KOTES
3085
on the gold anode confirmed the presence of (hydrated) gold oxide." When the oxidized hydrophilic gold surface was heated to 250' in clean air in the apparatus, the oxide disproportionated to free gold and oxygen, as evidenced by the disappearance of the oxide color, and the surface again became strongly hydrophobic. This experiment was repeated using different methods of surface preparation, always with the same result that the oxidized surface was hydrophilic and the oxide-free surface hydrophobic. When the oxidized gold was kept in clean air in the apparatus a t room temperature, it also became strongly hydrophobic after 5-10 hr. , with an attendant disappearance of the oxide color. All of the above experimental evidence leads to the conclusion that it is the oxide on a gold surface which makes it hydrophilic It seems likely that there would be more interaction o f water (and therefore more wetting) with a metal oxide than with a free metal surface because of dipole-dipole effects and hydrogen bonding of water with the oxide, these effects not being present on a free metal surface. It is also very likely that other metals are similar to gold in their wettability by water, the oxide-free metal surfaces being hydrophobic, with the formation of oxide causing the surface to become hydrophilic. These observations have been confirmed by some recent calculations of Fowkes,12who has shown that water should not spread on oxide-free nieta,l surfaces because of the large relative contributions of metallic bond forces and London dispersion forces to the total surface energy, these forces not contributing significantly to any inter-. action with water. (11) L. Young, "Anodic Oxide Films," A4cademicPress, New York, N. Y . , 1961. (12) F. M. Fowkes, 68th ASTM Meeting, Atlantic City, N. J., June, 1963.
Reactions of Large Cycloalkane Rings i n Hydrocracking
by R. J. White, Clark ,J. Egan, and G. E. Langlois California Research Corporation, Richmond, California (Received J u n e 17, 1964)
It was shown previously1 that alkylcyclohexanes having four or more carbons in alkyl side chains undergo the paring reaction. In this selective cracking reaction ,the cycloalkane character of the reactant is preserved
NUMBER OF CARBONS IN PRODUCT MOLECULE Figure 1. Product distribution from hydrocracking: A, n-hexadecane, 43.7% cracking a t 290"; B, hexamethylcyclohexane, 87.5% cracking a t 234"; C, cyclododeca,ne, 91.0% cracking a t 296"; D, cyclopentadecane, 94.9y0 cracking a t 291 '.
(both alkylcyclopentanes and alkylcyclohexanes of lower niolecular weight are formed), and the predominant alkane product from cracking is isobutane. In this paper the behavior of cyclododecane and cyclopentadecane under similar cracking conditions is reported. These large ring hydrocarbons having no side chain conceivably could either undergo the paring reaction after contraction of the ring or could undergo (1) C. J. Egan, G. E. Langlois, and R. J. White, J. Am. Chem. Soc., 84, 1204 (1962).
V o l u m e 68, N u m b e r 10 October, 1984
NOTES
3086
ring opening and crack as alkanes, which give essentially no cyclic products. Figure 1 shows the distribution by carbon number of the products from cracking an alkane, n-hexadecane,z and three cycloalkanes of increasing ring size, hexamethylcyclohexane, cyclododecane, and cyclopentadecane. Table I shows the reaction conditions and product composition. The product distribution from cyclododecane and cyclopentadecane, as determined from a combination of gas chromatographic and mass spectrometric analyses, is unusual in that: (1) the moles of cycloalkanes in the product from cracking equal the moles of cycloalkane that cracked-thus, no rings are lost in the cracking process; ( 2 ) the predominant cyclic products are alkylcyclopentanes and alkylcyclohexanes having seven or eight carbons; (3) the predominant alkane products are isobutane and isopentane; (4) no evidence for cycloheptanes through cycloundecanes is found in the mass spectrometric analysis of the product from cracking; (5) essentially no methane, no ethane, and only a small amount of propane are produced in cracking. This product distribution is quite similar to that obtained from the paring reaction of hexamethylcyclohexane (Fig. 1B). This suggests that cyclododecane and cyclopentadecane undergo a rapid ring contraction on the surface of the catalyst to form alkylcyclopentanes and alkylcyclohexanes. Some of these cycloalkanes are desorbed before they crack and appear as isomers as shown in Table I. The remaining isomers Table I: Reaction Conditions and Product Composition
________Reactant-------
Temp., “C. Pressure, a t m . Residence time, sec.’ First-order rate constant (cracking only), 8ec. -1 Conversion, total 5% Conversion, cracking % Product (moles/100 mole8 of reactant) CI-CS alkanes Ca-G isoalkanes Ca-C? unbranched alkanes Ca-Cla alkanes i-C16 alkanes CS-CII cycloalkanes C U cycloalkanes C I cycloalkanes ~ Reactant
nHexadecane
Hexamethylcyclohexane
Cyclododecane
Cyclopentadecane
290 82 7 6
2 34 82 146
296 82 16 6
291 82 15.5
0 088 51 4 48 7
0 125 100 87 5
The apparatus, procedure, and methods of analysis uscd have been discussed previously.’ In the present experiments, the catalyst was nickel sulfide (5.37& Ni) on commercial silica-alumina, the pressure was 82 atni., and the molal ratio of hydrogen to reactant was -10. Nost of the experiments were performed in duplicate or triplicate with reproducibility within 10%. Chemicals. n-Hexadecane was obtained from Humphrey-Wilkinson (99% pure). Only one peak was observed in gas chromatographic analysis. The cyclododecane contained no impurities detectable by gas chromatographic analysis. The boiling ~ point was 160”at 100 mm; n z 01.4504. Cyclopentadecane was obtained by reduction of cyclopentadecanone (Aldrich) 9S.6yo pure by gas chromatographic analysis. The melting point was 62.8-63.4 ”. Acknowledgments. The authors gratefully acknowledge the contributions of Mr, C . F. Spencer in the mass spectrometric analysis of the products and of kIr. J. Abell for assistance in obtaining the cyclododecane and cyclopentadecane.
0.192 98.5 94.9
(2) Data from R. F. Sullivan of this labolators. (3) D. J. Cram and G. S. Hammond, “Organic Chemistry,” 2nd Ed.: McGraw-Hi11 Book Co., New York, N Y , 1964, p. 161.
7 1 67 3 8 9
8 4 86 5 9 9 11 2
Diffusion Potential in Molten SaltaSystems
97 7
1.7 91.5 1.4
.., ...
82 1 12.5
96 4 6 Zb
...
2 6
...
...
3 6b 1 6
a Apparent time of hydrocarbon in volume occupied by catalyst; calculated assuming no conversion and perfect gas Mainly cyclopentane and law for hydrogen and vapor. cyclohexane rings.
The Journal of Phyaical Chemiatrv
Experimental
0.164 97.4 91.0
12.1 89.2 13.1 26.2 2.7
48.6
undergo selective cracking a t a slower rate. The mechanism of this cracking reaction has been described previously. The behavior of the cyclopentadecane is of interest because the ring strain present in medium-size rings containing 8-14 carbons has largely disappeared in rings containing 15 or more carbons (“Rings containing 15 or more carbons are folded in nearly random stacks and resemble open-chain compounds3”). It is concluded that as the ring size is increased, cycloalkanes containing up to 15 ring carbons still behave as cycloalkanes rather than as unbranched alkanes in hydrocracking.
by I. G. Murgulescu and D. I. hlarchidan Institute of Physical Chemistry, Bucharest 9,R o m a n i a (Received J u n e 1 , 1964)
In our previous worksl-a we have shown that the diffusion potential is nil in the concentration cells of the type
