Crystallization at low temperature

2 cannula. The washings can then be removed using the filter stick as before. The cooling bath can be removed and the crystals isolated and dried 

3 the usual way or the low temperature recrystallization can be repeated in fie same flask. 

The sintered disc of the filter stick should be of porosity 3 or larger in order to avoid blockage. A convenient alternative to a filter stick is to use an ordinary glass rod with filter paper wrapped round the end (Fig. 11.4b). Wrap some Teflon tape round the end of the tube, then carefully fold filter paper over the end and secure it with wire. The Teflon tape will give a better seal because the wire will sink into it. Another alternative, for smaller scale work, is to use a long syringe needle (Fig. 11.4c). Again, the end of the 

Small scale low temperature crystallizations can be carried out in the device recommended for ordinary small scale work. First of all salve the material in an appropriate solvent in the flask. Then purge the. rraratus with inert gas and seal the outlet with a small septum (Fig. 11.6). erse the flask in a cold bath, and when crystallization is complete,. ove the septum and filter the suspension rapidly under inert gas -5Sure. On a small scale the solution will not warm up significantly 

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Acetophenone. Acetophenone [98-86-2] (methyl phenyl ketone) is a colorless Hquid that forms laminar crystals at low temperature (mp 20°C). It has a characteristic sweet orange blossom odor, and is soluble in alcohols and ethers. It is found in nature in oil of casatoreum, obtained from beavers oil of labdanum, recovered from plants and in buds of balsam poplar. It can be prepared by the Friedel-Crafts reaction (qv) of acetyl chloride with benzene in the presence of aluminum chloride however, this route is of Htde commercial significance. 

The measured growth rates are illustrated by the circles in Fig. 7. The interface velocity is plotted versus the interface temperature T. The value of T is always greater than Tq because of the release of the latent heat at the interface. Dimensionless units for T and the velocity are used here. The maximum velocity corresponds to 80m /s for argon. The most surprising aspect is the rapid crystallization at low temperatures. Most materials exhibit sharply reduced rates at low temperatures, as expected for an activated growth process. That is, the kinetics can be represented as the product of an Arrhenius factor F(T) and a term that accounts for the net production of crystalline material as a result of the atoms ordering and disordering at the interface,... 

These results are significant in understanding the photochemical behaviour of organic crystals at low temperature and in the development of a new synthetic route to highly strained [2.2]paracyclophane derivatives. 

Freeze drying or lyophilization is a drying process, in which the solvent and/or the medium of suspension is crystallized at low temperatures and thereafter sublimated from the solid state directly into the vapor phase. 

Even though we define the atropisomerism as above for present purposes, there remain some ambiguities. sym-Tetrabromoethane was obtained in different modifications according to the method of crystallization at low temperature (13). These were found by spectroscopy to correspond to retainers. Similar situations occur in other alkyl halides and acetates (14,15). Such cases will not be included in the discussion, mainly because crystalline atropisomers are isolated at far lower temperatures than die ambient, and their barriers to rotation have not been determined by equilibration. Also excluded is the isolation of chlorocyclohexane (16). The isolation of the equatorial and axial conformational isomers was possible only by crystallization of the former at - 150°C, although it was possible to observe equilibration between the equatorial and the axial forms at higher temperatures. 

In order to obtain a-form crystal preferentially semi-batch cooling crystallization at low temperature below 284K Is considered more preferable as Investigated above sections. Authors studied the process In the beaker scale test and In the commercial operation. 

Similarly, ammonium dimolybdate, (NH4)2Mo20t, crystallizes when aqueous solutions of M0O3 containing excess ammonia are evaporated at 100°C. Crystallization at low temperatures, however, forms ammonium heptamolyb-date, (NH4)eMo7024 4H2O, instead of dimolybdate. 

Why Cryo-Crystallography What Happens to Crystals at Low Temperature . 34... 

In this chapter the author will focus on the theoretical aspects of crystals at low temperature, on the techniques to cool crystals, and on some illustrative examples of cryo-crystallographic studies. 

In the following we will mainly analyze the thermodynamics of a perfect crystal at low temperature and the physics of diffraction at low temperature, in order to understand better the expectations from a cryo-crystallographic study, eventually discussed in Sect. 4. 

In this chapter we have emphasized that experiments on crystals at low temperature may provide information on the chemical bonding and on the thermodynamics of a system. A tight connection is evident between theoretical chemistry and cryo-crystallography. 

Larsen FK (1995) Diffraction studies of crystals at low temperatures - crystallography below 77 K. Acta Crystallogr B 51 468 82... 

Cornmint oil, Japanese mint oil is produced by steam distillation of the flowering herb Mentha arvensis var. piperascens Malinv. The crude oil contains ca. 70% (-)-menthol, which can be isolated by crystallization at low temperature. 

Single crystals of the bis-ammonia adduct of 5, [(HC=C)4Zn]K2(NH3)2 (6), were obtained by crystallization from liquid ammonia at 195 K and special equipment was used to isolate the crystals at low temperature. The solid state structure of 6 was determined by single-crystal X-ray crystallography (Figure 4). Its solid state structure, a... 

In addition, the glass matrix has an essential merit in comparison with the solvent which crystallizes at low temperature. For example, Smith et al. irradiated several olefins at 77° K and examined their ESR spectra, and they found that the electrons were trapped in the frozen state of glass but never in the crystalline state (9). This is also the case with 3-methylpentane (70), and other compounds such as alcohols and ethers. This fact may imply that the radiation-formed ionic intermediates are much more stable in the glass matrix than in the crystalline matrix, though the reason has not yet been confirmed. 

The transition behavior of a number of liquid crystals with side-chain mesogens is summarized in Table 5. The most obvious feature of macromolecular liquid crystals is the frequent absence of fully ordered crystals at low temperatures. If fully ordered crystals are observed, crystallization is incomplete, i.e. the observed phase states are to be described by an area on the right side of Fig. 3. Glass transitions, which were hard to find in low molecular weight liquid crystals (see Table 3), are now prominent. 

What is the atomic radius (in picometers) of an argon atom if solid argon has a density of 1.623 g/cm3 and crystallizes at low temperature in a face-centered cubic unit cell ... 

It is generally stated in chemical books, that oxymuriatic gas is capable of being condensed and crystallized at low temperature I have found by several experiments that this is not the case. The solution of oxymuriatic gas in water freezes more... 

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