Oxygen of benzene

Alkyl- and aryl-hydrazones of aldehydes and ketones readily peroxidise in solution and rearrange to azo hydroperoxides [1], some of which are explosively unstable [2], Dry samples of the p-bromo- and p-fluoro-hydroperoxybenzylazobenzenes, prepared by oxygenation of benzene solutions of the phenylhydrazones, exploded while on filter paper in the dark, initiated by vibration of the table or tapping the paper. Samples were later stored moist with benzene at —60°C to prevent explosion [3], A series of a-phenylazo hydroperoxides derived from the phenyl-or p-bromophcnyl-hydrazones of acetone, acetophenone or cyclohexanone, and useful for epoxidation of alkenes, are all explosive [4], The stability of several substituted phenylazo hydroperoxides was found to be strongly controlled by novel substituent effects [5],... 

Scheme 176 Cathodic production of phenol by copper(l)-catalyzed oxygenation of benzene.

Addition to arene oxides (5, 480). Photosensitized oxygenation of benzene oxide (1) gives mainly phenol. However, singlet oxygen generated from... 

Although hydroxyl radicals are apparently the active species in oxygenation of benzene [40a], cyclohexane [40a] and even methane [40b] by oxygen-containing derivatives of xenon (which may be generated by dissolution of XeOs or Xep2 in water of aqueous acetonitrile), the mechanism of direct arene epoxidation as the first stage is not excluded [40a] ... 

The nickel(II) complex of a macrocyclic pentaamine (2) catalyzes the oxygenation of benzene to phenol at room temperature in borate buffer [11]. Tracer studies show that the phenolic 0-atom is derived entirely from dioxygen. The formation of a Ni -0 type superoxo... 

Ohkubo K, Kobayashi T, Fukuzumi S (2011) Direct oxygenation of benzene to phenol using quinolinium ions as homogeneous photocatalysts. Angew Chem 123(37) 8811-8814... 

Commercially, maleic anhydride is prepared more cheaply by the catalytic vapour phase oxidation (in the presence of vanadium pentoxide at about 400°) of benzene with atmospheric oxygen ... 

In a Lewis-acid catalysed Diels-Alder reaction, the first step is coordination of the catalyst to a Lewis-basic site of the reactant. In a typical catalysed Diels-Alder reaction, the carbonyl oxygen of the dienophile coordinates to the Lewis acid. The most common solvents for these processes are inert apolar liquids such as dichloromethane or benzene. Protic solvents, and water in particular, are avoided because of their strong interactions wifti the catalyst and the reacting system. Interestingly, for other catalysed reactions such as hydroformylations the same solvents do not give problems. This paradox is a result of the difference in hardness of the reactants and the catalyst involved... 

In their reactions with suitable nucleophiles, such as tt-aromatics or heteroatom donor nucleophiles, the readily polarizable linear acylium ions shift a Tt-electron pair to oxygen, bending the ions and developing an empty p-orbital at the carbocationic center. This enables the reaction with aromatics. The acetylation of benzene can be depicted as... 

Acetoxybenzene is prepared by the reaction of benzene with Pd(OAc)2[325,342-345], This reaction is regarded as a potentially useful method for phenol production from benzene, if carried out with only a catalytic amount of Pd(OAc)2. Extensive studies have been carried out on this reaction in order to achieve a high catalytic turnover. In addition to oxygen and Cu(II) salts, other oxidants, such as HNOi, nitrate[346,347], potassium peroxodisulfate[348], and heteropoly acids[349,3S0], are used. HNO is said to... 

Oxygen stabilized carbocations of this type are far more stable than tertiary carbocations They are best represented by structures m which the positive charge is on oxygen because all the atoms have octets of electrons m such a structure Their stability permits them to be formed rapidly resulting m rates of electrophilic aromatic substitution that are much faster than that of benzene... 

The metal-ion complexmg properties of crown ethers are clearly evident m their effects on the solubility and reactivity of ionic compounds m nonpolar media Potassium fluoride (KF) is ionic and practically insoluble m benzene alone but dissolves m it when 18 crown 6 is present This happens because of the electron distribution of 18 crown 6 as shown m Figure 16 2a The electrostatic potential surface consists of essentially two regions an electron rich interior associated with the oxygens and a hydrocarbon like exterior associated with the CH2 groups When KF is added to a solution of 18 crown 6 m benzene potassium ion (K ) interacts with the oxygens of the crown ether to form a Lewis acid Lewis base complex As can be seen m the space filling model of this... 

Treatment for acute exposure to benzene vapor involves removing the subject from the affected area, followed by artificial respiration with oxygen intubation and cardiac monitors may be necessary for severe acute exposures (125,127). Because of its low surface tension, benzene poses a significant aspiration hazard if the liquid enters the lungs. Emesis is indicated in alert patients if more than 1 mL of benzene per kg of body weight has been ingested and less than two hours have passed between ingestion and treatment (127). 

Pyrrole, furan, and thiophene, on the other hand, have electron-rich aromatic rings and are extremely reactive toward electrophilic aromatic substitution— rnore like phenol and aniline than benzene. Like benzene they have six tt electrons, but these tt electrons are delocalized over five atoms, not six, and ar e not held as strongly as those of benzene. Even when the ring atom is as electronegative as oxygen, substitution takes place readily. 

It should be expected that the orientation and rate of electrophilic substitution in the isoxazole nucleus would be affected by both hetero atoms. Because of the electron-accepting effect of the nitrogen atom, electrophilic substitution of the isoxazole nucleus should proceed less readily than in the case of benzene and should occur essentially at the position jS to the nitrogen atom, just as in pyridine and other azoles. Simultaneously the electron-donating oxygen atom should facilitate such reactions in isoxazole as compared with the substitution in pyridine. These predictions are confirmed by the available experimental evidence. 

The Simple Model RFG required the addition of oxygenates and it limited the amount of benzene, sulfur, olefins, and T. The RVP was also lowered for six months during the summer period. Given these requirements, companies can choose to comply on a per-gallon basis (Table 10-4) or adopt the 1990 industry average basis (Table 10-5). 

Starting January 1998, the EPA s Complex Model went into effect. The Complex Model provides a set of equations that predict VOC, NO, and toxic emissions, using eight gasoline properties. These properties are RVP, oxygen, aromatics, benzene, olefins, sulfur, E200. 

Numerous reactions have been described in which the oxygen of the oxepin system is removed to give benzene derivatives. The formation of the aromatic products can be rationalized by an arene oxide as intermediate. A suitable reagent for the elimination of an oxygen atom from this heterocycle is triphenylphosphane, e.g. formation of l,24 2a,12 and 2b.1,9... 

The diazonio group of one zwitterion is stabilized by intermolecular interactions with the carboxylato oxygens of two neighbouring zwitterions. The same type of coordination is observed in crystals of benzene diazonium chloride, tribromide, and tetrafluoroborate (Andresen and Romming, 1962 Romming, 1963 Cygler et al., 1982). 

When 0.113 g of benzene, C6H6, burns in excess oxygen in a calibrated constant-pressure calorimeter with a heat capacity of 551 J-(°C) I, the temperature of the calorimeter rises by 8.60°C. Write the thermochemical equation for... 

Aniline, C6H5NH2(1), is a derivative of benzene in which a hydrogen atom has been replaced by an NH2 group, (a) Write the balanced equation for the combustion of aniline, (b) What is the mass of each product when 0.1754 g of aniline is burned in excess oxygen (c) If the bomb calorimeter in which this reaction was carried out had a volume of 355 mL, what minimum pressure of oxygen at 23°C must have been used to ensure complete combustion Assume that the volume of the aniline is negligible. 

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