Page 182 - CW E-Magazine (26-9-2023)

Special Report

via Directed Evolution for the highly
selective enantioselective hydration of
styrenes to chiralarylethanols. The engi-
neered enzyme gave remarkable title
reaction. The yield was up to 98% and
enantioselectivity at more than 99.1.
(Angew. Chem. Intl. Ed.; DOI: 10.1002/
anie.202215093).
Catalytic chemical recycling of
post-consumer polyethylene
[This paper has appeared in the presti-
gious journal of the ACS, JACS]

A. Arroyave et al have worked on the
problems associated with limited recy- Insights into the mechanism Fabrication of beta-zeolite nano-
clability. These authors have converted
post-consumer HDPE into telechelic and reactivity of zeolite-cata- crystal aggregates for the alkyla-
macromonomers suitable for circular lysed alkylphenol dealkylation tion of benzene and cyclohexene
reprocessing. Here, unsaturation was M. Bocus and V. Van Speybroeckh have [This column has covered papers on the
introduced into the HDPE by catalytic referred to lignin being depolymerised selective hydrogenation of benzene to
dehydrogenation using an Ir-POCOP and demethoxylated into 4-alkylphe- cyclohexene where about 40% to 50%
catalyst without an alkene acceptor. nols. H-ZSM can be used to C-dealky- conversion is realised.]
Cross-metathesis with 2-hydroxyethyl late these products to phenol and ole- Post selective hydrogenation of benzene
acrylate, followed by hydrogenation, fins, in the presence of steam and high to cyclohexene there can be a follow-on
transformed the partially unsaturated temperature. 4-Ethylphenol is less re- alkylation to cyclohexylbenzene. The
HDPE into telechelic macromonomers. active than 4-n-isopropylphenol. DFT new procedure involved a dual-tem-
The direct repolymerisation of this has been used to unravel the mole- plate with poly(ethylene glycol) (PEG)
material gave a brittle material. Amino- cular and mechanistic observations. The and cetyltrimethylammonium bromide
lysis of telechelic macromonomers role of steam has been analysed. (ACS (CTAB) to make Beta-zeolites nano-
with a small amount of diethanolamine Catal., 2022, 12, No.22, 14227-14242; crystal aggregates with ultrafine and
resulted in an increased overall func- DOI:10.1021/acscatal.2c03844). hierarchical structure. This new catalyst
tionality. Further repolymerisation was extended the life 4.3 times compared
through transesterification to generate a Selective oxidation of 1,3- with the commercial nanosized beta-
polymer with comparable mechanical butanediol to 3-hydroxybutyric zeolite. This catalyst also allowed robust
properties of the starting post-consu- acid (HBA) over PtSb alloy regeneration. (Ind. Eng. Chem. Res., 2022;
mer HDPE waste. Recycling pathway 2 DOI: 10.1021/acs.iecr.2c03417).
is suggested. (J. Amer. Chem. Soc., 2022; Z. Zhong et al have worked on the
DOI: 10.1021/jacs.2c11949). title reaction as HBA is used to make Mild oxidation of toluene (T)
polyhydroxyalkanoates-biodegrad- to benzaldehyde (B) by air
able polymers. PtSb
2
alloy catalyses this C. Deng et al have reported the green
reaction and at oxidation of T to B by air under mild
95.5% conversion conditions with 99% selectivity at 35%
82.3% selectivity conversion at 180 C. The catalytic cen-
o
of HBA has been tre of hexadecylphosphate acid (HD-
realised. (ACS Sus- PA)-FeO /Al O is optimised as PPA-
2
x
3
tainable Chem. Eng., CuFeO /Al O and readily available
x
2
3
2022; DOI: 10.1021/ phenylphosphonic acid (PPA), in place
acssuschemeng. of HDPA, provides good performance.
2c05213). A 5 vol % acetone-water is used as a
182 Chemical Weekly September 26, 2023

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