Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-08-26
2004-02-10
O'Sullivan, Peter (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06689921
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for producing biphenols by oxidative coupling of dialkylphenols. More particularly it is directed to a method which proceeds in two stages using a copper amine complex which is catalytically effective in each stage. Still more particularly it relates to a novel copper amine complex with high catalytic activity for the oxidative coupling of substituted phenols under mild conditions which has dual (two stage) activity and can be readily recycled and reused. Still more particularly it relates to the method of reactivating the catalyst, which can be decomposed by exposure to elevated temperatures or interaction with other chemicals.
SUMMARY OF THE INVENTION
The invention is a process for producing tetraalkylbiphenols and, more particularly, 2,2′,6,6′-tetraalkyl-4,4′-biphenols by the stepwise oxidative coupling of 2,4-dialkylphenols or 2,6-dialkylphenols in the presence of a copper amine complex. The reaction of the 2,6-dialkylphenols is preferred. The first step of this reaction is the synthesis of 3,3′,5,5′-tetraalkyl-4,4′-diphenoquinones using oxygen as an oxidizer to couple the 2,6-dialkylphenols. The second step is the synthesis of 2,2′,6,6′-tetraalkyl-4,4′-biphenols using 3,3′,5,5′-tetraalkyl-4,4′-diphenoquinones as an oxidizer to couple 2,6-dialkylphenols. (Both steps usually employ an excess of the phenol.) In accordance with the invention, the same catalyst can be used in both steps. In addition, the reaction proceeds under extremely mild conditions used in the preferred embodiments of the invention and this results in highly selective syntheses in both steps. Thus in the first step of the preferred process only 3,3′,5,5′-tetraalkyl-4,4′-diphenoquinones are produced, and in the second step only 2,2′,6,6′-tetraalkyl-4,4′-biphenols are produced. Low temperature prohibits dealkylation of biphenols, which results in impurities such as polyphenols.
The reaction of the 2,4-dialkylphenols proceeds directly to the 2,2′-diphenol and does not proceed via the diphenoquinone.
The extremely high activity of the catalytic system used in the preferred embodiment of the invention enables the use of only a very modest amount (i.e. about 0.05 to 1% based on dialkylphenol) of catalyst. In addition, the oxidation proceeds well at modest concentrations of oxygen; thus headspace air pressures as low as 1 to 100 psi are useful and high pressures for oxygenation are not required. The catalyst is readily removed from the product stream and recovered for reuse. Typically, essentially no impurities are produced. The system described below also can permit the efficient recovery of any unreacted 2,6-dialkylphenol starting materials, permitting their reuse without subsequent additional purification.
With specific reference to the reaction of 2,6-dialkylphenol, it has been discovered that 2,2′,6,6′-tetraalkyl-4,4′-biphenols can be efficiently produced in a two-step process by using a copper-amino salt complex with dual catalytic activity and two oxidizing agents, first oxygen, then the corresponding 3,3′,5,5′-tetraalkyl-4,4′-diphenoquinone intermediate, to couple 2,6-dialkylphenols. The process utilizes a solvent, which significantly reduces the temperature at which the coupling occurs, permitting high selectivity to be achieved. In addition, the solvent permits the recovery of excess 2,6-dialkylphenol and catalyst for reuse without subsequent additional purification.
The catalyst has improved catalytic activity compared to a similar system described in U.S. Pat. No. 4,851,589. Unlike the catalyst described in that patent, the catalyst preferably used in the present invention, does not require an activation period, the use of acidic phenols, and can be removed from the products while retaining its full activity and reused. In addition, the catalyst can be prepared, recovered and stored in closed containers for over one year while retaining full catalytic activity, eliminating the need to prepare fresh catalyst for each reaction.
In accordance with another embodiment of the invention, tetraalkylbiphenols are dealkylated to produce a 4,4′-biphenol and its analogs. In a preferred embodiment, this reaction is conducted in the presence of a low boiling solvent to enhance and facilitate the removal of isobutylene and prevent the formation of polyisobutylene.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the preferred embodiments of the invention, the catalyst is prepared by reacting a copper halide (e.g., cuprous bromide, cupric chloride, cupric bromide, and preferably cuprous chloride (CuCl)), with a tetraalkylalkylenediamine. The preferred diamine is N,N,N′,N′-tetramethylethylenediamine (TMEDA), but other diamines that have been used in the preparation of copper amine complexes could also be used such as alkylamines, dialkylamines, arylamines, pyridines etc. In the preferred embodiment of the invention the copper-amino complex is prepared under aerobic conditions in the polar organic solvents such as acetone, tetrahydrofuran (THF), alkyl esters such as ethyl acetate, butyl acetate etc., other ketones such as methyl ethyl ketone (MEK), etc., and ethers such as dimethyl ether, methyl-t-butyl ether (MTBE), etc. These solvents are selected because the catalyst is essentially insoluble and precipitates as a dark brown solid. The catalyst clearly differs in its properties from the catalyst described in the U.S. Pat. No. 4,851,589. It is prepared in a different solvent resulting in precipitation and the dark brown solid that is recovered cannot be completely dissolved in methanol or ethanol. In addition, it can be readily removed from the products of the reaction while retaining its activity, permitting it to be re-used in subsequent reactions. In the presence of oxygen it converts 2,6-dialkylphenols to 3,3′,5,5′-tetraalkyl-4,4′-diphenoquinones. Under the conditions described herein, the diphenoquinones are typically produced exclusively and not as a mixture of 3,3′,5,5′-tetraalkyl-4,4′-diphenoquinones and 2,2′,6,6′-tetraalkyl-4,4′-biphenols which typifies other processes. The same catalyst catalyzes the oxidative coupling of the dialkylphenol and the reduction of the diphenoquinones in the second stage of the reaction.
The invention is not limited to the use of the preferred copper-amino complex. Known copper-amino complexes can also be adapted for use in the two stage dual catalytic reaction of 2,6-dialkylphenols as described herein.
Process Conditions
In a typical process in accordance with the present invention, the 2,6-dialkylphenol to be coupled is dissolved in methanol. While methanol is clearly the preferred solvent, those skilled in the art will recognize that other solvents, in particular other alcohols such as ethanol, isopropanol or butanol can be used. A solvent is selected which dissolves the dialkylphenol and the catalyst and water. It is also important to be able to remove water from this solvent, if it is to be reused in the next cycle. In addition to alcohols, ketones may also be useful. The concentration of the 2,6-dialkylphenol is typically about 1 to 5 molar.
An excess of the phenol is used for the reaction. As little as 0.05% by weight of catalyst based on phenol can be effective and is added to the solution of the phenol. The preferred catalyst is completely soluble in the methanolic solution of the 2,6-dialkylphenol. Oxygen or air is bubbled directly into reaction mixture, or is delivered to the headspace of the reactor at a modest pressure (i.e., about 5 to 20 psi air). The amount of oxygen is readily determined based on the stoichiometry of the reaction. The temperature of the reaction can be easily and preferably controlled in the range of about 30 to 50° C. Higher temperatures can be used particularly with solvents having a higher boiling point than methanol but in the interest of maintaining the
O'Sullivan Peter
Thompson Hine LLP
Wiley Organics, Inc.
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