Naphthalene crystallization

In the older method, still used in some CIS and East European tar refineries, the naphthalene oil is cooled to ambient temperatures in pans, the residual oil is separated from the crystals, and the cmde drained naphthalene is macerated and centrifuged. The so-called whizzed naphthalene crystallizes at ca 72—76°C. This product is subjected to 35 MPa (350 atm) at 60—70°C for several minutes in a mechanical press. The lower melting layers of the crystals ate expressed as Hquid, giving a product crystallizing at 78—78.5°C (95.5—96.5% pure). This grade, satisfactory for oxidation to phthaHc anhydride, is referred to as hot-pressed or phthaHc-grade naphthalene. 

Fig. 22 B. Exeitation spectrum at room temperature showing the intensity of delayed fluorescence of a naphthalene crystal as a function of the wavelength of the exciting light. The ordinate is proportional to the square of the singlet-triplet absorption coefficient. (From Avakian and Abramson, Ref.52))...

Naphthalene Crystal UV (Only naphthalene triplet state)... 

Birks 68) has proposed that the only change between the unexcited and excited pyrene pair is a reduction in the interplanar distance from 3.53 to 3.37 A, i.e. that the pyrene excimer is not a completely eclipsed sandwich pair either in solution or in the crystal. This proposal is consistent with the observed similarity of the excimer band position for the crystal and solution environment, and with the emission of excimer fluorescence from the crystal even at 4 K. For naphthalene, the greater separation and the nonparallel structure of nearest-neighbor pairs in the crystal apparently prohibits the formation of the sandwich excimer during the naphthalene singlet monomer lifetime. Thus, no excimer fluorescence is observed from defect-free naphthalene crystals. 

Kawakubo s fluorescence results 86> for methyl- and dimethylnaphthalene solids can be similarly related to the crystal structure. Both 2-and 2,6-substituted naphthalenes retain the same close-packed layer structure as seen in naphthalene. The only effect of the methyl substitution is to increase the crystal dimension along the naphthalene long axis87 . Less is known about the crystal structures of 1- and 1,6-substituted naphthalenes, except that the 1-substituent requires a different packing pattern than naphthalene and that 1- and 1,6-substituted naphthalenes have much lower melting points than the 2-substituted naphthalenes. The absence of sandwich pairs in 2- and 2,6-substituted naphthalene crystals certainly explains the lack of excimer fluorescence in the crystal spectra. Presumably, such pairs are also absent in crystalline 1-methylnaphthylene, but they seem to be present in glassy 1-methyl-naphthalene and in 1,6-dimethylnaphthalene solid. 

Figure 8.50 A comparison of the performance of atom-atom potentials using the UNI method80 and PIXEL potentials in the description of the energy landscape for 133 naphthalene crystal structures. The experimental crystal structure is represented by a cluster of 5 points representing very similar structures with different unit cell settings. Energies are given on the abscissa in kj mol 1. The plot shows the usual way of representing the results of crystal structure calculations with the expectation that the most stable structure should be at the lowest energy and exhibit the highest density. (Reproduced with permission from The Royal Society of Chemistry).

Naphthalene crystallizes in this space group with Z = 2 the measured molecular dimensions and molecular packing are displayed in Fig. 9.6.4. 

Such a model of surface modification has been used by Filippini, Gramaccioli, and Simonetta133 to investigate the naphthalene crystal (001) face. Their calculations, based on a Kitaigorodsky-type method,134 accounted for the reconstruction of the surface and the subsurface layers of the crystal. The principle of the calculation is to minimize the cohesion potential written as a sum of atom-atom potentials.134 The potentials include an attractive part in R"6 (of van der Waals or dispersion forces) which is of the type discussed in Section I.A.2, and a repulsive part which is generally given the form e cR to account for the impenetrability of the electronic clouds. The potentials are determined for each type of pair C , or by adjusting... 

Another estimate of t may be obtained by transferring the parameters calculated for the naphthalene crystal.133 They provide as surface cohesion energy a value 85% of that of the bulk ... 

Unfortunately, the molecules reorientation is not known. For a 4-kbar stress the coefficients measured at room temperature (they are presumably smaller at low temperatures) provide a variation of 0.1 A for the c dimension, and a variation of 0.3° for the angle ft. These values agree in order of magnitude with those calculated for the naphthalene crystal. 

Fio. XXV-12.—Structure of the naphthalene crystal as determined by x-ray analysis. From J. Monteath Robertson, Science Progress 32, 246 (1937) by permission of the author.)... 

Trithiadiazepine (12.1) is colorless, planar, and symmetrical, and has bond lengths intermediate between double and single as expected for a IOtt aromatic system the C—C bond length is 1.346 A. The benzo derivative (12.2) is also planar and symmetrical, but is bright yellow, and there is bond alternation in the benzene ring (see 12.2) akin to that found in naphthalene. Crystal discontinuities have prevented the accurate measurement of the structural details of 12.3, which is also colorless, but it is presumed to be planar. 

Bokhenkov ISP, Rodina EM, Sheka EF, Natkaniec I. Inelastic incoherent neutron scattering spectra at different temperatures and computer experiment for external phonon modes of naphthalene crystals. Phys Status Solidi B 1978 85 331-342. 

Belushkin AV, Bokhenkov fiL, Kolesnkiov AI, Natkaniec I, Righini R, Sheka EF. Spectrum of external phonons of a naphthalene crystal at 5K. Sov. Phys Solid State 1991 23 1529-1533. 

Naphthalene crystallized aS plates is very difficult to pulverize. If such material is to be used, it should first be melted and allowed to solidify in a compact crystalline mass which is much more easily pulverized. 

An experiment (91) has been carried out using a system satisfying the first condition. Quinoxaline is used as a donor. The acceptor is naphthalene x-traps, created by dissolving quinoxaline in the naphthalene crystal. The naphthalene located next to the quinoxaline molecules have their triplet state lower than the rest of the molecules in the crystal, including the neighboring... 

Exciton migration experiments on isotopic naphthalene crystals reveal a universal behavior with reduced donor concentra-... 

Photoconductivity induced by single-photon excitation of aromatic molecules in liquid hydrocarbons is thought to involve Rydberg states.A number of photophysical studies on glasses or crystals have appeared these include 2,4,5-trimethylbenzaldehyde in durene single crystals, identification of phenylcyclohexadienyl radicals in benzene crystals, hydronaphthyl radicals in dehydronaphthalene crystals,1-hydronaphthyl radicals in naphthalene crystals, phenylcyclohexadienyl radicals in biphenyl crystals, ... 

Time and temperature dependences of the delayed fluorescence in isotopi-cally mixed naphthalene crystals have been presented for various concentrations of traps. Coherent two-photon processes in naphthalene in the strong exciton-photon counting regime have also been investigated. Excited-state spectra of 1,5-naphthyridine in several solvents support those calculated using INDO molecular orbital formalism and show the lowest excited singlet state to... 

The absence of analogy is still more striking between naphthalene and monochloracetic acid, whose mixtures have been studied by Cady. Within these mixtures there are formed two kinds of mixed crystals the first, rich in naphthalene, are isomorphous with pure naphthalene crystals the others, rich in monochloracetic acid, are isomorphous with those furnished by this acid taken by itself. 

The dynamics of excitons in isotopically mixed naphthalene crystals has been reviewed and the effects of orientation of metal ion perturbers in naphthalene-crown ether metal ion complexes on the external heavy atom examined . ... 

The post-expansion temperature (in contrast to the pre-expansion temperature), was found to be Important both at high and low Naphthalene concentrations. Crystallizer temperatures from 8 C to -8 C resulted in the production of Naphthalene crystals with similar size distributions that ranged... 

The three process variables which were found to have significant effects on the precipitated Naphthalene crystals, namely solute concentration and pre- and post-expansion temperatures were further examined in the CO2/Lovastatin stem. Eight experiments were selected according to a two-level factorial design 112 Figure 10) and identified in order to study the primary and secondary effects of the three process variables (as weU as their interaction) on the mcnphology and particle size distribution of the precipitation products. The experiments were all conducted at extraction and precipitation pressures of 379 and 2 bars, respectively. A 25 pm diameter orifice was used throughout. 

Naphthalene crystals u 2B 26 TF fft Pott Magnum lo ASTM D543-84 4(... 

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