CA1095088A - Process for the preparation of cyclohexanedione-(1,4)- tetramethyl diketal - Google Patents

Abstract

Abstract of the Disclosure:

Hydroquinone dimethyl ether, which is a valuable intermediate for the dyestuff preparation, is obtained from cyclohexanedione-(1,4)-tetramethyl diketal by catalytic dehydrogenation.

Description

1~51)B8 p- Benzoquinone tetramethyl diketal of the formula ~ (I) 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 . :

~:

~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-, ~ :

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 ca~al; ~ ~ H2 + 2 CH30H

- ~

~ HOE 77/F_013 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.

~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 ~ 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.

Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of hydroquinone dimethyl ether in which cyclohexanedione-(1,4)-tetramethyl diketal is subjected to catalytic dehydrogenation and methanol is split off.

2. A process as claimed in claim 1 in which the reaction is carried out in the presence of a palladium catalyst supported on activated carbon at a temperature of from 200 to 300°C by refluxing under an inert gas atmosphere.