Download CHEM 320 PRAC 3

Name: Asande
Surname: Ndlovu
Student number: 221028326
Chem 320 experiment 3
Preparation of 2-Acetylcyclohexane
Aim
The aim of this experiment was to synthesise 2-acetylcyclohexanone. From cyclohexanone and
pyrrolidine, an addition-elimination reaction was performed to yield enamine. Enamine was
then acylated with acidic anhydride to form 2-acetylcyclohexanone by reaction with acidic
anhydride.
Introduction
Using a Dean-Stark apparatus, 2-acetylcyclohexanone is formed from pyrrolidine and
cyclohexanone. To collect water from a reactor, Dean-Stark apparatus is used. For continuous
removal of the water produced during the preparation of 2-acetylcyclohexanone, it is used with
a reflux condenser and a batch reactor. Toluene and water are azeotropes. The density of water
and toluene can be separated instead of distillation in an azeotrope because both are isotropic
solvents. Due to its lower density, toluene travelled to the top of the reaction vessel and reentered it, while water was collected in the trap. Many reasons can be given for the desire to
collect water from a reaction, including the fact that removal of water drives equilibrium.
Figure 1: Dean-stark trap
When a ketone or an aldehyde reacts with an acid and a secondary amine, enamines are formed.
The protonation of the carbonyl activates it and makes it more capable of being attacked by a
neutral nucleophile such as N of the secondary amine, where the carbonyl carbon can be a
powerful electrophile by weakening a C=O bond [4]. Cyclohexanone, a carbonyl molecule,
interacts with pyrrolidine, a secondary amine, to generate enamine. To create a bond with the
carbon of the ketone carbonyl on cyclohexanone, the pyrrolidine functions as a Lewis base.
The enamine will be physically separated from the reaction mixture through azeotropic
distillation to prevent the reaction from being reversible. Amines are more nucleophilic and
have a higher boiling point because of their cyclic structure, which allows for the synthesis of
enamine by heating. The basicity, sterical hindrance, and type of the carbonyl group of the
secondary amino group all have an impact on the rate at which enamines are produced [5].
After that, acetic anhydride acylates the enamine. Carbon-carbon bonds are created by
acylation in compounds. Due to their nucleophilic nature, -carbons react with electrophile. As
carbonyl compounds like aldehyde and ketone are difficult to convert to their anion by
removing hydrogen from their -carbon due to their high pKa value, there is a chance of side
products and side reactions. Enamine, a good nucleophile, is utilized in this experiment to
reduce the side reaction. Enamine was created by alkylating a secondary amine with the ketone
pyrrolidine. P-Toluene sulfonic acid is the catalyst that the reaction needs [6]. The enamine
reacts with the acetic anhydride to form 1-pyrrolidinocyclohexene (the intermediate) The
intermediate (1-pyrrolidino-1-cyclohexene) reacts with water to form final product 2acetylcyclohexanone. [6]
Experimental procedure
PART A (week 1)
5.0 ml of cyclohexanone, 4.0 ml pyrrolidine, 0.11 g toluene-4-sulfonic acid and 40 ml toluene
were added into a 100 ml round bottom flask with the addition of three anti-bumping granules.
The Dean and Stark apparatus were fit to the flask, and the reflux condenser protected with a
calcium chloride drying tube fit to the top of Dean and Stark apparatus. The mixture was heated
using a heating mantle, and the vigorous reflux of toluene and the water being collected in the
tap took place. The reflux was maintained for 40 minutes. A solution of acetic anhydride was
prepared by mixing 4.5 ml of acetic acid with 10 ml of toluene. The Dean and Stark apparatus
were removed and allow the solution to cool. The condenser was reassembled with a receiver
and a receiving flask for distillation with a still head and the thermometer fitted with the still
head. The flask was reheated to ensure that the excess pyrrolidine and water is distilled off. The
distillation process was carried out until the temperature of the solution reached 110 ℃. The
heat was removed, the flask was only containing toluene solution of the enamine was allowed
to cool. After all the apparatus had been removed, acetic anhydride solution was added whilst
stirring. The mixture was further stirred for 15 minutes. 5 ml of water was added to the flask,
a reflux condenser was fitted onto the round bottom flask and the mixture was heated under
reflux for 30 minutes with time taken as the solution starts to boil. The flask then stoppered and
stored safely for the next practical session.
PART B (week 2)
After reflux, the mixture was transferred into a separating funnel containing 10 ml of water.
The funnel was shaken to separate the organic layer from aqueous layer of the solution. The
organic layer was washed three times with 10 ml of HCl (3 M), followed by 10 ml of water
and dried over MgSO4. The drying agent was the filtered off and the solution was pre-weighed.
The mixture was returned to a vacuum distillation set whereby the toluene was then distilled
off until it reaches the boiling point of 110 ℃. And the flask was re-weighed to obtain the yield
of the product.
Results
Preparation of Enamine
Figure 4: mechanism of formation of an enamine by reaction of pyrrolidine with cyclohexanone
Preparation of 2-acetylcyclohexanone
Figure 5: reaction mechanism of formation of 2-acetycyclohexanone by reacting enamine with
acetic anhydride.
Calculations
Pyrrolidine
Molar Mass: 71.11 g mol-1
Volume Measured: 4.0 ml
Density: 0.866 g ml
P = m/v
m= density × volume
Mass = 0.866 g ml-1 x 4.0 ml
= 3.464 g
Number of Moles = m/MM
= 3.464 g ÷ 71.11 g mol-1
= 0.04871 moles
Cyclohexanone
Molar Mass: 98.15 g mol-1
Volume Measured: 5.0 ml
Density: 0.948 g ml 1
m= density × volume
Mass = 0.948 g ml-1 x 5.0 ml
= 4.740 g
Number of Moles = m/MM
= 4.740 g ÷ 98.15 g mol-1
= 0.04830 moles
Balanced Equation: C6H10O + C4H9NO→ C10H17NO + H2O
Therefore, the limiting reagent using a 1:1 ratio is Cyclohexanone.
Theoretical mass = 0.04830 moles × 140.08 g mol-1
= 6.77 g
2-Acytylcyclohexanone
Molecular Formula: C8H12O2
Molecular Mass: 140.08 g mol-1
Theoretical yield: 6.77 g
Actual Yield: 4.35 g
% Yield = Actual Yield / Theoretical × 100
= (4.35 / 6.77 g) × 100
= 64.25 %
Discussion
The objective of this experiment was to create 2-acetylcyclohexanone using an acid catalysed
addition-elimination process between cyclohexanone and pyrrolidine and an acylation reaction
between acidic anhydride and enamine. The reflux condenser and Dean Stark apparatus were
both used to successfully produce 2-Acytylcyclohexanone. These devices were designed to
make it easier to remove the water that was produced during the reaction. Cyclohexanone was
identified as the limiting reagent based on the data. Cyclohexanone was discovered to contain
0.04830 moles. Accordingly, a percentage yield of 64.25% was obtained between the product's
theoretical mass of 6.77 g and its actual mass of 4.35 g, indicating that some errors were made
during the experiment. Little of the organic layer was left in the storage beaker after the
experiment, and some of the product may have been distilled off along with garbage.
Additionally, given that the purification process was carried out at a high temperature, some of
the products may have been lost. We may have performed numerous extractions with smaller
amounts as opposed to one with a high volume of extractant to improve our results.
Conclusion
The aim was to prepare of 2-acetylcyclohexanone by means of an enamine formed by an acid
catalysed addition-elimination reaction from pyrrolidine and cyclohexanone. It can be said that
the experiment was moderately successful, since the product was successfully synthesized
however the percentage yield was low compared to theoretical yield which makes our results
less ideal and our experiment less successful as a percentage yield of 64.25 % was obtained.
References
1. "Dean–Stark Apparatus". University of Southampton, University of Birmingham,
University of Nottingham, and University of Sheffield. Archived from the original on
8 September 2011. Retrieved 17 November 2011.
2. Chem 320 practical manual, pg. 15-16.
3. Augustine, R. L., and Caputa, J. A."Ll 1.9-2-0ctalone." Organic Syntheses, Coll. Vol.
5 (1973): 869. Cook, A. G., ed. Enamines: Synthesis, Structure, and Reactions. New
York: Marcel Dekker, 1969. Dyke, S. F. The Chemistry of Enamines. London:
Cambridge University Press, 197.
4. Mundy, B. P. "The Synthesis of Fused Cycloalkenones via Annellation Methods."
Journal of Chemical Education, 50 (1973): 110
5. Stork, G., Brizzolara, A., Landcsman, H., S zmuszkovicz, J., and Terrell, R. "The
Enamine Alkylation and Acylation of Carbonyl Compounds." Journal of the American
Chemical Society, 85 (1963): 207