Cryoscopic

Nitration in the presence of strong acids or Lewis acids Solutions of dinitrogen pentoxide in sulphuric acid nitrate 1,3-dimethyl-benzene-4,6-disulphonic acid twice as fast as a solution of the same molar concentration of nitric acid. This is consistent with Raman spectroscopic and cryoscopic data, which establish the following ionisation ... 

Cryoscopic investigations suggest that in sulpholan nitronium tetrafluoroborate exists predominantly as ion pairs. - The specific conductivity of these solutions increases linearly with the concentration of the salt (up to 0-4 mol 1 ), and is attributed to the existence of ion-triplets rather than free ions. ... 

TABLE 11.2 Molecular Lowering of the Melting or Freezing Point Cryoscopic constants. 

The cryoscopic constant Kj gives the depression of the melting point AT (in degrees Celsius) produced when 1 mol of solute is dissolved in 1000 g of a solvent. It is applicable only to dilute solutions for which the number of moles of solute is negligible in comparison with the number of moles of solvent. It is often used for molecular weight determinations. 

The composition to the melting point is estimated to be 65% Na AlF, 14% NaF, and 21% NaAlF [1382-15-3], The ions Na" and F ate the principal current carrying species in molten cryoHte whereas the AIF is less mobile. The stmctural evidences are provided by electrical conductivity, density, thermodynamic data, cryoscopic behavior, and the presence of NaAlF in the equiUbtium vapor (19,20). 

V. P. Petto, Cryoscopic, Spectroscopic, and Conductimetric Study of Phosphorus Pentachloride in S electedNon Aqueous Solvent Systems, University Mictofdms, Ann Arbor, Mich. 

Bismuthides. Many intermetaUic compounds of bismuth with alkafl metals and alkaline earth metals have the expected formulas M Bi and M Bi, respectively. These compounds ate not saltlike but have high coordination numbers, interatomic distances similar to those found in metals, and metallic electrical conductivities. They dissolve to some extent in molten salts (eg, NaCl—Nal) to form solutions that have been interpreted from cryoscopic data as containing some Bi . Both the alkafl and alkaline earth metals form another series of alloylike bismuth compounds that become superconducting at low temperatures (Table 1). The MBi compounds are particularly noteworthy as having extremely short bond distances between the alkafl metal atoms. 

Annular nitrogen atoms can form hydrogen bonds, and if the azole contains an NH group, association occurs. Imidazole (84) shows a cryoscopic molecular weight in benzene 20 times that expected. Its boiling point is 256 °C, which is higher than that of 1-methyl-imidazole (198 °C). 

Isoxazole dissolves in approximately six volumes of water at ordinary temperature and gives an azeotropic mixture, b.p. 88.5 °C. From surface tension and density measurements of isoxazole and its methyl derivatives, isoxazoles with an unsubstituted 3-position behave differently from their isomers. The solubility curves in water for the same compounds also show characteristic differences in connection with the presence of a substituent in the 3-position (62HC(17)1, p. 178). These results have been interpreted in terms of an enhanced capacity for intermolecular association with 3-unsubstituted isoxazoles as represented by (9). Cryoscopic measurements in benzene support this hypothesis and establish the following order for the associative capacity of isoxazoles isoxazole, 5-Me, 4-Me, 4,5-(Me)2 3-Me> 3,4-(Me)2 3,5-(Me)2 and 3,4,5-(Me)3 isoxazole are practically devoid of associative capacity. 

The existence of the nitronium ion in sulfuric-nitric acid mixtures was demonstrated both by cryoscopic measurements and by spectroscopy. An increase in the strong acid concentration increases the rate of reaction by shifting the equilibrium of step 1 to the right. Addition of a nitrate salt has the opposite effect by suppressing the preequilibrium dissociation of nitric acid. It is possible to prepare crystalline salts of nitronium ions, such as nitronium tetrafluoroborate. Solutions of these salts in organic solvents rapidly nitrate aromatic compounds. ... 

Correction for boiling point, 59 Creatine, 132 -Cresol, 164 Cryoscopic method, 32 Crystallisation, 52 Cuprous chloride, 166 Cyclohexanol, 181... 

Consistent with this, the F nmr spectra of solutions at 0° showed the presence of HSO3F, and separate cryoscopic experiments with pure H2SO4 as the sole solute gave a value of u close to unity. 

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

Shatenshtein et al.5ia also found a similar dependence of rate coefficient upon the concentrations of stannic chloride and acetic acid in the dedeuteration of [l,4-2H2]-durene in benzene. Rate coefficients increased linearly with increasing stannic chloride concentration and at a constant value of this the rate increased only slightly with increasing acetic acid concentration, except at high concentrations of the latter when the rate then decreased (Table 155). Cryoscopic mea-... 

These early results have since been confirmed and extended by a vast and still growing body of research. All of the contemporary spectroscopic techniques (ir, uv, visible, nmr, esr) have been brought to bear on the problem, and further confirmation has come from cryoscopic and conductometric studies. The early confusion that resulted from the coexistence of both donor-acceptor or non-covalently-bonded complexes) has been clarified. This research has been extensively reviewed10,13-15 and will not be detailed here. 

EXAMPLE 8.9 Sample exercise Determining molar mass cryoscopically... 

J 9 Determine molar mass cryoscopically (Toolbox 8.2 and Example 8.9). ... 

During the study of the reaction products between six different co-lactams and triethylborane, monomeric (for 36, 39), dimeric (for 38), tetrameric (for 40) and oligomeric (for 35) species have been detected in solution by cryoscopic methods. For 37 [X = -CH2)5-] only lateral reaction products could be observed (Fig. 14) [66]. 

A differential vapour-pressure technique has been used to determine the molecular weights of phosphonic and phosphinic acids in 95% ethanol. Cryoscopic and n.m.r. studies have been made on solutions of phosphinic acids in sulphuric acid and oleum. Mass spectrometry has indicated the ready formation of phosphinylium ions after electron bombardment of phosphonic and phosphinic acids and their derivatives. However, the cryoscopic results in sulphuric acid indicated that reaction did not proceed beyond protonation, and the n.m.r. study on oleum solutions suggested that sulphonation occurred. 

Poly-(methacrylic acid) was prepared in 1880 by Fittig and Engel-horn. Mjoen separated the polymer by precipitation and attempted to determine its molecular weight by cryoscopic and ebullioscopic methods. He decided that his product, which he regarded as a colloid, was an octamer but reached no conclusions as to its constitution other than that it was an octabasic acid of the formula C24H4o(COOH)8. 

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