The water‐promoted Diels–Alder reaction in quaternary ammonium salts

Abstract

Prevailing classification of salts based on their effect in solubility and stability of proteins in aqueous solution predicts that tetraalkylammonium salts, guanidinium chloride (GnCl), LiClO 4 act as salting-in (S/I) and LiCl, NaCl act as salting-out (S/O) in aqueous conditions. In the same context the behaviour of GnCl, LiClO 4 and LiCl are contradictory in polar solvents like ethylene glycol and formamide. In these solvents, expected salt effect shows just opposite nature from their usual expectation. However, in the aqueous solution salts like tetraalkylammonium halide (R 4 NX, R = alkyl group, X = Br group) behave like salting-in salts. The physicochemical origin of the salting in effect of R 4 NX type of salts has been discussed elaborately in the present work. The role of cations in terms of substitution of various alkyl groups on R 4 NX has been systematically presented here on the basis of experimental kinetic and thermodynamic studies. The abnormal behaviour of R 4 NX salts in aqueous solution has also been explained by the Setschenov equation (k s ) and Δμ solvation values, which highlights their individual nature out of common properties of R 4 NX.

Diels–Alder Cycloaddition Reactions in Sustainable Media

“…The kinetics of the Diels-Alder cycloaddition reactions in water can be modified by the presence of inorganic salts, which can change the hydrophobic interactions involving the diene and dienophile, the internal pressure (by changing the cohesive energy) and the solvation of the transition states. The Kumar group studied the influence of quaternary ammonium salts in the cycloaddition of 9-hydroxymethylanthracene (54) and Nethylmaleimide (55a) in water, concluding that higher concentrations of salt in the reaction media lead to a deceleration of the reaction rate [93]. This was rationalized by the reduction in hydrophobic interactions, responsible for bringing the reactants closer, which were progressively blocked upon the continuous increase in the concentration of salt.…”

A Tandem Aldol Condensation/Diels‐Alder Sequence of Reactions for One‐Pot Synthesis of a New Series of Polysubstituted‐Decalines

“…ammonium chloride in the catalysis of DA reactions has precedence. [35,36] Experimental Section General Chemicals and starting materials were purchased from commercial sources. Aldehydes were redistilled or recrystallized before being used.…”

“…To support this hypothesis, control reactions between the dienes and acrylonitrile were conducted in the presence of ammonium chloride in H 2 O/PEG medium, leading to high yield formation of the adducts within the expected time periods. The use of ammonium chloride in the catalysis of DA reactions has precedence [35,36] …”

Statistical Thermodynamics Unveils How Ions Influence an Aqueous Diels‐Alder Reaction

“…This has been exploited fully in DA‐type reactions in aqueous salt solutions, which have the advantage of faster reaction rates in comparison to reactions in typical organic solvents . The low aqueous solubility of many reactants can be overcome by the addition of a solubilising agent, such as ethanol or salts; if salts are used, these can have special effects on DA reaction rates . Understanding the diverse effects of salts on DA reaction rates will be beneficial for the rational optimisation and control of DA‐style reactions in aqueous solution.…”

“…[6][7][8][9][10][11] The low aqueous solubility of many reactants can be overcome by the addition of a solubilising agent, such as ethanol or salts; if salts are used, these can have special effects on DA reaction rates. [12][13][14][15][16] Understanding the diverse effects of salts on DA reaction rates will be beneficial for the rational optimisation and control of DA-style reactions in aqueous solution.…”