EXPERIMENT 3 : ESTERIFICATION REACTIONS OF VANILIN : THE USE OF NMR TO DETERMINE A STRUCTURE

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CHM 556

ORGANIC CHEMISTRY (II)

EXPERIMENT 3 :

ESTERIFICATION REACTIONS OF VANILIN :

THE USE OF NMR TO DETERMINE A

STRUCTURE

Lab group : ASB3Ag

Lecturer’s name : Prof Assoc. Zurina Binti Mahmud Date of the experiment : 16 October 2014

Date of submission : 27 November 2014

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1. To investigate the reactions between vanillin and acetic anhydride under two conditions, basic and acidic condition.

2. To propose mechanism that will explain why the reaction proceeds differently under basic and acidic conditions.

3. To determine the melting points and the structure of product by using NMR and IR spectra.

Introduction :

Figure 3.0 : product when reacted in acidic and basic condition

Vanillin, (4-hydroxy-3-methoxybenzaldehyde), multifunctional compound that reacted with acetic anhydrite under acidic or basic condition to formed different products that is ester 1 and ester 2 as shown in the figure 3.0. One of the product is a monoester, formed by reaction at the phenol OH group in vanillin. The other is a triester, with one ester forming at the phenol OH group and two esters forming at the aldehyde group. The reaction of vanillin with acetic anhydride in the presence of base is an example of the esterification of a phenol. The product, which is a white solid, can be characterized easily by its IR and NMR spectra.It is expected to get the same compound in base reaction but the spectrum shows different compound formed when reacted under acidic condition.

Apparatus : 1. 250 ml Erlenmayer flask 2. Rubber stopper 3. Buchner funnel 4. Vacuum filtration 5. Measuring cylinder Chemicals : 1. 1.50 g vanillin 2. 25 ml 0f 10% NaOH 3. 30g crushed ice 4. 4 ml acetic anhydride

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5. 5 ml ice-cold water 6. 95% ethyl alcohol 7. Hot-water bath 8. 1.0 M sulphuric acid Procedure :

4- Acetoxy- 3- Methoxybenzaldehyde (Vinillyl Acetate) was prepared by 1.5g of vanillin was dissolved in 25 ml of 10% sodium hydroxide in a 250 ml Erlenmeyer flask.Then 30g of crushed ice and 4 ml of acetic anhydride are added. After that, stopper the flask with a clean rubber stopper, and the mixture was shaked several times for 20 minutes. After adding acetic anhydride, it was noted that a cloudy, milky white precipitate was formed immediately.In addition, the precipitate formed was filtered using Buchner funnel and the solid was washed with three 5 ml portions of ice-cold water. The solid was recrystallize from 95% ethyl alcohol. The solid was dissolved by adding small portions of hot 95% ethyl alcohol. If the solid dissolves, no more solvent is added. But if the solid has not dissolved, another portion of boiling solvent is added, as before, and the process is repeated until the solid dissolves. After all the solid have been dissolved, the solution was filtered into another conical flask. The flask that contains crystal was put in a beaker that had ice water bath for 10-15 minutes at room temperature. The flask was scratched with a glass rod. The crystal was collected by vacuum filtration using a Buchner funnel. The crystal was rinsed with a small portion of cold solvent. The crystals were dried, weight, and the percentage yield was calculated. The melting point, IR and NMR were obtained.

In esterification of vanillin in the present of acid site, 1.5g of vanillin was dissolved in 10 ml of acetic anhydride in a 125 ml Erlenmeyer flask. Magnetic stir bar was placed in the flask, and the mixture was stirred at room temperature until the solid dissolves.Then, 10 drop of 1.0M sulphuric acid was added to the reaction mixture.Stopper the flask, and the mixture was stirred at room temperature for 1hour. The flask was cooled in an ice water bath for 4-5 minutes at the end of reaction. 35 ml of ice-cold water was added to the mixture in the flask. The flask was stopper tightly and shake the flask vigorously. The product was filtered and washed with three 5 ml ice-cold water. The crude product was recrystallizing from hot 95% ethanol. The recrystallization step was repeated as mention in above procedure. The crystal was allowed to dry. The dried crystals was weighed and the percentage yield was calculated. The melting point, IR, and NMR were obtained.

Result :

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Mass of vanillin 1.5061 g

Mass of empty petri dish 17.4340 g

Mass of petri dish + crystal 18.1991 g

Mass of crystal 0.7651 g

Melting point of crystal 79.0oC

Acid condition :

Mass of vanillin 1.5009 g

Mass of empty petri dish 16.9932 g

Mass of petri dish + crystal 18.5114 g

Mass of crystal 1.5182 g

Melting point of crystal 91.0oC

FTIR result :

Compound (C=O-OR) /cm-1 (C=O)/ cm-1 (O-H)/ cm-1

Basic condition 1750.99(Ester)

1207.21 (Acetate) 1691.09(Aldehyde) 3422.43(Alcohol) Acid condition 1751.60 (Ester)

1206.74 (Acetate) 1690.32 (Aldehyde)

-Observation :

When preparing vinyllyl acetate, cloudy white and milky precipitate of product was formed. On the other hand, in esterification of vanillin in the presence of acid, the solution turns to purple orange after 1 hour.

Calculation :

Mole of vanillin : mass of vanillin/molar mass of vanillin =1.5061 g/152.15g/mol

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Mole of acetic anhydride : (volume x density) / molar mass of acetic anhydride =(10 ml x 1.082 g/ml) /102.09 g/mol

=0.1058 mol So, the limiting reactant is vanillin

For the reaction with basic product,

Theoretical yield : mol of limiting reactant x molar mass of product =9.8988 x 10-3 mol x 194 g/mol

=1.9204 g Actual yield : 1.0056 g

Percentage yield : (Actual yield/ Theoretical yield) x 100% =(1.0056 g/1.9204 g) x 100%

=52.36%

Percentage error of acidic reaction = (theoretical yield−actual yield )theoretical yield X 100

=

1.9204−1.0056

¿ ¿

1.9204 X 100 = 47.64%

For the reaction with acidic product,

Theoretical yield : mol of limiting reactant x molar mass of product =9.8988 x 10-3 mol x 296 g/mol

=2.9300 g Actual yield : 1.5182 g

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Percentage yield : (Actual yield/ Theoretical yield) x 100% =(1.5182 g /2.9300 g) x 100%

=51.82%

Percentage error of acidic reaction = (theoretical yield−actual yield )theoretical yield X 100

= (2.9300−1.5182)2.9300 X 100 = 48.18%

Discussion : In this experiment,

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In this experiment 3, the percentage yield of pure product in basic condition is 52.36% and for the acidic condition is 51.82%. The yield seems very small because the product was lost when we transferred it into filter paper during filtration. Another error is because we did not scratch the flask with carefully to initiate crystallization. The melting point for reaction under basic condition is 79°C while under acidic condition is 91°C. These melting points is under literature range values (base is 77°C-79°C) and (acid is 90°C-91°C).

For the mechanismof the basic condition, the acetic anhydride plays the part of the electrophile, undergoing nucleophile attack by the alcohol when an anhydride reacts with an alcohol for both acidic and basic conditions. The vanillin molecule has several functional groups, among them alcohol, ether, and aldehyde. The base-catalyzed reaction is a straightforward esterification and does not produce any other significant products because esterification stops at the ester. However, the acid-catalyzed esterification does not form only the ester. It forms the ester, but this ester continues to react because there are other functional groups present in the molecule that can react with the anhydride under base or acid conditions.

For esterification reaction of vanillin under acidic condition, vanillin react with acetic anhydride to produce vanillin triacetate while under basic condition, it produce vanillin acetate. These product formed was confirmed by using IR and NMR. The NMR showed that product formed under basic is vanillin acetate and under acidic is vanillin triacetate. For basic condition, one hydrogen is present at 10 ppm and this showed that the product formed consist of aldehyde. In acidic, this value is absent, means that product formed does not contain aldehyde group. In basic, there are present in hydrogen but three hydrogen at 2.3 ppm while in acidic is nine hydrogen.So, base contain only one ester while acid contain three ester groups. At 3.9 ppm, products in base and acid contain same number of hydrogen which is three hydrogen. These showed that the presence of –OCH3. At 7.5 ppm, there are three hydrogen present both in basic and acidic. These showed that the presence of hydrogen with aromatic ring. Based on the spectrum, we can conclude that the functional group of the product that produced is ester.

The functional group for both acid and basic product has been determined using IR spectrum. From the basic IR spectrum, there are (C=O-OR) group which present at the peak of 1750.99cm-1(Ester) and 1207.21cm-1 (Acetate) and for acidic condition is 1751.60 cm-1 (Ester) and 1206.74 cm-1 (Acetate).Besides, there are also (C=O) group which at frequency 1691.09 cm -1 (Aldehyde) for basic and 1690.32cm-1 (Aldehyde) in acidic condition.In addition, there is present in O-H group but only for basic condition that is 3422.43cm-1.

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The reaction between vanillin and acetic anhydride under two conditions are successfully investigated. .The products formed is determined using IR, NMR and melting point comparisons. The mechanism for products formed is successfully drawn. The percentage yield of product under basic condition is 52.36% and for the acidic condition is 51.82%. The experiment goals were achieved.

References:

[1] Laboratory textbook: Pavia, Lampman, Kriz and Engel, Introduction to Organic Laboratory Techniques 3rd Edition, Page 49

[2]Vanillin, http://en.wikipedia.org/wiki/Vanillin ,retrieve on 7 April 2013

[3]Acetic anhydride, http://en.wikipedia.org/wiki/Acetic_anhydride,retrieve on 7 April 2013 [4]Esterification reaction of vanillin,

http://www.lhup.edu/mmaresch/Chem430/CH430Lab/vanillin.htm, retrieve on 7 April 2013

[5]Experiment 2 ,

http://www.chem.moravian.edu/~rdlibby/_211-212Chem-PDF/Laboratory/Experiments/212-08Lab/Expt2-AcylSub/_Expt_2_AcylSub-Handout-wk1.pdf ,

retrieve on 7 April 2013

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