2026
WILLIAMA. BARBERAND CAROLL. SLOA?;
0-H band itself. (C-H interference varies with the different compounds). The actual centers are more likely to occur near the middle of each range. Figure 3 shows that the larger chemical shifts correspond to lower 0-H frequencies. Each of these respective trends is associated with stronger hydrogen bonding. A similar correlation has been found by Reeves, Allan and Strgimme for intramolecular bonds in phenols and naphthols. lo Figure 3 and the additional infrared data in Table I indicate that the 2-hydroxybenzophenones have the strongest hydrogen bonds. Double chelation of the carbonyl group in 2,2'-dihydroxybenzophenones appears to reduce the strength of each bond, although not markedly. Again, the relative independence of the n.m.r. and infrared parameters to temperature and concentration indicates that both hydroxyl groups in these compounds are chelated. According to Stuart-Briegleb atom models, coplanarity of the two aromatic rings with the carbonyl group of benzophenone is prevented by steric hindrance between the 6- and 6'-hydrogen atoms. The minimum angle between rings appears to be about 30'. The hydroxyl group and its phenyl ring, and the carbonyl group of 2-hydroxy(10) L. W. Reeves, E. A. Allan and K. 0. Strgmme, Can. J. Chem., 38, 1249 (1960).
Vol. 6.5
benzophenone can be coplanar. In a 2,2'-dihydroxybenzophenone, simultaneous planarity of both rings and their hydroxyl groups with the carbonyl group is impossible without distortion of bond angles. To line up with the carbonyl oxygen atom, each hydroxyl group must turn out of the plane of its phenyl ring. A 15O-offset of each ring from the carbonyl group would seem to be the required compromise, a t least for those derivatives in which both rings are identically substituted. It was noted that the separate hydroxyl proton resonances from compound 7 may arise because of unequal hydrogen-bond strengths. In this and other unsymmetrically substituted 2,2'-dihydroxybenzophenones, the phenyl ring whose hydroxyl group is more strongly chelated may be held more nearly coplanar with the carbonyl group than the other ring. A steric hindrance to planarity could partly account for the weaker chelation of each hydroxyl group in the 2,2'-dihydroxybenzophenones. Acknowledgments.-Helpful discussions were held with W. D. Phillips of our Central Research Department, and with H. Kobsa of the Pioneering Research Laboratory, Textile Fibers Department and R. Dessauer of Jackson Laboratory, Organic Chemicals Department, who also supplied the compounds for this study.
SOLUBILITY OF CALCIUM CARBIDE I N FUSED SALT SYSTEMS BY WILLIAMA. BARBERAND CAROLL. SLOAN Central Research Division, American Cyanmid Co., Stamford, Connecticut Received M a y 1.9, 1981
Calcium carbide, CaC2, has been found to be soluble in a number of pure alkali and alkaline earth salts and salt mixtures a t temperatures up to 1000'. The highest solubilities were observed with lithium salts. The variation of solubility with temperature has been determined in several of these solvents. Measured solubilities are compared with those predicted theoretically for the ideal case.
Introduction Informatmionon the solubility of CaC2 is exceedingly scarce. No material which is liquid a t or near room temperature is known to dissolve CaC2. It has been mentionedl incidental to some work on Li2C2 that CaCz is soluble in some hydride-containing melts, but no quantitative information has been presented. It is known that CaCz forms eutectics with Ca02and with CaCXz,3but, because these mixtures melt above 1000°, they have limited utility. We now wish to report the results of a study concerning the solubility of calcium carbide in fused alkali and alkaline earth salts and their mixtures below 1OOO". Experimental Apparatus.-For pre aring solutions a vertical, electrically heated furnace (Levi-Duty Electric Co.) was used which accommodates a cylindrical tube of 1.25 inches 0.d. Since Pyrex or Vycor glass containers were found to be attacked by some melts, especially those containing Li+, the experiments were performed using stainless steel tubes. Although stainless steel is not completely inert to the melt, (1) A. Guntz and F. Benoit, Compt. rend., 176, 970 (1923). (2) G. Fluein and C. Aall, ibid.. 801, 451 (3) H. Franok and H. Heimann, 2. EZelFtrochsm., 88, 469 (1927).
(1935).
no significant amounts of corrosion products appeared in the filtered mixtures (determined by ultraviolet emission spectroscopic analysis: Fe < 1 p.p.m.; Cr, Ni, Mn not detectable). The apparatus used is a modification of that deecribed by Solomons, et u E . , ~ and is pictured in Fig. 1 . The melt was supported either on a coarse porosity Micrometallic stainlesa steel filter or a solid stainless steel disc perforated with 1 / 3 2 1 1 holes. Since the remainder of the apparatus was of Pyrex glass, the joints of the furnace tube were wrapped with water-cooled copper coils to protect the glass connections from thermally caused stress. Temperatures were measured with a Chromel-Alumel thermocouple inserted in a stainless steel thermocouple well and read on a Leeds & Northrup Type K potentiometer. Materials.-Argon gas (Linde High Purity grade) was further dried bv Dassine it through activated alumina (medried a t 400' for keverar hours). The calcium carbide used was ordinary commercial grade material (about 85% pure). The major impurity, CaO, was found to be insoluble in most of the melts studied. The carbide was broken into approximately 1/s to 1/4 inch lumps a t the time of use, and finer material was discarded. Reagent grade salts were used without further urification. LiCl and CaCL were placed in graphite crucibfes and premelted in a Lindberg crucible furnace under a flow of argon gas. This procedure served to remove any water picked up in handling and provided blocks of salt which were easier to keep dry. Any additional water present in the salts was
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(4) C. Sglomons, et ol., J. Phys. Chew., 62, 248 (1958).
~.
Kov., 1961
S O L U B I L I T Y OF C.4LCIUM C h R B I D E I N
removed during the experiment either by vaporization or by reaction with excess CaCz. Such reaction produced CaO which was insoluble in the melt and acetylene which was pyrolyzed or swept away. The more satisfactory procedure for dehydrating molten chlorides in an atmosphere of HC15 could not be used in our stainless steel apparatus. Procedure.-In a typical experiment, the thermocouple well was inserted, and lumps of solid calcium carbide were added to the tube. (Powdered carbide could not be used since surface tension caused it to float and contact was poor.) The solid solvent salt was added next. If the molten salt was expected to have a density greater than the carbide, a tightly fitting stainless steel screen was placed above the carbide and below the salt layer to keep the carbide submerged when the salt was molten. After the glass equipment was assembled, the system was flushed thoroughly with a stream of dry argon passing upward through the tube. When the temperature was raised to the desired value, the gas flow, besides providing an inert atmosphere, served to keep the melt above the disc, to agitate the carbide particles in the melt, and to reduce by its stirring action any temperature gradients caused by uneven furnace heating. The temperature coould be held for extended periods a t the desired value =t
