Sciencemadness Discussion Board

Amateur route from R-OH to R-Cl

thors.lab - 27-10-2020 at 07:22

As far as I know this reaction can be done with thionyl chloride or phosphorous trichloride, both of which are really hard to get and rather dangerous. Are there are any amateur routes for this reaction?

DraconicAcid - 27-10-2020 at 07:26

Depends on the R group. A tertiary alcohol can usually be converted to a chloride just with cold concentrated HCl.

Tsjerk - 27-10-2020 at 07:35

Or benzyl alcohol, which is also easily converted with HCl.

teodor - 27-10-2020 at 07:36

HCl + ZnCl2 + reflux + good mixing also works for some primary and secondary alcohols.

thors.lab - 27-10-2020 at 08:47

Quote: Originally posted by DraconicAcid  
Depends on the R group. A tertiary alcohol can usually be converted to a chloride just with cold concentrated HCl.


I was thinking primary or secondary alcohols.

thors.lab - 27-10-2020 at 08:50

Quote: Originally posted by Tsjerk  
Or benzyl alcohol, which is also easily converted with HCl.


Due to resonance stabilization in Sn1 pathway I assume? Useful, but if we don't have the sn1 pathway available... what do we do?

Steam - 27-10-2020 at 09:32

Depending on what exactly you were working with you (if it obeyed Markovnikov or not) might be able to do an elimination reaction to form a alkene then treat it with the acid to from your product. You can influence the outcome with the introduction of peroxides in the reaction (see peroxide effect). If you provide a bit more information about what you are working with we could give more detailed answers.

Also for Benzyl alcohol, it is absolutely due to resonance stabilization. The reason is due to allylic carbon stabilization. Recognizing allylic carbon is a really handy tool when working on synthesis schemes.

thors.lab - 27-10-2020 at 11:05

Quote: Originally posted by teodor  
HCl + ZnCl2 + reflux + good mixing also works for some primary and secondary alcohols.


For some — whats the criterion here? Looks appealing since ZnCl2 and HCl are no problem to get.

thors.lab - 27-10-2020 at 11:08

Quote: Originally posted by Steam  
Depending on what exactly you were working with you (if it obeyed Markovnikov or not) might be able to do an elimination reaction to form a alkene then treat it with the acid to from your product. You can influence the outcome with the introduction of peroxides in the reaction (see peroxide effect). If you provide a bit more information about what you are working with we could give more detailed answers.

Also for Benzyl alcohol, it is absolutely due to resonance stabilization. The reason is due to allylic carbon stabilization. Recognizing allylic carbon is a really handy tool when working on synthesis schemes.


Thanks! I'm not working with any particular product here, this is theoretical. I've had to abandon ideas for projects in the past due to this problem (can't recall any off the top of my head right now), so it would be nice to figure out a way around it.

teodor - 27-10-2020 at 11:11

Quote: Originally posted by thors.lab  

For some — whats the criterion here? Looks appealing since ZnCl2 and HCl are no problem to get.


Just look in Vogel's "Practical organic chemistry", "Alkyl Halides". I did this route for n-butyl chloride, sec-butyl chloride and iso-amyl chloride. The yield of sec alcohol is very depending on mixing and is almost nothing without continuous vigorous (magnetic) stirring, because the mixture forms 2 layers. For n-butyl chloride I did it without any additional stirring.

Edit: also I changed the step "wash with NaOH" to "wash with NaHCO3". I was a bit puzzled why it was NaOH in the book.

[Edited on 27-10-2020 by teodor]

Tsjerk - 27-10-2020 at 12:51

Bromides are usually easier to make with in situ HBr and the short chain bromides are easier to condens compared to the chlorides. Depending on what you want to do with them the bromide might be worth considering.

Chemi Pharma - 27-10-2020 at 14:26

@Thors.lab, you can use also the TCCA/triphenyl phosphine route or use the cyanuric chloride/DMF route easily and with good yields. Papers attached.

Attachment: Alcohols to Chlorides with cyanuric chloride and DMF.pdf (54kB)
This file has been downloaded 271 times

Attachment: Alcohols to Alkyl Chlorides with TCCA and Triphenylphosphine.pdf (26kB)
This file has been downloaded 286 times

clearly_not_atara - 27-10-2020 at 15:00

If the resulting alkyl chloride is soluble in water, you might be able to use an iodide (or bromide) salt catalyst, since I- is a stronger nucleophile than Cl-, so performs the first Sn2 faster:

ROH2+ + I- >> RI + H2O

RI + Cl- <> RCl + I-

The second reaction is an equilibrium which usually weakly favors chloride but can be disrupted by solubility differences as in the Finkelstein reaction. However, the equilibrium will not be established if the alkyl iodide is not soluble in water.

[Edited on 27-10-2020 by clearly_not_atara]

Corrosive Joeseph - 27-10-2020 at 16:40

https://tinyurl.com/yy4ynfhb

https://tinyurl.com/yydl9kjl



/CJ

Attachment: A Systematic Study of the Preparation of Alkyl Chlorides from the Corresponding Alcohols.pdf (512kB)
This file has been downloaded 320 times

Cou - 2-11-2020 at 23:00

Alkyl chlorides and alkyl bromides are often carcinogenic. Use gloves and a lab coat, a respirator with organic vapor cartridges, and a heavy duty fan. Leave used glassware to sit outside for a day or two (to let alkyl halides evaporate) before bringing it inside for washing.