[1]United States Pat.ent Office f@@tented Dec. 2, 1958 862,952 METHOI) OF PREPARING B-HYDROCARBON. SUBSTITUTED BORON COMPOUNDS ti 8tephen J. Groszos, Darien, Conn., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application August 26, 1957 10 Serial No. 680,394 10 C12ims. (Cl. 260-462) Thig invention relates to a method of preparing B-,hyjr) drocarbon-substituted boron compounds. More particularly, the invention iS - CGncerned with certain new and useful improvements in a method of making such compounds by reacting an ester of an oxy acid of boron with a hydrocarbon halide while the reactants are in intimate 20 contact with metallic magnesium. The ester of the oxy acid of boron (i. e., the starting ester reactant) is one in which the ester comnonent thereof is represented by -(OR),, wherein R represents a hydrocarbon radical and n represents an inte-er from I to 3, inclusive. The 25 scope of the invention also includes the additional steps, if desired, of hydrolyzing, preferably under acidic conditions, the product obfained from the first reactio@,i and isolating the @ydrolyzed product as such or as aii isolable derivative thereof. The hydrolysis product comprises a 30 hydrocarbon-substituted boronic acid or a borinic acid when the starting ester reactant is, respectively, a borate or a hydrocarbon-sibstitiited boronate. - The prior methods of preparing, for instance, boronic acids have generally involved an organo-metallic com35 pound as one of the reactants and a boron trihalide or a trialkyl borate as a second reactant. Thus, Krause and Nitsche [Ber., 51, 2784 (1921); and Ber., 55, 1261 (1922)] used the technique represented by the following simplified equation: 40 02 H20 RMGX + BF3 - B R3 RB(OR)2 -RB(OH)2 (excess) Numerous other investi-ators le. g., Khotinsky and 45 Melamed, Ber., 42, 3090 (19091 have prepar.-d boronic acids by the addit;on of an ether soluti,-)n of a trialkyl borate to an ether solution of a Gri.@nard reagent maintained at about -70' C., as represented by the following 50 simplified equation: II Et2O R30+ B(OR)3+ R'MGX - R'B (O R)2 RIB(OH)2 standpoint of large volume of reactor space that is required; and, for this reason, is generally unsatisfactory for large-scale syntheses from a cost and design standpoint. It is a primary object of tne present invention to pro. vide an improved method of preparing certain B-hydrocarbon-substituted boron compounds, hereafter more fully described, which method obviates the above-mentioned disadvantages of the pri(>r-art methods, namely: eliminates the necessity for the separate preparation of a Grignard reagent and the use of ether (diethyl ether) or other solvent as a liquid medium in which the reaction is effected. Ancther object of the in@iention is to provide an improved m@- thod of preparing certain compounds of boron which requires less reactor space than the prior-art processes and, also, is more suitable for large-scale syntheses and makes it possible to produce the compound in a shoiter period of time than the prior methods. Oth.-r objects of the invention will be apparent to those skilled in the art from the following more detailed description of the invention' The 6bjects of the invention are attained by reactin(1) an ester of an oxy acid of boron of the kind set forth in the firstparagrat)h of this specificafion with (2) a hydrocarbon halide, more pa@rticularly, a hydrocarbon chloride- bromide or iodide, while the said reactants are intimat@ly associated with metallic magnesium, for instance, in the form of filings, turnings, shots or peli'ets, etc' Advantageously, the magnesium is suitably pretreated prior to use in order to cleanse its surfaces. For example, the pr,-treatment may take the form of et6hing with an aqueous solution oi. a strong mineral acid, e. g., hydrochloric acid, hydrobromic acid, sulfuric ac@id, phosphoric acid, etc., followed by washing to remove the acid, and then dryin,-- Other means of etching or of otherwise activating the magnesium may be employed. For example, the magnesium may be aetivated by treatment with iodine or by other means briefly described in Kharasch and Reinmuth's "Grignard Reactions of Nonmetallic Substances," pp. 8-15, Prentice-Hall, Inc., New York, 1954, and in the original references cited therein. When the starting boron reactant is a boron triester, the Teaction may be illustrated by the follo-@ving simplified equation: IH 0 R 0 R O H H30 + BOR+R'X+- Nfg R' B R' B O R O R O H Hydrocarbonsubstituted boronic acid When the starting boron reactant is a boron diester, Hydrolysis of the boronic ester, preferably under acidic ti5 the reacti@on may be illu strated by the following simplified conditions as indicated in the equation, liberates the free equation: acid. (In Equation II and in other equations herein the IV symbol H30+ means acidic water, which can also be OR R' RI represented by H+,H20-) I @ 1130+ @ \ The methods represented by Equations I and 11 each 60 R"B + RIX + Mg B-OR - / B-OH have the disadvantage of requiring the separate step of OR RI' RI' preparin g a GTignard reagent (or a lithium rea.-ent which Hydroc arbonalso has been employed in the prior art instead of a substitut ed Grignar d reagent). Additionally, the manipulation (as in boronic acid the, method of Equation 1) of water-sensitive -aseous reactants, such as BF3, is frequently troublesome, and 65 The hydrocarbon-substituted borinic acid can be dehythis is particularly true when the reactioh is carried out drated, by heating, to yield the corresponding b-@ronic on a small scale. Furthermore, there are the inher.,nt anhydride, thus: disadvantages in both methods of using diethyl ether or v RI RI R' other liquid medium in which the reaction between the 70 -H20 B-0-B/ primary reactants is effected. The use of a large volume 2 B-OH pf a liquid reaction medium is uneconomical from the P " A l l
[2]3 When the starting boron reactant is a boron monoester, the reaction may be Mustrated by the fouowing simplified equation: VI RI' R' B-OR + R'X +Mg B R" R... R... Hydroca,rb onsubstitut ecl borine In the above equations (including Equations I and H) R, R', R" and R... each represents a hydrocarbon radical and they may be the same or different. Illustrative examples of hydrocarbon radicals represented by R, R', R" and R... where they appear in Equations III, IV, V and VI are alkyl (including cycloalkyl), alkenyl (including cycloalkenyl), aralkyl, aralkenyl, aryl, alkaryl and alkenylaryl. More specific examples of such radicais are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec.-butyl, amyl, isoamyl, hexyl to octadecyl, inclusive (both normal and isomeric forins), cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, cycloheptyl, etc.; benzyl, phenylethyl, phenylpropyl, phenylisopropyl, phenylallyl, etc.; phenyl, biphenylyl or xenyl, naphthyl, etc.; tolyl, xyiyl, ethylphenyl, propylphenyl, isopropylphenyl, butylphenyl, allylphenyl, etc.; and vinyl, allyl, methallyl, propenyl, isopropenyl (p-allyl), 1-butenyl, 2butenyl (crotyl), 3- butenyl, pentenyl, hexenyl, butadienyl, etc. It wiII be noted that all of the foregoing examples of hydrocarbon radicals are those wherein any unsaturation between adjacent carbon atoms is a double bond. In the formula R'X appearing in Equations III, IV and VI, X represents a halogen selected from the class consisting of chlorine, bromine and iodine. In carrying the present invention into effect the hydrocarbon halide and metallic magnesium can be employed in stoichi6iihetric proportions, or with the one or the other in excess, e. g., from 1 to 100 percent of the one in excess over stoichiometric proportions with respect to the other. The ratio of boron ester tohydrocarbon hahde employed is in equimolar (equimolecular) or, preferably, in excess of equimolar proportions, e. g., from about 10 mole percent to about 1500 mole percent in excess of equimolar proportions. The excess to which reference is made in the preceding sentence can be achieved in, for example, two ways. Where the hydrocarbon halide and magnesium are in equimolar (equimolecular) amounts, the boron triester can be present in the molar ratios set forth in the second sentence of this paragraph. On the other hand, if the hydrocarbon halide and the said boron triester are present in equimolar ratio, the magnesium can be present in less than equimolar ratio as compared with the hydrocarbon halide. The excess boron ester functions primarily as a reaction medium (generally a liquid at the temperature of the reaction) in which the reaction between the primary reactants is effected, and thus aids in controlhng the reaction. The boihng point of the particular boron ester employed and the rate of adclition of the hydrocarbon haiide are each helpful in controhing the rate of reflux and/or the reaction temperature. Good results have been obtained, preferably in producing a boronate or a boronic acid, by using the boron-ester starting reactant in from 300 to 600 mole percent in excess of equimolar proportions with respect to the hy&ocarbon halide reactant. Within the ratios of reactants mentioned above, one also can control to some degree the proportions of predominating reaction products in the reaction mass. Thus, starting with a triester of boric acid and, when one desires to obtain mainly a boronate (or the corresponding boronic acid), one can use the said triester in a relatively large molar excess (e. g., from 10 to 100 mole percent in excess) over the hydrocarbon halide. If one desires to produce mainly a borinate (or, the corresponding borinic acid), one can use the said triester in equimolar 4 or only a slightly molar excess (e. g., from 0.1 to 9.9 mole percent in excess) over the hydrocarbon halide. And if one desires to obtain mainly a borine, one can use the hydrocarbon balide in equimolar or in molar excess with respect to the boron triester but greater than equimolar proportions with respect to the magnesium. The reaction between the primary reactants is effected at a temperature of from about 100' C. up to a temperature corresponding to the reflux tcmperature of the 10 reaction mass. In general, the temperature above about 10'@l' C. a' 17,@'lich the reaction is eitected is -Ovemed primarily by the boiling point of the mixture of organic reactants. When this temperature is below abotit 100' C., e. g., when the boron ester is trimetliyl bgrat-. (B. P., 67'- 15 69' C.), the reaction should be carried out under superatmospheric pressure sufficient to raise the boiling point to the desired degree. When the boiling point of the reaction mass is above about 100' C., the reaction is generally effected at atmospheric pressure; but superatmos20 pheric pressures can be employed as desired or as may be required in order to attain a sufficiently high reaction temperature. Reaction temperatures ranging, for instance, between about 100' C. and about 300' C., more particularly from about 125' C. to about 275' C., are 25 generally satisfactory. If desired, a catalyst and/or activator and/or promoter may be added to the reaction mass to shorten the induction period or otherwise to facilitate the reaction. A small amount of iodine, e. g., in crystalline form, is a suitable additive, more particularly an activator. Other examples are methyl iodide and an ether solution of methyl magnesium iodide. Additional examples are given in the aforementioned Kharasch et al. publication (see page 1363 of the General Index under "Activation f 35 0 Magnesium"). The amount of activator or other additive to facilitate the reaction, if.used, may be varied as described or as conditions may require, for instance from 0.00001% to 0.1% or more by weight of the hy&ocarbon-halide reactant. 40 The period of reaction will vary considerably and will depend upon such influencing factors as, for instanco, the particular starting reactants employed, the particular reaction products wanted, the temperature at which the reaction is effected, the kind of activator or other additive (if any) that is employed to facilitate the reaction, 45 the size, type and kind of reaction apparattis employed and other inffuencing factors. Thus, the pericd of reaction may range from 1/2 to 48 hours or more. Th@- processing steps subsequent to the termination of the reaction between the primary reactants will vary con50 siderably, and the particular procedure employ,-d is largely influenced by the particular starting reactants used and the particular product or products wantcd. As illustrative of the various techniques that can be used, the followin.- is mentioned. 55 A solvent such, for example, as diethyl ether, di-npropyl ether, di-n-butyl ether, the various diamyl ethers including di-n-amyl ether, "diglyme" (tlic dimethyl cth--r of diethylene glycol), dioxane, anisole, chlorob,-nzene, 60 benzene, toluene, phenetole, n-hexane, petroleum ether, and tertiary aniines (e. g., triethylamine, dltnethylaniline, pyridine, N-alkyl morpholines) can be added at the end of the initial reaction period and the precipitated magnesium salts (e. g., Mg(OR)X, MgX2, Mg(OR)2) filtered 65 off prior to distilling the filtrate to remove unreacted boron-ester startin.@ reactant and, if distillable witliotit decomposition, also the boron ester and borine products of the reaction [for example, R'B (OR) @, and R'R"B (OR) and R'R"R ... B]. In cases where the reaction products 70 undergo decomposition at the distillation teriaperatures, other means can be employed for isolating the products (e. g., recrystallization from a suitable solvent or a inixture of solvents). One also can isolate the boron-ester reaction products 76 LR'B(OR)2, R'R"B(OR)l and, under certain condi.
[3]tions, the borine, R'R"R ... B, by titrating the reaction mass with a saturated aqueous solution of an ammonium salt, e. g., ammonium chloride, ammonium sulfate etc., in order to decompose any unreacted Grignard reagent that may have been formed in the course of the reaction, 5 e. g. R'MGX, and to decompose the complexes formed betveen the boron esters and the magnesium salts liberated in the reaction. The precipitated magnesium salts can then be filtered off and the filtrate @ubjected to a fractional distillation in order to separate unreeicted borate, lo i. e., starting material, B(OR)31 the boronate, R'B(OR)2, the borinate, R'R'.'B(OR) and the borine, R'R"R ... B. Another means of isolating the boron-ester reaction ptoducts and the borine comprises addiiig to the reeiction mass a suitable active hydrogeii-containing compound, 15 e. g., an alcohol, a primary amine, a secondary amine, a compound containing both primary and secondary amino groups, an alkanolamine, glacial acetic acid, or the like. The solid that precipitates is filtered off, washed with a suitable anhydrous solvent, and the combined filtrate 20 and washings distilled to remove unreacted borate ester and any solvent, and also the reaction products. The hydrolysis products, mainly the boronic and borinic acids, are produced by hydrolyzing, preferably under aqueous acidic conditions, the isolated (if this has been 25 done) B-hydrocarbon-substituted boron-ester reaction product; or by hydrolyzing, also preferably under aqueous acidic conditions, the reaction mass containing the unisolated reaction products. In either case hydrolysis can be effected at temperatures ranging, for example, from -5o- 30 C. to 100' C. Hydrolysis is preferably effected at a tem_ perature sufficiently high to maintain the boron-ester reaction product, or reaction mass containing the same, in liquid state. Any acid can be used to provide the acidic conditions 35 for hydrolysis, in an aqueous medium, of the isolated boron-ester reaction product. To provide the acidic conditions for hydrolysis, in an aqueous mediuift, of the reaction mass containing magnesium - salts, any acid that will cause the ma.-nesium salts to dissolve can be used. A 40 mineral acid (or its obvious equivalent) can be employed, e. g., hydrochloric, hydrobromic, sulfuric, phosphoric, dichloroacetic, trichloroacetic, etc. A weak acid or an acidic or potentially acidic body can also be used to provide the acidic conditions, e. g., ammonium chloride, 45 ammonium sulfate, acetic acid. Since the borinic acids, R'R"BOH, are not isolable in a pure state, they can be converted to readily isolable derivatives (e. g., the anhydride, the monoethanolamine ester, etc.) which, if desired, can then be readily con- 50 verted to the borinic acid. The borines, R'R"R ... B, can be isolated in, for example, the following manner: The reaction mass, after being freed of the magnesium salts as described above, can be subjected to distillation carried out in such a man- 55 ner as to allow the separation of the borine from the boronate and borinate esters. In order that those skilled in the art may better ' understand how the present invention can be carried into effect, the following examples are given by way of illustration 60 and not by way of limitation. All parts and percentages are by weight unless otherwise stated. Example 1 Twenty-@five (25) ml. of tributyl borate, i. e., tr@l n-@ui . yi borate (of A tbtal!af 1085 ml.; 920 g., 4 iii6les), is added to a reaction vessel provided with a stitrer dnd tWo drO@7 ping fiihnels, to which vessel previously ha be(@n added 24.32 g. (I g. atom) of magnesium turhings. The magnesitiiii i@ pieireated by etching with 10 pefceiit aqueous hydrochl'oric acid, followed by guccessivd washings with wate@, ethaiiol, acetorid and ethet, aftet Which it is dried at 105' C. A small aniount bf br6in@iobefizene (of a total of l@7 g., I ihole) is then added to the reaction mass, to.ether w;th a crystal of iodine to initiate the reaction. The reaction niass is heated to reflux without stirrinl-. When the purplish iodite colot has disappeared at 120' C., indicating that the reaction has begun, stirring is started. The remaining tributyl borate (1060 ml.) is then added concurrently with the addition of the remainin.bromobenzene from the second dropping funnel. Thirty minutes after completing these additions a gummy solid separates on the sides of the vessel and the solution becomes yellow. As refluxing continues the solution becomes more viscous and the color intensifies. After maintaining the reaction teihperature for several hours at about 228' C., which is the boiling point of tributyl borate, heating and stirring are discontinued. The reaction mass, at the end of the reaction period, is a viscous liquid while hot but solid at room temperature. It is hydrolyzed by pouring the hot liquid or pourable mass over crushed ice or into water at room temperature (20'-30' C.), followed by acidification of the reaction mass with, for example, concentrated HC1. - Thereafter, the organic phase is separated and extracted with three 400-ml. portions of dilute aqueous sodium hydroxide. Upon acidification of this basic solution, for instance until acid to pH paper (i. e., a pH of I to 2), using concentrated HCI or other strong acid for this purpose, phenylboronic acid crystallizes from the solution. After filtration, the mother liquor is concentrated to yield more product. The total yield is 80.2 g. (66 percent of theoretical) of phenylboronic ac.id. Example 2 Exactly the same procedure is followed as described under Example 1 down to the hydrolysis step. The solid reaction mass is pulverized in a dry nitrogen atmosphere, and about 1500 cc. of anhydrous diethyl ether is added. Upon addition of a saturated aqueous solution of ammonium chloride, the ether becomes cloudy; and upon further addition solid material begins to separate from solution. The saturated ammonium chloride solution is added to the point at which the ether solution'becomes clear. The ether solution is then decanted from the precipitated magnesium salts and distilled. After removing solvent and butanol, the desired ester (di-n-butyl phenylboronate) is obtained in a high yield by distillation at reduced pressure. The use of a saturated aqueous solution of an acidicammonium salt of an acid having a pH value of less than 4.75, e. g., ammonium chloride, to decompose the complex obtained as an intermediate product of the reaction is not my invention, this improvement being broadly and specifically claimed in the copending application of Stanley F. Stafiej, Serial No. 680,388, filed concurrently herewith. Example 3 The same general procedure is followed as described The following equations iflustrate the reactions in- 65 under Example 1, but usin@ 12.2 g. (0.5 g. atom) magvolved in this example: nesiu m, 470 g. (2.5 moles) tri-n-propyl borate and 46.3 g. Vil 004H9 0 C4119 (0.5 mole) n-butyl chloride. After the addition of the c hloride has been completed, th-e reaction mixture is mainB 0 C4Ho + CoH5Br +Mg - HoCeB 70 tained -at reflux temperature for about 20 hours. Isolation oc4ug OC4]19 of the product as described under Example I gives n-butyl(excess) b oronic acid; M. P. 75'-94' C. vni / 6 cjirg H30+ oil Example 4 H5Co-B . E15Ct-- B Grignard grade magnesium turnings (2.5 g., 0.103 g. 0 CiHg OH 7r) atom), 146 g. (I mole) triethyl borate and a crystal of
[4]7 iodine are placed in a 200 ml. capacity rocking-type autoi@lave fitted with a Rekibl6 inlet tube through which a liquid cati be introduced under pressure. While the reaction mixture is a.@itated, the temperature is raised to 120' C. and 3 2.6 g. (0. I 1 mole) n-dodecyl iodide is intro- 5 duced in portions. An indication of reaction taking place is a rise in temperature and pressure in the autoclave during the course of the addition. Aftor additioii is complete, the reaction mixture is heated to 200'-250' C. and maintained in this temperature range for a period of about six 10 hours. At the end of the reaction period, the autoclave is allowed to cool tb room temperattire and opened cautiously by means of a valve to release any pressure tyat may remain. The autoclave is opened and the wet solid treated with 10% aqueous sull@'uric acid with cooling and 15 stirring until the reaction mass is acid to pH paper. The reaction mass is then exttacted with several portions of ether. The combined other solutions are extracted with 5% aqueous NAOH sblution, the aqueous layer acidified (to pH paper) with 10% aqueous sulfuric acid and then 20 extracted wiih three portions of ether. Tho wet, ether layer is evaporated on the water bath under a stream 6f nitro.,en to leave an oil which, on standing, turns to a li.-ht, yellow-colored waxy solid comprised of ii-dodecylboronic acid. 25 Example 5 Trimethyl borate (52 g., 0.5 mole), 1.22 g. (0.05 g. atom) magnesium turnings and a crystal of icdine are placed in a 100 ml. stainless steel autoclave which is part 30 of a rocking-type pressure apparatus. The autoclave is heated to about 120' C. under autogenous pressure and 7.9 g. (0.05 mole) bromobenzene introduced under iiitrogen pressure in portions over a 30-minute period. At the end of the addition, the temperature is raised to about 35 225' C. and maintained at this temperature, with agitation, for a period of about 10 hours. The reaction mass is then worked up in the manner described in Example 4 to give pure phenylboronic acid after recrystallization from hot water. 40 Example 6 n-Octyl bromide (19.3 g., 0.1 mode), 2.4 g. (0.1 g. atom) magnesium turnings and 92@O g. (0.4 mole) tri-nbutyl borate are reacted together in the manner described 45 in Example 1. At the end of the reilux period, the reaction mass is cooled and transferred in the form of a wet solid to a vessel containing enough ether to provide an easily stirred suspension. Saturated aqueous ammonium chloride is then added portionwise with rapid stirring ro tc, the point at which the solids separate quickly and leave a clear, supernatant liquid when stirring is stopped momentarily. The solution is decanted and filtered through anhydrous Na2SO4. The filtrate is then subjected to a fractional distillation to obtain the product, dimethyl(n- 55 octyl)boronate, which also may be named as the dimethyl ester of n-octylboronic acid. Example 7 Cyclohexyl bromide (81.5 g., 0.5 mole), 4.9 g. (0.2 g. 60 atom) magnesium turnings and 345 g. (1.5 moles) nbutyl borate are reacted together in the manner described iinder Example 1 with a 24-hour reflux period. The reaction mass is worked up in the manner described in Example 6 to yield n-butyl(dicyclohexyl)borinate and 65 some di-n-butyl(cyclohexyl)boronate. Example 8 The Preparation 6f di-n-amyl (allyl) boronate (di-namyl 70 ester of allylboronicacid) i,s carried out in the manner described under Example I by reacting l@.1 g. (0.1 mole) allyl bromide with 2.43 g. (0.1 9. atom) magnesium and 272 g' (I mole) tri-n-amyl borate. A polymerizal@.pn inhibitor can be added during the isolation steps. 8 Example 9 p-Bromotoluene (171 g., I mole) is added to 48.6 g. (2 g. atoms) magnesium turnings, 230 g. (I mole) tri-n-butyl borate and a small crystal of iodine over a period of 15 minutes at a temperature of 135' C. The reacdon mixture is refluxed for about 10 hours. The reaction mass @is then cooled and hydrolyzed to an acid pH with 10% aqueous hydrochloric acid. The reaction mass is extracted with ether, and the ether layer washed with two portions of 5% aqueous NAOH solution. After separating the organic layer and washing with water, the ether is removed by distillation under a nitrogen atmosphere. The residue is then fractionally distilled under nitrogen to give a fraction comprising tritolylborine. Example 10 Magnesium turnings (2.43 g., 0.1 g. atom), 104 g. (1 mole) trimethyl borate and a crystal of iodine are placed in an autoclave. Benzyl bromide (17.1 g., 0.1 mole) is added under pressure at 120' C. and the reaction conducted in the mannerdescribed in Example 4. The reaction ma-ss is then worked up as described in Example 1 to yield benzylboronic acid, M. P. 195'-215' C. Example 11 n-Butyl bromide, di-n-butyl(phenyl)boronate and magnesium metal are reacted in the mole ratios of 1:5:1 (I mole of Mg=l g. atom) in the manner described in EXample I to yield crude phenyl(n-butyl)borinic acid, a light yellow OiI. Distillation in vacuo of this oil yields the ttnhydride ix n-ClIrg B 0 (The symbol "O" represents the phenyl radical, C6H5-.) The oil can be treated with an aqueous ethanolic solution of ethanolamine which, results in the separation of the crystalline aminoethyl [phenyl (n-butyl) I borinate, x n-C4]Elg H2N-C Example 12 When n-butyl bromide, magnesium and tri-n-butyl borate are reacted together in the mole ratios 1: 1:2 in the manner described in Example 7, n-butyl(dibutyl)borinate is isolated in addition to some di-n-butyl(butyl)boronate. Example 13 Bromobenzene (157 g., I mole), 30.4 g. (1.25 g. atoms) magnesium turnin.-S and 230 g. (I mole) tri-n-butyl borate are allowed to react in the manner described in Example 6 to yield, after fractional distillation, n-butyl(diphenyl)borinate. 23.8 g. (0.1 mole) nbutyl(diphenyl)borinate obtained in this manner or by methods reported in the literature is reacted with 2.4 g. (0.1 g. atom) magnesium and 15.7 g. (0.1 mole) bromobenzene at 220'250' C. for a period of about 20 hours. The reaction mass is cooled and hydrolyzed by adding it to cold 10% aqueous sulfuric acid. An ether extract of this solution is in turn extracted with three portions of 5% aqueous NAOH, washed with waer, dried over anhydrous Na2SO4 and distilled, first at atmospheric pressure and then in vacuo. It is important to exclude oxygen during these operations and all manipulations are conducted in a nitrogen atmosphere. The fraction boiling at 203' C./15 mm. is triphenyl boron (triphenyl borine), M. P. 137' C. Example 14 Tri-n-butyl borate (I mole), n-hexyl bromide (2.5 moles) and magnesium (4 g. atoms) are reacted together under the conditions given in Example 13. The reaction product is hydrolyzed with 10% aqueous sulfuric acid and extracted with ether. The ether solution con-
[5]9 tains a mixture of n-hexylboronic acid, di-n-hexylborinic acid and tri-n-hexyl boron (tri-nhexyl borine). Extraction with 5% aqueous NAOH leaves the tri-n-hexyl boron in ether solution, and from which it can be isolated by distillation; B. P. 97' C./O.002 mm. 5 The basic solution of the boronic and borinic acids is acidified with aqueous hydrochloric acid and extracted with ether. The ether is removed on a water bath and the residue taken up in aqueous ethanol. Addition of monoethanolamine causes the borinic acid to crystallize 10 a. the aminoethyl(di-n-hexyl)borinate. The solution containing the boronic acid is evaporated on a steam bath to dryness, extracted with ether, the ether solution evaporated and the residue recrystaljized from hot water to yield n-hexylboronic acid. Recrystal- 15 lization from methylene chloride affords a product, M. P. 70' C. Recrystallization from water raises the M. P. to 88'-90' C. In all of the operations described above, oxygen is excluded by working in a nitrogen atmosphere. 20 I
