THE MERCAPTOLYSIS OF GLUCOSE AND GALACTOSE PENTAACETATES

1951 ◽  
Vol 29 (12) ◽  
pp. 1079-1091 ◽  
Author(s):  
R. U. Lemieux
Keyword(s):  
Carbon Atom ◽  
Zinc Chloride ◽  
Intermediate Formation ◽  
Acetoxy Group ◽  
Carbonium Ion ◽  
Chloride Catalyst ◽  
Derivatives Of

The mercaptolysis of the α-and β-pentaacetyl derivatives of glucopyranose and galactopyranose at 0 °C. with zinc chloride catalyst was studied. The β-pentaacetates were rapidly transformed to the corresponding ethyl tetraacetyl-1-thio-β-D-glycosides in excellent yields; however, the α-anomers were highly resistant to the mercaptolytic conditions. The results are interpreted on the basis of a participation by the C2-acetoxy group in the replacements at the lactol carbon atom of the β-pentaacetates with the intermediate formation of a resonance stabilized cyclic carbonium ion.

THE MECHANISMS OF GLUCOSE PENTAACETATE ANOMERIZATION AND LEVOGLUCOSAN FORMATION

1952 ◽  
Vol 30 (4) ◽  
pp. 295-310 ◽  
Author(s):  
R. U. Lemieux ◽  
Carol Brice
Keyword(s):  
Carbon Atom ◽  
Chloroform Solution ◽  
Intermediate Formation ◽  
Initial Step ◽  
Acetoxy Group ◽  
Stannic Chloride ◽  
Carbonium Ion ◽  
Carbonium Ions ◽  
The Stability ◽  
Rate Controlling Step

The stannic chloride catalyzed anomerization of the pentaacetyl-D-gluco-pyranoses in chloroform solution is specific for the C1-acetoxy group. The reactions involve complete dissociation of the C1-carbon atom to acetoxy group bond with an intermediate formation of carbonium ions. The initial step of the beta to alpha rearrangement is a rapid dissociation, involving the participation of the C2-acetoxy group, to a resonance-stabilized carbonium ion with the lactol carbon atom occupied in the α-configuration. The rate-controlling step in the reaction appears to be the rearrangement of this ion to other ions which are capable of recombining with acetate ion to yield the α-acetate. The α-acetate is highly stable, as compared to the β-anomer, and the dissociation of the C1-carbon atom to acetoxy group bond is the rate-controlling step in its rearrangement. The stability of the α-acetate toward a variety of acidic reagents which readily dissociate the β-form is pointed out. For example, although the α-acetate is highly stable toward titanium tetrachloride, the reaction of the β-anomer with this reagent, to yield tetraacetyl-β-D-glucopyranosyl chloride, is extremely fast. This product is unstable under the reaction conditions used and rearranges to the α-form at a measurable rate. 1,2,3,4-Tetraacetyl-β-D-glucopyranose with stannic chloride in chloroform solution yielded triacetyl-D-glucosan <l, 5 > β <1, 6>.The alkaline hydrolysis of triacetyl-D-glucosan <1, 5> α <1, 2> yielded D-glucosan <1, 5> β <1, 6>. The mechanisms of these reactions are discussed.

The Chemistry of the Zinc Oxide Cure of Halobutyl

1984 ◽  
Vol 57 (4) ◽  
pp. 813-825 ◽  
Author(s):  
I. Kuntz ◽  
R. L. Zapp ◽  
R. J. Pancirov
Keyword(s):  
Zinc Oxide ◽  
Zinc Chloride ◽  
Reaction Pathway ◽  
Diels Alder ◽  
Crosslinking Reaction ◽  
Conjugated Diene ◽  
Carbon Carbon Bonds ◽  
Carbon Bonds ◽  
Chloride Catalyst ◽  
Major Reaction

Abstract The studies described in this papier lead to certain conclusions. The crosslinking reaction of halobutyl with zinc oxide does not give rise to ether crosslinks. All the evidence indicates that the chemistry involves the formation of carbon-carbon bonds by an alkylation type chemistry. The dehydrohalogenation of the halobutyl to form a zinc chloride catalyst is a key feature of the crosslinking chemistry. But conjugated diene butyl and Diels-Alder reactions are not the major reaction pathway for the zinc oxide crosslinking reaction. These conclusions have significance for the zinc oxide cure of CR which has an active allylic halide structure formed by 1,2-monomer enchainment.

O-Benzylidene Derivatives of D-Arabinose Diethyl and Dipropyl Dithioacetal

1996 ◽  
Vol 49 (3) ◽  
pp. 273 ◽  
Author(s):  
J Kuszmann ◽  
E Gacsbaitz
Keyword(s):  
Hydrochloric Acid ◽  
Zinc Chloride ◽  
Partial Hydrolysis ◽  
Kinetic Control ◽  
Toluenesulfonic Acid ◽  
Thermodynamic Phase ◽  
Hydrolysis Of ◽  
Derivatives Of

Benzylidenation of D-arabinose diethyl and dipropyl dithioacetals with α,α-dimethoxytoluene in the presence of p-toluenesulfonic acid has been studied in detail. Under kinetic control the two terminal dioxolan -type 4,5-O-(R)- and 4,5-O-(S)-benzylidene diastereomers are formed first which are in equilibrium with each other In the thermodynamic phase of the reaction the corresponding dioxan -type 3,5-O-(R)- benzylidene isomer is formed too, but all three monobenzylidene isomers are gradually converted into the four possible dioxolan -type 2,3 : 4,5-di-O benzylidene diastereomers . The dioxan -type 2,4:3,5-di-O-benzylidene isomer was present only in trace amounts. When benzaldehyde was used as reagent in the presence of hydrochloric acid or zinc chloride only the 2,3: 4,5-di-O-benzylidene diastereomers were formed. Partial hydrolysis of the dibenzylidene derivatives yielded the corresponding 2,3-O-benzylidene diastereomers. Structures, including the chirality of the benzylidene groups, were determined by n.m.r. spectroscopy. A mechanism suggested for the reaction was partially supported by equilibration studies.

scholarly journals THE STEREOCHEMISTRY OF HALOGEN DISPLACEMENT BY NITRATE ION RACEMIZATION AND RETENTION OF CONFIGURATION IN THE SYNTHESIS OF DINITRATE ESTERS

1965 ◽  
Vol 43 (6) ◽  
pp. 1656-1660 ◽  
Author(s):  
L. D. Hayward ◽  
M. Jackson ◽  
I. G. Csizmadia
Keyword(s):  
Silver Nitrate ◽  
Steric Effect ◽  
Heterogeneous Reaction ◽  
Ion Pair ◽  
Alkyl Halides ◽  
Preferential Formation ◽  
Carbonium Ion ◽  
Carbonium Ions ◽  
And Inversion ◽  
Derivatives Of

The reaction of silver nitrate in dry acetonitrile with 2,5-dideoxy-2,5-diiodo-1,4;3,6-dianhydro-L-iditol resulted in formation of the dinitrate esters of the 1,4;3,6-dianhydrides of D-mannitol, D-glucitol, and L-iditol. Similarly both endo- and exo-nitrato groups were introduced in displacement of the endo-halogen in the 2-deoxy-2-iodo-5-O-acetyl and 2-deoxy-2-iodo-5-O-p-toluenesulfonyl derivatives of 1,4;3,6-dianhydro-L-iditol. Since both types of nitrato groups were stable to silver nitrate, the racemization occurred during the displacement and was attributed to formation of cyclic carbonium ion intermediates. The steric effect of the adjacent ring in the carbonium ions apparently suppressed the termolecular, ion-pair mechanism previously established for the metathesis of acyclic alkyl halides and caused preferential formation of the exo-nitrato derivatives.The heterogeneous reaction of meso-dibromostilbene with silver nitrate in acetic acid or acetonitrile gave meso-dihydrobenzoin dinitrate with overall retention of configuration. This result could be most readily reconciled with the contrasting sequence of retention and inversion previously reported for meso- and dl-2,3-dibromobutane if participation of neighboring phenyl groups occurred in the second displacement step.

Recovery of zinc chloride catalyst from coal hydrogenation char

1978 ◽  
Vol 1 (2) ◽  
pp. 151-165 ◽  
Author(s):  
A.H. Hill ◽  
R.E. Wood ◽  
W.H. Wiser
Keyword(s):  
Zinc Chloride ◽  
Chloride Catalyst

Synthesis of 5H-dibenzo[a,d]cycloheptene-5-carboxylic acid and related compounds. 1,5-Hydride transfer to inductively destabilized carbonium ions

1968 ◽  
Vol 46 (23) ◽  
pp. 3665-3670 ◽  
Author(s):  
D. E. Horning ◽  
J. M. Muchowski
Keyword(s):  
Carboxylic Acid ◽  
Carbonyl Group ◽  
Isotope Effect ◽  
Hydride Transfer ◽  
Large Magnitude ◽  
Carbonium Ion ◽  
Carbonium Ions ◽  
Acid Catalyzed ◽  
Derivatives Of ◽  
Related Compounds

The synthesis of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene-5-carboxylic acid (2) and several derivatives of 5H-dibenzo[a,d]cycloheptene-5-carboxylic acid (1; a–c) from 5-hydroxy-10,11-dihydro-5H-dibenzo[a,d]cycloheptene-5-carboxylic acid and derivatives thereof (3; a–c) is described.The p-toluenesulfonic acid-catalyzed elimination of water (at 110.6° in toluene) from the deuterated hydroxy ester (3b; C-10, 11 d2) resulted in the incorporation of deuterium at C-5 of the olefinic ester 1b with a KH/KD of 2.76. The large magnitude of this isotope effect indicated that the reaction proceeded via a rate-determining transannular 1,5-hydride transfer from one of the benzylic positions of 3b to the carbonium ion generated alpha to the methoxy-carbonyl group.

Carbon-13 Nuclear Magnetic Resonance Spectra of Some Dendroketose and Other Furanose Derivatives

1975 ◽  
Vol 53 (18) ◽  
pp. 2748-2754 ◽  
Author(s):  
Dolatrai M. Vyas ◽  
Harold C. Jarrell ◽  
Walter A. Szarek
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Carbon Atom ◽  
Nuclear Magnetic Resonance Spectra ◽  
Branched Chain ◽  
Derivatives Of ◽  
Anomeric Center ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The carbon-13 n.m.r. spectra of derivatives of the branched-chain sugars apiose and dendroketose, and of other furanose sugars, are reported. The study has permitted assignment of the configuration at the branching carbon atom and at the anomeric center in the dendroketose derivatives.

Silica-supported ZnCl2 — A highly active and reusable heterogeneous catalyst for the one-pot synthesis of dihydropyrimidinones–thiones

2007 ◽  
Vol 85 (3) ◽  
pp. 197-201 ◽  
Author(s):  
Raman Gupta ◽  
Monika Gupta ◽  
Satya Paul ◽  
Rajive Gupta
Keyword(s):  
Zinc Chloride ◽  
Biginelli Reaction ◽  
Catalyst Loading ◽  
Reaction Conditions ◽  
One Pot ◽  
Highly Active ◽  
Chloride Catalyst ◽  
Biginelli Compounds ◽  
The One ◽  
Low Catalyst Loading

A novel silica-supported zinc chloride catalyst was prepared and investigated for the Biginelli reaction. The key features of the catalyst include rapid reaction with 100% conversion of aldehyde, good catalyst recyclability, and high stability under the reaction conditions (passes hot filtration test successfully). A low catalyst loading (12 mol% of ZnCl2) was required to achieve a quantitative reaction. Other catalysts such as SiO2–AlCl2, SiO2–AlCl2–ZnCl2 were also prepared and their activity was compared with SiO2–ZnCl2 for the Biginelli reaction.Key words: silica gel, zinc chloride, Biginelli compounds, heterogeneous catalysis, reusability.

scholarly journals Synthesis and Screening of Biologically Active Schiff bases of Benzothiazoles and its Zinc and Lanthanum Metal Complexes

2021 ◽  
Vol 37 (1) ◽  
pp. 187-193
Author(s):  
D. G. Anuse ◽  
V. J. Desale ◽  
B. R. Thorat ◽  
D. D. Anuse ◽  
S. G. Jagadhani ◽  
...  
Keyword(s):  
Metal Complex ◽  
Metal Complexes ◽  
Schiff Bases ◽  
Zinc Chloride ◽  
Biological Activities ◽  
Biologically Active ◽  
Lanthanum Chloride ◽  
Schiff’S Bases ◽  
Schiff's Bases ◽  
Derivatives Of

The substituted 2-Aminobenzothiazole and ethyl 2-(4-formyl-3-hydroxyphenyl)-4-methylthiazole-5-carboxylate in methanol mix together and heat the reaction mixture for overnight, It gives Schiff’s bases (derivatives of substituted aminobenzothiazole) 3. This compound 3 when treated with Zinc Chloride it gives Zinc metal complex of Schiff’s bases 4 and if compound 3 was treated with Lanthanum chloride gives Lanthanum metal complex of Schiff’s bases 5, which shows marked biological activities.

Sign in / Sign up

Export Citation Format

Share Document