Re: Cyclohexane reaction with chlorine?

The biggest puzzle to me about this question is why you are asking it. 
Cyclohexane is an alkane, and even though it is a cyclic one, it mostly 
undergoes fairly ordinary alkane reactions. Here is what happens with a 
reaction under the conditions you describe (I will use an asterisk * to 
indicate a free radical reactive species with an unpaired electron:

(1) Chlorine molecules get broken up into chlorine atoms by the light:

Cl2 --> 2 Cl*

(2) A chlorine atom steals one of the hydrogen atoms bonded to a carbon 
atom:

Cl* + C6H12 --> HCl + C6H11*

(3) The cyclohexyl free radical steals another chlorine atom from a 
chlorine molecule

C6H11* + Cl2 --> Cl* + C6H11Cl

Steps 2 and 3 can continue as a chain reaction.

The product is simply C6H11Cl, which is called 'chlorocyclohexane'.

The overall effect of the reaction is simply to substitute a chlorine atom 
for one of the hydrogen atoms in cyclohexane. If there is an excess of 
chlorine present, you can get multiple substitution, because the chlorine 
atom can steal its hydrogen from chlorocyclohexane nearly as easily as from 
cyclohexane itself. The driving force for the reaction is the very strong 
bond that forms between hydrogen and chlorine atoms, and the big energy 
advantage you get in transforming chlorine to hydrogen chloride.

-------------

Now I will make a huge guess. The reaction between cyclohexane and chlorine 
is a fairly ordinary and uninteresting one. I wonder if you were really 
meaning to ask about the reaction between benzene and chlorine.

One reaction that organic chemists sometimes want to do is a chlorine 
substitution reaction on benzene or one of its close relatives

	CH=CH					CH=CH
   /    \				   /    \
 HC      CH    + Cl2 --> HC      C-Cl 	+ HCl
  \\    //				  \\    //
   CH -CH				   CH -CH

benzene + chlorine   --> chlorobenzene + hydrogen chloride

This reaction goes fairly slowly. We use acidic conditions, and often use 
one of a number of possible catalysts. But most importantly, the reaction 
is kept fairly dark. Because if light gets in, a fast reaction occurs that 
goes in quite a different way (and I think this might be the more unusual 
reaction that you are really interested in):

	CH=CH				   	    CHCl -CHCl
   /    \				       /       \
 HC      CH    + 3 Cl2 --> HClC         CHCl 	+ 6 HCl
  \\    //				       \       /
   CH -CH				        CHCl -CHCl

benzene +chlorine --> 1,2,3,4,5,6-hexachlorocyclohexane + hydrogen chloride
         (3 mole)     ('benzene hexachloride')              (6 mole)

This reaction again starts with light breaking up the chlorine molecule:

Cl2 --> 2 Cl*

The chlorine atom simply adds on to a carbon atom in benzene, turning a 
double bond into a single bond, and making the carbon atom at the other end 
of that bond a reactive site with an unpaired electron

	CH=CH				   	CHCl-CH*
   /    \				   /      \
 HC      CH    + Cl* --> HC        CH 	
  \\    //				   \\     //
   CH -CH				    CH - CH

In the second stage, the reactive carbon atom steals a chlorine atom from a 
chlorine molecule

	CHCl-CH*				CHCl-CHCl
   /      \				   /      \
 HC        CH  + Cl2 --> HC        CH 	+ Cl*
  \\      //			   \\     //
   CH -- CH				    CH - CH

The other two double bonds then get filled in with chlorine atoms in much 
the same way. The last molecule shown -- 5,6-dichlorocyclohexadiene -- is a 
very much more reactive molecule than benzene, so the reaction goes all the 
way to the hexachlorocyclohexane product.