Synthesis of 1-bromobutane
Flashcard maker : Lily Taylor
What are the three steps in which you can form 1 butanol into 1-bromo butane?
1) constant-boiling hydrobromic acid (47% HBr)
(2) an aqueous solu- tion of sodium bromide and excess sulfuric acid, which is an equilibrium mixture containing hydrobromic acid; or
(3) a solution of hydrobromic acid produced by bubbling sulfur dioxide into a suspension of bromine in water.
Why do you use sulfuric acid on only 1 primary alcohol?
Primary alcohols are more resistant to dehydration and can be converted efficiently to the bromides by the more economical methods
What would be the only case in which a primary alcohol would not work? what can you do?
high molecular weight that they lack adequate solubility in the aqueous mixtures.
Why can’t you use sulfuric acid or secondary and tertiary alcohols?
ulfuric acid at a concentration high enough to dehydrate secondary and tertiary alcohols to undesirable byproducts (alkenes and ethers);
What can you use for the tertiary and secondary then?
The HBr method is preferred for preparing halides of the types R2CHBr and R3CBr.
If you have 1 mole of butanol, how many moles of sodium bromide do you required?
One mole of 1-butanol theoretically requires 1 mole each of sodium bromide and sulfuric acid, but this procedure calls for using a slight excess of bromide and twice the theoretical amount of acid.
Why do you required and excess of sulfuric acid?
. Excess acid is used to shift the equilibrium in favor of a high concentration of hydrobromic acid, the reactive bromine species.
Where we will it shift the equilibrium? to the right (product) or to the left
To the right
What are the byproducts of mixing sodium bromide with sulfuric acid?
1-butene, dubiety ether and starting alcohol
How can you separate the alkene?
How about the other compounds? Why can’t you do simple distillation?
You can’t do distillation yet because they have the same boiling point as thehydrobromic acid
What can you do then?
Do an extraction with concentrated sulfuric acid to remove the other byproducts
What cause the reflux portion of the experiment?
t causes the hydrobromic acid that you created to convert into alkyl bromide (and has water too)
What do you dow with your alkyl bromide?
You need to do a simple distillation and make frequent readings until it reaches 115C
Why such a high boiling point?
Because of the azeotropic distillation of n-butyl bromide with water containing increasing amounts of sulfuric acid, which raises the BP
What do you do after the distillation?
You will do an extraction, add water, shake and you will see that the alkyl bromide will form in the lower layer remove the lower layer, discard the upper layer (water)
Why you then need to add sulfuric acid?
Why you then treat with sulfuric acid?
Then you will have two layers right?
Yes the alkyl bromide (1-bromo butane) and the sulfuric acid that you added, then do an extraction and remove sulfuric acid
How can you know which layer is the organic and which is the aqueous?
ou need to check the solubility if the lower layer is soluble in water is sulfuric acid, discard, if its insoluble its the organic- alkyl bromide (soon to be 1-bromobutane)- In our case the lower layer was the sulfuric acid
Why do you then use sodium hydroxide?
to remove the traces of the sulfuric acid
Do you then do another extraction?
Yes, you then remove the sodium hydroxide by extraction
Why do you have a cloudy mixture after the extraction
Because the 1-bromobutane has excess water
Do you then dry the components? IF SO, with what?
Yes, with calcium chloride. You add calcium pellets to the the cloudy mixture and from cloudy it turns clear
Why do you collect the materia at 99-103 range?
Because 1-bromobutane BP is 101.6C