OK, there are several routes to producing 1,4-B, but the most common is via what's known as the Reppe process, which is basically the addition of acetylene to carbonyl compounds. However, three other processes; acetoxidation of butadiene, the cis-butenedioic anhydride method and hydroformylation of an allyl alcohol have recently been introduced, so I don't know how much 1,4B is made via these methods.
Incidentally, in 1975 ~70,000 tons of 1,4B was produced annually. In 1990 this had risen to 498,000 tons and by 1999 it was ~700,000 metric tons. China stepped up it's production in 2000, and aimed to further increase it's production by 10% per year.
There are several other routes listed in literature, but from what I can gather, most of these aren't used for mostly economical reasons.
So the Reppe processes to 1,4-B involve
Acetylene + formaldehyde ---> propargyl alcohol + 2-butyne-1,4-diol
2-butyne-1,4-diol + H2 ---> 2-butene-1,4 diol
2-butene-1,4-diol + H2 ---> 1,4 butanediol
The hydrogenation (H2) processes, use copper acetylide as a catalyst. This compound is a shock sensitive explosive but would not be thought to be present in the final product.
From Kirk Othmer - Encyclopedia of Chemical Technology, the impurity found in 1,4 B made via the Reppe process is
Acetal (1,1, diethoxyethane) although it's only likely to be present in small amounts with very small amounts of water (~0.04% ).
The MSDS of acetal mentions;
The substance may be toxic to central nervous system.
Repeated or prolonged exposure to the substance can produce target organs damage.
The other processes use different catalysts- mostly cobalt carbonyl or rhodium carbonyl for hydorformylation. I don't know what catalyst is used with acetoxidation and whether there are identified contaminants from these processes.
