Haloalkanes from Alcohols

hey all.
i just wanted to ask how you get an haloalkane from an alcohol?

according to me revision guide you need phosphorous pentachloride for chloralkane, phosphorous (III) iodide for iodoalkane and sodium bromide and sulphuric acid for bromoalkane.

however, in the mark schemes to past papers, all it says is hydrogen chloride for the chloralkane, and it doesnt even mention phosphorous pentachloride!

so i wanted to know what i should do?

Reply 1

Excalibur

15

It depends on whether the question wants you to make a chloro-, bromo- or iodoalkane. If it doesn't specify then you should really be allowed all three. The question may also ask you which one can be done easily in a lab or something though, in which case the bromine/H2SO4 one may be a bit tricky.

Hm, I guess HCl can be used to make the chloroalkane seeing as HBr is used to convert alcohol to a bromoalkane. I've never heard that one before though.

Reply 2

Eau

15

markfung

hey all.
i just wanted to ask how you get an haloalkane from an alcohol?

according to me revision guide you need phosphorous pentachloride for chloralkane, phosphorous (III) iodide for iodoalkane and sodium bromide and sulphuric acid for bromoalkane.

however, in the mark schemes to past papers, all it says is hydrogen chloride for the chloralkane, and it doesnt even mention phosphorous pentachloride!

so i wanted to know what i should do?

Phosphorous pentachloride is used very often due to fast reaction. HCl would be too slow for primary and secondary alcohols. So HCl would be a bad choice. (http://www.chemguide.co.uk/organicprops/alcohols/halogen.html#top)

Markschemes do not tell you everything. It is just a guideline.

Reply 3

sophiebelle

Although you might use phosphorus pentachloride in real life the OCR syllabus (is that what you are doing?) says to use HCl, though you probably would get it marked correct anyway if you did put phosphorus pentachloride.

Reply 4

Flugtag

OP

Im doing edexcel nuffield. I m wondering that if i put phosphorous pentachloride, would it still be marked correct even though it doesnt say so in the mark scheme

Reply 5

Eau

15

markfung

Im doing edexcel nuffield. I m wondering that if i put phosphorous pentachloride, would it still be marked correct even though it doesnt say so in the mark scheme

What was the question exactly?

Reply 6

Flugtag

OP

C4H9OH-----> C4H9Cl

The Halogenoalkane C4H9Cl can be made from the alcohol C4H9OH.

What reagent could be used to bring about this reaction?

Reply 7

dhugga

1

i also do nuffield and am resitting unit 2 -

u need to add a halide (e.g. potassium chloride) and conc sulphuric acid to get a hydrogen halide (e.g. HCl) This hydrogen halide will react with the alcohol forming a halogenoalkane and water.

Reply 8

sweetiepieh

That is strange because i would have said PCl5 however if for example the alcohol C2H5OH reacts with PCl5 you get C2H5Cl and HCl as a product, maybe thats why the answer was HCl. hmmmm very strange

Haloalkanes from Alcohols

Related discussions

Latest

Trending

Trending

Articles for you