• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.881-884
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• 2012

We report a quantum chemical study of an extremely efficient nucleophilic aromatic fluorination in molten salts. We describe that the mechanism involves solvent anion interacting with the ion pair nucleophile $M^+F^-$(M = Na, K, Rb, Cs) to accelerate the reaction. We show that our proposed mechanism may well explain the excellent efficiency of molten salts for SNAr reactions, the relative efficacy of the metal cations, and also the observed large difference in rate constants in two molten salts $(n-C_4H_9)_4N^+\;CX_3SO_3^-$, (X=H, F) with slightly different sidechain ($-CH_3$ vs. $-CF_3$).

• Bulletin of the Korean Chemical Society
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• v.35 no.7
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• pp.2135-2138
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• 2014

A kinetic study is reported for the SNAr reaction of 1-Y-substituted-phenoxy-2,4-dinitrobenzenes (1a-1h) with OH- in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The second-order rate constant ($k_{OH^-}$) increases as the substituent Y in the leaving group changes from an electron-donating group (EDG) to an electronwithdrawing group (EWG). The Br${\o}$nsted-type plot for the reactions of 1a-1h is linear with ${\beta}_{lg}$ = -0.16, indicating that the reactivity of substrates 1a-1h is little affected by the leaving-group basicity. A linear Br${\o}$nsted-type plot with ${\beta}_{lg}=-0.3{\pm}0.1$ is typical for reactions reported previously to proceed through a stepwise mechanism in which formation of a Meisenheimer complex is the rate-determining step (RDS). The Hammett plot correlated with ${\sigma}_Y{^{\circ}}$ constants results in a much better correlation than that correlated with ${\sigma}_Y{^-}$constants, implyng that no negative charge is developing on the O atom of the leaving group (or expulsion of the leaving group is not advanced at all in the TS). This excludes a possibility that the $S_NAr$ reaction of 1a-1h with $OH^-$ proceeds through a concerted mechanism or via a stepwise pathway with expulsion of the leaving group being the RDS. Thus, the current reactions have been concluded to proceed through a stepwise mechanism in which expulsion of the leaving group occurs rapidly after the RDS.

• Bulletin of the Korean Chemical Society
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• v.27 no.8
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• pp.1203-1205
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• 2006

During the synthesis of 4-fluorobenzaldehyde via the SNAr reaction of 4-nitrobenzaldehyde with TBAF, it was found that an equivalent amount of TBAF could oxidize benzaldehyde to benzoic acid. The reaction of 4-nitrobenzaldehyde with tetrabutylammonium fluoride (TBAF) gave 4-nitrobenzoic acid in high yield. Depending on the reaction conditions, other aromatic aldehydes produced acids with fewer amounts of alcohols. However, this type of oxidation has limited practical applications. Nevertheless, the mechanism is quite different from the Cannizzaro reaction because the amounts of the acid salt and alcohol formed were different.

• Bulletin of the Korean Chemical Society
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• v.31 no.9
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• pp.2571-2574
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• 2010

We investigate the mechanism of $S_NAr$ fluorination reactions under the influence of protic solvents and ions. We find that counterion or protic solvent alone retards the $S_NAr$ reactions, but together they may promote the reaction. In this mechanism, the protic solvent acts on the counterion as a Lewis base, and the nucleophile reacts as an ion pair. We also show that an anion (mesylate) may exhibit catalytic effects, suggesting the role of ionic liquids for accelerating the $S_NAr$ reactions.

• Bulletin of the Korean Chemical Society
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• v.31 no.10
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• pp.2801-2805
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• 2010

A nucleophilic substitution reaction of 4-chloro-7-nitrobenzofurazan (NBF-Cl) with anilines in MeOH-MeCN mixtures was conducted at 25, 35, and $45^{\circ}C$. Based on the higher $\beta_{nuc}$ values (1.0 - 1.6) of the reaction and a good correlation of the rate constants with the reduction potentials of the aniline nucleophiles, the present reaction was initiated by a single electron transfer (SET). After this step, the reaction proceeds through a transition state similar to the normal $S_NAr$-Ad.E pathway.

• Bulletin of the Korean Chemical Society
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• v.5 no.3
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• pp.126-129
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• 1984

The reaction of aryl halides with phenoxides and alkoxides were investigated under phase transfer catalytic conditions. 2,4-Dinitro- and 4-nitrohalobenzenes reacted readily with phenoxides in NaOH(aq)-benzene in the presence of Bu4N+Br, affording the products quantitatively. Although the aryl halides did not react with alkoxides under the same condition, the reactions were completed within 2 hours at room temperature when conducted under solid-liquid phase transfenr catalytic condition. The reactivity of aryl halides was in the order, Ar = 2,4-dinitrophenyl > 4-nitrophenyl, and X = F > Cl, consistent with the SNAr mechanism. The reactivity of oxyanions increased with the change of reaction condition from liquid-liquid to solid-liquid phase transfer catalysis. The results were explained with the concentration and the degree of hydration of the anion in benzene.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2371-2374
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• 2014

A kinetic study is reported on SNAr reaction of 1-fluoro-2,4-dinitrobenzene with a series of primary amines including hydrazine in $H_2O$ at $25.0^{\circ}C$. The plots of $k_{obsd}$ vs. [amine] are linear and pass through the origin, indicating that general-base catalysis by a second amine molecule is absent. The Br${\o}$nsted-type plot exhibits an excellent linear correlation with ${\beta}_{nuc}$ = 0.46 when hydrazine is excluded from the correlation. The reaction has been suggested to proceed through a stepwise mechanism, in which expulsion of the leaving group occurs after the rate-determining step (RDS). Hydrazine is ca. 10 times more reactive than similarly basic glycylglycine (i.e., the ${\alpha}$-effect). A five-membered cyclic intermediate has been suggested for the reaction with hydrazine, in which intramolecular H-bonding interactions would facilitate expulsion of the leaving group. However, the enhanced leaving-group ability is not responsible for the ${\alpha}$-effect shown by hydrazine because expulsion of the leaving group occurs after RDS. Destabilization of the ground-state of hydrazine through the electronic repulsion between the nonbonding electron pairs is responsible for the ${\alpha}$-effect found in the current $S_NAr$ reaction.

• Applied Chemistry for Engineering
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• v.9 no.3
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• pp.440-444
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• 1998

Poly(phenylene sulfide-co-phenylene sulfide sulfone), PPS/PPSS copolymers were synthesized from p-dichlobenzene(DCB), p-dibromobenzene(DBB), p-diiodobenzene(DIB), 4-chlorophenyl sulfone(CPS) and sodium sulfide as comonomers under high temperature and pressure utilizing N-methyl-2-pyrrolidinone(NMP) as solvent. The yield of PPS/PPSS copolymer shoed maximum at $190^{\circ}C$ with [DBB]/[CPS] and [DIB]/[CPS] comonomer pair, while [DCB]/[CPS] pair exhibited maximum yield at $230^{\circ}C$. The change of yield is in the order of I>Br>Cl as leaving groups were in accordance with nucleophilic aromatic substitution reaction mechanism suggested for the synthesis of PPS type polymers. The molecular weight of PPS/PPSS copolymer was the highest($M_w=8,330g/mol$) with [DBB]/[CPS] comonomers in which [CPS] was 10 mole%. The PPS/PPSS copolymer made with 10 mole% of [CPS] showed about $15^{\circ}C$ higher $T_g$ and $15^{\circ}C$ lower $T_m$ than those of PPS homopolymer, which may be useful from the processing and thermal property point of view. The PPS/PPSS copolymer with 30 mole% of CPS or above did not exhibit Tm. The PPS/PPSS copolymer obtained with comonomer feed ratio of [DBB]/[CPS] = 95/5 mole% under $240^{\circ}C$ showed even higher molecular weight($M_w=10,300g/mole$) than PPS homopolymer made under similar reaction condition, retaining high crystallinity and thermal stability.