Melting Point Apparatus Research Articles

Synthesis of Methyl (E)-2-Cyanomethylcinnamates Derived from Baylis-Hillman Acetates and Conversion into Several 4-Hydroxy-2-naphthoic Acids and Benzylidenesuccinimides

chromatography was supplied by E. Merck. Analytical thinlayer chromatography (TLC) was carried out on Mercksilica gel 60 F254 TLC plates. Melting points were takenusing an Electrothermal melting point apparatus and areuncorrected. Infrared spectra were recorded on a NicoletMagna 550 FTIR spectrometer. The

THE ALKALOIDS OF TRIBULUS TERRESTRIS: A REVISED STRUCTURE FOR THE ALKALOID TRIBULUSTERINE

ISHS III WOCMAP Congress on Medicinal and Aromatic Plants - Volume 3: Perspectives in Natural Product Chemistry THE ALKALOIDS OF TRIBULUS TERRESTRIS: A REVISED STRUCTURE FOR THE ALKALOID TRIBULUSTERINE

Percutaneous absorption of cyclizine and its alkyl analogues

Cyclizine ( I) alkyl analogues ( II– IV) were synthesized and their skin permeation parameters evaluated in vitro. It was hoped that these compounds would possess physicochemical properties more favourable for percutaneous delivery than ( I). The identification and levels of purity for the compounds were confirmed by mass spectrometry (MS), nuclear magnetic resonance (NMR) spectrometry, and infrared spectrometry (IR) while melting points were determined by an electrothermal digital Bϋchi melting point apparatus. Aqueous solubilities (25 °C) and partition coefficients were determined and in vitro permeation studies were performed in buffer (37 °C) at pH 7.4 over a period of 24 h, using Franz diffusion cells fitted with human epidermal membranes. Generally, the analogues were more lipophilic, but nevertheless possessed higher aqueous solubilities as compared to ( I). ( II) and ( IV) exhibited two- to three-fold increase in aqueous solubility and their melting temperatures dropped by more than 55 °C. Compound ( III) had similar aqueous solubility to ( I), but its melting point dropped by about 35 °C. Measured steady-state fluxes indicated that ( II) is a far better penetrant ( J = 6.95 μg/cm 2/h) of human epidermis than ( I). Although fluxes of ( III) and ( IV) drop off markedly from that of ( II), they remained above the flux of ( I), which is (0.132 μg/cm 2/h). In conclusion, ( II) was the best skin permeant and also exhibited the highest aqueous solubility and lowest level of crystallinity as compared to ( I) and other analogues. ( III) and ( IV) were more lipophilic. The overall permeation data of this series indicated that the more water-soluble and the lowest melting point compound was the best skin permeant.

Amphiphilogels for Drug Delivery: Formulation and Characterization

This study examines the microstructure, gelation temperatures, and flow properties of novel amphiphilogels consisting solely of non-ionic surfactants. Gels were prepared by mixing the solid gelator (sorbitan monostearate or sorbitan monopalmitate) and the liquid phase (liquid sorbitan esters or polysorbates) and heating them at 60 degrees C to form a clear isotropic sol phase, and cooling the sol phase to form an opaque semisolid at room temperature. Gel microstructure was examined by light and electron microscopy and by small angle neutron scattering (SANS); gelation temperatures were measured by hotstage microscopy, a melting point apparatus, and high sensitivity differential scanning calorimetry (HSDSC). Flow rheograms were performed to establish the zero-rate viscosity of the gels and their performance under shear. Gel microstructures consisted mainly of clusters of tubules of gelator molecules that had aggregated upon cooling of the sol phase, forming a 3D network throughout the continuous phase. The gels demonstrated thermoreversibility. Gelation temperature and viscosity increased with increasing gelator concentration, indicating a more robust gel network. At temperatures near the skin surface temperature, the gels softened considerably; this would allow topical application. This study has demonstrated the formation/preparation of stable, thermoreversible, thixtropic surfactant gels (amphiphilogels) with suitable physical properties for topical use.

Melting behaviour of d-sucrose, d-glucose and d-fructose

The melting behaviour of d-sucrose, d-glucose and d-fructose was studied. The melting peaks were determined with DSC and the start of decomposition was studied with TG at different rates of heating. In addition, melting points were determined with a melting point apparatus. The samples were identified as d-sucrose, α- d-glucopyranose and β- d-fructopyranose by powder diffraction measurements. There were differences in melting between the different samples of the same sugar and the rate of heating had a remarkable effect on the melting behaviour. For example, T o, Δ H f and T i (initial temperature of decomposition) at a 1 °C min −1 rate of heating were 184.5 °C, 126.6 J g −1 and 171.3 °C for d-sucrose, 146.5 °C, 185.4 J g −1 and 152.0 °C for d-glucose and 112.7 °C, 154.1 J g −1 and 113.9 °C for d-fructose. The same parameters at 10 °C min −1 rate of heating were 188.9 °C, 134.4 J g −1 and 189.2 °C for d-sucrose, 155.2 °C, 194.3 J g −1 and 170.3 °C for d-glucose and 125.7 °C, 176.7 J g −1 and 136.8 °C d-fructose. At slow rates of heating, there were substantial differences between the different samples of the same sugar. The melting point determination is a sensitive method for the characterization of crystal quality but it cannot be used alone for the identification of sugar samples in all cases. Therefore, the melting point method should be validated for different sugars.

Synthesis and characterization of polyimides from novel 1-(3′,5′-bis(trifluoromethyl)benzene) pyromelliticdianhydride (6FPPMDA)

Mono-substituted dianhydride monomer, 1-(3′,5′-bis(trifluoromethyl)phenyl) pyromellitic dianhydride (6FPPMDA), was prepared via the Suzuki cross coupling reaction followed by oxidation and cyclodehydration. The monomer was characterized by FT-IR, NMR, elemental analyzer (EA) and melting point apparatus. For comparison, 1-(4′-trifluoromethylphenyl)pyromellitic dianhydride (3FPPMDA) and 1-phenyl pyromellitic dianhydride (PPMDA) were also utilized. The dianhydrides were used to prepare polyimides with aromatic diamines such as bis(3-aminophenyl) 3,4-bis(trifluoromethyl)phenyl phosphine oxide ( mDA6FPPO), bis(3-aminophenyl) 4-(trifluoromethyl)phenyl phosphine oxide ( mDA3FPPO), bis(3-aminophenyl) phenyl phosphine oxide ( mDAPPO) and 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane ( p3FDAm). The polyimides were synthesized via a two-step process; preparation of poly(amic-acid) in p-chlorophenol with isoquinoline, followed by solution imidization at the reflux temperature for 12 h. Polymer characterization was carried out by FT-IR, NMR, GPC, DSC and TGA, and their solubility, solution viscosity, water absorption, CTE, dielectric constant and refractive index were also evaluated.

PhCOCl-Py/Basic Alumina as a Versatile Reagent for Benzoylation in Solvent-Free Conditions

A solvent-free procedure using PhCOCl-Py/basic alumina under microwave irradiation has been developed for N-, O- and S-benzoylation.

Nα-Urocanylhistamine: A Natural Histamine Derivative

Nα-Urocanylhistamine and two related compounds were synthesized by using PyBOP coupling protocols. These compounds represent naturally occurring histamine derivatives.

A Supramolecular Array of Fullerenes by Quadruple Hydrogen Bonding

General remarks. All reagents and solvents were used as received or purified using standard procedures. [60]Fullerene (99.5%) was purchased from Southern Chemical Group, LLC and used without purification. All reactions were performed under a nitrogen atmosphere unless indicated otherwise. Flash chromatography was performed using Kieselgel Merck Type 9385 (230-400 mesh). Analytical thin layer chromatography (TLC) was performed using aluminum coated Merck Kieselgel 60 F254 plates. Melting points were determined with a Mettler FP1 melting point apparatus equipped with a Mettler FP2 microscope. H-NMR and C-NMR spectroscopy were performed on a Varian Unity Plus (500 MHz) instrument or on a Varian VXR-300 (300 MHz) instrument as indicated, at 298 K. Coupling constants (J) are denoted in Hz. Multiplicities are denoted as follows: s = singlet, d = doublet, t = triplet, q = quartet, p = pentet, dd = double doublet, m = multiplet, br = broad. FT-IR spectra were recorded on a Mattson Galaxy 4020 instrument. UV-Vis spectra were recorded on a Hewlett Packard HP 8452 UV-Vis spectrophotometer. High Resolution Mass Spectroscopy (HRMS) were performed on a JEOL JMS 600 spectrometer (positive ion EI mode). MALDI-TOF-MS measurements were performed on a Micromass TofSpec E apparatus (negative-ion reflector mode) by using elemental sulfur as a matrix (See: Brune, D. C. Rapid Commun. Mass Spectrom. 1999, 13, 384 389). Measurements were performed on aliquots of the analyte (1 mg/mL) and elemental sulfur (10 mg/mL) in CS2 or CHCl3. HPLC analyses were performed on a Hewlett Packard HP LC-Chemstation 3D (HP 1100 Series) using an analytical Cosmosil Buckyprep column (4.6 x 250 mm). Cyclic Voltammetry was performed using an Autolab PGStat 100. Elemental analysis were performed by the Microanalytical Department of this laboratory.

ChemInform Abstract: Towards Diversity-Oriented Stereoselective Syntheses of Biaryl- or Bis(aryl)metal-Containing Medium Rings.

Experimental Techniques and Apparatus Except as otherwise indicated, reactions were carried out under argon with dry, freshly distilled solvents. Tetrahydrofuran was distilled from sodium/benzophenone ketyl. Anhydrous 2-methyltetrahydrofuran (Aldrich, racemic) was stored over activated molecular sieves. Dichloromethane was distilled from calcium hydride. n-BuLi in hexane (Aldrich) and t-BuLi in pentane (Aldrich) were titrated with 1,10phenanthroline and anhydrous 2-butanol before use. All other reagents were purif ied in accordance with the instructions in “Purif ication of Laboratory Chemicals” or used as obtained from commercial sources. Yields refer to chromatographically and spectroscopically pure compounds. All reactions were monitored by thin layer chromatography (TLC) using glass plates precoated with E. Merck silica gel 60 F254 or aluminium oxide 60 F254. Visualization was by the quenching of UV f luorescence (λmax=254nm) or by staining with ceric ammonium molybdate or Dragendorff ’ s reagent (0.08% w/v bismuth subnitrate and 2% w/v KI in 3M aq. AcOH). Retention factors (Rf) are quoted to 0.01. Melting points were obtained using a Mel-Temp II melting point apparatus and are uncorrected. Infrared spectra were recorded either as a thin f ilm between NaCl plates or as a KBr disc on a Nicolet 5PC FT-IR spectrometer with internal referencing. Absorption maxima (νmax) are reported in wavenumbers (cm) and the following abbreviations are used: w, weak; m, medium; s, strong; br, broad. Proton magnetic resonance spectra were recorded on Varian Mercury400 (400MHz), Bruker Avance DMX500 (500MHz), and Varian Unity/Inova500 (500MHz) spectrometers. Proton assignments are supported by H-H COSY, HMQC, NOESY and GOESY spectra where necessary. Chemical shifts (δH) are quoted in ppm and are referenced to tetramethylsilane (internal). Coupling constants (J) are reported in Hertz to the nearest 0.5Hz. Data are reported as follows: chemical shift, integration, multiplicity [br, broad; s, singlet; d, doublet; t, triplet; q, quartet; qui, quintet; sept, septet; m, multiplet; or as a combination of these (e.g. dd, dt, etc.)], coupling constant(s) and assignment. Diastereotopic protons are assigned as X and X', where the ' indicates the lower f ield proton. Carbon magnetic resonance spectra were recorded on Varian Mercury400 (100MHz) and Varian Unity/Inova500 (125MHz) spectrometers. Carbon spectra assignments are supported by DEPT editing and where necessary C-H (HMQC) correlations. Chemical shifts (δC) are quoted in ppm to the nearest 0.01ppm, and are referenced to tetramethylsilane (internal). Fluorine magnetic resonance spectra (F) were recorded on a Varian Mercury300 (282MHz) spectrometer. Chemical shifts (δF) are quoted in ppm to the nearest 0.01ppm and are referenced to CF3CH2OH (external). 4

Towards Diversity-Oriented, Stereoselective Syntheses of Biaryl- or Bis(aryl)metal-Containing Medium Rings

Experimental Techniques and Apparatus Except as otherwise indicated, reactions were carried out under argon with dry, freshly distilled solvents. Tetrahydrofuran was distilled from sodium/benzophenone ketyl. Anhydrous 2-methyltetrahydrofuran (Aldrich, racemic) was stored over activated molecular sieves. Dichloromethane was distilled from calcium hydride. n-BuLi in hexane (Aldrich) and t-BuLi in pentane (Aldrich) were titrated with 1,10phenanthroline and anhydrous 2-butanol before use. All other reagents were purif ied in accordance with the instructions in “Purif ication of Laboratory Chemicals” or used as obtained from commercial sources. Yields refer to chromatographically and spectroscopically pure compounds. All reactions were monitored by thin layer chromatography (TLC) using glass plates precoated with E. Merck silica gel 60 F254 or aluminium oxide 60 F254. Visualization was by the quenching of UV f luorescence (λmax=254nm) or by staining with ceric ammonium molybdate or Dragendorff ’ s reagent (0.08% w/v bismuth subnitrate and 2% w/v KI in 3M aq. AcOH). Retention factors (Rf) are quoted to 0.01. Melting points were obtained using a Mel-Temp II melting point apparatus and are uncorrected. Infrared spectra were recorded either as a thin f ilm between NaCl plates or as a KBr disc on a Nicolet 5PC FT-IR spectrometer with internal referencing. Absorption maxima (νmax) are reported in wavenumbers (cm) and the following abbreviations are used: w, weak; m, medium; s, strong; br, broad. Proton magnetic resonance spectra were recorded on Varian Mercury400 (400MHz), Bruker Avance DMX500 (500MHz), and Varian Unity/Inova500 (500MHz) spectrometers. Proton assignments are supported by H-H COSY, HMQC, NOESY and GOESY spectra where necessary. Chemical shifts (δH) are quoted in ppm and are referenced to tetramethylsilane (internal). Coupling constants (J) are reported in Hertz to the nearest 0.5Hz. Data are reported as follows: chemical shift, integration, multiplicity [br, broad; s, singlet; d, doublet; t, triplet; q, quartet; qui, quintet; sept, septet; m, multiplet; or as a combination of these (e.g. dd, dt, etc.)], coupling constant(s) and assignment. Diastereotopic protons are assigned as X and X', where the ' indicates the lower f ield proton. Carbon magnetic resonance spectra were recorded on Varian Mercury400 (100MHz) and Varian Unity/Inova500 (125MHz) spectrometers. Carbon spectra assignments are supported by DEPT editing and where necessary C-H (HMQC) correlations. Chemical shifts (δC) are quoted in ppm to the nearest 0.01ppm, and are referenced to tetramethylsilane (internal). Fluorine magnetic resonance spectra (F) were recorded on a Varian Mercury300 (282MHz) spectrometer. Chemical shifts (δF) are quoted in ppm to the nearest 0.01ppm and are referenced to CF3CH2OH (external). 4

Thermal analysis of paraffins as model compounds for polyethylene

The n-paraffins C50H102, C44H90, and C26H54 were analyzed with standard and temperature-modulated differential scanning calorimetry. Crystallization and ordering from the melt to the condis phase showed practically no supercooling. These observations were confirmed with hot-stage microscopy and a melting-point apparatus. Only the organization of the C26H54 condis crystals to fully ordered crystals showed a supercooling of 4.0 K. The measurement of the apparent reversing heat capacity with a 0.05-K modulation amplitude revealed that the melting of C50H102 was completed within 1.0 K and the isotropization of C26H54 was completed within less than 0.6 K, but 62–78% of the total transitions occurred over a much narrower temperature range of 0.1 K or less. The link to polyethylene was made with fractions of the masses 15,520, 2150, and 560 Da. The 560-Da sample corresponded to C40H82 and showed also almost no supercooling, whereas the others, with folded and extended-chain crystals, supercooled by about 10 K. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2810–2822, 2000

The evolution of hot-stage microscopy to aid solid-state characterizations of pharmaceutical solids

A variety of techniques can be used to characterize the physical properties of pharmaceutical solids, including thermal analysis, hot-stage microscopy, X-ray powder diffraction, spectroscopic and micromeritic analysis. Comprehensive characterizations of the physical properties of pharmaceutical solids require a multi-disciplinary approach, since no single technique is capable of characterizing the materials completely. The combination of traditional hot-stage microscopy with new technologies such as high-resolution micrography, image capture, storage manipulation, and presentation, have permitted more comprehensive physical property characterizations to be conducted. As a result of these technological advances, it is possible to present the results of these microscopic analyses, as they were initially collected by the microscopist, outside of the laboratory. An evolutionary trail detailing the use of hot-stage microscopy in the Materials Science Group, from a simple melting point apparatus to the current hot-stage DSC microscopy instrument, will be presented. Examples of materials characterized using the hot-stage microscopy system will also be presented.

Separation properties of bis(β-diketonato)–copper(II) complexes in capillary gas chromatography

The bis[1-4′-(octyloxybiphenyl-4-yl)-3-(1′-methylpropyl)-1,3-dionato]– and bis[1-4′-(nonyloxybiphenyl-4-yl)-3-(1′-methylpropyl)-1,3-dionato]–copper(II) complexes were synthesized and successfully coated onto a fused-silica capillary column. The results obtained from differential scanning calorimetry and the melting point apparatus equipped with a polarization microscopy showed that they present a nematic phase and have a very limited liquid crystalline temperature range under cooling conditions. The chromatographic experiments show that these metal complexes possess good separation abilities for many different kinds of di- and tri-substituted benzene isomers, polycyclic aromatic hydrocarbons and constituents of volatile oils. In order to illustrate the influence of the presence of copper in the molecules of the stationary phase, the selectivities of 1,3-diones were compared with their corresponding bis(β-diketonato)–copper(II) complexes.

Base–compositional biases and the bat problem. I. DNA–hybridization melting curves based on AT– and GC–enriched tracers

We explored the interordinal relationships of mammals using DNA-DNA hybridization, with particular reference to the much-debated problem of whether the megabats and microbats are more closely related to each other than the megabats are to primates. To try to improve resolution when taxa are distantly related and the melting points of hybrids are low and difficult to distinguish, we increased the GC content of DNA by a fractionation method that used the same melting-point apparatus used in the hybridization studies. When we used GC-rich DNA as the tracer to make hybrids, the melting point of the self-hybrid shifted to a higher temperature as expected, but the behaviour of heterologous hybrids varied with the taxa being compared. When the melting point of the heterologous hybrid also shifted to a higher temperature so that the two compared taxa maintained the same or proportional distance, we called this 'following behaviour', because the heterologous hybrid made with GC-rich tracer 'followed' the GC-rich self-hybrid to higher temperatures. We also commonly saw anomalous behaviour, where the melting point of the heterologous hybrid shifted to a lower temperature when compared with an AT-rich hybrid. In these anomalous cases, the distance measured between the taxa increased markedly as a result of GC-enrichment, indicating that an underestimate of distance may have resulted from AT bias in DNA. This inference was supported by the finding that it was rare to observe a decrease in measured distance between taxa using GC-rich DNA, but very common to find an increase as would be expected from the generally higher AT contents of eutherian DNAs. Moreover, the most extreme cases, where distances changed most using GC-rich DNA, were usually those involving comparisons between taxa known to have the most extreme AT-biases among mammals, such as the megabats and rhinolophoid (including megadermatid) microbats. Our results show consistent underestimates of measured differences between eutherian taxa with extreme AT-biases.

The catalytic synthesis of polycarbosilane in the presence of boron tributoxide

Synthesis of substantially polycrystalline silicon carbide fibre, which has excellent mechanical properties and heat resistance, has been reported. Such a silicon carbide fibre can be prepared from preceramic polymers [1, 2]. Usually, the synthesis of precursor polycarbosilane (PC) was at high temperature and under high pressure. Then, in the synthesis process, polyborodiphenylsiloxane (PBSO) was used as a reaction catalyst [3-5], which is prepared from the slow, complex reaction between boric acid and diphenyldichlorosilane. In our experiment, polycarbosilane precursor containing titanium was obtained by the reaction between titanium tetrabutoxide [Ti(OBu)4] and liquid polysilane (LPS), which was derived from destructive distillation of polysilane (PS) in nitrogen gas [6]. Therefore, a similar reaction between boron tributoxide [B(OBu)3 ] and LPS was carried out in order to prepare polycarbosilane containing boron. The experimental results show that it seems to be difficult to introduce B(OBu)3 into the molecular structure of polycarbosilane, but the increase of molecular weight of polycarbosilane is accelerated remarkably in the presence of B(OBu)3. Evidently, the troublesome preparation process of PBSO can be eliminated by replacement of PBSO with B(OBu)3 as a catalyst. In the present work, the synthesis of polycarbosilane from LPS and B(OBu)3 according to different weight ratios is reported. The effects of B(OBu)3 on the structure and properties of polycarbosilane products are discussed. B(OBu)3 and LPS derived from destructive distillation in nitrogen gas up to 420 °C were mixed in certain weight ratios in a three-necked flask equipped with a quartz reactor tube, a recycling system and a thermometer. The mixtures were heated slowly in a nitrogen gas flow to a given temperature and the reaction proceeded at this temperature for 1 h, then the products were dissolved in toluene. After filtering and distillation, PC as a yellow solid was obtained. The infrared (IR) spectra of products were measured using a Hitachi 270-30 infrared spectrophotometer. The solid samples were measured by the KBr pellet method and the samples obtained at different t e m p e ~ e s during the reaction process were measured with a fixed-thickness (0.2 ram) cell of KBr in CC14 solution. The munber average molecular weights (Mn) and molecular weight distributions were measured using a Watters-244 liquid chromatograph with Ultrastyragel as the gel permeation chromatography (GPC) column in toluene solution. The melting points (Tm) were obtained with a melting point apparatus (model HMK, Germany). LPS can be regarded as a mixture of cyclic and linear low molecular weight polysilane, and its structure is assumed to be [6]:

Film Formation with Coating Systems of Aqueous Suspensions and Latex Dispersions of Ethylcellulose.

We examined the film formation of an aqueous suspension system using micronized ethylcellulose (EC) in comparison with an EC latex system. The minimum film-forming temperatures (MFT) of the two systems and the glass transition temperature (Tg) of EC were measured with a micro melting point apparatus and a differential scanning calorimeter, respectively. Replicas of the free films prepared from the two systems were examined under a transmission electron microscope. The release of theophylline from granules coated with the two systems was compared to investigate the effect of curing, in which the coated granules were heated for an hour at 80°C. MFT and Tg decreased as the amount of triethyl citrate used as a plasticizer increased in both systems. MFT of the suspension system was higher than Tg, while that of the latex system was lower than Tg. A replica of the free film from the suspension system showed no shapes of the EC particles used; in contrast, that from the latex system showed the shape of individual latex spheres in coalescence. Curing had no effect on the release behavior of the suspension-coated granules, whereas it remarkably delayed release from the latex-coated granules. The replica method revealed that the coalescence of latex particles was more complete after curing than before. These results demonstrate that the mechanisms of film formation of these two systems are different, and that this difference results in different properties of films prepared by the two systems.

Glass–Rubber Transitions of Cellulosic Polymers by Dynamic Mechanical Analysis

The glass–rubber transition temperatures (Tg) of several cellulosic polymers [hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC)] have been examined using dynamic mechanical analysis (DMA). The melting temperatures of the above polymers were examined using a hot stage melting point apparatus. The primary Tg of three different grades of HPMC (3, 6, and 15 cps) were determined to be 160, 170, and 175°C, respectively. The primary Tg of the HEC film was determined as 120°C. The HPC film did not indicate a primary Tg. These cellulosic polymers also displayed secondary transitions. Hot stage melting of HPMC and HPC was observed at 225 to 254°C and 190 to 195°C, respectively. The HEC powder did not exhibit a melting temperature, but became darker at temperatures >150°C.

Calibration of capillary melting-point apparatus to the international temperature scale of 1990 (ITS-90) by use of fluxed highly pure metals

Capillary melting-point measurements have always lacked traceability to internationally accepted or precisely determined temperature standards. Highly pure (99.999%) indium, tin, bismuth, and cadmium or lead, when covered with stearic anhydride acting as a flux, gallium covered with 3 M HCl and zinc covered with m-( m- phenoxyphenoxy)benzene containing triphenylboron, give sharp visual melting points which correspond to primary or secondary “fixed points” on the International Temperature Scale of 1990 (ITS-90). Melting is observed to begin with collapse and coalescence to a mush. It ends with the formation of a mercury-like spheroidal droplet, taken as the melting point; the entire range is less than 0.5°C. Readings may be interpolated either graphically or computationally to give tabular corrections yielding true temperatures. The performance of thermometers cannot safely be predicted from information engraved thereon, as > 10° errors were observed. It is recommended that organic chemical publications insist on the use of the phrase “The m.p. apparatus was metal calibrated to ITS-90”.

Thermal degradation of glycosides, II. Thermal effect on acetates of typical triterpenoid and steroid glycosides

AbstractThe termal effect on acetates of triterpenoid and steroid glycosides was examined. Contrary to the case of free glycosides, on heating the acetates of typical triterpenoid and steroid glycosides (including cardiac glycosides) on a melting point apparatus the cleavage reactions of sugar–aglycone and sugar–sugar linkage did not take place, and no aglycones or prosapogenins were obtained. However, two interesting and useful reactions did occur in the course of thermolysis of cardiac glycoside acetates. By taking into account the thermal effect on the glycoside acetates, and their FD mass spectra, an important suggestion on the mechanism of FD mass fragmentation of the glycosidic linkage was obtained.