Organic compounds -- part of the class 532-570 series – Organic compounds – Cyclohexadiene having atoms double bonded directly at the 1-...
Reexamination Certificate
2000-03-02
2001-10-16
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Cyclohexadiene having atoms double bonded directly at the 1-...
C552S309000, C568S804000
Reexamination Certificate
active
06303801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing alkyl-substituted hydroquinone compounds.
2. Description of Related Art
Hydroquinone compounds having mono-, di- or trialkyl-substituted aromatic ring have been industrially used as raw materials or intermediates for pharmaceutical or agricultural chemicals, resins, various additives, polymerization inhibitors, industrial chemicals and the like. Particularly, trimethylhydroquinone has been widely used as an intermediate for vitamin E, a pharmaceutical, a polymerization inhibitor and a resin additive. In particular, it is much in demand as an intermediate for vitamin E.
Conventionally, it is known that hydroquinone compounds having alkyl-substituted aromatic ring are produced by gaseous phase reaction in which a hydroquinone compound and an alcohol are vaporized and passed through a catalyst phase or by liquid phase reaction utilizing the Friedel-Crafts reaction. For example, JP-A-7-265710 discloses a process for producing hydroquinone compound having methylated aromatic ring by reacting, in gaseous phase, hydroquinone and methanol using basic magnesium carbonate, a fine powder of phenol resin, manganese oxalate as a catalyst. This process, however, has a problem that it needs a complicated reaction apparatus. In addition, JP-A-58-72530 discloses a process for producing trimethylhydroquinone by contacting, in gaseous phase, hydroquinone and methanol heated to 400° C. with a catalyst such as iron oxide, manganese oxide, chromium oxide and the like. This process, however, has a problem that about 7% by mole of tetramethylhydroquinone is produced as a byproduct. Moreover, U.S. Pat. No. 4,060,561 discloses a process for producing trimethylhydroquinone from p-methoxyphenol and methanol.
In the known processes described above, the reaction is usually carried out in gaseous phase or in liquid phase. When the reaction is carried out in liquid phase, a strong catalyst such as a Lewis acid, phosphoric acid or the like is required causing a corrosion problem of apparatus. On the other hand, when the reaction is carried out in gaseous phase, there is a problem that the apparatus becomes complicated by the presence of preheating part, evaporation part, reaction part and condensing part and also needs to be large-sized.
It is desired for a process for producing a mixture of mono-, di- and trimethylhydroquinones from hydroquinone or mono- or dimethylhydroquinone and methanol with less production of tetramethylhydroquinone as a byproduct and allowing easier isolation and purification of trimethylhydroquinone which is a useful intermediate.
An object of the invention is to provide a process for producing hydroquinone compounds having alkyl-substituted aromatic ring from a hydroquinone compound and an alcohol without using a highly corrosive catalyst and allowing the reaction in a relatively small reactor.
An object of the invention is also to provide a process for producing a mixture of mono-, di- and trimethylhydroquinones from hydroquinone or mono- or dimethylhydroquinone and methanol with less production of tetramethylhydroquinone as a byproduct.
Under these circumstances, the present inventors have conducted an extensive study on a process for producing hydroquinone compounds having alkyl-substituted aromatic ring from hydroquinone compound sand alcohols. As the result, the present inventors have found that the above problems can be resolved by reacting hydroquinone compounds with alcohols which are in a supercritical state and thus completed the present invention.
SUMMARY OF THE INVENTION
That is, the present invention relates to a process (hereinafter, referred to as the process (I) of the invention) for producing an alkyl-substituted hydroquinone, wherein said process comprises reacting a hydroquinone compound represented by the general formula (1):
wherein R
1
and R
2
independently represent a hydrogen atom or a straight or branched chain alkyl group having 1 to 10 carbon atoms, R independently represent a straight or branched chain alkyl group having 1 to 10 carbon atoms and n represents an integer of 0 to 2, with a monohydric or dihydric alcohol in the presence of a catalyst and under the condition in which said alcohol is in a supercritical state by substitution of at least one hydrogen atom on the aromatic ring in said hydroquinone compound.
Further, the present invention relates to a process (hereinafter, referred to as the process (II) of the invention) for producing an alkyl-substituted hydroquinone, wherein said process comprises reacting the hydroquinone compound represented by the general formula (1) with a monohydric or dihydric alcohol in the presence of a catalyst and carbon dioxide and under the condition in which a mixture of said alcohol and carbon dioxide is in a supercritical state.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described below in detail.
In the hydroquinone compound represented by the general formula (1), used as the starting material of the present invention, R
1
and R
2
include a straight or branched chain alkyl group having 1 to 10 carbon atoms, such as a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group and the like, and a hydrogen atom. R in the hydroquinone compound is not present or one or two of R is present on the aromatic ring. R includes a straight or branched chain alkyl group having 1 to 10 carbon atoms, such as a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group and the like. Specific examples of the hydroquinone compound represented by the general formula (1) include hydroquinone, monomethylhydroquinone, monoethylhydroquinone, 2,3-dimethylhydroquinone, 2,5-dimethylhydroquinone, 2,6-dimethylhydroquinone, p-methoxyphenol, 1,4-dimethoxybenzene and the like. Among them, one compound or a plurality of compounds can be used.
The alcohol, the other starting material in the present invention, is not particularly limited as far as it is a monohydric or dihydric alcohol, and preferably, a monohydric alcohol represented by the general formula (2):
R
3
—OH (2)
wherein R
3
represents a straight or branched chain alkyl group having 1 to 10 carbon atoms. R
3
includes a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group and the like.
Examples of the monohydric alcohol represented by the general formula (2) specifically include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, n-octanol, n-nonanol, n-decanol and the like. Among them, methanol, ethanol, n-propanol and n-butanol are preferred, methanol and ethanol are more preferred and methanol is further preferred.
Examples of the dihydric alcohol include ethylene glycol, propylene glycol and the like.
The hydroquinone compound and the alcohol, respectively, may be used independently or in combination thereof. The molar ratio of the alcohol to the hydroquinone compound is selected according to compounds used. Generally, it is 3 to 1,000 and preferably 3 to 300.
In the present invention, at least one hydrogen atom of aromatic ring is usually substituted by alkyl group derived from a monohydric or dihydric alcohol.
In the process (I) and the process (II) of the present invention, when hydroquinone as the hydroquinone compound and methanol as the alcohol are used, respectively, a mixture of monomethylhydroquinone, dimethylhydroquinone and trimethylhydroquinone is obtained as a mixture of hydroquinone compounds having mono-, di- and trialkyl-substituted aromatic ring. The ratio of said substituted compounds in the mixture depends on the reaction conditions such as temperature, pressure and so on. In addition, there may be a case wherein any one or two of said substituted compounds are not contained in said mixture and a case wherein any other byproducts are contained.
The process (I) of the present invention is characterized in that the r
Sasaki Toshio
Suzuki Tomoyuki
Birch & Stewart Kolasch & Birch, LLP
Covington Raymond
Rotman Alan L.
Sumitomo Chemical Company Limited
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