Note: Descriptions are shown in the official language in which they were submitted.
~ O.Z. 32,132
1~784~9
MANUFACTURE OF SWGAR ALCOHOLS
The present inventlon relates to an improved prooess for the
manufacture of sugar alcohols of the general formula I
CH20H
(CHOH)n
CH20H :
- where n is from 2 to 5.
Such sugar alcohols may be manufactured by reducing the cor-
responding aldoses (J. Stanek et al "The Monosaccharides", Academic
Press, London, 1963, page 626), but at the same time sugar acids,
or the lactones of these acids, form easily (Chemikerzeitung, 99
(1975), 450), and furthermore some aldoses are only obtainable with
difficulty.
me sugar alcohols I can further be manufactured by catalyti-
cally hydrogenating aldonic acid lactones over platinum oxide cata-
lysts (J. Am. Chem. Soc., 57 (1935), 2,204 et seq.), but both be-
cause of the expensive catalyst and because of the unsatisfactory
yields, this method is unsuitable ~or industrial syntheses. Finally,
D-gluconic acid lactone has been hydrogenated by m~ans of catalysts ; `
containing copper oxide and chromium oxide at 250C; however, this
did not give any sorbltol, but only propanediol and ethylene glycol
` as scission products.
Since the sugar alcohols I are of great importance, lnter alia
as a sugar substltute for diabetics, as intermediates ~or vitamins
(sorbltol, for example, belng an lntermediate for vltamin C) and
for other physlologlcally active compounds and also, for example,
'' '.:
. . , . . ., -
., . . . . -:
~ '78~ o. zo 32,1~2
in the manu~acture of alkyd resins and explosives, it is an object
of the present invention to provide a technically and economically
improved method of obtaining these compounds.
We have found that this ob~ect is achieved by an improved pro-
cess for the manufacture of sugar alcohols of the general formula I
,CH20H
(,CHOH)n
CH2H
where n is ~rom 2 to 5, by hydrogenating ~- or ~lactones (II),
which are derived from aldonic acids of the general formula IIa
COOH
(CHOH)n IIa
R
where R is -CH20H or -COOH, by means of hydrogen over catalysts
containing co~per oxide, in which process the catalyst used is a
mixed oxide comprising from 20 to 95~ by weight, calculated as CuO,
of copper oxide and from 5 to 80% by weight, calculated as Cr203,
o~ chromium oxide and/or aluminum oxide and the hydrogenation is
carried o~ at from 70 to 200C.
The Cu-Cr mixed oxides to be used as catalysts according to ;
the invention are disclosed in Organio Reactions, 8 (1954), 8 et seqO
As stated there, the mixed oxides are neither a mechanical mixture
of Cu oxide and Cr oxide nor copper chromite, but compounds inter-
mediate between these two extreme states. Since the material is pre- ;
sumably a mixture of the oxides at the atomic level, so that an inter-
action between the Cu atoms and Cr atoms can occur, the mixed oxldes
are best manu~actured by coprecipitation from aqueous solutions, con-
taining Cu salts an-d chromates, by means o~ bases, eg. ammoniaO Fur-
ther details may be found in the above publication and in the mono-
graph by F. Zymalko~ski, "Katalytlsche Hydrierungl' (Enke-Verlag,
Stuttgart), pages 32 et seq. In general terms, similar remarks apply
to catalysts contalning Cu and Al, or catalysts containing Cu, Cr
and Al, In addition, it is at times advisable to use up to 10~,
.
-2-
1~ 713409
O.Z0 32,132
~ased on the amount of the mixed oxides defined above, of promoters,
principally barium oxide.
The basic mixed oxides first obtained are converted, by heat-
ing in air, into the oxides. Since these only display their full ca-
- talytic activity after a certain start-up stage under hydrogenating
conditions, it is advisable to pretreat them at from 150 to 250C
and from 0.01 to lO0 bars partial pressure of hydrogen for from
a~out 2 to 8 hours before using them for their intended purpose.
Catalysts pretreated in this way are then fully active from the
start.
The active catalyst composition can also be applied to supports,
eg. silica gel, by conventional techniques.
Preferred catalysts are those where the atomic ratio of Cu to
Cr and/or Al is of the order of 1:1, ie. is from about 1:0.7 to
1:~.5-
The amount of catalyst used is preferably from 1 to 100 g of
: acti~-e metal oxide per mole of the lactone II to be hydrogenated.
~ithin the stated temperature range of from 70 to 200C, the
range from 120 to 150C is preferred. The hydrogen pressure is not
critical and may vary withln the wide limits of from 1 to 1,000 bars.
As a rule, the optimum for technological purposes is, however, from
lO0 to ~00 bars.
Since heterogeneous catalysis is concerned it is advantageous9
to achieve satisfactory space-time yields, if the starting compounds
II and products I are present in a homogeneous liquid phase. It ls
` therefore in most cases advisable to use an inert solvent, eg. wa-
ter or dioxane. Lower alcohols, eg. methanol, ethanol, propanols
` or butanols, may also be used. Suitable solvents, and their amounts,
can easily be found by a few preliminary experiments,
Suitable starting compounds II are ~ lactones or ~lactones
(having the D-, L- or DL-configuration) of aldonic acids of 4 to 7
carbon atoms, eg. gluconic acid, mannonic acid, gulonic acid, ga-
- lactonic acid, allonic acid, altronic acid, heptonic acid, ribonic
` -- 10784~9 o z~ 32,1~2
~cid, arabonic acid, xylonic acid, lyxonic acid, erykhronic acid
` and threonic acid, especially D-gluconic acid ~lactone, D-gluco-
nic acid S-lactone, D-mannonic acid ~-lactone, D-mannonic ~-lac-
tone, D-ribonic acid ~r-lactone and D-arabonic acid ~-lactone~ as
well as lactones of aldaric acids (sugar acids), egO D-saccharic
acid, D-mannonic and mucic acid. The said lactones are known from
the literature and some of them are commercially available, whilst
many a~e more easily accessible than the corresponding aldoses,
from which the sugar alcohols I have been manufactured hitherto.
On the other hand, in the last-mentioned reaction the lactones II
are formed as by-products which can then also be converted, by the
process of the invention, into the desired compounds I~
Generally, the corresponding sugar alcohols are obtained in
yields of from 70 to 95~, the remainder consisting almost exclusive-
ly of the epimeric alcohols which form under the reaction conditions.
If the pure products are requiredt the materials obtained may be
worked up by recrystallization in the conventional manner.
EXAMPLE 1
` 29.6 g (0.2 mole) of D-ribonic acid ~-lactone
. .
0~ I ,
- OH
, '
in 150 ml of dioxane were hydrogenated in the course of 48 hours
at 120C and 170 bars hydrogen pressure by means of 6 g of a mixed
oxide catalyst comprising 45% by weight of copper oxide and 55% by
weight of chromium-III oxide. After concentratlng the catalyst-~ree
solution, removing the crystals formed and recrystallizing the pro-
duct from 250 ml of` ethanol, the final product, ribitol
--4--
- '
~ 78~09 o. zo 32,1~2
OH
- OH
.~r OH
OH
was obtained in 89% yieldO The remainder consisted of isomeric
sugar alcohols of 5 carbon atoms.
The catalyst was manufactured by ~irst precipitating basic
oxides from aqueous Cu nitrate/Na chromate solutions by means of
~ ammonia~ and then converting these basic oxides to the oxides by
;~ heating in air.
EXAMPLE 2
74.2 g (004 mole) of D-gluconic acid ~-lactone
O= _ I
- OH
HO
- OH
i
OH
- were hydrogenated in 150 ml of dioxane at 1~5C and 250 bars hydro-
gen pressure in the course of 48 hours over 18 g of a catalyst com-
prising 52~ by weight o~ copper oxide and 48% by weight, based on
CuO, of aluminum oxlde, the catalyst having been pretreated under
hydrogenatlng conditions (200 bars of H2; 200C; 8 hours). Working
up in the conventlonal manner gave 70% of sorbitol and 15~ o~ man-
nitol.
The catalyst was manufactured from Cu nitrate and Na aluminate
by a method analogous to that described in Example lo
sorbitol OH - OH mannitol
- OH OH
HO- - OH
- OH OH
- OH OH
- OH -5- - OH
- . ... . . . . ~ .
.
~ 7 8 4~g OOZ. ~2,132
.' EXAMPLE 3
38 g (0.257 mole) of D-arabonic acid ~r-lactone
:', O= I :~
HO
.
_ '
OH ~ .
in 250 ml of dioxane were hydrogenated at.120C and 170 bars hy-
. drogen pressure, using 10 g of the catalyst described in Example 2.
The residue obtained after removing the catalyst and the solvent
consisted mainly of D-arabitol
; HO - :~
. HO- .:
' HO -
- OH
HO -
~,
and some ribitol.
;~
.
,
!
., .
,~ .
~ '~
- - ,; ,, .
