Hydrochloride method for the determination of monomer in the polycondensation of esters of α-amino acids

Summary A method is proposed for determining the monomer in the polycondensation of esters of-amino acids. The accuracy of the method was to within 1–1.5%.     

Nonstoichiometric polycondensation I. synthesis of polythioether from dibromomethane and 4,4′-thiobisbenzenethiol

High molecular weight poly(phenylene thioether) ( 3 ) was successfully obtained by the polycondensation of 4,4′-thiobisbenzenethiol ( 1 ) and dibromomethane ( 2 ) with a variety of feed ratios in the presence of 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) in 1-methyl-2-pyrrolidinone (NMP) at 75°C. The resulting polymer showed the maximum inherent viscosity (η_inh) of 0.50 dL/g in 4 h when 1.5 equivalents excess of 2 was used. The model reaction using benzenethiol ( 4 ) and dichloromethane ( 5 ) in the presence of DBU in deuterated dimethylsulfoxide (DMSO-d₆) at 25°C indicated that the rate of the second nucleophilic displacement reaction (k₂) is 61 times faster than that of the first one (k₁). The maximum of theoretical molecular weights calculated at various stoichiometric imbalance (S) under the condition of k₂/k₁ = 61 showed a good agreement with the experimental molecular weights at specific polymerization times.     

A novel polycondensation method for the synthesis of a two-faced β-1,4-glucan

Abstract  

The stereospecific synthesis of a chitosan derivative repeating 2-azido-3,6-di-O-benzyl-2-deoxy-β-d-glucopyranosyl-(1 → 4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-d-glucopyranose, which has two distinguishing faces, was achieved by polycondensation of the sole starting disaccharide, trichloroacetimidoyl 2-azido-3,6-di-O-benzyl-2-deoxy-β-d-glucopyranosyl-(1 → 4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-d-glucopyranoside in a short and efficient way.     

Synthesis and oxidative polycondensation of 4, 4−diethynylbiphenyl

Summary 4,4-Diethynylbiphenyl was synthesized. By polycondensing it an oligomer with alternating biphenyl (-4,4) and diacetylene chains was obtained.     

What does polycondensation mean?

This contribution has the function of an introduction to the entire volume. It deals with several fundamental definitions and classifications related to the chemistry of polycondensation processes, and it includes modifications of the classical theory of step-growth polymerizations.     

Alkaloids of Nitraria komarovii. XI. Structure of komavicine and the products of the dehydrogenation of the nitrarine method of dehydrogenation in the quinolinyl-β-carboline series

The new alkaloid komavicine has been isolated from the epigeal part ofNitraria komarovii, and its structure has been established on the basis of spectral characteristics and chemical transformations. The products of the dehydrogenation of nitrarine with selenium and sulfur have been studied. A method has been developed for the dehydrogenation of dihydro and tetrahydro derivatives in the quinolinyl--carboline series.Institute of Chemistry of Plant Substances, Uzbekistan Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 33–39, January–February, 1993.     

Anionic Polymerization of α-Methylstyrene. IX. Nature of the Propagating Species

Abstract

The nature of the initiating and propagating species involved in the anionic polymerization of α-methylstyrene has been explored. The earlier hypothesis that multimodal GPC molecular weight distributions in polymers arise solely out of different reaction steps or different ion-pair mechanisms being involved has been modified for poly-α-methylstyrene. Multimodal GPC molecular weight distributions in poly-α-methylstyrene initiated with potassium at 25°C and polymerized at 25°C or higher in THF, p-dioxane, or cyclohexane as solvents have been ascribed to the presence of two different types of tetramers which grow simultaneously but at different rates, each responding to its own well-defined thermodynamic equilibrium and yielding dormant and living polymers. Reaction schemes describing the initiation (at 25°C) and propagation reactions (between -25 and 60°C) in the polymerization (in solution of THF as well as in bulk) of α-methylstyrene initiated with potassium-naphthalene, butyl-lithium, and butyllithium-tetramethylethylenediamine (TMEDA) have been presented. The role of coordinating agents naphthalene and TMEDA in changing irreversible propagations into reversible ones has been emphasized.     

Assessing the activity concentration of β-emitters by means of the end-window g.m. tube

The activity concentrations of β-emitters including ³⁵S (0.15 MeV) and presumably also ¹⁴C (0.14 MeV) may be determined with satisfactory accuracy using an end-window G.M. counter. For single preparations (if weighed), the described procedure warrants that the standard error will not exceed 0.8%, if the amount of substrate is kept below 0.2 mg/cm², and if carrier-free solutions are avoided. With a minimum of 4 preparations per sample solution, the error of the mean should not exceed 0.4%,     

Polymorphism of Inclusion Complexes and Unsolvated Hosts. I. Trimorphism of the Host-Guest Complex of Gossypol with Dichloromethane. The Structure of the β-Phase

The formation of host-guest complexes of gossypol at different temperatures has been investigated for the same pressure and concentration. Gossypol forms three different clathrates with dichloromethane within the temperature interval of 22-36 °C. Single crystals of these three modifications (phases) were obtained and their crystallographic parameters measured. The structure of the -phase has been determined previously and the -phase is isostructural to the inclusion complex of gossypol with benzene, while the structure of the -phase has been solved during the present research. Crystals of C30H30O8·CH2Cl2 are triclinic, space group P1, a = 8.604(1), b = 11.858(2), c = 14.405(2) (Å), = 84.60(1), = 89.14(1), = 89.73(1)°, V = 1463(1) Å3, Z = 2, R = 0.089 for 2419 observed reflections.Under ambient conditions gossypol forms unstable tubulates of the -phase; the -phase is a stable cage-type clathrate (cryptate) and the host-guest complex of the -phase is a clathrate of intermediate tubulato-cryptate type.     

Polymorphism of Inclusion Complexes and Unsolvated Hosts. II. Structure of the β-Dimorph of the Host-Guest Complex of Dianilinegossypol with Ethylacetate

Depending on crystallization conditions, dianilinegossypol and ethylacetate form low (ambient temperature, -phase) and high temperature (t = 35°C, -phase) clathrate modifications. The structure of the -phase has been discussed earlier [1]. Crystals of the 1 : 1 -phase complex, C42H40O6N2·C4O2H8, are monoclinic, space group P21/c, a = 11.362(6), b = 19.479(9), c = 19.085(9) Å, = 103.21(4)°, V = 4112(3)Å3, Z = 4, R = 0.084 for 3210 observed reflections.In these complexes centrosymmetric dimers of dianilinegossypol molecules formed via O(5)—H···O(3) hydrogen bonds are associated into columns by a weak O(8)—H···O(7) H-bond. A difference in the structure of these two phases is in the packing mode of the columns. The angle formed by intersecting host columns is about 126° for the -phase and 104° for the -modification. Guest molecules are hydrogen bonded to the host molecules via an O(1)—H···O(10) bond and are accommodated in channels in -phase complex and in cavities in -phase complex.     

Esters ofβ -ketophosphonic acids. VII. The products of the reaction ofα-chlorocyclohexanone with the diethyl ester of ethylphosphonous acid and the sodium salt of the monoethyl ester of ethylphosphonous acid

Summary The action of diethyl ethylphosphonite on-chlorocyclohexanone gives cyclohexen-1-yl-1 -ethyl ethylphosphonate, Cyclohenen-1-yl-1-ethyl ethylphosphonate is also obtained by the action of sodium monoethyl ethylphosphonite on a-chlorocyclohexanone.