842
D.\SIEL T. HAWORTH AND L. I;. HOI-INSTEDT [ C O Y r R I B L r I U h F K O M THE D E P A R I M E N T O F C H E M I S T R Y ,
Vol. S l
ST. LOUISU h I V E R S I l l ]
Pyrolysis of the Borazine-Methanol Adduct BY DANIELT. HATf'ORTH
AKD
L. F. HOHNSTEDT~
RECEIVED JULY 15, 1958 As reported it1 the literature, borazine reacts with excess methanol a t room temperature to form a 1: 3 adduct, B3S&.3CHIOH. Pyrolysis of this adduct a t 100" has been reported to give 3 moles of HZper mole of adduct and a volatile monomer CH30BNH, which would represent the only case of a monomeric species of empirical formula corresponding t o a borazine derivative. Our repeated pyrolyses of B ~ N ~ H o ~ C Hgave ~ O the H predicted amount of Ha. The other products observed are ammonia-trimethoxyborane, HaSB(OCH3)3 (which has a gas phase molecular weight close to that calculated for CHIOBNH), B-trixnethoxyborazine [ B ~ ( O C H ~ ) ~ XaZlittle H ~ ] ,methanol and a non-volatile white solid of composition intermediate between B N and [B(OCHa)NH],. B ~ ( O C H ~ ) ~ X sublimes L H ~ in vacuo a t 60°, reacts quantitatively with methanol a t 100" t o produce H3NB(OCH3)3, and changes to a non-volatile solid when heated alone a t 100". I t appears highly improbable that a stable CHJOBSH monomer can be prepared by reaction of borazine and methanol. The reaction of borazine on mixing with ethanol is similar to that with methanol except that partial ethanolysis to break the borazine ring occurs a t room temperature and even lower. B-Triethoxyborazine may be obtained from borazine-ethanol mixtures by heating a t 100". The same compound melting a t 53-54' was prepared for comparison by the interaction of B3ClaNaHs with SaOCZHb.
Introduction To test this hypothesis B-trimethoxyborazitle was A volatile nionomeric compound CH30BNH has prepared by the reaction of sodium methoxide and been suggested as one of the products of the pyroly- B-trichloroborazine'j (eq. 3) and then treated with sis of the 1: 3 borazine-methanol a d d ~ c t . ~ -BsClaSaHa ~ 3iL'aOCHa + This is of interest because i t corresponds t o a 3SaC1 + B3(0CH3)aNsHa (3) depolymerized borazine B3(OCH3)3N3Ha and would methanol a t 100-120°. As described in the represent the only example of such a monomeric Experimental part, the reaction was in quantiB-N analog of a ~ e t y l e n e . ~ tative agreement with eq. 2. However, when We find in agreement with references 3 and 4 that samples of B-trimethoxyborazine were subjected borazine reacts with excess methanol a t room tem- to the same heating in the absence of added methaperature to form a 1: 3 borazine-methanol adduct. nol, only a trace of ammonia-trimethoxyborane As reported, pyrolysis a t 100' and slightly higher was formed even though considerable quantities yields three moles of hydrogen per mole of adduct. of methanol were produced and all the methoxyHowever, the other readily volatile products were borazine was converted to non -volatile material. identified by us as the addition compound am- Therefore the decomposition of B3N3He.3CH30H monia-trimethoxyborane and a small amount of to liberate hydrogen must be more complex than methanol. No volatile monomeric CH30BNH the single reaction indicated by equation 1. was produced in any of our pyrolysis runs. The The reaction of ethanol with borazine was inmethanol previously3 ascribed to the decomposition vestigated with efforts to produce B3N3H6.3of CHsOBNH into BN and CH3OH may be CzH60H by direct combination. Mixing borazine explained by the fact that the pyrolysis products and ethanol a t temperatures as low as -30' include a non-volatile polymer of composition resulted in partial ethanolysis to give B (OC2H& intermetiiate between that of (C&OBNH), and and "3. If the 1 : 3 borazine-ethanol adduct (BN),, so that the elements of methanol must is the first product of the interaction of its constithave been released from some of the B3N3H6- uents, it undergoes further reaction with ethanol XCHaOH on pyrolysis. This polymeric product under the experimental conditions used. mas converted into a substance approximating BN in formula only after prolonged heating a t 400'. Experimental Furthermore the pyrolysis products included the Materials.-Borazine was prepared by the reduction of borazine B3(0CH3)aN3H3.This suggested the B3C13N3H3with NaBHl in triethplene glycol-dimethy1 ether possibility that the first step in the pyrolysis was solvent? R8C13X3Hawas prepared by the reaction of BCll and XILthe formation of B-trimethoxyborazine (eq. 1) C1.8 The methanol after fractionation in a high V ~ C I I L I I ~ I B3N3He,~3CI130II----f 3Hz f B3(0cfIa)3pi3II3 (I) system exhibited a vapor tension of 30 mm. a t 0.0" (lit. mm.). If part of the B3(OCH3)3K3H3 polymerized with 30.4 Apparatus.-In general standard vacuum line equipment liberation of CI-130H, the CH30H could then was used which is described e l s e ~ h e r e . ~ Formation and Pyrolysis of B3N3H6,3CH80H.-Samples attack the remaining B3(OCH3)3N3H3 to produce of borazine and methanol, with methanol in excess of the the observed H3NB(OCH3)3 (eq. 2)
+
B3(0CH3)3L73EI3
+ GCHaOH +3IIaXB(OCH3)a
(2)
(1) Communications regarding this article should be directed t o
L. F. Hohnstedt, Department of Chemistry, St. Louis University. (2) T h e name borazine has been recommended t o replace borazole for BaNsHs. (3) E. Wiberg and A. Bolz, R e ? . , 73B,209 (1940). (4) E . Wiberg, i~alurwissenschuflen,36, 212 (1948). (5) Wiberg has also reported the existence of monomeric CHsBNCaHn, b u t Becher reports t h a t repetition of the Wiberg procedure gives a trimer and t h a t no monomer can be isolated. E. Wiberg and K. Hertwig, Z . onovg. ailgem. C h e m . , 267, 138 (1948). H. J. Becher, ibid., 289, 262 (1956).
stoichiometric amount required to form B ~ N ~ H ~ . ~ C H S O H , were condensed together in a bomb tube attached to the vacuum line, The tube and its contents were allowed to warm from -196" t o room temperature and kept at the latter temperature for G hr. During this time a glassp transparent solid was formed. The tube was then opened t o the vacuum line and the unconsumed methanol was distilled (6) J. R. Gould a n d C. Pearl, R l l I - 4 4 O - Q l (Oct. 9, 1952).
(7) L. F. Hohnstedt and D. T. Haworth, t o be published. (8) C . A , Brown and A . IV. Laubengayer, THISJ O U R N A L , 77, 3(j!l!) (1955). (9) R. T. Sanderson, "Vacuum hIanipulation of Vuldtile Ct~rupounds," John Wiley and Sons, Inc., New York, N . I?.. l!U8.
PYROLYSIS OF THE BORAZINB-METHANOL ADDUCT
Feb. 30, 1959
out and measured. The bomb tube was sealed off and heated at 100-120" for 4-5 hr. after which it was opened and H2 was measured volumetrically. The data are listed in Table I. TABLE I' CHsOH CHaOH Bal\'sHa/ CHaOH rereCHaOH Exp. BaNaHa added covered tained (retained)
HI
Bsl\'aHa/ H2
1 12.2 40.6 4 . 1 3 6 . 5 1/2.99 2 6 . 5 1/2.1? b 2 21.7 7 9 . 5 14.4 6 5 . 1 1/3.00 3 6 4 . 3 200.3 7 . 5 192.8 1/2.99 194.2 1/3.02 4 73.7 231.8 1 0 . 8 221.0 1/2.99 219.2 1/2.97 5 1 2 . 8 44.7 5 . 9 3 8 . 8 1/3.03 38.1 1/2.97 6 2 7 . 4 92.4 1 0 . 3 8 2 . 1 1/2.99 8 1 . 1 1/2.96 X o t measAll volumes are reported as cc. at S.T.P. ured. Heating time was less than 1 hour.
Volatile Products of Pyrolysis of B3N3H6.3CH30H.After removal of hydrogen, the products volatile a t room temperature were fractionated using a train of U-tubes cooled to -45, -78 and -196'. Most of the ammoniatrimethoxyborane was stopped by -45" and any methanol Since ammonia-trimethoxyborane was retained by -78'. is largely dissociated a t room temperature the methanol was separated by condensing all these volatile products in a Utube a t -196" and then replacing the -196' bath with a -45' bath and allowing the methanol to move out of the U-tube. The methanol was identified by its vapor pressure of 31 mm. at 0". A white solid with an appreciable vapor Pressure was retained a t -45'. The gas phase molecular weight of the material retained by the -45' bath was in the range of 59-61. This would appear to be consistent with CH30BNH (mol. wt. = 56.87); however, an infrared spectrum indicated the presence of ammonia and methyl borate which suggested that the volatile solid was 1:1 ammonia-trimethoxyborane adduct.''' The spectrum of a sample of ammonia-trimethoxyborane prevared by mixinn methvl borate and ammonia in a 1: 1 iatio proved to be rdenticd with that of the -45" fraction. Furthermore the equilibrium pressure over the solid agrees with that reported for the ammonia-trirnethoxyborane,l1 as shown in Table 11.
TABLE I1 PRESSURE OVER THE -45" FRACTION log p(mm.) = 12.365 T(OC.)
0.0 1.3 9.7 16.2 17.9 19.8 22.6 23 5 26.0
- 3010.0 (for H3NB(OCH3)3)11 ~
Obsd. (mm.)
21 24 49 85
97 110 133 155 188
Calcd. (mm.)
20.7 23.2 47.3 86.1 98.8 109 139 154 186
Identification of the volatile solid was confirmed by analysis. Calcd. for HaNB(OCH3)a: B, 8.95; N, 11.58. Found: B, 8.94, 8.93; N, 11.64, 11.62. Identification of B-Trimethoxyborazine.-Sublimation a t 55' of the residual solids in the bomb tube yielded Ba(OCH3)a N3H3 which was identified by its m.p. of 110-111" 112-112.5') and analysis. Calcd. for B3(OCH&N3Ha: B, 19.03; N,24.63. Found: B, 19.0, 19.0; N, 24.20, 24.51. A sample of the non-volatile solids remaining after sublimation contained B and N in a 1: 1 ratio, but the B and N content accounted for only 73.5% by weight of the sample which presumably also contained the elements of CHsOH. Preparation of B&OCH&N&&.-4.4 g. of B-trichloroborazine and 5.0 g. of sodium methoxide were reacted for 5 hr. in refluxing chlorobenzene. The solvent was distilled off under vacuum and 2.2 g . of the borazine (53.9% yield) was obtained by vacuum sublimation a t 60'. (10) J. Goubeau a n d U. Bohm, 2. anorg. allgem. Chem., 266, 161 (1951). (11) W. H. Schechter, U. S. Patent 2,629,732,
843
Methanolysis of B3(OCH3)3N3H3.-Measured samples of Ba(OCH&NaHa and CHaOH were mixed and heated a t 100' for 4 hr. in sealed Pyrex tubes. Methanolysis occurred according to eq. 2 to consume completely the methanol and give stoichiometric amounts of ammonia-trimethoxyborane. Typical results are listed in Table 111. For comparison this table includes the data for the pyrolysis of the B-trimethoxyborazine itself a t the same conditions. I t is of interest to observe that the borazine evolves methanol on pyrolysis but only relatively small amounts of ammonia-trirnethoxyborane. Thus the data of run no. 6 are consistent with reaction of the added methanol according to eq. 2 accompanied by decomposition of some of the excess borazine to produce methanol and a little ammonia-trimethoxyborane.
TABLE 111" Ratio -.-. .
Ba(0CHa)sBaKaHs CHaOH (OCH3)aNsHs -HaNB(OCHs)sused added CHaOH Theor. Obsd.
(1) (2) (3) (4) (5) (6) (7) (8)
CHsOH Recovered
... 0.0 1/0.0 8.6 0.0 0.2 1/0.0 0.0 11.0 ... 1.1 1/0.0 0.0 10.2 6.75 6.7 1/2.33 5 . 8 13.5 1/2.50 12.5 9.2 10.0 25.0 10.9 11.2 1/2.63 8 . 3 21.8 34.0 35.7 1/6.01 11.3 68.0 20.8 20.5 1/6.00 6 . 9 5 41.7 All volumes are reported in cc. a t S.T.P. .
I
.
8.17 5.00 6.5 0.0 0.0 4.9 0.0 0.0
Blank.-32.4 cc. of CHaOH and 32.3 cc. of NH3 were heated to 120' for 4 hr. in a Pyrex bomb tube. 31.5 cc. of CHaOH and 32.0 CC. of NHa were recovered from the tube: only a trace Of material which might have been HsNB(OCH8): was formed. Ethanol-Borazine Reaction .-Measured samples of bora196' and zine and ethanol were condensed together a t allowed to warm to reaction temperature, a t which they were maintained for 4 to 7 hr. The mixtures were then cooled to - 196' and any HZformed a t the reaction temperature was measured. Then the mixture was rewarmed to reaction temperature and volatile materials were distilled into the vacuum line and fractionated. The reaction temperatures studied were -45, -30, -23, 0' and room temperature. In all cases ethanol was present in greater than 3: 1 mole ratio with respect to borazine. There was no evidence of reaction at -45", but a t other reaction temperatures HI was evolved and NH, could be isolated from the volatile product mixture. In some runs B ( O C I H ~ could )~ be isolated but in others it appeared that in addition to NHa the volatile material contained a mixture of CZH~OH and B(OC?H6)3which could not be separated by the technique used. In no case was there any apparent stoichiometric relationship between the amounts of H2, NH3 and B(OC2H~)a produced. The borazine-ethanol reaction may be complex as is that of borazine-methanol (see below). B-Triethyoxyborazine .-In the above reactions the solids remaining in the reaction tubes after pumping off all volatile materials a t room temperature were heated to 100' for several hours. Further Ht. NH* and B(OC2Hs)s or B(OC2HS)3CsHsOH mixture were produced. The remaining solids were heated to 40" in a high vacuum and B1(OC2H~)rN3Ha sublimed away from a non-volatile white residue. The B3( O C ~ H S ) ~ Nm.p. ~ H ~53-54", , was identified by comparison with a sample of this substance prepared by the reaction of B3C13NzHa with NaOC2Hb. Four g. of BzCLNaH: and 4.4 g. of NaOCnHs reacted in refluxing chlorobenzene for 4 hr. The solvent was distilled away uider vacuum and the resulting solids were warmed to 40' in a high vacuum. A white crystalline material melting at 53-54' sublimed out of the heated zone and was collected in a -80' trap. It was identified as B3(OC~H6)3N3H8 by molecular weight and analytical data. Calcd. for B ~ ( O C Z H ~ ) ~ NB,~ H 15.26; ~: N, 19.76; mol. wt. 212.7. Found: B, 15.3, 15.4; N, 19.73, 19.83; mol. wt. (by benzene m.p. depression), 193-205. Analyses.-Samples of alkoxyborazines were digested a t 100' in a small amount of concd. H2SO4. Non-volatile solids were treated similarly, except that a few drops of 3070 H202 was added to the HzSOI. Boron was determined by titration of the mannitol complex, nitrogen by the Kjeldahl analysis.
-
HIRALAL
844
LTol. 81
Discussion
sulted in partial ethanolysis of the adduct. At The data given in the experimental part show 0’ ethanol was observed to have no effect on the that the pyrolysis of 1 :3 borazine-methanol adduct borazine-methanol adduct. These observations might tempt one to specua t 100-120° gives the volatile ammonia-trimethoxyborane and not the suggested CH30BNH. late as to the relative reactivity of methanol and Assuming complete dissociation in the gas phase the ethanol toward borazine-alcohol adducts. Howobserved molecular weight of the complex would be ever, the adducts, especially B3N3He.3CH~0H, 60.46, one-half that for H3NB(OCH3)3. The ob- appear to be only slightly soluble in their corserved value of 59-61 supports this assumption. responding alcohols. Therefore the observed difThe isolation of the trimer B3(OCHJ3N3H3 by ferences in behavior may well be due to differences vacuum sublimation a t 55’ makes it appear im- in solubility, and the apparent stability of BJprobable that there was present any stable mono- N3H6.3CH30H may arise from the slowness of a mer CH30BNH which was not detected by reason heterogeneous phase reaction occurring a t the of its being retained by the solids in the bomb tube. surface of the adduct. Some preliminary experiments support this sugThe existence of any such monomer stable with regard to polymerization a t room temperature ap- gestion. A sample of B3N3H6.3CHd0H was partiaIIy dissolved in benzene. When methanol wa5 pears to be highly doubtful. Pyrolysis of the borazine-methanol adduct added to the resulting solid-solution mixture, the evidently proceeds by a t least two paths, one of remaining solid rapidly dissolved with evolution which probably is represented by eq. 1 and another of a gas from the solid surface, although such of which may well be an intermolecular poly- evolution did not occur when the adduct initially merization of the borazine-methanol adduct to dissolved in the benzene. This suggests that furliberate HZ and some methanol and to form a ther studies of the reaction of borazines with alpolymer B,N,H,(OCH3),. Of course, intramolecu- cohols should be carried out in neutral solvent. lar reaction to give CH30H is not precluded and the Also, to prepare B3N3H6.3C2HjOH and other data are obscured by the fact that the trimeth- kinds of related adducts one should consider the oxyborazine produced during the pyrolysis is reaction of the desired borazine and alcohol in itself changed into a non-volatile residue, methanol solvents in which the adduct formed will be and a little ammonia-trimethoxyborane when relatively insoluble. If no such solvent can be found, then the addition of dilute solutions of the subjected alone t o similar pyrolysis. alcohol to solutions of the borazine may be conMethanol and Pyrex react to give methyl borate.12 However, a blank, as described in the sidered. The authors wish to express their appreciation to Experimental part, indicated that no significant amount of methyl borate was produced in this Dr. C. J. Barr and Mr. W.J. Meikle of the OlinMathieson Corporation for their] generosity in fashion under the pyrolysis conditions. making an infrared spectrograph available for use; The borazine-methanol adduct was practically and to hlr. R. Buxton for the determination and unattacked by excess liquid methanol, whereas interpretation of the infrared spectrum of amborazine underwent partial ethanolysis to B (OCZ- monia-trimethoxyborane. and NH3 a t temperatures as low as - 3 O O . We are appreciative of the generous assistance of An attempt to displace the methanol from the the Research Corporation which supported this borazine-methanol adduct by ethanol a t 25’ re- work by a Frederick G. Cottrell Grant. ST LOUIS,? ~ I I S S O ~ R I
(12) R . F. Porter, J . P h y s . Chein , 61, 1260 (1957)
[CONTRIBUTIONFROM THE
PHYSICAL
CHEMISTRY DIVISION,S A T I O N A L
Hydrogen Ion Equilibria and the Interaction of Albumin
CUI’
CHEMICAL
LABORATORY]
and Co” with Bovine Serum
BY HIRALAL* RECEIVED JULY 31, 1958 The interaction of Cu’I and Cor1 with bovine serum albumin has been followed by titration and distribution dialysis studies. It has been shown that Cor1 is bound t o bovine albumin through its imidazole sites. The existence of compound sites through which the first two cupric ions are bound t o bovine albumin has been confirmed; a log kO value of 6.8 + 0.3 for the intrinsic affinity of these sites for Cu” has been obtained. It has been shown that the subsequent binding of cupric copper with bovine albumin occurs 1: 1 with the imidazole sites. Evidence has been presented that cupric copper is partially hydrolyzed and bound as such to the protein in the neutral pH region.
Previous studies in acetate buffer medium of p H 6.5 have indicated that bovine albumin contains a class of two “compound” sites through which the first two cupric ions are bound to the protein molecule.1 The nature of these sites, adduced * Indian Institute of Technology, Worli, Bombay 18. (I) hI. S. N.Rao a n d H , Lal, THISJ o u A N . ~80, ~ , 3220 (1958).
essentially from electrophoretic studies, is such as to cause a release of two protons per metal ion bound.lV2 If these sites do exist, a direct evidence for their presence should be obtainable from titration studies. Studies in buffer solutions have also revealed that ColI is bound to the carboxyl (2) H. La1 and M. S. iS,Rao, ibid., 79, 3050 (1937).
