Flexible polyurethanes, renewable fuels, and flavorings from a microalgae oil waste stream

Article abstract of DOI:10.1039/d0gc00852d

Renewable polymers have become an important focus in next-generation materials, and algae biomass offers an environmentally low-impact feedstock that can serve multiple uses. This study aims to develop a scalable methodology for production of microalgae-based polyols for polyurethane synthesis from waste oils derived from algae biomass. Following separation of omega-3 fatty acids from algae oil, residual oils can offer valuable building blocks for petrochemical replacements. However, unlike vegetable oils, algae oils contain organic contaminants, including photosynthetic pigments and hydrophobic cofactors that can complicate preparative methodologies. Here we convert and purify waste streams from omega-3 depleted Nannochloropsis salina algae oil, with major components consisting of palmitic and palmitoleic acid, into azelaic acid (AA) as a building block for flexible polyurethanes, with a simultaneous production of heptanoic acid (HA) as a flavor and fragrance precursor. Conversion of free fatty acid mixtures into a soft soap allows extraction of organic contaminants, and urea complexation provides isolated palmitoleic acid, which is subsequently ozonolyzed to produce AA and HA. Bio-based polyester diols are prepared from AA via esterification to provide a polyol monomer for flexible polyurethane foam preparation. The HA co-product is modified to produce the flavoring agent methyl heptanoate and also decarboxylated to produce hexane as a renewable solvent. This scalable process can be performed on oils from multiple algal species, offering valuable monomers from a highly sustainable source.

Full text of DOI:10.1039/d0gc00852d

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DOI: 10.1039/D0GC00852D
COMMUNICATION
Flexible polyurethanes, renewable fuels, and flavorings from a
microalgae oil waste stream
a
b
b
b
Thien An Phung Hai , Nitin Neelakantan , Marissa Tessman , Suryendra Doron Sherman , Graham
a
a,c
c,d
a,c
Griffin , Robert Pomeroy , Stephen P. Mayfield , and Michael D. Burkart*
Received 00th January 20xx
th
Accepted 00 January 20xx
DOI: 10.1039/x0xx0000x
5
Renewable polymers have become an important focus in next-
generation materials, and algae biomass offers an environmentally
low-impact feedstock that can serve multiple uses. This study aims
to develop a scalable methodology for production of microalgae-
based polyols for polyurethane synthesis from waste oils derived
from algae biomass. Following separation of omega-3 fatty acids
from algae oil, residual oils can offer valuable building blocks for
petrochemical replacements. However, unlike vegetable oils, algae
oils contain organic contaminants, including photosynthetic
pigments and hydrophobic cofactors that can complicate
preparative methodologies. Here we convert and purify waste
streams from omega-3 depleted Nannochloropsis salina algae oil,
with major components consisting of palmitic and palmitoleic acid,
into azelaic acid (AA) as a building block for flexible polyurethanes,
with a simultaneous production of heptanoic acid that was
subsequently converted to flavor and fragrance. Conversion of free
fatty acid mixtures into a soft soap allows extraction of organic
contaminants, and urea complexation provides isolated palmitoleic
acid, which was subsequently ozonolyzed to produce AA and
heptanoic acid. Bio-based polyester diols were prepared from AA
via esterification to a provide polyol as a monomer for flexible
polyurethane foam applications. The heptanoic acid co-product was
used to produce the flavoring agent methyl heptanoate and
decarboxylated to produce hexane as a renewable solvent. This
scalable process can be performed on oils from multiple algal
species, offering valuable monomers from a highly sustainable
source.
feedstocks and food production . Algae biomass has experienced
growing interest as a future source for producing sustainable fuels
and materials due to fast growth rate, flexible habitat preferences,
6
and substantial yield . Algae produce more unsaturated fatty acids
compared to conventional vegetable oils, which have useful
applications to high-value products . In addition, residual microalgae
biomass, such as proteins, can be extracted and transformed to high-
value biobased products, such as polymers . Algae can be rapidly
cultivated on large scales and need not consume arable land or fresh
water . One of the major challenges of algae production has been to
identify strains with the highest growth rate, lipid content, and lipid
7
8
9
1
0
productivity for scalable production . Identifying the highest and
best use of algae oils will be important to ensure sustainability of the
market, and omega-3 fatty acids from microalgae currently offer a
1
1
high-value product within a growing nutraceutical market
.
Nannochloropsis strains of green algae offer high titers of
eicosapentaenoic acid (EPA, C20:5), roughly 25% of total lipid
content, and we reasoned that other high value applications could be
explored with the 75% of residual fatty acids. As an application, we
identified polyurethane (PU) foam to offer a promising market that is
predicted to show continuous growth in coming years, from a USD
54.2 billion in 2018 to over USD 79.8 billion predicted by 2023 .
Without fundamental change, this rapid upward trend of global
plastic demand is predicted to offset or reverse any decrease in
1
2
1
3
petroleum demand from the use of renewable energies by 2050 .
Additional co-products from this process, which include renewable
fuels and fragrances, have significant market value
1
4
.
To avoid fossil carbon use, renewable resources that offer
We previously established and developed a large-scale
the next generation of transportation fuels and chemical feedstocks
production system for cultivation of a variety of microalgae strains to
produce biomass in both photobioractors and open ponds , and the
1
,2
15
have been studied in recent years . Although plant oils are known
3
, 4
for low toxicity, renewability, and biodegradable properties , use of
food crops poses other problems, including high arable land, water,
and nutrient use. They also present a competition between biofuel
resulting algae oils have recently been applied to both biofuel
1
production and for polymeric material synthesis . The most abundant
components in algae oil are triacylglycerides (TAGs) which can be
easily hydrolyzed into saturated and unsaturated free fatty acids,
including palmitic acid (C16:0), palmitoleic acid (C16:1), oleic acid
(C18:1), and linoleic acid (C18:2). Unsaturations within these fatty
acids can be converted into oxygenated functional groups (carboxyl
a
Department of Chemistry and Biochemistry, University of California, San Diego, 9500
Gilman Drive, La Jolla, CA 92093-0358, USA. Email: mburkart@ucsd.edu
b
Algenesis Materials, 1238 Sea Village Dr. Cardiff, CA, 92007, USA.
The California Center for Algae Biotechnology, University of California San Diego,
c
1
6
or hydroxyl) , which can be valuable for a variety of chemical uses.
9
d
500 Gilman Drive MC 0368, La Jolla, CA 92093, USA.
Division of Biological Sciences, University of California San Diego, 9500 Gilman
Drive, Bonner Hall 2150C, La Jolla, CA 92093, USA.
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DOI: 10.1039/D0GC00852D
COMMUNICATION
urea
crystalization
O
O
renewable
polyurethane
88%
OH
OH
OH
C16:1
+
C16:1
C16:0
MDI
quant.
O ;
3
(hydro-
O
NaClO2;
NaHSO3
Nannochloropsis salina
treatment)
HO
EG
O
O
algae biomass
84%
renewable
fuel/solvent
OH
O
OH
extraction
C16:0
O
O
DBTDL
distillation;
algae oil
O
OH
quant.
saponification/wash
C20:5
C16:1
C16:0
Mes-Acr-Ph
435 nm LED
40%
78%
n
azelaic acid (AA)
polyester polyol
O
O
+
MeOH, H+
C20:5
nutraceuticals
HO
heptanoic acid (HA)
O
90%
methyl heptanoate
Scheme 1. Pathway to renewable polyurethane, n-hexane and methyl heptanoate synthesis from algae biomass.
The oxidative cleavage of olefins of unsaturated fatty acids is
of the low boiling point fractions from the omega-3 fatty acids by
distillation, the composition of the resulting mixture was identified by
GC-MS by converting free fatty acids into fatty acid methyl esters
(FAMEs). These peaks were identified using retention time and mass
spectral matching from the NIST reference library. The composition
of the fatty acids is listed in Figure S3 and Table S1: 8.3% myristic acid
(C14:0), 28.9% palmitic acid (C16:0), 58.7% palmitoleic acid (C16:1),
2.3% oleic acid (C18:1), and 1.8% linoleic acid (C18:2). The major
constituents are palmitoleic acid (C16:1) and palmitic acid (C16:0).
Importantly, the high percentage of palmitoleic acid is advantageous
as a rich source of monounsaturated fatty acids. Due to the presence
1
7
industrially carried out by ozonolysis for production of mono- and
dicarboxylic acids, which play an important role in a variety of
chemical applications including polyesters, polyamides, plasticizers,
1
8, 19
and pharmaceuticals
. The ozonolysis of oleic acid has been
1
8, 19
shown to be a rapid source of AA and nonanoic acid
which have applications in polymer manufacturing.
, both of
As monomers with multiple hydroxyl group within their
structures, polyols serve as precursors for production of polyurethane
2
0
products, such as flexible and rigid PU foams . Recently, bio-based
polyols have emerged as renewable and sustainable monomers for
the production of PU products. Previous publications showed the
syntheses of several bio-polyols from palm, soya, corn, and castor oils
o
of palmitic acid, with melting point of 62.9 C, the raw oil is a solid at
room temperature that quickly melts to liquid when it reaches
2
1, 22
o
,
however vegetable oils offer comparatively pure source of TAGs.
temperature of 70 C (Figure S4a).
Algae biomass, by contrast, may be extracted to provide “green
crude,” which contains significant photosynthetic pigments and other
small organic molecules. In order to prepare homogenously pure
feedstock for polymer synthesis, we have developed new
methodologies for isolation and conversion of algae fatty acids into
PU monomers.
Here we demonstrate a scalable approach to synthesize
flexible PUs from omega-3 depleted algae biomass through the
preparation of polyester polyols (Scheme 1). The procedure requires
five stages: purification of fatty acids from omega-3 depleted algae
oil; isolation of palmitoleic acid (C16:1) from free fatty acids; synthesis
of azelaic acid (AA, C9-dicarboxylic acid) from C16:1;
polycondensation of ethylene glycol and AA for polyester polyol
synthesis; and polymerization with methylenediphenyl diisocyanate
In addition to these fatty acids, multiple contaminants,
including chlorophyll fragments and carotenoids, were identified in
1
1, 24-26
the sample, as evidenced by H-NMR (Figure S5)
. Unlike seed
plants, which store primarily triacylglyceride small molecules, organic
extracts from microalgae contain a variety of metabolic components
that are insoluble in water but freely soluble in organic solvents such
2
7, 28
as acetone, diethyl ether, tetrahydrofuran and chloroform
. The
presence of these pigments with conjugated pi systems may decrease
downstream reaction efficiency, therefore their removal is a key
process in the production renewable chemicals from algae oil.
Multiple studies have described elimination of chlorophylls and
carotenoids, which include physical absorption, oxidative treatment,
phosphoric acid degumming, precipitation, and bleaching, but are not
2
9-33
practical for large scale applications
two-step process that includes bleaching combined with
saponification to remove chlorophylls from oil, however a large
. Recently, Li et al., published
(MDI).
a
We chose the N. salina as a strain for growing algae in large
scale because of its established high production of EPA and our ability
3
4
proportion of oil was also lost
.
2
3,15
to grow this strain for high biomass content
. Following separation
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DOI: 10.1039/D0GC00852D
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COMMUNICATION
In this study, we found a practical pathway to not only
As can be seen from Table S1, palmitoleic acid content of
86% ,with a yield of 80%, was obtained from the liquid phase of urea
complexation, while the palmitic acid content of 85.9% was recovered
from the solid phase. Importantly, most of saturated palmitic acid was
removed from the unsaturated fatty acid fraction (Figures S8-S9). The
improve the purity of the algae oil but also to obtain high purified
yield with a simple, cost-effective step through saponification. After
forming the carboxylate salts of free fatty acids, the obtained soap
was washed several times with acetone until the observed filtrate
turned from an orange to colorless solution with no UV absorption,
indicating that a removal of the pigments was complete. After
elimination of pigments, the resulting fatty acids were collected by
acidification with aqueous hydrochloric acid. Two classes of soaps
could be prepared depending on the cation used. Potassium
hydroxide forms a soft soap, retaining a liquid form that is more
amenable to large scale acetone extraction. Sodium hydroxide forms
a hard soap that requires more solvent and time to remove pigments
due to the solid, waxy state.
o
palmitic acid is a white solid that melts at 62.9 C, while palimitoleic
acid is yellow liquid at room temperature with a melting point of -0.1
o
1
C. Figure S10 shows the H-NMR spectra of the isolated palmitoleic
acid C16:1 and palmitic acid C16-0.
We next produced AA through oxidative cleavage of
palmitoleic acid with ozonolysis. Ozonolysis is well known to offer
excellent selectivity through a simple procedure that avoids toxic
waste products from oxidants such as nitric acid, permanganate, or
1
7
dichromate . The three-step mechanism for ozonolysis of mono-
1
7, 18
Treatment of washed soft soap with aqueous hydrochloric
unsaturated fatty acid has been reported
. A green, sustainable
acid recovered a mixture of fatty acids with a 85% yield. As shown in
Figure S6, the H-NMR of purified oil indicated that pigment
oxidizing agent, ozone is preferred as a safe alternative to most other
1
17, 50
oxidants and catalysts
. It is important to note that a continuous
impurities were eliminated. These pigments can be also accurately
detected by fluorescence measurement down to parts per million
flow process with ozone have been developed for industrial
applications, enabling conversions on the ton scale of product per
3
5,
3
6
50
.
As shown in Figure S7, the raw oil displayed a strong emission peak
day . Despite the advantages of ozonolysis, the process can suffer
*
35, 36
17, 19
at 668 nm, indicative of π-π transition
exhibited no emission peak. These color differences between raw oil
Figure S4a) and purified oil (Figure S4b) could also be clearly
visualized by eye.
In the next step, we employed a practical method to isolate
, while the purified oil
from sub-optimal yields, reported at around 70% for oleic acid
.
Published procedures report AAs yield of only 20%, although the
ozonolysis of oleic acid has been optimized by high temperatures of
(
o
19
up to 150 C for 2h . Most published ozonolysis procedures quench
1
9, 51
the intermediate ozonide using 30-60% aqueous H
producing aldehyde and carboxylic acid as products , and can result
in low yields of mono and di carboxylic acid products
2
O
51
2
, initially
palmitoleic acid (C16:1) from the purified oil mixture. A variety of
reported methods for separation of saturated and unsaturated fatty
1
9, 52
.
3
7, 38
acids have been published, such as urea inclusion complexation
,
To optimize the quench step, we evaluated a variety of
methods, with the goal of complete conversion to carboxylic acid. The
combination ozonolysis with oxidation using phosphotungstic acid or
tungstic acid and quaternary ammonium salts were found to produce
3
9, 40
41
nanoporous membranes
, ion-liquid solvent extraction ,
molecular distillation , chromatography , supercritical fluid
4
2
43
4
4
45
extraction , and lipase concentration . In many of the above-
mentioned methods, urea complexation has proven to be a favorable
technique for large-scale isolation of mono-unsaturated fatty acids
due to its high separation capacity and simple process. Urea and
thiourea are well known to form crystalline complexes with
hydrocarbons, saturated fatty acids and other straight-chain
5
3-55
AA at around 70%
. The obtained yield of AA was identical when
ozonolysis was combined with metal oxidation catalysts such as Mo-,
5
6, 57
V-, Mn-, Co-, Fe-, and Pb- oxides and tungstic acid . Ackman, et al.,
2 2
used in situ formed performic acid from H O and formic acid
incorporation in methanol with oleic acid. Although this approach
4
6
58
molecules . This is made possible by a crystalline tube structure
formed by urea that creates an inclusion site for linear compounds
when packed densely with the guest molecule 47. Therefore, the
straight-chained palmitic acid and other saturated fatty acids within
mixtures crystallize with urea, while the presence of cis-double bonds
increased the yield of AA to 95% , it is only suitable for small
laboratory scale due to safety concerns. Here, instead of quenching
with oxidative cleavage once completing ozonolysis, solvent was first
5
8
2 2 2
removed under vacuum, followed by addition of H O and HCO H .
As the formed ozonides or peroxides are potentially explosive, further
workup raised safety concerns.
4
8, 49
in unsaturated fatty acids results in a kinked molecular structure
,
and consequently they cannot enter the hexagonal crystal channel
and remain in the solvent. In addition, the urea complexation
procedure shown in Figure S2 benefits from facile recycling of
solvents (methanol and hexane) and urea using only physical
Recently, a mild one-pot ozonolysis oxidation process of
olefins was reported to synthesize carboxylic acids with yields of up
5
9
to 98% . This process, which employs sodium chlorite as an oxidant,
is reported to be a scalable procedure, safely converting over 20 kg of
3
7, 38, 49
59
methods (evaporation and crystallization)
.
Table S1
an alkene starting material in a high yield and purity . Therefore, we
summarizes the compositions of the initial fatty acid mixture, as well
as those of the palmitic and palmitoleic acid after separation by urea
complexation.
chose ozonolysis in combination with oxidative cleavage using sodium
chlorite to prepare AA from palimitoleic acid C16:1. Here we report a
mild one-pot, metal-free process to oxidatively cleave palmitoleic
5
9
acid to AA and heptanoic acid . Ozonolysis was conducted in an
3
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Journal Name
aqueous organic solvent (10%H
2
O-MeCN), and the generated
energy loss. We found that our synthesized polyurethanes gave 51%
energy loss, indicating that that they deform easily and cannot quickly
revert to their native state, and exhibited a pronounced memory
effect. The nine-carbon AA chain could be responsible for this;
relative to polyols based on shorter diacids, AA-based polyols have
more bonds capable of free rotation and fewer rigid ester bonds. It is
important to note that high energy loss is not an indicator of poor
performance. In fact, in certain products such as mattresses, this
effect is desirable.
intermediates were converted to desired carboxylic acids by
oxidation with sodium chlorite, which was then followed by a
reductive quench with sodium bisulfite. AA was extracted away from
heptanoic acid byproduct and hexane solvent with hot water,
followed by recrystallization. This ozonolysis - oxidation procedure
obtained AA and heptanoic acid in yields of 83%. For mass production
of HA and AA on kg scale, a continuous-flow ozonolysis process can
be implemented to improve safety through high transfer rates and
5
0, 51
small reaction volumes
.
A linear polyester with an average molecular weight of 4000
and a weight average molecular weight of 10,600 was prepared
through acid-catalyzed polycondensation of AA with ethylene glycol.
A detailed procedure is described in supporting information. The acid
number of the polyester polyol was in the range of 1-3, indicating
near-completeness of the polymerization reaction. The structure of
exo
(
a) polyester polyol
heating from 160 to -50
cooling from -50 to 160
50
1
o
polyester polyol was characterized by H-NMR spectroscopy (Figure
Peak: 25.02 C, H = 37.75 J/g
Area: 192.54 mJ
S14) and FT-IR (Figure S15). The IR spectrum displayed characteristic
-1
-1
polyester polyol peaks at 3500 cm and 1730 cm , showing OH and
C=O stretching from the hydroxyl and ester carbonyl groups,
0
-1
respectively. The double peaks at 2927 and 2852 cm were consistent
with C-H stretching from hydrocarbons, and the large peak at 1160
o
Peak: -16.5 C, H = -41.17 J/g
Area: -209.98 mJ
-1
cm in the fingerprint region was also identified as ester C-O
stretching. The broader OH peak in the algae-based polyol maybe
because of a combination of lower hydroxyl number and/or residual
0
50
100
150
o
T ( C)
1
acid content. H -NMR indicated the existence of both terminal
exo
60
alcohols and ester groups in the obtained polyol sample. The
molecular weight, OH number and acid number are summarized in
Table S2.
(b) PU foam
heating from -50 to 160
cooling from 160 to -50
As illustrated in Figure 1a, the obtained polyol shows a
o
40
melting point of 25 C and glass transition temperature (Tg) within the
o
range of -25 to -16.5 C. A broad and weak endothermic above Tg is
due to the crystallization of a short chain in the polyol structure. The
polyol exhibits a Tg below room temperature, a characteristic
property which indicates its elastomer behavior. A high mobility of
short chains in the polyol results in the elasticity at temperature
above the Tg .
The flexible polyurethanes synthesized here can be
2
0
0
6
0
described as a low density water-blown foam, similar to those
commonly made in the molded and slabstock industries. The foam
formulation (Table S3) was chosen to represent a basic flexible
polyurethane that can be used in a variety of applications ranging
from furniture to automotive cushioning. Resultant polyurethane
cubes were fabricated using a stainless steel mold, as described in the
supporting information. This allows for standard compression and
hardness tests to be done with accuracy and reproducibility. We used
a compression-decompression cycle (ASTM D3574-C) to determine
how quickly the foam cubes can respond to stress, as well as their
load-bearing capacity. This allowed us to understand whether the
foam is springy, and returns quickly to its original shape, or exhibits
viscoelastic behavior, i.e., 'memory effect'. By measuring the force
relative to displacement, integrating the compression curve,
subtracting the same integral for decompression, we determined
-
20
-50
0
50
100
150
o
T ( C)
Figure 1. DSC of (a) polyester polyol and (b) polyurethane foam
The DSC curve of resulting algae-derived PU foam is presented in
Figure 1b. The curve shows a glass transition temperature of 26.5 C
in a heating scan of PU foam. PU foam is a 3D network structure of
mobile soft segments (polyol) and rigid hard segments (MDI). The PU
matrix itself is highly cross-linked . Therefore, the flexibility of polyol
chains lead to good elasticity of PU foam at room temperature.
The properties of resulting algae-based PU cubes are shown
in Table 1. Mechanical properties strongly depend on the degree of
crosslinking and network structure of the PU foam. The diisocyanate
o
6
1
4
| J. Name., 2012, 00, 1-3
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react with algae polyol leads to urethane linkage which generates the
hard domain of PU foam because of the possibility of association by
hydrogen bond while the high molecular weight and mobility of algae
polyol represent the soft domain, resulting in superior mechanical
properties. The hysteresis and peak force values trend well with shore
hardness, and the more rigid algae PU cubes demonstrate lower
energy loss and higher peak force as is expected.
innumerable uses, including edible oil extraction, degreasing agents,
and as fuel additives. We note, however, in this photoredox catalyst,
catalyst is expensive, and the methodology would require significant
optimization for further exploration.
To explore the economic value of this process, we can
provide a conservative estimate based on the market value of AA and
methyl heptanoate. Assuming theoretical (quantitative) yields,
palmitoleic acid (16:1) represents ~50% of crude fatty acid waste
stream mass, and the ozonolysis process provides 70% AA (by
molecular weight). Taking into account our 58% overall yield to
prepare AA (over 3 steps), and that we purchase the crude algae fatty
acid waste stream for $1/kg (~$0.25/mol), our cost to produce AA is
Table 1. Azelaic Polyol Foam Cube Properties
Avg.
Density
kg/m )
Avg.
Avg.
Avg. Peak
Force
(N)
Formula
Hardness Hysteresis
3
(
(Shore A)
30 ± 3
(%)
$
1.22/mol ($6.48/kg). The bulk price of AA is currently $8.85/mol
Photosynthetic
PU foam
($47/kg), which is 7.25-fold value increase. We did not estimate the
297 ± 4
51 ± 3
217 ± 17
value of final PU products, given the size and complexity of the PU
market. Using similar metrics, our cost to produce methyl heptanoate
is $2.02/mol ($14.00/g), and bulk price is currently $72.10/mol
The other ozonolysis co-product was heptanoic acid.
Methyl heptanoate, an ester from the condensation of heptanoic acid
and methanol, is widely used in the flavor and fragrance industry,
(
$500/kg). This is a 36-fold value increase, although there is a limited
market for these flavors/fragrances.
In summary, AA and HA were successfully prepared from an
6
2-64
with a fruity, green aroma and flavor
. We prepared methyl
heptanoate from our algae based heptanoic acid via esterification
with a 90% yield (Schemes 2 and S4 and Figure S18). Methyl
heptanoate can be applied in a broad range of consumer products,
including food, beverages, fragrances, cosmetics, personal care and
algae oil waste stream and converted into a flexible PU foam, a bio-
based flavoring, and renewable solvent (Scheme 1). After separating
EPA for nutraceutical uses from algae oil, the resulting waste stream
consists of a mixture of fatty acids is purified and separated into C16-1
and C16-0 in at yield of 85-88% by urea complexation. Subsequent
ozonolysis cleavage results in AA and HA, both in 84% yield. This study
indicates that AA derived from an algae-sourced waste stream has the
potential to support material production of polyester polyols, a
precursor for polyurethane synthesis, and renewable solvents.
Valorizing a waste stream from omega-3 fatty acid production in this
manner, which would otherwise be converted into liquid fuels,
provides added cost benefits for algae biomass production. Heptanoic
acid co-product can be converted into methyl heptanoate (90% yield),
a valuable product for the flavors and fragrances industry, and
renewable hexane (40% yield). We plan to optimize and scale these
procedures to enable large scale production of AA and HA, where
continuous flow ozonolysis will allow achievement of large-scale
capacities. The exploration and utilization of algae biomass to prepare
high value products offers tools to sustainably transition from
petrochemicals to renewable chemical feedstocks.
6
3
household products.
MeOH, H+
reflux, 90%
O
O
O
Mes-Acr-Ph (5 mol %)
(
PhS)2 (10 mol %)
OH
i-Pr2NEt (20 mol %)
450 nm LEDs, TFE [0.5 M]
40%
Scheme 2. Synthesis of methyl heptanoate and hexane from
heptanoic acid.
In addition, carboxylic acids can be converted to
hydrocarbons and other chemicals by decarbonylation,
6
5-68
decarboxylation, and deoxygenation
. These conversion can be
challenging due to the requirement for higher temperatures (300-400
o
66
65
C) , nobel metal catalysts (Pd, Pt), low reaction rates and rapid
6
9
catalyst deactivation . In recent years, photoredox catalysis have
emerged at the forefront of synthetic organic chemistry for
decarboxylative functionalizations , including decarboxylative
alkylation , decarboxylative vinylation72 and decarboxylative
7
0
Conflict of Interest
7
1
7
3
arylation . Photoredox catalysis utilizes the energy of light to
M.D.B., S.P.M. and R.P. are founders and advisors to Algenesis
Materials, a biotechnology company interested in developing
renewable materials.
7
4
accelerate a chemical reaction via single electron transfer , which
avoids the use of traditional chemical reagents that are often toxic or
hazardous. A direct organocatalytic protocol for the decarboxylation
of carboxylic acids to alkanes has been reported . We applied this
procedure with algae-based heptanoic acid (Schemes 2 and S3 and
Figure S17). The procedure produced renewable hexane at 40% yield
by treatment with 450 nm light and a photocatalyst. Hexane has
Author Contributions
7
0
T.A.P.H., N.N., R.P., S.P.M., and M.D.B. designed the research. N.N.
prepared the polyol. S.D.S. and G.G. prepared the PU material. M.T.
5
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evaluated polyol and PU properties. T.A.P.H. performed all other
experiments. All authors prepared manuscript.
22
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Authors kindly acknowledge DOE funding (PEAK-21C42A). Authors
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