3730
s.
The following 1-methylcyclobutanolswere prepared by exchange Acknowledgment. Helpful discussions with H. with D20 in the mass spectrometer inlet system: 1-methylcycloB ~ G , ~G . H~ ~ ~ R., ~ ~ ~ ~fB. L.f M ~ ~ ~ ~~~ butanol-0-d(5g) (75 % d l , 25 do); 1-methylcyclobutanol-2,2,4,4-d4Widom are gratefully 0-d (Si) (41% dj, 55% d,, 3.6% d3); l-methyl-d3-cyclobutanol-0-d H* D. R* Schuddemage, and acknowledged. (5b) (7323 d4, 22% da, 5 % 4).
Vinyl Radicals. V. The Relative Reactivity of the 2-Methylpropenyl Radical P. G . Webb and J. A. Kampmeier*
Contribution f r o m the Department of Chemistry, Uniuersity of Rochester, Rochester, New York 14627. Receiued October 22, 1970 Abstract: The thermal decompositions of 3-ethyl-2-pentenoyl and 3-methyl-2-butenoyl peroxides and tert-butyl peresters have been studied as possible sources of 2-ethyl-1-butenyl and 2-methylpropenyl radicals. Intermediate acyloxy radicals are formed which partition between intramolecular H abstraction and decarboxylation. 2Methyl-2-butenoyl peroxide is shown to be a useful source of 2-methylpropenyl radicals for experiments competing benzylic hydrogen donors (klr) us. carbon tetrachloride (kcJ at 78". The relative reactivity of the 2-methylpropenyl radical toward benzylic hydrogens is primary : secondary :tertiary 1.O: 3.9 : 8.6, with a marked preference for ~ ltoluene = 0.048. The effects of para substituents on the reactivities of substituted chlorine abstraction, k ~ / kfor toluenes toward 2-methylpropenyl radicals are small.
V
inyl radicals are readily available from the thermal and photochemical decompositions of the corresponding a,@-unsaturated peresters and diacyl pero x i d e ~ ' -and ~ as intermediates in free radical additions to alkyne^.^-^ The details of these reactions and the behavior of the vinyl radicals have been studied in some detail. The vinyl systems show typical radical reactions such as displacement on hydrogen,'-? halogen, and and addition to aromatic rings. l o Because vinyl radicals represent a fundamental structural type of carbon radical, it seemed worthwhile to seek quantitative data on their cheniical behavior. This paper reports a study of the relative reactivity of the 2-methylpropenyl radical toward a series of benzylic hydrogen donors and carbon tetrachloride. Similar reactivity studies are already available for a large number of other types of free radicals. I1--fo The experimental technique (1) J. A. Kampnieicr and R . M. Fantazier, J . Amer. Cheni. Soc., 88, 1959 (1966). (2) 'L. A: Singer and N . P. Kong, ibid., 88, 5213 (1966). (3) 0. Siniamura, Iand relative intensities w i t h that for an authentic sample obtained by vpc-mass spectrometry of a standard solution of isobutene in carbon tetrachloride. Small-Scale Decompositions. The procedures described helow apply to all decompositions (0.75-1.50 ml of solution) in which product analyses were made by vpc. The desired amount of perester or peroxide was weighed into a 10-ml volumetric flask, and solvent added to the mark. Peroxide or perester solution (0.75-1.50 ml) was measured rirr a syringe into reaction tubes constructed from Pyrex tubing. The tube was degassed by three freeze-pump- thaw cycles at 0.02 mm and sealed. A silicone oil bath maintained at 200 i 1 ', an oil bath maintained at 110.0 t~ 0.5", and a refluxing 95% ethyl alcohol bath maintained at 78.2 % . 0.5" were used in the thermal decompositions. Tubes were removed from these baths at measured intervals and stored in Dry Ice-acetone; the tubes were cracked and fitted with serum caps shortly before analysis. Carefully measured amounts of internal standard solution were then added to the capped reaction tubes by a 100-pI Hamilton syringe fitted with a "Chaney adapter." Ethyl alcohol was used as the internal standard i n the quantitative determination of products from the decomposition of tc,r/-but).l 3-ethylper-2-pentenoic and tert-butyl 3-methylper-2-butenoate. A 100-pl sample of the reaction tube containing internal standard was analyzed on a Carbowax 20M column (10 ft X 0.25 in.. 257; 011 60-80 Chromosorb W) at 70" with an injector temperature 01 '
3131 Table VIII. Decomposition of ierr-Butyl 3-Ethylper-2-pentenoate in Cumene
-_--[PI, M
T , "C
0.004 0.078 0.004 0.100 0.122 0.334
200 200 110 110 110 110
t,
hr
1 1 6 6 24 20
yield--
2-EthylI-butene
Acetone
ieri-Butyl alcohol
11 9.2 3.9 3.1 3.5 3.P
26 28 12.2 8.0 7.2 9.6
57 56 62 59 72 77
cis- and tl.(iii.~-2-etliyl-2-butene were not observed. The limit of detectability corresponded to 0.1 yield.
desired amount of perester or peroxide was weighed into a IGml volumetric flask. Carbon tetrachloride was added to the flask by tuberculin syringe and weighed; the hydrocarbon solvent was then added to 10 ml and weighed. Into the reaction tubes, 1.00 ml of peroxide or perester solution was carefully measured by a 1.00-ml tuberculin syringe. The reaction tubes were degassed by three freeze-pump-thaw cycles, sealed, and heated as previously described. Tubes were removed at appropriate times and stored in Dry Ice-acetone; the tubes were then cracked and fitted with a serum cap shortly before analysis. Unreacted diacyl peroxide in low conversion runs was destroyed by the addition of a n appropriate volume of a standard solution of tripheiiylpliosphine (East man Kodak Co.) in carbon tetrachloride (1.0-1.1 M ) to the capped reaction tubes.29 Volumes of quench sufficient to produce a phosphine concentration equal to five times the initial peroxide
Table IX. Decomposition of teri-Butyl 3-Methyl-per-2-butenoate
______________ Solvent
[PI, M
T, "C
t,
hr
VH"
VCI"
CHCh
yield
CCla
VH
=
isobutene.
0 0 0 0 0 0 0 0
004 105 004 113 004 110
004 100
200 200 110 110 200 200 110
110
2 2 24 24 2 2 24 24
53 48 37 31 0 0 1 6 1 2
57
31 91 43 21 18 8 7
CrCle
~
~~
Cumene
7
fert-B ut yl Acetone alcohol CHjCl
Trace 7 7 Trace 10
82 60
78 85 54 84 36
40
8 9
VCI = I-chloro-2-methylpropene- I .
260", a detector temperature of 280", and a helium flow of 100 cc/min: 2-ethyI-l-butene, 2.8 min; acetone, 6.3 min; [err-butyl alcohol, 9.6 min; and ethyl alcohol, 12.3 min. /!-Pentane was used as an internal standard in the quantitative determination of products from the decomposition of twt-butyl 3-methylper-2butenoate. A 25-1.11 sample of the reaction tube containing internal standard was analyzed on an SF-96 column (15 ft X 0.25 in, 25 7; on 60-80 Chromosorb A) at 80' with an injector temperature of 240", a detector temperature of 280". and a helium flow of 50 cc/min: methyl chloride, 4.5 min; isobutene, 5.9 min: /I-pentane, 9.1 min; chloroform, 19.6 min; l-cliloro-2-metliyl-1propene, 21.2 min. Quantitatibe determinations of isobutene, I-chloro-2-methyl- 1propene, and chloroform in the decomposition of 3-methyl-2butenoyl peroxide were made by vpc analysis of equivolume injections of reaction and standard solutions. A 50-pl Hamilton syringe fitted %ith a "Chaney adapter" was used to make repetitive 25- or 50-pl injections on the SF-96 column under the conditions described above. Quantitative determinations of hexachloroethane and 3-methyl-2-butenoic acid were made using equivolume injections of reaction and standard solutions. Analyses were performed on an SE-30 methyl column ( I O ft X 0.25 in., 10% on 45-60 Chromosorb W (acid washed) at 100" with an injector temperature of 275', a detector temperature of 320', and a helium flow of 50 ml/min: 3-methyl-2-butenoic acid, 10.4 min; hexachloroethane, 15.9 min. Standard solutions were used to establish vpc response factors. To minimize evaporation of the solutes, a volumetric was partially filled with solvent: fitted with a serum cap, and weighed. Standards were then added through the serum cap with a syringe and the flask was weighed again. Dilution to the mark with solvent gave the standard solution. Volumes of methyl chloride and isobuteiie were measured in a gas buret and transferred quantitatively to an evacuated flask containing a measured volume of solvent to give standard solutions. The total estimated error for the volume measurement was + 2 % . The flask was closed with a stopcock and samples were removed through the stopcock with a syringe; the concentrations of the standards decreased only slightly (2-3 %) over a n 8-month period. All vpc peak areas were determined by repeated scans with a Gelman planimeter; reproducibility was within 1-277,. The data were recorded in Tables I, 11, V111, and IX. Small-Scale Decompositions to Determine k H / A . C I . The procedures described below apply to all small-scale decompositions (1.00 ml of solution) in which the relative yields of isobutene and l-cliloro-2-methyl-l-prope1iewere determined by vpc. The
concentrations were used. The peroxide-phosphine mixtures were allowed to stand for 3 hr at room temperature before vpc analysis. Quantitative determination of the relative amounts of isobutene and 1-chloro-2-methylpropene-1 was made by vpc analysis of equivolume injections of reaction and standard solutions. A 5 0 - ~ l Hamilton syringe fitted with a "Chaney adapter" was used to make iepetitive 25- or 50-p1 injections. Analyses were pel formed on an SF-96 column ( 1 5 f t X 0.25 in., 25% on 60-80 Chromosorb A. 70") on the F & M 700 instrument with an injector temperature of 1 7 5 , a detector temperature of 280 , and a helium flow of40 cc,"in; 33.4 min. The isobutene, 7.0 min; l-cliloro-2-1netliyl-l-~~ropene. column temperature was then raised to 300' to improve solvents and higher boiling products. The relative molar response l'actor for isobutene and I-chloro2-methylpropene-I was determined by the analysis of five standard solutions of varying concentrations to be 1.14 C 0.05. Subsequent measurements were used to confirm the validity of the correction factor for each particular analytical run. Peak areas of reaction products and standard reactions, as measured by five tracings with a Gelman planimeter, were generally reproducible to within 1-2y4. although slightly larger variations were evident on some of the smaller peaks. The measurement of peak areas is, in general, more precise under the conditions employed i n this study than the reproducibility of absolute or relative peak areas from injection to injection. The standard deviation i i i the determination or the relative molar response l'actor of -!=4:: represents a good measure of the precision of tlie determination of this study. The molar ratio of carbon tetrachloride to 1i)drogeii donor solvent was calculated from the weights of each. Each entry in Tables I11 and IV represents tlie results of a single reaction tube. Triplicate injections were made of some reaction tubes heated for the shortest times to determine the reproducibility of peak area and area ratios under these limiting conditions. A precision of +4% or better in absolute and relative peak areas was obtained in all cases. Decomposition of 3-MethyI-2-butenogl Peroxide in the Presence of 1-Chloro-2-methyl-1-propene.3-Metliyl-2-butenoy1 peroxide was decomposed in 6.22: 1 .OO cun1ene:carbon tetrachloride at 110.0 i 0.5" for 4 hr in the presence of deliberately added I-chloro2-metliylpropene-I. The peak arras for chloroolefin were detcrmined in the usual way for (A) 0.0618 M 3-metliyl-2-butrnoqI peroxide, (B) 0.0309 M peroxide and 0.0183 M chloroolefin, and (C) 0.0366 M chlorooletin. Results are shown in Table X. The ratio of chloride peak arealperoxide concentration due to peroxide decomposition was determined from A and assumed to apply to chloroolefin formed from peroxide in B. The ratio of peak areal
Webb, Kumpmeier
Reucfiuify of 2-Meihylpropenyl Radical
3738 Table X Tube
rii, M
Added IVCII. M
Peak area VCl(obsd)
A- 1 A-2 B- 1 B- 2 c-1 c-2 c-3
0.0618 0.0618 0.0309 0.0309 0 0 0
0 0 0.0183 0.0183 0.0366 0 0366 0.0366
175 171 254a 251a 328 338 3 24
I
Predicted peak area VCI = 252. chloroolefin concentration due to added chloroolefin was determined from C and assumed to apply to chloroolefin added to B, The sum of these predicted chloroo1ef.n peak areas for B gives a calculated peak area for B, which is compared to the observed chloroolefin peak area for B. The agreement between calculated and observed values demonstrates the stability of chloroolefin to the reaction conditions. Decomposition of 3-Methyl-2-butenoyl Peroxide in the Presence of 3-Methyl-2-butenoic Acid. A degassed carbon tetrachloride solution, 0.500 M in 3-methyl-2-butenoyl peroxide and 0.033 M in 3-methyl-2-butenoic acid, was heated at 78.0 f 0.2" for 12 hr. The solution was then analyzed for 3-metliyl-2-b~itenoicacid by vpc. Equivolume (50 p l ) injections of reaction solution and a standard solution of 0.033 I M in 3-metliyl-2-butenoic acid were injected on an SE-30 methyl column ( I O f t X 0.25 in., 10% on 45-60 acid-washed Chromosorb W, F & M 720 instrument) at 100" with an injector temperature of 240', a detector temperature 3-metliyl-2-buteiioic of 310', and a helitmi Row of 50 cc,"in: acid. 10.4 min. The average peak area for the solution containing acid was 280.8. Since the yield of acid produced in the thermal decomposition of 3-methyl-2-buteiioyl peroxide is immeasurably small
at this peroxide concentration, the added acid was therefore recovered unreacted. 2-Methylpropene was not detected; analysis of standard solutions showed that 0.25 2 yield was readily observable. 3-Methyl-1,1,1,3-tetrachlorobutane. Authentic material was prepared by the benzoyl peroxide catalyzed addition of carbon tetrachloride to 2-methylpropene: bp 79-83" (21 mm); u 1 7 , 5 ~1.4855 (M3*bp 64-75' (7 mm); i i Z 0 1.4850); ~ nmr 3.408 (s, 1 H), 1.85 (s, 3 H); ir 3040, 2990, 765, 705 cm-I. 3-Methyl-l,l,1,3-tetrachlorobutane was identified as a reaction product in k H / k C i runs by vpc retention time. Approximately 0.05 M 3-methyl-2-butenoyl peroxide in 17 : 1 to1uene:carbon tetrachloride solvent mixtures was decomposed at both 110.0 i 0.5" for 4 hr and 78.0 i 0.2" for 12 hr. Analysis on an SE-30 methyl column (10 ft X 0.25 in., 1 0 2 , temperature programmed at 2"/min from 70 to 90" and held at 90", He flow 100 cc/min, F & M 720 instrument, injector 250", detector 310") gave a peak which was enhanced i n size, but not altered in shape, by the coinjection of authentic 3-methyl-l,l,l,3-tetrachlorobutane. Decomposition of 0.1034 M 3-methyl-2-butenoyl peroxide in a 10.14: 1.00 p-chlorotoluene-carbon tetrachloride solvent mixture at 78.0 i 0.2" for 24 hr (100% conversion) also gave a peak which was enhanced in size, but not altered in shape, by the coinjection of authentic adduct. Decomposition for 10 min ( 1 7 z conversion) produced no detectable peak in this region, and the presence of a peak in this region was questionable for decomposition for 30 miii (37% conversion). Analyses of standard solutions of the isobutene to form adduct showed that reaction of 4 % would have been detected in the lowest conversion run (17%).
Acknowledgment, This work is described in detail in the Ph.D. Thesis of P. G. W., University of Rochester, 1970, and was supported, in part, by the National Science Foundation, GP 13475. (38) A. V. Topchiev, N. F. Bogomolova, and Yu. Ya. Gol'dfarb, Dokl. Akad. Narrk USSR, 107, 420 (1956).
Polyene Antibiotics. TI. The Structure of Tetrin A'*z Ramesh C. Pandey, Victor F. German, Yoshihiro Nishikawa, and Kenneth L. Rinehart, Jr.*3 Contribution f r o m the Department of Chemistry, Uniuersity of Illinois, Urbana, Illinois 41801. Received June 20, 1970 Abstract: Structure 1 (C31H51N013) has been assigned to tetrin A, from consideration of the structures of certain degradation products, including 3,15-dimethylhexacosane (7) and 12-methyl-13-hydroxy-2,4,6,8,10-tetradecapentam a l (15), and from nmr and mass spectral properties of a number of derivatives, especially N-acetyltetrin A and decahydrotetrin A.
T
he antibiotic tetrin, which inhibits the growth of yeasts and fungi, was first reported in 19604 and immediately recognized as a member of the family of antibiotics containing an isolated tetraene chroniophore.: Somewhat later we reported our initial chem(1) Paper I i n this series: I
