Butanediol

Butanediol, in full 1,4-butanediol, is a colorless, syrupy liquid with the formula C₄H₁₀O₂. Its molecule is a chain of four carbon atoms with an alcohol group (an oxygen bonded to a hydrogen) at each end. Having a reactive group at both ends is what makes it useful: it can link to other molecules on two sides and so become part of a long chain.

It is built from carbon, hydrogen and oxygen, but never directly from the elements. The classic route, the Reppe process, joins acetylene with formaldehyde to make butynediol, then adds hydrogen over a nickel catalyst. Newer plants start from butane, from propylene oxide, or from sugar fermented by engineered microbes.

In the Archive it is the second building block of PBT plastic, where it links with terephthalic acid into long polyester chains. Much of the rest goes into the solvent THF, polyurethanes and the stretchy fiber spandex. It freezes at about 20 °C, so on a cool day it can turn solid in the drum.