Lars Carlsen

β-Thioxo-ketones. Part 5. Photo-induced enol–enethiol interconversion of β-thioxo-ketones

Thioacetylacetone, which exists in 2-methylbutane–methylcyclohexane (5 : 1) solution at 95 K exclusively as the intramolecularly hydrogen-bonded enol tautomer, is converted upon irradiation at 353 nm into the corresponding enethiol tautomer, characterized by its absorption at 288 nm. The reverse process takes place upon irradiation of the enethiol tautomer at 288 nm. Both processes are successively repeatable. Other isomeric and/or tautomeric forms have not been observed. Monothiodibenzoylmethane behaves similarly upon photolysis at 95 K.

β-Thioxoketones. Part 6. Electronic absorption spectra of aromatic β-thioxoketones. A study of enol–enethiol tautomerism

Aromatic β-thioxoketones exist in solution as mixtures of rapidly interconverting Z-enol and Z-enethiol tautomers. The electronic absorption spectra exhibit in general four absorption bands in the u.v.–visible region at ca. 265 (ArCO, π,π*; ArCC π,π*), 330 (ArCS π,π*; OCCCS π,π*; CO n,π*), 415 (OCCCS π,π*), and 520 nm (CS n,π*), respectively. The β-thioxoketones are converted by sodium hydroxide into the corresponding anions. CNDO/B Calculations predict that the negative charge in the β-thioxoketonates is delocalized over the OCCCS system, suggesting simultaneously sickles or W shaped conformations. Two characteristic absorption bands found for the β-thioxoketonates at ca. 275 and 400 nm are assigned to π,π* transitions involving the Ar–CCC–Ar′ and SCCCO chromophores, respectively. The enol–enethiol tautomeric equilibrium has been studied by means of low temperature spectroscopy. At room temperature equilibrium constants (K293) of 3–5 have been found corresponding to a 4 : 1 enol–enethiol concentration ratio. The reaction entropy (ΔSr) has been found to be negative for the enethiol→enol conversion, reflecting the intramolecular O–H ⋯ S hydrogen bond to be considerably stronger than the corresponding O ⋯ H–S hydrogen bond. Variations in ΔSr and K293 as functions of substitution in the aryl group next to oxygen are discussed.

Thiocarbonyl azide s-oxide—II: The decomposition of thiobenzoylazide s-oxide

Abstract The reaction between thiobenzoyl chloride S oxide 4 , (R = C 6 H 5 ) and the azide ion at -80° leads to the labile thiobenzoyl azide S -oxide 5 , (R = C 6 H 5 ) Raising the temperature to -40° initiates decomposition of the latter to benzomtrile, nitrogen, sulfur and sulfur dioxide The thermally induced process was monitored by differential thermal analysis (DTA) which yielded a maximum heat effect at -11° The derived reaction enthalpy is ΔH=−45.6 kcal mole −1 and the activation parameters are ΔH ≠ = 20.2 kcal mol −1 ΔS ≠ = 6.3 eu (at −11°). The DTA shape index (S) and the reaction type index (M) are found to be in excellent agreement with a rate controlling first order reaction. Apart from the main peak at -11°, lack of a temperature difference signal throughout the range of measurement rules out an enthalpy-significant azide isomenzation and further suggests that decomposition takes place from a single isomer. Semi-empirical energy barrier calculations provide a rationale for the single conformer interpretation. The data are consistent either with a reaction in which N 2 and SO are expelled simultaneously or with the formation of a short-lived intermediate arising from N2 loss which rapidly eliminates sulfur monoxide. Intermediate formation of thiatriazole S -oxide cannot, however, be ruled out unambiguously. Since thioazides cyclize readily to thiatriazoles, whereas thioazide S oxides are not observed to cyclize, MO calculations have been carried out for the ring closures 2→3 and 5→6 (R= H) Orbital correlation diagrams for each potential energy surface show that ring formation is “allowed” in both cases. It is suggested that the variable chemical behavior of thioazides and their S -oxides is due to disruption of aromatic character in the hypothetical thiatriazole S -oxide product.

Carbonyl sulfides as possible intermediates in the photolysis of oxathiiranes

Abstract Diphenyl oxathiirane, formed by irradiation of thiobenzophenone S-oxide at 77 K, is photochemically converted into a blue, thermally unstable compound which decomposes at ca 100–110 K (λ max 550 nm, (ϵ ca 11,000). Lack of change in magnetic susceptibility during the light induced conversion of sulfine to ketone via the oxathiirane and the subsequent blue intermediate implies the absence of triplet and biradical singlet transients. The unknown carbonyl sulfide functionality, R 2 Cue5fbOue5fbS, thereby emerges as a strong candidate for producing the visible absorption. Comparison of the wave functions for CH 2 ue5fbSue5fbO and CH 2 ue5fbOue5fbS arising from MNDO limited CI geometry optimizations leads to the conclusion that the carbonyl sulfide structure is best described as a zwitterion rather than as a singlet biradical. The failure to observe cycloaddition products between the blue species and several dipolarophiles is rationlized in terms of a labile carbonyl suffide intermediate capable of facile sulfur extrusion from a long, weak O-S bond. Finally, the electronic absorption spectra of a series of para -substituted benzaldehyde O-sulfide model system have been calculated with CNDO/S-CI and correlated with the λ max s of the corresponding series of diaryl blue substrates. The sum of the available experimental and theoretical data is consistent with the existence of closed shell carbonyl sulfides as observable, though labile, intermediates from the photolysis of oxathinanes.

Tetrathiafulvalene S-oxide: a potential ‘donor impurity’ in the organic metal TTF–TCNQ

Tetrathiafulvalene S-oxide, which because of its size similarity with tetrathiafulvalene is a potential ‘donor impurity’ in the organic metal TTF–TCNQ, was prepared and characterized spectroscopically. Experiments in which tetrathiafulvalene S-oxide was purposely doped into TTF–TCNQ indicate, however, that the S-oxide is not of major importance for the electrical conductivity of the TTF–TCNQ crystals. The surface of TTF–TCNQ crystals, which had been exposed to air, was analysed by means of ESCA spectroscopy. The results strongly indicate the presence of a totally oxidized surface

5-phenyl-1,2,3,4-thiatriazole-3-oxide: A new class of heteroaromatic N-oxides

Abstract Oxidation of 5-phenyl-1,2,3,4-thiatriazole (1) with peroxytrifluoroacetic acid yields 5-phenyl-1,2,3,4-thiatriazole-3-oxide (2) a representative of a new class of heteroaromatic N-oxides. The structure is based on the mass spectral fragmentation of 2 and the isotope labelled with 15N at position 2. IR and ESCA measurements are consistent with this assignment. The thermal, photochemical, and chemical properties of the oxide are discussed.

The reaction between thiobenzoyl chloride S-oxide and azide ions

Thiobenzoylchlorid-S-oxid (I) reagiert mit Azidionen unter Annahme einer primaren Bildung des Azids (II) zu den Spaltprodukten (III)-(VI).

On hydrogen bonding in the intramolecularly chelated tautomers of enolic malondialdehyde and its mono- and dithio-analogues

The intramolecular hydrogen bondings in enolic malondialdehyde and it mono- and dithio-analogues have been evaluated by a semiempricial SCF–MO–CNDO method. The calculations predict that the hydrogen bonds play an important part in the stabilities of malondialdehyde and monothiomalondialdehyde, whereas dithiomalondialdehyde hardly exists as a hydrogen-chelated tautomeric form.

Oxathiirans. Part 5. Oxathiiran O-oxide, a possible intermediate in the reaction between singlet oxygen and thiocarbonyl compounds

The reaction between thioformaldehyde and singlet oxygen has been investigated theoretically within a CNDO/B framework. Potential energy surface calculations predict a multistep mechanism involving primary formation of an oxathiiran O-oxide, which rearranges into a 1,2,3-dioxathietan system. Two possible rearrangement pathways are discussed. The four-membered ring is tentatively suggested to decompose via a biradicaloid intermediate.

Oxathiirans as intermediates in the photolysis of sulphines

Irradiation of thiobenzophenone S-oxide (8) in the region corresponding to its long-wavelength absorption (λmax. 329 nm), in various solvents at room temperature, gave benzophenone in quantitative yield. At 85 K the photolytic transformation was monitored by electronic absorption spectroscopy. In EPA glass or PVC film a monomeric compound (390) with a long-wavelength absorption at 390 nm was formed. Heating gave rise to benzophenone in quantitative yield. On irradiation of (390) in its long-wavelength absorption region, a monomeric blue intermediate (550), with a long-wavelength absorption at 550 nm, is formed. Heating the glass containing (550) led to benzophenone and S- and O-phenyl thiobenzoate in 85, 14, and 1% yields, respectively (g.l.c.). Compound (390) is identified as 3,3-diphenyloxathiiran. Structures for the intermediate (550) are suggested.