Kinetics and mechanism of base-catalysed aldolization of 1,3-dimethoxy-2-propanone

1985 ◽  
Vol 50 (10) ◽  
pp. 2252-2259 ◽  
Author(s):  
Michal Fedoroňko ◽  
Mária Petrušová ◽  
Vladimír Kováčik
Keyword(s):  
Thermodynamic Parameters ◽  
Alkaline Solution ◽  
Equilibrium Constants ◽  
Kinetics And Mechanism ◽  
Reversible Reaction ◽  
Aqueous Alkaline Solution ◽  
Rate Determining Step ◽  
Catalysed Reaction ◽  
Starting Compound ◽  
Intermediate Anion

1,3-Dimethoxy-2-propanone (HA) in an aqueous alkaline solution undergoes specifically base-catalysed aldolization with the formation of a dimer, 4-hydroxy-1,3,5-trimethoxy-4-methoxymethyl-2-pentanone (H2A2). The reaction is reversible and involves the formation or decomposition of an intermediate anion, HA2-, as the rate-determining step. The formation of a carbanion ion, A-, of the starting compound and of the HA2- anion are rapid, preceding, and generally base-catalysed reaction steps. The activation and thermodynamic parameters of the reversible reaction were determined from the dependences of the rate and equilibrium constants on the temperature.

The aldol condensation of acetone with acetophenone

1992 ◽  
Vol 70 (4) ◽  
pp. 1055-1068 ◽  
Author(s):  
J. Peter Guthrie ◽  
Xiao-Ping Wang
Keyword(s):  
Kinetic Model ◽  
Alkaline Solution ◽  
Aldol Condensation ◽  
Equilibrium Constants ◽  
Analytical Data ◽  
Initial Compound ◽  
Aqueous Alkaline Solution ◽  
First Order ◽  
Carbon Acid ◽  
Best Fit

The kinetics and equilibria involved in the aldol condensation of acetone, acting as carbon acid, and acetophenone have been studied in aqueous alkaline solution. The enone isolated is the E isomer. The reactions are all first order in hydroxide, with rate and equilibrium constants (defined for E-enone as initial compound) of: k12 = (5.55 ± 0.17) × 10−6 M−1 s−1, k21 = (8.00 ± 0.40) × 10−6 M−1 s−1, K21 = (1.44 ± 0.55) (ketol to E-enone), K24 = 0.160 ± 0.033 (ketol to Z-enone), K32 = (1.89 ± 0.26) × 10−3 M−1 (acetone plus acetophenone to ketol), k23 = 0.180 ± 0.005 M−1 s−1, k32 = (3.41 ± 0.49) × 10−4 M−2 s−1. There is an equilibration of the two enones in base that is faster than hydration to the ketol: k14 = (3.14 ± 0.84) × 10−5 M−1 s−1; k41 = (2.81 ± 0.61) × 10−4 M−1 s−1; K14 = 0.112 ± 0.019. To analyze the behavior of the enone:ketol equililbrium system in acid we simultaneously fitted analytical data for all three species (E-enone, Z-enone, and ketol) to a kinetic model, so that the rate constants were determined by the best fit to all of the data for an experiment.

The aldol condensation of acetophenone with acetone

1991 ◽  
Vol 69 (2) ◽  
pp. 339-344 ◽  
Author(s):  
J. Peter Guthrie ◽  
Xiao-Ping Wang
Keyword(s):  
Alkaline Solution ◽  
Aldol Condensation ◽  
Equilibrium Constants ◽  
Mesityl Oxide ◽  
Initial Compound ◽  
Aqueous Alkaline Solution ◽  
First Order ◽  
Related Series ◽  
Carbon Acid ◽  
Condensation Of Acetophenone

The kinetics and equilibria involved in the aldol condensation of acetophenone, acting as carbon acid, and acetone have been studied in aqueous alkaline solution. The reactions are all first order in hydroxide, with rate and equilibrium constants (defined for enone as initial compound) of: k12 = 3.3 × 10−4 M−1 s−1, k21 = 3.2 × 10−5 M−1 s−1K12 = 10.2, k23 = 8.0 × 10−2 M−1 s−1, k32 = 3.3 × 10−4 M−2 s−1, K32 = 4.1 × 10−3 M−1. The series methylbutenal, mesityl oxide, and 3-methyl-1-phenyl-2-buten-1-one can now be compared with regard to regularities and deviations from regularity. The related series cinnamaldehyde, benzalacetone, and chalcone also provides insights into the behaviour of this system. Key words: aldol, dehydration, equilibrium, acetophenone, acetone.

scholarly journals Kinetics and Mechanism of Oxidation of Aliphatic Aldehydes by Benzyltrimethylammonium tribromide

1999 ◽  
Vol 23 (3) ◽  
pp. 176-177
Author(s):  
Garima Goswami ◽  
Seema Kothari ◽  
Kalyan K. Banerji
Keyword(s):  
Carboxylic Acid ◽  
Kinetics And Mechanism ◽  
Intermediate Complex ◽  
Aliphatic Aldehydes ◽  
Rate Determining Step ◽  
Mechanism Of Oxidation ◽  
Subsequent Decomposition

The oxidation of aliphatic aldehydes by benzyltrimethylammonium tribromide involves the formation of an intermediate complex and its subsequent decomposition in the rate-determining step to the corresponding carboxylic acid.

Enhanced Thermal Stability of Esterified Lignin in Different Solvent Mediums

2018 ◽  
Vol 9 (1) ◽  
pp. 39-49 ◽  
Author(s):  
Sharifah Nurul Ain Syed Hashim ◽  
Sarani Zakaria ◽  
Chin Hua Chia ◽  
Sharifah Nabihah Syed Jaafar
Keyword(s):  
Thermal Stability ◽  
Alkaline Solution ◽  
Room Temperature ◽  
Hydroxyl Groups ◽  
Aqueous Alkaline Solution ◽  
Alkali Lignin ◽  
Weight Percentage ◽  
H Nmr ◽  
Ft Ir ◽  
Thermal Stability Of

In this study, soda alkali lignin from oil palm empty fruit bunch (EFB-AL) and kenaf core (KC-AL) are esterified with maleic anhydride under two different conditions, namely i) pyridine at temperature of 120°C for 3h and ii) aqueous alkaline solution at room temperature for 4h. As a result, the weight percentage gain (WPG) of the esterified EFB-AL (EFB-EL) and esterified KC-AL (KC-EL) in pyridine demonstrated a higher compared to aqueous alkaline solution. The FT-IR results of EFB-EL and KC-EL in both solvents exhibited some changes at the carbonyl and hydroxyl groups. Furthermore, the esterification process induced the carboxylic peak to appear in both alkali lignin samples. The outcome is confirmed by conducting H-NMR analysis, which demonstrated ester and carboxylic acid peaks within the spectral analysis. Finally, the TGA results showed both EFB-EL and KC-EL that are exposed to aqueous alkaline actually possessed better thermal stability and higher activation energy (Ea) compared to the esterified samples in pyridine.

Thermochromism of Metal Exchange Reaction between Zinc(II) and Mercury(II) Porphyrins

1995 ◽  
Vol 50 (4) ◽  
pp. 545-550 ◽  
Author(s):  
Masaaki Tabata ◽  
Masahiro Ide ◽  
Kentaro Kaneko
Keyword(s):  
Aqueous Solution ◽  
Exchange Reaction ◽  
Thermodynamic Parameters ◽  
Distribution Curve ◽  
Equilibrium Constants ◽  
Metal Exchange ◽  
Free Base ◽  
Temperature Range ◽  
Base Form ◽  
Metal Exchange Reaction

Thermochromism was observed for an aqueous solution containing zinc(II) and mercury( II) cations and N-p-nitrobenzyl-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin anion (NO2Bz(Htpps)4-) in the temperature range 10 to 70 °C. The equilibrium constants and the thermodynamic parameters of Zn(NO2Bztpps)3- and Hg(NO2Bztpps)3- have been determined spectrophotometrically to elucidate the thermochromism at 10, 15, 20, 25 and 30 °C in 0.1 mol dm-3 NaNO3. The protonation and metalation constants of NO2Bz(Htpps)4- are defined as K2 = [H2P][H+]-1[HP]-1, K3 = [H3P][H+]-1[H2P]-1 and KMP = [M P][H+][M2+]-1[HP]-1, where HP and MP denote the free base form of the prophyrin and the metalloporphyrins of zinc(II) and mercury(II), respectively. Charges of the prophyrin and metalloporphyrins are omitted for simplicity. The following values were found: logK2 = 7.75 ±0.02 (25 °C), ΔH°/kJmol-1 = -21.2±0.5 and ΔS°/Jmol-1K-1 = 77±1, logK3 = 2.55±0.02 (25 °C), ΔH°/kJmol-1 = -25±0.8 and ΔS°/Jmol-1K-1 = -35±3 and log KZnP = 0.63±0.03 (25 °C), ΔH°/kJmol-1 = 31.0±0.8 and ΔS°/Jmol-1K-1 = 116±3, logKHgP = 6.22±0.03 (25 °C), ΔH°/kJmol-1 = 4.5±0.7 and ΔS°/Jmol-1K-1 = 134±2. The distribution curve calculated from the thermodynamic parameters sufficiently agrees with the observed metal exchange reaction between the metalloporphyrins.

scholarly journals Kinetics and mechanism of cetyltrimethylammonium bromide catalyzed oxidation of diethylene glycol by chloramine-T in acidic medium

2003 ◽  
Vol 68 (7) ◽  
pp. 535-542 ◽  
Author(s):  
V.W. Bhagwat ◽  
J. Tiwari ◽  
A. Choube ◽  
B. Pare
Keyword(s):  
Diethylene Glycol ◽  
Acidic Medium ◽  
Cetyltrimethylammonium Bromide ◽  
Reaction Rate ◽  
Chloride Ions ◽  
Kinetics And Mechanism ◽  
Product Analysis ◽  
Rate Determining Step ◽  
Chloramine T ◽  
Catalyzed Oxidation

The kinetics and mechanism of the C16TABcatalyzed oxidation of diethylene glycol (2,2?-oxydiethanol) by chloramine-T in acidic medium has been studied. The reaction has a first-order dependence on chloramine-T. With excess concentrations of other reactants, the reaction rate follows fractional order kinetics with respect to [diethylene glycol]. The micellar effect due to cetyltrimethylammonium bromide, a cationic surfactant, has been studied. The reaction is catalyzed by chloride ions as well. The small salt effect and increase in the reaction rate with increasing dielectric constant suggest the involvement of neutral molecules in the rate determining step. Addition of p-toluenesulfonamide retards the reaction rate. On the basis of product analysis, a pertinent mechanism is proposed.

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