Effect of hydroxide ion concentration on the partitioning of a monoanionic tetrahedral intermediate into di- and tri-anionic reactive intermediates in the alkaline hydrolysis of alloxan

1979 ◽  
pp. 1093 ◽  
Author(s):  
M. Niyaz Khan ◽  
A. Aziz Khan
Keyword(s):  
Alkaline Hydrolysis ◽  
Reactive Intermediates ◽  
Ion Concentration ◽  
Hydroxide Ion ◽  
Tetrahedral Intermediate ◽  
Hydrolysis Of

THE ALKALINE HYDROLYSIS OF N-ACYLTHIOUREAS

1974 ◽  
Vol 52 (5) ◽  
pp. 697-701 ◽  
Author(s):  
Wayne I. Congdon ◽  
John T. Edward
Keyword(s):  
Carboxylic Acid ◽  
Sodium Hydroxide ◽  
Alkaline Solution ◽  
Alkaline Hydrolysis ◽  
Potassium Hydroxide ◽  
Ion Concentration ◽  
Hydroxide Ion ◽  
Arrhenius Parameters ◽  
Hydrolysis Of

N-Benzoylthiourea (pKHA 10.9) and other N-acylthioureas ionize in alkaline solution, and then are rapidly hydrolyzed to thiourea and a carboxylic acid. The rates become independent of hydroxide ion concentration when this exceeds about 0.1 M and point to a mechanism in which hydrolysis takes place by attack of an hydroxide ion on the un-ionized molecule of N-acylthiourea. This mechanism accords with the Arrhenius parameters for the hydrolysis of N-benzoylthiourea in 0.2 N sodium hydroxide, and with the Hammett ρ value of 0.10 for the hydrolysis of m- and p-substituted N-benzoylthioureas in 1.0 N potassium hydroxide.

Flash photolysis production of the tetrahedral intermediate of the methanolysis of methyl benzoate. Direct measurement of the rate of breakdown of the conjugate base form

1990 ◽  
Vol 68 (3) ◽  
pp. 375-382 ◽  
Author(s):  
Robert A. McClelland ◽  
V. M. Kanagasabapathy ◽  
Steen Steenken
Keyword(s):  
Rate Constants ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Carbonyl Oxygen ◽  
Methyl Benzoate ◽  
Ion Concentration ◽  
Hydroxide Ion ◽  
Tetrahedral Intermediate ◽  
Conjugate Base

Laser flash photolysis in aqueous basic solutions of the ortho acid derivatives 1-(phenyldimethoxymethyl)benzimidazole 2 and 4-bromo-1-(phenyldimethoxymethyl)imidazole 3 results in production of the phenyldimethoxymethyl cation, which has λmax at 260 nm. The cation decays in reactions with water (k = 9.9 × 104 s−1) and hydroxide ion (2.5 × 108 M−1 s−1) to finally yield methyl benzoate, whose formation was monitored at 234 nm. In solutions with pH 10–12, rate constants measured at this wavelength are the same as those obtained at 260 nm, but with pH > 13 and pH < 9, rate constants at 234 nm are smaller. With pH 9–10 and pH 12–13, single exponential kinetics are not observed at 234 nm. This behavior is interpreted in terms of a scheme where at each pH there are two consecutive first-order reactions, cation → phenyldimethoxyhydroxymethane (5) → ester, and the pH dependencies of the rate constants are such that they cross twice over the pH range of this study. The intermediate 5 is the tetrahedral intermediate formed in the methanolysis of methyl benzoate, and the 234-nm buildup at pH > 13 and pH < 9 directly measures its breakdown. At pH > 13 the rate constant is independent of pH with k = 9 × 106 s−1. This represents the rapid expulsion of methoxide from the conjugate base of 5. At pH < 9 the rate constants are proportional to hydroxide ion concentration, with [Formula: see text]. In these solutions the neutral intermediate predominates and the dependence on [OH−] of its rate of conversion to ester is interpreted in terms of breakdown of the anion and protonation of this species by water occurring at comparable rates. Thus, [Formula: see text] represents a situation where there is partial rate-limiting deprotonation of the neutral intermediate by hydroxide. The intermediate of this study bears a close resemblance to the tetrahedral intermediate of the hydrolysis of methyl benzoate. The observation that the anionic forms of such intermediates undergo breakdown at rates similar to those associated with the establishment of proton transfer equilibrium explains why the ester undergoes carbonyl oxygen exchange in base at a rate slower than hydrolysis. Keywords: tetrahedral intermediate, flash photolysis, ester hydrolysis.

Thiohydantoins. XI Kinetic Studies of the Alkaline Hydrolysis of 1-Acyl-2-thiohydantoins

1972 ◽  
Vol 50 (23) ◽  
pp. 3780-3788 ◽  
Author(s):  
Wayne I. Congdon ◽  
John T. Edward
Keyword(s):  
Carboxylic Acid ◽  
Alkaline Solution ◽  
Alkaline Hydrolysis ◽  
Ground State ◽  
Kinetic Studies ◽  
Steric Effects ◽  
Hydroxide Ion ◽  
Entropy Of Activation ◽  
Hydrolysis Of ◽  
Conjugate Base

1-Acyl-2-thiohydantoins ionize in alkaline solution (pK ∼ 7). In solutions more alkaline than pH > 11 they are rapidly hydrolyzed to 2-thiohydantoin and a carboxylic acid, by attack of a hydroxide ion on the conjugate base of the 1-acyl-2-thiohydantoin. Possible mechanisms to accord with the entropy of activation, which is less negative than usual for base-catalyzed amide hydrolyses, are discussed. 1-Benzoyl-2-thiohydantoin hydrolyzes more rapidly than 1-acetyl-2-thiohydantoin, possibly because the ground state of the former molecule is destabilized by steric effects.

Alkaline Hydrolysis of 1-Iodomethyl-1,2,5-triphenylphospholium Iodide, a New Route to the 4-Phosphabicyclo[3.1.0]hex-2-ene System

1971 ◽  
Vol 49 (6) ◽  
pp. 879-884 ◽  
Author(s):  
A. N. Hughes ◽  
Chit Srivanavit
Keyword(s):  
Alkaline Hydrolysis ◽  
High Yield ◽  
Hydroxide Ion ◽  
Compound C ◽  
Hydrolysis Of ◽  
Very High

Alkaline hydrolysis of 1-iodomethyl-1,2,5-triphenylphospholium iodide gives 3,4,5-triphenyl-4-phosphabicyclo[3.1.0]hex-2-ene-4-oxide in very high yield. Three possible mechanisms are discussed and isolation of a key intermediate allows one of these mechanisms to be discarded. Alkaline hydrolysis of 1-allyl-1,2,5-triphenylphospholium bromide in methanol gives 1,2,5-triphenylphosphole and small quantities of a compound C26H27O2P which is an adduct of the original phospholium ion, hydroxide ion, and methanol.

Basic hydrolysis of some N-phenylcarbamates and basic methanolysis of some N-phenylacetamides containing an ortho nitro substituent

1984 ◽  
Vol 37 (10) ◽  
pp. 2005
Author(s):  
TJ Broxton
Keyword(s):  
Induction Period ◽  
Nitro Group ◽  
Resonance Effect ◽  
Kinetic Studies ◽  
Bond Breaking ◽  
Hydroxide Ion ◽  
Tetrahedral Intermediate ◽  
Group Reaction ◽  
Basic Hydrolysis ◽  
Hydrolysis Of

Kinetic studies of the basic methanolysis of N-(2-nitropheny1)acetamides indicate that unlike the 4-nitro isomer, no change of mechanism occurs on inclusion of an N-methyl group. Reaction occurs with rate-determining C-N bond breaking for both the N-H and N-methyl compounds. Basic hydrolysis of some methyl N-(2-nitropheny1)carbamates occurred by the BAC2 mechanism and the tetrahedral intermediate formed during the hydrolysis decomposed with preferential C-O bond breaking. This is in contrast to the basic hydrolysis of methyl N-methyl-N-4-nitrophenyl- carbamate, which has previously been shown to occur with preferential C-N bond breaking. For the hydrolysis of methyl N-methyl-N-(2-nitrophenyl)carbamate, an induction period in amine production was detected at 0.45 M hydroxide ion. This was interpreted to mean that the tetrahedral intermediate breaks down by loss of methoxide ion. At 0.93 M hydroxide ion, however, no induction period in amine production was observed. The possibility of reaction through a dianionic intermediate was raised to explain this observation. The amide ion (2-NO2C6H4NMe-) is a poorer leaving group than its 4-nitro isomer. This is explained by steric crowding in the 2-nitro compound, resulting in twisting of the nitro group out of the plane of the benzene ring and a consequent reduction in the electron-withdrawing resonance effect of the 2-nitro group compared to the 4-nitro group.

Effect of OH- Concentration on Alkaline Hydrolysis of Diphenyl (4-Nitrophenyl) Phosphate Catalyzed by 2-Iodosobenzoic and 3-Iodoso-2-naphthoic Acids

1994 ◽  
Vol 59 (5) ◽  
pp. 1137-1144 ◽  
Author(s):  
Aleš Ptáček ◽  
Jiří Kulič
Keyword(s):  
Alkaline Hydrolysis ◽  
Reaction Rate ◽  
Ion Concentration ◽  
Molar Ratio ◽  
Hexadecyltrimethylammonium Bromide ◽  
Ph Values ◽  
Nitrophenyl Phosphate ◽  
Naphthoic Acid ◽  
Iodosobenzoic Acid ◽  
Hydrolysis Of

The hydrolysis of diphenyl (4-nitrophenyl) phosphate catalyzed by 2-iodosobenzoic and 3-iodoso-2-naphthoic acids has been studied at different pH values in the presence of hexadecyltrimethylammonium bromide as a micellar agent. It was found that 3-iodoso-2-naphthoic acid is better catalyst than 2-iodosobenzoic acid. At amounts of the acids higher than stoichiometric, the reaction is independent of pH in the 8.00 to 10.00 region while on using substoichiometric amounts, the reaction rate depends on OH- ion concentration only when the acid to diphenyl (4-nitrophenyl) phosphate molar ratio amounts to 12.5 : 1 for 2-iodosobenzoic acid and 6.25 : 1 for 3-iodoso-2-naphthoic acid.

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