3,489,528 United States Patent 0 ice Patented Jan. 13, 1970 1 2 number of (BHZNHZ) groups, but the product is con 3,489,528 PREPARATION OF POLYAMINOBORANES sistent in composition, as shown by infra-red and ele William E. Zanieski, Pittsburgh, Pa., assignor to Mine mental analyses, and the average value of n is about 4. Safety Appliances Company, a corporation of In another example a solution of THF-EH3 contain— Pennsylvania ing 2.99 g. of B2H6 in 150 ml. of THF was prepared N0 Drawing. Filed Apr. 5, 1965, Ser. No. 445,707 in the same manner as the previous example and the Int. Cl. C01b 21/00 solution was warmed to -30° C. 3.12 g. of gaseous US. Cl. 23—358 6 Claims ammonia was bubbled into and dissolved in the solution at —30° C. and the resultant clear solution was warmed to 0° C, at which temperature hydrogen was evolved and polyaminoborane, identical to that obtained in the ABSTRACT OF THE DISCLOSURE previous example, precipitated from the reaction mix Ammonia and diborane are reacted in tetrahydrofuran ture. at a temperature below about —30° C.; polyaminoboranes ‘Although the invention is not limited to any particular are precipitated when the reaction mixture is warmed. 15 reaction mechanism, it appears that the reaction of NH3 Aging of an ammonia solution of the polyaminoboranes and BZHS in THF forms an intermediate that is formed so produced yields an ammonia insoluble, more highly and is stable only at temperatures below about —30° C. polymerized polyaminoborane. and that this intermediate decomposes at temperatures above about —30° C. with the evolution of hydrogen 20 to form polyaminoboranes. The second reaction step may be accomplished at any temperature above about --30° This invention relates to a method of preparing boron C.‘ and below the boiling point of tetrahydrofuran, but nitrogen polymers, and more particularly polyamino room temperature is preferred as it is easily obtained boranes having a plurality of BHZNHZ groups. and the reaction rate is reasonably fast. —Polyaminoborane (BH2NH2),, have been identi?ed as 25 It is preferred to use about stoichiometric quantities of minor or by-products of the decomposition of various reactants, that is 2 mols of ammonia for each mol of boron-nitrogen compounds. Polyaminoboranes have also diborane, since there is no apparent advantage in using been prepared (Shore et al., Preparation and Identi?ca other proportions and yields are optimized, typically over tion of New BHZNHZ Species, paper presented at 148th 90% yield. If more than about a 15% excess of diborane ACS Meeting, Chicago, 1964) by the reaction of di 30 is used the yield of polyaminoborane is drastically re borane diammoniate and an alkali metal amide in liquid duced, the major product being ammonia borane which ammonia. In this and other methods involving the re is soluble in tetrahydrofuran. action alkali metals and alkali metal compounds, a large Liquid ammonia dissolves and reacts with portion of the original diborane is lost by the produc tion of by-product alkali metal borohydride. Also, reac 35 tions of diborane in liquid ammonia are notoriously sen to remove the terminal BH, and 'NH3 groups forming am sitive to condition and techniques, so they are dif?cult monia borane and an ammonia insoluble polyamino to reproduce and scale up to commercial operations from borane made up of a plurality of BH2NH2 groups and laboratory operations is unreliable. having the empirical formula BNH4. Illustrative of the It is an object of this invention to provide a simple, 40 reaction, 40 ml. of ammonia was condensed at —78° C. economical and reliable method of preparing polyamino onto 3.5 grams of NH3(BH2NH2)nBH3 prepared in ac borane directly from ammonia (NH3) and diborane cordance with the foregoing examples in a Fischer (BZHS). Other objects will be apparent from the follow Porter tube. The resultant slurry was warmed and the ing description and claims. solids dissolved forming a solution below about 0° C. In accordance with this invention, diborane and am 45 On storage of the solution between 0° C. and room tem monia are introduced at a temperature below about —30° perature for several hours, a white precipitate formed. C. into tetrahydrofuran (THF) and the resulting mixture The ammonia was removed and the solid residue was is permitted to warm to a temperature above about washed with ethyl ether and tetrahydrofu-ran and vacu -—30° C. whereby hydrogen is evolved and solid poly um dried, yielding a 92.6% recovery of polyaminoborane aminoborane precipitates from the reaction mixture. The 50 having the empirical formula BNH4 as determined by polyaminoborane product so obtained may be dissolved elemental analysis. This product is very similar to in liquid ammonia from which solution a more highly (BH2NH2)5 reported by Shore et al. in its properties, polymerized polyaminoborane precipitates. but there are some differences in the X-ray and infra-red Exemplifying the invention, 10.0 g. of gaseous di patterns which show it is not identical to (BH2NH2)5. borane was bubbled into 250 ml. of THF at —78° C. 55 The temperature of the reaction is not critical, but it is to form a solution of tetrahydrofuran-borane adduct preferred to use a temperature above about 0° C., con (THF-EH3) in tetrahydrofuran. 11.8 g. of ammonia veniently room temperature, to obtain reasonably fast was condensed into the solution and the mixture was reaction rates. held at -—78° C. overnight, during which time a solid Both NH3(NH2BH2),,BH3 and the polyaminoborane material had formed in the reaction mixture. The reac 60 obtained from reaction of this material with ammonia, tion mixture was then allowed to warm and the solid sublime, with decomposition, at about 150° C. to give material dissolved at a temperature of about —40 to identical (BHZNHZ)n sublimates. I have found, however, —30° C. On further warming hydrogen was evolved that when the materials are compressed, as by com at about —l0° C. and polyaminoborane was precipitated pressing into a pellet at 25,000 p.s.i.g., to a coherent from the resultant clear solution on standing for about 65 compact, that they decompose upon heating without sub 2 hours or less at room temperature. The polyamino liming, giving hydrogen and leaving a boron nitride boranes were ?ltered from the reaction liquor, washed residue. Such compacts are therefore useful as a con with tetrahydrofuran, and vacuum dried. The product is venient hydrogen source, especially in ?eld use, as for a polyaminoborane having terminal ammonia and borane balloon ?lling. The NH3(NH2BH2),,BH3 yields more hy~ groups of the formula NH3(BH2NH2),,BH3. It has not 70 drogen on weight basis, and the polyaminoborane from been precisely determined whether the product is a single the ammonia reaction yields more hydrogen on a volume compound or a mixture of compounds having a dilferent basis, as its density is 1.05 as compared to a density of 3,489,528 3 4 0.93 for NH3(NH2BH2)n-BH3. The thermal decomposi essentially of a plurality of BH2NH2- groups comprising tion of the polyaminoboranes is also a convenient method contacting ammonia and diborane in tetrahydrofuran at a for producing refractory boron nitrides. The polyamino temperature below about ——30° C. inthe proportions of boranes made by the methods of this invention are par about 2 mols of ammonia for each mol of diborane, warm ticularly suited for use as ablative coating, e.g.'they ing the reaction mixture to a temperature above about slowly decompose when subjected to a ?ame, absorbing —30° C. to form a ?rst precipitate of polyaminoboranes, heat and leaving a desirable boron nitride residue. separating said ?rst precipitate, dissolving said ?rst pre According to the provisions of the patent statutes7 I cipitate in liquid ammonia, aging said solution until a have explained the‘ principle and mode of practicing my second precipitate forms and recovering said second invention and have described what I now consider to be precipitate. its best embodiments. However, I desire to have it under 5. A method according to claim 4 in which the am stood that, within the scope of the appended claims, the monia solution is aged at between about 0° C. and room invention may be practiced otherwise than as speci?cally temperature. described. ' 6. A method according to claim 4 in which the ?rst I claim: 15 precipitate is dissolved in liquid ammonia at a tempera 1. A method of producing polyaminoboranes comprising ture below about 0° C. contacting ammonia and diborane in tetrahydrofuran at a temperature below about —30° C. in the proportions References Cited of about 2 mols of ammonia for each mol of diboiane, UNITED STATES PATENTS warming the reaction mixture to a temperature above 20 about —30° C. to precipitate polyaminoboranes, and re 3,022,138 2/1962 Clark et a1. ________ _.._ 23——20'4 covering said polyaminoboranes. 3,159,451 12/1964 Gunderloy _________ __ 23—358 2. A method according to claim 1 in which the reac OTHER REFERENCES tion mixture is warmed to room temperature. Schae?er, George W., et al., “Journal of the American 3. A method of producing polyaminoboranes compris 25 ing absorbing diborane in tetrahydrofuran at a tempera Chemical Society,” vol. 78, pp. 725—728; 1956‘. ' Egan, B. Z., et al., “Journal of the American Chemical ture below about -3‘0° C., introducing about 2 mols of Society,” vol. 83, pp. 471849, 1961. ammonia for each mol of diborane into said diborane solution, Warming the resultant solution until gas is OSCAR R. VERTIZ, Primary Examiner evolved therefrom, and recovering the polyaminoboranes 30 precipitated thereby.