Process for the preparation of cyclohexanones

Details Process for the preparation of cyclohexanones Process for the preparation of cyclohexanones

1998-11-02

2001-04-10

Padmanabhan, Sreeni (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S338000, C568S364000, C568S365000

Reexamination Certificate

active

06215028

ABSTRACT:

The invention relates to a process for the preparation of cyclohexanones from the corresponding phenols by partial hydrogenation, the reaction mixture obtained by hydrogenation being treated with sulfonating agents before isolation of the cyclohexanone.
Cyclohexanones are important intermediates or final products in industrial organic chemistry. Appropriately substituted derivatives are particularly valuable intermediates for the synthesis of highly purified final products or are themselves final products of this type for the electronics industry, such as, for example, liquid crystals, for plant protection, such as, for example, fungicides, insecticides, herbicides or pesticides, or for the production of pharmaceutically highly active substances. Cyclohexanones are furthermore used in the industrial synthesis of plastics such as polyamides or in the field of coating and colourant production. Production of the appropriate cyclohexanones on a large industrial scale necessitates preparation which is as economical and environmentally compatible as possible.
It is known that cyclohexanones can be prepared by partial hydrogenation of corresponding phenols. U.S. Pat. Nos. 2,829,166 and 3,076,810 teach the hydrogenation of phenol to cyclohexanone in the presence of a palladium catalyst. In Bull. Chem. Soc. Jpn., 65, 824-830 (1992) and Bull. Chem. Soc. Jpn., 65, 2955-2959 (1992), the reaction of phenols to cyclohexanones as a function of the solvent and of the nature of the catalyst is described. U.S. Pat. Nos. 4,537,704 and 4,614,831 disclose the preparation of cyclohexanone carboxylic acid esters. JP 03181438 teaches the preparation of 4-isopropylcyclohexanone by partial hydrogenation in the presence of aliphatic and aromatic hydrocarbons. JP 03109346 finally describes the preparation of cyclohexane-1,4-dione by partial hydrogenation of hydroquinone in mesitylene or methanol.
As a rule, however, substance mixtures which, besides the desired cyclohexanones also contain the corresponding cyclohexanols and the unreacted phenols, are formed in the partial hydrogenation of phenols to cyclohexanones. The expenditure for the isolation of the cyclohexanone from the reaction mixture is therefore crucial for the economical utilization of the process.
Industrially applicable methods for the isolation of the cyclohexanone from a reaction mixture which is obtained by the hydrogenation of a phenol are primarily distillation and/or crystallization.
Frequently, however, differences in the properties of the structurally very similar mixture components are only small, such that distillative separation of the reaction mixture is associated with very high expenditure and moreover accompanied by yield losses. In the case of solids, compounds having very low vapour pressures or, in the case of sensitive substances, distillation can generally not be employed without problems.
Crystallization, too, cannot generally be carried out as a method of mixture separation, since the hydrogenated products cyclohexanone and cyclohexanol as a rule have a lower tendency to crystallize than the phenols employed. The industrial preparation of cyclohexanones is therefore frequently not possible in this way.
The object on which the invention is based was to discover a process for the preparation of cyclohexanones which does not have the disadvantages mentioned.
It has now surprisingly been found that cyclohexanones can be obtained in very good yields and high purities by partially hydrogenating the corresponding phenols and treating the reaction mixture obtained by this means with sulfonating agents before isolation of the cyclohexanone.
The invention thus relates to a process for the preparation of cyclohexanones by partial hydrogenation of phenols, in particular a process for the preparation of cyclohexanones of the formula I
in which
R is one of the following chiral or achiral radicals:
H, F, —CF
3
, —OCF
3
, —OCF
2
CF
3
or —OCHFCF
3
, —N(R
1
)
2
, —COOR
1
, —CON(R
1
)
2
, —CHO, a straight-chain or branched alkyd radical having 1 to 15 C atoms, which is unsubstituted, monosubstituted by —CF
3
or at least monosubstituted by fluorine, where in these radicals too one or more non-adjacent CH
2
groups can in each case independently of one another be replaced by —S—, —O—, —CO—, —CO—O—, —O—CO—, —O—CO—O— or
R
1
is an alkyl radical having 1 to 12 C atoms,
A
1
is a
(a) cyclohexane-1,4-diyl radical, in which one or more non-adjacent CH
2
groups can also be replaced by —O— and/or —S—,
(b) 1,4-phenylene radical, in which one or two CH groups can also be replaced by N,
(c) radical from the group consisting of 2,6-dioxaborane-1,4-diyl, 1,4-bicyclo-[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
where the radicals (a) and (b) can be substituted by one or more fluorine atoms,
Z, Z
1
independently of one another are —CH
2
O—, —OCH
2
—, —CO—O—, —O—CO—, —CH
2
S—, —SCH
2
—, —CH
2
CH
2
— or a single bond
m is 0, 1 or 2,
by partial hydrogenation of the corresponding phenols of the formula II
in which
R
2
assumes the meaning of R and is additionally also
A
1
m have the meanings indicated for the formula I and
Z
2
, Z
3
additionally the meaning indicated under Z and Z
1
are also —CH═CH— or —C≡C—, characterized in that the reaction mixture obtained by the partial hydrogenation is treated with sulfonating agents before the isolation of the cyclohexanone. Provided A
1
occurs a number of times in a compound of the formula I or II, it can assume the same or different meanings.
The same also applies to all other groups occurring a number of times.
The process according to the invention is particularly suitable for the preparation of intermediates for liquid crystal synthesis.
Preferably, those compounds of the formula II are used for the process in which the radical R
2
—Z
2
—(A
1
—Z
3
)
m
is in the para-position to the phenolic hydroxyl group, as a result of which cyclohexanones of the formula I substituted in the 4-position are obtained.
For the sake of simplicity, in the following Phe is a 1,4-phenylene group, in which one or two CH groups can also be replaced by N, where a 1,4-phenylene group can also be substituted by one or two fluorine atoms, Cyc is a trans-cyclohexane-1,4-diyl radical and Dio is a trans-dioxane-1,4-diyl radical. W is the following group:
The preferred compounds prepared by the process according to the invention include those of the formulae Ia to Ir:
W-Z-W
Ia
W—A
1
—Z
1
—W
Ib
R—A
1
—Z
1
—W
Ic
R—A
1
—Z
1
—A
1
—Z
1
—W—
Id
W—OOC—W
Ie
W—CH
2
CH
2
—W
If
W-Phe-W
Ig
W-Cyc-W
Ih
W-Dio-W
Ii
W-Phe-OOC—W
Ij
W-Cyc-CH
2
CH
2
—W
Ik
R-Phe-W
Il
R-Cyc-W
Im
R-Dio-W
In
R-Phe-OOC—W
Io
R-Cyc-CH
2
CH
2
—W
Ip
R-Cyc-Phe-W
Iq
R—Z—W
Ir
In the preferred compounds of the formulae above and below, R is preferably an alkyl or alkoxy group having 1 to 10 C atoms, H, F, —CF
3
, —OCF
3
, —OCF
2
CF
3
, —N(R
1
)
2
, —COOR
1
, —CON(R
1
)
2
, —CHO,
in particular a straight-chain alkyl or alkoxy group having 1 to 7 C atoms, H, F, —OCF
3
, —COOR
1
, —CON(R
1
)
2
,
Those compounds of the formula II are in particular used for the process according to the invention in which m is 0 or 1. A particularly preferred compound which is employed as a starting material for the process according to the invention is 4,4′-dihydroxybiphenyl. By this means, 4,4′-dioxo-bicyclohexyl is obtained. A further preferred starting compound is 4,4′-dihydroxystilbene, from which 4(4′-oxocyclohexylethyl)cyclohexanone is obtained by the process according to the invention.
A
1
is preferably Cyc, or Phe. In the compounds of the formulae above and below, Phe is preferably a 1,4-phenylene group (Ph), a 1,4-phenylene group which is mono- or disubstituted by F (PheF), a pyrimidine-2,5-diyl (Pyr), a pyridine-2,5-diyl (Pyn), a pyrazine-3,6-diyl or a pyridazine-2,5-diyl group, particularly preferably Ph, PheF, Pyr or Pyn. Preferably, the compounds prepared by the process according to the invention contain no more than one 1,4-phenylene group in which one

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