Page 163 - Chemical and process design handbook

Speight_Part II_B 11/7/01 3:11 PM Page 2.104

BUTENEDIOL

o
o
2-butene-1,4-diol (melting point: 11.8 C, boiling point: 234 C, density:
o
1.070, flash point: 128 C) is the only commercially available olefinic diol
with primary hydroxyl groups. The commercial product consists almost
entirely of the cis isomer. Butenediol is very soluble in water, lower alcohols,
and acetone, but is almost insoluble in aliphatic or aromatic hydrocarbons.
Butenediol is manufactured by partial hydrogenation of butynediol.
Although suitable conditions can lead to either cis or trans isomers, the
commercial product contains almost exclusively cis-2-butene-l,4-diol. The
trans isomer, available at one time by hydrolysis of 1,4-dichloro-2-butene,
is unsuitable for the major uses of butenediol involving Diels-Alder reac-
tions. The liquid-phase heat of hydrogenation of butynediol to butenediol
is 156 kJ/mol (37.28 kcal/mol).
The original German process used either carbonyl iron or electrolytic
iron as hydrogenation catalyst. The fixed-bed reactor was maintained at 50
o
to 100 C and 20.26 MPa (200 atm) of hydrogen pressure, giving a product
containing substantial amounts of both butynediol and butanediol. Newer,
more selective processes use more active catalysts at lower pressures. In
particular, supported palladium, alone or with promoters, has been found
useful.
Purity is determined by gas chromatography. Technical grade butene-
diol, specified at 95% minimum, is typically 96 to 98% butenediol. The cis
isomer is the predominant constituent; 2 to 4% is trans. Principal impurities
are butynediol (specified as 2.0% maximum, typically less than 1%),
butanediol, and the 4-hydroxybutyraldehyde acetal of butenediol. Moisture
is specified at 0.75% maximum (Karl-Fischer titration). Technical-grade
°
butenediol freezes at about 8 C.
Butenediol is noncorrosive and stable under normal handling condi-
tions. It is a primary skin irritant but not a sensitizer; contact with skin and
eyes should be avoided. It is much less toxic than butynediol. The LD is
50
1.25 mL/kg for white rats and 1.5 mL/kg for guinea pigs.

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