The Wittig Reaction of Ester Stabilized Ylides
Abstract: The purpose of this experiment was to investigate a carbon-carbon bond formation. P-nitrobenzaldehyde and phosphonium salts made in the previous lab session were used during the investigation. The reaction was conducted for 18 minutes under reflux in the presence of ethanol. A stabilized 5-trans ylide was synthesized. The purification of the crude product was performed using a vacuum filter. The result was a thick, off white solid (1.331g, 145.15% yield). Analysis of the data was performed using the H1NMR.
Chemical Equation:
Calculations:
C7H5NO3 + C22H22O2P à C11H12NO4 + C18H15PO
Limiting reagent Theoretical yield Percent yield
The mass of P-nitrobenzaldehyde used for the experiment was divided by its molecular weight. Subsequently, the same was done for the phosphonium salt. The reaction ratio was 1:1. The limiting reagent was P-nitrobenzaldehyde The theoretical yield for C11H12NO4 was obtained by converting grams of C7H5NO3 to grams of C11H12NO4. Thus the yield for C11H12NO4 was 0.917g % yield= (actual/theoretical) x 100
Final mass=1.331 g (actual mass)
% yield= (1.331g / 0.917 g) x 100
= 145.15%
Discussion:
While experimenting, the mixture was stirred at room temperature for about seven minutes. The color of the solution was dark yellow. After the reflux process, the solution changed color to brown. Vacuum filtration on the mixture yielded an off-white grayish solid.
Figure 1: Full spectrum of NMR (0-10 ppm)
This is an NMR spectrum illustration of all the peaks and integration from the Wittig reaction’s final product.
Table 2
Label Chemical shift (ppm) Splitting pattern Relative integration # of hydrogens
HA 1.2082 triplet 3.0000 3
HB 1.3344 triplet 0.9256 2
HC 6.5474 Doublet 0.2995 1
HE 7.6649 Overlapping triplet 0.7847 2
HF 7.7119 Singlet 0.1370 2
HD 8.2298 Doublet 0.5939 1
The 1H NMR spectrum showed six peaks of the unknown ylide. These peaks were a 3H triplet at 1.2082 ppm, 2H triplet at 1.3344 ppm, 1H doublet at 6.5474 ppm, 2H overlapping triplet at 7.6649 ppm, 2H singlet at 7.7119 ppm, and 1H doublet at 8.2298 ppm. A saturated methyl caused the formation of the peak at 1.2082 ppm, suggesting a correspondence between hydrogen and HA on the reaction scheme. The triplet splitting denotes the presence of two adjacent hydrogens and a neighboring saturated methylene group. This saturated methylene region is the triplet at 1.3344 ppm, and the splitting indicates a bond between the methyl group and HA. The HA peak is similar to HB. In the vinylic region, the apex at 6.5474 ppm corresponds to HC due to the presence of 1 neighboring hydrogen. The aromatic area has a peak at 7.6649 ppm, 7.7119 ppm, and 8.2298 ppm. The creat at 7.6649 ppm correlates with HE while that at 7.7119 correlates with HF. The singlet splitting indicates there are no neighboring hydrogens. The peak at 8.2298 ppm corresponds with HD due to a nearby aromatic ring. The splitting pattern also suggests the availability of one adjacent hydrogen, which is across the double bond corresponding to HC. The resulting product is a 5-trans product of a stabilized ylide.
Figure 2
Table 2
Hydrogen Constant Z gem Z cis Z trans d
Ha 5.25 +1.35 +1.13 +0 7.73
Hb 5.25 +1.10 +0.37 +0 6.72
The theoretical ppm calculations were computed for the hydrogens on the trans molecule.
Figure 3: NMR spectrum (6.5-7.8 ppm)
The appearance of a doublet at approximately 6.55 ppm and 7.65 ppm shows that the NMR spectrum supports the theoretical ppm calculations.