Kinetic Study on the Reduction of Room-Temperature NO_<i>x</i> in Etching Waste Gas by Na₂S₂O₅ and Urea in Alkaline Pretreatment

Etching waste gases derived from photovoltaic cell production are difficult to treat at room temperature. Therefore, the use of wet denitrification with Na2S2O5 is recommended to overcome this issue. The presence of O2, Cl2, and metals in gases leads to the consumption of 65% of SO32– within 2 h. Although alkaline pretreatment adsorbs most of the gases and metals, the high ceiling temperature results in a short residence time and incomplete reaction with the lye. Therefore, in this study, urea was added to Na2S2O5. After adding the optimum concentration of urea (0.5 mol L–1) to a 1.0 mol L–1 SO32– solution, the anodic potential measured using cyclic voltammetry shifted from 0.051 to −0.119 V, the electron transfer rate k0 decreased from 4.89 × 10–5 to 4.27 × 10–5 cm s–1, the exchange current density measured using the polarization curve decreased from 18.37 to 13.58 A cm–2, and the reaction activation energy increased from 37 to 63 kJ mol–1. Therefore, adding urea to generate hydroxyl functional groups can effectively block the free radical oxidation chain reaction of SO32–, hindering its oxidization. In summary, alkaline pretreatment and urea addition can increase the effective reaction between SO32– and NOx and reduce the costs. Our study provides data to support the application of wet denitrification at room temperature

A Stereoselective Process for the Manufacture of a 2′-Deoxy-β‑d‑Ribonucleoside Using the Vorbrüggen Glycosylation

A practical and scalable process for the manufacture of cladribine (<b>1</b>) is described. Vorbrüggen glycosylation of doubly silylated 2-chloroadenine <b>2</b> with protected 1-<i>O</i>-acetyl-2-deoxy-α,β-d-ribofuranose <b>3</b> under reversible conditions in the presence of 20 mol % triflic acid in a solvent that selectively precipitated the desired β-anomer β-<b>4a</b> whilst leaving the unwanted α-anomer α-<b>4a</b> in solution to isomerise allowed good overall stereoselectivity with exclusive regioselectivity. An aging step allowed anomerisation of α-<b>4a</b> to β-<b>4a</b>, thereby improving the isolable yield of the β-anomer. Direct filtration of the product mixture without a catalyst quench or aqueous workup furnished the crude β-anomer β-<b>4a</b> in good yield (up to 68%) and purity (>95% by HPLC) with no regioisomers detected and only ∼1–3% (by HPLC) of the undesired α-anomer. Deprotection of the crude, unpurified intermediate β-<b>4a</b> followed by recrystallisation provided drug-grade cladribine (<b>1</b>). The process includes three isolation steps and was demonstrated on kilogram scales using cGMP providing 99.8–99.9% pure cladribine in up to an overall 43% yield based on 2-chloroadenine (<b>5</b>). In contrast to previous methods, column chromatography and/or bulky directing groups were not required in the glycosylation step, a high pressure vessel was not needed in the deprotection step, and only one dedicated recrystallisation step was necessary