I
James 0. Schreckl Georgio Institute of Technology Atlanta
I
Chemistry of Methylenes -------,
T h e most important reaction interme diates in organic chemistry are probably those containing trivalent carbon. These are carbanions, free radicals, and carbonium ions, in which the trivalent carbon hears two, one, and no unshawd electrons, respectively. Simple examples are shown below. One of the most rapidly growing areas of physical organic chemistry is the study of reactions involving intermediates containing divalent carbon. As shown in the figure, methylenesZ consist of carbon atoms with two covalently bonded substituents and two unshared electrons.
methyl anion
methyl
methyl
cation
radical
methylene >7s%.g
character
linear or nearly linear
Each of these four intermediates is highly reactive and each usually has only a momentary existence. As previously mentioned, each is known to serve as an intermediate for certain reactions. Thus, carboninin ions are known to be formed in the rate-controlling step of SN1reactions, carhanions are reactive intermediates in hase-catalyzed aldol condensations and in Claisen condensations of esters, and free radicals are involved in the Kharasch addition of hydrogen halides to alkenes under the influence of ultraviolet light or in the presence of oxygen. In the past decade many reactions have been shown to involve methylene intermediates, and the literature abounds with reactions involving methylenes. However, in contrast to the large number of examples of reactions involving trivalent carbon, most current text-
U. S. Army Research Office (Durham) Postdoctoral Fellow, 19643. 2 According to Chemical Abstmcts, divalent carbon compounds are named a8 derivatives of methylene, the parent member of the series, rather than as earbenes. 260 / Journal of Chemical Education
books of organic chemistry either omit a discussion of methylene chemistry or devote only a paragraph or two to them. The most commonly mentioned examples are: (1) the formation of dihalomethylenes from the action of potassium t-bntoxide on hromoform or chloroform and its subsequent addition to an alkene to form cyclopropane derivatives (as discussed below), (2) the generation of dichloromethylene by decarboxylation of sodium trichloroacetate, 0
and (3) the photolysis of diazon~ethane(also discussed below). In the several textbooks3 examined, the familiar Reimer-Tienlann synthesis of aldehydes from phenols is correctly presented as involving n~ethyleneintermediates. However, some textbooks state that methylene can be generated by the action of the zinc-copper couple 011 methylene iodide, and in the presence of ether and an olefin a cyclopropane derivative is formed. This observation was explained by the suggestion that zinc removes two iodine atoms from the methylene iodide leaving free methylene, which then adds to the olefin. RCH=CHR
+ CH.L + Zn
-
RCH-CHR \
/
+ ZnIn
However, Simmons and Smith (I) found evidence that this is not so. Although their evidence will not be presented here, they concluded from their experiments that the methylene iodide reacts with the zinc-copper couple to form bis(iodomethy1)-zinc which reacts relatively rapidly, directly, and exothermically with cyclohexene forming hicyclo-[4.1.0]-heptane (I).
I n view of these shortcomings it seemed appropriate to present some of the more general aspects of methylene chemistry. Formation of Methylenes (1) Formation of Methylene from Diazonzethane. The first strong evidence for the formation of a methylene intermediate was described by Staudinger and T o r example, see CRAM,D. J., AND HAMMOND, G . S., "Organic Chemistly," 2nd ed., McGraw-Hill Book Co., New York, 1964, p. 406.
Icupfer (8) in the pyrolysis of diazomethane in the presence of carbon monoxide to give ketene.
However, the possibility of a direct reaction between carbon monoxide and diazomethane was not ruled out. (2) Formation from Ketene. Norrish, et al. (3) found that the photolysis of ketene yields twice as much carbon monoxide as ethylene and suggested the mechanism CH*=CO CHl
+ CHFCO
--
CHs
+ CO
CHn=CH2
+ CO
The mechanism was substantiated by Kistiakowsky and Rosenberg (4) who found that the rate of carbon monoxide formation can be almost halved by the addition of ethylene, which competes with the lceteue for methylene. (3) Direct Measurements on Methylenes. Herzherg and Shoosmith (5) were able to observe the spectra of CH,, CD,, and CHD in the vapor phase flash photolysis of CH2N2, CD2N2, and CHDN2. The methylene is initially formed in a singlet state (having no unpaired electrons), which subsequently decomposes to the more st,ahletriplet form (with two unpa-ired electrons). The triplet form absorbs around 1400 A (the blue end of the spectrum) and has a linear or nearly linear structure wit,h C-H bond distances of about 1.03 A. It has two sp bonding orbitals and an unpaired electron in each of the two remaining p orbitals. The singlet form, which absorbs in the 5500-9500 A range (the red end of the spectrum), has C-H bond distances of about 1.12 A and a H-C-H bond angle of about 103'. The empty orbital of a singlet methylene is probably p i n character. If the unshared electron pair is in an s orbital the two bonding orbitals should be p and the H-C--H bond angle 90". If the three occupied orbitals combine to give sp2 hybridization the bond angle will be 120". The observed bond angle is 103', and thus the bonding orbitals have more than 75% p character. Formation of Diholomethylenes
(1) Mechanism. Basic hydrolysis of methylene chloride is slower than the corresponding basic hydrolysis of methyl chloride. Contrary to what is expected, the basic hydrolysis of chloroform is a relatively fast reaction. Thus the hydrolyses of the three halides do not proceed by the same mechanism (although all three reactions are first order in halide and first order in base) (6). The enhanced reactivity of chloroform cannot be explained by any combination of Sxl and SN2 reactivity for halide hydrolysis. The basic hydrolysis of chloroform cannot he an SN1reaction since it is kinetically second-order and yet the reaction is much faster than would be plausible for the SN2mechanism. Moreover, in reactions with such weakly basic nucleophilic reagents as water, ethanol, and piperidine, the reactivities of the halomethanes is in the order CHsCl >> CH2Clz> CHCI,. This decrease in reactivity is attributable to the decrease in SN2reactivity brought about by e-chloro suhstituents. However, with strongly basic nucleophilic reagents, such as hydroxide and alkoxide ions, chloroform is far more reactive than methylene chloride and toward hydroxide ion in aqueous solution
is even more reactive than methyl chloride. Such reactivity is explained in terms of the following dichloromethylene mechanism, in which the concentration of the intermediate trichloromethyl anion is proportional to the concentration and the strength of the base by whose action it is formed. CHC4
+ OHCCI,
faat
H,O
-
OH-.
H,O
CO
+CCk + HCOc
There is good evidence for this type of mechanism. I n the presence of heavy water, chloroform undergoes base-catalyzed deuterium exchange at a rate that is much faster than its hydrolysis. This indicates that the trichloromethyl anion, CC13-, is formed rapidly and reversibly in the attack by hydroxide ion on chloroform. Perhaps the strongest evidence for the above mechanism comes from experiments in which the intermediate dichloromethylene is captured in various ways. For example, although chloroform is relatively inert to the action of thiophenoxide ion alone, it reacts rapidly in the presence of hydroxide ions, giving triphenyl orthothioformate (6). The much more basic hydroxide ions are needed to convert the chloroform to the intermediate dichloromethylene. Chloride, bromide, and iodide ions are capable of capturing dichloromethylene (7). At a salt concentration of 0.16 M, where weakly nucleophilic salts such as sodium perchlorate or sodium nitrate have no detectable effect on the reaction rate, sodium chloride decreases the rate of the basic hydrolysis of chloroform. This is due to the mass law effect; the chloride ions transform dichloromethylene to trichloromethyl anion and thus to chloroform. The reaction rate is decreased even more by the addition of sodium bromide and sodium iodide. With these however, the calculated rate constants increase as the reaction proceeds. This would be expected since the calculated rate constants are those not for the disappearance of chloroform, but for the disappearance of total haloform. I n capturing dichloromethylene, bromide and iodide prevent the hydrolysis of chloroforn~by transforming it to another haloform, w., CCI,
+ I-
- CCIII-
CHClzI
This interpretation of the rate data was supported by the isolation of dichloroiodomethane from the reaction of chloroform with iodide ion in alkaline solution. Furthermore, CHCIJ is not formed by the displacement of chloride by iodide in neutral solution and thus it cannot be formed by such a displacement in the trichloromethyl anion in basic solution. Doering and co-workers (8) have shown that when chloroform is treated with base in the presence of cyclohexene, 7,7-dichlorobicyclo-[4.1.0]-heptane (11) is formed.
Volume 42, Number 5, Moy 1965
/
261
Similarly, the action of potassium tbutoxide on bromoform in the presence of trans-2-butene yields dibromide (111) (9).
(2) Ease 01 Formation of Dihalomethylenes. The hydrolysis mechanism written above for chloroform may be expressed by the following generalized mechanism: CHXYZ
kt + OH- ,.= CXYZ- + HIO k
followed by rapid reaction of the X-C-Y, where X, Y, and Z are all halogen atoms that may or may not be different from each other. From the data in the table, it can be seen that the reactivities of haloforms, both in carbanion formation and over-all hydrolysis, vary over a wide range. The relative values of k,, the carbanion forniation rate constant, may he rationalized Rate Constants for Base-Catalyzed Carbanion Formation and Hvdrolvsis bv Haloforms Haloform
-lo5 k in liters mole-' sec-' st 0" in water-
Carbanion formation
CHBrF*
a
Hydrolysis
208
This compound gives concerted crdehydrohslogenstionrather than carbanion formation.
by the generalization that the relative extent of stabilization of carhanions by a-halo substituents is in the order I Br > C1> F. Qualitatively, it is reasonable to assume that k ~ the , rate constant for carbanion protonation, will show a variation of structure that is opposite of that shown by kl. Rationalization of the relative hydrolysis rates, kz, is not so simple but it can be done satisfactorily in terms of the dihalomethylene reaction mechanism shown above. In the formation of dihalomethylene, one halogen may be lost as an anion (as Z in the mechauism above) and the other becomes a substituent (such as X or Y above) on the dihalomethylene. Applying a semiempirical linear free-energy relationship to the data of haloform hydrolysis, quantitative estimates were made of the relative abilities of the various halogens to play each of these roles (10). These estimates showed that the relative ease of loss as an anion (I-Br > C1 > F) is about the same as that observed in a number of other organic reactions.' The abilities of the various
-
-
'For example, the reactivity of methyl halides with hydroxide ion is in the order RI RBr > RCI.
262 / Journal of Chemical Education
halogens to facilitate dihalomethylene formation, and hence their abilities to stabilize dihalomethylenes, is in the order F >> C1> Br > I. There are two reasons for this order. First, the stabilizing ability of a particular halogen is a function of its ability to stabilize the electron-deficient carbon atoms by use of their unshared electron pairs, as illustrated by the contribution of structures such as (IV) above. Second, in view of the high degree of p character (hond angle -103') in the bonds of singlet methylene, probably much of the stability of fluoromethylenes, relative to their precursors, is due to the decrease in the effective electronegativity of carbon that accompanies increases in the p character of the bonding. Since the strength of the C-X bond increases with the square of the difference in electronegativity between C and X there is considerably more increase in hond energy with fluorine than with any other halogen. (3) Concerted Dehydrohalogenation of Haloforms. Comparing the halogens, fluorine destabilizes trihalomethyl anions and stabilizes methylenes. From the table, it may be seen that a tribromomethyl anion decomposes to dihromomethylene about one time in every 420,000 that it is formed, but that dibromofluoromethyl anion decomposes to bromofluoromethyleneone time in every 13. One would expect then that the bromodifluommethyl anion would yield difluoromethylene a t such a rate that the initial carbanion formation would be the rate-controlling step. Actually, it is found that the effect of a second fluoro substituent is even more profound. Chlorodifluoromethane and iododifluoromethane also undergo alkaline hydrolysis a t a rate faster than they would be expected to form carbanions under the given conditions; this is interpreted as a change in mechanism. Thus, for CHFIX compounds the ease of difluoromethylene formation has become so great and trihalomethyl anion formation has become so difficult that the carbanion is bypassed and the difluoromethylene is formed directly in a concerted a-dehydrohalogenation (11). Evidence for this mechanism F SF 6I
I
has been supplied by the fact that the basic hydrolysis of CDFzBr is unaccompanied by deuterium exchange with the solvent, suggesting that the first step is rapid and irreversible. Other Reactions Involving Methylene Formation
(1) Double-Bonded Divalent Carbon. Carbon monoxide and isocyanides are the only common chemicals that are stable divalent carbon derivatives. Isocyanides are formed in a variety of reactions, e.g., the reaction of primary amines with haloforms in the presence of strong base and the reaction of silver cyanide with alkyl halides. Species such as &C=C are not as stable as carbor, monoxide and isocyanides for two reasons. Carbon being less electronegative than nitrogen or oxygen, the R2C= substituent is not as capable of electron withdrawal as is RN= or O=. Furthermore, since the RG= substituent lacks unshared electron pairs it is
not capable of resonance electron donation as is RN= or O=. For example, the reaction of lJ-diaryl-2haloethylenes with strong bases to give diarylacetylenes can be written as proceeding by a &C=C intermediate, but this mechanism has been ruled out by showing that the aryl group trans to the departing halogen migrates preferentially (12). However, the observation that the solvolysis of 3-chloro-3-methyl-1-butyne is greatly speeded by alkali suggests the unsaturated methylene (V) as an intermediate (13). CH~
I
CHa-C-C-c a '
e -
-
niediate in the preparation of tetracyauoethylene from dibroniomalononitrile and copper powder in boiling benzene (18). The isolation of cyclohexylidenemalononitrile (VIII) when the reaction is carried out in cyclohexene, but not in benzene, supports such a mechanism. I t was proposed that (VIII) arose from the isomerization of initiallv formed 7,7-dicyanobicyclo[4.1.0]hept,arie (VII).
CH~ CH3-bc=~
J
etc.
Support for this intermediate is given by the fact that 4chloro-4methyl-2-pentyne, (CH3)&ClC=CCH3, in which the acidic acetylenic hydrogen atom has been replaced by an alkyl group, is insensitive to base. Hartzler reported the capture of (V) by several olefins (14). (2) Base-Induced ol-Elimination Reactions. Swain and Thornton (15)studied the reaction of p-nitrobenzyldimethylsulfonium ions with sodium hydroxide to give cis- and trans-p,pl-dinitrostilbene. The following mechanism was suggested (Ar = p-nitrophenyl) :
VII
VIII
Reactions of Methylenes
(1) Addition of Itself and to Other Methylenes. It, would be expected that the addition of methylene to itself would require a third body because the ethylene molecule formed would possess the energy to dissociate again and thus n u s t give up some of its excess energy. Actually, the et,hylene fornied in reactions in which niethylene is generated as an intermediate has been shown to arise from attack of methylene on the initial react,ant rather than from dimerization. CHiN?
On t,he basis of the sulfur kinetic isotope effect, which is less than half as large as that observed in the solvolysis of tbutyldimethyl-sulfonium ions, they argue that the rnet,hylene does not dimerize but adds to carbanions. The niethylene is probably present in very small concentrations. In the reaction with the intermediate ~net,hyleneanother methylene n~olecule has the advant,age of leading directly t,o a stable molecule, hut t,he carbanion has the advantage of being present a t a higher concentration. (3) Substituted Methylenes. The methods for form ing met,hylene mnay also be used for the format,ion of suhst,ituted methylenes. The photolysis of diphenyldiazomethane leads to the format,ion of the corresponding ket,azine (VI) by the attack of the intermediat,e diphenylinethylene on diphenyldiazoinet,haue (16).
Parham and Hasek (17) obtained evidence for the iuternied~atediphenyhnethylene by decomposing diphenyldiazomethane in hot petroleum ether with subsequent isolation of tetraphenylethane and beozophenone azine. The former product arises from diphenylmethylene ahstracting hydrogeu atoms from saturated hydrocarbons accordingly
Diryanomethylene may be written as an inter-
CHx
+ CHINl
-
CH2
+ N2
+ CHz=CH2
+ N2
Wilson and Kistiakowsky (19) investigated the photolysis of ketene in the presence of I3C-labeled carbon monoxide. The extent of lac-labeled ketene increases wit,h increasing pressure due to increased efficiency of deactivation of the initially formed hot CH,=13C0 niolecules. By the use of quantitative measurenients it was shown that the 13C0 combines with niethylene rather t,han wit,h activated ketene. CH1=CO CH2
+ '"0
-h"
CH1
+ CO
CHCH~='~CO
(2) Insertion Reactions. One of the most conunon reactions of methylene consists of the insertion of the CH2group into a single bond. For example, the photolysis of diazomethane in isopropyl alcohol yields all the products that could arise from insertion into C-H aud 0-H bonds (20).
Evidence has been obtained that niethylene insertions occur by a direct one-step reaction (21) or by a free radical reaction (22) and that often these two niechanisnis operate concurrently. Doering and co-workers (25) showed that niethylene gives insertion reactions almost a t random. Reaction with n-pentane gives n-hexane, 2-methylpentane, and 3-methylpentane in the ratio 48:35:17 at -75' and 49:34:17 a t 1.5'. Random insertion would give the ratio 50:33.3:16.7. Volume 42, Number
5, May 1965 / 263
(3) Addition to Olefins. Methylene, generated by the photolysis of diazomethane (24), or dihalomethylene (8,25) reacts with cis and trans olefinsstereospecifically.
eons-2-butene
+
CH2
-
Me
However, if the reaction is carried out under nitrogen pressure, both cis- and trans-cyclopropanes are formed. This has been interpreted to mean that the methylene first formed is in the singlet state, TJCHz, but that on collision with a sufficient number of nitrogen molecules it loses energy and is transformed to the more stable triplet, ttCH2. The diradical IX loses its stereochemical homogeneity at a rate a t least comparable to its rate of cyclization to diiethylcyclopropane.
v
CH,C=C-C=CH,
CCl,
CCI,
CH,C=CC-CH,
/ \
I
CH, With 2-methylhexene-2-yne-4, the addition appears to have occurred to a significant extent a t each of the multiple bonds (28). (6) Reactions with Organic Oxygen and Halide Compounds and Amines. Di-n-butyl ether was found to react with ethyl diazoacetate to give 1-butene and ethyl n-butoxyacetate in addition to products of C-H insertion reactions ($9).
Me M e
cis
Aniline reacts on heating with various diazo compounds to yield N-substituted anilines, e.g.,
+
Me
(4) Additia to Triple Bonds. The best method of synthesis of cyclopropenones involves the addition of dihalomethylenes to acetylene. The reaction of the diphenylacetylene with bromofom and potassium tbutoxide followed by addition of water gives diphenylcyclopropenone via the intermediate formation of diphenyldibromocyclopropene (26). .
The thermal reaction of diphenylacetylene with phenyldiazoacetonitrile gives triphenylcyanocyclopropene, a precursor of the triphenylcyclopropenyl cation, the first aromatic species known with only two pi electrons (27) :
(5) Addition to Various Multiple Bonds. The electrophilic nature of dihalomethylene is shown by its reaction with 2-methylpentene-1-yne-3, in which the only product isolated resulted from addition to the double bond (28). 264
/
Journal o f Chemical Education
The photolysis of ethyl diazoacetate in the presence of triethylamine gave, in addition to the products expected from insertion a t a- and 8-carbon-hydrogen bonds, ethyl a-diethylaminoacetate (30). The latter product arises from attack of carbethoxymethylene on the nitrogen atom of the amine to give the following intermediate.
(7) Rearrangement of Methylenes. In the Wolff Rearrangement, a-diazoketones may rearrange in the presence of water to give carboxylic acids, in the presence of ammonia to give amides, and in the presence of alcohols to give esters (81).
Evidence for this mechanism is obtained in the absence of water and alcohols where the intermediate ketene may be isolated. I t is sometimes possible to isolate the hydroxy ketone, RCOCHgOH, when the reaction is
carried out in the presence of water. Even though it is possible that this could result directly from the diazo ketone itself, it seenis more plausible that it is formed by the hydration of the methylene X durin~;the short time interval hetveen the dcpzrture of nitrogen and the rearrangement to the ketene.
The mechanism given above for the Wolff Rearrangement seems plausible when the reaction is carried out thermally or photochemically, but when carried out ordinarily in the presence of the silver catalyst, it assigns no role to the silver. Summary
Methylenes are electrically neutral species, are covalently bonded to two substituents, and possess two unshared electrons. Although they are electrically neutral, methylenes contain a carbon atom with only a sextet of electrons and hence are, in general, electrophilie. They have only a transient existence and may exist in two states-a singlet in which the electrons are paired, and a triplet in which the electrons have parallel spins. Generally, the triplet state has a lower energy (is more stable) than the singlet state. Methylenes can he formed in a variety of ways. The most common of these involves (1) homolysis of a double bond (diazomethane or ketene), (2) loss of a group wit,h its bonding pair from a carbanion (forme, tion of dihalomethylene from chloroform or bromoform), and (3) a concerted or-elimination (difluoromethylene from difluoroehloromethane). Each of the types of reactions for the formation of methylenes, when written in reverse, is a reaction of a methylene. Thus, methylenes react with other methyleues (methylene and carbon monoxide give ketene), iodide ion reacts with dichloromethylene to form dichloroiodomethyl anion, and the reaction between difluoromethylene, water, and chloride ion gives difluorochloromethane. I n addition, methylenes undergo insertion reactions, add stereospecifically to cis- and trans-olefins, give addition products with alkynes, react with ethers, organic halides, and amines, and are involved in the Reimer-Tiemann reaction.
The author wishes to thank Professor Jack Hine for his helpful suggestions and discussions. Literature Cited (1) SIMMONS, H. E., AND SMITH, R. D., J . Am. Chem. Sac., 80, 5323 (1958); 81,4256 (1959); 86,1337, 1347 (1964). (2) STAUDINGER, H., AND KUPFER,O., Ber., 45, 501 (1912). (3) NORRISH, R. G., CRONE,H. G., AND SALTMIRBH, O., J. Chem. Soe., 1533 (1933). (4) K l s ~ ~ ~ a o w G. s n B., ~ , AND ROSENBERG, N . W., J . Am. Chem. Soe., 72, 321 (1950). (5) HERZBEKG, G., AND SHOOSMITH, J., Nature, 183,1801 (1959). (6) HINE,J., J . Am. Chem. Sac., 72, 2438 (1950). (71 A. M... JR... J . Am. Chem. Sac... 76,. , , HINE.J.. A N D DOWELL. 2688 (i954). (8) DOERING, W.V.E., ANDHOFFMAN, A.K., J . A m . Chem.Soe., 76, 6162 (1954). (9) SICELL, P. S., AND GARNER, A. Y., J . Am. Chem. Soe., 78, 3409 (1956). (10) S. J., J . Am. Chem. Soc., 80, 824 . . HINE,J., AND EARENSON, ( 19'58j. (111 P. B.. J . Am. Chem. Soc.. 79, 5497 , , HINE.J.. AND LANGFORD. ( 1i57 j. (12) BOTHNER-BY, A. A,, J. Am. Chem. Soc., 77, 3293 (1955).
CUR~N D ,. Y., FLYNN,E. W., NYSTROM, R. F., J. Am. Chem. Soc., 80, 4599 (1958). (13) HENNION, G. F., AND MALONEY, D . E., J . Am. Chem. Sac., 73, 4735 (1951). (14) HAKT~LER, H. D., J . Am. Chem. Sac., 81, 2024 (1959); 83, 4990, 4997 (1961). (15) SWAIN. C. G., AND THORNTON, E. R., J . Am. Chem. Sac., 83, 403.1 (1961 ~ -). ~ ~ - , ~ (16) STAUDINGER, H., ET AL, Ber., 44, 2194, 2197 (1911); 49, 1884, 1897, 1923, 1928, 1951, 1961, 1969, 2522 (1916). (17) PARHAM, W. E., AND HISEK, W. R., J . Am. Chem. Sac., 76, 935 (1954). (18) CAIRNS, T. L., J . Am. Chem. Soc., 80,2775 (1958). (19) T. B..AND KISTIAKOWSKY, G. B., J . Am. Chem. . . WILSON. SOC., 80,2934 (1958). (20) MEERWEIN, H., RATHJEN, H., AND WERNER, H., Be?., 75, 161011942). -.-. ~ (21) DOERING, W. v. E., AND PRINZBCH,H., Tetrahedron, 6, 24
- ..-.. .
11454) \ ,
(22) FREY,H. M., AND KISTIAKOWSKY, G. B., J . Am. Chem. Soc., 79, 6373 (1957). (23) DOERING, W. V. E., BUTTERY, R.G., LAUGHLIN, R. G., A N D CHAUDHURI, N., J. Am. Chem. Sac., 78, 3224 (1956). (24) R. C.. J . Am. Chem. Soc., . . SKELL.P. S.. AND WOODWORTH. 78,4496 (i956); 81,3383 (1959). (25) SKELL,P. S., AND GIP~NER, A. Y., J . Am. Chem. SOL, 78, 5430 (1956). (26) KWRSANOV, D. N., ET AL.,J . Gen. Chem. U S S R , 30, 2855 (1960). (27) BRESLOW, R., J . Am. Chem. Soe., 79,5318 (1957); BHESLOW, R., AND YUAN,C., J . Am. Chem. Soe., 80, 5991 (1958). (28) DYAKONOV, I. A., ET AL.,J . Gen. Chem. U S S R , 30, 3475 (19601. . . (29) DEGRAAFF, G. B. R., A N D VAN DEKoLR,G., Ree. trav. ehim. 77. . . -224 - - (19,581. ~----,. (30) FRANZEN, V., AND KUNTZE, H., Ann., 627, 15 (1959). (31) B A C H M ~W. N , E., A N D STRUVE,W. S., 0 r ~ Reactions, . 1,
.
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