The Role of the Apical Donor in the Decomposition of Copper(II) Benzoate under DOW-Phenol Conditions

Abstract

The synthesis and characterization of copper(II) benzoates with the apical donors pyridine, 2‐CH3‐pyridine, 2,4‐(CH3)2‐pyridine, 2,6‐(CH3)2‐pyridine, 2‐fluoropyridine, 2‐chloropyridine, 2‐bromopyridine, 3‐bromopyridine, 2,5‐dibromopyridine, 3,5‐dibromopyridine, and aniline, starting from copper(II) benzoate, is reported. Single‐crystal X‐ray structures of the products with four apical ligands show the usual paddle‐wheel structure of copper(II) carboxylates; in the case of aniline no paddle‐wheel dicopper(II) benzoate could be isolated. The products of thermal decomposition of the pure copper(II) compounds were analyzed by HPLC, LC‐MS, and GCFID, and the expected DOW‐phenol products were found in all cases other than that of aniline. This supports the assumption that a paddle‐wheel dicopper(II) benzoate is required for the DOW‐phenol reaction. Generally, high ortho‐selectivities (to phenyl benzoate and phenol; the selectivity increases with increasing basicity) are obtained, in good agreement with earlier findings on the role of the base. Small but significant steric effects are observed in the series of methylated pyridine donors and the monohalogenated pyridine donors used as apical ligands; with the two dibromopyridine donors there are large steric effects and the DOW‐phenol reaction is partially suppressed. With halogenated pyridine donors as apical ligands, a Cu[I]‐catalyzed process occurs, leading to dehalogenation.

Copper(II)‐Mediated Aromatic ortho‐Hydroxylation: A Hybrid DFT and Ab Initio Exploration

“…There are a number of simple hydroxylation processes, such as reactions with H 2 O 2 (H 2 O 2 -BF 3 or HF 3 ), [8] KMnO 4 -H 2 SO 4 mixtures, [9,10] COH radicals produced by X-ray radiolysis, [11] the classical or the modified Fentons reactions, [9,12] the thermal decomposition of cupric salts of benzoic acid, [13,14] and the copper-mediated industrial production of phenol by the pyrolysis of benzoic acid in the Dow-Phenol process. [15][16][17][18] Many of these reactions have deficiencies in terms of efficiency and/or selectivity. Therefore, there is a continuous search for new catalyst systems with improved efficiency and selectivity.…”

Thermo-analytical determination of intermediates in the copper catalysed rearrangement of o-toluic acid to meta-cresol

“…From thermal decomposition experiments of benzoic acid-1-14 C as well as cupric benzoate in the presence of 2 H 2 O, Schoo et al 19,20 could prove § Laser induced pyrolysis of metal carboxylates has been reported. 22 ¶ The formation of metallic copper from Cu(I) during the DOW-phenol process has been described by Buijs et al 9 and might be ascribed to the disproportionation of two Cu(I) moieties to Cu(II) and Cu(m).…”

“…The IR spectrum of 5 contained bands characteristic of syn-syn bidentate benzoate ligands 9,11 with typical n(OCO) assym (1568 cm À1 ) and n(OCO) sym (1393 cm À1 ) values and Dn = 175 cm À1 (Fig. 2a).…”

“…The DOW phenol process entails the thermal decomposition of copper(II) benzoate, presumably in dimeric form, [4][5][6] to phenyl benzoate via the decarboxylation of the preferred o-benzoyl salicylic acid, followed by hydrolysis of the phenyl benzoate in moist air yielding the desired phenol together with benzoic acid. [7][8][9] In an attempt to find the temperatures where crucial changes occur and to identify the intermediates involved in those steps, a crystal structure of the first intermediate, tetrakis(m 2 -2-methylbenzoato)bis(2-methylbenzoic acid)copper(II) 10 5 (vide infra), was obtained, which was subjected to heating under solventless conditions during differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA-MS). Intermediates and products were analysed using NMR spectroscopy, infrared spectrometry (IR) and Maldi-Tof mass spectrometry.…”

Synthesis and Characterization of Two New Chiral Copper(II) Compounds Constructed from (+)‐N‐Tosyl‐L‐glutamic Acid

“…The crystallographic independent part of compound [28][29][30] Notably, the carboxylate groups of the tsgluO 2ligands act as µ 4 -η 2 -η 2 , bridging tetradentate ligands towards four Cu(II) cations (Scheme(B)), with four carboxylic oxygen. Moreover, a remarkable feature of the structure is represented by the Cu(1) and Cu(2) centers in vander Waals contact with each other to generate a "paddlewheel" moiety, [Cu(1)…Cu(2) distance＝2.5 Å].…”