IQUID ACETYLENE A Reaction System f o r Safe Operation under Pressure R . J . T E D E S C H I , G . S. C L A R K , J R . , G . L . M O O R E , A L B E R T H A L F O N , A N D JOSEPH I M P R O T A Central Research Laboratories, Air Reduction Co., Inc., Murray Hill, K.J . 07971
A reaction system for safe liquefaction of acetylene and for carrying out a variety of experiments using liquid acetylene i s capable of operation from -60" C. up to and above the critical temperature (35" C.) of acetylene and at pressures as high as 4000 p.s.i.g. Two reactors were used: a pressure vessel containing two glass walls to permit visual inspection of liquid acetylene under experimental conditions, and a smallcapacity (125-cc.), double-walled, stirred autoclave. This reaction system was safely used for 6 months. Interactions of liquid acetylene with various donor and nonpolar compounds (ammonia, methylamines, Nmethylpyrrolidinone, dimethyl ether, diethyl ether, diisopropyl ether, hexane, water, mineral oil), and formation of complexes of acetylene with alkali metal (sodium, potassium, lithium) hydroxides were studied using this reaction system. HE manufacture and use of liquid acetylene have their Torigins in the birth of the acetylene industry a t the turn of the century (Clancy, 1952). Subsequently, a series of fires and explosions both here and abroad caused restrictive legislature to be passed, and today liquid acetylene is legally considered a n explosive above 9 p.s.i.g. and can no longer be shipped commercially (Miller, 1965). Recent studies (Mayes and Yallop, 1965) and earlier investigations (Berthelot and L'eille. 1896 ; Crafts, 1896 ; Miller? 1965) have shown that although the liquefied gas can be detonated (Miller, 1965) by ignition of the vapor phase, even in the presence ,of diluents, it is still rather insensitive to mechanical shock (Berthelot and Veille: 1896), heat (Crafts, 1896), and boiling and condensation (Miller, 1965). Additional work (Conta, 1954, 1956; Meade) 1963) a t these laboratories Lvith both liquid and supercritical acetylene, in which the effects of heat, shock, and pressurization changes \sere studied, confirmed the relative stability of liquid acetylene to mechanical effects. S o ignition of acetylene was noted a t a pressurization rate of 350,000 p.s.i. per second to a final pressure of 20,000 p.s.i. Generally, compounds which \vi11 Xvithstand pressurization rates of 30.000 p.s.i. per second are considered safe against accidental ignition, shock, and compression effects for use in rocket engines. T h e object of the present work \vas to develop a reaction system which could handle liquid acetylene safely in contact with its vapor up to its critical temperature (35" C . ) >and to study the interaction of the liquid with a variety of additives. Since the handling and hazards of acetylene under pressure have been well documented (Beller, 1958; Miller, 1965), the devising of a versatile reaction system presented no major problem. T h e reaction system was designed to provide maximum protection to personnel against accidental detonation via the use of a 1-inch steel cubicle, with a blast mat ceiling, external controls, and small sacrificial reactors. All operations were carried out in the absence of air (under nitrogen) and strong oxidizing agents. A convenient feature of this reaction system was the ability to view clearly initial interactions of liquid acetylene with various additives. T h e system \vas also versatile enough so that other hazardous substances could be handled under pressure. At least two reactions could be carried out in a given day. Liquid acetylene \vas handled in this system safely for over 6 months (approximately 2400 man-hours of work).
Main Components of Reactor System
The complete reactor system and some of its component parts are described in Figure 1.
Cubicle. T h e cubicle or barricade (Figure 2) is made of 1-inch armor plate steel equipped with a steel door which cannot be blown open. An inner wall of 1-inch plywood is located about 4 inches from the steel wall? and this space is filled with vermiculite to absorb shock waves from a possible detonation. T h e internal and external dimensions of the cubicle are 84 X 71 X 96 and 96 X 80 X 96 inches, respectively. The cubicle walls are rated to withstand an explosive force many times in excess of that possible from 50 cc. or less of liquid acetylene. T h e Plexiglas ivindows ( 2 3 / 4 X 12 inches) in the cubicle \valls consist of two rectangular, 4-inch-thick blocks of Plexiglas Lvith a softwood (pine) spacer or gasket in betlveen. A steel box frame (17l/2 X 4l/2 X 4l/2 inches) bolted through the steel walls holds the Plexiglas in place (Figures 2 to 4). The Plexiglas ports are capable of protecting personnel against the detonation of 1 pound of T N T placed against the inner Plexiglas. Under these extreme conditions only the inner block is cracked. A steel cable (1-inch 0.d.) blast mat is placed on top of the cubicle and bolted to steel girders. T h e mat is designed to allow compressed gases through it? but to contain small fragments of shrapnel. .A standard blower is utilized to ventilate the cubicle. Reactors. Two types of reactors (Figures 2 and 5) were employed : a grooved, double-walled, 125-m1., heat transfer type (Konvitch) autoclave (Autoclave Engineers, Erie: Pa.), and a pressure vessel (35-ml.) equipped lvith sight glass walls, cooled, and heated in a sec-butyl alcohol bath. The sight glass reactor shown in Figure 5 is a stainless steel, Strahman high pressure vessel equipped with glass sides and tested to 2000 p.s.i. Both reactors are equipped ivith blo\vout disks rated at 2250 p.s.i. and are attached to a 1-inch bloivout line free of any sharp bends. Reactor Control Panels. The outer panel board (Figure 3) with additional controls located on the door side of the cubicle (Figure 6) comprises the essential parts of this system. Inner Panel Board. The inner cubicle wall supports the following equipment (Figure 4) : PRESSUREGAGES. Acetylene buret, G-2 (600 p.s.i.g.). Accumulator, G-4 (1000 p.s.i.g.). Reactor, G-1 (1000 p.s.i.g.). VOLUMETRIC FEEDBURETS, M-3, M-4 (10-ml. capacity). ACETYLESE BURET,M-7 (1-liter volume, packed with l:4inch stainless steel Raschig rings). Accumulator and Accumulator Oil Reservoir System (Figure 5 ) . T h e primary purpose of this equipment is to provide acetylene a t higher pressures than is available from acetylene cylinders which average 180 to 250 p.s.i.g. A VOL. 7
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VENTS TO OUTSIDE
NITROGEN
ACETYLENE ACCUMULATOR A
ACETYLENE
v-22 ACETYLENE BURET
I I HEAT EXCHANGER
V-32
SIGHTGLASS REACTOR
I
M-7
BLOW-OUT DISC
6 R-2 I
HEAT I EXCHANGER I
v
_i
THERMOCOUPLE LEAD
V-14
FROM CYLINDER
Figure 1 .
Flow diagram of liquid acetylene system
Valves V-1. N2 to inner panel V-2. NPto exterior burets V-3, V-4. Vents for exterior burets V-5, V-6. N? to interior burets V-7, V-8. Vents for interior burets V-9, V-1 0. Liquid fill from exterior to interior burets V-1 1, V-1 2. Interior burets to reactors V-13, V-14. For metering from interior burets to reactors V-15. T-valve for filling exterior burets from cylinder V-16. N? and acetylene introduction to manifold V-17. Manifold and manifold gage vent V-18. Outer-inner panel isolation V-19. Vocuum system valve V-20. Pump control and gage V-21. Acetylene accumulator vent V-22. Acetylene, NP to accumulator V-23. Accumulator to acetylene buret V-24. Acetylene buret to autoclave V-25. Manifold to autoclave V-26. Autoclave, manifold vent V-27. O i l reservoir to accumulator V-28. O i l pressure bypass with gage V-30. Nz to reservoir
Sprague diaphragm oil pump and air compressor are used to compress acetylene in the accumulator by pumping oil from the accumulator oil reservoir into the accumulator until the desired pressure is obtained. T h e accumulator ( M - 8 , Figure 2) is a standard 2.5-gallon cylinder (Parker Hydraulics Division, Parker Hannifin, Cleveland, Ohio), which was filled with l/c-inch Raschig rings, followed by addition of a small volume of Nujol prior to acetylene addition. .4 low nitrogen pressure is always maintained in the accumulator oil reservoir to avoid accidental introduction of air through the oil system into the accumulator. Cooling-Heating System. This equipment provides operating temperatures from -60" to +50° C. for use in liquefy304
I & E C PROCESS D E S I G N A N D DEVELOPMENT
V-3 1. Compressed air inlet V-32. Acetylene buret to sight glass reactor V-33. Manifold to sight glass reactor V-34. Sight glass reactor vent Gages and regulators G-1. Autoclave gage G-2, G-3. Acetylene buret gages G-4. Accumulator gage G-5. Sight glass reactor gage G-6. Manifold gage G-7. Gage for exterior buret M-5 G-8. Gage for exterior buret M - 6 G-9. Nz pressure regulator G-1 0. Na regulator for oil reservoir Reactors R-1. Sight glass reactor R-2. Autoclave Miscellaneous M-3, M-4. Interior burets M-5, M-6. Exterior burets M-7. Acetylene buret M-8. Accumulator M-10. Accumulator oil pump M-1 1. Accumulator oil reservoir
ing and reacting acetylene a t various temperatures as well as providing a heat exchange system for controlling reactions (Figure 7). The system is composed of an insulated cold tank which utilizes dry ice and sec-butyl alcohol as refrigerants and a hot tank containing water, which is heated electrically, A gear pump is used to circulate methanol through copper lines insulated with Armaflex tubing. Temperature control is maintained in the system by mixing hot and cold flows a t a T connection and also by controlling the rate of either hot or cold flow to each reactor. A gravity-feed, return-flow methanol reservoir bottle maintains normal flow of methanol and a bypass a t the methanol pump is used in starting and stopping the circulation of methanol.
V-31
3 t
TO ACCUMULATOR
v-29
5. Accumulator oil system
Figure V-20. V-32.
O i l reservoir drain Acetylene buret to sight gloss reactor valve M-30. O i l level indicator
v-38
Figure 2. v-37. V-38. M-1. M-9. M-12. M-14. M-15. M-1 6. M-17. M-1 8. M-19. M-20. M-21. M-22. M-23. M-24.
Top view of cubicle
Cold flow control valves Hot flow control valves 1 -inch steel plate walls Oil line from reservoir to accumulator Acetylene line from accumulator to acetylene buret Heating-cooling bath for sight gloss reactor Mechanism for agitating sight glass reactor Multiple temperature indicators Outer (front) main panel Inner front panel Explosion-proof Plexiglas viewing ports Cold tank for cooling reactors Air exhaust duct Hot tank for heating reactors Pump for circulating heat exchange fluid (methanol) Vent lines
ci;\
.32
Figure 6.
I
~
1
\b '-12\V-9
V-13
Figure 3.
Sight glass reactor and heating-cooling tank
M-2. M-13. M-25. M-26. M-27. M-28. M-29. M-31. M-32.
I
\v-lO\V-li
M-13
Thermocouple lead Acetylene inlet line Liquid feed and vent line Heat exchange fluid outlet Heat exchange fluid inlet Copper line for heat exchange fluid Cover for heating-cooling both Sight glass Plexiglas enclosure
i 1
v-14
RETURN LINE THERMOCOUPLE WELL
Outer front (main) panel board
I
?- 1 " 3 5 T
I ?
VENT
I ~
4
+/
LINES^
INLET LINE
I
-1
I
I SIGH RE
AUTOCLAVE
,,
TO SIGHT GLASS REACTOR
RETURN FROM SIGHT GLASS REACTOR
IAUTOCLAVE
TO S I G ~ GLASS T
REACTOR
Figure 4.
Inner front panel board
++&
RETURN FROM AUTOCLAVE M-20
Figure 7. V-35. V-36. V-37.
V-36
Heating-cooling system
Head valve Heat exchanger pump bypass Cold flow controls
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Tdble I.
Vapor Pressures of Acetylene and Mole Per Cent in Liquid Phase in Presence of Various Donor and Nonpolar Compounds at Different Temperatures -30' C . - IO0 oo +lo" c. +20' +40° C . -~ Mole Mole Mole Mole Mole Mole Materials (Moles) P.s.i. yo P.s.i. Yo P.s.i. yo P . s . ~ . 70 P . s . ~ . 7o P.s.1. yo
c.
Liquid C2Hz ( 0 . 2 ) ~ C Z H Z - C H ~ N (0.2 H ~ each) CzH2 (0.2 each) CH3NH2 (0.4 each) CzHz (0.4) CHaNHz (0.2) CzHz-NMPb (0.2 each) C2H2-(CH3)2NH (0.2 each) C2H2-(CH3)3N (0.2 each) C2H2-(CH3)20(0.2 each) C2H2-(C~Hj)20(0.2 each) C2H2-[(CHs)2CH]~0 (0.2 each) C Z H ~ - C ~ (0.2 H I ~each) C2H2-NHs (0.2 each) C2H2-H20 (0.2 each) CzH2 (0.2)c MO (20 cc.)b a At 3 8' C.pressure was 678p.s.i.g. 6
c.
184 75 24
83 95 98
299 106 54
74 93 97
378 129 66
69 92 96
473 149 79
63 91 95
549 172 91
60 91 95
227 112
-
87
97
147
96
177
95
218
94
261
93
347
92
99+ 95 94 95 93 92 93 93
50 141 133 101 161 192 210 116
97 91 92 93 91 91 89 91
100 179 171 125 209 248 312 153 443 445
95 89 90 92 89 89 85 90 70 75
132 204 193 135 236 279 360 170 578 510
194 247 241 170 308 340 456 164 -
92 87 88 91 86
235
97 90 91 93 90 90 87 91 74 81
94
-
71 158 155 112 184 219 261 131 351 320
10 103 98 78 120 150 132 92 -
-
-
_
86
88
90 92 88 88
83 89 63 72
88
94
86 80 88
-
No liquidphase was left. IVMP, N-methylpyrroltdone; M O , light mineral oil ( U S P ) . When another 0.2 mole of acetylene was udded, it was not completely miscible with the oil up to 25' C .
Interaction of liquid Acetylene with Various Donor and Nonpolar Compounds
Pure acetylene, visually observed just above its critical temperature (35' C.), appeared as a single gas phase as the last of the liquid phase disappeared. However, when nitrogen gas (25' C.) was slowly introduced, a marked turbulence (striations) in the gas phase was seen, similar to that which is noticed when liquids of different densities are mixed. This effect showed the density of supercritical acetylene to be intermediate between that of the liquid and gaseous phases. Table I summarizes a number of experiments carried out in the sight glass reactor to study the interaction or association of liquid acetylene with well-known solvents. Vapor pressure-temperature data showed that in most cases there was considerable hydrogen bonding even a t and above the critical temperature (35' C.) of acetylene. Association of acetylene with donor centers is shown by the large decrease in pressure for the solutions compared with that of pure acetylene. For volatile polar materials, such as ammonia, methylamines, and dimethyl ether, introduced as liquefied gases, the decrease in acetylene pressure was two- to threefold. I n general, the pressure differential became greater as the temperature was increased up to the critical point, indicating stable complex formation in both the liquid and vapor phases. If 1 to 1 acetylene-solvent complexes of the types H-CG C-H:Nf or H-C=C-H:O< are postulated for stoichiometric mixtures of acetylene and polar additives, conversions to such species in the liquid phase are over 90% (Table I). In support of this view, a diacetylene-,V-methylpyrrolidone complex (Shachat, 1962) has been isolated, while a n ammonia-acetylene complex has been claimed as a n activated species in catalytic ethynylations (Tedeschi, 1965; Tedeschi et al., 1963). Also the complexing of ethynyl hydrogen with donor centers has been measured in terms of acetylene solubility (McKennis, 1955). T h e high degree of interaction of acetylene-methylamine mixfures in mole ratios of 1 to 1 and 1 to 2 (93 to 95% C2Hz in the liquid phase at 20' C.) indicated the possibility of other complexes such as 3 I\': H-CGC-H : N f (1 to 2 type) or a species in Ibhich one acetylene molecule is hydrogen-bonded to the nitrogen donor center while the other is pi-bonded to one of the protons on the donor center. A comparison of ether solvents at 20' C. and a 1 to 1 ratio 306
c.
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PROCESS DESIGN A N D DEVELOPMENT
showed the following order of interaction: dimethyl ether (92%), diethyl ether (88%), diisopropyl ether (88%). NMethylpyrrolidone, a typical high boiling polar solvent, was the best donor solvent (94%), although it is expected that dimethyl sulfoxide, dimethyl formamide, or hexamethyl phosphoramide would be comparable. Above the critical temperature a t 40°, donor solvents still retained 80 to 94% of the acetylene in the liquid phase. Hexane, lacking a donor center, was still an effective complexing agent for liquid acetylene at 20' and 40' C. with 83 and SOYo, respectively, remaining in a single phase us. 60% for pure acetylene at 20' C. Light mineral oil (USP grade) exerted a similar effect, dissolving up to 35y0 by volume of liquid acetylene before a second layer formed. Gaseous ' to 20' C. acetylene, in contrast, has a negligible solubility a t 0 and 200 p.s.i.g. Liquid acetylene, because of its surprising miscibility in nonpolar solvents, is probably associated in the liquid state and may resemble a polymeric molecule. Such weak van der Waals bonding probably involves attraction of the weakly acidic hydrogens of acetylene with the cylindrical ?r cloud of the triple bond. Speculatively, the result of such interaction would be a clathrate or cage structure which might be capable of hosting or solubilizing hydrocarbon molecules or hydrogen bonding with polar compounds. T h e surprising solubility of K O H in liquid acetylene (Table 11) further substantiates this view. The interaction of equimolar (0.2 mole) quantities of liquid acetylene and water resulted in the formation of a solid hydrate which melted at 20' C . to yield two liquid phases (acetyacetylene-HzO) T h e hydrate compositions varied lene from 0.1 to 0.2 mole of acetylene per mole of water. Freshly prepared hydrate had a composition of 1 mole of acetylene per 10 moles of water. However, after standing 10 to 15 hours below its melting point, the acetylene ratio doubled. A hydrate prepared from gaseous acetylene has been reported (Stackelberg, 1949; Stackelberg and Muller, 1954) to contain 17 moles of water per mole of acetylene. The low degree of interaction of liquid acetylene with water compared with donor solvents is probably due to the highly associated (Hbonded) or polymeric nature of water molecules, which prevents effective solvation with the relatively hydrophobic acetylene molecule.
+
.
Table II.
Alkali Hydroxide-Acetylene Complexes
Conversion to Com-
C2H2, Tzmj., Pressure, Time, plex,. Mole C. P.S.I.G. Hr. 70 0.60b 12-22 320-360 1 44 KOH 0.90 22-26 655-720 2 64 KOH 0.30 KaOH 0.30 0.90 21-24 600-665 2 59 0.90 22-28 610-690 3 70 LiOH 0.30 a After isolation and drying under an acetylene atmosphere. * 20 cc. liquid ammonia used asjossible soloent and cocatalyst. Base
Moles 0.14
Alkali Hydroxide-Acetylene Complexes
Preliminary experiments in the sight glass reactor showed that potassium hydroxide was readily soluble in excess liquid acetylene. This observation agreed well with the previous reported formation of a KOH-CzH? complex (Tedeschi, 1965). T h e data in Table II?obtained in the stirred autoclave, showed that potassium, sodium and lithium hydroxides readily formed complexes in conversions of 64, 59, and 707,, respectively, when an acetylene to base molar ratio of 3.0 was used. By venting excess acetylene through a calibrated gas meter, and correcting for the known internal volume of the system, the conversion to complex just after removal of acetylene could be readily calculated. T h e complexes were isolated and dried a t room temperature in a current of dry acetylene. However, on standing in a dry box acetylene was gradually lost. .4fter 144 hours at room temperature the KOH-CgH? complex had decomposed from an initial acetylene content of 20.3 to 10.5%. Storage a t 0’ C . under anhydrous conditions gave improved stability, the acetylene content being 11.9% after 312 hours. The LiOH complex, although it had the highest acetylene content, contained no acetylene after 168 hours. T h e rapid thermal decomposition of these adducts compared with the stability of known alkali metal acetylides has been reported (Tedeschi, 1965). Infrared and x-ray examination of the KOH-CIH? complex agreed with earlier data (Tedeschi, 1965).
Then the acetylene is further compressed by pumping oil from the accumulator oil reservoir (Figure 5) into the accumulator until the desired pressure (350 p.s.i.g. and higher) is reached. Then both the accumulator and buret are isolated, after which the exact, required quantity of acetylene can be added to either reactor from the buret. TVhen necessary, the buret is recharged from the accumulator. To avoid accidental introduction of air through the accumulator oil reservoir into the accumulator, a slight positive pressure of Nz is maintained above the oil in the reservoir.
Liquefaction of Acetylene. By using vapor pressuretemperature and density-temperature data (Clancy, 1952; h?iller, 1965), the temperature needed for liquefaction of acetylene a t a given acetylene pressure and the volume of liquefied acetylene that will be obtained from a specified pressure drop in the buret can be determined. T h e pressure generally used in the accumulator and acetylene buret is 400 p.s.i.g. At a reactor temperature of -10’ to -30’ C., this pressure is sufficient to allow rapid liquefaction of acetylene as it is being introduced from the buret into either reactor. A pressure drop of 100 p.s.i.g. on the acetylene buret gage is equal to 0.40 mole (about 20 cc.) of liquid acetylene. Addition of Materials to Reactors. Liquefied gases (ammonia, methylamines. carbon dioxide), liquids, and solutions can be added to either reactor from any of the liquid burets (Figures 3 and 4) by applying sufficiently high nitrogen pressure to the buret to overcome vapor pressures of materials already in the reactor. With the small metering (interior) burets (M-3. M-4), the rate of addition and quantity of material added are accurately controlled. Solid materials obviously must be charged into the reactors before the reactors are assembled for a given run Cooling-Heating System. Dry ice is added to the cold tank (Figure 7) containing sec-butyl alcohol. Generally, three 50-pound blocks of dry ice are required for a day’s operation a t reactor temperatures below -30’ C. The hot tank (Figure 7 ) . filled with water. is maintained a t 65’ to 75’ C., by controlled electric heaters. T o start circulating heat exchange fluid (methanol) through the copper lines the head valve, V-35, is opened, the pump is started, and the bypass valve is closed or partially closed. By controlling the cold-flow valves (V-37, Figure 7 ) both reactors can be simultaneously or individually cooled. Similarly by operating the hot-flow valves, V-38, either or both of the reactors can be heated.
Operating Procedures
Reactors. Both reactors can readily be assembled and operated by anyone experienced in carrying out chemical reactions in high pressure equipment; hence no detailed description is given. Agitation is accomplished in the case of the autoclave Lvith a stirring shaft and blade driven by an electric motor. whereas materials in the sight glass reactor are agitated by rocking this reactor back and forth (Figure 5) by means of a modified “rocker bomb” mechanism. Heating and cooling are carried out by circulating a heat exchange fluid (methanol) directly through the jacketed walls of the autoclave, or through copper coils immersed in the secbutyl alcohol bath in which the sight glass reactor is suspended (Figure 7 ) . Filling Accumulator and Acetylene Buret Followed by Compression of Acetylene. Initially both the acetylene buret and accumulator should be well purged with nitrogen and bled to zero gage pressure before acetylene is admitted for the first time. I t may even be preferable to evacuate the buret and accumulator to 1 to 5 mm. before adding acetylene. Then at least five purges with 100-p.s.i. portions of acetylene are used to flush the system out. The buret and accumulator can then be allowed to stand filled with acetylene (50 to 100 p.s.i.g.) when not in use. Just prior to carrying out a run, acetylene is added to full cylinder pressure (200 to 250 p.s.i.g.).
literature Cited
Beller, H., “Handling and Use of Acetylene at Elevated Pressures,” 1958 Annual Convention, International Acetylene Association, March 1958. Berthelot, M., Veille, P., Ann. chzm. p h i s . (7) 11, 5 (1897); 13, 5 (1898). Berthelot, M . , Veille, P., Compt. Rend. 123, 523 (1896). Clancy, V. J., “Liquid and Solid Acetylene. A Review o Published Information,” Explosives Research and Development Establishment Survey, England, 1/5/51, 1952. Conta, L , Central Research Laboratories, Air Reduction Co., Murray Hill, S . J., unpublished work, January 1954, January 1956. Crafts, J . M., Science 3, 377 (1896). McKennis, A . C., 2nd. Eng. Chem. 47, 850 (1955). Mayes, H. A . , Yallop, H . J., Chem. Eng. (London), No. 185, CE25CE28 (1965). Meade, G. A . , Central Research Laboratories. Air Reduction Co., Murray’Hill, N . J . , unpublished work, April 1963. Miller, S. A . , “Acetylene,” pp. 11-12, 503-16, $95-610, Academic Press, New York, 1965. Shachat, N., J . Org. Chem. 27, 2928 (1962). Stackelberg, M. V., ~~atur~’issenschaften 36, 327 (1949). Stackelberg, M . V., Muller, H . R . , Z . Elektrochem. 58, 25 (1954). Tedeschi, R . J., J . Org. Chem. 30, 3045 (1965). Tedeschi, R . J., Casey, A . tV., Clark, G. S., Jr., Huckel, R . I V . , Kindley, L. M., Russell, J. P., J . Org. Chem. 28, 1740 (1963). ~
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RECEIVED for review April 5, 1967 ACCEPTEDOctober 19, 1967 VOL. 7
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