Hexa sublimation

The vapor-pressure measurements were carried out with hexa sublimed in high vacuum. Pressures of 10 to 10 mm. Hg, corresponding to 20 to 85°, were measured with a quartz filament manometer 2, S). At temperatures of 120 to 210° a simple mercury manometer was used, and the vapor pressures were obtained by extrapolating the pressure-time curves plotted in Fig. 1 to time zero. 

Hexamethylenetetramine. Hexa, a complex molecule with an adamantane-type stmcture, is prepared from formaldehyde and ammonia, and can be considered a latent source of formaldehyde. When used either as a catalyst or a curative, hexa contributes formaldehyde-residue-type units as well as benzylamines. Hexa [100-97-0] is an infusible powder that decomposes and sublimes above 275°C. It is highly soluble in water, up to ca 45 wt % with a small negative temperature solubiUty coefficient. The aqueous solutions are mildly alkaline at pH 8—8.5 and reasonably stable to reverse hydrolysis. 

HEXANITROETHANE (HNEt) (Called Hexa-nitroathan, in Ger), (QjNjjC.CfNOgJa mw 300.07, N 28.01%, OB to C02 42.7% colorless crysts (from ether), non hygroscopic, si volatile at RT, mp 142°(with sublimation and partial decompn) explodes mildly on rapid heating above 360° and hy action of a detonator. 

Dienes react with molybdenum hexacarbonyl to give complexes of the type [Mo(CO)4(diene)] and [Mo(CO)2(diene)2], which are generally yellow, soluble in organic solvents, and readily sublimed. Cyclo-octa-1,5-diene (12, 79, 151), bicyclo[2,2,l]hepta-2,5-diene (175), a dimer of cyclo-octa-tetraene (12) and dimethyldivinylsilane (158) give the former type of complex with the structure (VI M = Mo), while butadiene (81) and cyclo-hexa-1,3-diene form the latter type (80). Tetracyclone gives the complex [Mo(CO)2(tetracyclone)2] (215). 

The tricyanomethyl compounds are a stable class of organic compounds whose solid products can be purified by sublimation. Their exceptional thermal stability is evidenced by the fact that 1,1,1,6,6,6-hexa-cyanobutyne-3 was sublimed at 170° C./0.05 mm. The infrared spectra of these compounds show a weak absorption for cyano at 4.4 /a. The properties of these compounds are summarized in Table I. 

The white needlelike crystals of tris(l,l,l,5,5,5-hexa-fluoro-2,4-pentanedionato)aluminum are insoluble in water but moderately soluble in carbon tetrachloride, cyclohexane, and benzene. The compound decomposes rapidly in acetone. It melts at 73 to 74° and sublimes at 45° and 0.05 mm. pressure. It has an absorption maximum at 307 mfi its molar extinction coeflicient is 3.23 X 10 1. mol cm. in cyclohexane. The proton magnetic resonance spectrum of the compound in deuterochloroform has a single peak at 6.53 p.p.m. relative to the reference compound, tetramethylsilane. 

Tungsten Hexafluoride, WFg, is obtained by the action of anhydrous hydrogen fluoride upon tungsten hexaehloride in platinum vessels, or by the interaction of antimony peiitafluoride with the hexa-chloride. It is a solid at low temjreratures just above 0° C. it sublimes to a heavy gas which fumes in moist air it reacts with water with production of tungstic acid. It attacks both glass and mercury by alkalies it is decomposed, and with alkali fluorides it forms double salts. 

During their work on the total synthesis of diazasteroids, Burckh lter and Abramson8 investigated, as a model, the synthesis of 2-(2-ethoxy-carbonylethyl)-3,4,5,6-tetrahydropyrimidine hydrochloride (16) via the condensation of 1,3-propanediamines (14) with ethyl 3-ethoxycarbonyl-propionimidate hydrochloride (13). When 16 was heated above its melting point, and the melt was allowed to sublime, 2,3,4,6,7,8-hexa-hydro-6-oxopyrrololl,2-a]pyrimidine hydrochloride (17) was isolated in excellent yield [Eq. (3). ... 

The sublimation pressure of hexa reaches considerable values even at moderate temperatures. Owing to the catalysis of the decomposition reaction at the surface of the crystal, sublimation occurred rather fast and hence the hexa crystals showed typical forms of dissolution. 

Another saturated, polycyclic hydrocarbon for which a heat of formation is available is hexa-cyclo[7,2, l,0 ,0 ,0 ]dodecane, the cage molecule shown in Fig. 15. From combustion data< the value has been obtained A (c) = + 12 06 0 27 kcal/mole, and taking a somewhat arbitrary heat of sublimation of 12 kcal/... 

The first fractions will contain some bromine and a small quantity of silicon tetrabromide. The disilicon hexa-bromide distills at a fairly constant temperature, depending upon the pressure employed. Thus a considerable proportion comes over at 130 to 140°, if the pressure is varied from 15 to 20 mm. This material may have a pale-yeUow color, but on redistillation or sublimation a pure-white well-crystallized substance may be obtained (m.p. 95°). Yield 80 per cent based on the bromine used or 60 per cent based on the calcium-silicon alloy. 

Subiimed Biue Lead, Sublimed blue lead. See Lead sulfate, blue basic Sublimed sulfur. See Sulfur Substituted hexa hydropyrimidine. See Hexetidine,... 

More care has to be taken for the preparation of binary chlorides and bromides, RCI3 and RBr3. The anhydrous salts are moisture-sensitive and they are obtained as (hepta- or hexa-) hydrates upon crystallization from hydrochloric or hydrobromic acid solutions. Simple dehydration of the hydrates in an HCl or HBr gas flow, respectively, appears to be possible (Seifert et al. 1985) but the less skfllliil chemist produces halide products more or less contaminated with oxyhahde, ROX. Sublimation of the raw product in an all-tantalum apparatus at higher temperatures (650 C to 950 C) and low pressures (10 bar) produces pure trihalides (with the exception of the rare-earth elements europium and 3dterbium where mixed-valent (+2/+3) or even dihalides are obtained under these conditions). 

Even though solution crystallization is always the method of choice, it has limited applicability in cases where the molecules have a strong tendency to form solvates. Solvent-free techniques such as melt crystallization and sublimation are suitable for certain compounds. For example. Das and Barbour obtained four polymorphs of a hexa-host, hexakis(4-cyanophenyloxy)benzene, upon melt crystallization, which otherwise forms a series of solvates with the solvent of crystallization. Sublimation is yet... 

The parent HBC as purifled by sublimation is a yellow microcrystalline solid [35]. A single crystal of HBC has been grown from molten pyrene using mesity-lene as a flux [41]. Single-crystal structure revealed that HBC crystallized in a y motif with the planar discs stacked in a tilted column. The single crystal structure of hexa-fert-butyl substituted HBC, however, displays a sandwich-herringbone stacking due to the bulky substituents [42]. 

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