Steric Effects in the Formation of Copper and Cobalt Complexes with the Epimeric Salicylidenementhylamines
IN a previous communication1, it was reported that cobaltous ions do not react readily with salicylidene-aniline bases bearing ortho substituents on the aniline ring. In the present communication are reported some further attempts to prepare similar complexes of cobalt and copper, using as the amine components of the salicylidene bases four epimeric forms of menthylamine which, with bulky isopropyl substituents and nonplanar ring forms, may be expected to exert considerable steric resistance to a tetrahedral grouping of ligands about cobalt ions. The complexes were prepared by mixing aqueous solutions of the metal acetates with an alcoholic solution of the salicylidene base2. The results of this work are indicated in Table 1, the complexes isolated being of the form bis (salicylidenementhylamine) cobalt (copper).
Structure of Cobalt Complexes with Salicylideneanilines
THE structures of cobalt inner complexes with salicylideneanilines have not been determined, whereas the planar form of copper complexes of this type has been established beyond doubt by the isolation of cis and trans isomers1 and by X-ray investigation2. A difference in reactivity has now been observed between copper and cobalt ions with various salicylideneaniline bases which suggests a tetrahedral structure for the cobalt complexes. Attempts have been made to prepare complexes of the type bis-(salicylideneaniline)cobalt with bases containing aromatic amines bearing substituents in the ortho, meta and para positions. The compounds prepared are tabulated below together with the corresponding copper complexes previously prepared3.
Development of new analytical methods for the determination of caffeine content in aqueous solution of green coffee beans
BackgroundThis study was conducted to develop fast and cost effective methods for the determination of caffeine in green coffee beans. In the present work direct determination of caffeine in aqueous solution of green coffee bean was performed using FT-IR-ATR and fluorescence spectrophotometry. Caffeine was also directly determined in dimethylformamide solution using NIR spectroscopy with univariate calibration technique.ResultsThe percentage of caffeine for the same sample of green coffee beans was determined using the three newly developed methods. The caffeine content of the green coffee beans was found to be 1.52 ± 0.09 (% w/w) using FT-IR-ATR, 1.50 ± 0.14 (% w/w) using NIR and 1.50 ± 0.05 (% w/w) using fluorescence spectroscopy. The means of the three methods were compared by applying one way analysis of variance and at p = 0.05 significance level the means were not significantly different. The percentage of caffeine in the same sample of green coffee bean was also determined by using the literature reported UV/Vis spectrophotometric method for comparison and found to be 1.40 ± 0.02 (% w/w).ConclusionNew simple, rapid and inexpensive methods were developed for direct determination of caffeine content in aqueous solution of green coffee beans using FT-IR-ATR and fluorescence spectrophotometries. NIR spectrophotometry can also be used as alternative choice of caffeine determination using reduced amount of organic solvent (dimethylformamide) and univariate calibration technique. These analytical methods may therefore, be recommended for the rapid, simple, safe and cost effective determination of caffeine in green coffee beans.