In homogeneous catalysis, the catalyst is in the same phase as the reactant. The number of collisions between reactants and catalyst is at a maximum.In a patent, 33282-15-4, name is 5-(4-Hydroxyphenyl)isoxazole-3-carboxylic acid, introducing its new discovery. SDS of cas: 33282-15-4
Substitution of the iodine of (E)- and (Z)-methyl beta-iodo-alpha-nitrocinnamates (5) by amines gives identical (Z)-enamines with aniline (Ani) and piperidine (Pip). No amine catalysis was observed with Pip, Ani, morpholine (Mor), orp-MeOC6H4NHMe (MMA) in MeCN nor with Pip or Mor in EtOH: kPip/kMor = 115-138 (MeCN), 3.3-6.9 (EtOH); kMeCN/kEtOH = 25.5 ± 2.2 (Pip), 0.79-1.16 (Mor); k(Z)-5/k(E)-5 = 1.3-2.9 (13.5 with MMA in MeCN). Replacement of the MeS group in six alpha-amethylthio-alpha-arylmethylene Meldrum’s acid (6-X) by Pip resulted in amine catalysis in MeCN and EtOH. In EtOH, the p-anisyl derivative (6-MeO) and in MeCN 6-MeO, 6-Me and 6-H displayed second order catalysis in Pip. Other 6-X compounds show orders between one and two in Pip with amine catalyzed (k3B)/non-catalyzed (k2) rate coefficient ratios of 281-731 (EtOH) and 504-635 (MeCN) at 30C. kMeCN/kEtOH = 3.0-4.9. In MeCN DeltaH? = -0.8 to -5.9 kcal mol-1 and DeltaS? = -50 to -72 e.u. An intermediate zwitterion, 3a, is formed in all cases. For system 5 the rate of I- expulsion from 3a exceeds its deprotonation rate, and the observed rate coefficient is composite: kobs = k1k2/k-1 in MeCN (k1 = rate coefficient of nucleophilic attack) but kobs = k1 in EtOH. In MeCN the deprotonation is faster than the expulsion rate of MeS-, and more so for 6-X with X = p-Br, p-CF3, m,m?-(CF3)2. Different electrophilicities of 6-X, different extents of hydrogen bonding, steric and electronic effects account for the kinetic differences.
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Reference：
Isoxazole – Wikipedia,
Isoxazole | C3H3NO – PubChem