GB1590548A

GB1590548A - Borane reducing resins

Info

Publication number: GB1590548A
Application number: GB50682/77A
Authority: GB
Original assignee: Rohm and Haas Co
Current assignee: Rohm and Haas Co
Priority date: 1976-12-10
Filing date: 1977-12-06
Publication date: 1981-06-03
Also published as: FR2397428B1; NO784167L; SU707524A3; ZA777052B; DE2755170C2; IT1093040B; FR2397428A1; CA1114547A; NO774196L; DE2755170A1

Description

(54) BORANE REDUCING RESINS (71) We, ROHM AND HAAS COMPANY, a Corporation organized under the laws of the State of Delaware, United States of America, of Independence Mall West, Philadelphia, Pennsylvania 19105, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention is concerned with cross-linked resins containing amine and/or phosphine borane adduct units with processes for their manufacture, with processes wherein they are used as reducing agents, with their use in the preparation of hydrogenation catalysts and with the catalysts so prepared.

It is known (M. L. Hallensleben, J. Polymer Science: Symposium No. 47, 1-9 (1974), that linear and cross-linked copolymers of 4-vinylpyridine borane, 4vinylpyridine, and styrene can be prepared and used as polymeric reducing agents for aldehydes and ketones. It is also reported in the literature, E. Cernia and F.

Gasparini, J. Applied Polymer Science, Vol. 19, 917-20 (1975), that 4-vinylpyridine borane polymers rapidly decompose in aqueous solutions of strong mineral acids and can only be used as reducing agents for aldehydes and ketones at or about neutral pH.

U.S. Patent 3,928,293 discloses solid cross-linked thiohydrocarbon borane polymers and their use as reducing agents for aldehydes ketones, lactones, oxides, esters, carboxylic acids, nitriles and olefins. These borane polymers although stable at room temperature can release borane (by3) under conditions of reduced pressure or heat and are disclosed as being useful as a convenient means of storing borane. U.S. Patent 3,609,191 discloses polyethylene imine borane complexes which are stable toward hydrolysis at a pH as low as 5.0. These compositions are useful as reducing agents in chemical plating baths for nickel, copper and silver in a pH range of 5 to 8. However, these products are viscous or solid polymers which range in water solubility from completely soluble to slightly soluble depending on the ratio of BH3 to amino groups in the polymer. The use of ion-exchange resins to extract heavy metals from aqueous solutions via ion-exchange mechanisms is also reported in the art.

This invention relates to novel cross-linked resins containing amine-borane and/or phosphine borane adduct units, especially units of the formula

wherein Q is a group of the formula CH2)rnTCH2)n wherein m and n are the same or different and are 0, 1, 2 or 3; and T is

R' and R2 are the same or different and are a) hydrogen; b) (C1-C8) alkyl optionally substituted as hereinafter described; c) (C8C,2) aryl optionally substituted as hereinafter described; or d) (C7-C12) aralkyl, optionally substituted as hereinafter described and Z is a nitrogen or phosphorous atom.

The term "alkyl" as utilized in the present specification and claims is meant to include both straight and branch chained alkyl groups. The alkyl groups in the resins of the invention can optionally be substituted with at most three, preferably at most two, more preferably with one of the following substituents: hydroxy, mercapto, fluoro, chloro, bromo, iodo, nitro, methoxy, ethoxy, isopropoxy, amino, methylamino, dimethylamino, ethylamino, diethylamino, amido, methylamido and dimethylamido.

Examples of the suitable aryl groups are phenyl, naphthyl and biphenyl, and the aryl groups can optionally be substituted with at most three, preferably at most two, more preferably with one of the following substituents: fluoro, chloro, bromo, iodo, nitro, methyl, ethyl, methoxy, ethoxy and trihalomethyl.

Examples of the suitable aralkyl groups are benzyl, phenethyl, phenylpropyl, naphthylmethyl and naphthylethyl and the aralkyl groups can optionally be substituted with at most three, preferably at most two, more preferably with one, of the following substituents: fluoro, chloro, bromo, iodo, nitro, methyl, ethyl, methoxy, ethoxy and trihalomethyl.

Preferred nonionic borane resins of this invention are those wherein T is the group

Z is nitrogen; particularly when R' and R2 are the same or different and are hydrogen, (C1-C8)-unsubstituted-alkyl, (C6-C1 2)-unsubstituted-aryl or (C7C,2)- unsubstituted-aralky1.

More preferred nonionic borane resins of this invention are those where T is the group

Z is nitrogen; particularly when R' and R2 are the same or different and are hydrogen, (C,-C,)-unsubstituted-alkyl or unsubstituted phenyl, biphenyl, benzyl or phenethyl.

Solid borane resins of this invention are particularly useful in selectively reducing at room temperature, from both aqueous and non-aqueous media, mercury, silver gold. platinum, palladium, rhodium, iridium, antimony, arsenic and bismuth ions; to the exclusion of copper, nickel, zinc, iron, lead, tin, cadmium, vanadium, chromium, uranium, thorium, cobalt, thallium, aluminum and the Group I and II members of the Periodic Table. The resins reduce the metal ions in solution via electron transfer and precipitate the reduced metals on and/or into the resin.

The borane resins can be used over a wide pH range, for example over a pH range of 1 to 8. They are preferably used at a pH of 2 to 4. The resins are not only stable in acidic and basic media but are also air stable.

The borane resins are useful as reducing agents for aldehydes, ketones, olefins and compounds containing other functional groups capable of undergoing hydroboration reactions. The resins reduce such compounds by hydride transfer and the resulting product can be liberated from the resin by strong acid hydrolysis.

An added feature of this reduction procedure is the ability of these resins to retain the products on the resin thereby concentrating and purifying the reduced products before hydrolyzing them off the resin. Although the macroreticular form of the resin is preferred, the gel form or any other particulate form of the borane resins of the invention can be used.

The reduced metals which can be precipitated on and/or into the borane resins of the invention can be either dissolved out of the resin by strong acid or, in the case of mercury, can be withdrawn by treatment with hot water. A more preferred method of obtaining the reduced precious metals from the resins however, is by burning the resin away from the metals since the value of the precious metals far exceeds that of the resin.

The borane resins have an advantage over ion exchange resins in that the latter tend to a greater extent, to allow leakage of the metals due to the ion exchange equilibrium for the metal ion in question and the ion exchanger. Since the resins of the invention do not rely on ion exchange mechanisms, this problem is avoided or reduced. The borane resins reduce the metals to their zero oxidation state and precipitate them. However the structure of the resins, in particular of the macroreticular resins, allows them to contain larger amounts of reduced metals before metal ions finally breakthrough into the treated medium. As will be seen below, the resins of the invention may however contain some ion exchange functionality which will operate in known manner along with the borane units of the resins of the invention.

The invention also provides processes in which the borane resins are used as starting materials for the preparation of novel metal catalysts for use in hydrogenation reactions. The resultant metal containing resins can either be pyrolyzed to give a carbon-metal reduction catalyst or they can be burned in the presence of oxygen to give the metal in bead form. Catalysts containing known percentages of metals or of mixed metals can conveniently be formed by this process.

In the preparation of the borane resins of the invention water insoluble crosslinked resin having functional groups of the formula

wherein Q, R', R2 and Z are as defined for Formula (I), may be reacted with a protonating mineral acid such as hydrohalic, phosphoric or sulfuric acid, preferably hydrochloric acid, to convert Formula (II) groups to cationic groups of the formula

This reaction may be carried out in either a batch or continuous, usually column, process at temperatures from 0 to 1000C, preferably at room temperature in a protic solvent, preferably water. The amount of protonating acid used can be as little as from 5% of the equivalents of weak base in the resin, there being no theoretical upper limit. However the acid is preferably utilized in a 25% excess over the equivalents of weak base in the resin. After the protonation step the resin is preferably water washed to remove any excess acid and then washed thoroughly with a drying solvent such as methanol, ethanol, propanol, acetone or dimethylformamide or can be air or vacuum dried. In a more preferred protonation step the reaction is a batch process and a stoichiometric amount of acid is added to protonate all the available protonizable groups. Longer reaction times are preferred in this process to allow complete diffusion of the acid through the resin beads. The borane is preferably incorporated into the protonated resin by treating the resin either in a continuous or batch process with an excess of a solution of lithium, sodium or potassium borohydride dissolved in an appropriate solvent such as methanol, ethanol, dimethylformamide, monoglyme or diglyme (glyme means ethylene glycol dimethyl ether) at temperatures from 0 to 150or preferably at about room temperature.

Another method for incorporating the borane into the resin is by directly treating the amine or phosphine functional resin with diborane gas, either in a continuous or batch process, or with a solution of diborane in an appropriate solvent such as diethyl ether or tetrahydrofuran at a temperature from 0 to 1 500C preferably at about room temperature.

Those resins which contain amide functions either in the T, R', or R2 groups can be converted into amines by the use of excess borohydride reagent thereby reducing the bulk and increasing the ratio of the amount of borane to the amount of resin.

In summary therefore, the invention also provides a process for the preparation of the borane resins of the invention which comprises treating an amine or phosphine functional resin with diborane gas, or a borohydride at a temperature of 0 to 1500C.

In preparations where less than an equivalent of borohydride or borane is used a mixed cationic and nonionic borane reducing agent is obtained which would remove metal complex anions and metal cations by both anion exchange and by reduction of the metal cation or metal complex anion by the borane to the zero oxidation state. It is these mixed resins which are referred to above and which are also included within the scope of this invention.

The presence and amount of borane functionality in the resins can be determined by reacting the resin with an aqueous iodine solution and titrating excess iodine with a standardized solution of sodium thiosulfate. In this determination it is imperative that the amount of iodine absorbed by the resin matrix be calculated for the blank. Thus, the amount of iodine reduced by the borane functionality is equal to the total amount of iodine removed minus the amount absorbed by the polymer. This absorption blank approach is only vaid for borane resins containing borane concentrations approaching the theoretical amount i.e. all weak base sites co-ordinated with borane.

Suitable cross-linked resins which can be utilized in the preparation of the borane resins of this invention are those described in U.S. Patent 2,675,359, U.S.

Patent 3,037,052, U.S. Patent 3,531,463 and U.S. Patent 3,663,467. The procedures described in those patents for making cross-linked resins in both gel and macroreticular form are incorporated herein by reference.

Some embodiments of the resins of this invention and their preparation and use are given in the following Examples.

Example I Synthesis of Acrylic Amine-Borane Resin Step A. Protonation A sample (50.0 g) of a cross-linked acrylic, macroreticular, weak base resin having a weak base capacity of 5.4 meq. of weak base per gram of dry resin is stirred with an aqueous hydrochloric acid solution containing 360 meq. of hydrochloric acid (30% excess) over equivalents weak base in resin for 5 hours. The resin is washed with deionized water to neutral pH, then with two 300 ml portions of acetone and then vacuum dried at 500C for 8 hours. Yield 59.9 grams.

Step B. Borane Addition To a 500 ml round bottom three neck flask equipped with a sealed mechanical stirrer, pressure compensating dropping funnel and mineral oil bubbler, is added a sample (52.8 g, 238.1 meq of H+) of dried acrylic, macroreticular weak base resin (in the hydrochloride form) containing 4.51 meq of H+ per gram of dry resin. A solution of sodium borohydride (10.0 g, 97% purity, 256 meq., 7% excess) in 250 ml of dry N,N-dimethylformamide is added rapidly with continuous stirring. The mixture is stirred at room temperature until no further hydrogen gas evolution is observed. The N,N-dimethylformamide is removed by filtration and the remaining resin is backwashed with deionized water until no chloride ion is detectable with silver nitrate and the pH is approximately seven. The resin is then vacuum dried at 30"C.

Example II Synthesis of Polystyrene Amine-Borane Reducing Resin Step A. Protonation Utilizing the procedure in Example I of Step A and a cross-linked polystyrene, macroreticular, weak base resin the desired intermediate protonated product is obtained.

Step B. Borane Addition Utilizing the procedure in Example I Step B and the resin of Step A the desired borane addition product is obtained.

Example III Synthesis of Polystyryl-Diphenylphosphine-Borane Reducing Resin Step A. Preparation of Polystyryl-Diphenylphosphine Utilizing the procedures in J. Org. Chem. Vol. 40, No. 11, p. 1669 (1975) the macroreticular form of polystyryl-diphenylphosphine is prepared.

Step B. Borane Addition A sample of the resin of Step A (10.0 g., 5.0 meq phosphine/gram) is allowed to react with tetrahydrofuran solution containing diborane (100 ml, 50 meq. BH3).

The mixture is stirred at room temperature for 3 hours. The resulting resin is washed with tetrahydrofuran and is vacuum dried.

Example IV Reduction of Cyclohexanone to Cyclohexanol With Amine-Borane Resin in Aqueous and Non-Aqueous Media Samples of the borane resins of Examples I and II as well as for comparison, the starting weak base analogs from which they were derived are exposed to both aqueous and tetrahydrofuran solutions of cyclohexanone of known concentration (4%) for a period of two hours. During this time no reaction of the cyclohexanone is observed as evidenced by a chromatographic determination of its original concentration. To each sample is added an amount of acid, HC1 for the aqueous system and BF3 for the tetrahydrofuran; in an amount equivalent to the concentration of the cyclohexanone. Both amine-borane resins caused an immediate decrease in the concentration of cyclohexanone. The formation of cyclohexanol is observed in the aqueous system. However, no cyclohexanol is observed in the tetrahydrofuran solution; which is to be expected in the presence of BF3 which would complex the alcohol. The loss of cyclohexanone is however indicative of the reaction of the amine borane resin with cyclohexanone.

Example V Batch Equilibrium Capacities for Several Precious Metals Batch equilibrium capacities are determined by reacting a known amount of amine-borane resin with an aqueous solution of the metal ion under investigation for a period of 16 hours with continuous shaking. The initial and final concentrations of the metal ion are determined by atomic absorption spectroscopy and capacities calculated from the difference.

According to this procedure samples of amine-borane resin are reacted with aqueous solutions of AuCl4-PdC2, and Pitch62 of known concentration. The results are as follows (in Table 1): TABLE 1 Amine-borane Initial Final resin weight Conc. Conc. Capacity resin in grams Metal ion grams grams g metal/gram 0.1090 AuCI4 0.315 0.0705 2.25 0.1020 PtCl6-2 0.322 0.122 1.96 0.1020 PdCh42 0.194 0.076 1.16 Example VI Precious Metal Recovery by Combustion Recovery of the metal from the metal filled beads is easily accomplished by burning the resin matrix away under an oxygen atmosphere.

A sample of gold filled borane resin (3.004 g) is burned at 8000C for 30 minutes in a furnace. Bright colored metalic gold beads are recovered (1.646 g) corresponding to an initial weight percent of 55%. The beads appear as uniform spheres with rough surfaces. Similar results are obtained from palladium and platinum filled resins under identical conditions.

Example VII Catalyst Formation Samples (1.00 g) of palladium and platinum filled beads are pyrolyzed at 6000C under a stream of nitrogen for 30 mins. The resulting spherical beads appear as carbon spheres of high density attributed to the presence of metal.

Example VIII Metal Reducing Selectivity The amine-borane resin reactivity for various metals is determined by placing a sample of the resin (0.10 g) in a vial and adding a concentrated solution of the metal ion or complex under investigation. The vial is allowed to stand for 3 weeks to ensure sufficient contact time. Reaction is confirmed by either a visible change in the beads such as a darkening in color, an increase in weight of the beads when washed with DI water and vacuum-dried, or the inability of the beads to further reduce solutions of AuC4. Likewise a positive reduction of AuC indicates that no reaction with the metal ion under investigation has occurred. Table 2 represents those metals investigated and their ability to be reduced.

TABLE 2 Metal Ion Source Not Reduced Reduced Na+ NaCI V - K+ KCl # - Li+ LiCI V - Mg+2 MgCl2 # - Ca+2 CaCI2 Cr+3 CrCl3 # - Cr+6 K2Cr2O6 # - UO+2 UO2NO3 V V Bi+3 Bi(NO)3 5 V As+3 As2O3 - Mn+2 MnCI2 # - Fe+2 FeCI2 # - Fe+3 FeCl3 V - Co+2 CoCI2 V - Ni+2 NiCI2 V - Cu+2 CuCI2 # -V Zn+2 ZnCl2 Rh+3 RhCl3 - 7 Pd+2 PdCI2 - V Ag+1 AgNO3 - V Cd+2 CdCl2 - 7 Ir+3 IrCI3 Pt+4 H2PtCI6 - V Au+3 HAuCI4 - Hg+2 HgCl2 - V Sb+3 Sb2O3 - # TABLE 2 (cont.).

Metal Ion Source Not Reduced Reduced Sr+2 SrC12 Pb+2 PbCI2 V Tl+' Tl2(SO4) 2 Pb+4 Et4Pb V - CH3Hg+ CH3HgCl - V Example IX Analytical Determination of Gold A gold solution containing 5 ppm Au+3 (1000 ml) is allowed to react with a sample of the amine-borane resin in a column operation under very slow flows (0.5 cumin). After loading is completed the resin is assayed for gold and it was determined that a quantitative amount of gold is present; thus, establishing the utility of the resin in an analytical method for determining trace amounts of gold or other reactive metals.

Example X A 1 gram sample of amine borane resin containing 2.5 meq of BH2 functionality and 2.5 meq of weakly basic anion exchange functionality was treated with an aqueous acidic ARC14 solution. The resin removed gold from this solution and the gold removed was found to be retained on the resin in both the metallic and anionic form. The anionic complex was extracted from the resin by contacting the resin with 4% aqueous NaCI. The anion exchange capacity of the resin was found to be 0.863 g of anionic gold complex per gram of resin. The reduced gold capacity was found to be 1.96 g. metallic gold per gram of resin.

The borane resins can thus be used to detect microquantities of metal ions in various aqueous and non-aqueous media due to their ability to quantitatively convert the metal ions to the zero oxidation state and concentrate the metal on and/or into the resin. The amount of metal present in the resultant metalcontaining resin can then be determined via gravimetric, spectroscopic or other analytical method and the microquantities of metal in the original volume of aqueous or non-aqueous media so treated can then be determined.

The ability of the resins to reduce ionic mercury salts and compounds and in particular methylmercury makes them especially useful in the detoxification of mercury polluted effluents.

Another area of application of borane resins of the invention is in the sugar refining industry as a decolorizing agent. Similarly such resins can be utilized as reducing agents for the removal of oxide impurities in chemicals such as alcohols, glycols, amines and amides.

Resins of the invention can also be used for reducing peroxides in peroxideforming organic compounds especially in ethers such as diethylether, tetrahydrofuran and diisopropyl ether. The resins can of course be utilized to remove peroxides in ethers already contaminated with peroxides as well as peroxide inhibitors in the storage or use of peroxide-forming compounds.

Resins of this invention when impregnated with metals such as silver, copper, arsenic, mercury, etc. can be used as microbiocides for examples, in the textile, paint, paper and laundry industries. They can also find application in the removal of trace amounts of hydrogen sulfide or sulfur dioxide from industrial gas streams such as natural gas streams, coal gasification streams, coal and oil burning utility plants and sulfuric acid plant effluents. In these latter applications the potential high surface area of the finely divided, supported metal provides a high capacity material. The borane resins can be used to remove elemental halogen and alkyl halides from aqueous and non-aqueous media by reducing them to halide ion and alkane respectively.

Certain of the amine-borane resins may be used in organic synthesis since the borane-resin adduct has the desirable features that the reducing support is easily removed from the reaction mixture and the reduced material is attached to the resin system providing for complete separation of the product from the starting material. The reduced material can then be recovered from the resin by acid or base hydrolysis providing a pure product. The reducing support can then be chemically regenerated to the starting amine borane resin bv procedures outlined above.

Another advantage of the borane reducing resins of this invention is their ability to provide a source of borane without the hazards associated with the use of this reagent in the free state. Another application for the amine-borane resins is in the petroleum industry. Petroleum refining plants utilize noble metals as catalysts.

These metals are presently recovered by dissolving them in aqua regia and then chemically reducing the metal chloride salts. However, the effluent from this process still contains about 10 to 15 ppm of metal ion. Anion exchange resins are presently used to remove these final trace amounts of metal. However, rhodium salts are not efficiently removed by anion exchange resins. Thus, the use of high capacity amine-borane resins of the present invention in place of the simple anion exchange resins in the above recovery process is advantageous.

WHAT WE CLAIM IS: 1. A borane reducing resin which comprises a solid, cross-linked copolymer containing amine-borane and/or phosphine-borane adduct units.

2. A resin according to Claim 1, wherein the amine- and/or phosphine-borane adduct units are of the formula

wherein Q is a group of the formula CH2)rnTCH2)n wherein m and n are the same or different and are 0, 1, 2 or 3; and T is the group

and R' and R2 are the same or different and are a) hydrogen; b) (C1-C8), optionally substituted, alkyl; c) (C6-C12), optionally substituted, aryl; and d) (C712), optionally substituted, aralkyl; and Z is a nitrogen or phosphorous atom.

3. A resin according to Claim 2 where R' and R2 are the same or different and are hydrogen, (C,-C,)-unsubstituted-alkyl, (C6-C12)-unsubstituted-aryl or (C7- C,2)-unsubstituted-aralkyl.

4. A resin according to Claim 2 or 3, wherein T is the group

and Z is nitrogen.

5. A resin according to any of Claims 2 to 4, wherein R' and R2 are the same or different and are hydrogen, (C,-C,)-unsubstituted-alkyl or unsubstituted-phenyl, biphenyl, -benzyl or -phenethyl.

6. A resin according to any preceding claim which is in macroreticular form.

7. A resin as claimed in Claim 1 substantially as described in any of the foregoing Examples.

8. A reducing process wherein a resin as claimed in any preceding claim is used as a reducing agent.

9. A process for the preparation of a resin as claimed in Claim 1 which comprises treating a resin having groups of the formula

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. this reagent in the free state. Another application for the amine-borane resins is in the petroleum industry. Petroleum refining plants utilize noble metals as catalysts. These metals are presently recovered by dissolving them in aqua regia and then chemically reducing the metal chloride salts. However, the effluent from this process still contains about 10 to 15 ppm of metal ion. Anion exchange resins are presently used to remove these final trace amounts of metal. However, rhodium salts are not efficiently removed by anion exchange resins. Thus, the use of high capacity amine-borane resins of the present invention in place of the simple anion exchange resins in the above recovery process is advantageous. WHAT WE CLAIM IS:

1. A borane reducing resin which comprises a solid, cross-linked copolymer containing amine-borane and/or phosphine-borane adduct units.

4. A resin according to Claim 2 or 3, wherein T is the group

and Z is nitrogen.

6. A resin according to any preceding claim which is in macroreticular form.

wherein R', R2, Q and Z are as defined in Claim 2, with diborane gas or a borohydride at a temperature of 0 to 1500C.

10. A process according to Claim 8 which comprises reducing one or more aldehyde, ketone and/or amine by contact with a resin according to any of Claims 1 to 7, hydrolyzing the reduced product off the resin and isolating the reduced product.

11. A process according to Claim 8 for the removal of ions from aqueous or non-aqueous media which comprises contacting a medium containing one or more of the following ions: mercury, methyl mercury, silver, gold, platinum, palladium, rhodium, iridium, antimony, arsenic and bismuth ions; with resin according to any of Claims 1 to 7.

12. A process according to Claim 8 which comprises contacting a platinum, palladium, rhodium or iridium containing aqueous or non-aqueous medium with a resin according to any of Claims 1 to 7, and separating the resultant metal containing resin to form an hydrogenation catalyst.

13. A process according to Claim 12 which contains the additional step of pyrolyzing the metal-containing resin.

14. A process according to Claim 12 which contains the additional step of burning the metal-containing-resin in the presence of oxygen.

15. An hydrogenation catalyst which comprises a resin according to Claim 1 containing one or more of the following metals in the zero oxidation state: platinum, palladium, rhodium and iridium.

16. An hydrogenation catalyst composition according to Claim 15 pyrolyzed.

17. An hydrogenation catalyst composition comprising said metal-containingresin, according to Claim 15, subsequently burned in the presence of oxygen.

18. A process according to Claim 8 comprising quantitative method for determining micro-quantities of metal ions in aqueous and non-aqueous media which comprises contacting a resin according to any of Claims 1 to 7 with a measured quantity of a metal-containing medium and then analyzing for the quantity of metal contained in the resultant metal-containing resin.

19. A microbiocidal composition which comprises a resin according to any of Claims 1 to 7 and reduced silver, copper, arsenic and/or mercury.