Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-08-28
2002-04-09
Pryor, Alton (Department: 1616)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S001000, C560S127000, C560S129000, C560S190000, C560S191000
Reexamination Certificate
active
06369263
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing hydroquinone diester derivatives.
BACKGROUND TECHNOLOGY
Hydroquinone diester derivatives (e.g., trimethylhydroquinone diesters, trimethylhydroquinone derived therefrom by hydrolysis) are useful as intermediates of medicines and also industrially important compounds, used as starting materials of vitamin E; antioxidants for resins, higher fatty acids, higher alcohols, fats, or oils; or polymerization inhibitors for polymerizable monomers.
Japanese Patent Application Laid-Open No. 7632/1972 (JP-A-47-7632) discloses a process of producing trimethylhydroquinone diesters by reacting 2,6,6-trimethylcyclohex-2-ene-1,4-dione (ketoisophorone, KIP) with an acylating agent in the presence of an acid catalyst (a protonic acid or a Lewis acid catalyst).
In this process, a pure trimethylhydroquinone diester is obtained by neutralizing the reaction mixture, extracting the reaction product, removing the acid catalyst by filtration, condensing the extract (filtrate) under reduced pressure, and then recrystallizing using hexane. Although its purification step is complicated, yet the yield of the trimethylhydroquinone diester is low. When hexane is employed as a solvent for recrystallization, the purity of the trimethylhydroquinone diester is improved only to a limited extent probably due to hexane's low solubility in by-products. This may be the reason why the melting points of trimethylhydroquinone diesters mentioned in the literature lie within the range of as wide as 97 to 107° C. In addition, hexane is a low-boiling point solvent and its solubility in the object compound is extremely low, which require hexane as the recrystallization solvent to be used in a large amount. Thus, when it comes to purification, the process is industrially disadvantageous.
Thus, an object of the present invention is to provide a process for obtaining a highly pure hydroquinone diester derivative from a reaction mixture through a simple procedure.
Another object of the present invention is to provide a process for producing a hydroquinone diester derivative in a high yield.
Still another object of the present invention is to provide a process for producing a highly pure hydroquinone diester derivative from a reaction mixture of a ketoisophorone derivative and an acylating agent in a high yield.
DISCLOSURE OF INVENTION
The inventors of the present invention made intensive and extensive studies to achieve the above objects, and finally found that a hydroquinone diester derivative can be crystallized directly from a reaction mixture of a ketoisophorone derivative and an acylating agent, and that a trimethylhydroquinone diester of high purity can be obtained with high yield by washing the crystallized product. The present invention is based on the above findings.
That is, in the process of the present invention, a hydroquinone diester derivative represented by the following formula (1):
wherein R
1
and R
2
are the same or different, each representing an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group
is produced by crystallizing the derivative from a reaction mixture containing the hydroquinone diester derivative and then washing the crystallized product. The crystallized product may be washed with warm or hot water of 40° C. or above. Employed as a solvent to be used in the crystallization may be a combination of an organic carboxylic acid and water. In the formula (1), R
1
and R
2
may be C
1-4
alkyl groups. Especially, the hydroquinone diester derivative may be crystallized out from a reaction mixture which can be obtained by reacting a ketoisophorone derivative of the formula (2):
wherein R
2
has the same meaning as defined above
with an acylating agent. A solid filtered out by washing the crystallized product may contain, on a solid matter basis, 0 to 2% by weight of a catechol diester derivative shown by the following formula (3):
wherein R
1
and R
2
have the same meanings as defined above.
BEST MODE FOR CARRYING OUT THE INVENTION
[Reaction Mixture]
In the present invention, a hydroquinone diester derivative of the formula (1) is obtained by crystallization from a reaction mixture containing the hydroquinone diester derivative.
In the formulae (1) and (2), exemplified as the alkyl groups designated by R
1
and R
2
are C
1-10
alkyl groups (e.g., C
1-8
alkyl groups such as methyl, ethyl, butyl, isobutyl, t-butyl, pentyl, hexyl group). Examples of the cycloalkyl group are C
3-10
cycloalkyl groups (e.g., cyclohexyl group). As the aryl group, there may be exemplified C
6-12
aryl groups (e.g., phenyl group, and substituted phenyl groups such as p-methylphenyl group). As the heterocyclic group, there may be mentioned aromatic or nonaromatic 5- or 6-membered heterocyclic groups having at least one hetero atom selected from nitrogen, oxygen and sulfur (e.g., furyl group, thienyl group, nicotinyl group, pyridyl group). In compounds represented by the formulae (1) and (2), the substituents R
1
and R
2
may be either the same or different.
Preferred as R
1
are C
1-8
alkyl groups, particularly C
1-6
alkyl groups (e.g., C
1-4
alkyl groups such as methyl and ethyl group), and preferred as R
2
are C
1-4
alkyl groups such as methyl group and ethyl group, with methyl group particularly preferred.
Exemplified as the hydroquinone diester derivative (1) are 2,5,6-triC
1-4
alkylhydroquinone diesters (particularly, 2,5,6-trimethylhydroquione diacetate (DAB)).
A reaction mixture containing such hydroquinone diester derivative (1) can be obtained by reacting a ketoisophorone derivative shown by the formula (2) with an acylating agent in the presence of a catalyst. In the formula (2), R
2
has the same meaning as defined for the formula (1).
As the ketoisophorone derivative (2), usually, 2,6,6-triC
1-4
alkylcyclohex-2-ene-1,4-diones (particularly, 2,6,6-trimethylcyclohex-2-ene-1,4-dione (ketoisophorone, KIP), can be used.
Either a protonic acid or a Lewis acid can be employed as the catalyst. Exemplified as the protonic acid are inorganic acids (e.g., sulfuric acid, hydrochloric acid, phosphoric acid, fluoroboric acid, hydrofluoric acid); organic acids (e.g., sulfonic acids such as p-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid, ethanesulfonic acid; halocarboxylic acids such as chloroacetic acid, trichloroacetic acid and trifuluoroacetic acid; picric acid), and superstrong acids having a Hammett acidity function H
0
of smaller than −11.93 (e.g., H
2
SO
4
—SO
3
, HF—NbF
5
, HF—TaF
5
, SbF
5
, HF—SbF
5
, SbF
5
—FSO
3
H, FSO
3
H—TaF
5
, SbF
5
—CF
3
SO
3
H). As the Lewis acid, there can be exemplified BF
3
, BF
3
OEt
2
, AlCl
3
, FeCl
3
, ZnCl
2
, TiCl
4
, and SnCl
2
. Included among the preferred catalysts are water-soluble catalysts.
The amount of the catalyst to be used need only be an effective amount, depending on the reaction conditions. For example, the amount of the catalyst is, relative to 100 parts by weight of the substrate of a ketoisophorone derivative (2) (e.g., KIP), about 0.001 to 100 parts by weight, preferably about 0.01 to 10 parts by weight, and more preferably about 0.1 to 5 parts by weight.
A solid catalyst (particularly, a solid acid catalyst) may also be used as the catalyst. Examples of the solid acid catalyst include strong acid ion-exchange resins (e.g., non-porous or porous ion-exchange resins containing a sulfonic acid group), superstrong acid ion-exchange resins (e.g., non-porous or porous ion-exchange resins having a superstrong acid group such as —CF
2
CF
2
SO
3
H), sulfates (e.g., CaSO
4
, Fe
2
(SO
4
)
3
, CuSO
4
, NiSO
4
, AlSO
4
, MnSO
4
, BaSO
4
, CoSO
4
, ZnSO
4
, (NH
4
)
2
SO
4
), metal oxides (e.g., SiO
2
, Al
2
O
3
, TiO
2
, Fe
2
O
3
, ZrO
2
, SnO
2
), double or complex oxides (SiO
2
—Al
2
O
3
, SiO
2
—TiO
2
, TiO
2
—ZrO
2
, SiO
2
—ZrO
2
), zeolites (e.g., zeolites of Y-type, X-type and A-type which have an acidic OH group; ZSM
5
, mordenite, VPI
5
, AlPO
4
-5, AlPO
4
-11), kaolin, and heteropolyacids (e.g., polyacids containing any of the elements P,
Daicel Chemical Industries Ltd.
Pryor Alton
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