Developing agents catechol

As a developing agent, catechol tans the surface gelatin of the negative (see Tanning Developers, below). It is also easy to use catechol to compound formulas that create a desirable image stain density when low quantities of preservative (e.g., sodium sulfite) are used (see Image Stain, below). Both of these properties it shares in common with pyro. 

Silver catalysis of the reduction of silver ions appears to be a necessary condition for normal development. The reaction of developing agents including several types of chemical compounds, e.g., hydroquinone, p-aminophenol, hydroxylamine, catechol, and p-phenylenediamine, are known to exhibit this catalysis to a high degree. 

Even though it has been in use since 1880 pyrocatechin (catechol) is one of the most overlooked developing agents. The working properties of catechol are very much like those of hydroquinone and it can even be used as a substitute for hydroquinone in many formulae, though it works more rapidly than hydroquinone. 

Hydroquinone [123-31 -9] represents a class of commercially important black-and-white chemical reducing agents (see Hydroquinone,RESORCINOL, AND catechol). The following scheme for silver haUde development with hydroquinone shows the quantitative importance of hydrogen ion and haUde ion concentrations on the two half-ceU reactions that describe the silver—hydroquinone redox system ... 

There is also some evidence for subtypes of COMT but this has not yet been exploited pharmacologically. Certainly, the majority of COMT is found as soluble enzyme in the cell cytosol but a small proportion of neuronal enzyme appears to be membrane bound. The functional distinction between these different sources of COMT is unknown. COMT inhibitors also exist (e.g. pyrogallol), mostly as catechol derivatives, but so far, most have proved to be highly toxic. Only recently have drugs been developed which are selective for COMT one of these agents, tolcapone, is used currently in treatment of Parkinson s disease (see Chapter 15). 

New materials are also finding application in the area of catalysis reiated to the Chemicals industry. For example, microporous [10] materials which have titanium incorporated into the framework structure (e.g. so-calied TS-1) show selective oxidation behaviour with aqueous hydrogen peroxide as oxidizing agent (Figure 5). Two processes based on these new catalytic materials have now been developed and commercialized by ENl. These include the selective oxidation of phenol to catechol and hydroquinone and the ammoxidation of cyclohexanone to e-caproiactam. 

The suggested mechanisms differ in detail (Mott, 66, 67 Berg, 68 Anastasevich, 69 Frank-Kamenetskii, 70 Bagdasar yan, 17, 71) but all involve the idea that electrons can be transferred to silver much more readily than to a silver halide crystal. Each mechanism can be criticized on some detail (cf. Sheppard, 15 James, 72). As a general criticism, however, none of the mechanisms has explained the fact that the rate of development under simplified conditions varies with the square root of the hydroquinone and catechol concentrations, whereas the rate of reduction of silver ions from solution by the same agents varies as the first or somewhat higher power of the concentration. 

Epinephrine. Epinephrine (Adrenalin) finds use in a number of situations because of its potent stimulatory effects on both a- and /3-adrcncrgic receptors. Like the other catecholamines, epinephrine is light sensitive and easily oxidized on exposure to air because of the catechol ring system. The development of a pink to brown color indicates oxidative breakdown. To minimize oxidation, solutions of the drug are. stabilized by the addition of reducing agents such as sodium bisulfite. As the free amine, it is used in aqueous solution for inhalation. Like other amines, it forms salts with acids, for example, those now used include the hydrochloride and the bitartratc. Epinephrine is destroyed readily in alkaline solutions and by metals (c.g.. Cu, Fe, Zn), weak... 

Chiarino et al. [43] described some potent and remarkably selective (3o-adrenoceptor agonists in a series of l-(3-substituted-5-isoxazolyi)-2-alkyl-aminoethanol derivatives in which the isoxazole ring replaces the catechol moiety in the (3-adrenergic compounds. From this series, the compound broxaterol (1) displayed a marked selectivity toward (32-receptors of the trachea and was selected for further development as a potential bronchodilatory agent. 

Evans and co-workers developed rhodium catalyzed hydroboration reactions, which enable the use of catechol borane and other boronate esters as hydroborating agents to afford organoboronic esters as products.9 These products have increased stability and can be used directly in palladium cross-coupling applications. However, the rhodium-catalyzed method is most effective for the hydroboration of monosubstitued olefins (i.e., 16), as lower reactivity is observed with more substituted alkenes. 

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