Hydrogenation side product: potential mechanisms for C-C bond making In the analysis of the product mixture of a new catalytic hydrogenation  reaction I'm trying out I am getting this side product molecule (in low quantities; less than 1% w/w). 



Is this a likely / explainable side product? What would be a potential mechanism?

I'm skeptical because the C8 increases to a C9. I assumed C-C bond making wasn't a very common occurrence in this sort of reaction? Or is it?

The reaction conditions are fairly mild: 10 barg &amp; 80 C. Somehow I associated this sort of hydrogenation with functional group identity changes &amp; not Carbon-backbone changes. 

Or am I wrong?

More info. Solvent is Methanol. pH is alkaline by small qty. of NaHCO3 initially added. Catalyst is Pd on C.

Edit: Supposing the MeOH solvent reacts with the starting material, would this be the reaction to expect? 



Any mechanism to go from this alcohol-ether to the impurity I'm seeing?
First of all, I would check for impurities in styreneoxide. There is a good chance it was prepared from styrene having some 2-phenylpropylene in it, and this could account for your impurity.  

Other than that, I would think among lines that hydrogenation is usually reversible, so above strong hydrogenation catalys phenylethanol is in equilibrium with corresponding aldehyde and methanol is in equilibrium with formaldehyde. Crotone condensation of said carbonyl compounds with subsequent hydrogenation may account for the impurity you see here.