[tuan12c1]

let me set up the situation first

RXN 1:  POCl3 plus cyclohexanol in pyridine @ 0 degrees celcius yields 1-cyclohexene (via E2)

RXN 2:  PCl3 plus cyclohexanol in pyridine when heated yields 1-chloro cyclohexane (via Sn2)

here's a few quick questions i suppose,

why in reaction 1 at 0 degrees, is the elimination product formed (the alkene) when the temperature should favor the substitution product (the alkyl chloride)?

Why in reaction 2 when heated, the substitution product is formed (the alkyl chloride)? again with the question in mind, why isn't the elimination product formed as it should be favored by the high temperature?

and the more important questions and the one my professor and i want to look into, why ISN'T the substitution product formed in the first reaction? it has the lower temperature (which should favor substitution over elimination) and in both mixtures, chloride ion in present (from being displaced for the P in both cases to form the intermediate) and why ISN'T the elimination product formed in the solution that was heated?

if you have any empirical data to show why these reactions behave the way they do, please provide as much information as you can, sparing no information that seems above my level of knowledge. (if i don't know what you're saying or what you mean, i'll look it up, ask professors and get involved more as this is pretty interesting to me)

and lastly, if there has been nothing to show why this is, don't steal my undergrad research idea as this is something i'd like to do to get my BS in Chem. 

thanks for any input/insight,

[orgopete]

If this was a primary alcohol, I think both conditions would greatly favor substitution. If it was a tertiary alcohol, then both would favor elimination. The example is a secondary alcohol and I would expect both could and would form. I thought the products would have been reversed. Heating results in elimination. Heating chlorocyclohexane with pyridine should result in elimination. However, despite the conditions seeming to be similar, they may not be. The molar ratios of reagents are not listed, nor are any quantitive results, the yields, or amounts of by-products.

I think as described, this could be a good undergrad project. I think the first objective of a research project would be to verify the results. For papers to become accepted to Organic Synthesis, another group of chemists have to verify the procedures. For a publication, that does not happen. As a research project, I predict that these reactions will not provide the indicated products in anything like the extremes of elimination for the first and substitution for the second. Even a simple change in stoichiometry could sway the results, for example a catalytic amount of pyridine in the first and pyridine as solvent in the second. I say go for it.