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2nd January 2017 @ 11:31

The aim of this experiment is to produce 2-piperidinylbenzaldehyde using a SNAr mechanism1. The starting materials being used are 2-fluorobenzaldehyde and Piperidine:

Figure 1: Preparation of 2-piperidinylbenzaldehyde via SNAr.

 Table 1: Table of Reagents used in experiment.

Reagent

Equivalents

Molecular Weight (g/mol)

Density (g/mL)

Moles (mmol)

Quantities

2-fluorobenzaldehyde

1

124.11

 

1.178

2

0.212 mL

Potassium carbonate

 

1

138.205

-

2

0.3014 g

Dimethylforamide (DMF)

-

-

-

-

2 mL

Piperidine

 

1

85.15

0.862

2

0.220 mL

Procedure 

To a stirred solution of DMF (2 mL), Potassium carbonate (0.3014 g, 2 mmol) was added in a flask. 2-fluorobenzaldehyde (0.212 mL, 2 mmol) and Piperidine (0.220 mL, 2 mmol) were added. The solution was heated and left under an air condenser for 12 hours.

 

Figure 2: Reaction mixture before it was left under air condenser to react.

The resulting mixture was burnt orange in colour.

A mini work up was carried out and TLC analysis was undertaken (EtOAc/Pet. Ether 1:1). It showed clear presence of a new product when the resulting mixture was compared to the starting material. Rf values of 0.64 and 0.58 respectively.

The TLC plate was then stained with potassium permanganate which showed a spot present for the resulting product but not the starting material, which also indicated the reaction had taken place.

 

 Figure 3: TLC plate stained with potassium permanganate showing no spot present for A (starting material). The only spots present are for A+B (mixture of starting material and product) and B (product)

The mixture was then extracted into Diethyl ether (3 x 20 mL), the organic phases were combined and washed with Brine (10 mL). The organic phase was then dried (MgSO4), filtered and the solvent removed in vacuo to give the crude material as a yellow-orange solution (0.1074 g)

The crude NMR showed promising results, therefore the product was purified via silica column chromatography. The eluting mixture used was EtOAc/Pet. Ether 1:9.

TLC analysis was undertaken (EtOAc/Pet. Ether 1:1) for each of the 10 fractions obtained, which suggested fractions 3 and 4 contained the product. Therefore, these were combined and dried under vacuo.  The product obtained was a yellow-oily solution.

1H NMR of the product was taken, which showed the presence of the desired product.

 Figure 4: NMR spectra of fractions 3 and 4 combined.

As the yield obtained was low (28%) but it the desired product was successfully synthesised, it was decided that the experiment would be repeated on a larger scale but the equivalents of the reactants would be altered slightly.

References

  1. X. Xia, X. Shu, K. Ji, Y. Yang, A. Shaukat, X. Liu and Y. Liang, J. Org. Chem., 2010, 75 (9), 2893–2902