Crystallization common solvents

Table 11.2 lists common crystallization solvents. The solvents used most commonly are listed in the table first. 

Nitrobenzene is an extremely versatile solvent, and may frequently be employed for the crystallisation of compounds which do not dissolve appreciably in the common organic solvents. The vapour is somewhat poisonous, so that recrystaUisations must be carried out in the fume cupboard. After the crystals have been collected, they should be washed with a volatile solvent, such as benzene, alcohol or ether, to remove the excess of nitrobenzene (compare Section 11,32). The only disadvantage of nitrobenzene as a solvent is that it has a pronounced oxidising action at the boihng point. 

The solubihty of alkylphenols in water falls off precipitously as the number of carbons attached to the ring increases. They are generally soluble in common organic solvents acetone, alcohols, hydrocarbons, toluene. Solubihty in alcohols or heptane follows the generalization that "like dissolves like." The more polar the alkylphenol, the greater its solubihty in alcohols, but not in ahphatic hydrocarbons likewise with cresols and xylenols. The solubihty of an alkylphenol in a hydrocarbon solvent increases as the number of carbon atoms in the alkyl chain increases. High purity para substituted phenols, through Cg, can be obtained by crystallization from heptane. 

Furthermore, about 1920 the idea had become prevalent that many common crystals, such as rock salt, consisted of positive and negative ions in contact. It then became natural to suppose that, when this crystal dissolves in a liquid, the positive and negative ions go into solution separately. Previously it had been thought that, in each case when the crystal of an electrolyte dissolves in a solvent, neutral molecules first go into solution, and then a certain large fraction of the molecules are dissociated into ions. This equilibrium was expressed by means of a dissociation constant. Nowadays it is taken for granted that nearly all the common salts in aqueous solution are completely dissociated into ions. In those rare cases where a solute is not completely dissociated into ions, an equilibrium is sometimes expressed by means of an association constant that is to say, one may take as the starting point a completely dissociated electrolyte, and use this association constant to express the fact that a certain fraction of the ions are not free. This point of view leads directly to an emphasis on the existence of molecular ions in solution. When, for example, a solution contains Pb++ ions and Cl- ions, association would lead directly to the formation of molecular ions, with the equilibrium... 

The Curtius rearrangement procedure described here is a modification of one reported by Winestock. The submitters have found this procedure to be considerably more reproducible when N,N-diisopropylethylamine is substituted for triethylamine. The procedure described for the preparation of trans-2,4-pentadienoic acid is a modification of an earlier one by Doebner. The submitters have found this method to give reproducibly higher yields, and to be more convenient, than other commonly used procedures for preparing this material. The use of dichloromethane as the extracting and crystallizing solvent greatly simplifies the isolation of polymer-free samples of the crystalline acid. 

Most gold(i) isocyanide complexes are colorless, crystalline materials, stable in air at room temperature, and soluble in common organic solvents. The compounds have been generally well characterized by IR/Raman and NMR spectroscopy, and crystal structures have been determined for almost a 100 examples. From the spectroscopic and structural data, it has been concluded that gold(i) isocyanides are strong cr-donors and poor 7r-acceptors. 

It should also be stressed here that many of these complexes are neutral and therefore relatively soluble in common organic solvents, an important issue for their purification and crystallization. Among all these paramagnetic complexes, only a fraction has been investigated for their magnetic properties in the solid state,... 

This leaves option 3b to be scrutinised closely. When the present writer did this, he realised that his puzzlement had arisen because he like others, had fallen into the trap of which he had frequently warned his students and which he has emphasised in his writings it is a serious error to attempt to understand electrochemical phenomena by thinking of ions in isolation, because this puts them putatively into a vacuum. But the ions of concern to us do not exist in a vacuum. Ions would not leave their positions of low energy in a crystal lattice to go into solution or be formed from neutral molecules by the transfer of a charged fragment from one molecule to another if those processes were not made exo-energetic by the interaction of the ions with polar or polarisable species in their environment, most commonly the solvent. For that reason, one should always think, and indeed talk, about... 

In contrast to these we have the equilibrium processes of sublimation, absorption, dissolution, precipitation, evaporation, and condensation, throngh which the physical states of solid, Uqnid, and gas are connected. For example, the common crystallization of salts from sea water involves all three phases. Distillation, which is essential for prodncing organic solvents, is a two-step evaporation (liquid => gas) condensation (gas => Uqnid) process. 

Figure 5. The relative solvent accessible areas (SAA) of the five most common faces on the sucrose crystal. Solvent radius 0 A.

Quinoline, when exposed to light, forms first a yellow liquid, and slowly a hrown liquid. It is only slightly soluble in water hut dissolves readily in many organic solvents. Isoquinoline crystallizes to platelets and is sparingly soluble in water but dissolves well in ethanol, acetone, diethyl ether, carbon disulphide and other common organic solvents. It is also soluble in dilute... 

The complex forms pale yellow crystals (mp 116-118 °C), which are stable in air for prolonged periods. It is very soluble in common organic solvents, but insoluble in water. The H NMR spectrum of a CS2 solution (TMS internal standard) contains resonances at <5 4.08 [t, J(HP) 1.0 Hz], assigned to the C5H5 protons, and 7.l3(m), for the aromatic protons. 

Compound 4 is an air-stable, orange-red, crystalline solid. It is soluble in common organic solvents such as hexane, benzene and dichloromethane. Solutions of 4 in these solvents are stable in air for several days. The IR spectrum of the compound contains the following CO absorptions (hexane) 2090(s), 2065(s), 2028(vs), 2022(m), 1995(w), 1983(w), 1936 (w) cm-1. The crystal structure of 4 has been reported.9... 

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