Preparation of haloalkane Essay

Published: 2020-02-19 19:20:20
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Introduction: In this experiment, 2-chloro-2-methylpropane will be prepared from methylpropan-2-ol and hydrochloric acid. This reaction takes place at room temperature as methylpropan-2-ol is a tertiary alcohol which undergoes substitution very readily. Zinc chloride could be added to be a catalyst to increase the reaction rate, but for tertiary alcohol the reaction rate is already fast enough. The equation of the reaction is: The synthesis is a nucleophilic substitution reaction. The OH group is being substituted by a chlorine ion.

Purification process includes removal of acid, dehydration and distillation. The product is purified by using the separation and removing the excess HCl with saturated sodium hydrogencarbonate solution followed by dehydrating with anhydrous sodium sulphate and finally distillation. Apparatus and chemicals: Apparatus: Separation funnel with stopper, 10cm3 and 25cm3 measuring cylinders, electronic balance, stands and clamps, 0-100oC thermometer, quick-fit apparatus for distillation, Bunsen Burner, tripod, wire gauze, boiling tubes with stopper, anti-bumping granules, safety spectacles.

Chemicals: 9cm3 of 2-methylpropan-2-ol 2g of anhydrous sodium sulphate granules 20cm3 concentrated hydrochloric acid 10cm3 saturated sodium hydrogencarbonate solution Precautions: 1. 2-chloro-2-methylpropane and 2-methylpropan-2-ol are flammable. So, these liquids must be kept away from direct flame. Flammable 2. Concentrated hydrochloric acid is very corrosive and there are HCl fumes above the concentrated HCl solution, so we should wear safety spectacles during the whole experiment and transfer of acid should be done in fume cupboard.

Procedures: Part 1: Reaction and purification 1. 9cm3 of 2-methylpropan-2-ol was measured with the measuring cylinder. 2. 20cm3 of concentrated HCl was measured using another measuring cylinder in a fume cupboard. 3. The 2-methylpropan-2-ol was transferred into a separation funnel. 4. Concentrated HCl was added to the separation cylinder for about 3cm3 at a time. 5. The funnel was stoppered and was inverted a few times after each addition. 6. The stopper was loosened briefly to release pressure.

7. The whole setup was placed in the fume cupboard for about 20 minutes after adding all concentrated HCl. 8. The lower layer (aqueous layer) was then discarded. 9. Sodium hydrogencarbonate solution was added 2cm3 at a time into the separation funnel in order to neutralize any excess hydrochloric acid. 10. The funnel was shaken gently after each addition and the stopper was frequently loosened to release the pressure. 11. The addition was stopped until no more gaseous bubbles were observed.

12. The lower (aqueous) layer was then discarded. 13. Three spatula-measures of anhydrous sodium sulphate were added to a boiling tube. 14. The remaining organic layer in the separation funnel was poured from the top to the boiling tube. 15. The boiling tube was stoppered and was shaken gently. 16. Another clean boiling tube was weighed with a stopper and the organic liquid was poured to that boiling tube. 17. The boiling tube was weighed again with stopper and the organic liquid.

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