[Cait]

  My organic chemistry lab class is learning about synthesizing cyclohexene from cyclohexanol using sulfuric acid as a catalyst. I understand how this reaction occurs, but am having trouble understanding one of the side reactions that may also occur.

   According to the handout given in class, the carbocation (which forms after the hydroxide in cyclohexanol is protonated) is attacked by a bisulfate ion. This results in the bisulfate ion being attached to the cyclohexane (I'm not sure about the name of the compound). 
   
   However, the information shows that this compound can also give rise to cyclohexene. I suppose my question is what causes the bisulfate ion to leave so that the carbocation can undergo elimination? Can the bisulfate ion also be protonated like the initial hydroxide in cyclohexanol so that the bisulfate is a good leaving group?

[zsinger]

Interesting.  I would imagine it has something to do with the strength of ALL acids in solutions (Both molar concentrations AND measurements of the lability risk to lose an H+).  I do not think that once H2SO4 becomes HSO4, it has much of an ability to react with the ring, as it is a big molecule compared to a hydride ion.  Interesting!  Proton transfers are FAST FAST FAST!!!!!  Hope this helps.
                 -Z

[zsinger]

This might Help…..

http://en.wikipedia.org/wiki/Bisulfate#Hydrogen_sulfate_.28bisulfate.29

[spirochete]

   
   However, the information shows that this compound can also give rise to cyclohexene. I suppose my question is what causes the bisulfate ion to leave so that the carbocation can undergo elimination? Can the bisulfate ion also be protonated like the initial hydroxide in cyclohexanol so that the bisulfate is a good leaving group?

The bisulfate ion is a good leaving group even when it has not been protonated. Protonation would make it an even more fantastic leaving group.

What is the chemical property that makes something a good leaving group?

[Cait]

   Ok, I understand now. Because the bisulfate ion is the conjugate base of a strong acid, it is a weak base and thus makes a good leaving group.

    The handout also says that the carbocation can be attacked by the cyclohexene that is synthesized in the experiment, forming either a 1,2-disubstituted cyclohexane or 1,2-disubstituted cyclohexene. It doesn't specify exactly what is attached to the ring in either case. Are there any ideas on how or why this occurs?

[zsinger]

    The handout also says that the carbocation can be attacked by the cyclohexene that is synthesized in the experiment, forming either a 1,2-disubstituted cyclohexane or 1,2-disubstituted cyclohexene. It doesn't specify exactly what is attached to the ring in either case. Are there any ideas on how or why this occurs?

MUCH slower to be attacked, but I suppose, as a matter of EXACT PRECISION, you might get something 1-2 substituted, but VERY VERY little IMO.