[CON~TRIBUTION FROM TRE BUREAU OF ANIMAL INDUSTRY, AGRICULTURAL RESEARCE ADMINISTRATION,UNITED STATES DEPARTMENT O F AGRICULTURE]
ULTRAVIOLET ABSORPTION SPECTRA OF SOME ALICYCLIC DIKETOXES AND TRIKETONES HARRY BASTRON, RUSSELL E. DAVIS,
AND
LEWIS W. BUTZ
Received July S, 194s
In connection with the characterization of some intermediates in projected syntheses, we have collected ultraviolet absorption data for sixteen alicyclic ketones. The compounds examined fall into four groups: Derivatives of 2-cyclohexene-l , $-diene, cyclane-1 ,2,4-triones, cyclane-1 ,3-diones, and compounds of incompletely known structure. All were crystalline solids, which were dissolved in ethanol for spectrophotometric examination. With the exception of the 2-methylcyclohexane-1,3-dione1 which mas prepared by methylation of cycIohe~ane-l,3-dione,~ all the ketones vere prepared by methods described in the literature. References to these publications, the melting points of the specimens used, and the concentrations in ethanol are given in Tables I-IV along with the results of the spectrophotometric measurements. In addition to the locations and intensities of the maxima and minima recorded in the tab!es, complete wave length-intensity curves are reproduced for eleven of the compounds in Figs. 1-7. A Bausch and Lomb large Littrow quartz spectrograph equipped with a sector photometer was employed. A condensed spark between high-speed steel electrodes served as light source. DERIVBTIVES O F
2-CYCLOHEXENE-1,4-DIDNE
This group consisted of six hexahydronaphthalene diketones-11, 111, IV, V, and T'I in Table I, and VI1 in Table IV-obtained by the addition of p-benzoquinonet; to conjugated dienes. Wassermann had previously investigated the ultraviolet absorption of xxxx-6 ,9-methano-2 ,7-naphthitadiene-1 ,4-dione, 1 . 3 Since those of his data which n-ere obtained with an ethanol solution are directly comparable m-ith ours and since his are the only measurements previously reported for a 2,7-naphthitadiene-l,4dione, we include this diketone in Table I. cis-2-Xethyl-2,7-naphthitadiene-l, 4-dione, 11, is structurally very like I, being a 5,lO-cis compound. The atoms attached to carbons 5 and 10 in the two compounds may differ a little in configuration because of the greater mobility of the cyclohexene ring in 11. The chief difference in the chromophore is the 2methyl group in 11. This substitution, if comparison be made directly with I, results in a displacement of the principal maximum of 150 toward longer wave lengths. This is exactly the displacement produced bp alkyl substitution, shown 1 This work was supported in part by an allotment from the Special Research Fund (Bnnkhead-Jones Act of June 29, 1935). Xot copyrighted. 2 By hIr. A. -\I. Gaddis of this laboratory. The specimen used was compared directly with a sample prepared by the method of Blaise (see Table 111). 3 Referred to by Wassermann as cyclopentadiene-p-benzoquinone. For the numbering and nomenclature employed here see the preceding three papers. For the configurational notation see Butz, Gaddis, Butz, and Davis, J . O r g. Chem., 6 , 3 8 3 , footnote (1940). 515
516
BASTRON, DAVIS, AND BUT2
by Woodward (1) and concurred in by Evans and Gillam (2), in cr,&unsaturated monoketones. TABLE I DERIVATIVES O F 2-CYCLOHEXENE-1, 4-DIONE M.P.
I xxxx-6,g-MethanoI1 cis-2-Methyl I11 5-Acetoxy-2,7,8-trimethyl IV xxxx-5-Acetoxy-6,9-ethano-2-methylb V xyyx-5-Acetoxy-6,9-ethano-2-methylb VI 2-Methoxy-5-methyl
("C)
mar(&
-2220
75-76 79.6-80.6
min
-
(A
MOLARITY
12800 3210
O.oooO5.005 .0000105.0021 ,00024.0024 .00016.0016 .000112.00112
-
116-117 8800
3290
84.7
2300 3690 2350
100 8200
-
93.5-95
2690
8400
-
123.4
-
-
-
REF. c
-
12" 13 14 14 14 6
The m.p. and absorption data in the table are taken from this reference. The configurations were assigned entirely on the basis of the Alder-Stein rule. Which of the two isomers is xxxx and which xyyx is therefore uncertain. 0
6
coMPouNLl
VI11 3-Methylcyclopentane-l,2,4-trione 3-Methylcyclopentane-l,2,4-trione monohydrate IX 5-Methyl-7-naphthitene-l-2,4-trione
M.P.(OC)
Am&)/
118.2-119.6 78-80 174-175
f
--
MOLARITY
PEF.
2750 2750 2750 2750
10500 7300 12500 9300
0.00087 .000087 .00096 ,000096
15
2560 3110
14500 3900
.000108
10
15
TABLE I11 CYCLANE-1 ,3-DIONES COMPOUND
M.P.(T)
~rnsx(A)
t
-__-
X I Cyclohexane-l,3-dione
105-107
X I 1 2-Methylcyclohexane1,a-dione XI11 2-Methylcyclopentane1,a-dione XIV 4-Hydroxy-2-methylcyclopentane-l,3-dione
205-208 212.2-214.6
2550 2800 2610 2620 2500
xmin(A
f
16000 20000 17000 15000
-
-
-
-
18000
-
-
MOLARITY
REF.
0.000158 .0000158 .000606 .000121 .000203
16
.OO085 ,000085
4
17 4
Moreover, the absolute value of the wave length of maximal absorption is the same, 2350 =k 50 A, in these enediones as it is in disubstituted enones (3). The
517
SPECTRA O F DI- AND TRI-RETONES
maxima of all five of our 2-methyl diketones fall within this range. Therefore, bringing a second carbonyl group into conjugation with an ct,p-enone system does not change the position of the short wave length maximum when the entire chromophore system i s within one six-carbon r i n g . If the enedione system is spread over two rings, the second keto group displaces the maximum toward longer wave lengths. There are many examples in the literature to illustrate this point. Thus 6-oxoprogesterone as a disubstituted enone should have its maximum a t about 2350 A; the experimentally found value is 2550 A (4). Ag~'O-0ctalindione-1 , 5 (5-naphthitene-l , 6-dione) as a trisubstituted enone might be expected to have it,s maximum a t about 2500 A; the experimental value (5) is 2630 A. It is interesting that a considerable difference was found, within the stated range, between the maxima for the two diastereoisomers, IV and V, while an analogous compound lacking the methano bridge (VII, Table IV) has the same TABLE IV OF INCOMPLETELY KNOWNSTRUCTURE SUBSTANCES
-
comom"
Y.P.
("c)
VI1 5-Acetoxy-2-methyl-6 109-110 (or 9)-vinyl-2,7-naphthitadiene-1 ,4-dioneb 206-210 X 5-Methyl-6(or 9)-vinyl7-naphthitene-l,2,4trioneb XV 4-Hydroxy-lO-methyl-7- 123.5, then 145-146 naphithitene-l,3dionec XVI Dimer of l-methylcyclo- 213.4-215.2 pentene-3,5-dione con taining a dicyclopenta -p-dioxin nucleus
f
2350 3450
8200 84
3160
MOLARlTY
REP.
0 .00014,0014
14"
2560 3050
13000 2830 3000
,00284,0013
140
2560
14000
,000146.00146
10
2520
19OOo
.00119
11
-
-
Probable structures or the two possible alternative structures. b Relative configurations a t carbons 5, 6, 10 (or 5,9, 10) unknown. e Relative configurations a t carbons 4, 5, 10 unknown.
4
maximum as V. The data for these three compounds, and those for I11 as well, show that the acetoxyl group at carbon 5, which is adjacent to the chromophore, has no infuence on the absorption. The chromophore in VI1 is certainly the same as those in 111, IV, and V; VI1 is placed here in Table IV because the position of the vinyl group has not been established. The principal maximum in the spectrum of 2-methoxy-5-methyl-2,7-naphthitadiene-1 ,4-dione, VI, is quite different from those of theo2-methyl analogs. Possibly the large displacement to longer wave lengths of 340 A is due to an additional olefin bond in conjugation. This could be furnished by enolization of the 1-carbonyl group. VI differs from the other diketones by its angle methyl group, but in view of the lack of effect of a similarly placed acetoxyl group upon the absorption, it seems unlikely that this methyl group makes an important contribution.
518
BASTRON, DAVIS, AND BUTZ
a$ H
io ' It
io
€I:
I
I1
I11 CHB
AcO 0
AcO 0
IV
V
VI
AcO 0
A
B
VI1
A IX
VI11
519
SPECTRA O F DI- AND TRI-KETONES
FIG.1. IlBSORPTION
I
I
3800
SPECTRUM OF CiS-2-METHYL-2,7-NAPHTHITADIENE-1,4-DIONEIN ETHANOL, O.ooOo5 TO 0.005 MOLAR
I
3800
I
3400
I
YM,
I
woo
I
I
A
I
2ao
FIG.2. ABSORPTION SPECTRUM OF 2-METHOXY-5-METHYL-2,7-NAPHTHITADIENE-1,4-DIONE IN ETHANOL, 0.000112 TO 0.00112 MOLAR
520
BASTRON, DAVIS, AND BUTZ
If 111,VI, and VI1 exist in ethanol solution principally as a diketone rather than the monoenol, we cannot be certain whether the absorption is due to the 5,lO-cis or 5,lO-trans isomers for reasons set forth in a discussion in the preceding paper (6). CYCLANE-1,2,4-TRIONES Closely related to the methoxy diketone, VI, are the 1,2,4-trione enols, IX and X. X is placed in Table IV because the position of the vinyl group is undetermined. The chromophores in IX and X are very similar, m can be seen from the positions recorded for the two maxima and the minimum. It will be ob-
FIG.3. ABSORPTION SPECTRA IN ETHANOL O F (1) Iv, TABLEI, 0.00024 TO 0.0024 MOLAR; (2) v, TABLEI, 0.00016 TO 0.0016MOLAR;(3) 111,TABLE I, o.oo@l1TO 0.005 MOLAR;(4) VII, TABLE Iv, 0.00014 TO 0.0014 MOLAR; AND (5) TABLEIv, 0.0013-0.00284 MOLAR
x,
served that the absorption due to the carbonyl group, maxima a t 3110 8 and 3050 A, is much more intense than in the 2-methylnaphthitadienediones. Indeed with some of the latter (I11 and V), and also the niethoxy compound VI, carbonyl absorption was either absent or masked. A comparison of the short wave length maxima of the two trione enols with the same maxima in the diketones shows that replacement of a 2-methyl group by a hydroxyl shifts the maximum about 200 to longer wave lengths while, as previously noted, replacement by a methoxyl group causes a still greater displacement of 340 8. While this effect of a methoxyl group seems not to have been
SPECTR.4 O F DI- AND TRI-KETONES
FIG.5 .
52 1
522
BASTROS, DAVIS, AND BUT2
observed before, the effect of the hydroxyl group has been observed and a number of examples have been brought together and discussed by Gillam et al. (7). Thus these investigators found that the monoketone, piperitone, shows the maximum 2355 8, while a-hydroxypiperitone (diosphenol, an enolic 1 ,2-diketone) has its maximum a t 2740 8. It is perhaps significant that 3-methylcyclope~tane-1,2,4trione, VIII, and its hydrate (Table 11)exhibit a maximum a t 2750 A. CYCLANE-1,3-DIONES
Having in mind the lack of influence of the second carbonyl group in the naphthitadienediones upon the ultraviolet absorption, it occurred to us that the
I
m-
I
I
I
I
I
I
/ ob=&!
a
I
I
I
I
I
maxima exhibited by the naphthitenetrione enols might be largely due to the 1,3-dione (or P-hydroxyenone) part of their structures. Examination of some simple 1,3-diones has proved this idea to be correct, and has demonstrated some other interesting effects of alteration of structure upon absorption. Cyclohexane-1 ,3-dione, XI, a t the higher concentration in ethanol, exhibited a maximum at 2550 8, which is almost identical with that found for the two naphthitenetriones. Woodward and Blout have recently (8) found a maximum a t 2580 A for 5,5-dimethylcyclohexane-l,3-dione.The usual effect of methzl substitution for hydrogen at an olefin carbon is seen in the maximum, a t 2610 A, shown by 2-methylcyclohexane-1,3-dione(XII). Next, passing from XI1 to its
SPECTRA O F DI- AND TRI-KETONES
523
analog in the cyclopentane series, XIII, we observe a shift in the maximum of 110 toward shorter wave lengths, a remarkable confirmation of the decrement of 110 d found by Gillam and West (9) while studying monoketones of the cyclohexene and cyclopentene series. The maximum found for 4-hydroxy-2-methylcyclopentane-l , 3-dione, X ,!I is very nearly the same as that of 2-methylcyclopentane-1,3-dione; a t 2490 A with the higher concentration in ethanol.
c
'KK)o
A
2aoo
2400
FIG.7. ABSORPTION SPECTRUMOF XVI, TABLEIV, IN ETHANOL, O.OOO119 TO 0.00119MOLAR EFFECT OF CONCENTFLATION UPON THE POSITION O F THE PRINCIPAL MAXIMUM I N ETHANOL SOLUTIONS O F CYCLANE-1,3-DIONES
It was with the hydroxy diketone, XIV, that we first observed a considerable shift in the position of the maximum on dilution. This is clearly seen from Fig. 5. Since this compound could exist in a great variety of tautomeric forms, three of which are shown in the figure, a change in the composition of the mixture of tautomers in solution was not surprising. We later found, however, that cyclohexane-1 3-dione behaves in the same way. Reference to Table 111 and Fig. 6 will show that ten-fold dilution results in a shift of the maximum from 2550 to 2800 A, and the intensity of the latter is actually greater than that of the former. The more dilute solution perhaps contained a greater proportion of 1,3-cyclohexadiene-l,3-diol.
524
BASTRON, DAVIS, AND BUTZ
APPLICATION OF THE ULTRAVIOLET ABSORPTION DATA I N STRUCTURE AKALYSIS
From a group of possible intermediates in the synthesis of polycyclic compounds, we have selected four cases (Table IV) to illustrate the use of the new absorption data. The close relationship of diketone VI1 to diketones 11,111,IV, and V, and of triketone X to triketone IX has already been indicated. Reduction of the triketone I X gave a dihydro derivative (10) which might, ,4-dione from its method of preparation, be 2-hydroxy-5-methyl-7-naphthitene-1 (XVII). XVII is not an a , P-enone and no intense absorption in the ultraviolet
0
0
XI
XI1
0
XI11
xv
XVI
CH8 0
XVII
XVIII
would be expected. The dihydro derivative obtained exhibited exactly the same maximum (XV, Table IV) m cyc1ohexane-ll3-dioneand the triketones IX and X, and therefore cannot be XVII and is almost certainly a 1,&diketooctalin. No derivatives of this compound have yet been made, but the absorption spectrum, taken with the observation that the compound is a strong acid, indicates it to be ,3-diones1XV. one of the diastereoisomeric 4-hydroxy-10-methyl-7-naphthitene-1 Finally it was found that dehydration of 4-hydroxy-2-methylcyclopentane1,3-dione, XIV, gave a beautiful crystalline compound which did not have the
SPECTRA O F DI- AND TRI-KETONES
525
chemical properties of the expected 4-methylcyclopentene-l , 3-dione, XVIII. Cryoscopic examination showed the substance to be a dimer, which finding immediately posed the question of structure. Literature background suggested structure XVI, containing two chromoph2re systems very similar to cyclane-1 ,3diones. The maximum found, a t 2520 A, is very similar to that exhibited by 2-methylcyclopentane-l , 3-dione, ahd XVI appears more reasonable than two alternative structures (11) and is supported by the chemical evidence. E~ELTSVILLE, &ID. REFERENCES (1) WOODWARD, J. Am. Chem. SOC.,63, 1123 (1941). (2) EVANSAND GILLAM, J. Chem. SOC.,815 (1941). J. Am. Chem. SOC.,64, 76 (1942). (3) WOODWARD, J.Org. Chem., 4, 512 (1939). (4) EHRENSTEIN, (5) CAMPBELL A N D HARRIS, J. A m . Chem. SOC.,63,2721 (1941). (6) ORCHIN AND BUTZ,J. Org. Chem., 8,509 (1943). (7) GILLAM,LYNAS-GRAY, PENFOLD, AND SIMONSEN, J. Chem. SOC., 60 (1941). AND BLOUT,J. Am. Chem. SOC.,66,562 (1943). (8) WOODWARD (9) GILLAMAND WEST, J. Chem. SOC.,486 (1942). (10) BUTZAND BUTZ,J. Org. C h a . , 8. 497 (1943). (11) ORCEINAND BUTZ,J. Am. Chem. SOC.,in press. (12) WASSERMANN, J. Chem. SOC.,1513 (1935). AND HAN,Ber., 68, 876 (1935). (13) CHUANG (14) BUTZAND BUTZ,J. Org. Chem., 7 , (a) 199; (b)208 (1942). (15) DIELB,SIELISCH,AND MULLER,Ber., 39, 1336 (1906). (16) HOFFMANN-LA ROCHE,German Patent 606,857 (April 4, 1933). (17) GADDIS,unpublished; BLAISEAND MAIRE,Bull. SOC. chim., (4) 3, 421 (1908).
