[Lo.Lee.Ta.]

I am working a problem that wants me to prepare 3-fluoro-1,1,-dimethylcyclopentane using an alcohol.

Well, in my book it says to use PBr3 or SOCl3 when you're dealing with a primary or secondary alcohol.
Only for tertiary alcohols can you use a halogen acid, e.g. HCl

The solution says to add HF with pyridine.
But how could we do that? It looks to me like the carbon attached to the OH is seconday, not tertiary.

The carbon directly attached to the OH has an H substituent. Having 1 H substituent would make it secondary.

Is it really not secondary? Or else, how could this be?

Thanks for your *delete me*

[Hunter2]

Who says you can not use the Hydrogen halides directly? Of course Phosphorous or sulfur halides react more better and higher yield. You component is of course a secondary alcohol before you exchange to fluoride.

[AWK]

Monatshefte für Chemie / Chemical Monthly
September 2005, Volume 136, Issue 9, pp 1579-1582
Practical and General Method for Direct Synthesis of Alkyl Fluorides from Alcohols under Mild Conditions
Babasaheb P. Bandgar, Vinod T. Kamble, Ankush V. Biradar

A variety of alcohols were treated with Ph₃P and KF in CCl₄-DMF at room temperature to afford the corresponding fluorides in very good yields.

[orgopete]

Monatshefte für Chemie / Chemical Monthly
September 2005, Volume 136, Issue 9, pp 1579-1582
Practical and General Method for Direct Synthesis of Alkyl Fluorides from Alcohols under Mild Conditions
Babasaheb P. Bandgar, Vinod T. Kamble, Ankush V. Biradar

A variety of alcohols were treated with Ph₃P and KF in CCl₄-DMF at room temperature to afford the corresponding fluorides in very good yields.

This looks like a modified Appel reaction, http://en.wikipedia.org/wiki/Appel_reaction.

I didn't think and don't think HF/pyridine will give a fluoride. HF is not a strong acid and pyridine/HF is less strong. I think this is simply a fluoride source. I suggest that a bromide, mesylate, or some kind of leaving group be formed first.

[Babcock_Hall]

Orgopete, I am not familiar with these reagents, but your point about having tosylate or something equivalent as a leaving group is well taken.  I wonder, though, if the purpose of pyridine is to produce some fraction of fluoride ion, F^-, as a nucleophile.

[orgopete]

Orgopete, I am not familiar with these reagents, but your point about having tosylate or something equivalent as a leaving group is well taken.  I wonder, though, if the purpose of pyridine is to produce some fraction of fluoride ion, F^-, as a nucleophile.

I presume.