Note: Descriptions are shown in the official language in which they were submitted.
1~51)B8
p- Benzoquinone tetramethyl diketal of the formula
CH30 X OCH3
~ (I)
CH30 OCH3
may be prepared, for example bv anodie oxidation of anisol or of
hydroquinone dimethyl ether in methanol/KOH according to N.L.
Weinberg and B. Belleau, Tetrahedron 29 (1973), pages 279 to 285.
The compound (I) may be prepared especially suitable by anodic
oxidation of benzene, likewise in metnanolic solution, this
process, however requiring special conductive salts (cf. British
Patent 836,949).
The catalytie reduction of (I) with hydrogen in neutral to
slightly aeid medium with stoichiometric consumption of hydrogen
give hydroquinone dimethyl ether in good yield (Cf. German
Offenlegungsschrift 25 47 464), which is a desired intermediate
for the preparation of dyestuffs. It is quite natural that the
catalytic reduction of (I) to hydroquinone dimethyl ether in
neutral to slightly acidic medium is advisable only when anisol
or, in particular, benzene is used as the starting compound.
Said catalytie reduetion, however, involves some difficulties,
since frequently an undesired decomposition of (I) occurs. When
further investigating the reaction possibilities of (I), in
particular during the catalytic hydrogenation, it has been found
surprisingly that the catalytic hydrogenation in a basic medium
results in a product, which is completely different from that
obtained in hydrogenation in a neutral to slightly acidic medium,
namely cyclohexane-(1,4)-dione tetramethyl diketal of the formula
.:
'I . :
~:
1095088
CH30 OCH3
~S
~ (II)
CH30 ~ OCH3
The present invention, consequently, provides a process for
the preparation of cyclohexanedione -(1,4)-tetramethyl diketal
of the formula (II) which comprises reducing p-benzo-quinone
tetramethyl diketal of the formula (I) with hydrogen in the
presence of a hydrogenation catalyst, in a basic medium, at a
temperature of from about -10 to +150 C, preferably of from
about +10 to 50 C, in particular of from about +15 to +~0 C.
The reduction may suitably be carried out in solvents of
usual purity which are conventional for use for catalytic hydro-
genation such as, for example, acetic acid methyl and -ethyl
esters, dioxane, tetrahydrofurane etc. Preferred solvents are
methanol and the reaction product (II) itself. Generally the
solutions used for the reaction contain of from about 10 to 80 %
by weight, preferably of from about 20 to 50 ~ by weight, of the
compound (I).
Preferred catalysts are the nohle metal catalysts belonging
to group VIII of the periodic table which are conventional for
use for catalytic hydrogenations, as such as well as in the form
of their oxides, with or without a carrier material, for example
active carbon. Preferred catalysts are palladium and platinum.
A suitable catalyst which does not belong to said group is in
particular Raney-nickel. The catalysts are used in usual amounts,
preferably in an amount of from about 0.005
: , . .
, HO~ 77/F 013
lO~S()81~
to about 0~2 ~ by weight (metal), calculated on the starting
compound (I~.
The pH of the hydrogenation solution is adjusted at a
value greater than 7 by the addition of a base~ A pH in the
range of from about 8 to 10, measured with humid pH paper, is
preferred. Suitable bases are the conventional inorgani~c or
organic bases, for example alkal~ metal hydroxid~s or alcoho-
lates such as NaOH, KOH, NaOCH3, KOCH3, NaOC2H5 and others or
nitrogen bases, for example triethylamine, cyclohexylami~ne,
pyridine and others. They are generally used in an amount
of from about 0.0001 to 5 % by weight, preferably of from
abou. 0.01 to 2 % by weight, in particular of from abGut 0.1
to 1 ~ by weight, calculated on the substance (I1.
The hydrogenation takes place already under a hydrogen
~5 pressure of from about 0.2 to about 200 bars and more. A
pressure of from about ~ to 100 bars, in part~cular of from
about 10 to 50 bars, is preferred.
The hydrogenation proceeds according to the gross equa-
tion
CH30 OCH3 3 ~ 3
2 H2 cat. ~ ~ (II)
CH3 OCH3 CH3~ 0CH3
and is performed under said conditions until about 1.9 to 2.0
mols of hydrogen per mol of compound (I) are consumed or until
no more hydrogen is consumed. As hydrogenation devices there
may be used apparatuses ~hich are conventional for reactions of
this type, for exampie agitator or shaking autoclaves or ade-
-- 4
, ~ :
HOE 77/F 013
1095~88
quate glass or enamel vessels provided with a stirrer. Upon
completion of the hydrogen absorption, the reaction product
is treated in known manner, for example by cooling and expand-
ing the reaction vessel, fiitering off the catalyst, distilling
off the solvent and by subsequently distilling or crystallizing
the compound obtained of the formula (II).
The cyclohexanedione tetramethyl diketal is an interest-
ing intermediate which is variable in use. Cyclohexanedione-
(1,4), in particular, which is generally difficultly obtain-
able, can be prepared from said diketal in good yield byacid hydrolysis, for example in aqueous methanol, in the pre-
sence of a trace of a mineral acid, for example H2S04 or HCl
at a pH smaller than 7 and at a temperature of from 30 to 40C,
Eor example. This diketal is a desired starting product for
syntheses in the field of semiconductors (for example tetra-
cyanoquinodimethane, cf. J.Am.Chem.Soc. 84 (1962), 3372). On
the other hand, hydroquinone dimethyl ether, which is a valuable
intermediate for the dyestuff preparation, in particular for
the preparation of yellow pigment dyestuffs, may be obtained
likewise in good yield, from the compound II by catalytic
dehydrogenation and splitting off of methanol. These proces-
ses proceeding according to the gross equation
CH30 OCH3 OCH3
ca~al; ~ ~ H2 + 2 CH30H
CH30 OCH3 OCH3
- 5 -
- ~
~ HOE 77/F_013
109S088
succeed in tne presence of known (hydrogenation) and dc-
hydrogenation catalysts, especially Pd catalysts, for example
- supported by active carbon, at a reaction.temperature of from
about 200 to 300 C, especially of from about 230 to 260 C,
by simply refluxing (II) in a slight inert gas atmosphere,
for example of ni:trQgen. The reacti.on time. es.sentially depends
on the catalyst quantity employed and is generally in the
range of from about 0,001 to 1 ~ by weight, preferably of
from about Q~01 to 0.1 ~ by weight, calculated on the com-
pound (II). Upon completion of the dehydrogenation and
splitting off of methanol, the catalyst is filtered off and
the reaction product is purified, for example by distillation.
'rhe latter method comprises two reaction steps: a catalytic
hydrogenation of (I~ in a basic medium to yield the compound
(LI) and a subsequent catalytic dehydrogenation and splittins
off of methanol to yield hy~^oquinone dimethyl ether~hereas thAe ini-.
tially described catalytic hydrogenation of (I) in a neutral
to slightly acid medium yields directly hydroquinone dime-
thyl ether in one step. The preparation of hydroquinone di-
methyl ether vi~a the stage of cycl.ohexane-(1,4)-dione-tetra-
methyl diketal, ho~ever, proceeds more uniformous]y and can
be more readily repeated.
The following e~amples illustrate the invention:
E X A M P L E 1;
398 g (~.99 mols) of p-benzoquinone tetramethyl diketal
are dissolved in 1000 g of methanol and after addition of 1 ml
of triethylamine and 1 g of Pd supported by active carbon
(in 5 ~ concentration), hydrogen is introduced under pressure
29 while stirring, until a pressure of 50 atmospheres is set up.
-- 6 --
~9S088 IIOE_77/F 013
After absorption of 46.8 liters of hydrogen (liters measured
under normal conditions of temperature and pressure), within
a period of 30 minutes, at a temperature of from 20 to 40 C,
the reactor is expanded, the catalyst is filtered off and the
solvent (methanol) is distilled off under atmospheric pressure.
When cooling the residue, cyclohexanedione-(1,4)-tetramethyl-
diketal (345 g), ~hich has a melting point of 75 C is obtain-
ed in a crystalline form. The mother liquor comprises 30 % by
weight of hydroquinone dimethyl ether and 65 % by weight of cyc-
lohexanedione-(1,~)-tetramethyldiketal. The total yield, con-
sequently, is 92.5 % of the theory.
E X A M P L E 2:
... .
To 412 g of p-benzoquinone tetramethyl diketal, dissolved
in 630 g of methanol, are added 1,5 g of freshly prepared Raney-
nickel and 5 g of sodium methylate and hydrogen is introducedunder pressure, at room temperature, while stirring, until a
pressure of 70 atmospheres is attained. Within half an hour
- 40.5 Iiters of hydrogen have been absorbed while the tempera-
ture has increased to 38 C. Thereafter the pressure in the
reactor is released, ~he catalyst is filtered o~f and the sol-
vent is evaporated. Cyclohexanedione-(1,4)-tetramethyl diketal
is obtained in a pure crystalline forme in a yield of 79 % of
the theory (332 g). The mother liquor contains among others
some hydroquinone dimethyl ether and a further 29 g of cyclo-
hexanedione-(1,4)-tetra,nethyl diketal. The total yield of the
reaction product, consequently, is 86 % of the theory.
E X A M P L E 3:
50 g of p-benzoquinone tetramethyl diketal are dissolved
29 in 150 ml of methanol, 1 g of NaOCH3 and 1 g of Pd~C (in a
-- 7
~ HOE 77/F (J13
~0~508~
concentration of 5 %) are added and hydrogenation is carried
out while shaking under a hydrogen pressure of 15 atmospheres
- until hydrogen is absorbed no longer. The reactor is expanded,
the catalyst is filtered off, the solvent is evaporated and
the crystalline mass is recrystallized from a little methanol.
The total yield of cyclohexanedione-(1,4)-tetramethyl diketal
is 45.9 g which corresponds to a yield of 90 % of the theory.
E X A M P L E 4:
Cyclohexanedione (1,4) from cyclohexanedione-(1,4)-tetramethvl
diketal
50 g of cyclohexanedione-(1,4)-tetramethyl diketal are
suspended in 150 ml of methanol, 20 ml of 1N H2SO4 are added
and the batch is stirred for 3 hours at 40 C. By recrystal-
li~ation from ethanol are obtained 20 g of cyclohexanedione-
(1,4) which corresponds to a yield of 74 % of theory. Melting
point 78 C.
E X A M P L E 5:
Hydroquinone dimethYl ether from cyclohexanedione-(1,4)-tetra-
methyl diketal
40 g of cyclohexanedione-(1,4)-tetramethyl diketal are re-
fluxed with 1 g of Pd/C (of 5 % concentration) at 230Q C. At
the same time a slight nitrogen current is passed through the
reaction batch. Subsequentl~r the mixture is distilled in
vacuo (60 torrs, 131 C). There is obtained 21 g of hydroqui-
none dimethyl ether (86 % of the theory) in addition to 4 g Gf
non modified starting product.
This appllcation is a divisional application of Canadian
Patent Application Serial No. 295,619, filed January 25, l978.
- -- 8 --
