NOTES
120
While the crystallite size was determined primarily by the firing temperature, a relationship between crystallite size and firing time also was established. Log-log plots of crystallite size versus firing time for oxides at various firing temperatures are shown in Fig. 6. The growth curves fit an equation of the form D =
taeA-BIT
where D is the crystallite diameter, t the time and T the absolute temperature; CY, A and B are constants. The constant, a, appears to be characteristic of oxide prepared by the thermal decomposition of thorium oxalate. For D in hgstroms and t in hours, a! equals 0.14. The temperature dependent function, eA-'IT is typical for rate processes requiring an energy of activation, the constant B being equal to AH/R where AH is the heat of activation. The heat of activation was determined to be 10.97 kcal./g. mole. The low value is in accordance with growth taking place only among well ordered groups of crystallites. The intercept, A , being an entropy term is characteristic of a particular oxide preparation and must be determined for each new preparation. Acknowledgment.-The authors wish to acknowledge the assistance of several members of the ORNL staff: T. E. Willmarth for the electron microscopy, G . W. Leddicotte for sedimentation particle size analyses, and R. M. Steele for the X-ray crystallite size determinations.
Vol. 61
Fiilnegg and Riesenfeld,2 who prepared it by extended heating of pyridine-boric acid mixtures. Experimental Materials.-Reagent grade orthoboric acid from several sources was employed without further treatment. The dioxane, 4-picoline, 2,&lutidine and 2,4,6-collidine were pure grades from Matheson, Coleman and Bell, used without further treatment. The pyridine was Raker and Adamson reagent grade. The other pyridine bases and cyanuric acid were obtained from Eastman Organic Chemicals Department, Distillation Products Industries. The quinoline, isoquinoline and cyanuric acid were pure grades, used as received. The other materials were practical and technical grades which were subjected to a single distillation before use. Solubility Determinations.-Orthoboric acid and the organic solvent were loaded into 2-02. polyethylene bottles, the screwcaps sealed with paraffin. The bottles were rotated end-over-end in a constant temperature (f0.1') water-bath for periods of one to five weeks. The two phases were separated by filtering rapidly a t temperature. Two samples of each liquid phase were taken and made up to 50 ml. with the appropriate solvent. The boron content of each resulting solution was determined using a neutron absorption techni ue developed by Leddicotte, Brooksbank, and Strain of t%is Laboratory.3 The method depends on the fact that the neutron density in a paraffin block containing a neutron source is greatly lowered by the presence of nuclides with high thermal-neutron absorption cross-sections. The apparatus consists of a B"JFs-filled neutron detector, mounted coaxially in a 40-ml. Teflon cell. The cell is mounted within a block of paraffin containing also a Po-B neutron source. The time necessary for the detector to accumulate a fixed number of counts is proportional to the concentration of the high cross-section nuclide, in this case B*O. The a aratus was calibrated using known concentrations of 3 03 in water. The method was used differentially to minimize errors due to the use of several different solvents. The results are shown in Table I.
14%
TABLE I
THE REACTION OF BORIC ACID WITH SOME PYRIDINE BASES BY MARKT. ROBINSON Solid Slate Division, Oak Ridge National Laboralory, Oak Ridge, Tennessee Received August $3,lS66
It was reported recently by Astakhov, Elitsur and Nikolaev' that water could be extracted from orthoboric acid, H3BOa,by either pyridine or dioxane, leaving behind either metaboric acid, HB02, or pyroboric acid, H2B407,depending on the temperature of extraction. Their claims were based on determination of the volume of hydrogen released by their solutions on treatment with calcium hydride, the gas being attributed solely to reaction with water extracted from the solid HaB03. I n an unsuccessful attempt to use such an extraction for the preparation of metaboric acid, it has been found that pyridine and its homologs react very readily with H3B03. The apparent solubility of HaBOain dioxane and in pyridine has been determined and the solid phases have been examined by X-ray diffraction and by analytical methods. It was immediately apparent that the solid phase in equilibrium with the dioxane solution was unchanged H3B08. Pyridine, on the other hand, reacts with boric acid to produce a stable solid salt. This product is presumably the same as the uncharacterized material reported a generation ago by Gebauer(1) K. V. Astakhov, A. 0. Elitsur and K. M. Nikolaev, Zhur. Ob-
rhchd Rhim., 31, 1753 (1951).
APPARENTSOLUBILITYOF HaB03 I N PYRIDINE AND DIOXANE Temp.,
OC.
25.3 32.5 40.0
IN
Solubility (moles HsBOa/l. of soln.) In pyridine In dioxane
1.04, 1.13, 1.31
1.08 1.19
0.213 .234, .236 .266, .274
Crystalline Pyridine-Boric Acid Compounds .-The reaction of boric acid with pyridine and many of its homologs proceeds extremely rapidly. If pyridine is simply poured onto coarsely crystalline boric acid, the solid sinters immediately and must be crushed before complete reaction can be obtained. The product is independent of the reaction tern erature in the range from 0 to 115'. Cursory study of t f e thermal stability of the pyridine compound shows that, a t a pressure of 0.01 mm., it does not decompose appreciably until heated above about 120". The vapor evolved appears to be principally water. The resulting solid is amorphous. The crystalline compounds used for X-ray diffraction studies were generally prepared by loading boric acid and the appropriate base into a polyethylene bottle which was rotated end-over-end a t 1 r.p.m. for several day8 a t room temperature. The solid product was filtered and a portion was air-dried. X-Ray diffraction powder patterns were obtained on a Norelco diffractometer, using Ni-filtered, Cu Densities a t room temperaK a radiation (A = 1.5418 i.). turt! were determined by toluene displacement in 25-ml. pyciAometers. Aqueous solutions of the compounds were analyzed for boric acid by the usual mannitol method and for base by direct titration with standard acid. Tests using pyridine and boric acid solutions showed no interference of one substance with the analysis for the other. Karl Fischer analyses were carried ?ut on methanol solutions, determining (2) E. Gebauer-Fanegg and F. Riesenfeld, German Patent 482266 (Dec. 24, 1926). (3) W.A. Brooksbank, Jr.. 0. W. Leddiootte end J. E. Strain. AEC Report ORNL-1961 (unpublbhed).
Jan., 1957
NOTES
121
water and boric acid together. Some samples were analyzed for carbon and hydrogen by conventional combustion methods. The reaction of pyridine with cyanuric acid was carried out in the same way. A similar sintering effect was noted and an appreciable amount, of heat was evolved.
Results of chemical analyses on several samples of the pyridine-boric acid compounds are presented in Table 111. The formula CsHbN.3HBOz is believed to represent the ideal composition, although the last sample would be better represented by the formula Cd&N.3HBOs.H3B03. Chemical analyses Results and Discussions obtained on toluene-washed samples of each of the The products of the reaction of the pyridine bases other compounds are presented in Table IV. It is with H3B03are all white, non-hygroscopic crystal- clear from these analyses that, while most of the line solids, much softer than the original boric acid. samples approximate to derivatives of metaboric They dissolve completely in methanol, forming acid (Bz03:HzO: : 1 :l), there is no simple formumethyl borate and water. All of the compounds lation which will satisfy all of the analyses. Analydissolve in water, with complete hydrolysis, except ses of air-dried samples of the 2,4- and 2,6-lutidine for the piperidine derivative which is probably un- compounds gave ratios, base :BzOs:HzO, 1: 1.4:0.89 hydrolyzed. The X-ray diffraction patterns ob- and 1:0.49: 1.5,respectively. tained on these materials were characterized by TABLE 111 large numbers of well-resolved lines a t quite small diffraction angles (2 9), useful resolution being ob- CHEMICALCOMPOSITION OF PYRIDINE-BORIC ACID COMPOUND COMPOSITION (WT. %) tained only below about 40" (d >2.5 A.). I n this Hydrorange, 30 to 40 diffraction lines were observed for Samplea Carbon gen Boron Pyridine Waterb each compound. I n the range 2 9 > 40", the lines PB-15b 29.7 3.6 16.1 34.6 53.7 were much weaker and very diffuse. The diffrac- p B - 1 5 ~ 29.7 3.7 16.0 34.2 53.3 tion patterns obtained can all be described in terms PB-15d 28.9 3.6 16.1 35.5 52.8 of sets of orthorhombic lattice constants, listed in PB-15e 29.4 3.8 15.8 35.3 52.8 Table 11. Using these constants, the calculated .. .. 15.7 29.1 59.6 lattice spacings, d, agree with the observed values PB-17b Calculated to within 1%, agreement to 0.5% being obtained for most lines. The possibility that one or more CdIsN.3HBOs 28.5 3.8 15.4 37.6 51.3 of these crystals may have symmetryless thanorthoa The first four samples were freed of excess pyridine by drying to constant weight a t room temperature a t pressures rhombic is not completely excluded. If the compounds of boric acid with 2,3- and 2,6- ranging from 10 p to atmospheric. The fifth sample (from different batch) was thoroughly washed with toluene and lutidine, 2,4,6-collidine and quinoline are washed aair-dried. Karl Fischer determination: includes water with toluene, the densities are markedly increased produced by reaction of sample with methanol. (as might be expected, since the powders probably TABLE IV contain excess base) and the X-ray diffraction patCOMPOSITION OB SUBSTITUTED PYRIDINE-BORIC terns are altered very extensively. I n the other CHEMICAL ACID COMPOUNDS (TOLUENE WASHED) compounds, no changes occur in the diffraction BpOi ~ ~ 0 5 patterns on washing with toluene, nor are the denBase (moles/mole of base) (moles/mols of base) sities much altered. I n each case where the X-ray 2-Picoline 2.1 3.5 pattern is altered, one set of lattice constants suf- 3-Picoline 1.7 2.0 fices to explain the results, the changes being at- PPicoline 1.3 1.4 tributed solely to alterations of intensities of im- 2,3-Lutidine 2.8 4.6 portant lines. 2,4-Lutidine 2.4 3.1 TABLE I1 ORTHORHOMBIC LATTICECONSTANTS FOR COMPOUNDS OF BORICACID WITH SOMEPYRIDINE BASES" Base
a
(A.1
b
(A.)
c
(A.)
Exptl. density WmlJ
Pyridine 16.9 17.7 14.6 1.47* 2-Picoline 17.0 18.5 16.1 1.22** 3-Picoline 17.9 18.6 15.1 1.38* 4Picoline 17.2 18.2* 14.6 1.36 2,3-Lutidine 15.6 18.9 12.8 1.49* 2,4Lutidine 17.6 22.4 16.4 1.25b 2,6-Lutidine 19.4 21.9 18.0 1.47* 2,4,6-Collidine 17.6 18.6* 14.6 1.20b Quinoline 15.2 20.8 13.7 1.45* Isoquinoline 16.2 17.2 12.5 1.22' Piperidine 19.7* 25.5** 14.6 l.lOb Pyridine-c yanuric acid compound 16.0 21.7 17.5 All lattice constants 1 0 . 1 b., except those indicated by *, f0.2 8. and by **, 1 0 . 3 b. Density values, 1 0 . 0 1 g . / d . , except those indicated by *, =t0.02 Jd.,and by **, 1 0 . 0 3 g./ml. b These values determine1 only on toluene-washed samples.
....
2,bLutidine 12 33 2,4,6-Collidine 2.5 1.6 Quinoline 5.7 7.5 Isoquinoline 2.2 1.1 Piperidineb 2.4 1.4 a Karl Fischer method; corrected for Be03 content. Analyses corrected on assumption that piperidine is a strong base.
The most satisfying rationalization of the X-ray data is to interpret all of the compounds as being based ultimately on the layered structure of orthorhombic HBOz (111)4 which has been reported6 to be constructed of parallel sheets of B,Oe-* ions, bound togethzr in the plane by hydrogen bonds. The 17 to 19 A. spacing found in all the compounds but two (Table 11) is taken to be six times the interlayer spacing in HBOz (111) (3.12 A.). Each pyridine ring has a unique direction, allowing three different orientations relative to a parallel B803 ring, which, taken with the fourfold symmetry re(4) F. C. Kraaek, G. W. Morey and H. E. Merwin, Am. J . Sn'., [5l 868,143 (1938). (6) H. Taiaki, J . Sci. Hiroshima Uniu., AlO. 37, 55 (1940).
NOTES
122
quired by the HBOz structure accounts for the presence of six layers per unit cell in the compounds as opposed to two layers in the original acid. The structure is then made up of alternate sheets of HBOz and organic base. The electronic structure of the B306-3 ion is similar to that of the isoelectronic ion of cyanuric acid, C3N303-S,and the crystal structure of cyanuric acid6 is very similar to that of HBOz (111). Pyridine has also been found to react readily with cyanuric acid, yielding a product with an X-ray diffraction pattern very similar to that of the pyridine-boric acid compound. The chemical analyses may be rationalized by noting that the major deviations from metaborate composition are found where the bases have limited miscibility with water. There is thus insufficient solvent for all the water produced by reaction of the base with H3B03,leading to products with more water than expected for metaborates. In a test of this idea, the reaction of H3B03was studied with a limited amount of pyridine. Analysis of the product showed a molar ratio, base: Bz03:H20 of 1:3.5:7.9. Treatment of this product with additional pyridine produced a material of analysis very similar to those of the first four samples of Table 111. The function of toluene seems to be removal of small amounts of base from the crystal, the excess HBO2 being converted to H3B03 by atmospheric moisture. Because of the composition variations resulting from toluene treatment as well as from the limited solvent properties of some of the' bases, no clear-cut formulation can be given to most of the reaction products. It appears likely also that steric requirements of the larger organic molecules are incompatible with simple chemical formulations. This is believed to be the explanation of the apparent increase in relative amounts of B203and HzO as the base molecules increase in size. Acknowledgments.-Grateful acknowledgment is made of the assistance of G. E. Klein, who prepared the X-ray diffraction patterns, of W. A. Brooksbank, Jr., who performed the neutron-absorption boron analyses and of L. C. Henley, who carried out most of the other boron and base analyses.
Vol. 61
pared in a vacuum system, identified by chemical analysis, and its X-ray diffraction pattern was obtained.
THE TERNARY SYSTEM SODIUM OXIDE-WATER-METHANOL1
Experimental Sodium oxide, purchased from A. D. Mackay, Inc., was found to be 99.4% NazO despite the fact that some of the particles were gray. It was not as hygroscopic as sodium hydroxide. Baker and Adamson reagent grade absolute methyl alcohol was used. Fisher Certified Reagent sodium hydroxide was used after the pellets were pulverized in a dry atmosphere. Sodium methoxide was prepared by Dr. Edgar F. Westrum, University of Michigan, and was found to be 100.0% NaOCHa. No attempt was made to purify any of these materials. A series of 20-g. samples was prepared by weighing appropriate amounts of sodium oxide, methanol and distilled water into a 50-ml. round-bottom Pyrex flask. It was found necessary to add the sodium oxide to the liquid very slowly, with shaking, while the mixture was cooled in a room temperature-bath. The flask was closed with a rubber stopper and agitated with a wrist-action s F k e r for a t least Equilibration 16 hours in a bath maintained at 25 f 0.1 of several mixtures for longer periods up to 64 hours indicated that equilibrium was attained within 16 hours. The equilibrium mixture was filtered through a coarse frittedglass funnel with the aid of dry nitrogen gas pressure. The solid was partially dried by quickly pressing it between sheets of absorbent paper. Samples of this solid residue, still ,slightly wet with mother liquor, and the saturated liquid were transferred to 1-ml. glass-stoppered weighing bottles for analysis. Samples were titrated for sodium with 0.2 N hydrochloric acid td a brom cresol green end-point. Methanol was determined in duplicate by the method of Alexander, Bourne and Littlehale,* with certain modifications. Excess standard 0.1 N ceric ammonium nitrate containing 100 ml. of 15 N nitric acid per liter was added directly through the reflux condenser to the sample which was cooled in an ice-bath. The mixture was refluxed for ten minutes to oxidize the methanol to formic acid, then back titrated, while still hot, with standard 0.1 N ferrous ammonium sulfate containing 10 ml. of 36 N sulfuric acid per liter. Sodium Hydroxide Methanolate.-A 0.3847-g. sample. of sodium hydroxide was placed in a small bulb equipped with a ground joint. The bulb was attached to a vacuum system where it was directly connected to a mercury manometer and to a calibrated volume through a stopcock. Small portions of methanol were measured as a gas in the calibrated volume and then transferred to the sodium hydroxide bulb by condensation with a liquid nitrogen bath. After each addition of methanol the stopcock was closed, the bulb was warmed to 20' by means of a constant temperature waterbath, and the equilibrium pressure was recorded. For some ppints, as much as 24 hours was required to reach equilibrium. From the data, listed in Table I, it is evident that sodium hydroxide forms a monomethanolate with a dissociation pressure of 1 mm. at 20". The slight displacement of the break from the 50 mole % value was undoubtedly due to impurities (e.g., water) in the sodium hydroxide. At the pressure break the solid was removed from the tube. Anal. Calcd. for NaOHCHaOH: Na, 31.9; CHaOH, .44.5. Found: Na, 31.7; CHaOH, 43.9. The compound is hggroscopic, and melts with decomposition at approximately
BY C. F. BOYNTON, J. F. MASI, P. E. GALLAGHER AND R. E. WHAN
Further evidence for identifying this solid as the methanolate of sodium hydroxide rather than the hydrate of so-
(6) C. Wiebenga and N. F. Moerman, Nature, 141, 122 (1938); 2. KTiet., 99, 217 (1938).
Contribution from C4&3ry Chemical Co., Cullsry, P a . Received Auguat SO, lBb6
In the course of fundamental research on solutions of sodium borates in aqueous methanol, the phase diagram for the system sodium oxide-watermethanol became desirable. As the work progressed there were indications that the adduct NaOH.CH30H was one of the solids in equilibrium with saturated liquid. Since this compound has not been reported in the literature, it was pre(1) Presented at 129th American Chemical Society Meeting, Dallas, Texas, April 8, 1956.
.
~~
280'.
TABLE I DISSOCIATION PRESSURES OF SODIUM HYDROXIDE METHANOLATE AT
Mole % methanol
9.4 17.5 24.4 29.9 34.9
20'
Pressure, mm.
Mole % methanol
Pressure, mm.
0.3
39.1 43.1 46.8 49.6
1.2 0.9 1.0 23.3
0.7 1.1 1.4 1.0
(2) A. P. Alexander, P. G.Bourne and D.9. Littlehale, Anal. Chem., 27, 105 (1955).
