JOURNAL OF CHEMICAL EDUCATION
FRAGMENTS OF CHEMISTRY CHARLES A. KRAUS Brown University, Providence, Rhode Island 7.
BORON
Reactions of Triallcyl and Arylboranes. With ammonk and the amines, the alkyl and aryl boranes form rather of the type R3B'NHa. these compounds are treated with alkali metals in liquid ammonia, hydrogen is evolved and the resulting amide ion complexes with boron. Reaction takes place according to the equation:
~(CIHDLB = (C4Ho)aB
+ CIHQB
(4)
The monobutylboron, C ~ H ~ is B a, solid and is doubtless highly polymerized. In all likelihood, dibutylboron also exists as a polymer of some sort, In one experiment, a small quantity of a diEculty volatile material was obtained whose corresponded closely to that of dibutylboron. It K + R1B.NH3= FbB.NHIK '/rHr (1) would be of much interest to obtain dialkylboron in the ~~~~~~~d~ of the typeR ~ B N H ~are M strongelectro- pure state. However, it would be advantageous to lytes and are surprisingly stable. Thus, the compound work with a compound of one of the lower alkyls, such p h 3oxidizes ~ as themethyl or ethyl derivatives. With amorevolatile p h 3 B ~ H z is Xfairly stable in air readily and KNH2 oxidizes explosively. It may be compound, it might be possible to volatilize the dialkyl noted that the boranes form stable complex compounds boron without decomposition. The product of reaction (3), MB(C4Hg)2,yields a red with salts of several small ions such as OH-, F-, etc. colored solution; therefore, it is a simple matter to Thus, tetrabutylammonium triphenylborofluoride Burdetermine the end point of reaction (2). The product NPh3BF, is quite stable in air. of reaction (3) cannot well be isolated and studied. ~h~ dialhyl or aryl boron Dibutylboron However, its existence may be established by its rehalides, R2BX, ammonolyse in liquid ammonia, Therefore, they cannot be reduced by means of the actions. On adding methyl iodide to the product of reaction alkali metals in that solvent. However, they may be (3), we should expect to obtain methyldibutylboron in reduced by means of sodium-potassium alloy in ether accordance with the equation: solution. It is, perhaps, more accurate to say that dibutylboron bromide may be so reduced; similar MB(C,HI)S + CHJ = CHsB(C,H& + MI (5) reactions with other dialkyl or aryl boron halides, while they probably would occur, have not been The expected compound is obtained with a 67 per cent yield. Only two-thirds of the dibutylboron reacts in studied. The reduction of dibutylboron bromide by means of accordance with equation (3). Other observations and Na-K alloy takes place in two stages; in the first reactions indicate that reaction (3) is not quantitative. Seemingly, dibutylboron exists in two (probably polystage, reaction occurs according to the equation: meric) forms only one of which is reduced to MB(C,H& (C4H&BBr M = (C4H&B MBr by sddium-potassium alloy. While there is no question as to the formation of the metal boride to the extent of In the second stage we have: approximately 67 per cent, it seems equally certain that (CIH&B M = MB(C4Hdr (3) the dibutylboron, as initially formed, is not all of the Dibutylboron and metal dibutylboride are both soluble same kind. Further investigation is required to estabtish the nature of the products of reaction (2). By all in ether. If, after reaction (2), the solvent is evaporated and the means, the reaction of more volatile dialkylboron comtube containing the product is exhausted a t higher pounds should be investigated. At the same time, it temperatures, and the volatile products are condensed would be of interest to investigate the reduction reand collected, the butylboron disproportionates accord- actions of diphenylboron halides. The reaction of compounds of the type MB& with the halides of diierent ing to the equation:
+
+
+
+
NOVEMBER, 1952
organic and orgmo-metallic groups would he of interest. NaGePha and BC&. Sodium triphenylgermanide reacts readily with boron trichloride in ether. Seemingly, the reaction is straightforward; no hexaphenyldigermane is formed nor is there evidence of a product other than one of boron and germanium. However, the
549
material was obtained as a rather viscous oil which could not be crystallized. The germanium/boron ratio approximated 3: 1. It is likely that the compound may have been complexed with ether. Treatment with liquid ammonia might serve to yield a manageable product.
