Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

CHAPTBK XI
NATUEAL PRODUCTS
1. FURFURAL 1
BRAN
c.c. of
(300
concentrated
g.) is stirred
sulphuric
in a
acid
three-litre
and 800
flask
c.c.
with
of
a
water.
mixture
Abo
of
tion
900
with
c.c. of
sodium
the liquid
carbonate,
are distiled
is saturated
and the
with
distilate,
common
after
salt
neutralis
Of this solution 300 c.c. are again distiled and the distilate
(250
is
g
and
tracted
the
with
ether
ether
evaporated.
after saturation
Then the
with
furfural
salt. The
is distiled.
extract is
Boiling
dried
point 162°. Yield 5-7 g.
of
The
water
pentoses,
and are converted
when
into
boiled
furfural.
with mineral acids, lose thre
CHOH—CHOH HC- CH HC—CH
I I —•> I I —• I I
H0CH2 CHOH.CHO HC C.CHO HC C.CHO.
V Y
The two most important natural pentoses, 1-arabinose and \-xylose,
occur in nature as polymeric anhydrides, the so-called pentosans, viz.
araban, the chief constituent of many vegetable gums (cherry gum,
gum arable, bran gum), and xylan, in wood. From these pentapolyoses
there are produced by hydrolysis first the simple pentoses which are
then converted by sufficiently strong acids into furfural. This aldehyde
is thus also produced as a by-product in the saccharification of
wood (cellulose) by dilute acids. Furfural, being a " tertiary " aldehyde,
is very similar to benzaldehyde, and like the latter undergoes the
acyloin reaction (furoin) and takes part in the Perkin synthesis. It
also resembles benzaldehyde in its reaction with ammonia (p. 215).
Experiments.-—Allow furfural to stand for a short time with five
parts of aqueous ammonia ; after three hours, separation of the
1 Stenhouse, Annalen, 1841, 35, 302 ; Fownes, Annalen, 1845, 54, 52.
386