2 research outputs found
Kinetic Study on the Reduction of Room-Temperature NO<sub><i>x</i></sub> in Etching Waste Gas by Na<sub>2</sub>S<sub>2</sub>O<sub>5</sub> 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