Labile forms

Benzophenone. Benzophenone [119-61-9] (diphenyl ketone) exists in a stable form as colorless orthorhombic bisphenoidal prisms when crystallized from alcohol or ether. Other labile forms of lower melting point exist. Benzophenone has been identified as a flavor component of wine grapes and has a geranium-like odor. It is soluble in most organic solvents, and is insoluble in water. 

Dichloronitrobenzene. This compound crystallizes in needles from ethanol and has both a stable and labile form. The stable a-form has... 

Ring opening polymerization of strained cyclic olefins, discussed previously, might exemplify such a system. The metalla-carbene, Met=CHR, is the active, and presumably labile form, while the ring species,... 

As reported earlier by Han (1998) and Han et al. (2001c), heavy metals were transferred and redistributed from the soluble and labile forms into the stable forms with time. The transformation pathways of Cu, Ni and Zn in soils were strongly affected by the soil moisture regime, while Cd and... 

Calculation of the microbial quotient can make treatment effects much more obvious. For example, in Fig. 2 the microbial quotient was greater in the row than inter-row and greater under residue return than burning, both to a depth of 30 cm. In addition, values declined with depth as soil organic matter content declined and the proportion of organic C present in labile form declined. 

Whether or no both forms of a tautomeric substance are capable of isolation in the free state depends chiefly on the velocity of rearrangement of the more labile form. The isolation of keto- and enol-forms in a permanent crystalline state was first carried out with unsymmetrical dibenzoylacetone (Claisen, 1896) ... 

Two reports in the Uterature have dealt with alleged isomers of Paludrine. A sample of this compound, obtained in 1947 by Russian workers 45) by the standard s5mthesis had m.p. 129 (from benzene) and thus appeared to be identical with the material of Curd, Rose et al. 143). Prolonged drying and seeding allegedly converted this labile form" (m.p. 129 ) into a "stable form", m.p. 144 (45). 

Frozen Nitroglycerol. NG crystallizes in two forms a stable form, dipyramidal rhombic crystals which melt or freeze at 13.2—13.5°, and a labile form, glassy Tappearing tri clinic crystals, mp 1.9—2.2°. It does not freeze readily or quickly. NG in Dynamite freezes in crystals if the expl is stored for a considerable length of time at low temps, its form... 

Fury[- acrylic Acid (Furfuralacetic Acid or Furacetic Acid), O.CH CH.CH C.CH CH.CQ0H mw 138.12. Exists as stable and labile isomers. The stable form. ndls(w), rap 141° bp (with quick heating) 255—65°(286°) sol in ale, eth, benz, HAc hot w steam distils. Can be prepd by refluxing furfural with NaAc (Refs 1, 2 4). The labile form prisms plates (benz), mp 103—04° sol in benz hot w. Was prepd by refluxing furfuridine malonic acid with Ac30 and cecrystn as its piperidine salt from benz (the salt of the stable form is more sol in benz (Ref 3)... 

After the addition of acetonitrile the mixture is refluxed for 3 hr or longer until, in cooling, the sodium salt or 3-iminobutyronitrile and sodium cyanide crystallize from the reaction mixture. The product salts are filtered, suspended in 1 liter of ether, and water is slowly added until the salts dissolve. The ether layer is separated, dried, and the ether removed by atmospheric distillation. After a few hours the residue crystallizes to yield 121 gm (49.7 %) of crude product. Recrystallization from benzene yields 91 gm (37.4%), m.p. 63°-71°C. Von Meyer [19d] has reported that this compound exists in a stable form with m.p. 50°-54°C, and in a labile form, m.p. 79°-84°C. 

Dinitro-2,2 -diaminobiphenyl formula as above, rhmb crysts + AcOH (from AcOH), mp 180°, on heating in air for several hrs or on washing with ale the crysts lose AcOH exists in two forms yel mp 143-44° 8t orn, mp 179-80° 170-72°(Ref 5), the labile form is obtd by addg w to its soln in HCI, by washing the crysts of the acetate with ale, and by hydrolyzing the disuccinyl di-Ac... 

Dinitro-3,3-dibromobenzene, mp 84.8-86°, trimorphic stable form, monoclinic prisms (from coned so In of eth-alc or ale, d 2.274 metastable form, monoclinic prisms (from cooling a saturated soln in eth acet), d 2.317 and labile form, rhmb bipyramidal crysts (from seeding an alc-eth soln) prepd by nitrating l-nitro-3,5-dibromobenzene with mixed acid... 

Dinitro-N, N-diethylaniline, exists as a- modification or stable form, orn-colored crysts (from acet), mp95° and a /3-modification or labile form, It-yel lfts (from MeOH), mp - stable in dry state at RT but goes to a- form at 90°or above forms an addn compd with 2,4-Dinitro-N,N-diethyl-aniline, 43 304 + c1oH13N3°4> mp 57-59°, which, on crystn from chlf + petr, separates into its components (Ref 3)... 

There are two modifications of nitroglycerine, differing in freezing point and crystalline forms. With respect to crystal structure the form melting at the lower temperature represents a labile form (Fig. 6) which can be transformed spontaneously into the higher melting stable form of nitroglycerine (Fig. 7). 

The conditions necessary for the formation of each crystal form were examined by Hibbert [15]. He found that if recently produced nitroglycerine is mixed with wood meal or pulverized glass and cooled to the temperature of —40°C, while being stirred vigorously, the labile form is produced. By introducing a crystal obtained in this way into another portion of cooled nitroglycerine, crystallization of the labile form can be induced. 

Hackel has extended Hibbert s observations concerning the influence of certain substances on the formation of nitroglycerine crystals of different forms. Thus, adding urethane, phenylurethane, collodion, nitrocotton, cyclonite, tetryl, dinitrobenzene, or centralites I and II promotes the formation of the labile form. Admixtures of siliceous earth, trinitrobenzene, TNT, favour the creation of the stable form. 

Hibbert [15] assumed that the labile form of nitroglycerine belongs to the triclinic system, while according to Flink [19] the stable form has orthorhombic bipyramidal crystals. 

Dinitro-1-chlorobenzene or l,3-Dinitro-4 -chlorobenzene. Three polymorphs exist orthorhmb crysts or alpha(stabile form), mp 53.4°, bp 315°, d 1.697 at 22°/4° vsol in hot ale, eth, benz or CS2 si sol in ale insol in w can be prepd by nitration of chlorobenzene with mixed acid(Refs 1, 2a, 5, 9, 10) rhmb crysts or beta(labile form), mp 4 3°, d 1.680 at 20°/4° solubility same as alpha can be prepd by rapid cooling of the alpha form(Ref 3) and gamma, mp 27°(Refs 1 10). Halpern(Ref 8) reported an expln occurred during distillation of 2 4 -DNCB at 1 mm press... 

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