C15- Haloalkanes Flashcards
Why add conc HCl slowly (dropwise) to a reaction
Addition of concentrated acid to liquids causes heating.
If the all of the acid was added at once, the temperature of the mixture may become hazardously high.
At the end of the reaction (synthesis of a haloalkane), what impurities contaminate the organic product? How are each of these impurities removed?
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Any unreacted starting product will remain in the aqueous layer, which is run off after the reaction.
Addition of the hydrogencarbonate neutralises any remaining hydrochloric acid, which results in release of carbon dioxide - the gas given off in this washing step. When no more gas is given off, this shows that all hydrochloric acid has reacted.
Anhydrous sodium sulfate removes any traces of water from the organic product.
Finally, the distillation separates the desired product from any organic by-products.
How does the final distillation step allow a check to be made on the identity and purity of the organic product?
The boiling point measured during the distillation gives information about both the identity and the purity of the product.
If the expected boiling point is observed this is an indication that the correct product has been obtained.
If the boiling point is a range, as opposed to a well-defined temperature, this indicates the presence of impurities.
Discuss the factors that can lead to a percentage yield less than 100%.
synthesis of a haloalkane
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a. production of side-products in the reaction
b. incomplete reaction
c. loss of some of the product in the washing steps
d. loss of some of the product in running the liquid off from the separating funnel into the flask, and in decanting the liquid from the flask into the pear-shaped flask
e. loss of product in the distillation.
