Cryoscopic studies

Cryoscopic studies have shown that a-acylamino acids undergo... 

Attempts to trap the digermene 74 in solution with benzil afforded only the cycloadduct 109 because of the [1 + 4] cycloaddition with germylene 10863 [Eq. (26)]. Another proof of the formation of germylene 108 in solution from 74 was given by cryoscopic studies.63... 

Schlenk was the one who first took triphenylmethyl-type radicals to the monomeric extreme and thus produced the final evidence for the existence of free radicals. The first example in this direction was phenylbis(biphenylyl)-methyl (11), which was isolated as white crystals from operations carried out in the apparatus described by Schmidlin. " Upon dissolution of 11 in benzene, a red color developed, and cryoscopic studies revealed that the monomeric phenylbis(biphenylyl)methyl constituted 80% of the equilibrium mixture. Trisbiphenylylmethyl (12) was even more extreme it formed black crystals and was a 100% monomeric free radical in an almost black solution. Finally, Schlenk et al. established the connection between the conducting solutions of triphenylhalomethanes and the free radical triphenylmethyl by showing that the cathodic reduction of triphenylbromomethane in liquid SO2 gave rise to triphenylmethyl. These findings were considered the definitive evidence for the free radical hypothesis, and Schlenck was nominated for the Nobel Prize in 1918 and several times afterwards for this achievement, amongst others (Table 2). 

Sulfuric acid has received considerable study as a nonaqueous solvent (see Chapter 5). It is, of course, a strongly acidic solvent, and it has a Kf value of -6.15 °/molal. In 100% H2S04, conductivity measurements and cryoscopic studies show that protonation of many substances occurs even though they are not normally bases in the usual sense. For example, organic compounds such as acetic acid and ether function as proton acceptors ... 

Several other techniques have been used to determine the structure or aggregation state of organocuprates. Cryoscopic studies in THF found that discrete monomeric species were formed when RLi (R = Me, t-Bu) was added to CuCN in various ratios. A dimeric species resulted, however, when PhLi was used for cuprate formation. X-ray absorption spectroscopy (XAS) was utilized in an investigation of Cul- and CuCN-based dimethyl cuprates. " Both extended... 

The dialkylzinc compounds are extremely moisture sensitive and even react explosively with bulk water. Nevertheless, cryoscopic studies carried out on the controlled hydrolysis of diethylzinc show the formation of organozinc hydroxide EtZnOH as intermediate. This intermediate, which is thought to have the dimeric structure (EtZnOH)2, is very unstable and reacts further to give polymers of the form Et(ZnO) (equation 19). Some of these products exhibit a good catalytic activity for the polymerization of lactones and cyclic ethers. 

In addition to solubility and cryoscopic studies, the association of solute molecules may be investigated by the variation of the dielectric constant with concentration. If the solution is non-polar, the value of the dipole moment calculated from the value of the dielectric constant at infinite dilution, obtained by extrapolation, may be close to the value obtained in the gaseous phase. If this be so, there are no anomalous solvent effects, but cases exist where this is not so and such behaviour may be explained by two theories. The first assumes that association of solute molecules persists at low concentrations and may be illustrated with reference to the curious variation of polarization of ethyl alcohol in hexane solution. As the concentration is increased, the polarization falls, passes through a minimum, rises to a maximutn value and then falls to the value for the polarization of pure ethyl alcohol. In dilute solution the molecules are evidently associated in such a way that the dipole moment is decreased, this may occur through the formation of quadrupoles by means of hydrogen bonds, viz... 

II. Unimolecular Acid-Catalyzed Reactions Involving Acyl-Oxygen Fission. At least one instance is known in which decomposition of the protonated complex does not seem to depend upon the attack of water or an alcohol molecule. It is the formation or hydrolysis of esters of 2,4,6-trimethylbenzoic acid in sulfuric acid solution. Since cryoscopic studies have shown that the acid gives a molar freezing point depression of four (p. 39), and the ester five (p. 225), we must conclude that decomposition of the protonated complex to the acyl carbonium ion 0... 

M. Hassanein and N.S. Youssep, Cryoscopic Studies in Molten Salts. Dissociation of Some Alkali Isopolymolybdates and Some Related Molybdenum(VI) Compounds in Molten Potassium Dichromate and Potassium Nitrate, Indian J. Chem. A21 (1982) 72-74. 

The solvating abilities of a number of polar organic solvents towards GaCla were deduced from a cryoscopic study, to be in the order dioxan < acetone < THF[Pg.135]

FAU/DER] carried out acid titrations of solutions with composition similar to that of the solutions used in the cryoscopic study, both in the absence and in the presence of ZrOCb. From the offset of the titration curves with respect to a reference curve resulting from titrating the KHCO3/KOH solution without addition of Zr (Fig. 2, op.cit.) the authors concluded that Zr(COj)4" must be the dominating complex and excluded the presence of Zr(0H)2(C03)4". 

KEN] Kenttamaa, J., A cryoscopic study of ionic association in bivalent metal sulphates using saturated aqueous solutions, Acta Chem. Scand., 12, (1958), 1323-1329. Cited on pages 181, 182, 183, 187, 188, 189, 284,288, 292. 

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