The acid-catalyzed rearrangement of methyl 3,4-O-benzylidene-β-D-ribopyranoside

1977 ◽  
Vol 55 (23) ◽  
pp. 4071-4077 ◽  
Author(s):  
David M. Clode
Keyword(s):  
Acid Concentration ◽  
Equilibrium Mixture ◽  
Nmr Spectrum ◽  
Ring Contraction ◽  
Acidic Conditions ◽  
Acid Catalyzed ◽  
Sole Product

Methyl 3,4-O-(R)-benzylidene-β-D-ribopyranoside (2) rapidly rearranged, under anhydrous acidic conditions, to give methyl 2,3-O-(R)-benzylidene-β-D-ribopyranoside (6). Further rearrangement of 2 and 6 gave the (S)-isomers 4 and 8, an equilibrium mixture of the four pyranoside acetals 2, 4, 6, and 8 resulting. At higher acid concentrations, the rearrangement proceeded, with ring contraction, to give the diastereomeric forms of methyl 2,3-O-benzylidene-β-D-ribofuranoside (11 and 13) as the sole product. Treatment of methyl 3,4-O-(S′)-benzylidene-β-D-ribopyranoside (4) with acid resulted in the immediate formation of the equilibrium mixture of pyranoside acetals. On increasing the acid concentration this mixture again underwent ring contraction to give the diastereomers 11 and 13 as the final product. The rearrangement of 2 and 4 was monitored by following the change in signals in the benzyl proton region of the nmr spectrum.

Hydration equilibria of 9-acridinecarboxaldehyde

1994 ◽  
Vol 72 (11) ◽  
pp. 2333-2338 ◽  
Author(s):  
Robert A. McClelland ◽  
Pratima Sukhai ◽  
Karen M. Engell ◽  
Poul E. Sorensen
Keyword(s):  
Equilibrium Constants ◽  
Acidity Constant ◽  
Separate Species ◽  
Ph Profile ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Free Aldehyde ◽  
Acidic Conditions ◽  
Acid Catalyzed ◽  
Heterocyclic Aldehydes

Hydration rate constants and equilibrium constants have been obtained for 9-acridinecarboxaldehyde in aqueous solution. Under acidic conditions where the acridine is protonated, signals for the hydrate and free aldehyde forms can be observed as separate species in the 1H NMR spectrum. Integration provides the hydration equilibrium constant[Formula: see text] Using an apparent acidity constant obtained from a spectroscopic titration curve, the rate–pH profile was fitted to provide the hydration constant for the equilibration of the neutral acridines, KH = 0.07. This analysis also provides the acidity constants for the two acridinium ions, the aldehyde with pK = 3.78 and the hydrate with pK = 5.36. A comparison with the 4-pyridinecarboxaldehdye system reveals that the [Formula: see text] ratios for the acridine and pyridine are the same within experimental error, but that the acridine and acridinium aldehydes are 20-fold less hydrated than their pyridine analogs. A comparison with benzaldehydes reveals that, in their reactivities, the two heterocyclic aldehydes behave in a similar manner. Thus, for example, plots of log kH for the acid-catalyzed dehydration and hydrations versus log Kh for the equilibrium hydration show single correlation lines including the points for the benzaldehydes and heterocyclic aldehydes (but not the aliphatic aldehydes).

ChemInform Abstract: ACID-CATALYZED RING CONTRACTION OF STEROIDAL 1α,2α-EPOXY-4-EN-3-ONES

1977 ◽  
Vol 8 (10) ◽  
pp. no-no
Author(s):  
A. M. MAIONE ◽  
I. TORRINI ◽  
A. ROMEO
Keyword(s):  
Ring Contraction ◽  
Acid Catalyzed

Bioenergy II: Furfural Destruction Kinetics during Sulphuric Acid-Catalyzed Production from Biomass

2009 ◽  
Vol 7 (1) ◽  
Author(s):  
Gianluca Marcotullio ◽  
Miguel A. Tavares Cardoso ◽  
Wiebren De Jong ◽  
Ad H.M. Verkooijen
Keyword(s):  
Sulphuric Acid ◽  
Acid Concentration ◽  
Reaction Products ◽  
Arrhenius Law ◽  
Exponential Factor ◽  
Oil Derivatives ◽  
Destruction Kinetics ◽  
Acid Catalyzed ◽  
Effects Of Temperature

The interest for furfural has increased in the last years due to its potential for competing with oil derivatives as platform chemical. In addition, furfural, derived from C5 sugars, can play a key role in the valorization of the hemicellulose contained in biomass when considering the development of a modern biorefinery concept. The development of such new and competitive biorefinery processes must be based on accurate kinetic data for the reactions involving furfural in the conditions used for its production.This work addresses the determination of furfural destruction kinetics in aqueous acidic environment, using sulphuric acid as catalyst, in the temperature range 150 - 200°C, acid concentration range 36.4 - 145.5 mM and furfural initial concentration between 60.4 and 72.5 mM. These studies were carried out using a recently built lab-scale titanium reactor that enables liquid phase reactions in a relatively broad range of conditions.The obtained results show that destruction of furfural follows first-order reaction kinetics within the range of temperature and acid concentration evaluated. Moreover, the proposed kinetic model takes into account the effects of temperature and acid dilution on the ions activity, and thus H3O+, by using the electrolyte Non-Random Two-Liquid (eNRTL) model. By using this approach, the rate constant dependence on temperature could be described by the Arrhenius law and thus the activation energy could be estimated as being 125.1 [kJ/mol] and the pre-exponential factor 3.71•1011[s-1]. Separation of different reaction products was achieved by means of HPLC, these products were not yet completely identified. Contrarily to what is reported in previous works, formic acid formation from furfural under the tested conditions can be regarded as playing a far less pronounced role than suggested before.

The acid-catalyzed demetalation of 1-(tri-n-butylstannyl)-2-phenylethyne. A surprisingly small β-stannyl effect

1996 ◽  
Vol 74 (7) ◽  
pp. 1366-1368 ◽  
Author(s):  
I. Egle ◽  
V. Gabelica ◽  
A.J. Kresge ◽  
T.T. Tidwell
Keyword(s):  
Key Words ◽  
Isotope Effect ◽  
Acid Concentration ◽  
Rate Constant ◽  
Perchloric Acid ◽  
Hydronium Ion ◽  
Stabilizing Effect ◽  
Aromatic Product ◽  
Acid Catalyzed ◽  
The Difference

Rates of conversion of 1-(tri-n-butylstannyl)-2-phenylethyne to phenylethyne in H2O and D2O solutions of perchloric acid were found to be proportional to acid concentration, giving the hydronium ion rate constant [Formula: see text] and the isotope effect [Formula: see text]. The magnitude of this isotope effect suggests that the reaction occurs by rate-determining hydron transfer to the substrate, producing a vinyl carbocation; this carbocation then loses its tributylstannyl group, giving phenylacetylene as the only detectable aromatic product. The hydronium ion rate constant, when compared to the rates of protonation of phenylethyne and 1-(trimethylsilyl)-2-phenylethyne, gives a β-stannyl stabilizing effect of δΔG≠ = 6.6 kcal mol−1 and a differential β-stannyl/β-silyl effect of δΔG≠ = 3.2 kcal mol−1. These stabilizations are very much smaller than previously reported β-stannyl effects. Possible reasons for the difference are suggested. Key words: β-stannyl effect, β-silyl effect, carbocation stabilization, protodemetalation.

Acid-catalyzed rearrangement of cyclobutanones. V. Preparation of polycyclic aromatic dihydrofurans and dihydropyrans

1980 ◽  
Vol 58 (1) ◽  
pp. 51-54 ◽  
Author(s):  
Paul Duperrouzel ◽  
Edward Lee-Ruff
Keyword(s):  
Polycyclic Aromatic ◽  
Acidic Conditions ◽  
Acid Catalyzed

Cyclobutanones derived from α-phenyl, α,α-diphenyl, and bisphenyleneketene cycloaddition to dihydrofuran and dihydropyran were rearranged under acidic conditions to polycyclic aromatic dihydrofurans and dihydropyrans respectively. A mechanism for these rearrangements is proposed.

Some reactions of 2,4-dimethoxytetrahydropyrans

1969 ◽  
Vol 47 (17) ◽  
pp. 3099-3106 ◽  
Author(s):  
M. J. Baldwin ◽  
R. K. Brown
Keyword(s):  
Room Temperature ◽  
Equilibrium Mixture ◽  
Anomeric Effect ◽  
Temperature Reaction ◽  
Trans Isomers ◽  
Kcal Mole ◽  
A Value ◽  
Cis And Trans Isomers ◽  
Acid Catalyzed ◽  
Cis And Trans

Acid-catalyzed elimination of methanol from 2,4-dimethoxytetrahydropyran (1) produces 2-methoxy-5,6-dihydro-2H-pyran (3) rather than the expected olefin 4-methoxy-3,4-dihydro-2H-pyran (2).The reaction of 1,3-dibromo-5,5-dimethylhydantoin with 3 in ether – methanol gives a 2:1 mixture of the isomers 3β-bromo-2α,4α-dimethoxytetrahydropyran (5a) and 3α-bromo-2α,4β-dimethoxytetrahydropyran (5b) respectively. A rationale is given to explain the preponderance of 5a over 5b and the highly selective attack of the bromine of the hydantoin and the methanol on C-3 and C-4 respectively of the double bond of 3. Reduction of 5ab with zinc in ethanol provides only compound 3.The room temperature reaction of 1 in a mixture of water and 1,2-dimethoxyethane containing Amberlite IR-120, produces 2-hydroxy-4-methoxytetrahydropyran (6) as an equilibrium mixture of cis and trans isomers in the ratio 1:1. This gave a value of 0.9 kcal/mole for the anomeric effect in 6. Pyrolysis of the derivative, 2-acetoxy-4-methoxytetrahydropyran failed to produce the olefin 2 and resulted only in extensive decomposition.

The acid-catalyzed oxido-reduction of spiroketals. Evidence for stereoelectronic control in hydride transfer to cyclic oxenium ions

1981 ◽  
Vol 59 (18) ◽  
pp. 2787-2802 ◽  
Author(s):  
Pierre Deslongchamps ◽  
Daryl D. Rowan ◽  
Normand Pothier
Keyword(s):  
Hydride Transfer ◽  
Reduction Reaction ◽  
Sodium Cyanoborohydride ◽  
Oxidation Reduction ◽  
Oxidation Reduction Reaction ◽  
Stereoelectronic Control ◽  
Acidic Conditions ◽  
Acid Catalyzed ◽  
Ether Ketone ◽  
Catalyzed Oxidation

Tricyclic spiroketal 1 undergoes an acid-catalyzed oxidation–reduction reaction which yields equatorial bicyclic ether aldehyde 5 specifically. Similarly, spiroketals 2, 3, and 4 give equatorial bicyclic ether ketone 12. These results are interpreted by invoking an internal hydride transfer from an alcohol function to a cyclic oxenium ion which takes place with stereoelectronic control. The reduction of tricyclic ketals 1 and 22 with sodium cyanoborohydride under acidic conditions is also reported.

Cis- and trans-2,4-dimethoxytetrahydropyran. Models for the study of the anomeric effect

1968 ◽  
Vol 46 (9) ◽  
pp. 1543-1548 ◽  
Author(s):  
F. Sweet ◽  
R. K. Brown
Keyword(s):  
Good Yield ◽  
Methoxy Group ◽  
Equilibrium Mixture ◽  
Anomeric Effect ◽  
Kcal Mole ◽  
Mild Acid Hydrolysis ◽  
Acid Catalyzed ◽  
Cis And Trans ◽  
Hydrolysis Of ◽  
Mild Acid

Acid-catalyzed methanolysis of 2-methoxy-5,6-dihydro-2H-pyran gave, in good yield, a 4.0:1.0 mixture of trans- and cis-2,4-dimethoxytetrahydropyran. Mild acid hydrolysis of 2-methoxy-5,6-dihydro-2H-pyran followed by acid-catalyzed reaction with methanol gave a cis-trans mixture of 4-hydroxy-2-methoxytetrahydropyran in very poor yield.From the equilibrium mixture of trans- and cis-2,4-dimethoxytetrahydropyran (4.0:1.0), the magnitude of the anomeric effect of the 2-methoxy group was calculated to be 1.4 kcal/mole.

scholarly journals Organic Acid-Catalyzed Subcritical Water Hydrolysis of Immature Citrus unshiu Pomace

Foods ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 18
Author(s):  
Sang-Bin Lim
Keyword(s):  
Citric Acid ◽  
Organic Acid ◽  
Acid Concentration ◽  
Subcritical Water ◽  
Biological Activities ◽  
Citrus Unshiu ◽  
Citric Acid Concentration ◽  
Acid Catalyzed ◽  
Inhibitory Activities ◽  
Hydrolysis Of

Immature Citrus unshiu pomace (ICUP) was hydrolyzed under organic acid-catalyzed, subcritical water (SW) conditions to produce flavonoid monoglucosides (hesperetin-7-O-glycoside and prunin) and aglycons (hesperetin and naringenin) with high biological activities. The results of single-factor experiments showed that with 8 h of hydrolysis and an increasing citric acid concentration, the yield of flavonoid monoglucosides (hesperetin-7-O-glycoside and prunin) increased from 0 to 7% citric acid. Afterward, the hesperetin-7-O-glycoside yield remained constant (from 7 to 19% citric acid) while the pruning yield decreased with 19% of citric acid, whereas the aglycon yield increased continuously. In response surface methodology analysis, a citric acid concentration and hydrolysis duration of 13.34% and 7.94 h were predicted to produce the highest monoglucoside yield of 15.41 mg/g, while 18.48% citric acid and a 9.65 h hydrolysis duration produced the highest aglycon yield of 10.00 mg/g. The inhibitory activities of the SW hydrolysates against pancreatic lipase (PL) and xanthine oxidase (XO) were greatly affected by citric acid concentration and hydrolysis duration, respectively. PL and α-glucosidase inhibition rates of 88.2% and 62.7%, respectively, were achieved with 18.48% citric acid and an 8 h hydrolysis duration, compared to 72.8% for XO with 16% citric acid and 12 h of hydrolysis. This study confirms the potential of citric acid-catalyzed SW hydrolysis of ICUP for producing flavonoid monoglucosides and aglycons with enhanced enzyme inhibitory activities.

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