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Teaching complex chemistry concepts such as kinetics using inquiry-based learning techniques can be challenging in a high school classroom setting. Access to expensive laboratory equipment such as spectrometers is typically limited and most reaction kinetics experiments have been designed for advanced placement (AP) or first-year undergraduate courses. Therefore, we developed a new and inexpensive laboratory experiment specially tailored for high school students. The activities include in situ monitoring of iodide oxidation using individual UV-visible spectrophotometers, data analysis with a spreadsheet, and interpretation. The experiment introduces chemical kinetics, offers practice problems, and teaches students the technique of flooding to acquire data and make connections with reaction mechanisms based on trends observed in the rate constants. The exercise was successful in solidifying the concepts of rates, rate laws, reaction order, and their relation to mechanistic studies. The provided handout and notes are tailored to help high school science teachers implement the Next Generation Science Standards in their classrooms.

Renewable terephthalic and 1,4-cyclohexanedicarboxylic acids can be produced from biomass via muconic acid using a combination of biological and chemical processes. In this conversion scheme, cis,cis-mucononic acid is first obtained by fermentation using either sugar or lignin monomers as a feedstock. The diunsaturated cis,cis-diacid is then isomerized to trans,trans-muconic acid, reacted with biobased ethylene through Diels–Alder cycloaddition, and further hydrogenated or dehydrogenated to yield the desired 100% renewable cyclic dicarboxylic acid. The isomerization of cis,cis- to trans,trans-muconic acid represents the main bottleneck in this process due to undesired side reactions that promote ring closing to form lactones. Therefore, new technologies for the selective isomerization of muconic acid are urgently needed. Here, we studied the corresponding reaction kinetics to elucidate the mechanisms involved in both the isomerization and cyclization reactions with the objective to identify conditions that favor the selective formation of trans,trans-muconic acid. We demonstrate that the reactivity of muconic acid in aqueous media strongly depends on pH. Under alkaline conditions, cis,cis-muconic acid is deprotonated to the corresponding muconate dianion. This species is stable for extended periods of time and does not isomerize. Conversely, cis,cis-muconic acid readily isomerizes to its cis,trans-isomer under acidic conditions. Prolonged heating further triggers the intramolecular cyclizations through reaction of the carboxylic acid and alkene functionalities. The formation of the muconolactone and its dilactone is kinetically favored over the isomerization to trans,trans-muconic acid over a broad range of conditions. However, strategies involving the chelation of the carboxylates with inorganic salts or their solvation using polar aprotic solvents were found to hamper the ring closing reactions and allow the isomerization to trans,trans-muconic acid to proceed with high selectivity (88%). The obtained compound was further reacted with ethylene and hydrogenated to 1,4-cyclohexanedicarboxylic acid, an important monomer for the polyester and polyamide industries. [ABSTRACT FROM AUTHOR]

Introduction: Approximately 10.4 million Americans over the age of 12 have used methamphetamine (meth) for non-medicinal reasons (ONDCP 2005). Meth is easily made, and Midwest states like North Dakota have [...]

Laser flash photolysis of 4-benzoylpyridine N-oxide (BPyO) at 308 nm in aqueous solutions generates a triplet excited state 3BPyO* that absorbs strongly in the visible, λmax 490 and 380 nm. 3BPyO* decays with the rate law kdecay/s−1 = (3.3 ± 0.9) × 104 + (1.5 ± 0.2) × 109 [BPyO] to generate a mixture of isomeric hydroxylated benzoylpyridines, BPy(OH), in addition to small amounts of oxygen atoms, O(3P). Molecular oxygen quenches 3BPyO*, kQ = 1.4 × 109 M−1 s−1, but the yields of O(3P) increase in O2-saturated solutions to 36%. Other triplet quenchers have a similar effect, which rules out the observed 3BPyO* as a source of O(3P). It is concluded that O(3P) is produced from either 1BPyO* or a short-lived, unobserved, higher energy triplet generated directly from 1BPyO*. 3BPyO* is reduced by Fe2+ and by ABTS2− to the radical anion BPyOṖ− which exhibits a maximum at 510 nm, ε = 2200 M−1 cm−1. The anion engages in back electron transfer with ABTSṖ− with k = 1.7 × 109 M−1 s−1. The same species can be generated by reducing ground state BPyO with ṖC(CH3)2OH. The photochemistry of BPyO in acetonitrile is similar to that in aqueous solutions. [ABSTRACT FROM AUTHOR]

Teaching complex chemistry concepts such as kinetics using inquiry-based learning techniques can be challenging in a high school classroom setting. Access to expensive laboratory equipment such as spectrometers is typically limited and most reaction kinetics experiments have been designed for advanced placement (AP) or first-year undergraduate courses. Therefore, we developed a new and inexpensive laboratory experiment specially tailored for high school students. The activities include in situ monitoring of iodide oxidation using individual UV-visible spectrophotometers, data analysis with a spreadsheet, and interpretation. The experiment introduces chemical kinetics, offers practice problems, and teaches students the technique of flooding to acquire data and make connections with reaction mechanisms based on trends observed in the rate constants. The exercise was successful in solidifying the concepts of rates, rate laws, reaction order, and their relation to mechanistic studies. The provided handout and notes are tailored to help high school science teachers implement the Next Generation Science Standards in their classrooms. [ABSTRACT FROM AUTHOR]