Process for the preparation of 2,3,5-trimethy1-p-Benzoquinone

Details Process for the preparation of 2,3,5-trimethy1-p-Benzoquinone Process for the preparation of 2,3,5-trimethy1-p-Benzoquinone

2001-03-08

2002-06-25

Pryor, Alton (Department: 1616)

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

Organic compounds

Oxygen containing

C568S377000

Reexamination Certificate

active

06410798

ABSTRACT:

This application claims priority from German Application No. DE 100 11 405.9, filed on Mar. 9, 2000, the subject matter of which is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a new process for the preparation of 2,3,5-trimethyl-p-benzoquinone by oxidation of 2,3,5- or 2,3,6-trimethylphenol using oxygen or a gas mixture containing oxygen in the presence of a two-phase liquid reaction medium composed of water and a neocarboxylic acid having 8 to 11 carbon atoms with a catalyst system containing copper(II)halide at elevated temperature.
2. Background Information
2,3,5-Trimethyl-p-benzoquinone is an intermediate which is used, inter alia, for the preparation of &agr;-tocopherols (vitamin E).
The oxidation of trimethylphenols to 2,3,5-trimethyl-p-benzoquinone is well known.
Of the many processes described, oxidation using oxygen or a gas mixture containing oxygen with catalysis by copper salt-containing catalyst systems in two-phase liquid reaction media is of particular industrial interest. The advantage of these processes, apart from the excellent yields and selectivities which may be obtained, lies mainly in the use of an inexpensive and simple to prepare catalyst system which is present in the aqueous phase and may thus be separated after the reaction from the organic phase containing the product by simple phase separation and recycled with minimal expenditure and practically without loss of activity and selectivity.
According to EP 0 127 888, the oxidation of trimethylphenol to trimethyl-p-benzoquinone can be achieved in good yields using molecular oxygen in the presence of a separately prepared alkali metal or ammonium halogen cuprate of the copper oxidation state+2, optionally with the addition of an alkali metal or ammonium halide. A mixture of water and an aliphatic alcohol having four to ten carbon atoms is described here as the reaction medium. According to EP 0 167 153, the trimethyl-p-benzoquinone yield can be further increased and the formation of by-products further reduced if catalytic amounts of copper (I) hydroxide and/or copper (I) chloride are added additionally to the alkali metal or ammonium halogen cuprate described, and the alcoholic trimethylphenol solution is fed slowly to the aqueous catalyst solution.
EP 0 294 584 describes a process for the oxidation of trimethylphenol to trimethyl-p-benzoquinone by molecular oxygen using an aqueous solution of copper (II) chloride and lithium chloride as catalyst. A mixture of an aromatic hydrocarbon, preferably benzene, toluene, xylene or chlorobenzene, and a lower aliphatic alcohol having one to four carbon atoms is used as the solvent for the starting product and thus as the second liquid phase.
According to EP 0 475 272, alkaline earth halides as an aqueous solution in combination with copper (II) chloride may catalyse the described reaction efficiently instead of lithium chloride. Suitable organic solvents include both aliphatic alcohols having five to ten carbon atoms and mixtures of aromatic hydrocarbons and aliphatic alcohols having one to four carbon atoms.
EP 0 369 823 describes the oxidation of trimethylphenol to trimethyl-p-benzoquinone using a catalyst system which additionally contains, apart from copper (II) chloride, a salt of a hydroxylamine, oxime or amine with an inorganic acid, or a free oxime. The organic phase used in this process is either aliphatic alcohols having four to ten carbon atoms or mixtures of aromatic hydrocarbons and aliphatic alcohols having one to six carbon atoms.
A disadvantage of all the processes described is that the reaction is carried out at temperatures above or only just below the flash point of the solvents used. The associated risk of explosion conceals enormous risks for the industrial implementation of the processes, mainly because, on account of the need for the presence of molecular oxygen as oxidising agent, it is not possible to render the reaction mixture inert, this being otherwise customary when operating near or above the flash point of the solvent used. It is therefore absolutely vital, for the reaction described, to provide a sufficient safety margin between the reaction temperature and the flash point of the organic constituents so that a safe method of operating the plant can be guaranteed even in the event of temperature rises due to a short-term uncontrolled course of the reaction or in the event of technical plant problems. Without exception, this is not the case in the processes described. The preferred reaction temperatures in question of 60° C. or above which are required in order to obtain good yields are either above or only just below the flash points of the organic solvents described (cf. Table 1).
TABLE 1
Solvent
Flash point [° C.]
Methanol
11
Ethanol
12
1-Propanol
15
1-Butanol
30
1-Pentanol
47
1-Hexanol
60
1-Heptanol
73
1-Octanol
81
1-Nonanol
75
1-Decanol
82
Benzene
−11
Toluene
6
p-Xylene
25
Chlorobenzene
28
This problem of conducting the reaction in an unsafe manner is discussed for the first time in EP 0 387 820. The solution to the problem described is the use of aliphatic alcohols having twelve to eighteen carbon atoms and flashpoints above 120° C. as the organic solvent with the use of copper (II) halide in combination with alkali or alkaline earth halides in the form of an aqueous solution as the catalyst of the reaction. At the preferred reaction temperatures from 80° C. to 90° C., the risk of explosion of the reaction mixture is thus reliably avoided with slightly reduced trimethyl-p-benzoquinone yields. A further advantage of the long-chain alcohols used lies in their high boiling point which is markedly above that of trimethyl-p-benzoquinone. As a result, the reaction product may be isolated easily by distillation from the crude product mixture, after phase separation, as a low-boiling product. A disadvantage of the alcohols used having twelve to eighteen carbon atoms, however, is their relatively high melting point (Table 2). These compounds are thus present as waxy solids at room temperature which entails several problems in relation to the industrial execution of the process. The solvent has to be melted first before the reaction commences, which means an additional process step and expenditure of energy. In addition, care has to be taken at not inconsiderable expense to ensure that all parts of the plant are kept at a temperature above the melting point of the alcohol at all times, even in the event of technical faults, since otherwise there is a risk of the organic phase solidifying in the plant and thus of plant parts becoming blocked.
TABLE 2
Solvent
Flash point [° C.]
Melting point [° C.]
1-Dodecanol
127
22-24
1-Tetradecanol
141
37-39
1-Hexadecanol
135
49
1-Octadecanol
192
55-58
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a process on the basis of the prior art which permits the oxidation of trimethylphenol to trimethyl-p-benzoquinone in good yields and with the reliable exclusion of the risk of explosion of the reaction mixture, and at the same time avoids the disadvantages of the existing processes listed in the assessment of the prior art.
It has now been found that this object can be achieved if a mixture of water and a neocarboxylic acid having 8 to 11 carbon atoms, preferably neodecanoic acid, is used as the solvent system, more particularly if the catalysts used are copper (II) halides to which alkaline earth, alkali or transition metal halides or halides of an element of the rare earths are added to increase the activity.
Neodecanoic acid denotes a mixture of octanoic, nonanoic and decanoic acid (producer: Exxon Chemical).
This result was surprising in so far as neodecanoic acid with <0.01 wt. % has a very low solubility in water, so it was to be expected that the aqueous catalyst phase would exhibit poor interaction with the organic substrate phase and also that neodecanoic acid would thus be relatively unsuitable for oxidation in the two-phase syst

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