Studies in ring-opening polymerization. II. Cyclohexane spiro-5-1,3,2-dioxathiolan-4-one 2-oxide

The effect of spiro cyclohexane substitution on the polymerizability of the 1,3,2-dioxathiolan-4-one-2-oxide ring in various solvents has been examined. The steric hindrance of the cyclohexane ring inhibits the bimolecular chain propagation reaction which involves direct attack by a terminal hydroxyl group on the ring and which has been shown to occur in simpler dioxathiolan systems. The conjoined cyclohexane ring does not, however, markedly affect the “thermal” polymerization which occurs in nonhydroxylic solvents and in which chain propagation is thought to involve a reactive α-lactone intermediate. The rate-determining step in the sequence of reaction leading to polymer formation is a ring-scission process in which sulfur dioxide is evolved and the α-lactone intermediate formed. The values of the activation energy (25–30 kcal/mole) and frequency factor (10¹¹–10¹³sec^?1) associated with this reaction are, therefore, those which govern the the overall polymerization, since the subsequent steps are sensibly instantaneous. In the presence of adventitious traces of water the resultant polymer, poly(1-hydroxycyclohexanecarboxylic acid) has one carboxyl and one hydroxyl endgroup per chain. Polymers having M?_n ～ 15,000 are readily obtained; these are amorphous materials, in contrast to the analogous poly-β-ester and dialkyl-substituted poly-α-esters which are crystalline. At temperatures in excess of 120°C a competitive first-order fragmentation reaction leading to the formation of cyclohexanone, carbon monoxide, and sulfur dioxide was observed. Kinetic studies demonstrated that this reaction, which is characterized by an activation energy of ～40 kcal/mole is unimportant, in the sense that it does not interfere with polymer formation at temperatures below 100°C.     

The Synthesis and Liquid-Crystal Transition Temperatures of Some Fluoro-Substituted Benzonitriles

Various laterally fluoro-substituted benzonitriles have been prepared containing a trans-4-(n-alkyl)cyclohexane ring linked to the 4-position of the benzonitriles either through a methyleneoxy (? CH₂O–) or an ethylene (? CH₂CH₂-) bridge. The bridging group links the benzonitrile and cyclohexane rings either directly or through an additional 1,4-bonded cyclohexane or benzene ring. The synthesis and liquid-crystal transition temperatures of these new compounds are described. In several cases the nematic-isotropic transition temperatures of F-substituted benzonitriles are found to be higher than those of the non-laterally substituted analogues.     

Stereoselective total synthesis of Patulolide C

Abstract

Stereoselective total synthesis of Patulolide C has been accomplished from easily available and inexpensive (S)-chiral epoxide. The key steps involved in the concise synthesis of Patulolide C utilizes ring opening of chiral epoxide, cleavage of 1,2-diol, deprotection of benzyl ether of hydroxyl acid and Yamaguchi macrolactonisation dilution conditions as key steps. The advantage of this method include inexpensive starting material, mild reaction conditions and high purity of products.     

Unusual Conformational Behavior of 3,7-Dihetera(N,N-;N,O-;N,S-) Bicyclo[3.3.1]Nonan-9-Ols Via Nmr Analysis

Abstract

Based upon the analysis of ¹H NMR data, along with molecular modeling, it was shown that the reduction of 3,7-dihetera(N,N-; N,O-; N,S-)bicyclo[3.3.1]nonan-9-ones by LiAlH₄ led to a mixture of two stereoisomeric secondary alcohols with different orientations of the hydroxyl groups in one of the ring systems. Diaza derivatives in deuterochloroform exist in predominant chair-boat conformations. However, the replacement of nitrogen in one of the heterocycles by oxygen or sulfur led to stereoisomers one of which existed in chair-boat conformation and another in a chair–chair conformation. In all cases the boat conformation is stabilized by formation of an intramolecular hydrogen bond (IMHB) between a lone electron pair of the nitrogen atom and a proton on the pseudo axial hydroxyl group of the other ring.     

Incorporation of an Amino Function in a (1S,2S,3R)-3-Hydroxy-2-methoxy-1-cyclohexane Carboxylic Acid

(1S,2S,3R)-3-Hydroxy-2-methoxy-1-cyclohexanecarboxylic acid was synthesized for the construction of an amino acid to be used in a constrained ring didemnin B analog ( 2 ). The amine functionality was introduced into the cyclohexane ring by reductive amination using sodium triacetoxyborohydride or by oxime formation followed by reduction.     

First examples of a new class of discogen

Abstract

Two examples of a new class of discotic liquid crystals are presented. Their molecular architecture consists of a trisubstituted central core (either a benzene or a cyclohexane ring) and three regional cores, with three decyloxy-chains in the 3,4,5-positions of a particular benzene ring. These regional cores are linked to the central core via ester groups. Polarizing microscopy and calorimetric measurements reveal the existence of monotropic and enantiotropic discotic mesophases respectively. The products exhibit a pronounced hindering of crystallization at room temperature.     

Solubility of Anthracene in Binary Carbon Tetrachloride + Alkane Solvent Mixtures

Abstract

Experimental solubilities are reported for anthracene in binary solvent mixtures containing carbon tetrachloride with n-hexane, n-heptane, n-octane, cyclohexane, methylcyclohexane and isooctane at 25°C. Results of these measurements, combined with the excess Gibbs free energies of the binary solvents, are used to test predictive expressions derived from the nearly ideal binary solvent (NIBS) model. Expressions based on a volume fraction average of solute properties in the two pure solvents predict anthracene solubilities to within a maximum deviation of 4.5% and an overall average deviation of 1.8%.     

The effect of lateral fluoro-substitution on the liquid crystal behaviour of some 4'-alkylphenylethyl- and trans-4'-alkylcyclohexylethyl-4,4'-disubstituted biphenyls

Abstract

The preparation of several 4'-alkylphenylethyl- and trans-4'-alkylcyclohexyl-ethyl-4,4'-disubstituted biphenyls and their 2-fiuoro derivatives is described and their transition temperatures are reported. The effect on the transition temperatures caused by the replacement of a cyclohexane ring by a benzene ring and the effect of fluoro-substitution on nematic, smectic A and smectic B thermal stabilities is discussed. In these systems, and in others, when the lateral fluoro-substituent points towards the longer terminal aliphatic unit (alkyl or alkylcyclo-hexylethyl) it causes a greater depression of smectic properties.     

Smectic liquid crystals. VIII. Some new laterally substituted smectic C compounds

Abstract

The synthesis and liquid crystal transition temperatures of a new class of compounds incorporating a trans-1,4-disubstituted cyclohexane ring have recently been reported. Many of these novel materials exhibit an enantiotropic smectic C mesophase over a wide temperature range and are suitable for commercial display device applications. The influence of several lateral substituents in various positions on the liquid crystal transition temperatures of these compounds has now been investigated systematically. A linear relationship between the size of the lateral substituent and the magnitude of the transition temperatures of various liquid crystal mesophases has been established for several of the series synthesized. A number of series incorporating a lateral substituent and an optically active centre have also been prepared and similar effects have been found.     

SYNTHESIS AND CONFORMATIONAL STUDIES OF A NUMBER OF SATURATED BICYCLIC SIX-MEMBERED RING PHOSPHITES

Abstract

An ¹H NMR study of the conformation of the dioxaphosphorinane ring of a number of diastereoisomeric bicyclic saturated six-membered ring phosphites (3ab-10ab) has been performed. The dioxaphosphorinane ring of these phosphites is transannelated with a tetrahydrofuran, cyclopen-tane, tetrahydropyran or cyclohexane ring. The substituent on the phosphorus atom is a methoxy or phenoxy group. It is shown that the cis isomers 3a-10a prefer a chair conformation of the dioxaphosphorinane ring, independent of the substituent on the phosphorus atom and of the nature of the transannelated ring. In contrast, for the trans isomers 3b-10b a twist rather than a chair conformation of the dioxaphosphorinane ring is preferred. The fraction of the twist conformer in the trans isomers is mainly determined by the substituent on phosphorus. The size and composition of the transannelated ring are relatively unimportant in this respect. For both cis and trans isomers the preferred geometry is solvent-independent. The measured ^3JPOCH couplings of the cis isomers 3a-10a are used to formulate an expression for the dependence of such couplings upon dihedral angles in bicyclic phosphites.     

Thermal properties of polyamides containing 1,3–cyclohexane rings

The effect of the 1,3–cyclohexane rings in the chain backbone on thermal properties of polyamides, especially the glass-transition temperature, has been studied using polyamides based on 1,3–cyclohexanebis(methylamine). The increase in glass-transition temperature was far greater than that obtained with the analogous polymers containing m–benzene rings. However, the effects of 1,4–cyclohexane and p-benzene rings are nearly equal. Several possible causes for this difference are examined. It is concluded that restricted chain mobility due to steric hindrance of the cis-1,3–cyclohexane ring, the predominant isomer, is the most likely cause of the difference.     

Radiolysis of aqueous DCH18C6 solutions at 77 K

Low-temperature (77 K) γ- and X-ray radiolysis of aqueous DCH18C6 solutions was studied by ESR-spectroscopy. OH radicals, trapped electrons and macrocyclic radicals -CH₂-CH-O- resulting from H-atom abstraction from methylene groups of polyether ring were identified as predominant radiolysis products. Increasing the crown ether concentration in aqueous solution leads to the growth of relative yields of the trapped electron and macrocyclic radicals as well as the decrease of that of hydroxyl radical. Neither radical products of macrocycle rupture nor H-atom abstraction from cyclohexane rings were observed.     

Comparing the Affinities of Flavonoid Isomers with Protein by Fluorescence Spectroscopy

Abstract

Dietary flavonoids can be detected in plasma as protein‐bound conjugates. Flavonoids–protein interaction is expected to modulate the bioavailability of flavonoids. In this work, the binding flavonoid isomers (galangin, baicalein, apigenin, and genistein; MW=270.25) and B‐ring hydroxylation flavonols (galangin, kaempferol, quercetin, and myricetin, which share the same structure on the A and C rings but have 0, 1, 2, and 3 moieties of ‐OH on the B‐ring, respectively) to protein were investigated by fluorescence quenching method. The apparent binding constants (K _a ) of were flavonoid isomers determined as: flavones (10⁶–10⁷ L mol^?1)>isoflavone≈flavonol (10⁵ L mol^?1). For B‐ring hydroxylation flavonols, the binding affinity increased with increasing number of hydroxyl groups on the B‐ring. The binding constants (K _a ) were determined as follows: myricetin>quercetin>kaempferol>galangin.     

An Efficient Method for the Synthesis of A 1,6-Anhydro-α-D-Galactofuranose Derivative and its Application in the Synthesis of Oligosaccharides

ABSTRACT

Synthesis of 1,6-anhydro-2,3,5-tri-O-benzoyl-β-D-galactofuranose (3) has been achieved in good yield by stannic chloride catalysed ring closure of methyl 2,3,4-tri-O-benzoyl-6-O-benzyl-β-D-galactofuranoside (1). The anhydro compound 3 was converted to the furanoside donors 6 and 7 with an easily removable O-6 acetyl group. The donors 6 and 7 were utilised for the synthesis of a di- and a trisaccharide containing β-D-galactofuranosides.     

DISQUAC predictions of phase equilibria,molar and standard partial molar excess quantities for 1-alkanol+cyclohexane mixtures

Literature data for phase equilibria: vapor-liquid VLE, liquid-liquid LLE, and solid-liquid SLE; molar excess Gibbs energies G ^E , molar excess enthalpies H ^E ; activity coefficients _i and partial molar excess enthalpies H _i ^E,o at infinite dilution for 1-alkanol (1)+cyclohexane (2) mixtures are examined by the DISQUAC group contribution model. For a more sensitive test of DISQUAC, the azeotropes, obtained from the reduction of the original isothermal VLE data, are also examined for systems characterized by hydroxyl, alkane and cyclohexane groups. The alkane/cyclohexane and alkane/hydroxyl interaction parameters have been estimated previously. The cyclohexane/hydroxyl interaction parameters are reported in this work. The first dispersive parameters increase regularly with the size of the alkanol; from 1-octadecanol they are constant; an opposite behavior is encountered for the third dispersive parameters, which are constant from 1-dodecanol. The second dispersive parameters decrease as far as 1-propanol and then increase regularly; from 1-octadecanol they are constant. The quasichemical parameters are equal to those for the alkane/hydroxyl interactions. Phase equilibria, the molar excess functions, and activity coefficients at infinite dilution are reasonably well reproduced. Poor results are found for H _i ^E,o and DISQUAC predictions for H _i ^E,o are strongly dependent on temperature.     

Orientational ordering of 4-substituted phenylcyclohexanes studied by carbon-13 two-dimensional N.M.R.

Abstract

An N.M.R. method combining the techniques of separated local field spectroscopy (SLF) and variable angle spinning (VAS) is valuable in the investigtion of nematic liquid crystals. Rapid sample spinning causes the nematic director to align along the spinning axis, resulting in narrow peaks in the C-13 N.M.R. spectrum. SLF is a two-dimensional N.M.R. method which produces a first order splitting pattern for each carbon signal from which C–H dipolar coupling constants can be determined. The order parameters for all segments of the liquid crystal molecule can then be calculated. Results for three 4′-cyanophenylcyclohexanes are considered here. These compounds are trans-substituted at the 4 position of cyclohexane ring with n-pentane (PCH5), 1-pentene (3d ₁CP) and 3-pentene (1d ₃CP), respectively.     

Studies of the Synthesis of Rubranitrose and Crystal Structure of Methyl 2,3,6-Trideoxy-3-C-Methyl-3-Nitro-α-D-Ribo-Hexopyranoside

Abstract

The branched-chain nitro sugar methyl 2,3,6-trideoxy-3-C-methyl-3-nitro-α-D-ribo-hexopyranoside 4 was investigated as a precursor to D-rubranitrose, a nitro sugar found in the antibiotic rubradirin. X-ray cyrstallographic analysis of 4 shows that the pyranose ring adopts the ⁴ C ₁ conformation with the methoxy group at C-1 and the nitro group at C-3 in a 1,3-diaxial relationship. There is an intermolecular hydrogen bond involving a nitro group oxygen of one monosaccharide residue and the C-4 hydroxyl group of the adjacent residue in the crystal lattice. This interaction results in a helical crystal packing. A series of nucleophilic displacement reactions was carried out on the triflate derivative of 4 in an attempt to introduce an axial carbon-oxygen bond at C-4 required for rubranitrose. Displacements with acetate and propionate gave as products the monosaccharide esters with the desired D-xylo configuration.     

Application of Computer-Assisted 13C NMR Spectrometry for Separation and Determination of Heptane Isomers in the Feed Stocks of Cyclohexane Used in Purification Process

Abstract

A computer-assisted ¹³C NMR spectrometric method for separation, identification and quantitative determination of C₇ hydrocarbons in cyclohexane has been developed. A simulated library containing chemical shift and multiplicity data of 131 compounds of C₇ hydrocarbons has been prepared. The method incorporates the unique features of quantitative and edited ¹³C NMR spectra for separation and identification of mixture of hydrocarbons. It serves as an alternative method to GC-MS for monitoring the composition of feed stocks used for cyclohexane purification process.     

The Preparation and the Assignment of the 1H and 13C NMR Spectra of Methylated Derivatives of Inulin Oligosaccharides

Abstract

The complete assignment of the ¹H and ¹³C NMR spectra for permethylated sucrose, 1-kestose and nystose are given. Methylation of these inulin oligosaccharides did not change the conformation of the ring structures. A partially methylated derivative of nystose has been prepared using water as the solvent. The difference in reactivity of the various hydroxyl groups of nystose appeared to be very small.     

Evaluation of Excess Gibbs Energy of Mixing in Binary Mixtures of Di-Isobutyl Ketone (Dibk) and Nonpolar Solvents

Abstract

Excess Gibbs energy of mixing in binary mixture of Di-isobutyl ketone (DIBK) in nonpolar solvents namely n-heptane, p-xylene, cyclohexane, dioxane, benzene and tetra-chloromethane have been evaluated at 303°K. The results indicate that (ΔG_AB)_maxima is in the order, n-heptane > p-xylene > cyclohexane > benzene > dioxane > tetra-chloromethane.