The Synthesis of Arylsulfonylphthalimides and Their Reactions with Several Amines in Acetonitrile

In this study, several N-(p-substituted-arylsulfonyl)phthalimides (1a-e) were synthesized. The synthesized compounds were then examined with respect to their substitution reactions with t-butylamine, diethylamine, cyclohexylamine, and trans-1,2-diaminocyclohexane in acetonitrile. In order to determine the mechanism, substituent effect, activation entropy, and nucleophile effect were used as criteria.


Introduction
N-Alkyl and N-arylsulfonyl phthalimides were prepared by Heller [1] from the reaction of potassium phthalimide and sulfonyl chlorides.Earlier attempts by Evans and Dehn to prepare several N-aryl derivatives [2][3] and later by Scott and Lutz to prepare some N-alkyl derivatives by this reaction had been unsuccessful [4].Later, potassium phthalimide was reported to interact with p-toluenesulfonyl chloride at 140˚C or in dimethylformamide at 5˚C to 40˚C to yield N-(p-tolylsulfonyl)phthalimide [5].The mechanism of acid-catalyzed hydrolysis of N-(p-substituted-arylsulfonyl)phthalimides was studied in detail in our laboratory [6].We now report a complementary study of the nucleophilic substitution reactions of a series of N-(p-substituted-arylsulfonyl)phthalimides (1a-e) in acetonitrile (Scheme 1).
Second order kinetics, showing dependence both on the nucleophile and on the substrate, are widely observed in nucleophilic substitutions [10].It was also observed that the reactions with cyclohexylamine, and trans-1,2-diaminocyclohexane nucleophiles took place much faster than those with t-butylamine and diethylamine nucleophiles as shown in Table 2.
In the light of the overall evidence, we propose that the substitution reactions of a series of N-(p-substitut ed-arylsulfonyl)phthalimides with t-butylamine, diethylamine, cyclohexylamine and trans-1,2-diaminocyclohexane occur with S N 2 mechanism or an addition-elimination mechanism, as shown in Schemes 2 and 3 respectively.

Materials and Methods
N-(p-Substituted-arylsulfonyl)phthalimides 1a-e were prepared from the corresponding p-substituted-arylsulfonyl chlorides with potassium phthalimides in acetonitrile as described by Heller [1].All melting points were determined using an electrothermal digital melting point apparatus.

Kinetic Studies
The rates of substitution reactions of N-(p-substituted-arylsulfonyl)phthalimides were followed spectrophotometrically using a GBC Cintra 20 Model UV-VIS spectrophotometer with a thermostatted cell compartment (0.05˚C).Values of k 1 were calculated from the standard equation using a least-squares procedure.All kinetic mea-surements were duplicated, and the average deviation from the mean was 3%.Second-order rate constants (k 2 ) were calculated from the slope of the plots of pseudo-first-order rate constants versus nucleophile concentrations (at least three different concentrations).
where k, is Boltzman's constant, h, Planck's constant and the other symbols have their usual meanings.Expressing Equation (1) in logarithmic form, Equation ( 2) is obtained.From a plot of Ink 2 versus 1/T, ΔS ≠ and ΔH ≠ can be obtained from the intercept and slope respectively.

Product Analysis
N-t-Butyltoluenesulfonamide was prepared from t-butylamine with p-toluenesulfonyl chloride and cupric oxide in acetonitrile at room temperature [13].m.p. 112˚C -113˚C [14].Analysis of the products was also determined by comparing the UV spectrum obtained after completion of the kinetic experiment with the spectrum of the expected products at the same concentration and under the same conditions.Thus, for the reaction of N-(p-toluenesulfonyl)phthalimide with t-butylamine, the UV spectrum recorded at the end of the reaction was identical with that of a 1:1 mixture of phthalimide and N-t-butyltoluenesulfonamide.

Figure 1 .
Figure 1.Hammett Plots of logk 2 /k 0 versus  for the reactions of 1a-e with t-butylamine at 30.0˚C  0.1˚C in acetonitrile.

Figure 2 .
Figure 2. Hammett Plots of logk 2 /k 0 versus  for the reactions of 1a-e with diethylamine at 30.0˚C  0.1˚C in acetonitrile.

Figure 3 .
Figure 3. Hammett Plots of logk 2 /k 0 versus  for the reactions of 1a-e with cyclohexylamine at 30.0˚C  0.1˚C in acetonitrile.