Haster syntese

Procedure

100gram (86,2mL) of furfural is placed in a 500mL three-necked round-bottomed flask equipped with a mechanical stirrer, dropping funnel and a thermometer and surrounded by an ice/water bath. The stirrer is started and the furfural i cooled to 5-8ºC. When the temperature has fallen to this range, a solution of sodium hyrocide (83g of a 32,5% aquous solution) is added from a dropping funnel at such rate (ca. one hour) that the temperature does not exceed 15ºC and does not drop below 6-8ºC, in which case the reaction will stop. The rate of addition will depend on the efficiency of the cooling. The stirring is continued for around one hour after the addiotion of the sodium hydroxide solution. Follow the reaction with TLC and use this as a guide to know when to stop the reaction.

During the reaction a considerable amount of sodium 2-furancarboxylate separates in fine scale-like crystals. The reaction mixture is allowed to come to room temperature and water (75mL) is added. The solution is transferred to a separatory funnel and brine (100mL) is added. The aqueous phase is extracted with ether (4 X 100mL). The combined ether fractions are dried with sodium sulfate, and the sodium sulfate is filtered off. The ether is evaporated in vacuo and the residue is distilled under reduced pressure on a standard claisen column. Some ether and water may come over first, and the temperature then rises rapidly to the boiling point of 2-furylcarbinol.

The aqueous solution containing the sodium 2-furancarboxylate contains small amount of ether, which is removed in vacuo using rotovap with the temperature not exceeding 30ºC. The solution is cooled on an ice bath and made acidic to ca. 1 pH by adding concentrated HCL solution with magnetic stirring. 

The 2-furancarboxylic acid crystallizes and is filtered with suction. the crude acid is deeply coulored. For purification it is dissolved in minimum boiling water and treated with decolorizing carbon (6g) and the solution is boiled for about 45 min. The suspension is then filtered hot and the filtrate is cooled on an ice/water bath and the 2-furancarboxylic acid which crystallizes is filtered by suction. The product obtained is light yellow in colour but darkens somewhat by standing.

1. Calculate the theoretical pH of the reaction mixture after the addition of water. 

2. Why is the product mixture extracted with ether? What happens? 

-Det er vel for at adskille de to faser. 

3. Why is HCL not added to the reaction mixture before extraction with ether? What would happen in that case?

Er der nogen, der kan hjælpe mig med at besvare disse spørgsmål. På forhånd tak.