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.