Oleochemicals I: Studies on the preparation and the structure of lithium soaps.

Abstract

RESUMENOleoquímica I: Estudios sobre la preparación y la estructura de los jabones de litio.Se han preparado estearato, palnnitato, miristato, laurato, caprato y caprilato de litio por fusión. Se ha realizado el análisis elemental, los espectros de absorción en el infrarrojo y las difracciones de rayos X de los Jabones de litio preparados, además del análisis termogravimétrico de los mismos.Las sales de litio anhidra de los ácidos con 12 átomos de carbono o menos mostraron una estabilidad térmica hasta los 300 ± 78 °C dependiendo de la longitud de la cadena. Por otro lado las sales con 14 átomos de carbono o más se descompusieron a 126 ± 4 °C formándose carbonato de litio.Los jabones homólogos de litio mostraron una estructura cristalina similar, siendo los enlaces metal-oxígeno del mismo tipo para los ácidos grasos de número de átomos de carbono entre 8 y 18.Sin embargo el ángulo de inclinación que forma la molécula con el plano basal aumentó con la disminución del número de átomos de carbono, lo que se observó por difracción de rayos X.Se comprobó por espectroscopia infrarroja la intensificación del carácter iónico del enlace metal-oxígeno al disminuir el número de átomos de carbono. PALABRAS-CLAVE: Análisis elemental -Análisis termogravimétrico -Difracción de rayos X -Espectrofotometría infrarrojaHidróxido de litio -Jabón metálico. SUMMARY Oleochemicals I: Studies on the preparation and the structure of lithium soaps.Lithium stéarate, palmitate, myristate, laurate, caprate and caprylate were prepared by means of fusion method. Elementary analysis and the infrared absorptions spectra of the prepared lithium soaps as well as their X-ray diffractions and the thermogravimetric analyses were carried out.The anhydrous lithium salts of fatty acids with 12 carbon atoms or less showed thermal stability up to ca. 300 ± 78 °C depending on the chain length. On other hand the salts with 14 carbon atoms or more were decomposed at 126 ± 4 °C leading to formation of lithium carbonate.The homologous lithium soaps had very similar crystal structure among them and their metal -to-oxygen bonds were similar for the acyl chains between 8 and 18 carbons. However the angle of inclination of the molecular axes to the basal plane increased with the decreasing of the number of carbon atoms of the fatty acid chain, as determined by X-ray diffraction. In addition, the ionic character of the metal -to-oxygen bond was enhanced with the decrease of the number of carbon atoms as shown by infrared spectroscopy.

Thermal and odd–even behaviour in a homologous series of lithium n-alkanoates

“…This indicates that these carbons are in a similar chemical environment. Also, no odd-even alternation was observed in the asymmetric stretch of 1.12 ⁄ LiC 10 1.08 1.07 LiC 11 1.12 ⁄ LiC 12 1.06 1.06 LiC 13 1.10 ⁄ LiC 14 1.05 1.05 LiC 15 1.10 ⁄ LiC 16 1.05 1.04 LiC 17 1.09 ⁄ LiC 18 1.04 1.04 LiC 19 1.08 ⁄ ⁄No available data, q exp ± 0.02 Á 10 3 kg Á m À3 . the methyl groups in the IR spectra [9].…”

“…However, for the short chain length compounds, at least up to lithium pentanoate, a monoclinic crystal structure with P2 1 /c symmetry is indicated [11]. Since the strength of the lithium-oxygen bond is reported to be chain length dependent [9,10,12], it is entirely reasonable to expect that the thermal behaviour of these compounds will be governed by chain length, the relative strength of van der Waals interaction between hydrocarbon chains and the arrangement of the chains within the molecular lattice.…”

Fourier‐transform infrared spectra of fatty acid salts—Kinetics of high‐oleic sunflower oil saponification

“…These absorption bands were associated with a rocking vibration of successive methylene groups, -(CH 2 )-, of the soaps and depended on their mode of crystallization. The splitting into a doublet or a triplet was attributed to interchain interactions with neighboring hydrocarbon chains of the soap molecules (8,9).…”

“…The region between 4000 and 3000 cm −1 was associated with the O-H stretching vibration of hydrated water. Soaps have a broad absorption around 3400 cm −1 , which is characteristic of the existence of different types of hydrogen bonding attributable to the presence of many oxygen atoms in the polar head of the soap molecule in a crystal lattice (8,9). The absorption band at 3400 cm −1 was stronger for Ca and Na soaps (relative intensity vs. 2922 cm −1 peak: 50 and 35%, respectively) than for Li soaps (relative intensity vs. 2922 cm −1 peak: 17% for anhydrous soap and 30% for aqueous soap).…”

“…Many absorption bands approximately equally spaced and with weak or medium intensities, were observed in this region. They were assigned to wagging and twisting vibrations of successive methylene groups of the soap molecules (8,9).…”