetylation, a hydrogen atom is substituted for an acetyl group in a compound. The
products formed in acetylation reactions typically have an acetoxy functional group. When the
hydrogen atom belonging to an alcohol group replaced with an acetyl group in an acetylation
reaction, an ester is formed as the product. Acetylation is an organic esterification reaction
using acetic acid in chemistry. An acetyl group is introduced into a chemical molecule. These
chemicals are known as acetate esters.[3]
OH
OAc
O
HO
HO
+
OH
OH
Ac2O
NaOAc AcO
AcO
O
OAc
OAc
AIMS

To produce D-glucose pentaacetate from d glucose and obtain IR spectrum, yield
OBJECTIVES




To synthesise D-glucose pentaacetate
To perform thin layer chromatography and column chromatography
To obtain IR spectrum of the D- glucose pentaacetate
To obtain the melting point of the product
PROCEDURE
Weigh 2g of glucose powder and 1.4 grams of iodine then put it in a 100 mL round bottom
flask. Add 12 mL of acetic anhydride and magnetic stirring chip. Allow the reaction to stir at
room temperature for one hour. After that, transfer the mixture into a 250 mL separatory funnel
and add 100mL of dichloromethane. Wash the reaction successively with 2 x 20 mL saturated
sodium sulphate until a clear organic layer persist. Also wash the organic layer with saturated
sodium bicarbonate [15 mL x 2], then twice with 10 mL of Brine. Dry the organic layer with a
spatula scoop of Magnesium Sulphate to remove any excess water then filter into a round
bottom flask. Spot the TLC plate. Evaporate the solvent using the distillation apparatus.
THIN LAYER CHROMATOGRAPHY
Carefully place a small drop of the organic solution on to the solvent line of the TLC plate.
Develop the plate in the tank containing 12 mL of a solvent mixture of Hexane: Ethyl acetate
(2:1). Spray the plate with p-Anisaldehyde spray. Heat the plate in the oven for 2 minutes. The
product has a dark sport on the plate.
COLUMN CHROMATOGRAPHY
Set up the apparatus for column chromatography. Add silica gel upto 50 mL mark of a 250 mL
beaker and add approximately 50 mL of the eluent prepared when doing thin layer
chromatography to form a slurry. Place a small cotton plug into the bottom of the column and
pour the silica suspension into the column. Gently tap the column with a cork ring until the
level of silica stabilizes. Allow the eluent to flow out of the bottom of the column until the level
is the same as the silica. It is of importance that the silica does not run dry. Carefully pipette
the DCM solution on to the top of the silica column without disturbing the silica, and allow the
solution to run into the silica. Top up the column with the eluent. Collect fractions of
approximately 15 mL, and monitor each fraction making use of TLC. Combine the fractions
that contain clean product and remove the solvent.
RESULTS AND DISCUSSION
The melting point of the product was determined and it was found to be 117 degrees Celsius.
The literature value for the melting point for α-D-Glucose pentaacetate is 110 degrees Celsius.
The determined value for the melting point is high compared to the literature value and this
suggest that the product might have been contaminated. The mass of the product was measured
using the method of weighing by difference. The mass of product + sample vial was found to
be 12.0180g and the mass of the sample vial was found to be 11.1470 g, hence the mass of the
product is 0.871 g
Theoretical yield =[(mass of product x molar mass of product)/ (molar mass of starting
material)]
Theoretical yield = [ (0.871g x 390.165g/mol)/ (180.156 g/mol)] = 1.886 g
% yield = [actual yield/ theoretical yield] x 100
= (0.871 g/ 1.886 g) x 100% = 46.18 %
The percentage yield obtained is very low. This shows that some of the product was lost during
the experiment. Some of the product might have been left in the round bottom flask as it was
stuck at the bottom of the flask.
Thin layer chromatography was also done to see which vial has the product. Vial
6,7,8,9,10,11,12 showed colour on the TLC plate which indicates that they contain the product.
Distillation was performed for the vials containing the product. The product was left to dry in
the fume hood for few days.
The IR spectrum of the product was determined and the expected peak for the acetyl functional
group was observed at 1742 wavenumbers. when comparing the spectrum of the product (α-DGlucose pentaacetate) to that of the starting material which is the D-glucose we can see that
the spectrum of the glucose show a broad peak around 3100 wavenumbers yet the spectrum of
the product does not show that peak. This proves that a substitution reaction occurred, the –OH
has been substituted by the acetyl group which shows a narrow sharp medium peak at 1742
wavenumbers. CH stretches are also observed from the spectrum of the product at 2900 wave
numbers.
CONCLUSION
The experiment was fairly executed as a product was obtained. The aim and objectives of the
experiment were clearly executed. The percentage yield of the product was obtained. The IR
spectrum of the product was also obtained and the expected peak of D-glucose pentaacetate is
observed for the acetyl functional group. Thin layer chromatography was also done to see
which vial has the product, distillation was performed for the vials containing the product.
Errors might have occurred during the course of the experiment that led to the attaining of low
yield. It is recommended that in future the liquid product should be left in the fume hood and
monitored daily until it is dry to get a proper product.
ANSWERS TO QUESTIONS
1. IR spectrum of the product show peak at 1742 wavenumbers which represents the acetyl
group, yet the IR spectrum of the product show peak at 3100 wavenumbers which
represents the –OH functional group of the glucose.
2. MECHANISM
Iodine serves as a catalyst in the formation of glucose pentaacetate , it is regenerated at
the and of the reaction.
Firstly, iodine reacts with the acetic acid anhydride to form an iodine- acetic anhydride
complex
I2 + (CH3CO)2O  I(CH3CO)2O
The iodine- acetic anhydride complex then reacts with the glucose , initiating
acetylation.
The glucose molecule attacks one of the acetyl groups in the complex, which results in
the formation of an acetyl-glucose intermediate .
The intermediate leads to the formation of alpha D glucose product and acetic acid.
I2 + (CH3CO)2O + glucose  (CH3CO)2- glucose + HI + CH3COOH
3. A good protecting group should be easy to put on, easy to remove and in high yielding
reactions, and inert to the conditions of the reaction required.
REFERENCES
1. Chemistry 3719L – Week 13 Synthesis of ,D-Glucose Pentaacetate
http://pnorris.people.ysu.edu/Semesters/3720W2004/Labs/3720Lweek13.pdf ( accessed 01
August 2023)
2. Grace Basumatary, Ghanashyam Bez, Ethyl acetate as an acetyl surrogate for the iodine
catalysed acetylation of alcohols,
Volume 58, Issue 45, 2017, https://doi.org/10.1016/j.tetlet.2017.10.005.
https://www.sciencedirect.com/science/article/pii/S004040391731273X (accessed 01 August
2023)
3.Gujarat, Tamil Nadu, Kamataka, Kerala, Andhra Pradesh The iodine catalysed reaction of Dglucose ACETYLATION https://byjus.com/chemistry/acetylation/ (accessed 01 August 2023)
4. The University of Houston–Clear Lake is a public university in Pasadena and Houston,
Texas, with branch campuses in Pearland and Texas Medical Center.
https://sceweb.sce.uhcl.edu/wang/orglab/glucose%20pentaacetate.doc (accessed 02 August
2023)