Janusz Sokolowski

Products from the Action of Hydrochloric Acid on Pentitols

Abstract The treatment of pentitols in concentrated hydrochloric acid causes 1, 4 (or 2, 5) intramolecular dehydration with either retention or change of configuration, 1, 5-dehydration and chlorine for hydroxyl substitution. These mono- and dichloroalditol derivatives mostly with the configuration of arising anhydro compounds, are formed from the alditols themselves or 1, 4-anhydro-pentitols.

Isomerisation during dehydration of pentitols in acid media

Abstract The products of dehydration of pentitols in aqueous sulfuric acid have been studied by g.l.c.-m.s. Four isomeric 1,4-anhydropentitols were formed from d -arabinitol, but only two from xylitol and ribitol. The number of products could only be explained by assuming inversion of configuration at C-2 or C-4 during 1,4- or 2,5-cyclisation reactions. No product which involved inversion of configuration at C-3 was observed. Various mechanisms of isomerisation are considered.

Cyclization of Pentitols in Pyridine Via Their O-Tosyl Derivatives

Abstract Heating of equimolar quantities of pentitols with p-toluenesulfonyl (tosyl) chloride in pyridine at 60 °C for 4 h afforded 1, 4- or 2, 5-mono-anhydropentitols, which retained configuration of the asymmetric carbon atoms 2 or 4, together with small amounts of products with altered configuration at these centers. Variation of the reaction conditions by using a triple-molar excess of tosyl chloride and elevation of the temperature up to 115 °C gave mainly 1, 4-anhydro-5-chloro-5-deoxy-pentitols and small amounts of 1, 4-anhydro-2, 5- and 3, 5-dichloro-2, 5- and 3, 5-dideoxy-pentitols. The stereochemistry of the molecule of D-arabinitol was shown to favor the formation of 1, 4: 2, 5-dianhydro-D-arabinitol, a compound with two tetrahydrofuran rings. All mixtures were separated by capillary GC, and their components were identified by co-injection of standards by GC-MS.

Cyclization of N(Tetra-O-acetyl-d-gluco- and d-Mannopyranosyl)-Pyridinium Salts in a Methanolic Solution of Sodium Methylate

Abstract N-(2,3,4,6-Tetra-O-acetyl-α-d-gluco-, β-d-gluco- and β-d-mannopyranosyl)-pyridinium salts were obtained and their structures were determined by 2D 1H NMR spectroscopy. The compounds obtained were treated with a methanolic solution of sodium methylate. The β-anomer of the d-gluco derivative cyclizes via Brigls anhydride but the α anomer is competitively transformed according to the SN2 and SN1 mechanisms. The β-d-manno derivative does not cyclize under the conditions used. Comparison of the qualitative and quantitative results of the reaction studied enabled estimation of the influence of configuration at C-1 and C-2 on the course of cyclization. All product mixtures were separated by capillary gas chromatography (CGC) as exhaustively O-acetylated derivatives and their components were identified by coinjection with authentic materials.

Dehydration of Some Hexitols

ABSTRACT Heating galactitol, D-glucitol, D-mannitol and L-iditol in a 5% aqueous sulfuric acid solution at 200 °C for 30 min afforded 1, 4-, 3, 6-, 1,5-, 2,6- and 1,6-monoanhydrohexitols with retained configuration as well as 2,5-monoanhydrohexitols with inverted configuration at C-2 or C-5. 1, 4;3,6-, 1,5;2,6- and 1,4;2,6- s 1,5;3,6-Dianhydrohexitols were also identified. Cyclization of the hexitols via their O-tosyl derivatives in pyridine gave products completely free of 2,5-anhydrohexitols but with increased amounts of dianhydrohexitols. All mixtures were separated by capillary GC (CGC) and their components identified by CGC-MS and by co-injection with standards.

Equilibration of alditol anhydrides in acetic acid

Abstract Dehydration of pentitols in acetic acid containing an acidic catalyst parallels that in aqueous sulfuric acid; 1,4(2,5)-dehydration occurs with inversion of configuration at C-2 or C-4. Acetylated alditols undergo similar processes via intermediates having free hydroxyl groups. Configurational inversion of 1,4- or 1,5-anhydroalditols is attributed to intermediate acyloxonium ions that are also proposed as intermediates in the structural isomerisation. Drastic treatment of each alditol gives equilibrium mixtures. The equilibrium concentrations are used to calculate free-energy differences.

1,6-Cyclization Reactions of Selected Aldohexopyranoses via Their 1-O-Tosyl Derivatives

Abstract 2,3,4,6-Tetra-O-acetyl-d-gluco-, d-galacto- and d-mannopyranoses were tosylated with p-tolenesulfonyl chloride to afford their 1-O-tosyl derivatives which were cyclized “in situ” in a methanolic solution of sodium methoxide. 1,6-Cyclization products were obtained only with d-glucose and d-galactose derivatives. Cyclization of derivatives of d-glucose i.e. 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl chloride, 3,4,6-tri-O-acetyl-1,2-anhydro-α-d-glucopyranose (Brigls anhydride) and 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide enabled the estimation of the influence of configuration at C-1 and C-2 on the course of cyclization. All product mixtures were separated by capillary gas chromatography (CGC) and their components were identified by coinjection with standards.

Capillary gas chromatographic separations of a multi-component mixture of polyalcohol compounds

Capillary gas chromatographic separation conditions were established for a 31-component mixture of polyhydroxy compounds containing two tetritols, three pentitols, six hexitols, seven monoanhydropentitols, eight monoanhydrohexitols, three dianhydrohexitols, pentaerythritol and myoinositol. Mixtures of per-O-acetyl or per-O-trimethylsilyl derivatives of these compounds were separated on fused-silica columns using highly polar DB-23 and non-polar HP-5 stationary phases, respectively. Relative retention times for each compound with respect to pentaerythritol and myoinositol and methylene units were determined.

Microsynthesis of Dianhydrohexitols

Abstract Conditions have been established for the microsyntheses of dianhydro-hexitols by reaction of 1, 4-monoanhydro-D, L-galactitols and 1, 5-monoanhydro-D-galactitol as well as of 1, 4- and 1, 5-monoanhydro-D-glucitols and -D-mannitols with tosyl chloride in pyridine followed by cyclization of the resulting 6-O-tosyl derivatives in methanolic solution of sodium methoxide. The dianhydrohexitols were formed by intramolecular nucleophilic substitution of the C-6 O-tosyl group with a properly stereochemically oriented hydroxyl group. Components of the mixtures were separated by capillary gas chromato-graphy using columns coated with SP-2340 and identified by GC-MS. The identities of the synthesized dianhydrohexitols were confirmed by comparison with the GC retention times and mass spectra of authentic samples.

Kinetics and Mechanism for the Epimhrization of Aldopentonic Acid Potassium Salts in Aqueous Alkali

Abstract The epimerization of the potassium salts of L-arabinonic, D-ribonic, D-lyxonic and D-xylonic acids in aqueous alkali was followed kinetically by gas Chromatographie analyses of the silylated samples. Mass spectrometric measurements indicated that the reaction proceeded by a complete proton exchange at C2, the kinetic deuterium isotope effect, k-H/k-D being 4.2. Most probably the proton transfer from the C2 atom to hydroxiae ion is the rate-limiting stage of the epimerization.