The Insect Repellent OFF Issue

This experiment demonstrates the synthesis of the active ingredient containing an amide. The reagent in which this was conducted is the insect repellent “OFF”, N,N-diethyl-mtoluamide. The reagent will be converted to an amide. The methods used in this experiment will be the preparation of an amide and an extraction. The extraction will take place with the use of a separatory funnel. First, m-toluic acid is combined with thionyl chloride to create the main product of acid chloride. Next, the acid chloride is combined with diethylamine to create N,N-diethyl-m-toluamide "OFF". The diethylamine is combined with hydrochloric acid to break down into diethylamine hydrochloride. This multistep reaction aids in successfully performing the methods listed above.

Introduction

This study was performed to study the multistep synthesis of the insect repellent "OFF", N,N-diethyl-m-toluamide. This substance belongs to the class of compounds called amides. The amide to be prepared in this experiment is a Disubstituted amide. That is, two of the hydrogens on the amide - NH2 group have been replaced with ethyl groups. Amides cannot be prepared directly by mixing a carboxylic acid with an amine. If an acid and an amine are mixed, an acid-base reaction occurs, giving the conjugate base of the acid, which will not react further while in solution. However, if the amine salt is isolated as a crystalline solid and strongly headed, the amide can be prepared. Because of high temperature required for this reaction, this is not a convenient laboratory method. Amides are usually prepared via the acid chloride, as in this experiment. In step 1, m-toluic acid is converted to its acid chloride derivative using thionyl chloride. The acid chloride is not isolated or purified, and it is allowed to react directly with diethylamine in step 2. An excess of diethylamine is used in this experiment to react with the hydrogen chloride produced in step 2. The specific purpose of this experiment is to prepare the amide, the insect repellent “OFF”, N,N-diethyl-mtoluamide.

Experimental Procedures

First, place 0.272 g m-toluic acid in a clean, dry 10-mL round bottom flask. Add 0.3 mL of thionyl chloride to the flask. Next, heat the mixture to 90°C for fifteen minutes over a hot plate. After fifteen minutes, remove the flask from the heat and allow it to cool to room temperature. Once cooled, add 4.0 mL of ether anhydride to the mixture, and stir until it is completely dissolved.

Separately, combine 0.66 mL of ice-cold diethylamide and 1.33 mL of Et20. Add this to the reaction mixture dropwise. Stir the mixture for ten minutes.

Extract the two layers, discarding the bottom layer. Add 2 mL of 10% NaOH and extract. Add 2 mL of ether and extract. Add 2 mL of hydrochloric acid and extract. Add 2 mL of water and extract.

Transfer to a preweighed small container, and add sodium sulfate. Record the new mass. Finally, compare it to the IR spectrum.

Results

In the beginning, 0.270 g of m-toluic acid was used. The final result was 0.240 g of the insect repellent “OFF”, N,N – diethyl-m-toluamide. This is a percent yield of 88.9%. There was little error in this experiment.

Discussion

The IR spectrum of the product matches that of the insect repellent "OFF", N,Ndiethyl-m-toluamide. There is a small amount of unreacted diethylamine appearing near 3400 cm', but that can be ignored. Based off the 'H NMR spectrum of the product, it is also a match. The 500 MHz spectrum determined at 20°C shows interesting pattern for the ethyl groups attached to a nitrogen. The two methylene carbon atoms in the ethyl groups appear as a pair of broad peaks between 3.2 and 3.6 ppm, indicating non-equivalence.

Conclusion

Due to the amount of error being relatively low, the experiment did show a large amount of success. The high percentage yield also dictates that the experiment was a large success.

References (Literature cited)

  • Pavia, Donald. 2013. A Microscale Approach to Organic Laboratory Techniques. Fifth Edition. Belmont: Cengage Learning.