Question

This procedure was conducted for diethyl n-butylmalonate. The question is: What is the purpose of the tricaprylmethylammonium chloride and why is it used in a nomstoichiometric?

Chapter 42 Malonic Ester of a Barbiturate 541 Into a 5-mL long-necked, round-bottomed flask, weigh 40 mg of tricaprylmethylammonium chloride, 400 mg of diethyl malonate, 350 mg of 1-bromobutane, and 415 mg of anhydrous potassium carbonate. Attach the empty distillation column as an air condenser and reflux the mixture for 1.5 hours (Fig. 42.1). Allow the mixture to cool somewhat; then cool further in ice. Using 2.5 mL of water, transfer the reaction mixture to a reaction tube, shake the mixture draw off the organic layer, and extract the aqueous layer with two 1.5-mL portions of ether. Dry the combined organic extracts over anhydrous calcium chloride pellets, remove the ether solution from the drying agent, and complete the drying of the ether over Dri-Rite (commercial anhydrous calcium sulfate) or molecular sieves. Place the dry ether solutions in a dry, tared 5-mL round-bottomed, long- necked flask and remove the ether by dslation or evaporation in the hood Complete the removal of the ether by connecting the flask to an aspirator. Determine the weight and calculate the yield of product. Analyze the product by thin-layer chromatography (TLC) on silica gel using dichloromethane as the eluent. Compare the product to a sample of authentic, pure diethyl n-butylmalonate and to the starting materials diethyl malonate and bromobutane. The sample must be pure to be used as a starting material in the next reaction. It must be perfectly clear in appearance and absolutely dry. It can also be analyzed by gas chromatography using a Carbowax column at 160°C.

Answer 1

tricaprylmethylammonium chloride is a phase transfer catalyst (PTC).

Diethylmalonate and the 1-bromobutne are organic compounds and K2CO3 is inorganic base (water soluble).

Inorder to maintain contact between the base and the diethyl malonate need to have a phase transfer catalyst.

Without the catalyst the reaction proceeds with very slow rate.

Role of the the PTC is to promote the solubility and is not participating in the reaction, so PTC used in a nonstaichiometric ratio.

Hope you understand.

Good Luck.