Micellar catalysis of organic reactions. Part 33. Amide hydrolysis in neutral solution in the presence of a copper-containing micelle

1993 ◽  
Vol 71 (5) ◽  
pp. 670-673 ◽  
Author(s):  
Trevor J. Broxton ◽  
Robin A. Coa
Keyword(s):  
Cetyltrimethylammonium Bromide ◽  
Cupric Chloride ◽  
Buffer Concentration ◽  
Neutral Solution ◽  
Hydroxide Ion ◽  
Amide Hydrolysis ◽  
Mechanism Of Reaction ◽  
Rate Of Reaction ◽  
Hydrolysis Of ◽  
Micelle Surface

The hydrolysis of 5-nitro-2-(trifluoroacetylamino)benzoic acid (1) has been studied at pH 7 in water and in the presence of micelles of cetyltrimethylammonium bromide (ctab) and of copper-containing micelles formed from the reaction of N,N,N′-trimethyl-N′-hexadecylethylenediamine and cupric chloride. It has been found that the hydrolysis of 1 is inhibited by micelles of ctab but strongly catalysed by the copper-containing micelle at this pH. At a higher pH where the hydroxide ion reaction becomes important the reaction is catalysed by micelles of ctab as well, but the catalysis is stronger by the copper-containing micelle. The effect of added sodium chloride on the rate of reaction is shown to be larger for reaction in the presence of ctab than for reaction in the presence of the copper micelles. Also reported are the effects of the buffer concentration on the rate of reaction at various pH for both micelles. It is concluded that the mechanism of reaction in the copper-containing micelle involves a metal-bound hydroxyl rather than a free hydroxide ion loosely associated with the cationic micelle surface. It is interesting that the catalysis of this reaction by the copper-containing micelle is large enough to allow amide hydrolysis at a reasonable rate at neutral pH at ambient temperature.

Micellar catalysis of organic reactions. Part 37. A comparison of the catalysis of ester and amide hydrolysis by copper-containing micelles

1997 ◽  
Vol 75 (2) ◽  
pp. 202-206 ◽  
Author(s):  
Trevor J. Broxton ◽  
Abdulla Nasser
Keyword(s):  
Metal Ion ◽  
Cetyltrimethylammonium Bromide ◽  
Acid Group ◽  
Ester Hydrolysis ◽  
Reaction Centre ◽  
Rate Determining Step ◽  
Amide Hydrolysis ◽  
Low Concentrations ◽  
Triton X ◽  
Hydrolysis Of

The hydrolysis of a number of nitroactivated esters and amides has been studied in the presence of copper-containing metallomicelles at neutral pH. The relative rates of hydrolysis in the pure metallomicelle and in co-micelles with either cetyltrimethylammonium bromide (ctab) or Triton X-100 depends on the hydrophobicity of the substrate and whether it is completely solubilized by the copper micelle. Thus it depends on the concentration of the copper micelle. At low concentrations of copper micelle (0.2 mM) where the substrate is incompletely solubilized, the reaction is faster when 2 mM ctab is added. At higher concentrations (>0.6 mM) where the substrate may be almost completely solubilized by the copper micelle, the reaction is slower when 2 mM ctab is added. For ester hydrolysis the presence of either a carboxylic acid group or a heterocyclic nitrogen atom close to the reaction centre resulted in much larger catalysis by the metallomicelle than for model compounds without these additional groups. It is postulated that these groups coordinate with the metal ion and thus present the reaction centre close to a metal-bound hydroxyl resulting in a significant increase in the rate of bond formation, which is the rate-determining step for ester hydrolysis. For amide hydrolysis the presence of a carboxyl group ortho to the reaction centre did not lead to larger catalysis by the copper micelle than for the compound without this group. This difference is attributed to the different rate-determining steps for amide and for ester hydrolysis. Keywords: metallomicelles, ester and amide hydrolysis.

Micellar catalysis of organic reactions. VII. The effect of the micellar counter ion in nucleophilic reactions of hydroxide and nitrite ions

1981 ◽  
Vol 34 (11) ◽  
pp. 2313 ◽  
Author(s):  
TJ Broxton
Keyword(s):  
Sodium Nitrite ◽  
Cetyltrimethylammonium Bromide ◽  
Ion Pairs ◽  
Micellar Catalysis ◽  
Nucleophilic Reactions ◽  
Counter Ion ◽  
Rate Of Reaction ◽  
Exchange Constants ◽  
Basic Hydrolysis ◽  
Hydrolysis Of

The rates of basic hydrolysis of N-methyl-N-(4'-nitrophenyl)octanamide and N,4-dimethyl-N- (3'-nitrophenyl)benzamide in the presence of cetyltrimethylammonium fluoride and acetate and the SNAr reactions of sodium nitrite with 2,4-dinitrofluorobenzene and 1-chloro-2,4-dinitrobenzene in the presence of cetyltrimethylammonium fluoride have been measured and compared to the rate in the presence of cetyltrimethylammonium bromide. The identity of the micellar counter ion (i.e. fluoride, acetate or bromide) has only a small effect on the rate of reaction despite quite substantial differences in exchange constants for the appropriate nucleophile/counter ion pairs; this is explained by a considerable amount of reaction between substrate molecules in the micellar pseudophase and the nucleophile in the aqueous intermicellar phase.

Trapping of the Intermediate Formed in the E1cB Hydrolysis of Some Alkyl and Aryl N-(4-Nitrophenyl) carbamates in a Hydroxy Functionalized Micelle

1985 ◽  
Vol 38 (1) ◽  
pp. 77 ◽  
Author(s):  
TJ Broxton
Keyword(s):  
Hydroxy Group ◽  
Alkaline Solution ◽  
Cetyltrimethylammonium Bromide ◽  
Rate Of Reaction ◽  
Hydrolysis Of

The basic hydrolyses of some alkyl and aryl N-(4-nitrophenyl) carbamates in the presence of micelles of cetyl (2-hydroxyethyl) dimethylammonium bromide ( chedab )were studied. For compounds which react by the BAC2 mechanism, verysimilar results were obtained in cetyltrimethylammonium bromide ( ctab ) and in chedab micelles. However, for compounds which react by the E1cB mechanism, the intermediate p- nitrophenyl isocyanate was trapped by the hydroxy group of the functional micelle to form a new carbamate directly bound to the detergent molecules of the micelle. It was shown that this new carbamate decomposed by a BAC2 mechanism. p- Nitrophenyl isocyanate added to an alkaline solution of chedab gave N-(4-nitrophenyl)- carbamate ion. Thus, the isocyanate has to be generated within the micelle for trapping to occur. The rate of reaction of p-nitrophenyl isocyanate with OH-/H2O is faster than the rate of solubilization within the micelle.

Micellar Catalysis of Organic Reactions. XXX. A Study of the Mechanism of Hydrolysis of Oxazepam and 2'-Methyldiazepam in the Presence of Micelles and in Water

1991 ◽  
Vol 44 (1) ◽  
pp. 103 ◽  
Author(s):  
TJ Broxton ◽  
S Wright
Keyword(s):  
Cetyltrimethylammonium Bromide ◽  
Sodium Dodecyl ◽  
Basic Solution ◽  
Acidic Hydrolysis ◽  
First Order ◽  
Amide Hydrolysis ◽  
Mechanism Of Hydrolysis ◽  
Basic Hydrolysis ◽  
High Base ◽  
Hydrolysis Of

Acidic hydrolysis of oxazepam in water involved initial azomethine cleavage at low acid concentrations (0.1-0.2 M) with initial amide hydrolysis occurring concurrently at higher acid concentrations (0.3-0.6 M). In the presence of micelles of sodium dodecyl sufate the percentage of initial amide cleavage increased. For the basic hydrolysis of oxazepam in water the rate was dependent on [ NaOH ] indicating at least some initial amide hydrolysis. At higher base concentrations the rate became independent of [ NaOH ], because of the ionization of the NH group of oxazepam, producing an unreactive nitranion. In the presence of cetyltrimethylammonium bromide, the rate of basic hydrolysis was slower than in water, due to the increased amount of ionization in the presence of micelles. Acidic hydrolysis of 2′-methyldiazepam in water was independent of [ HCl ] in the range 0.1-0.3 M, indicating initial azomethine hydrolysis. The rate was slower than for diazepam itself, indicating the existence of steric hindrance by the 2′-methyl group to water attack at C5. In basic solution, a biphasic reation was observed. The rate of the first phase was dependent on [ NaOH ], indicating the presence of initial amide hydrolysis for 2′-methyldiazepam, cf. initial azomethine hydrolysis for diazepam. At high base concentrations, a greater than first-order dependence on base concentration was observed. This was attributed to the formation of dianionic intermediates, as previously reported for the hydrolysis of similar anilides at high base concentrations.

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.

Substituent Effects on the Micelle-Catalysed and Uncatalysed Basic Hydrolysis of a Series of Substituted N-Methyl-p-toluanilides

1979 ◽  
Vol 32 (8) ◽  
pp. 1717 ◽  
Author(s):  
TJ Broxton ◽  
NW Duddy
Keyword(s):  
Substituent Effects ◽  
Cationic Micelles ◽  
Mechanism Of Reaction ◽  
Rate Of Reaction ◽  
Hammett Correlation ◽  
Rate Of Hydrolysis ◽  
Linear Plot ◽  
Basic Hydrolysis ◽  
Hydrolysis Of ◽  
Reaction In Water

The rate of hydrolysis of a series of substituted N-methyl-p-toluanilides has been measured in water and in the presence of cationic micelles [cetyltrimethylammonium bromide (ctab)]. A Hammett correlation of the rates of hydrolysis gave a curved Hammett plot for the reaction in water (k2,W) but a linear plot for the rate of reaction at optimal concentrations of ctab (k2,max) and for derived rate constants within the micelle (k2,m) These results are discussed in terms of the mechanism of reaction, and for two compounds a micelle-induced change of mechanism is indicated.

Kinetic salt effects in the hydrolysis of ethyl malonate, methyl glutarate and ethyl adipate semiesters

1986 ◽  
Vol 51 (12) ◽  
pp. 2781-2785 ◽  
Author(s):  
M. Martín Herrera ◽  
J. J. Maraver Puig ◽  
F. Sánchez Burgos
Keyword(s):  
Salt Effect ◽  
Alkaline Media ◽  
Salt Effects ◽  
Coulombic Interaction ◽  
Hydroxide Ion ◽  
Ethyl Malonate ◽  
Hydrolysis Of

A study is made on the kinetic salt effect on the reaction of hydrolysis of several charged esters in alkaline media. The results are interpreted on the basis of the coulombic interaction, the salting in of hydroxide ion and a third component depending on size of the substrate.

Micellar catalysis of organic reactions. VIII. Kinetic studies of the hydrolysis of 2-acetyloxybenzoic acid (aspirin) in the presence of micelles

1982 ◽  
Vol 35 (7) ◽  
pp. 1357 ◽  
Author(s):  
TJ Broxton
Keyword(s):  
Aqueous Solution ◽  
Cetyltrimethylammonium Bromide ◽  
Cetylpyridinium Chloride ◽  
Kinetic Studies ◽  
Base Catalysis ◽  
Plateau Region ◽  
General Base ◽  
Mechanism Of Hydrolysis ◽  
Ph Range ◽  
Hydrolysis Of

The hydrolysis of 2-acetyloxybenzoic acid in the pH range 6-12 has been studied in the presence of micelles of cetyltrimethylammonium bromide (ctab) and cetylpyridinium chloride (cpc). In the plateau region (pH 6-8) the hydrolysis is inhibited by the presence of micelles, while in the region where the normal BAC2 hydrolysis (pH > 9) occurs the reaction is catalysed by micelles of ctab and cpc. The mechanism of hydrolysis in the plateau region is shown to involve general base catalysis by the adjacent ionized carboxy group both in the presence and absence of micelles. This reaction is inhibited in the presence of micelles because the substrate molecules are solubilized into the micelle and water is less available in this environment than in normal aqueous solution.

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