NO784167L - PROCEDURES FOR REDUCING A SUBSTANCE - Google Patents

Description

Procedure for reduction of a

substance.

The present invention relates to a method

to the reduction of a substance.

It is known from M.L. Hallensleben, J. Polymer Science, Symposium No. 47, 1-9 (1974), that linear and crosslinked copolymers of 4-vinylpyridineborane, 4-vinylpyridine and styrene can be prepared and used as polymeric reducing agents for aldehydes and ketones. It has also been reported in the literature,

E. Cernia and F. Gasparini, J. Applied Polymer Science, 19,

917-20 (1975), that 4-vinylpyridineborane polymers are rapidly decomposed in aqueous solutions of strong mineral acids and can only be used as reducing agents for aldehydes and ketones at or around neutral pH.

From US patent 3,928,293 solid, cross-linked thio-hydrocarbon borane polymers and their use as reducing agents for aldehydes, lactones, oxides, esters, carboxylic acids, nitriles and olefins are known. Although these borane polymers are stable at room temperature, they can release borane (BHj) under conditions of reduced pressure or heat, and are described as useful as a convenient way to store borane. From US patent 3,609,191, polyethyleneimineborane complexes are known which are stable against hydrolysis at a pH as low as 5.0. These substances are usable as reducing agents in chemical plating baths for nickel, copper and silver in a pH range of 5-8. But these products are viscous or solid polymers that have water solubility ranging from completely soluble to slightly soluble, depending on the ratio of BH^ and amino groups in the polymer. The use of ion exchange resins for the extraction of heavy metals from aqueous solutions by means of ion exchange mechanisms is also known in the art.

The method according to the invention is characterized by the fact that the substance is brought into contact with a resin containing a solid, cross-linked copolymer containing amine and/or phosphine adduct units with the formula

where Q is a group of the formula -(CH~) -T-(CH-) - where rir 2 m 2 n m and n are the same or different and are 0, 1, 2 or 3 and T is the group

R" .1 and R 2 are the same or different and are hydrogen, (C-^-Cg)-alkyl which is optionally substituted, (Ci~Ci2^~aryl which is optionally substituted or (C-,-C12)-aralkyl which optionally is substituted, and

Z is a nitrogen or phosphorus atom.

Alkyl means both unbranched and branched alkyl groups. The alkyl groups in the resin may optionally be substituted with no more than 3, preferably no more than 2, preferably 1 of the following substituents: hydroxy, mercapto, fluorine, chlorine, bromine, iodine, nitro, methoxy, ethoxy, isopropoxy, amino, methylamino, dimethylamino, ethylamino, diethylamino , amido, methylamido and dimethylamido.

Examples of suitable aryl groups are phenyl, naphthyl and biphenyl, and the aryl groups can optionally be substituted with at most 3, preferably at most 2, preferably 1 of the following substituents: fluorine, chlorine, bromine, iodine, nitro, methyl, ethyl, methoxy, ethoxy and trihalomethyl .

Examples of suitable aralkyl groups are benzyl, phenethyl, phenylpropyl, naphthylmethyl and naphthylethyl, and the aralkyl groups can optionally be substituted with at most 3, preferably at most 2, preferably 1 of the following substituents: fluorine, chlorine, bromine, iodine, nitro, methyl, ethyl, methoxy , ethoxy and trihalomethyl.

Preferred nonionic borane resins are those resins where T is the group

Z is nitrogen, especially when R 1 and R 1 -> are the same or different and are hydrogen, (C 1 -C 8 )-unsubstituted alkyl, (cg~c^2^ unsubstituted aryl or (cj~ 12^~^substituted aralkyl .

Particularly preferred non-ionic borane resins according to the invention are those resins where T is the group

1 2

Z is nitrogen, especially when R and R are the same or different and are hydrogen, (C₁-C₁)-unsubstituted alkyl or unsubstituted phenyl, biphenyl, benzyl or phenethyl.

Solid borane resins according to the invention are particularly useful in selective reduction at room temperature, where from aqueous and non-aqueous media, of mercury, silver, gold, platinum, palladium, rhodium, iridium, antimony, arsenic and bismuth ions, excluding copper, nickel, zinc, iron, lead, tin, cadmium, vanadium, chromium, uranium, thorium, cobalt, thallium, aluminium, and the members of groups I and II of the periodic table. The resins reduce the metal ions in solution via electron transfer and precipitation of the reduced metals on and/or in the resin.

The borane resins can be used over a wide pH range, e.g. over a range of 1-3. They are preferably used at pH 2-4. The resins are not only stable in acidic and basic media, but are also stable in air.

The borane resins are useful as reducing agents for aldehydes, ketones, olefins, and compounds containing other functional groups capable of undergoing hydroboration reactions. The resin reduces these compounds by hydride transfer, and the resulting product can be released from the resin by hydrolysis with strong acids. An additional feature of this reduction process is the ability of the resins to retain the products on the resin and thereby concentrate and purify the reduced products before they are removed from the resin by hydrolysis. Although the macronet form of the resin is preferred, the gel form or any other particulate form of the borane resin according to the invention can be used.

The reduced metals which can be precipitated on and/or in the borane resin according to the invention can either be dissolved out of the resin with strong acid, or in the case of mercury, extracted by treatment with hot water. A more preferred method for obtaining the reduced, precipitated metals from the har piks, however, is to burn the resin away from the metals, since the value of the noble metals is low. exceeds the value 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 between the relevant metal ion and the ion-exchanger. As the resin according to the invention is not based on an ion exchange mechanism, this problem is avoided or reduced. The borane resins reduce the metals to their 0-oxidation state and precipitate them. But the structure of the resins, especially of the macronet-shaped resins, means that they can contain large amounts of reduced metals before metal ions finally break through into the treated medium. As will appear below, however, the resins according to the invention may contain some ion exchange functionality which will function in a known manner together with the borane units in the resins according to the invention.

The invention also relates to a process where the borane resins are used as raw materials for the production of metal catalysts for use in hydrogenation reactions. The resulting metal-containing resins can either be pyrolysed, whereby a carbon-metal reduction catalyst is formed, or they can be burned in the presence of oxygen, whereby the metal is obtained in pearl form. Catalysts containing known percentages of metal or of mixed metals can conveniently be prepared by this method.

In the production of the borane resins according to the invention, water-insoluble, cross-linked resins with functional groups with the formula

where Q, R 1 , R 2 and Z are as indicated for formula (I), is reacted with a proton-releasing mineral acid, such as hydrohalic, phosphoric or sulfuric acid, preferably hydrochloric acid, to convert the groups of formula (II) into cationic groups of the formula

This reaction can be carried out either batchwise or continuously, usually in a column, at temperatures of from 0 to 100°C, preferably at room temperature in<et>Solvent, preferably water. The amount of deprotonating acid can be as low as 5% of the equivalents of weak base in the resin while there is no theoretical upper limit. However, the acid is preferably used in an excess of 25% in relation to the equivalents of weak acid in the resin. After the protonation step, the resin is preferably washed with water to remove any excess acid and then thoroughly washed with a drying solvent,

such as methanol, ethanol, propanol, acetone or dimethylformamide, or it 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 available protonatable groups. Longer reaction times are preferred according to this method so that the acid can diffuse through the resin beads. The borane is preferably embedded in the protonated resin by treating the resin either in a continuous or a batch process with an excess of a solution of lithium, sodium or potassium borohydride dissolved in a suitable solvent such as methanol, ethanol, dimethylformamide, monoethylene glycol dimethyl ether or diethylene glycol dimethyl ether by temperatures of from 0 to 150°C, preferably at approx. room temperature.

Another method for embedding the borane in the resin is by direct treatment of the amine- or phosphine-functional resin with diborane gas, either in a continuous or in a batch process, or with a solution of diborane in a suitable solvent such as diethyl ether or tetrahydrofuran by a temperature now from 0 to 150°C, preferably at approx. room temperature.

The resins containing amide functions either in T-,

The R 1 - or R 2 groups can be converted to amines using an excess of borohydride reagent, whereby the main mass is reduced

and the ratio between the amount of borane and the amount of resin is increased.

In summary, the invention has thus produced a method for the production of the borane resins according to the invention, whereby an amine- or phosphine-functional resin is treated with diborane gas or a borohydride at a temperature of from 0 to 150°C.

When less than 1 equivalent of borohydride or diborane is used, a mixed, cationic and non-ionic boron reducing agent is obtained which will remove metal complex anions and metal cations by both anion yield and by reduction of the metal cation or metal complex anion with the borane to the 0-oxidation state. Then these mixed resins which are referred to above and which are also within the scope of the 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 the excess iodine with a standard solution of sodium thiosulfate. For this determination, it is absolutely necessary that the amount of iodine absorbed by the resin base mass is calculated for the determination. The amount of iodine that is reduced by the borane functionality is thus equal to the total amount of iodine that is removed minus the amount that is absorbed by the polymer. This approximate absorption determination is only valid for borane resins containing borane concentrations that approach the theoretical amount, i.e. that all sites for the weak base are coordinated with borane.

Suitable cross-linked resins which can be used for the production of the borane resin according to the invention are those described in US patents 2,675,359, 3,037,052, 3,531,463 and 3,663,467.

Some exemplary embodiments of the resins according to the invention and their production and use will be given in the following examples.

Example I

Production of acrylamine-borane resins.

Step A. Protonation.

A 50.0 g sample of a cross-linked acrylic macroreticle weak base resin having a weak base capacity of 5.4 meq. cool base per g of dry resin was stirred with a hydrochloric acid solution containing 360 meq. hydrochloric acid (30% excess)

relative to the equivalents of weak base in the resin for 5 hours. The resin was washed with deionized water to neutral pH, then with two 300 ml portions of acetone and then vacuum dried at 50°C for 8 hours. Yield 59.9 g.

Step B. Boron addition.

Into a 500 mL three-necked round-bottomed flask equipped with a sealed mechanical stirrer, a pressure-compensating dropping funnel and mineral oil bubbler was placed 52.8 g (238.1 meq. H<+>) of macronet-shaped, weakly basic acrylic resin (in hydrochloride form) which contained 4.51 meq. H+ per g of dry resin. A solution of 10 g of borohydride with 97% purity (256 meq., 7% excess) in 250 ml of dry N,N-dimethylformamide was added rapidly with constant stirring. The mixture was stirred at room temperature until no further evolution of hydrogen gas could be observed. The N,N-dimethylformamide was removed by filtration, and the remaining resin was washed with deionized water until no chloride ions were detectable with silver nitrate and the pH was ca. 7. The resin was then vacuum dried at 30°C.

Example II

Production of polystyrene-amine-borane-reducing resin. Step A. Protonation.

By using the method in example I, step A,

and a weakly basic resin of crosslinked macroreticulated polystyrene, the desired protonated intermediate was obtained.

Step B. Boron addition.

By using the method in example I, step B, and the resin in step A, the desired borane addition product was obtained.

Example III

Preparation of polystyrene-diphenylphosphine-borane-reducing resin.

Step A. Preparation of polystyrene diphenylphosphine.

By using the method according to J. Org. Chem., 40,

No. 11, 1669 (1975), polystyrene diphenylphosphine was prepared in macronet form.

Step B. Boron addition.

A sample of 10.0 g of the resin from step A (5.0 meq. phosphine) was allowed to react with 100 ml of tetrahydrofuran solution containing diborane (50 meq. BH 2 ). The mixture was stirred at room temperature for 3 hours. The resulting resin was washed with tetrahydrofuran and vacuum dried.

Example IV

Reduction of cyclohexanone to cyclohexanol with amine-borane resin in aqueous and non-aqueous media.

Samples of the borane resins according to examples I and II as well as, for the sake of comparison, the starting analogues of the weak bases from which they were derived were exposed to both aqueous and tetrahydrofuran solutions of cyclohexanone with a known concentration (4%) for a period of 2 hours. During this time, no reaction of cyclohexanone was observed, as evidenced by chromatographic determination of its initial concentration. To each sample was added a quantity of acid, HCl to the aqueous system and BF^ to tetrahydrofuran, in a quantity equivalent to the concentration of cyclohexanone. Both amine-borane resins caused an immediate lowering of the cyclohexanone concentration. The formation of cyclohexanol was observed in the aqueous system. However, no cyclohexanol was observed in the tetrahydrofuran solution, which is expected in the presence of BF^ which would form a complex with the alcohol. However, loss of cyclohexanone is indicative of the reaction between the amine borane resin and cyclohexanone.

EczemaPart V

Equilibrium capacities for batches of several precious metals. Equilibrium capacities for batches were determined by reacting a known amount of amine-borane resin with an aqueous solution of the relevant metal ion for a period of 16 hours under constant shaking. The initial and final concentrations of the metal ion were determined by atomic absorption spectroscopy and the capacities calculated from the difference.

According to this procedure, samples of amineborane were

-2 -2 the pitch reacted with an aqueous solution of AuCl^PdCl4 and PtClg of known concentration. The results are shown in table 1 below.

Example VI

Recovery of precious metal by incineration.

Recovery of the precious metal from the metal-filled beads was easily achieved by burning away the resin matrix in an oxygen atmosphere.

A 3.004 g sample of gold-filled borane resin was fired at 800°C for 30 minutes in a furnace. 1.646 g of clear metallic gold pearls were recovered, corresponding to an initial weight percent of 55. The pearls appeared as smooth spheres with a rough surface. Similar results were obtained with palladium- and platinum-filled resins under the same conditions.

Example VII

Catalyst production.

1.00 g samples of palladium- and platinum-filled beads were pyrolyzed at 600°C under a stream of nitrogen for 30 minutes. The resulting spherical beads appeared as carbon spheres which had a high density due to the metal content.

Example VIII

Metal reducing selectivity.

The reactivity of the amine-borane resin towards various metals was determined by placing a 0.10 g sample of the resin in a bottle and adding a concentrated solution of the relevant metal ion or complex. The bottle was set aside for 3 hours to ensure sufficient contact time. The reaction was confirmed either by a visible change in the beads, such as a darkening of the color, an increase in the beads' weight by washing with deionized water and vacuum drying, or by the beads not being able to reduce more solution of AuCl^ . Likewise, a positive reduction of AuCl^ indicates that no reaction had taken place with the metal in question. Table 2 below indicates the metals that were examined and their ability to be reduced<

Example IX

Analytical determination of gold.

1000 mL of a yellow solution containing 5 ppm Au+"^ was allowed to react with a sample of the amine-borane resin in a column under very slow flow (0.5 mL/min). After loading was complete, the resin was assayed for gold, and it was demonstrated that a quantitative amount of gold was present.It is thus possible to use the resin in the analytical determination of trace amounts of gold or other reactive metals.

Example X

A 1 g sample of the amine-borane resin containing 2.5 meq. BH^ functionality and 2.5 meq. weakly basic anion-exchanger functionality was treated with an aqueous acidic AuCl^ soln. The resin removed the gold from this solution,

and the recovered gold was found to be retained in the resin in both metallic and anionic form. The anion complex was extracted from the resin by bringing it into contact with 4 percent aqueous NaCl. The anion exchange capacity of the resin was found to be 0.863 g of anionic cull complex per g resin. The capacity for reduced gold was found to be 1.96 g of metallic gold per g resin.

The borane resins can thus be used for the detection of microquantities of metal ions in various aqueous and non-aqueous media because the resins can quantitatively convert the metal ions to the 0-oxidation state and concentrate the metal and/or in the resin. The amount of metal present in the resulting metal-containing resin can be determined via gravimetric, spectroscopic, or other analytical methods, and the microamounts of metal in the original volume of aqueous or non-aqueous media thus treated can then be determined.

The ability of the resins to reduce ionic mercury salts and compounds, especially methylmercury, is particularly useful in the detoxification of mercury-poisoned effluents.

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

The resin according to the invention can also be used for the reduction of peroxides in peroxide-forming organic compounds, particularly in ethers such as diethyl ether, tetrahydrofuran and diisopropyl ether. The resins can of course be used for the removal of peroxides in ethers that are already contaminated with peroxides and as peroxide inhibitors when storing or using peroxide-forming compounds.

The resins according to the invention, when impregnated with metals such as silver, copper, mercury etc., can be used as microbiocides, e.g. in the textile, paint, paper and laundry industries. They can also be used for the removal of trace amounts of hydrogen sulphide or sulfur dioxide from industrial gas flows, such as natural gas, coal gas flows, effluents from coal and oil burning plants as well as sulfuric acid plants. In these latter applications, the potentially high surface area of the finely divided metal deposited on a support provides a high-capacity material. The borane resins can be used for the removal of 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 can be used in organic syntheses as the borane resin adduct has the desired properties that the reducing carrier can be easily removed from the reaction mixture and the reduced material adheres to the resin system and causes complete separation of the product from the starting material. The reduced material can then be recovered from the resin by acid or basic hydrolysis, producing a pure product. The reducing carrier can then be chemically regenerated to the starting amine-borane resin by the methods described above.

Another advantage of the borane-reducing resins according to the invention is that they provide a source of borane without the dangers associated with the use of this substance in the free state.

Another application for the amine-borane resins is in the petroleum industry. Petroleum refineries use precious metals as catalysts. These metals are recovered according to known techniques by dissolving them in aqua regia and then reducing the metal chloride salts. But the effluent from this process still contains 10-15 ppm metal ions. Anion exchange resins are currently used to remove these remaining trace amounts of metal. But rhodium salts are not effectively removed with anion exchange resins. The use of the high-capacity amine-borane resins according to the invention instead of the simple anion exchange resins in the above-mentioned recovery process is thus advantageous.

Claims (7)

1. Method for reducing a substance, characterized in that the substance is brought into contact with a resin containing a solid, cross-linked copolymer containing amine and/or phosphine adduct units with the formula where Q is a group of the formula -(CH2 )m -T~ (CH2 ) <-> where m and n are the same or different and are 0, 1, 2 or 3 and T is the group R 1 and R 2 are the same or different and are hydrogen, (C-j^-Cg)-alkyl which is optionally substituted, (C-L-C12)-aryl which is optionally substituted or (C7-C12 )-aralkyl which is optionally substituted, and Z is a nitrogen or phosphorus atom. 2. Process in accordance with claim 1, whereby at least one aldehyde, ketone and/or amine is reduced, characterized in that the product after reduction upon contact with the resin is hydrolysed by the resin and isolated. 3. Method according to claim 1, whereby ions are removed from aqueous or non-aqueous media, characterized by a medium containing at least one of the ions mercury, methylmercury, silver, gold, platinum, palladium, rhodium, iridium, antimony, arsenic or bismuth is brought into contact with the resin. 4. Method according to claim 1, characterized in that a medium containing platinum, palladium, rhodium or iridium is brought into contact with the resin, after which the resulting metal-containing resin is separated to form a hydrogen catalyst containing the metal in the O-oxidation state. 5. Method in accordance with claim 4, characterized in that the metal-containing resin is pyrolysed. 6. Method in accordance with claim 4, characterized in that the metal-containing resin is burned in the presence of oxygen. 7. Method in accordance with claim 1, used as a quantitative method for determining microamounts of metal ions in aqueous and non-aqueous media, characterized in that the resin... is brought into contact with a measured amount of metal-containing medium, and that this concentration is then analyzed regarding the amount of metal in the resulting metal-containing resin.