Donald Mitcham

Fatty acid polymorph identification by infrared

IR spectra in the 7.5–25.0 µm region are shown to be unique for polymorphic modifications of long chain saturated fatty acids of even carbon number and also for the individual fatty acids. IR spectra are presented for the A-, B-, C- and E-forms of stearic acid and for the C-form of myristic, palmitic, arachidic and behenic acid and the differences discussed. X-ray determined crystal long spacings for the A-, B-, C- and E-forms of a series of homologous even carbon-numbered acids are presented and compared with literature values. The formation of the different polymorphic forms are found to be temperature-concentration related and affected little by polarity of the solvent. Wideline nuclear magnetic resonance second moment values are given for the polymorphic forms of stearic acid.

Improved method for determining gossypol in crude cottonseed oils

SummaryThe p-anisidine method for the determination of gossypol in crude cottonseed oils has been reinvestigated and modified to make it applicable to all crude oils obtained by the newer methods of processing cottonseed. The modifications included a change in the composition of the solvent, a higher reaction temperature, and the use of a more concentrated panisidine reagent. The modified method was found satisfactory where different colorimeters and spectrophotometers were used for measuring the color developed.Comparison of aniline and p-anisidine as reagents for the analysis of gossypol pigments showed that the presence of modified gossypol in some crude oils resulted in an over-correction for background absorption and led to significant errors when aniline was used as the color development agent.

Identification of fatty acid polymorphic modifications by infrared spectroscopy

IR spectra in the 7.5–25.0 μ region are shown to be unique for the individual long chain odd carbon numbered saturated fatty acids and for the monounsaturated even carbon numbered fatty acids, their isomers, and polymorphic modifications. IR spectra are presented which illustrate similarites and dissimilarities resulting from chain length differences and polymorphic variations for monounsaturated acids. X-ray crystal long spacings for the saturated odd carbon numbered acids are compared with literature values. X-ray crystal long spacings for monounsaturatedtrans acids are shown to be related to carbon chain length and independent of the location of unsaturation. Diffractograms and IR spectra of the 2 polymorphic modifications of elaidic acids are presented. IR spectra illustrating band differences forcis andtrans isomers are shown.

Unit cell dimensions of some long chain fatty acid polymorphs

Unit cell dimensions and space group assignments for several polymorphic fatty acids have been determined by using single-crystal X-ray precession photography. This technique is useful to distinguish the closely similar B- and E-forms of stearic acid which have nearly identical crystal long spacings but significantly different unit cell dimensions and monoclinic angles. Other samples studied were the B-form of arachidic and behenic acids and the unsaturated acids,trans-9-octadecenoic andtrans-5-eicosenoic.

A new polymorphic form of elaidic acid

A new polymorphic modification of elaidic acid has been prepared and characterized. The common crystalline form, mp 43.7C, is shown to be metastable. The crystals of the new, stable form have a higher melting point, 44.8C, and a lower solubility. The two modifications give distinctive x-ray diffraction patterns: stable form, long spacing 94.0Å (or possibly 47.0Å), characteristic short spacings at 4.55Å (s), 4.44Å (vs), 3.81Å (vs), and 3.68Å (s); metastable form, long spacing 48.7Å, characteristic short spacings at 4.12Å (vs) and 3.71Å (s). The short spacings of the stable form are similar to those reported for thetrans-6-, 8-, 10-, and 12-octadecenoic acils, and the short spacings of metastable form are essentially the same as those of thetrans-7- and 11-octadecenoic acids. Solubility data have been obtained for both polymorphic forms in methanol.

Cold Stage for X-ray diffractometer studies of lower-melting polymorphs of triglycerides

Fabrication of an inexpensive cold stage attachment for an X-ray diffraction unit that gives satisfactory results to −21 C is described. X-ray diffraction data for several lower-melting polymorphs of cocoa butter are included.

Silica content of dusts from five texas cottonseed oil mills

Total dust samples, collected with high-volume samplers, were ashed and then analyzed for aluminum, silicon and silica (SiO2). Ash and aluminum contents agreed with earlier reported data, but the silicon content was lower. The amounts of silica ranged from 2–7% in dusts from the cleaning rooms to 0.01–0.05% in dusts from the baling rooms. Agreement with silica contents determined by infrared (IR) spectrometry was good. IR spectra indicated silica particle diameters were in the range of 6–8 µm in the cleaning rooms and 10 µm or more in the delintering and baling rooms. Threshold limit values (TLV) calculated on the basis of total silica in the high-volume samples suggest silica values above the limit in 4 of the cleaning rooms, and possibly one at the delintering rooms. Calculation of respirable silica concentrations and TLV for respirable silica was precluded by the sampling method.

Long spacings of six alkyl esters of two octadecenoic acids

X-ray powder diffraction data are presented for some normal alkyl esters of two octadecenoic acids. The crystal long spacings observed for esters of elaidic acid are shown to be linearly related to the length of the carbon chain of the ester group. Little difference in crystal long spacings was observed between esters ofcis andtrans acids. Melting points of alkyl esters of elaidic acid are reported.