Download Synthesis of a fragrance ester

SYNTHESIS OF A FRAGRANCE ESTER
SHAUN LYNN
J9106574
Abstract
An unknown alcohol was subjected to a nucleophilic acyl substitution reaction (Fischer
Esterification) with acetic acid, using sulfuric acid as a catalyst. It was dried using anhydrous
magnesium sulfate and then purified by distillation, collecting only the centre fraction and
noting the temperature for a boiling point to compare against cited literature. The purified
ester then underwent Transmission IR spectroscopy using a Diamond ATR device and a
refractive index was obtained of both the ester and the unknown alcohol product.
Introduction
Esters are derived from carboxylic acids and alcohols. They are organic functional groups
that form many sweet-smelling compounds. Esters have a general formula of 'R-CO-OR',
where R’ is either an alkyl or aryl group. Esters with a low molecular mass are usually used
as fragrances.
Esters can be formed by two routes, Fischer esterification, which involves reacting a
carboxylic acid and an alcohol in the presence of a strong acid. The reaction is reversible;
hydrolyzing the ester will produce an organic acid and an alcohol.
The second route of creating esters is by alcoholysis. This involves an alcohol reacting with
acid chlorides and acid anhydrides. This type of reaction however is irreversible. (Unknown,
2011)
Esters are less polar than alcohols; however they are still quite soluble in water. Their water
solubility is due to their ability to participate in hydrogen bonding. They act has hydrogen
bond acceptors however, they cannot act as hydrogen bond donors which means they
cannot associate with themselves. The structural flexibility of an ester is due to the rotation
about the C-O-C bond. (Clark, 2011)
Esters have many uses; they are used as synthetic hydrocarbons, lubricants, polymer
synthesis. They are especially used for their fragrances. For instance, methyl salicylate (oil
of wintergreen) is used to flavour toothpaste, chewing gum and confectionary. It also has
medicinal properties, having the ability to relieve rheumatic aches and pains. Benzyl acetate
is used largely in jasmine and gardenia fragrances. Aromatic esters are not all pleasant
smelling, some, such as bitrex, are very bitter tasting and is used as an additive to cleaning
fluids and nail polish removers to act as a deterrent to young children who could ingest
them. Benzyl benzoate however, has almost no odour, is used as a base in many perfumes.
Aim
To prepare purify and identify a fragrance ester
Hazard assessment




Sulfuric acid - Corrosive, reacts violently with water
Acetic acid – Causes burns, flammable and has a highly irritating vapour.
Magnesium sulphate anhydrous – Harmful by inhalation, in contact with skin and if
swallowed.
The unknown alcohol is highly flammable.
Method
Into a round bottomed flask, acetic acid (10cm³) and the unknown alcohol (10cm³) (ID.
SNC4) was added. A few drops of the unknown alcohol was saved in order to aquire a
refractive index nD value at a later time.
A few anti bumping anti bumping granules and sulphuric acid (0.5cm³) were added and the
reaction vessel was swirled in order to ensure a homogenous mixture resulted.
A distillation head with a stoppered side arm, topped by a water condenser was connected
to the flask.
The apparatus was tilted in such a way that the condensed liquid could collect in the side
arm.
The solution was then allowed to heat at reflux for 40 minutes. When the allocated time
was up, the solution was allowed to cool to room temperature. The apparatus was then
tipped slightly, allowing the top layer of collected condensate in the side arm to run back
into the reaction vessel.
The mixture was then poured into a separating funnel and rinsed with cold water (20cm³).
The funnel was shaken, then, the mixture was left to settle and the two layers were allowed
to separate. The lower aqueous layer was then drained.
Aqueous sodium hydrogen carbonate (20cm³) was added to the organic layer in the
separating funnel. The contents were then shaken; carbon dioxide gas evolved and was
released. The funnel was shaken repeatedly shaken until no more carbon dioxide gas
evolved.
The lower aqueous layer was removed and tested with litmus paper. (if the result indicated
the solution to be acidic, the extraction would be repeated with portions of sodium
hydrogen carbonated(20cm³).
The aqueous layer was then discarded and the product ester was poured through the top of
the funnel onto anhydrous magnesium sulphate (2.005g) in a small flask.
The ester was filtered from the drying agent into a small round bottomed flask, it was then
distilled and the centre fraction (94°C – 97°C) was collected into a clean pre weighed dry
flask.
Discussion
The mass of the unknown ester =
5.0271g
The boiling point of the unknown ester =
94°C – 97°C
The refractive index of the unknown ester = nD20 1.385
The refractive index of the unknown alcohol = nD20 1.347
The Dictionary of organic compounds, 6th edition, Chapman and Hall, London, Volume 3(&
Volume 6), 1996 states that n-Propyl acetate has a refractive index value of 1.38200 to
1.38700 at 20.00 °C. With a boiling point of 101.00 to 102.00 °C.
Therefore the Unknown ester is propyl acetate and the unknown alcohol was Propan-1-ol.
The balanced equation for this reaction; the esterification acetic acid with propan-1-ol will
be:𝐶𝐻3 𝐶𝑂𝑂𝐻 + 𝐶𝐻3 𝐶𝐻2 𝐶𝐻2 𝑂𝐻 → 𝐶5 𝐻10 𝑂2 + 𝐻2 𝑂
For acetic acid (AcOH):
𝐷=
𝑀
𝑉
= 𝑀 = 𝐷 𝑥 𝑉 = 𝑀 = 1.049𝑔𝑐𝑚³ 𝑥 10𝑐𝑚³ = 10.49𝑔
10.49𝑔 𝑥
1
= 0.17468 𝑚𝑜𝑙𝑒𝑠
60.00519
𝟏𝟎. 𝟒𝟗𝒈 𝑨𝒄𝑶𝑯 → 𝟎. 𝟏𝟕𝟒𝟔𝟖 𝒎𝒐𝒍𝒆𝒔 𝑷𝒓𝑶𝑨𝒄
For propan-1-ol (PrOH):
𝐷=
𝑀
𝑉
= 𝑀 = 𝐷 𝑥 𝑉 = 𝑀 = 0.8034 𝑔/𝑐𝑚³ 𝑥 10𝑐𝑚³ = 8.034𝑔
8.034𝑔 𝑥
1
= 0.1337 𝑚𝑜𝑙𝑒𝑠
60.095
𝟖. 𝟎𝟑𝟒𝒈 𝑷𝒓𝑶𝑯 → 𝟎. 𝟏𝟑𝟑𝟕 𝒎𝒐𝒍𝒆𝒔 𝑷𝒓𝑶𝑨𝒄
The limiting reagent is therefore Propan-1-ol
Moles are then converted to grams
0.1337 𝑚𝑜𝑙𝑒𝑠 𝑥
60.095
= 8.034𝑔
1
Theoretical yield = 8.034g
5.0271
Percentage yield = 8.0347 𝑥100 = 62.567 %
This reaction is an example of a nucleophilic acyl substitution reaction, also known as
Fischer Esterification. The mechanism for this reaction is:
The transferred proton now gives the oxygen atom on the acetic acid a positive charge, which will be
delocalised throughout the ion.
The positive charge is delocalised over the ion, which can be shown as:
The ester is now formed and the sulphuric acid catalyst has been regenerated.
IR Spectrum Interpretation
The black ring on the spectrum, cirlcling the peak labelled 2970.69cm-1 indicates the
presence of O-H and C-H bonds. This will be present due to the C-H bonds in the ester,l
however the presence of O-H bonds could suggest that some unreacted acetic acid could
still be present.
The green ring cirles the peak labelled 1738.62 this represents the presences of a C=O
stretch. Peak that is always present in ester spectrums.
The red ring circles the peak labelled 1230.07. This peak is assigned to the presence of C-O
bonds, which are also present in esters.
WORKS CITED
Chapman & Hall. (1996). Dictionary of Organic Compounds (6th ed., Vol. 3). London.
Clark, J. (2011, march 31). an introduction to esters. Retrieved march 31, 2011, from Chemguide:
http://www.chemguide.co.uk/organicprops/esters/background.html
Unknown. (2011, 04 01). Organic Chemistry Esters. Retrieved 04 01, 2011, from TutorVista.com:
http://www.tutorvista.com/chemistry/organic-chemistry-esters
Loudon,G. Mark. Organic Chemistry. Oxford: Oxford University Press, 2002
Dictionary of organic compounds, 6th edition, Chapman and Hall, London, Volume 3(& Volume 6), 1996
McMurry, J. (2008). Organic Chemistry. J. McMurry, organic Chemistry . London: Thompson Brooks/Cole.