Wednesday, December 12, 2012

Synthesis of Butyl Benzoate


Intro
The purpose of this experiment was to explore the methods by which a phase transfer catalyst facilitates the synthesis of the ester Butyl Benzoate from Sodium Benzoate and 1-Bromobutance. The full balanced molecular equation for the synthesis is NaC6H5CO2 + CH3CH2CH2CH2Br -> C6H5CO2CH2CH2CH2CH3 + NaBr.

How was it done?
First sodium benzoate was placed into a round bottom flask containing H2O. Next 1-Bromobutane, a boiling stone and Aliquat 336 were added to the same round bottom flask. The round bottom flask was fit with a reflux condenser and was set into a heating mantel attached to a variac set at 45%. Note the joints of the glassware were greased while keck clips and clamps were used to keep the glassware upright and stable. The mantel should be turned on and allowed to run for an hour under reflux conditions.
            After an hour the round bottom flask was removed from the mantel and cooled in room temperature water. The cooled contents were transferred to separatory funnel and the flask was rinsed with dichloromethane, which also went into the funnel. An additional 10 mL of dichloromethane were then added to the separatory funnel. The funnel was gently swirled and inverted the opening the stopcock to release pressure. The mixture was allowed to sit in a ring stand until 2 layers were visible.
            The lower organic layer was drained and placed into a clean labeled Erlenmeyer flask. The aqueous layer was poured out the top and placed into another clean labeled Erlenmeyer flask. The organic layer was transferred back into the separatory funnel where it was washed wit 5 mL of 15% NaCl solution. The lower organic layer was placed into the appropriate Erlenmeyer. Next anhydrous sodium sulfate was added to the Erlenmeyer with the lower organic layer (containing the ether) and was allowed to sit for 15 minutes.
            Meanwhile a 25 mL Erlenmeyer was washed, dried and weighed and Pasteur pipettes were fitted with cotton and prepared (shown left). The Pasteur pipette was used to transfer the organic solution into the newly cleaned Erlenmeyer.
            Next the dichloromethane was removed via a stream of nitrogen air while in a warm water bath.  Measurements of the weight of the beaker with contents were taken till two consecutive measurements are within .03 grams within one another. Once the weight was in the appropriate range the product was prepared for IR and checked for evidence of the product.

Results, Questions, Calculations and stuff like that...

Limiting reactant: There is a 1:1 molar ration of 1-Bromobutane to Sodium Benzoate. The experiment used 2.0 mL of 1-Bromobutane with density 1.27 grams / mL = 2.54 grams of 1-Bromobutane. Compared to the 3.05 grams of sodium benzoate. Hence 1-Bromobutane is the limiting reagent.

Theoretical Yield

__g 1-Bromobutane x 1 mole 1-Bromobutane x 1 mole Butyl benzoate x 178 grams   =  ____ g Butyl benzoate expected
                                    137 grams                  1 mole 1-Bromobutane    1 mole Butyl benzoate
  
Percent Yield

Observed yield     x 100%  = ______%
Expected yield   
 
Infrared spectroscopy absorption bands of significance
Major Absorption peak or band
Suggested reason for peak
Functional group
Strong peaks near 1600 and 1500-1430
C6H5  Benzene ring
Benzene ring
Activity between 1602 and 1782
C=O
Carbonyl
Strong peaks between 1070 and 1274
C-O
Ether
Strong peaks near 2850-2959
C-C-H
Carbon Hydrogen stretching vibration

Carbon-13 Nuclear magnetic resonance imaging results
Peak in ppm
Significance
13.8345
Methyl (CH3)
19.3615
CH2
30.8584
CH2
64.8986
 C-O
76-77
CDCl2
128.3910
Aromatic Carbon
129.6049
Aromatic Carbon
130.6125
Aromatic Carbon
132.8722
Aromatic Carbon
166.7674
 C=O

Proton Nuclear magnetic resonance
Approximate ppm
Splitting
Integration
Group Significance
.99
Multiplet
3
CH3
1.4
Multiplet
2
CH2
1.7
Multiplet
2
CH2
4.3
Triplet
2
CH2 expected to be near electron withdrawing group
7.4
Multiplet
2
In monosubstituted benzene ring
8.0
Multiplet
2
In monosubstituted benzene ring

DEPT analysis
Approximate Peak location ppm
Positive or negative region
Potential significance
11
Positive
CH3
29
Negative
CH2
64
Negative
CH2
128
Positive
CH most likely in aromatic region
130
Positive
CH most likely in aromatic region
132
Positive
CH most likely in aromatic region
 
As indicated by Infrared spectroscopy it is clear that the yielded product obtains a Benzene ring and has activity in regions associated with carbonyl and ether functional groups. The data from the Infrared spectroscopy also suggests that there is a carbon chain in the product. The data from the Carbon 13 Nuclear magnetic resonance imaging results suggests that there is a Carbon double bond with oxygen (C=O) and a Carbon Oxygen single bond (C-O). Absorption peaks near 130 ppm indicate Carbons in an Aromatic ring while the more upstream peaks suggest the presence of CH2 and CH3 most likely in a Carbon chain. Proton Nuclear magnetic resonance and DEPT analysis suggest a monosubstituted benzene ring is in the product and the presence of multiplets in the spectrum suggests that there are neighboring unequivalent Carbons attached to hydrogen and suggests electron withdrawing groups that increase deshieleding. Overall data collected from the spectra support the expected result of Butyl Benzoate being synthesized from 1-Bromobutane and Sodium Benzoate via use of the phase transfer catalyst.


 

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