Quinoid compounds

Similarly, indole itself could be converted by 2-methylsulfanyl-l,3-dithiolium iodide to its 3-dithiolium derivative, which gave 27 quantitatively with DBU. However, treatment of indoles, which bear the benzo-dithiolium moiety in the 2-position with tertiary amines, resulted in a black reaction mixture. All attempts to isolate the o-quinoid compound 28 failed (Scheme 7). 

The chemistry of quinone dyes has been discussed in a series of books entitled The Chemistry of Synthetic Dyes, edited by Venkataraman.1 The general chemistry of quinoid compounds has been discussed by Patai.2 There have been many books that cover quinoid compounds as dyes and pigments but very few discuss the chemistry of the corresponding leuco dyes. Traditional vat dyes are applied to cellulosic fiber in the leuco form. The chemistry of the leuco form of vat dyes is rather simple. Some leuco quinones are quite stable in the solid state and can be stored for a year. Other leuco dyes are unstable in solution and gradually undergo aerial oxidation. 

Some quinones, having the ability to form intra- and/or intermolecular hydrogen bonds, exhibit high molecular hyperpolarizability and are third-order nonlinear optical (NLO) materials. Compound 39 has a %(3) of 5 x 10 11 esu at 1.9 pm, and is a third-order NLO material.23 The optoelectric properties of quinoid compounds correlate with their structures in crystals or on thin films.23... 

Keywords Heterophene Phosphorus Phosphoryl compounds Quinoid compounds Thiophene... 

One of the most important properties of quinoid compounds is the two step redox reaction. Quinoid compounds undergo one electron reduction to so-called semiquinone anion radicals, and further one electron reduction of semiquinone anion radicals gives dianions (Scheme 14). 

Patai S (ed) (1974) The chemistry of the quinoid compounds, parts 1 and 2. Wiley, London... 

However, because of the mostly very slow electron transfer rate between the redox active protein and the anode, mediators have to be introduced to shuttle the electrons between the enzyme and the electrode effectively (indirect electrochemical procedure). As published in many papers, the direct electron transfer between the protein and an electrode can be accelerated by the application of promoters which are adsorbed at the electrode surface [27], However, this type of electrode modification, which is quite useful for analytical studies of the enzymes or for sensor applications is in most cases not stable and effective enough for long-term synthetic application. Therefore, soluble redox mediators such as ferrocene derivatives, quinoid compounds or other transition metal complexes are more appropriate for this purpose. 

Pulping additives such as quinoid compounds increase the yield of the pulp mass up to 4% [128]. For commercial application the most promising additives are anthraquinone (AQ) or the more convenient soluble salt of tetrahydroan-thraquinone (THAQ). If AQ or THAQ could be obtained at a price below 2/kg it would find a substantial market as a pulping additive [129], Commercial production of THAQ is now based on the partial thermochemical oxidation of naphthalene. In recent years, however, the lure of the pulp market has promoted several attempts to develop a process for the electrosynthesis of THAQ based on the indirect electrooxidation of naphthalene to naphthaquinone (NQ) with Ce4+, according to the stoichiometry of the reactions 1, 2 and 3. 

The combination of the di(l-azulenyl)methylium units produced dicationic species with high stabilities. However, transformation of the dication 212+ to the quinoid compound 21 as a Wurster type violene-cyanine hybrid was not achieved due to the instability of the reduced species. 

To understand the overall biological activity of quinoid compounds, it is necessary to study the chemical properties of these substances. Inasmuch as the cellular damage that is induced by quinones resembles that seen after radiolysis, the most prominent reactions involving quinones are probably DNA damage and generation of oxygen free radicals. 

S. Patai, The Chemistry of Quinoid Compounds, Teil 1, S. 2, John Wiley Sons, London New York Sydney Toronto 1974. 

Finally, some diradicals can be made in situ by an internal hydrogen-transfer reaction from a suitable hydrogen donor to a carbene or nitrene. In benzene derivatives, this is a well-tested route to o-quinoid compounds, which are not biradicals, although a biradical valence structure probably makes a significant contribution to their electronic structure. However, if the donor and the carbene or nitrene are... 

Quinones and quinoid compounds (e.g., 1,4-quinone, 1,2-quinone, 1,4-quinonedii-mine, 1,4-quinonemethide) (Figure 14.24) are electrophiles capable of reacting with... 

The quinoid compound 315 was synthesized by photochemically converting 313 to its deep-blue closed form 314 in acetonitrile, followed by the addition of excess potassium ferricyande and aqueous potassium hydroxide. Irradiation of a solution of 313 resulted in the appearance of a deep-blue color and absorption bands at 590 and 340 nm due to the generation of the closed isomer 314 (94JCS(CC)1011 95CEJ285). 

S. Patai (ed.) The Chemistry of the Quinoid Compounds, Parts 1 and 2, J. Wiley Sons, London-New York, 1974. 

Commercial anthraquinoid vat dyes are dye preparations that consist of a vat-table colored pigment and a dispersing agent. Such vattablepigments are polycyclic quinoid compounds that contain two or more carbonyl groups in a closed system of conjugated double bonds (Section 3.4). 

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