Organic Fluorine Compounds. Part XXXVII the Preparation of ω-Amino-α-Fluroacids

γ-Amino-α-fluorobutyric acid (V) and ?-amino-α-fluorocaproic acid (VII) have been prepared from the corresponding phthalimido-α-bromo-acid anilides (or other amides) through reaction with potassium fluoride and subsequent hydrolysis.     

Photochemistry of α,α′-Disubstituted Azoalkanes. I. Photosolvolytic Inversion and Substitution of α,α′-Dichloro- and α,α′-Dialkoyloxyazoalkanes

A series of α,α′-dichloro (α DClA), α,α′-dialkoyloxy- (αDAlA) and α,α′-dibenzoxy-azoalkanes (αDBeA) without α-aryl substituents was found to undergo meso ? dl photointerconversion upon direct irradiation through Pyrex in the presence of oxygen in a number of solvents. Furthermore, irradiation of α,α′-dipropionoxy-azoalkanes in benzene in the presence of excess acetic acid leads to substitution of the propionoxy groups by acetoxy groups in addition to meso ? dl photointerconversion. Similar irradiation in the presence of CH₃CO₂D does not lead to deuterium substitution of the β-hydrogens. The presence of benzenethiol radical scavenger does not affect the course of these photoreactions. Photosolvolysis schemes involving heterolysis (in the case of αDAlA and αDBeA) or an unstable intermediate (in the case of αDClA) are proposed.     

Polymorphie von zweisäurigen Triglyceriden der Stearinsäure- und Behensäure-Reihe

Polymorphism of Diacid Triglycerides of the Stearic Acid and Behenoic Acid Series Short- to medium-chain saturated diacyl derivatives of 1-monostearin and 1-monobehenin were synthesized in highly pure state and tested for their polymorphous behaviour. With the exception of the dicaprylo derivative the triglycerides of the behenoic acid series were strikingly stable in a wax-like plastic and stretchable α- resp. subα-modification which is obviously stable in the stearic acid series. The most stable modification of both series was the β-form, only the dibutyro-1-monobehenin by no manner could be transformed to a β′- or β-form. On heating the chilled samples or vice versa on cooling of the α-form two adjacent reversible phase transitions (subα₂ ? subα₁ ? α) could be observed with most of the triglycerides investigated here whereas in literature in case of the 1-monostearin derivatives the existence of only one subα-form has been described up to now.     

Seeds-induced synthesis of SiC by microwave heating

α-SiC particles were used as heating seeds to prepare SiC from coal minerals with microwave heating method. Coating technique was carried out to prepare composite raw powders in three different methods. Heating temperatures were at 1000?°C, 1050?°C, 1100?°C, 1150?°C, 1200?°C for 10min, respectively. XRD, SEM techniques were carried out to characterize samples. It was found that different distribution between C and α-SiC particles from different mixing method leads to different microwave heating behavior and growth mechanisms. V-V reaction leads to in situ nucleation and grain growth on the surface of α-SiC seeds which contact with C particles. Well-grown β-SiC particulates appear. Hybrid V-V reaction V-L reaction lead to local microwave plasma and diffusion-precipitation with a very thin layer of SiO₂ between raw C particles and α-SiC seeds. Local fine β-SiC whiskers and particulates on the surface of α-SiC seeds co-exist. Primary V-V reaction leads to nucleation and grain growth along reacted C-SiO₂ interface with very thick layer of SiO₂ between raw C and α-SiC seeds. Substantial β-SiC whiskers appear. Transformation from β-SiC to α-SiC on the surface of as-formed whiskers will be enhanced by microwave plasma at high temperature.     

Application of nickel(II) complexes to the efficient synthesis of α- or β-amino acids

Nonproteinogenic α- or β-amino acids have attracted tremendous attention, as they are widely utilized for biological, biochemical, pharmaceutical, and asymmetric chemical investigations. Recently, we developed a series of new strategies for preparing achiral and chiral nickel(ii) complexes for the synthesis of amino acids. We applied these new methods utilizing chiral nickel(ii) complexes for the asymmetric Mannich reaction to synthesize enantiopure α,β-diamino acids, the enantioselective tandem conjugate addition-elimination reaction to prepare glutamic acid derivatives, the Suzuki coupling reaction to yield β(2)-amino acid derivatives, the asymmetric Mannich reaction to synthesize 3-aminoaspartate, the asymmetric Michael addition reaction to give β-substituted-α,γ-diaminobutyric acid derivatives, the asymmetric alkylation reaction to prepare linear ω-trifluoromethyl containing amino acids, and the asymmetric Michael addition reaction to synthesize syn-β-substituted tryptophans.     

Synthesis of ionones on solid Brønsted acid catalysts: Effect of acid site strength on ionone isomer selectivity

The effect of Brønsted acid site strength on the liquid-phase conversion of pseudoionone to ionone isomers (α-, β- and γ-ionone) was studied on resin Amberlyst 35W, silica-supported heteropolyacid (HPAS) and silica-supported triflic acid (TFAS). Catalyst acidity was probed by temperature-programmed desorption of NH₃ coupled with infrared spectra of adsorbed pyridine. The initial pseudoionone conversion rate followed the order: TFAS > Amberlyst 35W ≈ HPAS. Synthesis of the three ionone isomers occurred via a common cyclic carbocation intermediate formed from the activation of the pseudoionone molecule on Brønsted acid sites. Initial ionone mixtures containing a α:β:γ isomer distribution of about 40:20:40 were formed, irrespective of the acid site strength. But the ionone mixture composition changed with the progress of the reaction because γ-ionone was consecutively converted to α-ionone on HPAS and Amberlyst 35W, whereas the stronger acid sites of TFAS converted γ-ionone to β-ionone.     

Phase formation and microstructural evolution of Ca α-sialon using different Si3N4 starting powders

Silicon nitride has two polymorphous structures, α-Si₃N₄ and β-Si₃N₄. In this study three different Si₃N₄ starting powders (∼100%α, 40%α+60%β, ∼100%β) were used to prepare Ca α-sialon with the composition Ca_1.8Si_6.6Al_5.4O_1.8N_14.2 by pressureless sintering. Comparison was made concerning the densification process, reaction sequence and microstructure of the corresponding materials. The sluggish reactivity of β-Si₃N₄ resulted in poorer densification during sintering. All the three starting powders produced a similar final phase assembly, namely α-sialon together with a small amount of AlN and AlN polytypoid except that traces of unreacted β-Si₃N₄ remained until 1800° in samples prepared with ∼100%β-Si₃N₄ powders. Elongated α-sialon grain morphology has been identified in the samples prepared using all the three different Si₃N₄ starting powders. Coarser elongated α-sialon grains with lower aspect ratio were found in samples using higher β phase starting powders.     

Konfigurative Zuordnung über sterisch definierte Epoxidringe. XI. Glycidonitrile. IV.1. Synthese von 1α-Methyl-2α-aryl-cyclohexan-1ß-carbonsäuren aus 4α-Aryl-2-methyl-1α-oxaspiro. octan-2-nitrilen

Determination of Configurations by the Aid of Sterically Corresponding Epoxides. XI. Glycidic Nitriles. IV. Synthesis of 1α-Methyl-2α-aryl-cyclohexane-1ß-carboxylic Acids from 4α-Aryl-2-methyl-1α-oxaspiro[2, 5]octane-2-nitriles The opening of an epoxide ring of the C-2-isomeric glycidic nitriles 1a–b with anhydrous HCl in dry Et₂O yields the corresponding chlorocyanohydrines 2a–b . Treatment of these chlorocyanohydrines with diluted NaOH does not give the expected α-chloroketones 3a–b , but only the original glycidic nitriles. Dehydrocyanation of the chlorocyanohydrines 2a–b is carried out by column chromatography on silica or neutral Al₂O₃. Favorskii rearrangement of the resulting α-chloroketones 3a–b gives the angular methylated carboxylic acid methyl esters 4a–b , which are converted to the acids 5a–b by saponification with NaOH in quantitative yield. Better reaction conditions for the Favorskii rearrangement of 1-acetyl-1-chloro-cyclohexanes are described.     

Poly-α-amino acid fibres

Poly-α-amino acid fibre being rich in β-form has a silky quality. The fibre being rich in α-form becomes woolly. When there is a strong interaction force through side chains of poly-α-amino acid molecules, the polymer solution is not spinnable regardless of the film forming ability. As it is difficult to spin a strong fibre directly from a polymer in α-form, the spinning solution should contain some parts of random coil in the α-form and the fibre molecules should be oriented in a parallel with the axis by stretching. Finally, most of the remaining β- or random-parts should be retransformed into the α-form. The β-form of poly-L-alanine is most stable and most analogous to silk, but most of β-form in poly-L-leucine stretched fibre is transformed into the α-form in boiling dioxane and the woolly character appears. The character of poly-α-amino acid fibres seems to depend on the contents of α- and β-form. Poly-L-leucine fibre in the α-form is stable in boiling water and it seems to be unnecessary to introduce a cystine bridge into the fibre to maintain a woolly character. By copolymerizing a small amount of methionine into a polymer, the dyeability of fibres is remarkably improved.     

Effect of starting Si3N4 powder type and sintering conditions on grain morphology of α-SiAlON ceramics

Abstract

Nitrogen rich multication α-SiAlON ceramics doped with Y-Ce have been densified by gas pressure sintering using α-Si₃N₄ or mixed β/α-Si₃N₄ starting powder. The effects of α-SiAlON nucleation and growth mechanisms were investigated by using di fferent sintering cycles. X-ray diffraction studies after sintering revealed that 21R polytype phase was present in addition to α -SiAlON matrix phase. Microstructural characterisation of sintered materials prepared using α-Si₃N₄ powder in the starting composition revealed a typical equiaxed grain morphology, as expected if the α-SiAlON nucleation step was not applied before grain growth. However, needlelike α-SiAlON grains were observed if a nucleation step was carried out before final sintering. In starting powders containing mixed β/α-Si₃N₄, needlelike grain morphology was also observed. The effects of different Si₃N4 starting powders and sintering conditions on the grain morphology and mechanical properties are discussed.     

Neue,hochechte organische pigmente

Malonic acid dianilides, which are readily obtainable from malonic ester and anilines, are suitable coupling components for the production of azo pigments, and yield, for example when using amino-anthraquinones as diazo components, pigments with in some cases excellent fastness values. The reaction of malonic ester with anthranilamide produces, under specific conditions, 2,2′-methylene-bis-4-hydroxyquinazoline, a new intermediate which is particularly suitable for the production of pigments.Anthraquinone azomethine pigments obtained from amino-anthraquinones and methylene-active intermediates can easily be produced; for example, using orthoformic acid esters. By reaction with methylene-bis-4-hydroxy-quinazolines, β-hydroxynaphthoic acid anilides, dihydroxyquinolines and pyridones, new, deeply coloured, azomethine pigments, often with excellent fastness values, are thereby obtained.     

Comparison of the fracture and failure behavior of injection-molded α- and β-polypropylene in high-speed three-point bending tests

The fracture and failure mode of α- and β-isotactic polypropylene (α-iPP and β-iPP, respectively) were studied in high speed (1 m/s) three-point bending tests on notched bars cut from injection-molded dumbbell specimens and compared. The fracture response of the notched Charpy-type specimens at room temperature (RT) and −40°C, respectively, was described by terms of the linear elastic fracture mechanics (LEFM), namely fracture toughness (K_c) and fracture energy (G_c). K_c values of both iPP modifications were similar, while G_c values of the β-iPP were approximately twofold of the reference α-iPP irrespective of the test temperature. It was demonstrated that β-iPP failed in a ductile and brittle-microductile manner at RT and −40°C, respectively. By contrast, brittle fracture dominated in α-iPP at both testing temperatures. Based on the fracture surface appearance, it was supposed that β-to-α (βα) transformation occurred in β-iPP. The superior fracture energy of β-iPP to α-iPP was attributed to a combined effect of the following terms: morphology, mechanical damping, and phase transformation. Results indicate that their relative contribution is a function of the test temperature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2057–2066, 1997     

Studies of relaxation phenomena in polymers. III. Superimposed transition mechanisms in polyisobutylene and poly(vinyl acetate)

Based on the general properties of the function log J₂ = g_α{log J₁}, discussed in earlier papers,^1,2 the existence of two superimposed dispersion mechanisms in the glass–rubber transition of polyisobutylene (PIB), and poly(vinyl acetate) (PVAc) is discussed. A simple weighting model is used for separation of the two mechanisms. For the interpretation of the β-mechanism, in PIB, the following facts are taken into account: (a) The loss maximum of the β-mechanism appears in a zone where only very reduced segment movements occur. (b) The methyl side groups in PIB require special conformations of the main chains before they can rotate. (c) The apparent activation energy for the β-mechanism is approx. 20 kcal/mole. Thus, for PIB the following interpretations for the α- and β-mechanisms are proposed: (1) The α-mechanism is due to simple segment movements. (2) The β-mechanism appearing in the “T_g region” is due to coupled movements between the main chain and methyl side groups. The ester groups of poly(vinyl acetate) need a lot more space for their rotations than the carboxy groups of poly(methyl acrylate) and can be expected to give considerable steric hindrance. It is therefore reasonable to suppose that a transition mechanism similar to the β-mechanism of polymethacrylates will appear in the “freezing” region of poly(vinyl acetate). The analysis of the β-mechanism is made using the same separation method as for polyisobutylene.     

Synthesen von β-Fur-2-yl-α-halogenacrylonitrilen

Syntheses of β-Fur-2-yl-α-halogenacrylonitriles Syntheses of β-fur-2-yl-α-halogenacrylonitriles 2a–f by Wittig-olefination of furfurales, Hunsdiecker-reaction of β-(5-nitro-fur-2-yl)-α-cyanoacrylic acid 3 , halogenation of β-fur-2-yl acrylonitriles and reaction of furfurales with β-azido-α-halogen-γ-methoxy-Δ^α,β-crotonolactones 9 are described.     

Studies of the Ramberg-Bäcklund Rearrangement. Part I. Rearrangement of α-Bromo-β-Keto- and α-Bromo-α-Carbethoxy-Sulphones

α-Bromosulphones, carrying negative substituents (keto or carbethoxy-groups) next to the bromine atom, undergo the Ramberg-Bäcklund rearrangement and give α,β-unsaturated ketones and esters. β-Disulphones are converted into α, β-unsaturated sulphones under these conditions.     

Wear behaviour of α- and α/β-SiAlON ceramics stabilized with Nd2O3 and Y2O3

α- and α/β-SiAlON compositions, doped with Y₂O₃ or Nd₂O₃, were densified by gas pressure sintering (GPS). The wear and mechanical properties of the materials were investigated and compared to β-Si₃N₄ materials. Microstructure evolution and its change with composition as well as the influence of the microstructural changes on the mechanical and tribological properties were reported. Wear tests were performed using a tribometer with ball-on-plate geometry in reciprocating sliding contact under dry condition. It was observed that α/β-SiAlON compositions, doped with Y₂O₃, have better wear properties in comparison to α-SiAlON and β-Si₃N₄ samples. Field emission scanning electron microscopy (FESEM) was used to analyse the worn surfaces after wear tests. The results showed that α/β-SiAlON and β-Si₃N₄ materials have different wear behaviour.     

乙酰丙酸反应分离一体化制α-当归内酯

以生物质基平台化合物乙酰丙酸为原料,磷酸为催化剂,在较低温度下合成了α-当归内酯。通过对反应规律的考察,发现α-当归内酯在反应工艺条件下不稳定,只有及时将生成的α-当归内酯导出反应体系,才能有效提高反应收率。作者采用反应分离一体化工艺,分别考察了反应温度、磷酸质量分数和体系压力对α-当归内酯收率的影响,确定的最佳反应条件为:反应温度140℃,磷酸质量分数3%,体系压力9kPa。在该反应条件下α-当归内酯的选择性达96%,收率达88%。     

α-Substituierte Phosphonate. 37. α-Pyrrolomethanphosphonsäurederivate und N-Vinylpyrrole

α-Substituted Phosphonates. 37. Derivatives of α-Pyrrolomethanephosphonic Acid and N-Vinylpyrroles Diethyl α-aminomethanephosphonate 5a and its α-aryl derivatives 5b–d react with 2,5-diethoxytetrahydrofuran 1 to give diethyl α-pyrrolomethanephosphonate 9a and the α-aryl derivatives 9b–d , respectively. The pyrrolo derivatives 9 can be converted into the lithium salts 15 and 16 , respectively, which with carbonyl compounds undergo the HORNER reaction yielding E/Z-mixtures of N-vinylpyrroles 18 . In certain cases the intermediate of the HORNER reaction, the β-hydroxyphosphonate 17 , can be isolated. The pyrrolo-analogue of stilbene, 18a , is formed only as E-isomer. On treating the lithium salts 15 and 16 with 9 or with alkyl halides α-C-alkylated pyrrolo-phosphonates 22 and 23 , respectively, are obtained.     

Mechanism of the solvent-mediated transformation of taltirelin polymorphs promoted by methanol

Taltirelin, a central nervous system activating agent, has two crystal forms (α- and β-forms). Previously it has been reported that methanol (MeOH) as a co-solvent promoted the solvent-mediated phase transformation from α-form to β-form. In the present study, the mechanism of the promotion was investigated. Of the three processes in the solvent-mediated transformation, namely dissolution of the metastable form, nucleation of the stable form, crystal growth of the stable form, MeOH promoted the latter two processes. In particular, the nucleation was strongly promoted. The nOe (nuclear Overhauser effect) data suggested that MeOH promotes the conformational change from the α-form to the β-form. The solute–MeOH interaction resulted in the formation of pseudo-polymorphs of the β-form (2H₂O·MeOH or H₂O·2MeOH solvate), although these pseudo-polymorphs were exchangeable to the β-form (4H₂O solvate) under a humid atmosphere. Based on these findings, a possible mechanism of the transformation of taltirelin polymorphs in the presence of MeOH was discussed.