Phenol ions, decomposition

Diazotization Diazonium ion decomposition gives a phenol in water and reduction in SDS Abe etal., 1983... 

The rate coefficient 2 is proportional to the concentration of phenolate ion thus for 2-hydroxy-pyridine (pA A = 11-6) oxidation below pH 8 is slower than the spontaneous decomposition of peroxodisulphate. For the reaction of 2-hydroxy-P5rridine in 2 M sodium hydroxide, the variation of 2 with temperature is expressed by... 

Effective Charge Map for a Putative Stepwise Process. Effective charge maps can also be employed to discount a stepwise process if estimates of the effective charge change from reactant and product to putative intermediates are not consistent with expectation. Consider the Bronsted dependence for reaction of substituted phenolate ions with 4-nitrophenyl acetate (Figure 6). The value of Pnu is approximately 0.80 for attack of substituted phenolate ions on 4-nitrophenyl acetate when the second step of the putative two-step mechanism (decomposition of the putative tetrahedral intermediate) would be rate limiting (pA pA a ) (Scheme 11). 

An example of the above method is the estimation of for the formation of ketene from aryl esters of 9-fluorene carboxylic acid these esters ionise and the conjugate base decomposes to ketene with the liberation of phenolate ion [13]. The overall equilibria are illustrated in Eqn. 20 and we may assume that for the overall reaction is 1.7 the decomposition of ketene to acid is of course substituent-... 

The excited state properties of hydroxyaromatic compounds (phenols, naphthols, etc) are of interest to a wide audience in chemistry, including those interested in the environmental decomposition of phenols, chemical physicists interested in the very fast dynamics of excited-state proton transfer (ESPT) and excited-state intramolecular proton transfer (ESIPT), physical chemists interested in photoionization and the photochemical pathways for phenoxyl radical formation, and organic photochemists interested in the mechanisms of phenol and hydroxyarene photochemistry. Due to space limitations, this review is restricted to molecular photochemistry of hydroxyaromatic compounds reported during the last three decades that are of primary interest to organic photochemists. It also includes a brief section on the phenomenon of enhanced acidity of phenols and other hydroxyaromatics because this is central to hydroxyarene photochemistry and forms the basis of much of the mechanistic photochemistry to be discussed later on. Several reviews that offer related coverage to this work have also appeared recently. This review does not cover aspects of electron photoejection from phenols or phenolate ions (and related compounds such as tyrosine) or phenol OH homolysis induced photochemically, as shown in Eq. (39.1), as these are adequately covered elsewhere ... 

The oxidation by cupric ions of aryl radicals generated Y 93%. by diazonium ion decomposition constitutes a promising method for the prepn. of phenols. 

The controlled thermal decomposition of dry aromatic diazonium fluoborates to yield an aromatic fluoride, boron trifluoride and nitrogen is known as the Schiemann reaction. Most diazonium fluoborates have definite decomposition temperatures and the rates of decomposition, with few exceptions, are easily controlled. Another procedure for preparing the diazonium fluoborate is to diazotise in the presence of the fluoborate ion. Fluoboric acid may be the only acid present, thus acting as acid and source of fluoborate ion. The insoluble fluoborate separates as it is formed side reactions, such as phenol formation and coupling, are held at a minimum temperature control is not usually critical and the temperature may rise to about 20° without ill effect efficient stirring is, however, necessary since a continuously thickening precipitate is formed as the reaction proceeds. The modified procedure is illustrated by the preparation of -fluoroanisole ... 

There is a difference in the behavior of benzenediolatoborate and naphthalenedio-latoborate solutions on the one hand, and lithium bis[2,2 -biphenyldiolato(2-)-0,0 ] borate (point 5 in fig. 8) lithium bis[ sali-cylato (2-) Jborate (point 6) or benzene-diolatoborate/phenolate mixed solutions on the other (Fig.8). This can be tentatively explained by the assumption of different decomposition mechanisms due to different structures, which entail the formation of soluble colored quinones from benzenediolatoborate anions and lithium-ion conducting films from solutions of the latter compounds (points 5 and 6) [80], The assumption of a different mechanism and the formation of a lithium-ion conducting, electronically insulating film is supported by... 

Thermal properties of several chlorinated phenols and derivatives were studied by differential thermal analysis and mass spectrometry and in bulk reactions. Conditions which might facilitate the formation of stable dioxins were emphasized. No two chlorinated phenols behaved alike. For a given compound the decomposition temperature and rate as well as the product distribution varied considerably with reaction conditions. The phenols themselves seem to pyro-lyze under equilibrium conditions slowly above 250°C. For their alkali salts the onset of decomposition is sharp and around 350°C. The reaction itself is exothermic. Preliminary results indicate that heavy ions such as cupric ion may decrease the decomposition temperature. 

Astatohalobenzenes have also been prepared from the corresponding haloaniline isomers by decomposition of their diazoniiun salts under conditions similarly described for astatotoluenes vide supra). Here again, relatively low radiochemical yields (10-26%) were obtained. Again, this has been attributed to the competing reaction of hydroxyl ions present in the aqueous solution in a much higher concentration than At , leading to the by-product formation of phenols 99,100,105). 

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