1-Naphthol naphthoquinone formation

Oxidation. Naphthalene may be oxidized direcdy to 1-naphthalenol (1-naphthol [90-15-3]) and 1,4-naphthoquinone, but yields are not good. Further oxidation beyond 1,4-naphthoquinone [130-15-4] results in the formation of ortho- h. h5 ic acid [88-99-3], which can be dehydrated to form phthaUc anhydride [85-44-9]. The vapor-phase reaction of naphthalene over a catalyst based on vanadium pentoxide is the commercial route used throughout the world. In the United States, the one phthaUc anhydride plant currently operating on naphthalene feedstock utilizes a fixed catalyst bed. The fiuid-bed process plants have all been shut down, and the preferred route used in the world is the fixed-bed process. 

Fig. 47. Catalytic selectivity as a function of Ti content in Ti-MCM-41 for 1-naphthol hydroxylation with aqueous H202. H202 selectivity (mol%) = (number of moles of H202 utilized in product (1, 4-naphthoquinone, 1,4-dihydroxynaphthalene and 1,2-dihydroxynaphthalene) formation/-number of moles of H202 fed) X 100 [data from Chaudhari et al. (277)].

It is pertinent at this point to refer briefly to the sources of quinone methides, though these have been reviewed (B-74M122400). The general approach used in chroman syntheses involves the thermal elimination of HX from an -substituted phenol. Commonly the eliminated molecules are water, methanol or dimethylamine (287 X = OH, OMe, NMe2, respectively). However, these methods are not entirely suitable because the eliminated molecules may promote side reactions. In the case of 1,2-naphthoquinone 1-methide, the thermal dissociation of the spirodimer (288) is a better source than the other methods. Its formation represents another example of dimerization by a [4+2]-cycloaddition, since it is prepared by heating l-dimethylaminomethyl-2-naphthol in dodecane or xylene with careful exclusion of moisture (73JCS(P1)120,81CJC2223). 

Many reactions afford, in addition to the naphthalene derivatives, mixtures of products. One of the major side reactions is the formation of indene derivatives directly from the metathesis intermediate without insertion of carbon monoxide. Other products frequently isolated as minor components are furans, cyclobutanones, and cyclopentenediones. The product distribution is dependent on numerous factors, including solvent, reaction temperature, concentration of the alkyne, and the nature of the aryl substituent. Molybdenum carbenes give, depending on the alkyne, either naphthols or indenes exclusively. The molybdenum Fischer carbenes can be tuned to give naphthoquinones by replacing one of the carbon monoxide ligands with a phosphine (Scheme 45). 

The photonics of Nph molecules on the surfaces of the zeolite X as well as on aerosil has been studied. Nph in zeolite voids is present as physically adsorbed molecules and bound in donor-acceptor complexes (CTC). Water vapor admission to an adsorbed Nph causes oxidation under formation of luminescent products of a-naphthoquinon on the Na-forms and its mixture with b-naphthol in presence of the alkaline-earth cations. Assumption about participation of oxygen chemisorbed on acid centers in an oxidation reaction is substantiated. In presence of transition metal ions the Nph luminescence is totally quenched. The Nph molecules adsorbed on the dehydroxylated aerosil surface form bimolecular excimer-like associates with a stable ground state and resistance to UV irradiation. 

An important support for this theory is the circumstance that the bodies formed by the action of aromatic hydrazines on quinones are identical with those obtained from phenols and diazo-compounds. Phenylhydrazine, for example, reacts with a-naphthoquinone, producing the same compound which is formed by combination of a-naphthol with diazobenzene [3j. The first method of formation renders the formula... 

Carbaryl is photolyzed in aerated aqueous solution with a low quantum yield (2.1 x lOY to give sevCTal naphthoquinone derivatives, whereas in organic solvents, it is mainly converted into 1-naphthol, and no PFR products were found (Scheme 31.21). Laser flash photolysis in water reveals formation of the triplet excited state (A =410nm, ca. 3ps), in addition to naphthoxyl radicals and solvated electrons [186]. 

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