Isotopically-enriched boranes and methods of preparing them
View Patent ↗The invention provides new methods for synthesis of large boron hydride clusters e.g., boron hydride molecules of the formula B n H m where 5≦n≦96 and m≦n+8, wherein m and n satisfy the electron counting rules of macropolyhedral boranes. The invention is particularly useful for synthesis of octadecaborane (B 18 H 22 ). Preferred methods of the invention include iteratively generating a conjugate acid from a salt of the [B a H b ] c− or [B n+2 H m−4 ] 2− anion followed by degradation under conditions conducive to concentrating and drying of the conjugate acid to provide a borane B n H m and residual salt of the [B a H b ] c− or [B n+2 H m−4 ] 2− anion which is reused in the method of synthesis. The invention further provides isotopically enriched boranes, particularly isotopically enriched 10 B 18 H 22 and 11 B 18 H 22 .
1. A method of synthesizing a borane having n boron atoms and m hydrogen atoms, the method comprising the steps of:
(a) contacting a mixture of a borane anion of the formula [B a H b ] c− and at least one solvent with an acidic ion-exchange resin to produce H c [B a H b ] or a hydrate thereof;
(b) degrading at least a portion of H c [B a H b ] or the hydrate thereof to generate at least one borane of the formula, B n H m , by concentrating the mixture comprising H c [B a H b ] or the hydrate thereof under reduced pressure;
(c) separating residual borane anion from product borane B n H m ;
(d) repeating steps (a)-(c) with residual borane anion recovered in step (c),
wherein n is an integer of from 5 to 96, a>n, b≦a+8, c is an integer of 1-8, and m≦n+8.
2. A method of synthesizing a borane having n boron atoms and m hydrogen atoms, the method comprising the steps of:
(a) contacting a mixture of a borane anion of the formula [B n+2 H m−4 ] 2− and at least one solvent with an acidic ion-exchange resin to produce H 2 [B n+2 H m−4 ].xH 2 O;
(b) degrading at least a portion of H 2 [B n+2 H m−4 ].xH 2 O to generate B n H m by concentrating and drying the mixture comprising H 2 [B n+2 H m−4 ].xH 2 O;
(c) separating residual borane anion from product B n H m ; and
(d) repeating steps (a)-(c) with residual borane anion recovered in step (c), wherein n is an integer of from 5 to 96, m≦n+8, and x is a non-negative real number.
3. The method of claim 2 , wherein the degradation step is conducted at reduced pressure, in a flow of dry gas, or in the presence of at least one desiccant.
4. The method of claim 2 , wherein the degradation step is conducted at reduced pressure.
5. The method of claim 2 , wherein n is an integer selected from the group consisting of 10, 12, 14, 16, 18, 20, and 22.
6. The method of claim 2 , wherein the borane anion of the formula [B n+2 H m−4 ] 2− is [B 20 H 18 ] 2− and the boron hydride of the formula B n H m is B 18 H 22 or the borane anion of the formula [B n+2 H m−4 ] 2− is [B 22 H 22 ] 2− and the boron hydride of the formula B n H m , is B 20 H 24 .
7. The method of claim 2 , wherein steps (a)-(c) are repeated at least twice.
8. The method of claim 2 , wherein steps (a)-(c) are repeated between about 2 and about 20 times.
9. The method of claim 2 , wherein steps (a)-(c) are repeated between about 4 and about 12 times.
10. The method of claim 2 , wherein the acidic ion-exchange resin is an aromatic or partially aromatic polymer comprising a plurality of sulfonic acid residues.
11. The method of claim 10 , wherein the acidic ion exchange resin is a crosslinked sulfonated polystyrene.
12. A method of synthesizing B 18 H 22 comprising the steps of
(a) contacting a mixture of a [B 20 H 18 ] 2− salt and at least one solvent with an acidic ion-exchange resin to produce H 2 [B 20 H 18 ].xH 2 O;
(b) degrading at least a portion of the H 2 [B 20 H 18 ].xH 2 O to generate B 18 H 22 by concentrating and drying the mixture comprising H 2 [B 20 H 18 ].xH 2 O;
(c) extracting the residue with water and at least one water immiscible solvent to provide an aqueous solution;
(d) contacting the aqueous solution with an alkyl amine or an alkyl ammonium salt to precipitate (B 20 H 18 ) 2− salts; and
(e) repeating steps (a)-(d) at least once, wherein x is a non-negative real number.
13. A method of synthesizing B 18 H 22 comprising the steps of
(a) contacting a mixture of a [B 20 H 18 ] 2− salt and at least one solvent with an acidic ion-exchange resin to produce H 2 [B 20 H 18 ].xH 2 O;
(b) degrading at least a portion of the H 2 [B 20 H 18 ].xH 2 O to generate B 18 H 22 by concentrating and drying the mixture comprising H 2 [B 20 H 18 ].xH 2 O;
(c) extracting the residue with hydrocarbon solvent;
(d) contacting the residue with acetonitrile to dissolve B 20 H 18 2− salts; and
(e) repeating steps (a)-(d) at least once, wherein x is a non-negative real number.