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.

Micellar catalysis of organic reactions. XII. Basic hydrolysis of some alkyl and aryl N-(4-Nitrophenyl)carbamates

1984 ◽  
Vol 37 (1) ◽  
pp. 47 ◽  
Author(s):  
TJ Broxton
Keyword(s):  
Cetyltrimethylammonium Bromide ◽  
Kinetic Studies ◽  
Micellar Catalysis ◽  
Organic Reactions ◽  
Bond Breaking ◽  
Tetrahedral Intermediate ◽  
Stable Product ◽  
Methyl Derivatives ◽  
Basic Hydrolysis ◽  
Hydrolysis Of

The basic hydrolysis of a number of alkyl and aryl N-(4-nitrophenyl)carbamates in the presence and absence of micelles of cetyltrimethylammonium bromide (ctab) are reported. In water the stable product at 26�C was N-(4-nitrophenyl)carbamate ion (3). At higher temperatures this carbamate ion slowly decomposed to 4-nitroaniline. In ctab the decarboxylation of the N-(4-nitrophenyl)carbamate ion was strongly catalysed (× 45) and thus the observed final product even at 26�C was 4-nitroaniline. Kinetic studies in water and in ctab were consistent with decomposition of the methyl carbamate (la) by a BAC2 mechanism and the 2,2,2-trifluoroethyl carbamate (lc) by an E1cB mechanism. The extent of ionization of the substrate carbamates to nitranion (4) was enhanced in ctab as was the rate of spontaneous decomposition of the nitranion. This is in contrast to other E1cB reactions reported in the literature, for which the rate of spontaneous decomposition of the carbanion was inhibited by ctab. For compounds reacting by the BAC2 mechanism, the tetrahedral intermediate (2) partitioned in favour of C-OR bond breaking rather than C-N bond breaking observed previously for some N-methyl derivatives.

Basic hydrolysis of some alkyl and phenyl N-Aryl-N-methylcarbamates

1983 ◽  
Vol 36 (11) ◽  
pp. 2203 ◽  
Author(s):  
TJ Broxton
Keyword(s):  
Rate Constants ◽  
Cetyltrimethylammonium Bromide ◽  
Ester Hydrolysis ◽  
Micellar Catalysis ◽  
Bond Breaking ◽  
Methyl Ethyl ◽  
Hydroxide Ion ◽  
Tetrahedral Intermediate ◽  
Basic Hydrolysis ◽  
Hydrolysis Of

Rate constants for the basic hydrolysis of methyl, ethyl and phenyl N-aryl-N-methylcarbamates in the presence and absence of micelles of cetyltrimethylammonium bromide are reported. Hammett plots for the methyl and ethyl carbamates were curved, and this is explained by consideration of the competition between C-N and C-OR bond breaking for decomposition of the tetrahedral intermediate. In one case (p-nitro-substituted), rate-determining formation of the tetrahedral intermediate is suggested, whereas for other compounds rate-determining C-N bond breaking or C-OR bond breaking is proposed. Micellar catalysis for each of the reactions is reported, and large catalysis (× 50) was observed for compounds where C-N bond breaking was kinetically significant. This is compared with results in the literature for amide and ester hydrolysis. Whereas, for ester hydrolysis, loss of alkoxide ion from the tetrahedral intermediate is favoured over loss of hydroxide ion, in carbamate hydrolysis, loss of hydroxide ion is favoured. A possible reason for this reversal of nucleofugicity of OH- and OR- is proposed.

The Importance of Conformation of the Tetrahedral Intermediate in the Hydrolysis of Amides. Selective Cleavage of the Tetrahedral Intermediate Controlled by Orbital Orientation

1973 ◽  
Vol 51 (10) ◽  
pp. 1665-1669 ◽  
Author(s):  
Pierre Deslongchamps ◽  
Claude Lebreux ◽  
Roland Taillefer
Keyword(s):  
Experimental Evidence ◽  
Lone Pair ◽  
Tetrahedral Intermediate ◽  
Basic Hydrolysis ◽  
Hydrolysis Of ◽  
Orbital Orientation

The basic hydrolysis of N-disubstituted imidate salts proceeds via a hemi-orthoamide tetrahedral intermediate which can in principle give amide–alcohol or ester–amine products. Experimental evidence has been obtained which shows that the specific conformation of the tetrahedral intermediate determines products formation and it is further suggested that the orientation of the lone pair orbitals of the heteroatoms governs this remarkable selective decomposition.

Formation of a cyclic tetrahedral intermediate by the addition of water to 2-methyl-4H- 3,1-benzoxazine followed by ring opening to 2-aminobenzyl acetate and 2-acetylaminobenzyl alcohol; pH-dependence of rate of reaction and product ratio

1999 ◽  
Vol 77 (5-6) ◽  
pp. 1035-1041 ◽  
Author(s):  
Wendy J Dixon ◽  
Frank Hibbert
Keyword(s):  
Ring Opening ◽  
Ph Dependence ◽  
Kinetic Studies ◽  
Ph Profile ◽  
Hydroxide Ion ◽  
Product Ratio ◽  
Tetrahedral Intermediate ◽  
Rate Of Reaction ◽  
Buffer Base ◽  
Carbonyl Addition

Kinetic studies have shown that addition of water to protonated 2-methyl-4H-3,1-benzoxazine occurs to give a cyclic tetrahedral carbonyl addition intermediate. At pH <5, the intermediate is protonated and reacts to 2-aminobenzyl acetate, whereas at pH >7.5, the unprotonated intermediate collapses to give 2-acetylaminobenzyl alcohol. The former reaction is catalysed by buffer base but the latter is uncatalysed. At pH 9-12, reaction of hydroxide ion with protonated 2-methyl-4H-3,1-benzoxazine to give 2-acetylaminobenzyl alcohol becomes important, and at pH >12, the same product is formed by reaction of hydroxide ion with unprotonated 2-methyl-4H-3,1-benzoxazine.Key words: mechanism, addition, tetrahedral intermediate, hydrolysis, pH profile.

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.

The Hydrolysis of Imidate Salts. Stereoelectronic Control in the Cleavage of the Hemiorthoamide Tetrahedral Intermediate

1975 ◽  
Vol 53 (18) ◽  
pp. 2791-2807 ◽  
Author(s):  
Pierre Deslongchamps ◽  
Serge Dubé ◽  
Claude Lebreux ◽  
Dennis R. Patterson ◽  
Roland J. Taillefer
Keyword(s):  
Alkyl Group ◽  
Lone Pair ◽  
The Other ◽  
Tetrahedral Intermediate ◽  
Hydrolysis Products ◽  
Anti Conformation ◽  
Stereoelectronic Control ◽  
Basic Hydrolysis ◽  
Hydrolysis Of ◽  
Nitrogen Bond

A new stereoelectronic theory for the cleavage of the tetrahedral intermediate (hemiorthoamide) in the hydrolysis of amides is presented. In this new theory, the precise conformation of the tetrahedral intermediate controls the nature of the hydrolysis products. It is postulated that the breakdown of the tetrahedral intermediate depends upon the orientation of the lone pair orbitals of the heteroatoms. Specific cleavage of a carbon–oxygen or a carbon–nitrogen bond in any conformer is allowed only if the other heteroatoms (oxygen and nitrogen) each have an orbital oriented antiperiplanar to the leaving O-alkyl or N-alkyl group. Experimentally, a study of the basic hydrolysis of a variety of N,N-dialkylated imidate salts having either a syn or an anti conformation demonstrates clearly that there is a stereoelectronic control in the cleavage of the hemiorthoamide.

Substituent effects on the basic methanolysis of a series of substituted N-Methyl-p-toluanilides

1980 ◽  
Vol 33 (4) ◽  
pp. 903 ◽  
Author(s):  
TJ Broxton ◽  
NW Duddy
Keyword(s):  
Substituent Effects ◽  
Bond Breaking ◽  
Straight Line ◽  
Breaking Mechanism ◽  
Basic Hydrolysis ◽  
Line P ◽  
Hydrolysis Of

The rate of basic methanolysis of a series of substituted N-methyl-p- toluanilides (1) has been measured at 373 K. A Hammett plot of these results resulted in a straight line (p 3.1, r 0.998) indicative of reaction by solvent-assisted bond breaking (mechanism B) throughout the series. The relevance of these results to previous results for the basic hydrolysis of N-methyl-p-toluanilides (I) and basic methanolysis of N-methylbenzanilides (2) is discussed.

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