1400
DONALD RbY MARTIN
SUMMARY
Catalytic vapor-phase oxidation of aniline by air over a thallic oxide catalyst has been studied, and optimum conditions for the production of aeobeneene and phenazine have been determined. Two types of catalytic reactor are described. REFEREKCES
GRILLS: J. Phys. Chem. 43, 805 (1939) (2) BROWN, BROTHERS, A K I ~ETZEL:J. Phys. Chem. 32, 457 (1928). (3) HENKEANI) BROWN:J. Phys. Chem. 26, 321 (1922). (4) HENKEANLI BROWS:J. Phys. Chem. 26, 631 (1922). (1) BROWN, RORIASD, JOHSSTON, .4m
COuRDIXATION COMPOUNDS O F BOROS TRICHLORIDE. V RELATIONSHIP OF DIPOLEMOMENT OF CHLORIDES TO COMPOGXD FORMATIOK~ DONALD R A T bIARTIX Solies Chemical Laboratory, Lhirersily of Illinois, Crbana, Illinwis
Received 'Yocember 26, 1946
In thermal analysis studies conducted in this Laboratory of systems composed of alkyl chlorides and boron trichloride, it was found that there seemed to be a correlation between the dipole moments of the alkyl chlorides and the ability of the alkyl chlorides to form compounds with boron trichlqride. Further, it was observed that the stability of the resulting compounds increases as the dipole moment of the alkyl chloride increases. On the assumption that the C-CI bond dipole is proportional t o the dipole moment of the molecule, it appears that t,he donating ability of the chlorine atom of the alkyl chloride to the boron atom of boron trichloride is related to the ionic character of the C-CI bond. For evidence to substantiate this hypothesis a survey of the literature was made of the molecular compounds of boron trichloride in which the donor atom is thought to be chlorine. Stock and Preiss (14) found that chlorine, with practically no dipole moment, Graff and boron trichloride do not react at room temperature nor at -8OOC. ( 5 ) made a thermal analysis of the system chlorine-boron trichloride and found only a eutectic point at, 65.5 weight per cent boron trichloride and - 135.4%. He obtained a similar result in his study of the system hydrogen chloride-boron trichloride (6). Hydrogen chloride in the vapor phase has a dipole moment of 1.03 D (18). The eut,ectic point in this system occurs at 44 weight per cent boron trichloride and - 134.5"C. This particular system is of interest, inasmuch as there is no evidence for the esistence of chloroboric acid, even at these low temperatures. On the other hand, fluoboric acid and the fluoborates are well known. This fact may be 1
Presented before the Division of Physical and Inorganic Chemistry at the 110th Meeting
of the American Chemical Society, Chicago, Illinois, September 12, 1016.
COORDIS.4TIOiX
COYPObTDS OF BOROlC TRICHLORIDE. 1 '
1401
explained on the basis of the hypothesis being presented. The ionic character of the H-F bond is 43 per cent (7), whereas it is only about 17 per cent for the H-C1 bond (13). Therefore, if the ionic character of the halogen bond t o the remainder of the molecule is responsible for the donor properties exhibited by the halogen atom, it follows that the fluorine atom in hydrogen fluoride should be a much better donor than the chlorine atom in hydrogen chloride. A second factor to be considered is the relative positive nature of the boron atom in boron trifluoride as compared with the boron atom in boron trichloride. Inasmuch as the fluorine atom is more electronegative than the chlorine atom, it follows that the boron atom in boron trifluoride is more positive than the boron atom in boron trichloride. Therefore the boron atom in boron trifluoride should have a greater affinity for the donor halogen atom. However, this second factor is not as important as the first, as is shonn by the results of Booth and Martin (3) in a study of the system hydrogen chloride-boron trifluoride. In this system there is no evidence for compound formation. The eutectic point lies at 72.3 mole per cent boron trifluoride and - 134.2"C. Thus it is seen that the chlorine atom of hydrogen chloride does not coordinate with the boron atom of boron trifluoride. Wiberg and Sutterlin ( l i ) observed that hydrogen fluoride fluorinates boron trichloride, forming hydrogen chloride and boron trifluoride. It has been observed also that fluorides in general coordinate more readily with boron trifluoride than do chlorides (2). Thus it is observed that with molecules such as chlorine and hydrogen chloride, in Tvhich the chlorine bond is predominantly covalent, no tendency for compound formation Jvith boron trichloride is displayed. The studies v i t h the alkyl chlorides and boron trichloride mentioned above \\-ere undertaken by Martin and Hicks (IO) to determine the effect on the donor property of the chlorine atom when it is attached to a methyl group instead of a hydrogen atom. I t was thought that a coordination compound might be formed in this case, inasmuch as the dipole moment of methyl chloride is larger than that of hydrogen chloride. The dipole moment for methyl chloride in the liquid state is 1.84 D (1). However, the thermal analysis indicated only a eutectic point a t 51.8 mole per cent boron trichloride and -125.1"C. Inasmuch as the dipole moment of ethyl chloride in the liquid state is 2.01 D (I), Martin and Hicks (10) studied the system ethyl chloride-boron trichloride by thermal analysis. A very flat maximum occurs at 07 mole per cent boron trichloride, corresponding to a compound having a composition most simply expressed at CgHbC1: (BC18)g. Evidently the compound is highly dissociated above its melting point, and therefore the donating ability of the chlorine atom is not very pronounced. Martin and Humphrey (11) extended this study t o the propyl chlorides. The dipole moments in the liquid state of n-propyl and isopropyl chlorides are calculated t o be 1.97 and 2.02, respectively.* A maximum in the phase rule diagram
* Audsley and Goss ( l ) ,in referring to the research of Stuart (Physik. Z.31, 80-3 (1930)), state that the dipole moment of liquid n-propyl chloride is less than that of liquid ethyl chloride and that as one ascends the homologous series the dipole moment decreases 0.07 D per additional CH? group. Inasmuch as the moments for ethyl chloride and n-butyl
1402
DONALD RAY MARTIS
at 25 mole per cent boron trichloride indicates the presence of a compound most simply expressed as (~-C~H,CI)~:BCIZ. This maximum is much sharper than in the case of ethyl chloride, indicating a more stable compound, and as predicted from dipole-moment data, the donor properties of the chlorine atom are somewhat more pronounced. Although the differenceis quite small, the melting point of the isopropyl compound is higher than that of the ethyl compound, the values being -105.2" and -115.8"C., respect,ively ( 1 0 , l l ) . In the study,of n-propyl chloride, only a eutectic point was found at 41.8 mole per cent boron trichloride and -141.8OC. Inasmuch as the dipole moment of n-propyl chloride is less than that of ethyl chloride, compound formation would not be expected. Admittedly the differences betxeen the dipole moments for the alkyl chlorides that do coordinate with boron trichloride and those that do not are very small. However, the above studies may be summarized by stating that it appears that the dipole moment of an alkyl chloride must be at least 2.00 D if the alkyl chloride is t o coordinate with boron trichloride. There is additional evidence to be found among other compounds of boron trichloride with molecules containing chlorine in which the chlorine bond is more ionic in character and t,he resulting coordination compound more stable. Triphenylchloromcthane reacts ivith boron trichloride a t room temperature or a t 0°C. t o form yelloi~crystals, which upon analysis mere found t o have n composition corresponding with the formula (C6H6)&C1:BC1, (lG). Upon being heated t,o 200°C. these crystals turn brown but do not melt. They distil with decomposition at 80°C. iri u wcuum. Such physical properties indicate a much more stable compound than any of those described above. Tarible (15) has pxparrd the compound PC&:RCl3 by allowing chlorine to displace the bromine from PRrr:BBr3 at room temperature, and the bromine from PBr6:13Brg in t,he cold. The existence of this compound supports t'lie hypothesis that an ionic character to the chlorine bond enhances the donor property of t h c chlorine atom, inasmuch as solid PCI, is considered t o be comprised of the ions PCllf and Pcl6- (4). and ,Tessop (9) consider SClc to be composed of the ions s&+ and CI-. This compound reacts with boron trichloride to form the molecular compound SClr:BC13. Moissan (12) synthesized this compound in two ways. He allowed boron trisulfide to react with chlorine, and he allowed chlorine to pass into a solution containing sulfur monochloride and boron trichloride. The molecular compound has a melting point of -23°C. The chlorides of iron and manganese have been reported t o form molecular compounds with boron trichloride. Certainly these metallic chlorides have a chloride are listed as 2.01 arid 1.90 D, respectively, i t is estimated t h a t a fair value for n-propyl chloridc would be 1.97 D. In the vapor state, Groves and Sugden (,J. Chem. SOC. 1937, 158-62) have reported isopropyl chloride to have a dipole moment 0.05 D higher than that of n-propyl cliloride. Thcrcfore, in the liquid state, isopropyl rhloride probab!y has a dipole moment around 2.02 D.
COORDINATION
COMPOUKDS OF BORON TRICHLORIDE.
v
1403
higher percentage of ionic character in the metal-to-chlorine bond than is exhibited in any of the chlorides of the non-metals previously discussed. Hoffman (8) allowed chlorine gas t o pass over the borides of iron and manganese which were heated t o glowing. Under these conditions, colored solids were obtained which upon analysis were found to have compositions corresponding to (FeCl&: BC13, (FeC1&:BC13, and (MnC12)2:BCI3. SL’MhLIRY
Experimental evidence seems to support the hypothesis that the ability of a chlorine atom in a compound t o act as a donor to the boron atom of boron trichloride is related to the amount of ionic character in the bond attaching the chlorine atom to its molecule. .Is seen in table 1, the dipole moment seems t o be a good criterion by which to predict if a coordination compound with boron trichloride will be formed with the alkyl chlorides (i.e,, an alkyl chloride having TABLE 1 COMPOUND
DIPOLE MOMENT
COYPOCND WITS
BCla
D
c1*.. . . . . . . . . . . . . . . HCI.. . . . . . . . . . . . . . . CHIC]. . . . . . . . . . . . . CzHjCI. . . . . . . . . . . . . n-CaH?Cl.. . . . . . . . . i-C3HiC1. . . . . . . . (CsHs)3CC1.. ....... PClS (PCl:,PCl;) SClr (scl;,cl-),. . . FeCla. . . . . . . . . . . . . . FeCL. . . . . . . . . . . . . . hlnCl2. . . . . . . . . . . . .
0 1.03 1.84 2.01 1.07 2.02
MELTING POINT OF COMPOUND
“C.
Xone None None CzH5Cl: (BCI3)z Sone (i-C3H,Cl) 3 : BC13 (CsH6)zCCl:BC13 PCls:BCl3 SCli:BC13 IFeC12)d:BCI.
-115.8 -105.2 Above 200
- 23
a dipole moment of 2.00 D will coordinate, while one having a moment less than 2.00 D will not coordinate). Boron trichloride also forms molecular compounds with sulfur tetrachloride and phosphorus pentachloride, which are considered t o form ions, and with the metallic chlorides ferric chloride, ferrous chloride, and manganous chloride. REFERESCES (1) AUDSLEY,A . , AND Goss, F. R.: J. Chem. SOC.1942, 497-500, 35g66. (2) BOOTH,H . S.,AKD ~ I A R T I SD. , R.: “The Coordinating Power of Boron Trifluoride”, Paper S o . 16, 6th Annual Symposium of the Division of Physical and Inorganic Chemistry, Columbus, Ohio, December 31, 1941. (3) BOOTH,H . S., A N D MARTIN,D. R . : J . Am. Chem. SOC.64, 219g2205 (1941). (4) CLARK,D . , POWELL, H . bl., A K D WELLS,A. F.: J. Chem. SOC. 1942, 642-5. ( 5 ) GRAFF,W . : Compt. rend. 196, 139&2 (1933). (6) GRAFF,W . : Compt. rend. 197, 754-5 (1933). (7) I I A N S . 4 Y , N.B., h S D SYYTH, c. P . : J. Am. Chem. SOC. 68, 171-3 (1946).
1404
EVANS, HORN, SHAPIRO LVD WAGNER
(8) HOFFMAS, J.:Z. angew. Chem. 21, 2515-6 (1905); Z . anorg. allgem. Chem. 86, 361-99 (1910). (9) LOWRY,T. M., AND JESSOP, G . : J. Chern. SOC.1931, 323-0. (10) MARTIN,D . R., AND HICKS,W. B . : J . Phys. Chern. 60, 422-7 (1946). (11) MARTIN,D. R., A N D HUMPHREY, A . s.: J. Phys. Colloid Chem. 61, 425-30 (1947). (12) MOISSAN,€1.: Compt. rend. 116, 103-8 (1892). (13) PAULING,L . : T h e Nature of the Chemical Bond and the Slructure of Molecules and Crystals, p. 46. Cornell University Press, Ithaca, New York (1938). (14) STOCK,A , , AND PREISS,0 . : Ber. 47, 3109-13 (1914). (15) TARIBLE, J . : Compt. rend. 118, 1521-4 (1893). (16) WIBERG,E . , AND HEUBACM, U.: Z. anorg. allgem. Chern. 222, 98-106 (1935). (17) WIBERG,E . , AND SUTTERLIS, W . : Z. anorg. allgem. Chem. 202, 3 7 4 8 (1931). (18) ZAHN,C. T.: Phys. Rev. 69, 400-17 (1924).
T H E CHEMICAL EROSION OF STEEL BY HOT GASES UNDER PRESSURE' RICHARD C. EVANS? F. HUBBARD HORN,3 ZALMAN M . SHAPIR0,4 AND RICHARD L. WAGNER
Department of Chemistry, T h e Johns Hopkins University, Baltzmore, Maryland and Ballzstzc Research Laboratories, Aberdeen Proving Ground, Aberdeen, Maryland Received J u n e 11, 1947
INTRODUCTION The destructive effect on steel of hot, high-pressure gases such as are ordinarily found as products of combustion is a problem difficult t o solve because of the complexity of those gases. This paper describes an attempt to simplify the problem by studying the two gases largely constituting the products of combustion, carbon monoxide and carbon dioxide, and then adding to them one by one gases often found as traces, such as hydrogen sulfide, sulfur dioxide, ammonia, nitrous oxide, and hydrogen. Quite obviously, great care must be exercised t o prevent the melting of the surface of the sample from becoming appreciable and masking the chemical effects. The first part' of the paper will therefore survey the conditions present when the temperature is higher and erosion is principally a melting phenomenon and will attempt to set the limits t o such a state; the second part will consider the peculiar chemical effects present when the temperature is lower and melting is negligible. 1 The results reported here are largely from studies begun under N D R C contract OEMsr463 and continued under contract W-36-034-ORD-4126 between the Army Service Forces and T h e Johns Hopkins University. * Present address: Ballistic Research Laboratories, Aberdeen Proving Ground, Maryland. a Present address: Research Laboratory, General Electric Company, Sohenectady, New York.
