PREPARATION OF BIS (AMINE-CONTAINING) BENZENEDIOLS

Abstract: Bis (amine-containing) benzenediols are prepared by the hydrogenation and dehalogenation of bis (amine-containing) dihalobenzoquinones using formic acid, formate salts or mixtures thereof in the presence of a noble metal catalyst. An example of a compound produced by this process is 2,5-diamino-1,4-benzenediol. The benzenediols produced by the process of this invention are useful as monomers in the preparation of polybenzoxazoles of high thermal stability and compressive strength.

Description: PREPARATION OF BIS (AMINE-CONTAINING) BENZENEDIOLS This invention relates to the hydrogenation of benzoquinone compounds. More specifically, it pertains to a process for the hydrogenation of bis (amine-con- taining) dihalobenzoquinone to produce bis (amine-con- taining) benzenediol. Bis (amine-containing) benzenediols are useful as monomers in the preparation of polybenzoxazoles (PBO). Polybenzoxazoles can be prepared by reacting amine-containing benzenediols with bisacids, bisacid halides, bisesters or bisnitriles. Polybenzoxazole fibers have high tensile strength and thermal stability and are desirable for military, aerospace and other applications requiring rigid materials. The known methods for preparing the benzenediol monomers typically involve a multi-step synthesis wherein " expensive reagents are required and overall yield is poor. For example, one method involves σxi- dative bishydroxylation of hydroquinone with hydrogen peroxide and an alkali to produce 2,5-dihydroxy-p-ben- zoquinone. The reaction of hydrogen chloride and meth- _2- anol with the dihydroxybenzoquinone yields 2,5-dimeth- oxy-p-benzoquinone which is aminated with ammonia and then reduced with stannous chloride in concentrated hydrochloric acid to give 2,5-diamino-1 ,4-benzenediol with an overall yield of only about 20 percent. See R. Wolf, M. Okada and C. S. Marvel, J. Polymer Science, Part A, 6, 1503 (1968). Other methods involve the reduction of a dihalodiaminobenzoquinone to the corre¬ sponding dihalodiaminohydroquinone without the elimi¬ nation of the halogen substituents. See, e.g., U.S. Patent 4,337,196; Brit. 1,130,275 and Fr. 1,544,504. A simple economical process is needed that would provide a high yield and allow both the reduction of the benzoquinone and the elimination of the halogen substituents without the production of byproducts which are hazardous and difficult to dispose of properly. Such a process would allow the effective production of bis (amine-containing) benzenediol monomers for use in preparing the highly desirable polybenzoxazoles. The present invention is such a straightforward and inexpensive one-step process that provides a high yield of bis (amine-containing) benzenediols. This process comprises contacting bis (amine-containing) dihalobenzoquinones with a molar excess of a reducing agent selected from the group consisting of formic acid, a formate salt and mixtures thereof in the presence of a noble metal-containing catalyst under reaction conditions such that the corresponding bis (amine-containing) benzenediol is produced. In this context, "amine-containing" refers to compounds having -NH2, -NHR, or - 2 substituents wherein R is independently in each occurrence hydrogen, C-*_-J Q alkyl, -3- arylalkyl or alkylaryl. It has surprisingly been found that the process of the present invention results in a high yield and provides for reduction of the benzoquinone and elimination of the halogen sub¬ stituents in a single step. The bis (amine-containing) benzenediols so pro¬ duced can be condensed with bisacids, bisacid halides, bisesters or bisnitriles to produce polybenzoxazoles. Polybenzoxazole fibers, as indicated above, are highly useful in various industrial applications. According to the process of the present inven¬ tion, the benzoquinone starting material is contacted with formic acid, a formate salt or a mixture thereof in the presence of a solvent and a catalyst. The pre¬ ferred benzoquinone compounds used as the starting material in the present invention correspond to the following general formula: wherein B is 1 , -benzoquinone; each X is independently chlorine, bromine, fluorine or iodine; and R' and R 2 are independently hydrogen, C•-_- ]Q alkyl, arylalkyl or alkylaryl. It is preferred that X is chlorine and that R' and R 2 are each hydrogen. Typical benzoquinone compounds include 2,5- -dichloro-3 > 6-diamino-1 ,4-benzoquinone; 2,5-dibromo- -3,6-diamino-1 ,4-benzoquinone; 2,5-dichloro-3-.6- -bis(benzylamino)-1 ,4-benzoquinone; 2,5-dichloro-3,6- -bis(methylamino)-1 , -benzoquinone; 2,5-dichloro-3 > 6- -bis(dimethylamino)-1 ,4-benzoquinone; 2,5-dichloro-3 > 6- -bis(ethylamino)-!,4-benzoquinone; with 2,5-dichloro- -3 > 6-diamino-1,4-benzoquinone; 2,5-dichloro-3,6-bis- (methylamino)-! ,4-benzoquinone and 2,5-dichloro-3,6- -bis(benzylamino)-! ,4-benzoquinone being preferred. The most preferred benzoquinone starting material is 2,5-dichloro-3 » 6-diamino-1,4-benzoquinone. These ben¬ zoquinone starting materials can be prepared by methods well-known in the art. The typical preparation usually involves the reaction of excess ammonia or ammonium hy¬ droxide with tetrahaloquinone. See, e.g., U.S. Patent 4,337,196. 5 -A catalyst is advantageously employed in the practice of the present invention. The catalyst can be any material which contains a noble metal and will catalyze the conversion of the benzoquinone starting material in the presence of formic acid, a formate salt 0 or a mixture thereof to the desired benzenediol. The catalyst may be unsupported or may be supported on sup¬ ports well known in the art such as, for example, alu¬ mina, silica, zeolites, titania, alkaline earth metal r carbonates or carbon. Examples of catalysts useful in the practice of the process of this invention include noble metals on carbon, noble metal oxides, and noble metals supported on alkaline earth carbonates. The term noble metals as used herein refers to gold, sil- 0 ver, platinum, palladium, iridium, rhodium, mercury, ruthenium and osmium. Preferred catalysts include pal¬ ladium on carbon, platinum on carbon, and platinum . oxide. The most preferred catalyst is palladium on carbon. The catalyst is employed in an amount which is i sufficient to catalyze the conversion of starting ma¬ terial in the presence of formic acid, formate salts or mixtures thereof to the corresponding benzenediol. Preferably, from 0.005 to 0.1 molar equivalents of catalyst are present per equivalent of benzoquinone starting material. More preferably, from 0.02 to 0.06 equivalents of catalyst are present throughout the reaction. It is preferred to add the catalyst to the reaction mixture under an inert atmosphere. Examples of inert atmospheres include argon, helium and nitrogen with nitrogen being preferred. A solvent .is advantageously employed in the process of the present invention. Solvents employed in ' the process of the present invention are polar sol¬ vents in which the benezenediol products are soluble. Preferred solvents include water and low molecular weight organic polar compounds. Specific examples of preferred solvents include water, methanol, ethanol, propanol, dimethylformamide and dioxane. Water is the most preferred solvent. Preferably, from 1 to 50 volumes of solvent are employed per volume of benzoquinone starting Material. More preferably, from 5 to 10 volumes of solvent are employed per volume of benzoquinone starting material. Formic acid, formate salts or mixtures thereof are used in the process of the present invention as hydrogen transfer agents. When formic acid is used, it is preferred that it be aqueous formic acid. The concentration of the aqueous formic acid is preferably no less than 5 percent on a weight basis and no greater than 90 percent on a weight basis. It is more -6- preferred that it be no less than 20 percent on a weight basis and no greater than 60 percent. It is most preferred that the concentration of formic acid be 30 percent on a weight basis. Any formate salt which will function as a hydrogen transfer agent to reduce the benzoquinone and remove the halogens therefrom may be used in the prac¬ tice of this invention. Preferred formate salts corre¬ spond to the formula HCO M wherein M is Na, K, Ce, or (R3)gNH and R^ is hydrogen or hydrocarbyl. Examples of hydrocarbyl substituents useful in the practice of this invention include C- j _g alicyclic or aliphatic substituents. It is more pre¬ ferred that M be (R-^J-^NH and that R3 be hydrogen in each instance. The formate salt is preferably in a polar solvent. Representative examples of suitable polar solvents include water, lower alkanols, and ace- tic acid. It is preferred to use acetic acid as a solvent for the formate salt. The hydrogen transfer agent is used in the practice of this invention in an amount sufficient for the reduction of the benzoquinone starting material to the benzenediol product and the removal of the halogen substituents on the benzoquinone starting material. It is preferred to use the reducing agent in a molar excess based on the molar amount of benzoquinone starting material that is used. It is more preferable to use a 4 to 100 molar excess based on the hydroqui¬ none. It is most preferable to use a molar excess of from 10 to 25. The reactants may be added in any order or amount which will allow the reaction to proceed. It is preferred to first mix the benzoquinone reactant and the aqueous formic acid, formate salt or mixtures thereof and then to add the catalyst. The process of the present invention can be carried out at any temperature and pressure at which the reaction will proceed. Preferably, the process is carried out at a temperature between 20°C and 100°C, more preferably between 40°C and 70°C. The process can be carried out at sub- or superatmospheric pressures with atmospheric pressure being preferred for conve¬ nience. The reaction may be allowed to proceed for any length of time sufficient to allow the conversion of at least 50 percent of the starting material. A total reaction time of from 10 minutes to 1 hour is preferred and from 10 minutes to 30 minutes is more preferred. A very small amount of an additional reducing agent such as stannous chloride is added to the reac¬ tion mixture to prevent oxidation of the product. The product can be recovered using known recovery methods such as filtration. The product is generally isolated and stored as a hydrohalide salt in order to prevent oxidative decomposition. It is common practice to iso¬ late the product as a salt of any mineral acid such as hydrochloric, sulfuric, nitric or phosphoric acid. -8- The conversion of the benzoquinone starting material is at least 70 percent, preferably at least 80 percent and more preferably at least 95 percent. The selectivity to the desired benzenediol is also at least 70 percent, preferably at least 80 percent and more preferably at least 95 percent. Thus, the overall yield is at least 50 percent, preferably at least 75 percent and more preferably at least 90 percent. . The process can be conducted in a batch or continuous mode. Surprisingly, in the process of the present invention, the halogen atoms are removed from the ben¬ zoquinone ring system and the benzoquinone is converted to the corresponding benzenediol in a single step. The byproducts of the process are carbon dioxide and/or ammonia. The benzenediol compounds prepared by the process of the present invention correspond to the following general formulas- R 2 ) wherein R' and R 2 are as defined above. Typical ben¬ zenediols include 2,5-diamino-1 ,4-benzenediol, 2,5- -bis(benzylamino)-1 ,4-benzenediol, 2,5-bis(meth l- -amino)-1 ,4-benzenediol, 2,5-bis(ethylamino)-1 ,4- -benzenediol, with 2,5-diamino-1,4-benzenediol, 2,5- -bis(methylamino)-1 ,4-benzenediol and 2,5-bis(benzyl- amino)-1 ,4-benzenediol being preferred. The most preferred benzenediol is 2,5-diamino-1 ,4-benzenediol. The following examples are given to illustrate the invention. Unless stated otherwise, all percentages and proportions are given on a weight basis. Example 1 -Preparation of 2,5-diamino-1 ,4-benzenediol Using Formic Acid A 400-mg portion of a 10 percent palladium-on- -carbon catalyst was added to a reaction vessel containing a vigorously stirred suspension of 4.14 g (20 mmole) of 2,5-dichloro-3,6-diamino-1 ,4-benzoquinone in 30 ml of water and 20 ml of 88 percent formic acid under a nitrogen atmosphere. The nitrogen was removed and mixture was stirred and heated to 60°C during a 15-minute period. The mixture was kept at 60°C for 10 minutes. About 50 mg of stannous chloride was added and the mixture was filtered and washed with 15 ml of water. Hydrogen chloride gas was passed into the fil¬ trate to saturation. The mixture was cooled overnight and the colorless needles of 2,5-diamino-1 ,4-benzene- diol as the bishydrochloride salt were filtered and washed with ethanol and water in a yield of 4.14 g or 98 percent based on the benzoquinone. The product is. -10- confirmed by proton magnetic resonance to be 2,5- diamino-1 ,4-benzenediol. Example 2 -Preparation of 2,5-diamino-1 ,4-benzenediol Using Formate Salt A 400-mg portion of a 10 percent palladium-on- -carbon catalyst was added to a reaction vessel containing a vigorously stirred suspension of 1.40 g (7 mmol) of 2,5-dichloro-3»6-diamlno-1 ,4-benzoquinone, 3-15 g (50 mmol) of ammonium formate, 20 ml of water and 5 ml of acetic acid under a nitrogen atmosphere. The nitrogen was removed and the mixture was stirred at ambient temperature for one hour. The mixture was then heated and stirred at 60°C-80°C for 2 hours. About 50 mg of stannous chloride and 10 ml of HC1 was added and the catalyst was filtered off. Then 20 ml of concentrated HC1 was added to the filtrate. The filtrate was cooled overnight and the colorless needles of 2,5-diaminσ-1 ,4-benzenediol as the bishydrochloride salt were filtered and washed with ethanol and water. The yield was 1.4 g or 98 percent based on the benzoquinone starting material. The product was determined by elemental analysis and proton magnetic resonance to be 2,5-diamino-1 ,4-benzenediol. These examples demonstrate that the process of the present invention is a simple and efficient method capable of producing surprisingly high yields of bis (amine-containing) benzenediols.

Claims: CLAIMS: 1. A process for the preparation of bis (amine-containing) benzenediols comprising contacting a bis (amine-containing) dihalobenzoquinone with a molar excess of a reducing agent selected from the group con¬ sisting of formic acid, a formate salt and mixtures thereof in the presence of a noble metal-containing catalyst under reaction conditions such that the corresponding benzenediol is produced. 2. The process of Claim 1 wherein the benzo¬ quinone starting material corresponds to the following general formula: (X-) 2 B-(NR 1 R 2 ) 2 wherein B is 1 ,4-benzoquinone, X is chlorine, bromine, fluorine or iodine and R' and R 2 are independently hydrogen, C•*_•-- • ) alkyl, arylalkyl or alkylaryl. 3. The process of Claim 1 wherein the molar excess of reducing agent is between 4 and 100 based on the benzoquinone starting material. 8 -12- 4. The process of Claim 1 wherein a polar solvent is employed. 5. The process of Claim 1 wherein the catalyst c is a noble metal supported on an alkaline earth carbon¬ ate. 6. The process of Claim 1 wherein the catalyst is a noble metal supported on carbon. 10 7. The process of Claim 1 wherein the catalyst is present in from 0.005 to 0.1 molar excess based on the benzoquinone starting material. 15 8. The process of Claim 4 wherein the solvent is water. 9. The process of Claim 6 wherein the catalyst 20 is palladium-on-carbon. 10. A process of Claim 1 wherein bis(amine- containing) benzenediol is produced with a selectivity of at least 70 percent and a conversion of at least 70 25 percent based on the starting bis(amine-containing) dihalobenzoquinone. 30

Inventors: INBASEKARAN MUTHIAH N, INBASEKARAN, MUTHIAH, N.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1988
Main classification: C07C91
IPC codes: B01J23, B01J27, C07B61, C07C213, C07C215