Adsorption and Reactions of 3-Bromopyridine and 2-Bromopyridine on Cu(100) and O/Cu(100)

Abstract

Adsorption and reactions of 3-bromopyridine and 2-bromopyridine on Cu(100) and O/Cu(100) have been investigated, attempting to explore the chemical processes by identifying a variety of possible reaction intermediates and products, such as bipyridine, pyridyne, pyridine, pyridine oxide, hydroxypyridine, pyridone, and so forth. They can be generated from the Ullmann reaction, dehydrogenation, hydrogenation, hydroxylation, and oxidation of pyridyl groups on the surfaces. Temperature-programmed reaction/desorption, reflection–absorption infrared spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations have been employed for this research. At a monolayer coverage of 3-bromopyridine on Cu(100), a perpendicular 3-pyridyl is generated on the surface below 300 K because of the C–Br bond scission. This surface species undergoes loss of hydrogen, hydrogenation, and ring rupture at ∼450 K. The first two processes result in the pyridine formation. The dissociated fragments continue to react to form H2, HCN, and (CN)2 at higher temperatures. The relative amounts of the products of pyridine, H2, HCN, and (CN)2 are dependent on the coverage of 3-pyridyl. In the presence of surface oxygen atoms (O(ad)), dissociation of 3-bromopyridine also generates 3-pyridyl first. However, the pyridine formation from this intermediate is terminated, with decreased H2, HCN, and (CN)2. Additional products of H2O, CO, CO2, and HNCO are generated. For 2-bromopyridine (1.0 L) on Cu(100), at a coverage slightly higher than a monolayer, a perpendicular 2-pyridyl is generated below 300 K, and its decomposition generates pyridine (∼525 K), together with H2, HCN, and (CN)2 at higher temperatures. At a large exposure of 10.0 L of 2-bromopyridine, additional pyridine is generated at 650 K, which is suggested to be originated from an electronically/structurally strongly perturbed C5NH4 intermediate. On O/Cu(100), no 2-pyridyl intermediate is measured from the primary 2-bromopyridine decomposition; however, 2-oxypyridine is formed instead. This intermediate can be produced from nucleophilic attack on the 2C atom of 2-bromopyridine by O(ad) and/or from recombination of 2-pyridyl and O(ad). The 2-oxypyridine further reacts to form H2O, HCN, CO, CO2, HCNO, and (CN)2.

Surface Reaction Mechanisms: 3-Bromopropanoic and 2-Bromopropanoic Acids on Cu(100) and O/Cu(100)

“…For the bromine, the spin−orbit coupling components of 3d 5/2 and 3d 3/2 at 69.0 and 70.0 eV, respectively, are from adsorbed Br atoms (Br (ad) ). 15 The other two peaks of 70.5 and 71.4 eV are from intact BrCH 2 −. In terms of the relative fitting peak areas (A(BrCH 2 −)/A(Br (ad) )), the amount ratio of BrCH 2 −/Br (ad) is estimated to be ∼1.6.…”

“…A deconvoluting procedure has been performed for the 110 K spectrum, with the fitting peaks of 283.6, 286.2, 288.8, and 290.4 eV for C 1s, 531.7 and 533.1 eV for O 1s, and 69.0, 70.0, 70.5, and 71.4 eV for Br 3d. For the bromine, the spin–orbit coupling components of 3d 5/2 and 3d 3/2 at 69.0 and 70.0 eV, respectively, are from adsorbed Br atoms (Br (ad) ) . The other two peaks of 70.5 and 71.4 eV are from intact BrCH 2 –.…”

DFT study of low-energy electron interaction with pyridine, pyrazine and their halo derivatives

“…Halogenated derivatives of pyridine and pyrazine are crucial intermediates for pharmaceuticals and agrochemicals [35][36][37]. Forming of pyridyl radicals from halopyridines is important in, e.g., astrochemical [38], environmental [39] or corrosion [40] experimental studies. The effect of the substituent on the orbitals in pyridine has been studied extensively (e.g., [41,42] and references therein).…”