The manufacture of 1,4-butanediol in the Reppe process as practiced by, e.g, BASF, Du Pont, or GAF/Huls is characteristic of the third point. is still currently an economical base for the manufacture of 2-butyne-1,4-diol, a precursor of 1,4-butanediol.

In the manufacture of 1,4-butanediol, acetylene is first converted with 10-30% aqueous formaldehyde at 100- 110°C and 5-20 bar in the presence of modified copper acetylide to produce 2-butyne-l ,4-diol:

The reaction is conducted in a trickle-column reactor containing the copper acetylide catalyst with Bi as promoter on SiO₂ or magnesium silicate.

The intermediate propargyl alcohol is recycled, together with formaldehyde, to the reaction. The butyne-diol selectivity amounts to 80% (C₂H₂) and > 90% (HCHO). In the second step, 2-butyne-1,4-diol is hydrogenated to 1,4-butanediol:

The hydrogenation can be conducted in the liauid Dhase at 70- 100°C and 250-300 bar in the presence of Raney nickel catalyst. Alternatively, the hydrogenation can take place in the trickle phase at 180 - 200 °C and 200 bar employing Ni catalysts with Cu and Cr promoters. The selectivity to 1,4-butanediol reaches about 95% (based on 2-butyne-1,4-diol).

This acetylene-based manufacturing method profits more from the increasing worldwide interest in 1,4-butanediol than other processes based on C₄ feedstocks, especially in the USA and Western Europe.

In 1992, about 85% of the production capacity for 1,4-butanediol in the USA was based on acetylene.

In Japan, on the other hand, the manufacture of 1,4-butanediol from butadiene by acetoxylation and chlorination (to be described later) has been developed and is used commercially. The worldwide production capacity for 1,4-butanediol was about 620000 tonnes per year in 1996, with the USA, Western Europe, and Japan accounting for 310000, 220000, and 110000 tonnes per year, respectively. Production figures for these countries are given in the adjacent table.

An additional industrially useful intermediate can be obtained from the acetylene process for 1,4-butanediol. If the hydrogenation of 2-butene-1,4-diol is conducted in the presence of catalysts whose activity has been reduced either by their manufacturing process or by additives, then the reaction stops at the 2-butene-1,4-diol stage. catalysts, nickel catalysts with iron additives and possibly amine inhibitors or palladium catalysts, usually partially poisoned with zinc, are employed industrially.

is a reactive trifunctional intermediate which, as the diacetate, takes part in the Diels-Alder reaction with hexachloro-cyclopentadiene to form a precursor of Thiodan insecticide.

The hydrogenation of maleic anhydride is another manufacturing process which has been used by various firms for several years. This route has now become sufficiently attractive that plants are being operated in, for example, South Korea, Japan and Western Europe.

Two other processes are industrially important. They are based on butadiene, a less expensive and more reactive starting material, and go through the intermediates 1 ,4-dichloro-Zbutene and 1,4-diacetoxy-2-butene.

Thus Mitsubishi Chemical has developed a technology of concerted manufacture of 1,4-butanediol and tetrahydrofuran from simultaneous acetoxylation/AcOH addition to butadiene, and has employed this technology commercially in a 20000 tonne-per-year plant since 1982.

In the first step, butadiene and acetic acid are converted to 1,4-diacetoxy-2-butene with more than 90% selectivitv. The reaction is done in the liquid phase at about 70 °C and 70 bar over a Pd/C catalyst with promoters such as Sb, Bi, Se or (preferably) Te. This is then hydrogenated, also in the liquid phase, at about 60 °C and 50 bar over a conventional hydrogenation catalyst to produce 1,4-diacetoxybutane with more than 98% selectivity. This is then reacted on an acidic ion exchange resin. Depending on the temperature and residence time, different mixtures of 1,4-butanediol and tetrahydrofuran are obtained with 90% selectivity by hydrolysis and dehydration cyclization, respectively. The acetic acid is recycled to the first reaction step:

Another synthetic route to 1,4-butanediol consists of hydroformylation of allyl alcohol or allyl acetate followed by hydrogenation of the 4-hydroxy or 4-acetoxybutyraldehyde and, in the case of the monoester, the requisite hydrolysis. Numerous firms have investigated this method, and Arco (USA) has used it since 1991 for the simultaneous production of tetrahydrofuran and N-methylpyrrolidone in a 34000 tonne-per-year unit.