SUBSTITUENT EFFECTS ON THE SPECTRAL BEHAVIOR AND SYNTHESIS OF MERCURY 1,5-DIARYLTHIOCARBAZONATES

Symmetric and unsymmetric substituted 1,5-diarylthiocarbazones, and their mono- and bismercury complexes, were synthesized for spectral analysis. The first singlet-singlet transition of the mercury complexes was determined and the spectral shift produced by trifluoromethyl substitution was compared with that caused by different substituents in similar complexes. The large magnitude of the hypsochromic shift produced by the trifluoromethyl substituent can be explained by concerted steric and inductiveeffects, while the smaller bathochromic shift induced by the methoxy substituent is a result of opposing steric and electronic effects. In the trifluoromethyl substitution, a hypsochromic shift caused by steric influences was found to be 500cm-I in the photochromic unactivated state, and 250 cm-I in the photochromic activated state. A similar shift caused by inductive influences was found to be 750 cm-I in the photochromic unactivated state, and 600 cm-I in the photochromic activated state. The smaller spectral shift observed in the photochromic activated state is consistent with the elucidated structure of the unsymmetric 1,5-diarylthiocar- bazone, 6d, which was shown that the trifluoromethyl substitution was on the phenylazo portion of the molecule by chemical and spectral studies. (1981). En vue d'en faire une analyse spectrale, on a synthktise des diaryl-1,5 thiocarbazones substituees de faqon symdtrique et non symetrique ainsi que leurs mono et bis complexes de mercure. On a determine la premiere transition singulet-singulet des complexes de mercure et on a compare les deplacements produits dans les spectres par le substituant trifluoromCthyle avec ceux provoques par d'autres substituants dans des complexes semblables. On peut expliquer I'ampleur du deplacement hypsochrome . . provoque par le substituant trifluoromdthyle en se basant sur des effets inductifs et ste;iques concertes alors que la vale;; plus faible du deolacement bathochrome induite oar le substituant methoxv serait le resultat d'effets electroniaue et steriaue oo~oses. Dans le . - - cas du substituant trifluoromethyle, on a trouve que le deplacement hypsochrome provoque par des influences steriques est de 500 cm-I dans I'etat photochrome inactiveet de 250 cm-I dans I'etat photochrome active. On a trouve qu'undeplacement semblable provoque par des influences inductives est de I'ordre de 750 cm-I dans I'etat photochrome inactive et de 600 cm-I dans I'Ctat photochrome active. Les deplacements plus faibles observes dans I'etat photochrome active sont en accord avec la structure trouvee pour la diaryl-1,5 thiocarbazone non symetrique (6d) pour laquelle des etudes chimiques et spectrales on montre que le substituant trifluoromethyle se trouve sur la portion phenylazo de la molecule.

(E -4 x lo4). When irradiated by sunlight, solutions develop an intense blue color which changes back to orange when solutions are placed in the dark. The color change upon irradiation is due to a new absorption centered at 606 nm (E -4 x lo4), and to decreased absorption at 485 nm. The photochromic change is minimized in hydroxylic solvents, organic acids, and bases, and is most dramatic in dry, nonpolar solvents (3).
The absorption of 1 in the visible region of the spectrum can be attributed to the ligand since a solution of 1,5-diphenylthiocarbazonate ion (2b) exhibits a single strong absorption maximum at 470 nm (E -2 x lo4). l,5-Diphenylthiocarbazone  Closer examination of the spectral blue shifts produced by ortho substituents reveals that only relatively bulky substituents at this position cause a spectral shift. Steric influences cannot, however, explain the large spectral blue shift produced by 2-trifluoromethyl substituents in comparison with 2-ethyl substituents. This is demonstrated spectrally in mercury bis[l,5-di(2'-methylpheny1)thiocarbazonate], which shows an absorption maximum at 475 nm (as does the 2-ethyl substituted material), since the size of a methyl group is about the same as a trifluoromethyl group.
In order to explain the large spectral shift produced by 2-trifluoromethyl substitution, an investigation of the spectral behavior of symmetric and unsymmetric mercury 1,5-diarylthiocarbazonates with trifluoromethyl substitution has been undertaken.
Structure Determination of 1-(2'-Trijluoromethyl-pheny1)-5-phenylthiocarbazone Two isomeric products, 6d and 6e, could have been obtained in the synthesis of 1-(2'-tri-fluoromethylpheny1)-5-phenylthiocarbazone from oxidation of 5d. The. absorption properties of these two isomers, and their mercury complexes, would be different. Therefore, it was important to establish whether the isolated product was a mixture of 6d and 6e, or one favored product. This was of particular importance since it had previously been demonstrated by X-ray analysis (10) that the azo and hydrazo functions in the symmetric 1,5- The structure determination, Scheme 3, was achieved by employing the reported (1 1) reaction of thiocarbazones with phosgene to give 1,3,4-thiodiazol-5-ones. Phosgene reacts with the hydrazo portion of thiocarbazone to afford a relatively stable 1,3,4-thiodiazol-5-one (7d-f). Subsequent reduction (12) by zinc of the thiodiazolone produces an aryl amine (9d-f) and a thiosemicarbazide (10d-f). If the isolated thiocarbazone product were a mixture of 6d and 6e, then this sequence of reactions would yield amines 9d and 9e, and thiosemicarbazides 10d and 10e as products of reduc-tion. Isolation of a single amine and thiosemicarbazide pair (9d and 10d or 9e and 10e) would indicate that a single thiocarbazone product had been isolated. Further, if a single amine and thiosemicarbazide pair were produced, the position of the substituted aryl ring relative to the azo or hydrazo function of the thiocarbazone product would be established by the presence of the trifluoromethyl substituent on either the aryl amine (azo portion) or thiosemicarbazide (hydrazo portion).
When the reaction sequence was performed on Isomer R, R 1,5-diphenylthiocarbazone (6f), aniline (9f) was obtained from reduction of 2-phenylazo-4-phenyl-1,3,4-thiodiazol-5-one (7f), as identified by gas chromatographic and infrared spectral analyses (1 1). Reaction of the isolated thiocarbazone product (6d and/or 6e) with phosgene afforded a single orange crystalline product with elemental analysis (Cl5H9F,N,OS) and spectral properties suggesting a thiodiazolone structure. Reduction of the thiodiazolone with zinc and NaOH afforded two major products, a solid and a liquid. Infrared and gas chromatographic analyses of the liquid, when compared with a known standard, demonstrated the presence of 2-trifluoromethylaniline (9d) exclusively; no aniline was observed at the limit of detection sensitivity. The solid product melted at 198-2WC, and its infrared spectrum was identical to 1-phenyl-3-thiosemicarbazide (lOd).Z The isolated thiocarbazone product was therefore a single tautomer, 6d, with the 2-trifluoromethyl substituted aryl ring bound to the azo portion of the thiocarbazone group.  Table 1. It is observed that monosubstitution at the meta or para position does not change the position of the absorption greatly though a large spectral shift is induced by a relatively bulky ortho substituent or a trifluoromethyl group.

Spectral Properties of Mercury Complexes of 1,5-Diarylthiocarbazones
The spectral shifts produced by ortho substituents can be explained by steric and inductive effects. X-ray crystallography (13) shows that the atoms of both ligands in mercury bis(l,5-diphenylthiocarbazonate) exist primarily in a planar configuration. This configuration maximizes the interaction of x-electrons of the benzenoid rings and the chain. It seems likely that 2-methyl or 2-ethyl substituents will force the benzenoid rings out of the -N=N-C 4S \ plane and increase the energy required for photochromic activation, causing the observed blue shift. This explanation is consistent with the observation that fluorine or chlorine in the ortho position does not cause spectral shifts (while 2-methyl substitution does) since these substituents are smaller than methyl. However, the large spectral shift caused by methoxyl and trifluoromethyl substituents cannot be accounted for by steric effects alone, as asserted by Coleman et al. (5).
10-15 nm relative to bis-complexes, (e.g., I), Table  2. This small hypsochromic shift may result from purely steric effects. Since the Hg-S-C bond angle is likely to be the same as in the bis-complex, the azo-benzenoid ring is twisted out of the chromophoric plane due to the presence of the phenyl group.
In order to assess the individual contributions of the steric and inductive effects, 1,5-diphenylthiocarbazones with a trifluoromethyl substituent in only one of the benzenoid rings, and the mono-and bismercury complexes of these ligands, were studied, Table 2. From these data, one can infer the magnitude of the blue shift produced by steric effects to be about 500 cm-' in the unactivated state, and about 250 cm-I in the activated state, assuming that the blue shift observed in phenylmercuric 1 3diphenylthiocarbazonate (11) is only due to steric effects. The magnitude of the blue shift induced by the inductive effect of the trifluoromethyl group is about 750 cm-I in the unactivated state, and about 600 cm-I in the activated state, if we assume the blue shift observed in mercury bisll-(2'-trifluoro-methylpheny1)-5-phenylthiocarbazonate], 12, is solely due to inductive effects. The observed blue shift produced by the electron-withdrawing trifluoromethyl group is adequately explained in this manner.
The bathochromic shift, 1000 cm-l, observed in mercury bis[l,5-di-(2'-methoxypheny1)thiocarbazonate], Table 1, is most likely the result of opposing steric and electronic effects. Assuming steric hindrance is responsible for a blue shift of about 500 cm-l, as above, the actual electronic effect of the two methoxyl groups in this complex can be estimated to be 1500 cm-l. Along these lines, the observed spectrum of mercury bis[l,5-di-(2'-methyIphenyl)thiocarbazonate] is consistent with the very weak electron donating power of methyl groups.
It is interesting to note that inductive and steric effects in the activated form, e.g., phenylmercuric 1-(2'-trifluoromethylpheny1)-5-phenylthiocar-bazonate (13), are smaller than those in the unactivated form. This is consistent with the proposed photochromic mechanism which involves a cistrans isomerization of the azomethine group and a rate determining proton shift (4). Since the main chromophore responsible for absorption is on the phenylazo portion of the molecule which, upon activation, is changed to hydrazo bonding whose contribution to the observed absorption is much smaller. The benzenoid ring with the trifluorome-thy1 substituent is no longer conjugated with the absorbing chromophore upon activation, and the inductive and steric effects of the trifluoromethyl group are reduced.

General
The absorption spectra of the mercury complexes were recorded on a Cary 14 spectrophotometer. The infrared source, a General Electric CPR tungsten lamp having a color temperature of 3075 K, of the spectrophotometer was used to irradiate the photochromic solutions and the absorption spectrum of the equilibrium mixture between the activated and unactivated forms was measured. Infrared spectra were recorded on Perkin-Elmer 567 and 180 spectrophotometers. Analytical gasphase chromatography was performed using a Varian Aerograph Model 920 chromatograph, with a 6 ft by 114 in. SS 10% Carbowax 1540, 40% Chromosorb P/W PAW 80-100 mesh column. Melting points were determined on either a Thomas-Hoover capillary or Fischer-Johns melting point apparatus. Elemental analyses were determined by Galbraith Laboratories, Inc., Knoxville, TN.
Trifluoromethylanilines were purchased from Aldrich Chemical Co., Milwaukee, WI. All other chemicals were reagent grade and used without further purification.
A maroon precipitate was filtered and purified by two recrys-   tallizations from 400 mL of boiling EtOH, yielding 60 g 4a. Meta and para derivatives (4b, 4c) were prepared in a similar fashion. Elemental analyses and prominent infrared bands are reported in Table 3 and was suspended in EtOH (400 mL), treated with (NH,),S solution (60 mL), and stirred until the solid dissolved. The mixture was poured into 2 L of ice water, the light yellow thiocarbazide, Sa, was filtered and dissolved in 2% aqueous NaOH (600 mL) with heating. After cooling the solution in an ice-water bath, it was titrated with 1 N HCI to pH 5. A green prec~pitate (6a) was filtered and purified by repeated dissolution and titration. Meta and para derivatives (6b, 6c) were similarly prepared. The prominent infrared bands and melting points are tabulated in Table 5. Compound 4d was converted to unsymmetric thiocarbazone in the same fashion to compound 6d: mp 112-1 14°C; ir(KBr): 3200, 1602, 1586, 1524, 1496, 1464, 1442, 1320,1276, 1220, 1198, 1166, 1104, 1054, 1032,752 cm-I.
(2) Preparation of Mercury Complex of Thiocarbazones The mercury complexes were prepared by reacting thiocarbazone with equal molar amounts of either phenylmercuric chloride or mercuric chloride to form mono-or bis-complex, respectively, in a CH2C12/H20 (I: I) mixture. The organic layer was separated and the complex was precipitated out by the addition of MeOH.