INTRODUCTION:

The three well known experimental studies which explain the outcome of reactant are thermodynamics, kinetics and chemical equilibrium. Of the three, the kinetic study plays an important role in the determination of rate and mechanism. Without determination of reaction rate, the mechanism of the reaction cannot be fully depicted. Moreover, the kinetic methods have become an essential technique in photochemical, enzymatic and catalytic reactions etc. The study of oxidation of organic compounds is of immense importance both from mechanistic and synthetic points of view. Investigation of the kinetics and mechanism of oxidation and reduction reactions has attracted the attention of chemists world over and mechanisms of several reactions have been clearly defined. The literature on the oxidation of amino acid in the absence of surfactant has been summarized in our earlier communication.¹ Very few kinetic studies have been reported in the presence of surfactant. Oxidation of DL-alanine by potassium permanganate in sulphuric acid medium,² the reaction was first order with respect to both [substrate] and [oxidant].

Saxena et. al.³ have studied the kinetics of oxidation of alanine by N-bromosuccinimide (NBS) in perchloric acid medium and Palladium used as catalyst. The reaction exhibits a first order rate dependence with respect to [NBS]. With respect to substrate concentration the reaction order undergoes a change from first to fractional order in the presence of catalyst.

MATERIAL AND METHODS:

General:

DL-alanine (SRL), HCl (E.Merck), NaClO₄ (Loba chemie), sodium dodecyl sulfate (SDS) (BDH), cetyl pyridinium chloride (CPC) (Loba chemie) and chloramine-T (Loba chemie) were used without further purification. The procedure adopted for kinetic investigation has been reported earlier.¹

Analysis of products:

For identification of the products, the calculated amount of chloramine-T (CAT) and acidified solution of amino acid was mixed together under the reaction conditions identical to those of the kinetic experiment. The reaction mixture was kept overnight at 30 C. The presence of aldehyde in the product was detected by their characteristic colour reaction with Schiff’s reagent.⁴ The evolution of ammonia was confirmed by the reaction with the Nesseler’s reagent.⁵ The presence of amine was detected by carbylamine test.

Carbondioxide evolved during the oxidation of amino acids in the absence and in presence of surfactants was measured volumetrically on passing through the pyrogallol solution interceptors. There was no change in the amount of gas evolved under different conditions for the oxidation of DL-alanine in the presence of SDS but in the presence of CPC the amount of gas evolved decreased on passing through the pyrogallol solution indicating the presence of oxygen as end product. The oxidation of water is dependent on the formation of Cl⁺ which is slow process as shown in Figure -A.

Stoichiometry:

Varying ratios of amino acid and CAT were mixed in HCl medium at 30ºC and kept for 24 hours. Estimation of unreacted alanine determined by ninhydrin reaction showed that one mole of alanine consumed one mole of CAT.

R^/CH(NH₂)COOH + RNCl^-Na⁺ + H₂O R^/CHO + CO₂+ RNH₂ + NH₃+ Na⁺ + Cl^-

Where, R = CH₃C₆H₄SO₂ and R^/ = CH₃ (Ala)

RESULTS AND DISCUSSION:

The kinetics of oxidative decarboxylation of amino acids by acid permanganate was studied by Hussain and Ahmad ^6-11 both in the absence and in presence of sodium dodecyl sulphate (SDS). However, chloramine-T which can be used under physiological condition to bring about decarboxylation of amino acid, has not been fully investigated in the presence of anionic and cationic surfactants. The active oxidizing species in chloramine-T system may involve a cationic species (Cl⁺) and /or neutral species (HOCl) and/or anionic species such as (RN¯Cl). In view of such diverse mode of action, the effect of anionic and cationic micelles may be significant in modifying reaction kinetics.

General features of kinetics of decarboxylation of DL-alanine:

It is observed that the decarboxylation of alanine in the absence of surfactant as well as in the presence of anionic micelle of sodium dodecyl sulfate (SDS) has identical kinetic features as observed in the case of decarboxylation of glycine. However, in the presence of cationic micelle of cetylpyridinium chloride (CPC), the reaction follows different mechanism and cationic micelle of CPC follow a pseudo first order kinetics. The slopes of the plots of ⁰¹k_obs versus [amino acid] at different concentration of surfactant, hydrogen ion and temperature give the second order rate constant (Table 1). The observed rate law may be written as

d[CAT]

- = ²ⁱk [amino acid] [CAT] ---------- (1)

Where ²ⁱk in the absence of any surfactant is represented as ⁰²k and in the presence of SDS as ^-²k and in the presence of CPC as ⁺² k.

The preliminary investigations showed that the ionic strength of the medium had no effect on the observed rate constant. In view of the above, effect of variation of hydrogen ion concentration on the reaction was observed by changing the concentration of HCl. It was observed that the reaction slows down with increasing concentration of hydrogen ion both in the absence and presence of any surfactant. In all these cases a plot of second order rate constant ²ⁱk versus 1/[H⁺] was found to be linear. These plots gave a positive intercept, indicating that the reaction consisted of two simultaneous routes of which one remained unaffected by hydrogen ion concentration. This reaction path is represented by the intercept of the plots, giving the second order rate constant ⁰²k_H, ^-²k_H and ⁺²k_H in the absence of any surfactant, in the presence of SDS, and in the presence of CPC, respectively. On the other hand, the slopes of these plots represented a reaction path adversely affected by the hydrogen ion concentration. From these slopes the first order rate constant ⁰¹k_H, ^-¹k_H and ⁺¹k_H (Table 2) were determined. The equation(1) may, therefore, be written as,

d[CAT]

- = { ²ⁱk + ¹ⁱk /[H⁺]} [amino acid] [CAT] ----(2)

The above equation may be obtained from the mechanism proposed and all major kinetic features may be justified.

Reaction mechanism in the absence of surfactant:

The oxidative decarboxylation of amino acids has raised several interesting questions. Some authors have suggested that amino group is the most likely reactive site,¹²^-¹⁴ but others have favoured attack at the carboxylic group.^15,16 In certain cases protonated amino group has been proposed as the active reaction site. It is reasonable to assume that the oxidant attack requiring withdrawal of electron from the protonated amino acid is less likely to occur even though strong acidic medium amino acid is completely protonated.

Under these conditions the oxidant attack at the carboxylic group may be favoured. The oxidant, sodium N-chloro-p-toluenesulphonamide, may also produce a large number of oxidizing species such as, HOCl, Cl₂ and H₂OCl⁺. However, it has been shown that at low pH the principal species present in the acidic medium are RNHCl and RNCl¹⁷.

In view of the above, the proposed mechanism for oxidative decarboxylation of DL-alanine is given in Scheme 1 in the absence of any surfactant.

Scheme 1

The Scheme 2 gives the following rate law

[A]_o [OX]_T

reaction rate = (k₁ K_A [H⁺]+k₂ K_A K_o +k^/₂ K_A K_o K_os [S^n-]+k^/₁ K_AK^/_os [H⁺] [S^n-] ) ¾¾¾¾¾

D_s [H⁺]

[A]_o [H⁺] [OX]_T

+ ( k₃ [H⁺] + k₄K_o ) ¾¾¾¾¾¾¾

D_s[H⁺]

k₂K_A K_ok^/₂K_AK_oK_os [S^n-][A]_o [OX]_T

=(k₁K_A+ ¾¾¾¾ + ¾¾¾¾¾¾¾ + k^/₁K_AK^/_os [S^n-] + k₃ [H⁺] + k₄K_o ) ¾¾¾¾¾

[H⁺] [H⁺] D_s

Where D_s = {(K_A + K_o) + (K_A K^/_os+K_oK_os)[S^n-]}

reaction rate = (k₁K_A + k₄K_o + k^/₁K_A K^/_os [S^n-])

k₂K_AK_o + k^/₂ K_AK_oK_os [S^n-] [A]_o [OX]_T

+ ¾¾¾¾¾¾¾¾¾¾¾ ¾¾¾¾¾¾¾¾¾¾¾¾¾¾ …………..(6)

[H⁺] (K_A+ K_o) + ( K_AK^/_os + K_oK_os ) [S^n-]

assuming k₃ << 1

(a) At constant SDS the equation (6) may be simplified to

reaction rate = ^-²k_H + ^-¹k_H . ¾¾¾ [A]_o [OX]_T

[H⁺]

= ^-²k [A]_o [OX]_T = ^-¹k_obs [OX]_T …………………………...(7)

^-²k = ^-²k_H + ^-¹k_H ¾¾ ..…………………….....(8)

[H⁺]

The plots between ^-¹k_obs versus [A]_o are linear and pass through the origin at different conditions (vide Fig.3)

where

(k₁K_A + k₄K_o + k^/₁K_AK^/_os [Sⁿ^-] )

^-²k_H = ¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾

(K_A + K_o ) + ( K_AK^/_os + K_oK_os ) [Sⁿ^-]

^-²k_H represents second order rate constant in the presence of SDS associated with reaction path not affected by [H⁺]

and

K_A ( k₂K_o + k^/₂K_oK_os [Sⁿ^-] )

^-¹k_H = ¾¾¾¾¾¾¾¾¾¾¾¾¾¾

(K_A + K_o ) + ( K_AK^/_os + K_oK_os) [Sⁿ^-]

^-¹k_H represents the first order rate constant in the presence of SDS associated with reaction path adversely affected by [H⁺].

The above equation stands verified as plots between ^-²k versus 1/[H⁺] are found to be linear at different temperatures (vide Fig.4). From the slopes of these plots, the first order rate constant ^-¹k_H showing dependence on hydrogen ion concentration was calculated at different temperatures whereas, from the intercepts, the second order rate constant signifying the hydrogen ion independent reaction path was also calculated at different temperatures.

(b) At constant [H⁺] the equation (8) may be rearranged to give the Menger²⁰ equation

1 1 1 1

¾¾¾¾ = ¾¾¾¾ + ¾¾¾¾ ¾¾¾ ……………(9)

⁰²k - ^-²k ⁰²k - ^-²k_m ⁰²k - ^-²k_m K_- [Sⁿ^-]

The concentration of micelles, [Sⁿ^-], may be obtained using Shinoda and Hutchinson ²¹ assumption that above cmc the concentration of unassociated surfactant remains constant.

D_o - cmc

[Sⁿ^-] = ¾¾¾¾

Where D_o is the concentration of SDS used and N represent the aggregate number. The value of cmc of SDS has been taken as 8.1 x 10^-3 which is only marginally affected by temperature from 25^o to 40 ^oC ²².

The above equation takes the form,

1 1 1 N 1

¾¾¾¾ = ¾¾¾¾ + ¾¾¾¾ . ¾¾ . ¾¾¾¾ ………………..(10)

²k -^-²k ⁰²k - ^-²k_m ⁰²k - ^-²k_m K_- (D_o-cmc)

This equation has been tested by plots of 1/ ⁰²k - ^-²k versus 1/(D_o-cmc) which is found to be linear (vide Fig. 5), and the reciprocal of the intercept gives (⁰²k - ^-²k) from which values of ^-²k_m at different temperatures have been calculated and its activation parameters have also been evaluated. The ratio of slope versus intercepts of the above equation gives the value N/K_-_. Using the aggregate number for SDS, N=62.0 ²³, the value of K has been also obtained (Table 3). It may be pointed out that K_- in the above reaction mechanism does not represent simple binding parameters between oxidant and the micelles. Rather it is a complex function of K_os and K^/_osrepresenting oxidant surfactant equilibria.

Oxidative degradation of DL –Alanine in the presence of CPC:

In the case of alanine it has been observed that plot between ⁺¹k_obsversus [alanine] give a small positive intercept, it may be recalled that in case of glycine these plots were passing through origin. The above observation may be accomodated by marginal modification of the scheme proposed for glycine. It is to be noted further that this difference is not observed in the absence of surfactant and also when reaction is carried out in the presence of SDS. It is, therefore, suggested that the interaction of CPC-oxidant complex, (OXDS)^m+ with water is catalyzed in the presence of alanine. This may be shown by the following reaction model.

Figure -A

fast

Cl⁺H₂O HCl + H⁺ + 1/2O₂

In view of the above, a reaction path for the oxidation of water has to be included as shown in step(b).

Reaction Mechanism and Rate Law :

The total concentration of CPC is represented by [D_o] and concentration pre-micellar aggregates including monomer is [D⁺], and concentration of positively charged micelle is represented by [S^m+].

[D⁺] = [D_o] - [S^m+] ----------(a)

With the assumption that oxidant-surfactant complex concentration is always comparatively low, the following mechanism may be proposed in scheme 3.

k^/ _H2O

(OXDS)^m+ + H₂O -------------- -------(b)

Scheme 3

Using the mass-balanced equation for amino acid [A] and [AH⁺] may be obtained in terms of total concentration of amino acid.

[A]_o = [A] + [AH⁺]

K_A [A]_o[H⁺] [A]_o

[A] = ¾¾¾ and [AH⁺] = ¾¾¾¾

[D] [D]

where D = ( K_A + [H⁺] )

Using the mass balanced equation for the concentration of oxidant species, the values of oxidizing species may be obtained in terms of [OX]_{T .}

[OX]_T = [OX] + [OXH] + [OXD] + [OXDS]^m+

= [OX] (1 + [H⁺]/K_o + [D⁺]/K_d + K_os [S^m+][D⁺]/K_d)

[OX]

= ¾¾¾ (K_dK_o + K_d [H⁺] + K_o [D⁺] + K_oK_os [D⁺] [S^m+])

K_dK_o

[OXH]

[OX]_T = ¾¾¾ (K_dK_o + K_d [H⁺] + K_o [D⁺] + K_oK_os [D⁺] [S^m+])

K_d [H⁺]

[OXD]

= ¾¾¾ (K_dK_o + K_d [H⁺] + K_o [D⁺] + K_oK_os [D⁺] [S^m+])

K_o [D⁺]

[OXDS]^m+

= ¾¾¾¾¾¾¾ (K_dK_o + K_d [H⁺] + K_o [D⁺] + K_oK_os [D⁺] [S^m+])

K_oK_os [D⁺] [S^m+]

[OXDS]^m+

= ¾¾¾¾¾¾¾ D

K_oK_os [D⁺] [S^m+]

Where

D = (K_dK_o + K_d [H⁺] + K_o [D⁺] + K_oK_os [D⁺] [S^m+])

Simplifying

DD = (K_A + [H⁺]) (K_d K_o + K_d [H⁺] + K_o [D⁺] + K_oK_os [D⁺] [S^m+]) ---------(11)

from equation (a), putting the value of [D⁺] = [D_o] - [S^m+] in equation (11)

DD = K_A (K_dK_o + K_o [D_o-S^m+] + K_oK_os [D_o-S^m+] [S^m+]) + (K_A K_d+K_dK_o+ K_o[D_o-S^m+]

+ K_oK_os [D_o-S^m+] [S^m+])[H⁺] + ..........

neglecting [H⁺]² and [S^m+]² and assuming K_A< 1 and K_o <1

DD = (K_A K_d+K_dK_o+ K_oK_os [D_o] [S^m+]) [H⁺]

= D^/_s [H⁺]

where

D^/_s = (K_A K_d+K_dK_o+ K_oK_os [D_o] [S^m+]) ---------------- (12)

The rate law may obtained from scheme 3 is given below:

Reaction rate = (k₁[OXH] + k₂[OX]+k^/₅[OXDS]^m+)[A]+(k₃[OXH]+k₄[OX])[AH⁺]

+ k^/ _H2O [OXDS]^m+

K_A[A]_o[OX]_T

= (k₁K_d[H⁺]+k₂K_dK_o+ k^/₅K_oK_os[D_o] [S^m+]) ¾¾¾¾¾¾

D^/_s [H_H⁺]

[A]_o[OX]_T[H⁺] k^/_H2O K_oK_os[D_o] [S^m+][OX]_T

+ (k₃K_d[H⁺]+k₄K_dK_o) ¾¾¾¾¾¾¾ + ¾¾¾¾¾¾¾¾¾¾¾¾

D^/_s [H⁺] D^//

[A]_o[OX]_T

= {k₁K_AK_d+k₂K_AK_dK_o/[H⁺]+k^/₅K_AK_oK_os[D_o] [S^m+]/[H⁺] + k₃K_d[H⁺]+k₄K_dK_o} ¾¾¾¾¾

D^/_s

k^/_H2O K_oK_os[D_o] [S^m+][OX]_T

+ ¾¾¾¾¾¾¾¾¾¾¾¾

D^//

Assuming k₃ << 1

k₂K_AK_dK_o+ k^/₅K_AK_oK_os[D_o] [S^m+] [A]_o[OX]_T

Reaction rate = (k₁K_AK_d+k₄K_dK_o) + ¾¾¾¾¾¾¾¾¾¾¾¾¾¾ ¾¾¾¾ + k_s[OX]_T

[H⁺] D^/_s

Reaction rate = (⁺²k[A]_o+ k_s) [OX]_T= ⁺¹k_obs[OX]_T

where ⁺¹k_obs= ⁺²k[A]_o+ k_s ----------(13)

k^/_H2OK_oK_os[D_o] [S^m+][OX]_T

k_s = ¾¾¾¾¾¾¾¾¾¾¾¾

D^//

and

(k₁K_A+k₄K_o ) K_d (k₂K_AK_o+ k^/₅K_AK_o K^/_os[D_o] [S^m+] ) K_d 1

⁺²k = ¾¾¾¾¾¾¾¾¾¾¾¾ + ¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾ ¾¾¾

( K_A+ K_o + K_o K^/_os[D_o] [S^m+])K_d (K_A+ K_o + K_o K^/_os[D_o] [S^m+]) K_d [H⁺]

----------(14)

and K_os/K_d = K^/_os

equation (13) has been verified from the linear plots between ⁺¹k_obs versus [A]_o which k_s as intercept and the second order rate constant, ⁺²k, is given by the slopes under different conditions (figs. 6)

At Constant CPC :

The dependence of reaction rate on hydrogen ion concentration has been studied at constant CPC and other kinetics parameters. The equation (13) may be rearranged to show that the dependence of ⁺²k on [H⁺] as below

reaction rate = [{⁺²k_H + ⁺¹k_H . 1/[H⁺]} [A]_o + k_s][OX]_T

= ⁺²k[A]_o [OX]_T+ k_s[OX]_T

⁺²k = {⁺²k_H + ⁺¹k_H . 1/[H⁺]} -----------(15)

Where, from equation (14)

k₁K_A+k₄K_o k₂K_AK_o+ k^/₅K_AK_o K^/_os[D_o] [S^m+]

⁺²k_H= ¾¾¾¾¾¾¾¾¾¾¾¾¾ and ⁺¹k_H= ¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾

( K_A+ K_o) + K_o K^/_os[D_o] [S^m+] (K_A+ K_o) + K_o K^/_os[D_o] [S^m+]

The equation (15) is verified as plots between ⁺²k versus 1/[H⁺] are found to be linear at different temperatures (vide Fig. 7). The intercepts of these plots give ⁺²k_H and the slopes, ⁺¹k_H.

At Constant hydrogen ion concentration

On keeping hydrogen ion concentration constant, the dependence of observed rate constant on [CPC] may be obtained as under from equation (15)

k₁K_A+k₄K_o k₂K_AK_o+ k^/₅K_AK_o K^/_os[D_o] [S^m+] 1

⁺²k = ¾¾¾¾¾¾¾¾¾¾¾¾ + ¾¾¾¾¾¾¾¾¾¾¾¾¾¾ ¾¾

( K_A+ K_o)+K_o K^/_os[D_o] [S^m+] (K_A+ K_o) + K_o K^/_os[D_o] [S^m+] [H⁺]

k₁K_A+k₂K_AK_o/[H⁺] + k₄K_o k^/₅K_AK_o K^/_os[D_o] [S^m+]/[H⁺]

= ¾¾¾¾¾¾¾¾¾¾¾¾ + ¾¾¾¾¾¾¾¾¾¾¾¾ -------(16)

( K_A+ K_o) + K_o K^/_os[D_o] [S^m+] (K_A+ K_o) + K_o K^/_os[D_o] [S^m+]

Dividing equation (16) by (K_A + K_o), we get

⁰²k ⁺²k_mK₊[D_o] [S^m+]

⁺²k = ¾¾¾¾¾¾¾¾ + ¾¾¾¾¾¾¾¾ -------(17)

1 + K₊[D_o] [S^m+] 1 + K₊[D_o] [S^m+]

where

k₁K_A+k₂K_AK_o/[H⁺] + k₄K_o

⁰²k = ¾¾¾¾¾¾¾¾¾¾¾

( K_A+ K_o)

as obtained for reaction in the absence of surfactants

k^/₅K_AK_o K^/_os

⁺²k_m = ¾¾¾ and K₊ = ¾¾¾¾

[H⁺] ( K_A+ K_o)

Subtracting ⁰²kfrom both side in equation (17).

⁰²k ⁺²k_mK₊[D_o] [S^m+]

⁺²k - ⁰²k= ¾¾¾¾¾¾¾ + ¾¾¾¾¾¾¾¾ - ⁰²k

1 + K₊[D_o] [S^m+] 1 + K₊[D_o] [S^m+]

⁰²k +⁺²k_mK₊[D_o] [S^m+] - ⁰²k - ⁰²kK₊[D_o] [S^m+]

= ¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾¾

1 + K₊[D_o] [S^m+]

(⁺²k_m - ⁰²k) K₊[D_o] [S^m+]

⁺²k - ⁰²k= ¾¾¾¾¾¾¾¾¾¾¾ ----------------(18)

1 + K₊[D_o] [S^m+]

Taking the reciprocal of equation (18), we get,

1 1 1 1

¾¾¾ = ¾¾¾¾ + ¾¾¾¾ ¾¾¾¾¾¾ .

⁺²k - ⁰²k ⁺²k_m - ⁰²k ⁺²k_m - ⁰²k K₊[D_o] [S^m+]

where

D_o - cmc

[S^m+] = ------------

then

1 1 1 N

¾¾¾¾ = ¾¾¾¾¾ + ¾¾¾¾ . ¾¾¾¾¾¾

⁺²k - ⁰²k ⁺²k_m - ⁰²k ⁺²k_m - ⁰²k K₊(D_o - cmc)D_o

Where D_o is the concentration of CPC used and N represents the aggregate number. The value of cmc for CPC has been taken as 9.0x10^-4 which is only marginally affected by temperature change from 25^o to 40^o C²². The above equation has been tested by plots of 1/⁺²k -⁰²k versus 1/(D_o -cmc) D_o which is found to be linear (vide Fig. 8) and the reciprocal of intercept of these plots gives (⁺²k_m - ⁰²k ) from which values of ⁺²k_m at different temperatures have been calculated alongwith its activation parameters and K₊ calculated (Table-4). It may be pointed out again that K₊ does not represent simple binding parameter between oxidant and the micelles.

The thermodynamics activation parameters related to different k’s have been shown in table-5.

Table 1. Temperature dependence of ²k for alanine

Temps. (°C)

In the absence of surfactant

[SDS] = 0.01 M

[SDS] = 0.02 M

[SDS] = 0.03 M

[CPC] = 0.002 M

[CPC] = 0.003 M

[CPC] = 0.004 M

⁰²k ×10⁴

(s^-1mol^-1dm³)

^-2k ×10⁴

(s^-1mol^-1dm³)

^-2k ×10⁴

(s^-1mol^-1dm³)

^-2k ×10⁴

(s^-1mol^-1dm³)

⁺²k ×10⁴

(s^-1mol^-1dm³)

⁺²k ×10⁴

(s^-1mol^-1dm³)

⁺²k ×10⁴

(s^-1mol^-1dm³)

170.0

240.0

324.0

132.0

190.0

240.0

104.0

144.0

190.0

92.0

126.0

170.0

190.0

270.5

360.0

230.0

312.5

400.0

264.0

360.0

480.0

[H⁺] = 0.05 mol dm^-3 and [CAT] = 2 × 10^-3mol dm^-3

Table 2. Temperature dependence of ¹k_H and ²k_H^*

Temps. (°C)

In the absence of surfactant

In the presence of SDS ^ψ

In the presence of CPC ^†

0.72

0.84

1.10

3.0

6.9

12.0

0.48

0.60

1.00

3.2

5.4

8.5

0.80

1.04

1.40

6.4

8.0

11.0

*¹k_H and ²k_Hare obtained from slopes and intercepts of ²k versus 1/ [H⁺]

ψ[SDS] = 0.01 mol dm^-3 † [CPC] = 0.002 mol dm^-3 , [Ala] = 0.15 mol dm^-3 and [CAT] = 2 × 10^-3 mol dm^-3

Table 3. Temperature dependence of ^-2k_m and K_{_} in the presence of SDS

Temps. (°C)

^-2k_m ×10³/s^-1mol^-1dm³

K_{_}/10⁴mol^-1dm³

9.0

11.5

15.8

2.8

2.2

2.9

Table 4. Temperature dependence of ⁺²k_m and K₊ in the presence of CPC

Temps. (°C)

⁺²k_m ×10³/s^-1mol^-1dm³

K₊/10⁴mol^-1dm³

57.0

64.0

72.4

2.3

3.6

4.3

Table 5. Kinetic data for the oxidation of Alanine by Chloramine-T in acidic medium.

Rate constant used

Thermodynamic parameters ^*

Nature of rate constant

Ea/kj mol^-1

ln A

ΔG^# kJ mol^-1

ΔH^# kJ mol^-1

ΔS^# Jmol^-1K^-1

⁰²k

^-2k

⁺²k

⁰²k_H

^-2k_H

⁺²k_H

⁰¹k_H

^-1k_H

⁺¹k_H

^-2k_m

⁺²k_m

58.2

49.9

41.6

97.7

74.8

49.8

24.9

49.8

41.5

49.8

20.7

19.0

15.5

12.5

33.8

23.9

14.7

2.7

12.2

9.4

15.1

5.4

84.5

85.2

84.2

88.9

88.7

86.9

92.5

76.1

92.2

86.1

81.5

55.7

47.4

39.1

97.2

72.3

47.3

22.4

47.3

38.9

47.3

18.2

-95.0

-124.7

-148.8

27.4

-54.1

-130.7

-231.4

-95.1

-175.9

-128.1

-208.9

⁰¹k_obs / [A]

^-1k_obs / [A]

⁺¹k_obs / [A]

Associated with reaction path unaffected by [H⁺]

Associated with reaction path adverse affected by [H⁺]

Associated with reaction in micellar phase

* Thermodynamic parameters were determined in the absence and presence of SDS and CPC in HCl medium at 303 K

(a) [H⁺] = 0.05 mol dm^-3, (b) [Ala] = 0.15 mol dm^-3,

[SDS] = 0.01 mol dm^-3, [CPC] = 0.002 mol dm^-3 and

[CAT] = 2 × 10^-3 mol dm^-3

REFERENCES:

Farhat Hasan Khan and Mahboob Alam*

*Corresponding Author E-mail: mahboobchem@gmail.com

INTRODUCTION:

Analysis of products:

Stoichiometry:

General features of kinetics of decarboxylation of DL-alanine:

Reaction mechanism in the absence of surfactant:

Reaction mechanism in the presence of surfactant: