Bulk Methanol Research Articles

Spectroscopic detection of free “lone-pair” groups or terminal methanol molecules in methanol solutions

When basic aprotic solvents are added to methanol they become hydrogen bonded, and there is a consequent growth in non-bonded lone-pairs, (LP) free. Although corresponding non-bonded OH groups, (OH) free, have been detected for alcohols and for water, using overtone infrared spectroscopy, no different spectroscopic evidence for (LP) free groups has previously been reported. We have found that unique OH stretching bands develop when strongly basic solvents such as dimethylsulphoxide are added to methanol. Band maxima assigned to (LP) free groups occur at 3440 cm −1 in the fundamental and 6790 cm −1 in the overtone region. These are at considerably higher frequencies than those for bulk methanol (3340 cm −1 and 6600 cm −1) showing that the hydrogen bond is weakened in this unit, as expected. Proton resonance shifts for the OH protons of methanol on adding basic aprotic cosolvents are reported, and explained in terms of these results.

Solvation spectra. Part 54.—A low temperature infrared spectroscopic study of the solvation of ions in methanol

Broad featureless bands in the O—H stretching region for CH3OH in CH3OD containing a range of 1:1 electrolytes become narrower on cooling below the glass point and usually display several features. Lithium and sodium salts up to ∼3 mol kg–1 show narrow bands on the high-frequency side of the bulk methanol band that are assigned to solvent molecules bonded to the anions. The bulk methanol bands are broadened and shifted by the cations, but separate bands for the cation solvates are not resolved. At higher concentrations of salt, the anion bands are also shifted by the cations to give new high frequency bands assigned to solvent shared ion-pairs. Tetra-alkyl-ammonium salts in the 1 mol kg–1 region give new bands characteristic of the anions only.Sodium tetraphenylboron gives a narrow component at 3520 cm–1 and a very broad component centred at ∼3360 cm–1. The former is assigned to two O—H groups bonded to a single methanolic oxygen atom: the latter is assigned to oscillators in short chains or cyclic structures. A broad band at ∼3360 cm–1 for other concentrated electrolyte solutions is assigned similarly.

Solvation spectra. Part 50.—Spectrophotometric studies of the solvation of nitrate ions in protic and aprotic media

Nitrate ions in aprotic solvents exhibit a single band at ∼1 353 cm–1, in the absence of ion-pair formation. However, in protic solvents, (H2O, MeOH)text-decoration:overlineν3 is split into a doublet (∼1 345 and 1 400 cm–1). This indication of descent in symmetry is interpreted in terms of relatively strong hydrogen-bonding to one or two oxygen atoms only. This effect, which contrasts with the behaviour of perchlorate ions, is interpreted in terms of the high polarisability of the nitrate ion. Application of simple equations for weak interactions in a trigonal-planar system suggests that a single strong hydrogen bond is favoured. This is supported by e.s.r. spectroscopic studies of irradiated aqueous and methanolic glasses containing nitrate ions, which show that the product nitrogen dioxide is not hydrogen bonded to the matrix. Addition of low concentrations of methanol to solutions of tetra-n-butylammonium nitrate in methylene chloride caused shifts and splittings of the text-decoration:overlineν1 and text-decoration:overlineν3 modes indistinguishable from those obtained with bulk methanol. This occured in parallel with changes in the O—H stretching mode indicative of strong 1:1 hydrogen-bonding between methanol and nitrate, thus supporting the concept of strong mono-solvation. Ion-pairing with sodium ions in aprotic solvents results in a comparable splitting of the text-decoration:overlineν3 absorption.Studies of the O—H stretching mode of interacting solvent molecules show that the strength of the hydrogen-bonds to nitrate are comparable to those formed by iodide ions and are far stronger than those formed by perchlorate ions.

Interactions and reactions in restricted polar media. Binding of cyanide ion to hemin in surfactant-solubilized methanol in benzene

One molecule of monomeric hemin is solubilized by 2100 ± 400 molecules of uncharged surfactant lgepal CO-530 in benzene containing 0·2%(v/v) methanol. The substrate–surfactant binding constant in this system is (3·5 ± 0·5)× 104 l mol–1. The environment of hemin in this restricted methanol pool is less polar than in bulk methanol. The interaction of cyanide ion with hemin, localized in the polar cavity of surfactant aggregates in benzene, has been treated in terms of a two-step process. Rate (k1, k–1, k2, k–2) and equilibrium (K) constants have been determined. Values for K, k–2, K2/k–1 and k1 in 0·70M lgepal CO-530 in benzene, containing 1·0%(v/v) methanol are 960-times greater, 200-fold smaller, 10-fold greater, and identical, respectively, to those in bulk methanol. The significance of these results are discussed and compared to those available in aqueous surfactant systems.

Solvation of Co(II) in Methanol and Water Enriched in Oxygen-17

The solvation sphere of cobaltous ion in oxygen-17-enriched methanol and water solutions was observed by oxygen-17 magnetic resonance. The chemical shift between the coordinated methanol molecules and the bulk methanol and the transverse relaxation times of oxygen-17 in the two environments were measured in the temperature range of −27.5° to +21°C. The hyperfine coupling constant between the cobaltous ion unpaired electrons and the oxygen-17 nuclei was found to be temperature independent and its value −(1.70 ± 0.03) × 107 Hz. The relaxation time of the unpaired electrons of the cobaltous ion was calculated and found to be 7 × 10−13 sec at 25°C, assuming T1e = T2e. The dipolar contribution to the relaxation rate of the oxygen-17 was calculated and found to be about 1% of the hyperfine contribution. The oxygen-17 chemical shift between the coordinate water molecules and the noncoordinated water molecules and their transverse relaxation times were measured at temperatures of −15°, −10°, and −5°C. The hyperfine coupling constant and the unpaired electron relaxation time were found to be A / h = − (1.74 ± 0.03) × 107Hz and τe = 1.7 × 10−12sec at −10°C assuming T1e = T2e.

Oriented Overgrowths on Sodium Chloride

Replica studies of a freshly-cleaved surface of a NaCl single crystal which had been treated for 15 seconds with a relatively impure (bulk) methanol revealed the presence of a large number of three-dimensional oriented overgrowths having cubic symmetry (Fig. 1). Attempts to reproduce such morphological surface phenomena about 6 months later with the same methanol were not successful, possibly due to “aging” of the methanol. Treatment for 15 seconds with A.C.S. methanol did not result in any significant surface morphology. So far, the nature of the impurity in the bulk methanol has not been identified; however, analyses indicate that it is present in an amount less than 0.15%. All surface treatments of NaCl were followed by a 5-second rinse in A.C.S. acetone and another 5-second rinse in petroleum ether (Skelly B). Neither rinse contributed to surface morphology. Freshly cleaved NaCl surfaces were also treated with 1.25% by weight of A.C.S. NH4Cl in A.C.S. methanol and 1.36% by weight of U.S.P. 37% formaldehyde-water-methanol solution in A.C.S. methanol.

Proton Relaxation in Dilute Solutions of Cobalt(II) and Nickel(II) Ions in Methanol and the Rate of Methanol Exchange of the Solvation Sphere

The nuclear relaxation of the hydroxyl and methyl protons in methanol containing low concentrations of Co++ and Ni++ ions has been investigated between —80°C and +80°C. This work complements previous studies of the NMR spectra of the solvation complexes in similar solutions. Over the temperature range studied, the relaxation due to the dissolved paramagnetic ions changes over two or three orders of magnitude. This dependence, as well as a corresponding temperature dependence of the chemical shift of the methanol peaks, can be quantitatively interpreted in terms of chemical exchange of methanol molecules between the coordination sphere of the paramagnetic ions and the bulk methanol. It is found that the dominant exchange process involves whole methanol molecules, i.e., proton transfer is relatively unimportant. The exchange rate is characterized by ΔH‡=13.8 kcal mole—1 and ΔS‡=+7.2 eu for Co++ ions; and ΔH‡=15.8 kcal per mole and ΔS‡=+8.0 eu for Ni++ ions. The hyperfine interaction between the paramagnetic ion and a methanol molecule in the coordination sphere is for Co++:+4.1×105 cps for the CH3 protons, and +80×105 cps for the OH proton; the corresponding numbers for Ni++ are: +5.7×105 cps and +6.8×105 cps. Proton relaxation times of the methanol in the coordination sphere are also obtained.

Nuclear Magnetic Resonance Study of the Solvation of Co++ in Methanol and Methanol—Water Mixtures

Proton magnetic resonance spectra of solutions of Co(ClO4)2 in acidified methanol, and in methanol—water mixtures are reported. At temperatures below about —50°C separate peaks for the bulk methanol and for the methanol bonded to Co++ are observed, and methanol exchange is too slow to contribute appreciably to the observed linewidths. Peak intensity measurements give a coordination number of six for Co++ with respect to methanol. From the temperature dependence of the peak frequencies, values of the hyperfine interaction between the bonded methanol protons and the Co++ ion were obtained. The results are +8.8×105 cps for the OH protons and +3.9×105 cps for the CH3 protons. The linewidths are shown to be predominately determined by electron—proton dipole—dipole interaction. The relevant correlation time is the electron relaxation time, which is approximately 5×10—13 sec at —60°C. This time decreases with increasing temperature, with an apparent activation energy of 0.9 kcal mole—1. In methanol—water solutions, additional lines, due to mixed methanol—water complexes of cobalt, are observed. Equilibrium constants for the formation of the mono- and dihydrated mixed complexes were obtained from measurements of peak intensity as function of water concentration. At temperatures above about —50°C the rate constant of methanol exchange between complexes and bulk solvent was obtained from the excess widths of the peaks. Comparison of the OH and CH3 linewidths shows that whole methanol molecules exchange, i.e., proton exchange between the complexes and the solution is relatively unimportant.

Nuclear Magnetic Resonance Study of the Solvation of Ni++ in Methanol and Methanol—Water Mixtures

Proton magnetic resonance spectra of solutions of Ni(ClO4)2 in acidified methanol and in methanol—water mixtures are reported. Separate peaks for the bulk methanol and for the methanol bonded to Ni++ are observed. From the temperature dependence of the peak frequencies a hyperfine interaction constant between the Ni++ and the methyl protons of the bonded methanol of +7.9×105 cps was obtained. At low temperatures, the linewidth is determined predominantly by electron—proton dipole—dipole interaction. The relevant correlation time is the electron relaxation time, which is about 3×10—12sec. This time decreases with increasing temperature, with an apparent activation energy of 1.3 kcal mole—1. At the higher temperatures methanol exchange contributes to the linewidth. The addition of water to the solvent increases the rate of exchange. This is ascribed to the formation of mixed water—methanol complexes.