2,900,414 Pce Patented Aug. 18, 1959 2 The closed reaction vessel is then brought to the de sired operating temperature. With the more reactive 2,900,414 aromatic hydrocarbons having hydrogen on at least one SYNTHESIS OF ARYLBQRGN HALIDES of the annular carbons, e.g., benzene, in the presence 5 of a catalyst, e.g., iodine, an exothermic reaction may‘ Earl L. Muetterties, Chariots Ford, Pa, assignor to E. I. take place when the reaction mixture reaches a tempera du Pont de Nernours and Company, Wilmington, Del., ture of just above 0° C. In such cases the reaction _ a corporation of Delaware - mixture temperature rises to about 120° C. in a few N0‘ Drawing. Application .lune 3, 1957 minutes. Serial No. 662,971 10 Reaction takes place very rapidly at temperatures above 100° C. and the reaction mixture can be cooled immedi 6 Claims. (Cl. 260-543) ately after such temperatures are reached. If desired, the reaction mixture can be maintained at lower tempera~ tures by external cooling but in this case longer reaction This invention relates to organoboron compounds. 15 times may be required. Since temperatures above 150° More particularly, it relates to a new method for mak C. tend to cause decomposition of the arylboron di ing arylboron halides. halide, it is preferred to employ short contact times at Arylboron halides are a known type of organoboron the higher temperatures, i.e., at temperatures of 120° compounds that are of use' in various applications, for C. and higher. For example, contact times of l-60 min example, as intermediates in the formation of hetero 20 utes at temperatures of 120-200° C. are preferred. cyclic boron compounds and arylboronic acids, and as After the reaction mixture has been heated at the ionic polymerization catalysts. However, the hitherto desired temperature for the desired time, the reaction ' known methods for making arylboron halides are rela vessel is cooled to room temperature, i.e., 20—30° C. tively complex and are not economically attractive for The reaction vessel is opened and the reaction mixture, ' manufacturing such compounds on a large scale. 25 which usually’ consists of a slurry of solid and liquid It is therefore an object of this invention to provide products, is ?ltered and the ?ltrate is distilled to recover a new and improved method for making arylboron halides. any, unused reactants and to isolate the reaction prod A further object is provision of an extremely simple ucts. In some cases, the reaction mixture may consist and economical method for making arylboron halides. solely of solid product. Still another object is provision of a novel process for 30 i The process of this invention is also quite capable of preparing arylboron halides from readily available raw being carried out continuously by passing liquid and materials. gaseous reactants through a reactor containing aluminum These objects are accomplished in accordance with the particles or chloride of said aluminum heated to the desired present invention by a process which comprises contact temperature. “This embodiment of the process is par ing a boron halide whose halogen has an atomic num 35 ticularly desirable for carrying out the reaction at tem ber of at least 17, i.e., boron trichloride, tribromide or peratures of ISO-200° C. since short contact times are triiodide, "with an aromatic hydrocarbon having hydro more easily maintained. ' ' - gen on at least one of the annular carbons at a tempera The reactants used in the process of this invention can ture of from about 0° to about 200° C. in the presence be of the grades commercially available. The aluminum of aluminum and aluminum chloride. 40 can be of any of the types and degrees of purity com Aluminum is preferred for use in the process of this mercially available, for example, aluminum powder, invention since it gives the best conversions to aryl granules, or turnings of various sizes are operable. Be boron halides and since it is the most active. cause of more rapid reaction rates and generally higher The proportions of reactants employed in the process conversions obtained, it is preferred to use aluminum are not critical and can be varied widely. Molar ratios 45 particles having as high a surface area per unit weight of aromatic hydrocarbon having hydrogen on at least as practical.‘ ' one of the annular carbons to boron halide that are The process of, this invention is illustrated in further operable range from 1:5 to 5:1. Similarly, the molar detail by the following examples in which the propor ratios of boron halide to aluminum or aluminum chlo tions of ingredients are expressed in parts by weight ride can vary from 1:40 to 40: 1. unless otherwise speci?ed. The use of a catalyst in the process of this invention is not essential. However, it is sometimes bene?cial to Example I use a catalyst such as iodine, methyl iodide or mixtures A stainless steel-lined pressure vessel is charged with of these in any proportion. The amount of catalyst 35 parts of aluminum dust, 120 parts of benzene and employed can range from ‘about 0.1% up to about 2% 55 0.1 part of iodine. The vessel is cooled to .—78° C. of the weight of the reaction mixture. and then evacuated. Sixty parts of boron trichloride is The process of this invention is conveniently carried distilled into the reaction vessel after which the reaction out in a corrosion-resistant reaction vessel capable of vessel and its contents are allowed to warm up. On withstanding superatrnospheric pressure and equipped reaching a temperature of about 3° C., an exothermic with means for heating the reaction mixture to tempera 60 reaction sets in. The interior temperature f?ashes up tures up to about 200° C. and means for cooling the to 120° C. during the period of about 10 minutes. The reaction mixture to ‘a temperature of about 0° C. A vessel is immediately cooled, about 20 minutes being . pressure vessel lined with stainless steel is satisfactory for use in this process. required to reach- room temperature (25° C.). The reaction mixture is a liquid slurry amounting to 213 The reaction vessel is charged with the non-gaseous 65 parts. This slurry is ?ltered and there is obtained 130 reactants, e.g., aluminum or aluminum chloride and the parts of ?ltrate and 35-40 parts of solid. 7 The ‘X-ray aromatic hydrocarbon having hydrogen on at least one i diifraction pattern of this solid shows the presence of of the annular carbons, and optionally a catalyst. The aluminum and aluminum trichloride. The liquid re reaction vessel is then cooled to between 0° and —78° 70 action product is distilled and after removing 70 parts C., evacuated, and the gaseous reactant, e.g., boron tri of benzene there is obtained 54 parts of phenylboron chloride, is introduced and the reaction vessel closed. dichloride, boiling at 95° C./48 mm. T l 2" 2,900,414. A. Example 11 Example VI Following the procedure described in Example I, the Following the procedure described in Example I, a reaction vessel is charged with 120 parts of benzene, 60 reaction vessel is charged with 120 parts of p~xylene, parts of boron trichloride, 35 parts of aluminum, dust, 60 parts of boron trichloride, 35 parts of aluminum dust, 0.1 part of iodine, and 01 part of methyl iodide. The 0.1 part of methyl iodide, and 0.1 part of iodine. The reaction vessel is heated to 150° C. during a period. of closed reaction vessel is heated to 150° C. during a pe about 45 minutes and is then. immediately cooled back riod of 45 minutes and is immediately cooled to room to room temperature (about 25° C.) during a period temperature during another 11/2 hours. The reaction of about 11/2 hours. The reaction. mixture is ?ltered mixture is a liquid slurry amounting to 212 parts. This and the ?ltrate, amounting to 210 parts, is distilled. 10 slurry is ?ltered and 60 parts of this ?ltrate is distilled. Three fractions are obtained, the ?rst being benzene, There is obtained a fraction boiling at 158° C./ 110 mm. the second a mixture of benzene and phenylboron di consisting mainly of xylylboron dichloride, contaminated chloride, and the third fraction, amounting to _59 parts, with a little xylene. being phenylboron dichloride, boiling at 95° C./48 mm. 15 Analysis.—Calc’d for C8H9BCl2: C, 51.3%; H, 4.85%; Analysis.—Calc’d for C6H5BCl2: C, 45.3%; H, 3.17%; B, 5.78%; CI, 37.9%. Found: C, 55.71%; H, 6.24%; B,,6.82%; Cl, 44.7%. Found: C, 46.23%, 45.87%; H, B, 5.10%; Cl, 33.61%. 3.61%, 3.54%; B, 7.39%, 7.56%; Cl, 44.28%, 44.31%. A portion of the impure xylylboron dichloride of Ex A portion of the phenylboron dichloride of Example II ample V1 is hydrolyzed by treatment with excess water is contacted with an. ice-water mixture whereupon the 20 and the hydrolysis product is recrystallized from diethyl boron compound hydrolyzes instantaneously. The re ether. sulting product is recrystallized from diethyl ether. Example VII Infrared analysis of the hydrolysis product shows it to be phenylboric acid. A pressure vessel is charged as described in Example Analysis.--Calc’d for C6H5B(0H)2: C, 59.1%; H, I with 100 parts of naphthalene, 30 parts of aluminum dust, 0.1 part of iodine, 0.1 part of methyl iodide, and 5.77%. Found: C, 58.86%; H, 6.04%.