COLORED PHOTOPRODUCTS OF CHROMENES AND SPIROPYRANS
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Proof of Structure of the Colored Photoproducts of Chromenes and Spiropyrans
by Jaroslav Kolc and Ralph S. Becker Department of Chemistry, University of Houston, Houston, Tezas
77004 (Received March 19, 1967)
Based on infrared, nuclear magnetic resonance, independent synthesis, and ultraviolet data, strong evidence for the structures of the colored photoproducts of the chromenes and spiropyrans is presented. The structure in the case of the chromenes is o-quinoneallide (11). A parallel structure is appropriate for the spiropyrans.
Introduction I n the course of investigation of spectroscopic and photochromic properties of spiropyrane, photochromism of the chromene half of such molecules was discovered in this laboratory’ and structure I1 proposed for the colored f0rm.l
I
R
’
qyq
a
O
R
RR
Va, R = H, R’ = CHBO b,R=C,Hs,R’-H
VI /
A
LiAIH,
11
Photochromism of spiropyrans has been known for some time, although, up to the present time, only one indirect piece of evidence has been given for the nature of the colored form of spiropyrans, which is considered to be as in IV
VII,R=C&, R’-H
W I , R = H, R’ = CHBO
The colored product is expected to react with lithium aluminum hydride giving phenol VI1 or VIII. Such a phenol can be identified using infrared, nuclear magnetic resonance, and ultraviolet spectroscopy as well as by comparing such spectral data with those of independently synthesized compounds.
Experimental Section 111
Iv
This evidence was based on the resemblance of the absorption spectrum to that of merocyanine dye.2 The purpose of this paper is to give more direct evidence for the structure of the colored photoproduct 11. This will be based on the reduction of the photoproduct with lithium aluminum hydride a t temperatures a t which the photoproduct is being produced (-30 to -75”) and the identification of such reaction product. The reaction sequence would be expected to be
For photoconversion of chromenes, quartz cells were immersed into a cooling bath (hexane-Dry Ice) in a quartz dewar flask and irradiated with ultraviolet light from a low-pressure mercury lamp, filtered through a Corning 9-30 filter. For thin layer chromatography Chroma-Plates 7GF (Mallinckrodt) with Silicar (pH 6.5-7.2) were used, and detection was made by ultraviolet light. (1) R. 5. Becker and J. Michl, J . A n . Chem. SOC.,88, 5931 (1966). (2) R.Heiligman-Rim, Y. Hirshberg, and E. Fischer, J . Chem. SOC., 156 (1961); J . Phys. Chem., 66,2465 (1962).
Volume 71, Number 1.9 November 1967
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Infrared spectra (in carbon tetrachloride) were taken on Beckman IR-10 apparatus. The nuclear magnetic resonance (nmr) spectra (in the same solvent) were obtained on a Varian HA-100 high-resolution spectrometer. Ultraviolet spectra were taken on Cary Model 15 instrument using quartz optical cells. The 2,2-diphenyl-2H-chromene was obtained from Dr. Livingstone of Huddersfield College of Technology, England ; lapachenole (2,2-dimethyl-6-met hoxy-7 ,8benzo-2H-chromene) from Dr. J. W. Morgan of the Forest Products Research Laboratories, England; and 6-methoxy-2H-chromene from Sankyo Co., Ltd., Japan. The 2-allyl-4-methoxyphenol and 2-propenyl-4-niethoxyphenol necessary for comparison were synthesized3~~ from p-methoxyphenol (Eastman White Label). The intense red color of the photoproduct, created by ultraviolet irradiation of the solution of 2,2-diphenyl-2s-chromene in 2-methyltetrahydrofuran (2MeTHF) at -75”, rapidly disappeared by addition of lithium aluminum hydride at this temperature. The reaction mixture was treated with water and sodium hydroxide solution, acidified, extracted into ether, and evaporated to dryness. Thin layer chromatography revealed a spot with Rr 0.6 in addition to the main spot of the starting chromene (going with the front of the solvent mixture CC14-CHC13 = 2 : 1). The same substance was produced in much greater quantity when a solution of the chromene in a slurry of lithium aluminum hydride in 2-RleTHF was simultaneously mixed and irradiated at -75” for 75 min. Whenever mixing during the irradiation was interrupted, the red color of the photocolored form of the chromene was created on the inner surface of the cell facing the source of irradiation and disappeared when the mixing was continued. The reaction product was purified using column chromatography on neutral silica gel (pH 6.95) and spectra of the pure product (ca. 50% of weight of starting chromene) were taken. No such product was detected when the chromene was treated with a slurry of lithium aluminum hydride in 2-MeTHF under the same conditions (temperature, time) without irradiation. 6-Rlethoxy-2H-chromene and lapachenole were converted into phenols under similar conditions. Again, no products were detected when the chromenes were treated with lithium aluminum hydride without irradiation.
Results and Discussion Conversion of 2,2-Diphenyl-2H-chroene into Phenol V U . There are two peaks in the infrared 0-H region of the product, Figure 1A (plus a shoulder a t higher The Journal of Physical Chemistry
JAROSLAV KOLCAND RALPHS. BECKER
I 000
1000
2000
1600
1200
W A V E L E N G T l (CM-‘)
Figure 1. Infrared spectra: (A) phenol \TI, (B) phenol IX, (C) 2-allyl-4-methoxyphenol, (D) phenol VIII, and (E) 2-propenyl-4-methoxyphenol.
concentrations). The same pattern is obtained for oallylphenol~,~ where the peak a t higher energy corresponds to the 0-H frequency of the free OH group, and the second one, to the intramolecular hydrogen-bonded OH species of the type CH2-CH
&-)The nmr spectrum, Figure 2A, shows a doublet of two protons a t 7 6.75 (-CH2-), a triplet of one proton centered a t 7 3.98 (-CH=C-, conjugated), and a set of 14 aromatic protons (T 2.7-3.6). Both the infrared and nmr spectra are fully consistent with structure VII. (3) D. S. Tarbell in “Organic Reactions,” Vol. 2, John Wiley and Sons, Inc., New York, N. Y., 1947, p p 1-48. (4) J. H.Fletcher and D. S. Tarbell, J . Am. C h m . SOC.,65, 1431 (1943). (5) A. W.Baker and A. T. Shulgin, ibid., 80, 5358 (1958).
COLORED PHOTOPRODUCTS OF CHROMENES AND SPIROPYRANS
Nmr peaks in Figure 2B corresponding to four aromatic protons H-Hd in I X as well as the singlet 6.20 (MeO-) are a t the same position as in the lapachenole. A single >CMe2 in the lapachenole (7S.5S) was changed to the singlet r 8.25 in the product, corresponding to C=CMe2. Further, there is a doublet of two protons a t 7 6.72 (-CH2-), a triplet of one proton at r 4.75 (-CH=G--, nonconjugated), a singlet a t T 3.70 belonging to the Hs in IX, and a singlet a t T 5.06 which can be depressed by deuteration with D2O and thus corresponds to OH. The ultraviolet spectrum of the product in 3-methylpentane a t room temperature is quite similar to the spectrum of the simple 1-naphthol. On the basis of the foregoing evidence we can write the reaction product as
I 2.0
6.0
4.0
8.0
I
L ' 4.0
6.0
2.0
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8.0
H 2
IX
CmwerSim of 6-Methoxy-2H-chromene into Phenol VIII. I n this case the structure of the product was proved by comparison of the infrared, Figure lD, and
I 2.0
6.0
4.0 PP*
8 1
f,)
Figure 2. Nmr spectra: (A) phenol VII, (B) phenol IX, and (C) phenol VIII.
Conversion of Lapachenole (2,2-Dimethyl-6-methozy7,8-benzo-2H-chromene) into Phenol I X . As in the previous case, the infrared spectrum of the product, Figure lB, shows two peaks in the 0-H region (a free OH and intramolecular bonded OH). I n this case, the peak corresponding to the intramolecular bonded OH is especially strong. It seems to be due to the fact that basicity of the T electrons in the double bond of the side chain are increased by the presence of two attached methyl groups, which increases the strength of the hydrogen bond.s The spectrum of the deuterated phenolic product shows essentially no change in the mutual ratio of both 0-D peaks compared with the 0-H peaks.
nmr data, Figure 2C, with those of the independently synthesized authentic 2-allyl-4-methoxyphenol, Figure lC, and 2-propeny1-4-methoxypheno1, Figure 1E. The spectra are identical with those of the last named compound. Creation of the propenylphenol in this case is possible to explain as a consequence of the absence of conjugative substituents and/or steric effects of substituents in the photoproduct. Results obtained from the three investigated chromenes with different structures are fully consistent with structure I1 as that for the photocolored product of a chromene. Moreover, the indoline portion of indolinospiropyrans does not play an active role in the formation of their colored form. At least studies by us on 1,3,3-trimethyl-2-phenyl-2-hydroxyindolineshow that the indoline does not exhibit photochromism. This, plus the results on the chromenes, provides strong evidence that the structure of the indolinospiropyran photoproduct is that given (IV). Other photochromic spiropyrans such as dibenzo-, K-methylquinolino-, acridinospiropyran, etc., should have colored photoproducts with parallel structures.
Acknowbdgments. We wish to thank Dr. 11. R. Willcott of this university for his assistance in the interpretation of the nmr data as well as those who Volume 71,Number 1.9 Nosember 1967
4048
NODA,SAITO, FUJINOTO, A N D NAGASAWA
gave us compounds as noted in the Experimental Section. This investigation was sponsored by U. S. Air
Force, Systems Engineering Group, Wright-Patterson AFB, Ohio, Contract AF 33(615)-1733.
Relationship between the Intrinsic Viscosity and the Sedimentation Coefficient of a Monodisperse Polymer
by Ichiro Noda, Satoshi Saito, Teruo Fujimoto, and Mitsuru Nagasawa Department of Synthetic Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan (Received April 3, 1967)
To study the hydrodynamic properties of dilute polymer solutions, the measurements of intrinsic viscosity and sedimentation coefficient of monodisperse poly (a-methylstyrene) in toluene (t) a t 25" and in cyclohexane (c) a t 39" were carried out. The observed sedimentation coefficient was extrapolated to meniscus to obtain the sedimentation coefficient a t 1 atni by using Fujita's equation. From the comparison between the intrinsic viscosity [ q ] and the frictional coefficient [f]in the same solvent, the relationship of [?It/ [qlc = ([fit/ [j]a)2*4 was obtained. This relationship is discussed in comparison with the current theories.
Introduction To investigate the hydrodynamic properties of dilute polymer solutions, it is no doubt pertinent t,o study both the intrinsic viscosity and the sedimentation coefficient (or diffusion coefficient) simultaneously, since different types of flow of the polymer coil are observed in those measurements, that is, the rotational flow in intrinsic viscosity and the translational flow in sedimentation and diffusion.' It cannot always be assumed that both the intrinsic viscosity and the sedimentation coefficient can be interpreted by using the same hydrodynamic radius. The intrinsic viscosities of flexible polymers have been extensively studied, but the rotational flow is so complicated that we are usually obliged to introduce some approximations into a theory which gives a relationship between intrinsic viscosity and molecular parameters.2 I n contrast to the intrinsic viscosity, according to the Kirkwood general theory of irreversible processes in polymer solutions, the translational frictional coefficient can be unambiguously related to the The Joztrnal
o/
Physical Chemistry
segmental distribution of polymer coil, ie., to the molecular parameters at partial drainage as well as a t the limit of nondrainage, whether the excluded volume effect exists or not. We believe that the translational frictional coefficient can be more clearly understood than the intrinsic viscosity. Unfortunately, however, it seems to us that most data of the sedimentation coefficients of flexible polymers should be carefully reexamined, because of the ambiguity arising from the polydispersity of the samples and also because the effect of the hydrostatic pressure on the sedimentation coefficient in organic solvents was not properly taken into account in the experiments so far reported. I n particular, there are only a few reliable and consistent data to clarify the relationship between the sedimentation coefficient and the intrinsic viscosity of flexible polymer^.^,^ The purpose of the present paper (1) J. G:Kirkwood and J. Riseman, J . Chem. Phys., 16, 565 (1948). (2) M. Kurata and H. Yamakawa, ibid., 29, 311 (1958). (3) J. G. Kirkwood, J . Polymer Sci., 12, 1 (1954).
