US3439046A - Process for oxidation of hydrocarbylborane compounds to alcohols - Google Patents

Description

United States Patent 3,439,046 PROCESS FOR OXIDATION OF HYDROCARBYL- BORANE COMPOUNDS T0 ALCOHOLS Herbert C. Brown, 1840 Garden St., West Lafayette, Ind. 47906 No Drawing. Continuation of application Ser. No. 221,880, Sept. 6, 1962. This application Apr. 18, 1967, Ser. No. 631,843

Int. Cl. C07c 29/00, 35/08 US. Cl. 260-617 14 Claims ABSTRACT OF THE DISCLOSURE Cross reference to related applications This application is a continuation of application Ser. No. 221,880 filed Sept. 6, 1962, now abandoned.

Background of the invention There have been attempts to accomplish the oxidation of organoboron compounds by the controlled reaction of the organoboron compounds with air or oxygen. This, of course, is highly desirable because of the high economics possible using either air or oxygen. However, there are inherent disadvantages in the known prior art tech niques of controlled oxidation either with air or oxygen. For example, when moist air is employed for oxidizing a trialkylborane, only one alkyl group is oxidized resulting in only one mole of alcohol after hydrolysis per mole of trialkylborane. The employment of dry air on the other hand results in the oxidation of two of the alkyl groups which is, of course, more advantageous than the moist air technique but more costly in that the air must be dried. In only one instance is there any report of oxidizing the so-called last alkyl group with air or oxygen and this has been when employing dry air. However, the amount of oxidation of the last carbon to boron linkage was very slow requiring many days in order to obtain appreciable controlled oxidation. Further, the process requires stringent control in order to eliminate the presence of any water since when the same reaction was attempted using moist air, no oxidation was obtained even after maintaining the system under pressure for 18 months. The literature is abundant in pointing out the problem that with air or oxygen it has been impossible to oxidize more than two alkyl groups and if there were only one alkyl group present in the initial organoborane reactant, e.g., RB'(OR) there is no convenient or practical technique known for oxidizing this so-called last carbon to boron linkage.

It has also long been known that organoboron compounds, for example, trialkylboranes, can be oxidized by various techniques to form the corresponding boron esters which in turn can be hydrolyzed to result in the alcohols. For example, it is known that the trialkylboranes can be reacted with various peroxides, such as hydrogen peroxide, in the presence of bases to produce the esters. These procedures are of limited utility because of the dangerous aspects of the reaction and the cost involved. Consequently, these procedures have not been employed on a commercial scale. Accordingly, there is a need for a more "ice economical method for oxidizing organoborane compounds and others have attempted with little or no success to fulfill this need. Therefore, it is highly desirable to provide the art with a method for oxidizing organoboranes by which all boron to carbon linkages are reacted in order to effect complete oxidation to ROB moities and result in the most eificient utilization of this intermediate for forming the desirable alcohol product.

Accordingly, an object of this invention is to provide a novel process for the controlled oxidation of organoboron compounds, that is, compounds having carbon linked directly to boron. Another object of this invention is to provide a more efiicient and economical method for the controlled oxidation of the organoboron compounds in higher yield and purity. A particular object is to provide a method whereby all carbon to boron linkages in an organoboron compound are selectively oxidized to the intermediate HOB moities. A still more specific object is to provide a method whereby in addition to oxidizing all the carbon to boron linkages in an organoboron compound, an alcohol is directly produced in the reaction mixture in high yield and readily recoverable therefrom.

The above and other objects of this invention are accomplished by reacting an organoboron compound having at least one carbon to boron linkage with an alkali metal oxyhalide compound in an aqueous system to effect controlled oxidation of the carbon to boron linkages. Alkylboranes in which the alkyl group(s) each have up to about 40 carbon atoms are generally the preferred organoboron compounds. The temperature at which the reaction is conducted is subject to considerable latitude. Generally temperatures ranging from about 0 C. up to about 200 C. or higher may be employed. It is preferred in most instances, however, to employ temperatures ranging from about 10 C. up to about 90 C. since excellent results are obtained within this range. It is most particularly preferred to employ temperatures ranging from about 45 C. up to about C. since higher yields of the desired product are obtained within this range. A further embodiment of the present invention comprises reacting in an aqueous system an organoboron compound having at least one carbon to boron linkage with an alkali metal oxyhalide compound in the presence of a metal hydroxide. It is preferable in the novel processes of this invention to employ a diluent such as an ether since high yields of the desired product are obtained under these conditions. Thus, one particular embodiment of the present invention comprises reacting a trialkylborane with an alkali metal oxyhalide in the presence of an ether diluent. However, an alternative and preferable embodiment of the invention is to conduct the above-described reaction in the presence of a metal hydroxide. By doing so, any harmful side reaction which might occur between reactants and diluents are minimized. The product produced by this novel process is an alcohol which corresponds to the organo group of the organoboron reactant. The al cohol so-produced is readily recovered by conventional techniques. These and other embodiments of the invention will be brought forth in greater detail in the discussion which follows.

The process of this invention is of particular advantage in that the controlled oxidation of organoboron compounds is accomplished in an efficient and practical manner. This is in direct contrast to the hazardous use of peroxide in the oxidation of organoboranes. A further advantage is the fact that complete oxidation takes place whereby all carbon to boron linkages are oxidized. Furthermore, the present-process represents a more economical procedure than peroxide oxidation. Still further, high pressure apparatus is not required as in the prior art air oxidation processes.

The process involves the employment of organoboron compounds, particularly hydrocarbon boron compounds, which have at least one carbon to boron linkage. The carbon to boron linkage is the primary requisite 'of this reactant since this linkage is what is oxidized and desired to be reacted in the process. The remaining valences of the boron can be other ligands including those which are reactive to oxygen provided that they do not destroy the reactivity of the oxygen with the carbon to boron linkages. Thus, such other ligands can be, for example, moities such as the hydrocarbon radicals, alcohol residues (OR), hydrocarbon, halogens, hydroxyl' groups, inorganic acid anions, organic acid anions, particularly of the alkanoic acids, salt structures (-OM), particularly where M is an alkali metal, and the like. It is preferable, however, that such other ligands be selected from the same or different hydrocarbon radicals, and hydroxyl groups. Thus, included among the organoboron reactants employed in the process of this invention are the trialkylboranes as, for example, trimethylborane, triethylborane, tributylborane, tri-S-methylbutylborane, tri-4- methylpentylborane, trihexylborane, trioctylborane, tri decylborane, tn'undecylborane, tridodecylborane, trioctadecylborane, trieicosylborane, tri-triacontylborane, tri-tetracontylborane, and the like; trialkenylboranes as, for example, trivinylborane, tri-l-butenylborane, tri-2-octenylborane, trioctadecenylborane, tri-triacontenylborane, and the like; alkynylboron compounds as, for example, tril-hexynylborane, tri-2-octynylborane, and the like; cycloalkyland cycloalkenylboron compounds as, for example, tricyclobutylborane, tricyclohexylborane, tricyclooctylborane, tricyclobutenylborane, tricyclohexadienylborane, and the like; arylboron compounds as, for example, triphenylborane, trinaphthylborane, tri-(2-phenylethyl)borane, tribenzylboranc, tritolylborane, and the like; mixed organoboranes as, for example, methyldiethylborane, octyl-dihexylborane, phenyl-dioctadecylborane, and the like; cyclic or polymeric hydrocarbon boron compounds as, for example, butane-1,4-bis(l-boracyclopentane),

pentane-l,5-bis( l-boracyclohexane) l-n-butylboracyclohexane; 1-n-butylboracyclopentane; compounds having the moiety Hg-C Hr- B C Hz-C Hr n where n is at least 2; and the like; hydrocarbonboron acids as, for example, benzyl boronic acid, ethyl boronic acid, phenyl boronic acid, dioctadecyl boronous acid, and the like, and their corresponding salts of metals, particularly the alkali metals, as for example, sodium, lithium, potassium, and cesium; hydrocarbonboron halides as, for example, dihexylboron chloride, dioctadecylboron fluoride, dioctylboron bromide or iodide, and the like; hydrocarbon borines as, for example, dihexylboron hydride, tetradecyl diborane, and the like; and hydrocarbonboron compounds also containing inorganic and organic acid anions as, for example, dihexylboron sulfate, dihexylboron nitrate, dihexylboron acetate, dihexylboron octadecanoate, and the like. Another type of cyclic organoboron compound also employable are those illustrated by, for example, trimethyl boroxine (MeBO) trihexyl boroxine, trioctadecyl boroxine, and the like. The above compounds are presented by way of illustration and it is not intended to be limited thereto. In general, the hydrocarbon moieties contained in such compounds will have up to and including about 40 carbon atoms. It is to be understood that the hydrocarbon groups can be further substituted to result in branch chains and insomers thereof as Well as being substituted by other functional groups which are essentially inert in the reaction or do not defeat the oxidation of the carbon-boron linkages desired.

The organoborane reactants, as described above, can generally be produced by any prior art technique. One such standard procedure for the internal hydroboration of olefins to produce organoboranes is as follows, In a reaction vessel containing diglyme and sodium borohydride, a solution of the desired olefin is added. Boron trifluoride in a diglyme solution is added to the reaction mass. All of these steps are completed under an anhydrous nitrogen atmosphere. The borohydride BF solution olefin mixture is stirred for about 1 hour until an essentially quantitative yield of the desired organoborane is obtained.

As stated herein above, the process of this invention involves a controlled oxidation of the carbon to boron linkages. For this purpose, an alkali metal oxyhalide compound is employed. The alkali metals include lithium, sodium, potassium, rubidium, and cesium. The halides include fluorine, chlorine, bromine, and iodine. Typical examples of the alkali metal oxyhalides employed are lithium hypobromite, lithium hypochlorite, lithium hypofluorite, sodium hypobromite, sodium hypofluorite, potassium hypofluorite, potassium hypochlorite, potassium hypobromite, rubidium chlorate, cesium perchlorate, sodium iodate, sodium metaperiodate, sodium chlorate, sodium perchlorate, and the like. The most particularly preferred alkali metal oxyhalide employed in the process of this invention is sodium hypochlorite since this compound is cheap, easily obtained, and gives excellent results in the process of this invention.

The process of this invention is preferably conducted in the presence of a metal hydroxide. The metal hydroxide is preferably employed when the process is conducted in the presence of a solvent such as tetrahydrofuran. The advantages of employing a metal hydroxide are many. For example, side reactions, if any, occurring between the solvent and the oxidizing agent are prevented since the hydroxide generally has a strong inhibiting effect on said side reactions. Typical examples of the metal hydroxides which may be employed in the process of this invention are lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide, barium hydroxide, chromium hydroxide, and the like. The particularly preferred hydroxides are the alkali metal hydroxides since these compounds are cheaper and more easily obtained. The most particularly preferred metal hydroxide is sodium hydroxide since excellent results are obtained when this hydroxide is employed.

Although not essential, inert diluents may be employed in the reaction system as an additional means for controlling reaction temperature or to provide greater solubility for the reactants. Generally it is preferred toemploy diluents that are essentially inert to the reactants, --i.e., they do not react with the reactants or the products obtained. Thus, liquid hydrocarbons having up to about 18 carbon atoms may be employed. For example, hexane, decane, cyclohexane, cyclopentane, toluene, xylene, benzene, mineral oil, gasoline, kerosene, and the like may be used. It is preferable to employ ethers in the process of this invention. Generally, aliphatic monoethers, cyclic ethers, glycol ethers, and the like may be employed. Typical examples of ethers which may be employed are tetrahydrofuran, dioxane, tetrahydropyran, the dimethyl ether of diethylene glycol, the diethyl ether of diethylene glycol, diethyl ether, dibutyl ether, and the like. The cyclic and glycol ethers are preferred since excellent results are obtained, e.-g., high yields and pure product. The proportion of alkali metal oxylhalide to the organoboron reactant generally ranges from about 2:1 up to about :1 (alkali metal oxyhalide to organoboron). When sodum hydroxide is also employed in the reaction system, the weight proportion of alkali metal oxyhalide to organoboron can generally be considerably less than 100:1. Thus, it is preferred when an alkali metal hydroxide is used that the proportion of halide to boron compound be from about 2:1 to

employed in the reaction ranges from about :1 up to about 50:1 (metal hydroxide to organoboron).

The manipulative operations of the process of this invention are subject to considerable latitude. In general, however, the hydrocarbon boron compound and ether diluent are admitted to the reactor in any order of addition. Thereafter, an aqueous solution of the alkali metal oxyhalide reactant is slowly added to the system. The oxydation takes place upon stirring of the reaction mixture and the products and diluents are readily recovered by conventional techniques.

The present invention will be more completely understood from a consideration of the following examples wherein all parts are by weight unless otherwise indicated.

Example I Employing a reactor equipped with internal agitation and a means for introducing and discharging the reactants, there was added 4.95 parts of tri-n-hexyl borane, 50 parts of the dimethyl ether of diethylene glycol, and 4 parts sodium hydroxide in an aqueous solution. To this mixture was added 4.44 parts of sodium hypochlorite. While add ing the sodium hypochlorite, the reaction mixture was maintained at 25 to 30 C. Stirring was conducted for 2 hours. The aqueous phase of the reaction mixture was separated and treated with parts of sodium hydroxide pellets and extracted 4 times with diethyl ether. The alcohol mixture thus obtained from the aqueous phase was dried and filtrated after which the product was analyzed by vapor phase chromatography. The yield determined from the vapor phase chromatograph was 90 to 91 percent n-hexanol.

Example II To a reactor was added 10.9 parts of tricyclopentyl borane, 50 parts of the dimethyl ether of diethylene glycol, and 4 parts of sodium hydroxide in an aqueous solution. To this was added 4.44 parts of sodium hyprochlorite. While slowly adding the sodium hypochlorite, the reaction mixture wasmaintained at to 28 C. After 2 hours of stirring, the aqueous phase was separated from the reaction mass and treated in the same manner as set forth in Example I. The alcohol, cyclopentanol, was obtained in an 89.6 percent yield as determined by vapor phase chromatography on a tris(,8-cyanoethoxy)propane column at 95 C. using cyclohexanol as standard.

Example III Tris-trimethylpentyl borane (1.73 parts) and 30 parts of diglyme were added to a reaction vessel. To this mixture was added 4 parts of sodium hydroxide in an equeous solution and 4.44 parts of sodium hypochlorite. The reaction mass was maintained at a temperature of 24 to 26 C. for 2 hours while stirring. The alcohol, 2,4,4-trimethylpentanol was recovered in the same manner as set forth in Example I. The yield of 2,4,4-trirnethylpentanol as determined by vapor phase chromatography was 91-935 percent using tri(;8-cyanoethoxy)propane at 100 C.

Example IV Tricyclooctylborane (1.73 parts), and 50 parts of the dimethyl ether of diethylene glycol was added to a reaction vessel. To this mixture was added 4.44 parts of sodium hypochlorite mixed with 4 parts of sodium hydroxide in an aqueous solution. The reaction mass was maintained at a temperature of from 25 to 30 C. for a period of 2 hours while stirring. The alcohol, cyclooctanol, was obtained in a 94 percent yield as determined by vapor phase chromatography.

Example V Norbornylene (15 parts) was hydroborated in diglyme (100 parts) to produce dinorbornyl borane. Water (50 parts) was added to the reaction mixture while stirring for 2 hours at 25 C. The product so-obtained was dinorbornyl borinic acid. To this product was added 8 parts of sodium hydroxide and 9.25 parts of sodium hypochlorite dropwise, at a temperature of 25 to 28 C. The reaction mass was stirred for 2 /2 hours. By vapor phase chromatographic analysis, using cyclohexanol as an internal standard, a yield of 75.6 percent of norborenol was obtained.

Example VI a-Pinene (8 parts) was hydroborated to produce diisopinocamphenyl borane. The diisopinocamphenyl borane was treated with 4.4 parts of sodium hypochlorite in the presence of 4 parts of sodium hydroxide in an aqueous solution for 2% hours at a temperature of 25-30 C. The alcohol so-obtained and recovered as set forth in Example I was isopinocampheol in an 84 percent yield. The product was distilled and had a melting point of 48 to 52 C. The material was redistilled at 112 to 114 C. at 17 mm. of mercury and was determined to be optically active (showing the optical activity in benzene of [a =+32.1]).

Example VII Cyclooctadiene (5.4 parts) was hydroborated in (20 parts) of diglyme. The product was thereafter hydrolyzed with water and treated with a solution mixture of 4 parts of sodium hydroxide. The color of the solution thereupon changed to a dark yellow. Sodium hypochlorite (4.4 parts) was added slowly at 2528 C. with stirring. The reaction was permitted to continue with stirring for 2 /2 hours. The product obtained was cyclooctanediol in 28.5 percent yield as indicated by the vapor phase chromatographic analysis.

Similar excellent results are obtained when other organo-boranes are employed in the process of Example I-VII such as triphenylborane, tritolylborane, and methylphenylborane.

Example VIII Tri-n-hexyl borane (4.95 parts) was added to a reaction flask containing 30 parts by volume of tetrahydrofuran. To this mixture was added 4.44 parts of sodium hypochlorite and 4 parts sodium hydroxide. The reaction mass was maintained at a temperature of 2329 C. and stirred for 2 /2 hours. The alcohol was extracted and dried by normal procedure. The product, n-hexyl alcohol, was obtained in a 78.9 percent yield as indicated by vapor phase chromatographic analysis.

Example IX Tri-n-hexyl borane (4.95 parts) was introduced into a reaction vessel. No diluent or solvent was added. To the tri-n-hexyl borane was added 5 parts of sodium hypochlorite and 5 parts of sodium hydroxide. The reaction mass was maintained at a temperature of 26-28" C. and stirred for 2 hours. The product, n-hexyl alcohol was extracted in the usual manner and analyzed by vapor phase chromatography. The n-hexyl alcohol was obtained in a 94 percent yield.

Example X Tri-n-hexyl borane (5 parts) was added to a reaction flask containing 30 parts by volume of tetrahydrofuran. To this mixture was added 5 parts of sodium hypochlorite. The reaction mass was maintained at a temperature of 20-23 C. and stirred for 2 hours. The alcohol was extracted and dried by normal procedure. The product, nhexyl alcohol, was obtained in a 62.8 percent yield as indicated by vapor phase chromatographic analysis. No sodium hydroxide was employed.

The excellent results as shown in Examples I-X are also achieved when other alkali metal oxyhalide reactants are employed such as sodium iodate, sodium perchlorate, lithium chlorate, lithium fiuorate, cesium perchlorate, sodium bromate and rubidium iodate.

Similar results are obtained when other cyclic or polymeric hydrocarbon boron compounds are substituted in the above examples as, for instance, pentane-],5-his(1- boracyclohexane) to produce 1,5-pentanediol, l-n-butylboracyclopentane to produce a mixture of n-butyl alcohol and 1,4-butanediol which can be separated, if desired, the reaction product of diborane with acetylene in a molar ratio of 1 to 3 respectively to produce ethylene glycol, and the like.

The above examples are presented by way of illustration and the invention is not to be limited thereto. It is evident that similar results are readily obtainable when substituting other organoboron compounds, and conditions described hereinbefore.

Having thus described the process of this invention, it is not intended that it be limited except as set forth in the following claims.

What is claimed is:

1. A process for selectively oxidizing hydrocarbylboron compounds to essentially alcohols which comprises oxidizing a hydrocarbylborane having at least 1 carbon to boron linkage with an alkali metal oxyhalide compound in an aqueous system at a temperature of from about 0 C. to about 200 C., said alkali metal oxyhalide compound being present in a weight ratio to said hydrocarbylborane of from about 1 to 1 to about 100 to 1.

2. The process of claim 1 wherein said hydrocarbylborane is a trialkylborane.

3. The process of claim 1 wherein said hydrocarbylborane is tri-n-hexylborane.

4. The process of claim 1 wherein said hydrocarbylborane is tricyclopentylborane.

5. The process of claim 1 wherein said hydrocarbylborane is a dinorbornylborane.

6. The process of claim 1 wherein said hydrocarbylborane is a diisopinocamphenyl borane.

7. The process of claim 1 wherein said alkali metal oxyhalide is sodium hypochlorite.

8. A process for selectively oxidizing hydrocarbylboron compounds to essentially alcohols which comprises oxidizing a hydrocarbylborane compound having at least 1 carbon to boron linkage with an alkali metal oxyhalide compound in the presence of a metal hydroxide in an aqueous system at a temperature of from about 0 C. to about 200 C., said alkali metal oxyhalide compound being present in a weight ratio to said hydrocarbylborane of from about 1 to 1 to about 100 to 1.

9. The process of claim 8 wherein said hydrocarbylborane is a trialkylborane.

10. The process of claim 8 wherein said hydrocarbyl: borane is tri-n-hexylborane.

11. The process of claim 8 wherein said hydrocarbylborane is tricyclopentylborane.

12. The process of claim 8 wherein said hydrocarbylborane is a dinorbornylborane.

13. The process of claim 8 wherein said hydrocarbylborane is a diisopinocamphenyl borane.

14. The process of claim 8 wherein said alkali metal oxyhalide compound is sodium hypochlorite.

References Cited UNITED STATES PATENTS 3,061,626 10/ 1962 Pearson et al. 3,161,686 12/1964 Brown. 3,008,997 11/1961 Sagebarth.

OTHER REFERENCES Brown et al.: J. Org. Chem, vol. 22, pp. 113748, (1957).

Meyers: J. Org. Chem, vol. 26, pp. 1046-50, (1961).

Sneed et al.: General Inorganic Chemistry (1942), pp. 272-3.

BERNARD HELFIN, Primary Examiner.

T. G. DILLAHUNTY, Assistant Examiner.

U.S. Cl. X.R.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, 0.6. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,439 ,046 April 15 1969 Herbert C. Brown It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 18, "HOB" should read ROB line 54, "are" should read is Column 3, line 74, "insomers" should read isomers Column 4, line 68, "oxylhalide" should read oxyhalide Column 5, line 29, "filtrated" should read filtered lines 35, S1 and 61, "was", each occurrence, should read were Column 6, line 5, "norborenol" should read norborneol Signed and sealed this 14th day of April 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.