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.

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 the basic hydrolysis of anilides. III. α-Substituted N-methyl-N-p-nitrophenylacetamides

1980 ◽  
Vol 33 (8) ◽  
pp. 1771 ◽  
Author(s):  
TJ Broxton ◽  
NW Duddy
Keyword(s):  
Cetyltrimethylammonium Bromide ◽  
Substituent Effects ◽  
Micellar Catalysis ◽  
Single Parameter ◽  
Parameter Analysis ◽  
Basic Hydrolysis ◽  
Presence And Absence ◽  
Hydrolysis Of ◽  
Acetic Acids

The basic hydrolysis of a number of α-substituted N-methyl-N-p- nitrophenylacetamides has been studied both in the presence and absence of micelles of cetyltrimethylammonium bromide (ctab). Unlike the related p-nitrophenyl esters of a-substituted acetic acids, no evidence for the operation of the E1cb mechanism in the basic hydrolysis has been detected. Reasons for the differences between the amides and esters are discussed. Substituent effects on the hydrolysis of the amides have been studied both by single-parameter and dual-parameter analysis.

Micellar catalysis of organic reactions. 22. A comparison of the basic hydrolysis of benzodiazepinones in the presence of reactive counterion micelles and vesicles

1988 ◽  
Vol 66 (7) ◽  
pp. 1566-1570 ◽  
Author(s):  
Trevor J. Broxton ◽  
Xenia Sango ◽  
Sallyanne Wright
Keyword(s):  
Surfactant Concentration ◽  
Biological Membranes ◽  
Micellar Catalysis ◽  
Organic Reactions ◽  
Conductivity Measurements ◽  
Amide Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Basic Hydrolysis ◽  
Hydrolysis Of ◽  
Good Agreement

The basic hydrolysis of diazepam and several N-alkyl nitrazepam derivatives has been studied in the presence of reactive counterion micelles of cetyltrimethylammonium hydroxide (CTAOH) and vesicles of didodecyldimethylammonium hydroxide (DDAOH). In both surfactants, the rate of hydrolysis of all compounds was found to be dependent on the hydroxide concentration at constant surfactant concentration and this was interpreted as evidence for initial amide hydrolysis. The hydrolysis in CTAOH was inhibited by added salts in the order Br− < NO3− < SO42−. At concentrations above 3 mM surfactant, the rate of hydrolysis of each compound was similar in CTAOH and in DDAOH. At lower concentrations of CTAOH, however, the rate of hydrolysis was significantly lower than that in DDAOH. On the basis of this evidence, it was concluded that the cmc of CTAOH was between 2–3 mM, which is in good agreement with the value of 1.8 mM obtained by Zana from conductivity measurements. For diazepam, a mechanistic change is indicated on transfer from water to either micelles or vesicles and since vesicles are considered good models of biological membranes, this suggests that conclusions concerning the bioavailability of diazepam should not be based on studies in water but rather on studies in either micelles or vesicles.

Micellar catalysis of the basic hydrolysis of N-methyl-N-(4'-nitropheny1)-2-phenoxyacetamide. Variation of the magnitude of catalysis for differentsources of hydroxide ions

1981 ◽  
Vol 34 (8) ◽  
pp. 1615 ◽  
Author(s):  
TJ Broxton
Keyword(s):  
Sodium Hydroxide ◽  
Cetyltrimethylammonium Bromide ◽  
Reaction System ◽  
Micellar Catalysis ◽  
Buffer System ◽  
Nucleophilic Catalysis ◽  
Carbonate Ions ◽  
Basic Hydrolysis ◽  
Hydrolysis Of ◽  
Triethylammonium Chloride

The hydrolysis of N-methyl-N-(4'-nitrophenyl)-2-phenoxyacetamide has been studied in the presence and absence of micelles of cetyltrimethylammonium bromide. The micellar catalysis depends on the reaction system being used. Hydrolysis in the presence of sodium hydroxide, and in the presence of borate, carbonate/bicarbonate and triethylamine/triethylammonium chloride buffers has been examined. The magnitude of catalysis is shown to depend on the buffer system used, the concentration of detergent, the concentration of the buffer, the pH and the presence of any added salts. The results confirm that it is unrealistic to compare independent sets of results on different compounds unless the conditions for obtaining those results are identical. ��� Hydrolysis in the presence of carbonate/bicarbonate buffers is shown to be subject to buffer catalysis and, by analogy with results for p-nitrophenyl acetate, nucleophilic catalysis by carbonate ions is suggested.

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