Food Chemistry: Metabolism of Naphthalene, Methyl, and Ethyl Compounds

This assignment delves into the food chemistry of naphthalene and its related compounds, exploring their properties and metabolic pathways. The student analyzes naphthalene's structure, comparing it with alkylated derivatives like 1-methyl and 2-methyl naphthalene, and 1-ethyl and 2-ethyl naphthalene, examining the presence of aromatic rings and side chains. The assignment details the metabolic pathways of these compounds, including the breakdown of naphthalene into various metabolites like 1,2-Dihydroxyl-naphthalene, and the subsequent formation of compounds such as salicylaldehyde, salicylate, catechol, and ultimately, succinate and Acetyl CoA. The metabolic pathways of 1-methyl and 2-methyl are also explored, highlighting the role of enzymes like xanthine oxidase and cytochrome P450 oxidase. The student also discusses the impact of adding alkyl groups on the aromatic ring and the differences in metabolism between alkyl side chains and condensed aromatic rings, differentiating between alkylated PAHs, non-alkylated PAHs, and naked PAHs. The analysis highlights the importance of these compounds in environmental science and food chemistry, including their sources, characteristics, and environmental implications.

Food Chemistry 1
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Food Chemistry 2
Question 1
● Naphthalene is a compound.
○ With substituent
○ Without substituent
■ Explain why?
Naphthalene is a compound with substituents. This is because, in its chemical reactions, it shows
aromatic behavior related to benzene and it simple substituents. And the reaction is basically the
substitution of the hydrogen atom by hydrogen atom (Cerniglia, 2013).

Food Chemistry 3
● Naphthalene is:
○ Naked PAHs
○ Alkylated PAH
○ Has Aromatic ring
■ Explain why?
Naphthalene has an aromatic ring. This is because aromatic rings organic compound which
usually occurs as the substructure of more complex molecules and these aromatic compounds are
indole, cyclotetradecaheptaene, and benzene, but Naphthalene is the simplest condensed ring
compound of hydrocarbon made up of two benzene ring.
● Naphthalene has:
○ A side chain
○ No side chain
○ Substituted
○ Unsubstituted
■ Explain why?
Naphthalene has substituted. This is because it contains two composed compound of benzene
rings having common two adjacent carbon atoms. It also contains hydrocarbon raw material
which gives a host substitution products which are employed in making of synthetic and dyestuff
resins (Chen, 2012).
● Naphthalene is
○ Mineral Oils
○ MOAH

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○ PAHs
■ Explain why?
Naphthalene is MOAH(mineral oil aromatic hydrocarbons). This is true from the above
discussions that Naphthalene is oil aromatic hydrocarbon compound. MOAH is a part under 1-
and 2- methylnaphthalene .
● MOAH consists of
○ Substituted aromatic hydrocarbon
○ Polycyclic aromatic hydrocarbon
○ Naked PAHs
■ Explain why?
MOAH consisted of polycyclic aromatic hydrocarbon. This due to the fact that the mineral oil
product from the crude oil via distillation methods and has a fraction of MOAH including n-
alkane , cycloalkane, and this MOAH basically has alkylated polyaromatic hydrocarbon
(Vermerris, 2015).
● MOAH consists of
○ alkylated PAHs
○ Non-alkylated PAHs
○ Naked PAHs
■ Explain why?

Food Chemistry 5
MOAH consisted of alkylated PAHs. Because the mineral oil basically from crude oil which is
MOAH usually has alkylated polyaromatic hydrocarbon which alkylated PAHs in full.
● Commercially available 1-methyl
○ Is With a side chain
○ Has No side chain
○ Is With substituent
○ Is Without substituent
○ Has Aromatic ring
○ Is Substituted
○ Is Unsubstituted
■ Explain why?
Is with a substituent. This is because 1-methyl will be part (substituent) of the benzene which is
a constituent of Naphthalene. But it is a hydrocarbon without an aromatic ring since the aromatic
rings are found in 2-methyl.
● Commercially available 2-methyl
○ Is With a side chain
○ Has No side chain
○ Is With substituent

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○ Is Without substituent
○ Has Aromatic ring
○ Is Substituted
○ Is Unsubstituted
■ Explain why?
Commercially available 2-methyl has aroma ring. 2-methyl of the naphthalene shows aromatic
nature related to benzene and its simple end product.
● Commercially available 1-ethyl
○ Is With a side chain
○ Has No side chain
○ Is With substituent
○ Is Without substituent
○ Has Aromatic ring
○ Is Substituted
○ Is Unsubstituted
■ Explain why?
Commercially available 1-ethyl is substituted. This is because this compound still has the
benzene parts which makes naphthalene. It is the only ethyl which is introduced at the first
carbon as seen in the figure below;

Food Chemistry 7
Fig 1: shows 1-ethylenaphthalene (Vermerris, W)
● Commercially available 2-ethyl
○ Is With a side chain
○ Has No side chain
○ Is With substituent
○ Is Without substituent
○ Has Aromatic ring
○ Is Substituted
○ Is Unsubstituted
■ Explain why?
The commercially available 2-ethylenaphthalene is with a side chain. This is because the branch
of the ethyl group attached at the second carbon atom will form a chain as seen in the figure
below;
Fig 2: showing a side chain hydrocarbon (Vermerris, W)

Food Chemistry 8
● Methylated metabolites can be metabolized much faster?
○ True
○ False
■ Explain why?
True. This is because the methylate in metabolites will increase the rate of reaction therefore by
increasing the rate of chemical reaction it will make the metabolites to be metabolized faster.
Question 2
The Naphthalene pathway is illustrated by the fig 2 below;
The metabolic pathway of Naphthalene entails several stages where Naphthalene is broken down
into 1,2-Dihydroxyl-naphthalene (Ritchie, 2012). This compound is then broken down by the
help of some enzymes like naphthalene oxygenase to form salicylaldehyde which is broken
further to salicylate by the same enzyme. From this point, salicylaldehyde dehydrogenase will
disintegrate salicylate to form catechol which is then broken down by the help of salicylate
hydroxylase enzyme into two major pathways (META and ORTHO pathways). And these then
disintegrate as shown in figure 2 below until succinate+ Acetyle CoA is formed at the ORTHO
pathways and 4Hydroxy-2-oxo-volerate at the META pathways.

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Fig 3: Pathway of Naphthalene (Vermerris, W)

Food Chemistry 10
Metabolic pathway of 1-methyl entails two concurrent stages where the in the first stage 1-
methyl is broken into 1-methyl-xanthine by the help of enzyme xanthine oxidase. This is further
broken down into theophylline by the same enzyme. Theophylline is finally disintegrated to
caffeine by cytochrome P450 oxidase enzyme (WILLIAMS, 2011). On the second stage is 1-
Methyl being broken down to 7-Methylxyanthine by the help of 7-Methylxanthine demethylase.
This will then be broken down to theobromine by the help of theobromine synthase enzyme.
Theobromine is finally broken down to form caffeine and this will be achieved by the help of
paraxanthine enzyme. This pathway can be illustrated by the diagram below;
Fig 4: Showing pathway of 1-methyl ( (WILLIAMS, 2011))

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2-Methyl is broken down in the following pathways as seen in the figure below;
Fig 5: Showing pathway of 2-methyl (https://www.google.com/imgres?imgurl=http%3A%2F
%2Fwww.nature.com%2Fnature%2Fjournal%2Fv431%2Fn7006%2Fimages%2Fnature02922-
f1.2.jpg&imgrefurl=http%3A%2F%2Fwww.nature.com%2Fnature%2Fjournal
%2Fv431%2Fn7006%2Ffig_tab
%2Fnature02922_F1.html&docid=fnqcdD81CzzXBM&tbnid=lcTRWAFUGPhcMM
%3A&vet=10ahUKEwjS9ODK1KvWAhXJAcAKHYQDBikQMwg5KBMwEw..i&w=600&h=
356&client=opera&bih=658&biw=1326&q=what%20is%20metabolism%20pathway%20of
%20methyl
%20naphthalene&ved=0ahUKEwjS9ODK1KvWAhXJAcAKHYQDBikQMwg5KBMwEw&iac
t=mrc&uact=8)

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Just like the 1-Methyl, 2-Methyl is also broken down in two concurrent stages, where the first
stage is 2-Methylnaphthalene is broken down to 2-naphthylmethylsuccinic acid this is promoted
by addition of Fumarate, this is then broken down to 2-naphthoic acid by the help of synthetase
enzyme. This naphthoic acid is combined with the first stage which entails the breaking of
Naphthalene to Carboxylation and then forms 2-naphthoic acid too. 2-naphthoic acid is then
broken down to form 5,6,7,8 tetrahyhydro-2-naphthoic acid, this will be achieved by the use of
synthetese enzyme. 5,6,7,8 tetrahyhydro-2-naphthoic acid is further broken down to form other
products and Decahydro-2-naphtholic acid as the final product during metabolic reaction.
When alkyl group is added to an aromatic ring the rate of metabolism will reduce. This is
because the aqueous solubility will be reduced, with the reduction of the solubility aqueous
substance on addition of alkyl group to aromatic ring (Chen, 2012). Information indicates that in
within a defined lipophilicity range, increase alkyl group on aromatic ring will result to
decreased solubility. With reduced solubility the rate of metabolism will as well reduce.
In both naphthalene and 1-methyl, 2-methyl, 1-ethyl, 2 ethyl there is at least a ring of carbon
atoms, for example in Naphthalene there are two rings of carbon atoms ( benzene ) which when
combined form Naphthalene as seen in the figure below;

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Fig 6: showing structures of Naphthalene (https://www.google.com/imgres?imgurl=http%3A
%2F%2Fwww.chem.ucla.edu%2F~harding%2FIGOC%2FN
%2Fnaphthalene01.png&imgrefurl=http%3A%2F%2Fwww.chem.ucla.edu%2Fharding
%2FIGOC%2FN%2Fnaphthalene.html&docid=f29ai09yF4N8FM&tbnid=UFd5XCIu69bh8M
%3A&vet=10ahUKEwjUwYz50qzWAhXqDsAKHY3MDRwQMwhHKAAwAA..i&w=703&h
=556&client=opera&bih=658&biw=1326&q=structure%20of
%20naphthalene&ved=0ahUKEwjUwYz50qzWAhXqDsAKHY3MDRwQMwhHKAAwAA&ia
ct=mrc&uact=8)
Also in the 1-methyl, 2-methyl, 1-ethyl, 2 ethyl, there is one ring of carbon atoms (benzene) with
methyl at first carbon and second carbon and ethyl group in first and second carbon atom. Both
will have at least a benzene ring (Grover, 2010). This can be seen in the figure below;

Food Chemistry 14
Fig 7 : Showing structure of 1-methyl, 2-methyl, 1-ethyl, 2 ethyl(Grover, P. L., 2010.)
Another relationship is the ability of both to have attachment which can allow attachment of
other organic compound (Cerniglia, 2013) to form a different compound. This is true since in
both there is one hydrogen attached to every one carbon atom in the benzene structure which is
their parent compound. There other attachment can be seen in the following figure.

Food Chemistry 15
Fig 7: showing attachment on 1-methyl, 2-methyl, 1-ethyl, 2 ethyl and Naphthalene respectively
(Bianchi, T. S., 2011)
The difference between the metabolism that occurs on the alkyl side chain and the metabolism
that occurs on condensed aromatic ring are as below. The metabolism that occurs on the alkyl
side chain entails a branched –chain amino acid also known as BCAA, it involves a complete
reaction ior breaking down of organic compound. This BCAA has aliphatic side –chain and
another branch at the center. BCAA metabolically upholds protein synthesis and turnover,
metabolism and signaling pathway. In this metabolism the breaking down is done effectively by
some enzymes presence in the cell like decarboxylase and dehydrogenase. While the metabolism
that occurs on condensed aromatic ring involves incomplete breaking down of organic matter.
This metabolism can occur in engine cars and incinerators (Bianchi, 2011). This metabolism may
occur in many reactions where there is incomplete combustion or breaking down.
alkylated PAHs
These are basically contained in Crude oil but are relatively have small concentrations of the
unsubstituted parent of PAHs Alkylated PAHs are categorized by the total number of alkyl
carbon atoms available in the parent PAH compound.
Non-alkylated PAHs
These are basically obtained from combustion sources for example carbon substances like wood
among other combustible carbon substance. These non-alkylate PAHs in marine environment
help since they have low molecular weight that can taint fish among other aquatic life.

Food Chemistry 16
Naked PAHs
These are type of Polycyclic aromatic hydrocarbons which are hydrocarbon without the rings
and chain. Just as its name suggest, it is a naked hydrocarn of polycylic aromatic (Vermerris,
2015). These type of Polycyclic aromatic hydrocarbons can be obtain in organic compound.
Alkylate PAHs undergo the oxidative metabolism through incomplete pyrolysis of the organic
substances which are present in relatively big quantity of fuels (fossils) that are released through
multiple processes of combustion. This will require oxidase catalyst in many occasions.
The kind of metabolites which should be from Naphthalene include 1-naphthol which is
bioactivated by human by heptic microsome.

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Food Chemistry 18
Bibliography
Bianchi, T. S., 2011. Chemical Biomarkers in Aquatic Ecosystems. 2nd ed. London: Princeton
University Press.
Cerniglia, 2013. metabolism of polycyclic aromatic hydrocarbons: past, present and future
applications in bioremediation. 2nd ed. Hawaii: springer .
Chen, H., 2012. Biotechnology of Lignocellulose: Theory and Practice. 3rd ed. Leicester :
Springer.
Grover, P. L., 2010. Polycyclic Aromatic Hydrocarbons: Metabolism, Activation and Tumour
Initiation. 2nd ed. Chicago: Springer.
Ritchie, T. J., 2012. The impact of aromatic ring count on. 2nd ed. Hull: Elsevier.
Vermerris, W., 2015. Phenolic Compound Biochemistry. 3rd ed. Stoke: Springer Science &
Business Media,.
WILLIAMS, P., 2011. Metabolism of Naphthalene, 2-Methylnaphthalene. 1st ed. Manchester :
Great Britain press.