Naphthalene conversion processes

An internal conversion process recently discovered in our laboratory may shed light on the subject. Murovla found that quadricyclene, 6, is a powerful quencher of the excited singlet states of naphthalene and other aromatic hydrocarbons. In the course of the quenching reaction, the quencher was extensively converted to bicyclo [2.2.1] hepta-2,5-diene, 7. The following mechanism was suggested. 

Figure 4 Average energy of the nonequilibrium vibrational population distribution computed for the vibrational cascade in crystalline naphthalene in Fig. 3. At T = 0, the peak moves toward lower energy at a roughly constant rate, the vibrational velocity of 8.9 cm-1 ps. The initial 1627 cm-1 of vibrational energy is dissipated in 180 ps. The vibrational velocity is the same at 300 K. In the limit that cubic anharmonic coupling dominates [Equation (6)], increasing the temperature increases the rates of up- and down-conversion processes, but has no effect on the net downward motion of the population distribution. Although the lifetimes of individual vibrational levels will decrease with increasing temperature, VC is not very dependent on temperature in this limit. (From Ref. 5.)...

The transient T-T absorption in the gas phase has been measured recently for aromatic molecules such as naphthalene (119,211) and anthracene (80,81) using flash kinetic spectroscopy and tandem laser pulse absorption techniques. Particularly, the later technique (211) provides time-dependent absorption spectra of the "isolated" unrelaxed triplet molecules because of its capability for rapid monochromatic excitation and detection. It will certainly provide a wealth of Important kinetic and spectroscopic information about the evolution and decay of triplet states. Direct observation of the formation of transient hot ground-state (Sq) molecules through an internal conversion process has also been achieved with laser excitation and laser... 

Some years ago it was conventional wisdom to assert that for aromatic hydrocarbons Sx - S0 internal conversion was an improbable process compared with Sx - 7i non-radiative decay. However, it has recently been demonstrated that in naphthalene and related compounds the internal conversion can be the dominant decay process, particularly for vibrationally excited species.494 It is of interest to note that calculated rates for the internal-conversion process in naphthalene could only be made to fit experimental values if some redistribution of vibrational energy occurred, but not complete statistical distribution among normal modes. 

An array of products can be made via coal conversion processes. For example, refined coal tar is used in the manufacture of chemicals, such as creosote oil, naphthalene, phenol, and benzene. Ammonia gas recovered from coke ovens is used to manufacture ammonia salts, nitric acid, and agricultural fertilizers. Thousands of different products have coal or coal by-products as components soap, aspirins, solvents, dyes, plastics, and fibers, such as rayon and nylon. 

Next to the Kawasaki Kasei process, which is used commercially and has a high naphthalene conversion rate, mention should be made especially of the Bayer pro-cess, which involves only partial conversion of the naphthalene through oxidation, and further reaction of the crude oxidation product with butadiene. 

The theory of sublimation, t.e. the direct conversion from the vapour to the sohd state without the intermediate formation of the liquid state, has been discussed in Section 1,19. The number of compounds which can be purified by sublimation under normal pressure is comparatively small (these include naphthalene, anthracene, benzoic acid, hexachloroethane, camphor, and the quinones). The process does, in general, yield products of high purity, but considerable loss of product may occur. 

Naphthalenesulfonic Acid. The sulfonation of naphthalene with excess 96 wt % sulfuric acid at < 80°C gives > 85 wt % 1-naphthalenesulfonic acid (a-acid) the balance is mainly the 2-isomer (P-acid). An older German commercial process is based on the reaction of naphthalene with 96 wt % sulfuric acid at 20—50°C (13). The product can be used unpurifted to make dyestuff intermediates by nitration or can be sulfonated further. The sodium salt of 1-naphthalenesulfonic acid is required, for example, for the conversion of 1-naphthalenol (1-naphthol) by caustic fusion. In this case, the excess sulfuric acid first is separated by the addition of lime and is filtered to remove the insoluble calcium sulfate the filtrate is treated with sodium carbonate to precipitate calcium carbonate and leave the sodium l-naphthalenesulfonate/7J(9-/4-J7 in solution. The dry salt then is recovered, typically, by spray-drying the solution. 

Fourth, kinetic data of the sulfur extrusion reaction of thiepin will provide direct evidence for the transition state of the process. Data on the conversion of the thiepin 34 into its corresponding naphthalene derivative are available 2SK The substantially large negative activation entropy (AS si —24 cal mol-1 deg-1) points to the existence of a highly ordered transition state, namely a thianorcaradiene, in the reaction. 3,4-Bis(methoxycarbonyl)-5-hydroxybenzo[/>]thiepin 33 thermally... 

Although the superior properties of PEN have been known for many years, the unavailability of the naphthalate monomer has delayed the development of commercial markets, until relatively recently (1995) when the Amoco Chemical Company offered high purity naphthalene-2,6-dimethyl dicarboxylate (NDC) in amounts of up to 60 million pounds per year. This diester is produced by a five-step synthetic route, starting from the readily available compounds, o-xylene and 1,4-butadiene [3], Prior to this, the NDC diester was obtained by extraction of 2,6-dimethylnaphthalene (DMN) from petroleum streams, where it was present in relatively low abundance. Oxidation of DMN to crude 2,6-naphthalene dixcarboxylic (NDA) is conducted by a similar process to that used for conversion of p-xylcnc to purified terephthalic acid (TA), crude NDA is esterified with methanol, and is then distilled to yield high purity NDC. Other companies (e.g. the Mitsubishi Gas Chemical Company) followed Amoco s introduction with lesser amounts of NDC. Teijin [4] has manufactured PEN for many years for its own captive uses in films. 

Phthalic anhydride is the most important product in the oxidation of o-xylene, which has become competitive with naphthalene as a feedstock for the industrial production of this component. This process is carried out at 350— 400°C and the industrial catalysts consist of doped V2Os or V2Os—Ti02 mixtures, pure or supported. Maximum yields of 70—75 mol. % (95—105 wt. %) are reported. Carbon oxides are the main by-products, besides minor amounts of tolualdehyde and maleic anhydride. Tolualde-hyde is the main product at low conversion and an essential intermediate in the phthalic anhydride formation, while maleic anhydride is mainly formed as a side-product directly from o-xlyene. 

The insight of photoinitiation is complicated. Even when CT absorption is observed, the initiation process may not start from a charge transferred state or form ion-radicals. An alternative mechanism is triplet excitation via charge transfer absorption. Namely, when the CT excited level is higher than the triplet level, a considerable amount of the CT excitation would be converted to the triplet state. The TMPD+-naphthalene pair fits in this case (20). Conversely, the contribution of CT might be predominant even when the CT interaction in the ground state is not observed. As shown in Eqs. (14) and (16), charge transfer interaction will not take part in photoexcitation but occurs in the excited state. Possible reaction mechanismus may be explained as follows. 

Dehydrogenation (the conversion of alicyclic or hydroaromatic compounds into their aromatic counterparts by removal of hydrogen - and also, in some cases, of other atoms or groups) has found wide application in the determination of structure of natural products containing complex hydroaromatic systems. Dehydrogenation is employed also for the synthesis of polycyclic hydrocarbons and their derivatives from readily accessible synthetic hydroaromatic compounds. The general process is illustrated by the conversion of tetralin into naphthalene. 

The chemistry of the process, using naphthalene as an example, may be simply represented as the selective removal of carbon from the hydrocarbon feedstock and further conversion of a portion of this carbon to hydrogen ... 

Sublimation is a process that involves the direct conversion of a solid to a gas without passing through the liquid state. Relatively few solids do this at atmospheric pressure. Some examples are the solid compounds naphthalene (mothballs), caffeine, iodine, and solid carbon dioxide (commercial Dry Ice). Water, on the other hand, sublimes at — 10°C and at 0.001 atm. Sublimation temperatures are not as easily obtained as melting points or boiling points. 

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