PREPARATION OF TETRAALKYL AMMONIUM BOROHYDRIDES

Abstract: Tetraalkyl ammonium borohydrides are produced by reaction of tetraalkyl ammonium hydroxide with an alkali metal borohydride.

Description: PREPA ΆTION OF TETRAALKYL AMMONIUM BOROHYDRIDES FIELD OF THE INVENTION This invention is a method for the preparation of tetraalkyl ammonium borohydrides. BACKGROUND OF THE INVENTION It is known to produce tetraalkyl ammonium borohydrides by exchange of the cation of an alkali metal borohydride with a tetraalkyl ammonium cation exchange resin. See, Guillevic, et al., Bulletin de la Societe Chimigue de France (1976), No. 7-8; 1099-1100. See also, Mongeot, et al., Bulletin de la Societe Chimigue de France (1986), No. 3 . :385-389. DETAILED DESCRIPTION OF THE INVENTION Pursuant to the invention, a particulate solid alkali metal borohydride is added with agitation to a solution of tetraalkyl ammonium hydroxide in a non- interfering solvent to produce the desired tetraalkyl ammonium borohydride. The reaction is illustrated by the equation OHN(R) 4 + MBH 4 > N(R) 4 + BN 4 _ + MOH (solution) (solid) (stir) in which R is any straight or branched chain alkyl group, preferably an ethyl group, having one to ten carbon atoms, and M is any alkali metal, preferably sodium. The tetraalkyl ammonium hydroxide may be in solution in any non-interfering solvent, such as water, or an alkanol, such as methanol or ethanol. Water is the preferred solvent. Any desired concentration, for example, any 40% to 60% by weight solution of tetraalkyl ammonium hydroxide in a non-interfering solvent is useful in the practice of the invention. A commercially available 40% aqueous solution of tetraalkyl ammonium hydroxide may be utilized. The tetraalkyl ammonium hydroxide and alkali metal borohydride may be reacted in any desired relative proportions. Stoichiometric amounts are preferred. The reaction may be conducted at any desired temperature. A preferred temperature range is 20 °C. to 30°C. A specific embodiment of the invention entails addition of a particulate solid alkali metal borohydride to a 20% to 60% by weight aqueous tetraalkyl ammonium hydroxide solution. The addition is accomplished with agitation to facilitate solution of said alkali metal borohydride in said aqueous tetraethyl ammonium hydroxide. An exothermic reaction occurs readily at room temperature. When the reaction is substantially complete, aqueous alkali metal hydroxide or aqueous alkali metal alkoxide is added in an amount sufficient to cause separation of the reaction mixture into a lower aqueous alkali metal hydroxide or alkoxide containing layer and an upper aqueous layer containing the desired tetraalkyl borohydride as a hydrate, e.g., N(R) 4 + BH ~ 4 * 5H 2 0. The upper layer is separated and dried by vacuum or heat to provide solid ammonium tetraalkyl borohydride hydrate. Drying by heat is undertaken with care to avoid the decomposition of the product which may occur at a temperature of 260 °C. The dried product is purified by recrystallization from an appropriate solvent, preferably an alkanol such as methanol, ethanol or 2-propanol. EXAMPLE 1 1838 grams of 40% aqueous tetraalkyl ammonium hydroxide was charged to a reaction vessel. 193.5 grams of particulate solid sodium borohydride was added, and the reaction mixture stirred at 25 °C for 30 minutes until the reaction was substantially complete. The aqueous sodium hydroxide was separated. The upper product was an aqueous solution of tetraalkyl ammonium borohydride hydrate N (C 2 H 5 ) y ■ BH 4 ~ ■ 5H-.0. The upper layer was separated and dried by vacuum distillation. The resulting dry N(C 2 H 5 ) 4 _ ■ BH 4 ~ product was recrystallized from 2-propanol. Yield 645 grams, 89% yield. It will be apparent to the skilled individual that alkali metal borohydride in solution in a non- interfering solvent may be combined with the tetraalkyl ammonium hydroxide solution. The use of a solid alkali metal borohydride is cost effective and is preferred for other practical reasons. For example, a 20% to 40% by weight aqueous alkali metal borohydride solution may be used in lieu of particulate solid alkali metal borohydride.

Claims: I CLAIM: 1. A method for producing a tetraalkyl ammonium borohydride which comprises reacting a tetraalkyl ammonium hydroxide with an alkali metal borohydride, wherein a tetraalkyl ammonium borohydride reaction product is produced. 2. A method for producing a tetraalkyl ammonium borohydride which comprises combining a solution of tetraalkyl ammonium hydroxide in a non-interfering solvent for reaction with a solid alkali metal borohydride, wherein a reaction mixture is formed which contains said tetraalkyl ammonium borohydride in solution in said non-interfering solvent. 3. The claim 2 method in which said tetraalkyl ammonium hydroxide is tetraethyl ammonium hydroxide and in which said solid alkali metal borohydride is sodium borohydride and wherein said reaction mixture that is formed contains an aqueous solution of tetraethyl ammonium borohydride hydrate. 4. A method for producing tetraethyl ammonium borohydride which comprises: (i) providing an aqueous solution of tetraethyl ammonium hydroxide; (ii) adding a solid alkali metal borohydride to said aqueous solution of tetraethyl ammonium hydroxide, wherein said addition is accomplished with agitation to facilitate dissolution of said alkali metal borohydride in said aqueous solution of tetraethyl ammonium hydroxide, and wherein said tetraethyl ammonium hydroxide of step (i) and said alkali metal borohydride of step (ii) react to form a reaction mixture containing said tetraethyl ammonium borohydride; and (iii) separating said tetraethyl ammonium hydroxide from said reaction mixture. 5. The claim 4 method further comprising a step (iv) recrystallizing said tetraethyl ammonium borohydride separated in step (iii) from an alkanol solution thereof. 6. The claim 4 or claim 5 method wherein said solid alkali metal borohydride added in step (ii) is sodium borohydride. 7. The claim 4 or claim 5 method in which said aqueous solution of tetraethyl ammonium hydroxide provided in step (i) is a 40% to 60% by weight aqueous solution. AMENDED CLAIMS [received by the International Bureau on 15 April 1998 (15.04.98); original claim 4 amended; original claims 1-3 cancelled; new claims 8-10 added; remaning claims unchanged ( 3 pages)] 1. [CANCELLED] [CANCELLED] [CANCELLED] 4. A method for producing tetraethyl ammonium borohydride which comprises: (i) providing an aqueous solution of tetraethyl ammonium hydroxide; (ii) adding a particulate solid alkali metal borohydride to said aqueous solution of tetraethyl ammonium hydroxide, wherein said addition is accomplished with agitation to facilitate dissolution of said alkali metal borohydride in said aqueous solution of tetraethyl ammonium hydroxide, and wherein said tetraethyl ammonium hydroxide of step (i) and said alkali metal borohydride of step (ii) react to form a ET ARTfCL reaction mixture containing said tetraethyl ammonium borohydride; and (iii) separating said tetraethyl ammonium hydroxide from said reaction mixture. 5. The claim 4 method further comprising a step (iv) recrystallizing said tetraethyl ammonium borohydride separated in step (iii) from an alkanol solution thereof. 6. The claim 4 or claim 5 method wherein said solid alkali metal borohydride added in step (ii) is sodium borohydride. 7. The claim 4 or claim 5 method in which said aqueous solution of tetraethyl ammonium hydroxide provided in step (i) is a 40% to 60% by weight aqueous solution. 8. A method which comprises: (i) providing a 20 to 60% by weight aqueous solution of a tetraalkyl ammonium hydroxide; (ii) adding a particulate solid alkali metal borohydride wherein said addition is accomplished with agitation, wherein said alkali metal borohydride described in said step (i) aqueous solution reacts with said tetraalkyl ammonitim hydroxide, and wherein a reaction mixture which is an aqueous solution of a tetraalkyl ammonium borohydride and an alkali metal hydroxide is formed; (iii) upon substantial completion of said reaction, adding aqueous ammonium hydroxide and aqueous metal alkoxide to said step (ii) reaction mixture, wherein said step (ii) reaction mixture separates into a lower aqueous alkali metal hydroxide or alkali metal alkoxide containing layer and an upper layer containing an ammonium tetraalkyl borohydride hydrate; (iv) separating said step (iii) upper and lower layers; and (v) drying and separating said upper layer, wherein a solid ammonium tetraalkyl borohydride product is obtained. 9. The claim 8 method further comprising: (vi) recrystallizing said step (v) product from an alkanol . 10. The claim 8 or claim 9 method wherein, said step (i) aqueous solution of a tetraalkyl ammonium hydroxide is a 40% to 60% by weight aqueous solution of tetraethyl ammonium hydroxide, said step (ii) particulate solid alkali metal borohydride is sodium borohydride, said step (iii) is conducted at a temperature of 20° to 30°C, and said drying step (v) is accomplished by vacuum distillation.

Inventors: SULLIVAN JEFFREY M, SULLIVAN, JEFFREY, M.
Applicants: BOULDER SCIENT CO, SULLIVAN JEFFREY M, BOULDER SCIENTIFIC COMPANY, SULLIVAN, JEFFREY, M.
Application year: 1997
Main classification: C07F5
IPC codes: C07C209, C07C211, C07F5