1692
Inorg. Chem. 1981, 20, 1692-1697 Contribution from the Union Carbide Corporation, Medical Products Division, Tuxedo, New York 10987
Simplified Synthesis of B10H14 from NaBH4 via BllH14- Ion GARY B. DUNKS,*' KATHRYN BARKER, EDDIE HEDAYA,* CATHERINE HEFNER, KATHY PALMER-ORDONEZ, and PETER REMEC Received August 21, 1980 The synthesis of BllHl; ion from BH, ion and acids, including BF3.O(C2HJ2, BCl,, SiC14,or alkyl halides, and the subsequent using Na2Cr207,KMn04, H202, or H202/FeS04is described. An optimum oxidation of the BllH14-ion to produce BIOH14 procedure is suggested which can be scaled-up.
Introduction A facile synthesis of tetradecahydroundecaborate( 1-) ion, B I I H l < ,from BF3.0(C2H5)2and NaBH4 was previously described.2 The major neutral product obtained from the sodium dichromate oxidation of an aqueous solution of BllH14- ion so prepared was decaborane(l4), B10H14.3Thus BIOH14 was made generally available for the first time by a relatively low-cost procedure which can be performed in standard laboratory apparatus. A probable sequence of steps which results in the formation of B l l H l < ion begins with the reaction of BF3.0(C2H5),with excess BH4- ion in diglyme solvent to produce B2H6 (eq l), 3BH4- + 4BF3-O(C2H5)2 2B2H6 + 3BF4- 40(C2H5), (1) '/2B*H,j + BH4B2H7(2) B3Hg- BH4- H2 2B2H7(3)
-
+
+
+
+
5BH4-
+ 4BF,.O(C2H,)z 2B3H8-
+
-+
+ 3BF4- + 2H2 + 40(C2H5), (4)
-+
+ 16BF3*O(CzH5)2 5BllHI4-+ 12BF4- + 33H2 + 160(C2H5), (5) 17NaBH4 + 20BF3.0(C2H5)2 17B3Hg-
2NaBl1Hl4+ 15NaBF4 20H2 + 200(C2H5), (6) which reacts further with BH4- ion to form B2H7- ion4 (eq 2). The B2H7-ion thermally decomposes to B3HB-ion and BH4ion5 (eq 3), and thus the sequence continues until the BH4ion is consumed. The overall process can be accomplished in one vessel,6producing B3HB-ion in approximately 65% yield on the basis of the stoichiometry of eq 4. If, however, BF3.0(CHzH5), is added beyond the quantity represented by eq 4, the B3H8-ion reacts to form B l l H I 4 -ion2 (eq 5). This sequence of reactions suggests that, under appropriate conditions, any reagent capable of producing B2H6in the presence of BH4- ion may form B l , H l < ion as in the case of BF,. o(c2H5)? (eq 6). In addition to BF3.0(C2H5)2,other Lewis acids and Bronsted acids have been shown to produce B2H6 when reacted with BH4- ion including BCl,: A1C13,7ZnC12,*SnC12,9H2SO4,I0H3P04,11and CH3COOH,12and indeed BzH6has been (1) To whom correspondence should be addrased at Rockwell International Corporation, Canoga Park, California 91304. (2) G. B. Dunks and K. P. Ordonez, Inorg. Chem., 17, 1514 (1978). (3) G. B. Dunks and K. P. Ordonez, J. Am. Chem. Sw.,100,2555 (1978). (4) H.C. Brown and P. A. Tierney, J. Am. Chem. SOC.,80, 1552 (1948). (5) D. Gaines, Inorg. Chem., 2, 523 (1963);D. Gaines, R. Schaeffer, and R. Tebbe, ibid., 2, 526 (1963). (6) W. J. Dewkett, M. Grace, and H. Beall, Inorg. Synth., IS, 115 (1974). (7) H.C.Brown and B. C. Subba Rao, J . Org. Chem., 22, 1136 (1957). (8) H.C. Brown, K.J. Murray, L. J. Murray, J. A. Snover, and G. Zweifel, J . Am. Chem. Soc., 82,4233 (1960). (9) W. Jeffers, Chem. Ind., 431 (1961). (10) H.G.Weiss and I. Shapiro, J . Am. Chem. Soc., 81, 6167 (1959). (1 1) A. D. Norman and W. L. Jolly, Inorg. Synth., 11, 15 (1 968). (12) V. Hach, Synfhesis, 340 (1974).
0020-1669/81/1320-1692$01.25/0
Table 1. Synthesis of B,,H,;
Ion from NaBH, and Acids
acid
B,,H,,- yield,a %
BF, H1 BCl, SEI, CH,Cl CH,Cl, n-C,H,Cl n-C ,HI,Br n-C,H,,Br
63
46 55 54 26 25
67 18
eq 6 8 9 7 7 7 7 7
Isolated as (C,H,),N+, (CH,),N+, or (CH,),NH+ salts
prepared from BH4- ion and alkyl With this background, a study directed toward the optimization of the synthesis of Bl0HI4via BllHI4-ion was initiated. We report here the synthesis of BllH14-ion from BH,- ion and acids including BF3*O(C2H5)2,BCl,, SiC14, and alkyl halides and the subsequent oxidation of the BllHI4-ion to produce Bl0HI4employing Na2Cr207,KMnO,, H 2 0 2 , and H,O2 in the presence of ferrous sulfate. Results and Discussion The procedure for the synthesis of B10H14 from BH4- ion involves three steps: (1) the synthesis of BllHl80 O C . Thus water could be added to reaction mixtures in which diethylcarbitol was employed and the solution heated. The diethylcarbitol layer could be decanted, leaving the BllH14-salts and other ionic reaction products in the aqueous layer. This method of solvent exchange proved difficult to operate in large-scale preparations and cannot be applied to reactions employing diglyme, which is miscible with water a t all temperatures. (3) Both diglyme and diethylcarbitol form constant-boiling mixtures with water (bp 99.6 and 98.4 “C a t 1 atm, respectively). The distillate contains approximately 20 vol % ethereal solvent in each case.15 Thus, addition of water to the cooled reaction mixture subsequent to the synthesis of B,,H14-and the distillation (1 atm) of the ethereal solvent/water azeotrope (14) H. C. Miller, N. E. Miller, and E. L. Muetterties, Inorg. Chem., 3, 1456 (1964). (15) L. H. Horsley, Adu. Chem. Ser., No. 116, 32 (1973).
Inorganic Chemistry, Vol. 20, No. 6,1981 1693 proved to be the most facile solvent-exchange procedure attempted. Water was added to the reaction mixture a t a rate equal to the rate that distillate was removed; thus the volume of the solution in the reaction vessel could be maintained constant to minimize stirring and over heating difficulties. Distillation was continued until the appropriate quantity of distillate had been collected. The cooled aqueous solution was suitable for use in the final oxidation step. During the distillation of the diglyme/water azeotrope from the reaction mixture, which contained BllH14-ion and the other nonvolatile products, a small quantity of white solid was occasionally observed to collect in the condenser. A sample of the solid was characterized by spectral methods as nBl8HZ2.l6 It was reported previously that n-B,8H22was the major product of the protonation of BllHI4-ion under anhydrous conditions.17 The mechanism of the production of the n-B18H22in the present system is unknown; however, its presence suggests that condensation of BllH14-ions may occur in the aqueous medium. The significance of such coupling reactions will be discussed below. For economy, the ethereal solvents could be isolated from the aqueous solutions resulting from the above distillation and reused. The addition of toluene to the water/ether solutions followed by distillation of the toluene/water azeotrope (bp 85 OC, 1 atm, 18 vol % water15) using a distillation head capable of returning the toluene to the pot allowed complete removal of the water. Distillation of the toluene and a forerun of the ethereal solvent provided diglyme (bp 162 OC, 1 atm) or diethylcarbitol (bp 189 OC, 1 atm) sufficiently dry and pure for direct reuse in the synthesis of BllHI4-ion. Step 3: Oxidation of BllH14- Ion to Bl$I14. The aqueous solution of B, 1H14- ion from the solvent-exchange step above was acidified and treated with excess aqueous oxidizing agent. B1J-II4produced was continuously extracted from the aqueous phase by a layer of immiscible organic solvent. The conversion of BllHI4-ion to BI0Hl4via the in situ oxidation of the BllHI4- ion produced in step 1, in which diglyme solvent had been used, was as high as 53% (on the basis of a 70% yield of BllHI4-ion in step 1 as indicated by IlB NMR). A similar in situ oxidation of BllHI4-ion synthesized in diethylcarbitol solvent produced BI0Hl4in only 26% conversion (again on the basis of the yield of BllH14-ion as indicated by llB NMR). Moreover, when isolated, pure (CH3)3NHBllH14was converted to the potassium salt (to increase solubility) and subsequently oxidized under similar conditions, the conversion to BI0Hl4was only 15%. These results suggest that diglyme was instrumental in producing high yields of B10H14 in the oxidation step. For a test of this, the “diglymate”, NaBl l H 1 4 ~ 2 C b H 1 4was 0 3 prepared and crystallized from aqueous solution. Oxidation of the pure NaBllH14-2C6H1403 produced BI0Hl4 in 48% conversion (comparable to the conversion obtained in the in situ oxidation of BllHI4-ion above). A similar oxidation of the “dioxanate”, NaBIIH14.2.5C4H802,’B produced BI0Hl4in only 13% conversion. The diethylcarbitol/B, 1HI4-ion complex was an oil and could not be compared. Thus, in the in situ oxidation of BllH14-ion to BIOHI4,the active species may be the BllHI4ion/diglyme complex. Passage of air or oxygen through an aqueous BllH14-ion solution which contained FeS04 failed to produce BI0Hl4in detectable quantities. Hydrogen peroxide (30%) produced BIOHI4; however, the reaction was very slow, requiring 42 h to maximize the BI0Hl4yield. Potassium permanganate and (16) A. R. Pitochelli and M. F. Hawthorne, J . Am. Chem. Soc., 84, 3218 (1962); F. P.Olson, R. C. Vasavada, and M. F. Hawthorne, ibid., 90, 3946 (1968). (17) J. S. McAvoyand M. G. H. Wallbridge, Chem. Commun., 3178 (1969). (18) H. C. Miller and E. L. Muetterties, Inorg. Synrh., 10, 81 (1967).
1694 Inorganic Chemistry, Vol. 20, No. 6, 1981
Dunks et al.
Table 11. Oxidation of B. H . . - Ion" with Various Oxidizing Agents equiv of mL of oxidizing oxidant oxidizing time agent soln agent required, h I
H 0JFe(W Na,Cr,O, KMnO,
12 105 1600 130
HzO2
1.34 2.40 1.70 1.72
2.7 1.0 0.7 42
g
mol
8.55 7.82 9.13 7.99
0.070 0.064 0.075 0.065
Based on eq 6 and 11.
Prepared in situ from NaBH, (1.59 mol) and BF,.O(C,H,), in diglyme.
BIOH,, yield,b % 74.9 68.5 80.0 70.0
conversion: % 44.0 40.2 47.0 41.1
Conversion of NaBH, to BlOH,,.
sodium dichromate both rapidly (
