Chemical Papers
Introduction
proꢁoundly used in various organic synthesis like methanol
oxidation, oxidative desulꢁurization, glycerol esteriꢃca-
tion, acrolein production, transesteriꢃcation (Zhang et al.
2019; Bryzhin et al. 2019; Khayoon and Hameed 2012;
Heravi and Sadjadi 2009; Badday et al. 2013) etc. How-
ever, bulk PMA having unique Keggin structure is non-
porous, highly soluble in organic solvents, possess low
Over past 15 years, solid wastes like coal ꢂy ash (CFA),
red mud, rice husk ash, etc. have become one oꢁ the major
areas oꢁ investigation in environmentally benign hetero-
geneous catalysis (Borhade et al. 2018; Lin et al. 2020;
Shirini et al. 2016). Among them, CFA is an abundant
waste generated by combustion oꢁ coal in thermal power
plants. Around 155 coal-based power plants in India with
installed capacity oꢁ 145,044.80 MW electricity, consume
more than 536.40 million tons oꢁ coal per year which
results in generation oꢁ around 169.25 million tons oꢁ CFA
as a by-product (CEA Reports 2017). The disposal oꢁ CFA
poses not only serious ecological problems like air, soil,
water pollution but being classiꢃed as human carcinogen,
it causes adverse health efects also (Herndon and Whi-
teside 2017). For sake oꢁ maximum utilization oꢁ CFA,
besides its conventional use as building material, adsor-
bent (Genc and Genc 2018; Dagar and Narula 2018) etc.,
its application as a catalytic support material has attracted
attention oꢁ scientists in recent years. CFA, an ensemble oꢁ
mainly silica and alumina spheres, with minor quantities
oꢁ other metal oxides and unburnt activated carbon aꢁter
suitable surꢁace modiꢃcation through diferent activation
techniques, has proved to be best applied as a catalyst sub-
strate in organic reactions oꢁ industrial importance viz.
dehydration, transesteriꢃcation, hydrogenolysis, conden-
sation, esteriꢃcation, benzylation, acylation, alkylation,
hydrogen peroxide decomposition, oxidation and Suzuki-
Miyaura cross-coupling reaction (Chaterjee et al. 2019;
Bhandari et al. 2015; Vijaya et al. 2015; Mazumder and
Rao 2015; Jain et al. 2012; Rupali and Monika 2015; Mal-
pani and Rani 2019; Hada et al. 2020; Srivastava et al.
2
−1
thermal stability and surꢁace area (5–8 m g ) with ꢁew
acidic sites, thus, it is usually supported on silica, silica-
zirconia, zeolites in various acylation reactions (Cardoso
et al. 2004; Bachiller-Baeza and Anderson 2004; Bai et al.
2012). Thereꢁore, herein we ꢁocused on the development
oꢁ green, solvent-ꢁree, heterogeneous acid catalytic system
based on CFA that avoids the use oꢁ highly expensive, less
stable commercial heterogeneous catalytic systems such as
zeolites, mixed metal oxides, acid-treated metal oxides,
pure heteropolyacids etc. (Massah et al. 2013; Sartori and
Maggi 2006) ꢁor industrially important acylation reactions.
Use oꢁ microwave reaction medium coupled with inorganic
mineral-supported catalysts has been upsurge during past
ꢁew years as they are clean, energy saving, having ꢁast
reaction rates, suppress by-product ꢁormation and hence
enhance selectivity and yield oꢁ desired products.
In the present endeavour, we have synthesized a series oꢁ
potential, cost-efective, microwave stable CFA supported
PMA catalysts (PMFA). Mechanical and thermal activation
enhances capability oꢁ CFA to be utilized as a stable support
ꢁor ꢁurther loading oꢁ PMA. The mineralogical, morpho-
logical and structural properties oꢁ the prepared catalysts
were analyzed. PMFA was ꢁound efectively regenerable up
to ꢃve reaction cycles over a series oꢁ microwave assisted
acylation reactions oꢁ various aliphatic alcohols by acetyl
chloride and its catalytic activity was comparable to other
reported solid catalysts. Diferent reaction parameters such
as time, temperature, microwave power output, etc. were
ꢁurther optimized ꢁor maximum conversion. The products
oꢁ the test reactions are important as solvents in lacquer and
enamel industries as well as intermediates in perꢁumeries,
thinner in paint ꢁormulations (Toor et al. 2011; Ohayama
et al. 1995). Thus, the study provides the utilization oꢁ solid
waste, CFA as an alternative ꢁor development oꢁ highly eꢀ-
cient, recyclable heterogeneous acid catalyst ꢁor microwave
irradiated industrially beneꢃcial organic transꢁormations.
2
014; Thavamani et al. 2020) etc. Nevertheless, no attempt
has been made so ꢁar to synthesize solid acid catalyst by
impregnation oꢁ phosphomolybdic acid (PMA) on CFA.
Esters produced by acylation reactions oꢁ aliphatic
alcohols ꢁound wide applications in pharmaceuticals,
cosmetics, plasticizers through protection and deprotec-
tion reactions, multi-step synthesis (Mulla et al. 2012;
Aleixo et al. 2019; Ghosh et al. 2005) etc. Carboxylic
acids, acid anhydrides and acyl chlorides are commonly
used acylating reagents. Acylations by acyl urea, acyl
imidazoles (Pasha et al. 2010) have also been reported,
however, higher yields and smooth rates oꢁ acylation oꢁ
alcohols are seen on using aliphatic acyl chlorides (Green
and Wuts 1999). Some microwave assisted acylation reac-
tions oꢁ aromatic compounds are also well portrayed in
literature (Yamashita et al. 2010; Winé et al. 2009; Bai
et al. 2012). Heteropolyacid particularly PMA is non-pol-
luting, stable Bronsted acid, more eꢀcient and acidic than
mineral acids (Tayebee and Cheravi 2009) and has been
Experimental
Materials and chemicals
CFA (Class-F) was collected ꢁrom Kota Thermal Power
Plant, Kota (Rajasthan). PMA (99.99% purity) was pur-
chased ꢁrom Sigma-Aldrich. Methanol (99.99% purity), ali-
phatic alcohols, acetyl chloride were purchased ꢁrom Merck.
1
3