Yes you would also end up with the oxidized methyl group...to the acid. You can separate this from the acetic acid though.
Reactions are usually very specific and even if alternatives were to work there is usually only few reactions which are realistically plausible given the product one desires. This is why I doubt that the wittig reaction would be a good choice (more input later).
CH3Cl + Mg -- CH3MgCl (grinhar)
acetylene + 2CH3MgCl -- ClMg-CC-MgCl + 2CH4
ClMg-CC-MgCl + H2 --- ClMg-CH=CH-MgCl (cat: Pd)
2C6H5CH2Cl + ClMg-CH=CH-MgCl --- The (cis- product) + by product
This simply will not work, there are many flaws. First of all, the hydrogens of acetylene are acidic, the reaction is too costly and too long, some of the products are incorrect.
I hope I did not sound condenscending.
I'll reply to Polly's question on the next post.