Transcript Title

CHAPTER 5
THE WONDERFUL WORLD OF CARBON: ORGANIC
CHEMISTRY AND BIOCHEMICALS
From Green Chemistry and the Ten Commandments of
Sustainability, Stanley E. Manahan, ChemChar Research,
Inc., 2006
[email protected]
5.1. RINGS AND CHAINS OF CARBON ATOMS
Most carbon-containing compounds are organic chemicals and are
addressed by the subject of organic chemistry
Carbon atoms can form straight chains, branched chains, and rings as
well as single, double, and triple bonds so that there are millions of
known carbon (organic) compounds:
Organic Chemicals
Organic chemicals include
• Synthetic polymers • Agricultural chemicals
• Important industrial compounds • Biological materials
Pollution of the water, air, and soil environments by organic
chemicals is an area of significant concern.
Chemically, most organic compounds can be divided among
• Hydrocarbons • Oxygen-containing compounds
• Nitrogen-containing compounds • Sulfur-containing compounds
• Phosphorus-containing compounds • Organohalides
• Combinations of these kinds of compounds
All organic compounds contain carbon
Most organic compounds contain hydrogen, at least one C-H bond
The simplest organic compounds are hydrocarbons composed only
of carbon and hydrogen
5.2. COMPOUNDS OF CARBON AND HYDROGEN:
HYDROCARBONS
Alkanes
Alkanes, also called paraffins or aliphatic hydrocarbons, are
hydrocarbons in which the C atoms are joined by single covalent
bonds (sigma bonds) consisting of two shared electrons
• Straight-chain alkanes • Branched-chain alkanes
• Cycloalkanes
Hydrocarbons (Cont.)
Formulas of alkanes
Molecular formulas, such as that of octane (C8H18), give the number
of each kind of atom in a molecule of a compound.
The formula of C8H18, for example, may apply to several alkanes,
each one of which has unique chemical, physical, and toxicological
properties.
These different compounds are designated by structural formulas
showing the order in which the atoms in a molecule are arranged.
Compounds that have the same molecular, but different structural,
formulas are called structural isomers.
Figure 5.1. Some Examples of Hydrocarbons Showing the
Bonding Diversity of Carbon
H H H H H H H
H C C C C C C C H
H H H H H H H
H
H
H C H H C H
H
n-he ptan e
H C C
3-e th yl -2,5- H H
H H
dim eth ylh e xane
H C H
H
H C
C H
H
C ycloh e xan e
H H
H C C C H
H
H
H
C C C H
H H
H
prope n eH
H H
C C C
H H
C H
C H
H H C
H
C H
H
C H
Ace tyle n e
Names of Hydrocarbons and Other Organic Compounds
Alkanes and alkyl groups
H
H
H C H
C H
H
H
H H
H C C H
H H
H H
C C H
H H
Me th an e (C H
) Ethan e (C
4 ) Me th yl grou p (C3H
2 H6 ) Eth yl grou p (C
2 H5 )
Names of alkanes and organic nomenclature
Systematic names, from which the structures of organic molecules
can be deduced, have been assigned to all known organic compounds.
The more common organic compounds, including many toxic and
hazardous organic sustances, likewise have common name.
Naming of Alkanes in Figure 5.1
The fact that n-heptane has no side chains is denoted by “n”, that it has
7 carbon atoms is denoted by “hept,” and that it is an alkane is
indicated by “ane.”
The names of compounds with branched chains or atoms other than H
or C attached make use of numbers that stand for positions on the
longest continuous chain of carbon atoms in the molecule.
For the second compound in Figure 5.1, the hexane part of the name
comes from the fact that it is an alkane with 6 carbon atoms in its
longest continuous chain.
Because it has an ethyl group (C2H5) attached on the third carbon
atom is denoted by 3-ethyl.
The two methyl groups on carbon atoms 2 and 5 are shown by 2,5dimethyl.
The name of the compound is 3-ethyl-2,5-dimethylhexane.
The cyclic compound with 6 carbon atoms is cyclohexane.
Reactions of Alkanes
Combustion reactions
C3H8 + 5O2  3CO2 + 4H2O + heat
• Major source of fossil fuel energy
Substitution reactions
CH4 + 2Cl2  CH2Cl2 + 2HCl
(9.2.2)
(9.2.1)
Alkenes and Alkynes
Two common alkenes and an alkyne
Double bonds, 4 shared electrons
H
H
H
C C
C C
H
H
H
Ethyle ne
H
T riple bond, 6 shared electrons
H
C C
H
H C
H
C H
Ace tyle n e
1,3-Butadie ne
The double and triple bonds in alkenes and alkynes have “extra”
electrons capable of forming additional bonds, and are therefore said
to be unsaturated.
Alkenes and alkynes both undergo addition reactions in which pairs
of atoms are added across unsaturated bonds as shown by the
hydrogenation reaction below:
H
H
C C
H
+ H H
H
H H
H C C H
H H
Alkenes and Alkynes (Cont.)
Addition reactions add to the chemical and metabolic versatility of
compounds containing unsaturated bonds and contribute to their
generally higher toxicities.
The reactivity of unsaturated bonds makes unsaturated compounds
much more chemically reactive, more hazardous to handle in
industrial processes, and more active in atmospheric chemical
processes, such as smog formation.
Polymerization reactions of alkenes:
H
H
H
H H
H
C C + C C + C C
H
H H
H H
H
H H H H
H
H C C C C C C
H
H H H H H
(5.2.3)
Aromatic Hydrocarbons
Benzene is the simplest of a large class of aromatic or aryl
hydrocarbons.
Many important aryl compounds have substituent groups containing
atoms of elements other than hydrogen and carbon and are called
aromatic compounds or aryl compounds.
Aromatic compounds have ring structures and are held together in
part by particularly stable bonds that contain delocalized clouds of socalled π (pi, pronounced “pie”) electrons.
H
H
H
C
C
C
C
H
H
C
C
H
H
H
H
C
C
C
C
C
C
H
H
H
Resonance structures of benzene, Benzene and the aromatic
C6H6
benzene ring are represented by a
hexagon with a circle
Aromatic Hydrocarbons (Cont.)
Many toxic substances, environmental pollutants, and hazardous
waste compounds are aromatic compounds.
Benzene is a volatile, colorless, highly flammable liquid with many
important uses that is hazardous both for its ignitability and toxicity
(exposure to benzene causes blood abnormalities that may develop
into leukemia).
Some aromatic hydrocarbons, such as naphthalene, contain fused
rings.
Naphthal ene , 10
C H8
C
C H
Polycyclic Aromatic Hydrocarbons, Benzo(a)pyrene
Formed by the incomplete combustion of other hydrocarbons, a
process that consumes hydrogen in preference to carbon.
• Engine exhausts • Wood stove smoke • Cigarette smoke
• Charbroiled food • Coal tar • Petroleum residues
Toxicological concern because of conversion to metabolites that can
cause cancer
C H
C
Be n z o(a)pyren e , 20
CH12
Aromatic Compounds
Compounds that contain at least one element other than carbon and
hydrogen
CH3
Tolue ne
x
NH2
Anil ine
OH
Phe nol
Fig 5.3. Lines Showing Structural Formulas
H H H H H H
H C C C C C C H
H H H H H H
n-He xan e
H
H
H
C C C C
H
H
H
H
M iddle carbons, C
H
H
End carbon, C H
H
H
Double-bonded end carbon,
Double-bonded middle carbon,
1,3-Bu tadie n e
H H
H C H
HC
CH
HC
CH
H C H C ycloh e xan e
H H
Carbons single-bonded H
to 2 other carbons,
C
H
C
H
C
H
Fig 5.3. Lines Showing Structural Formulas (Cont.)
H
H C H
H
End carbon, C H
H
Carbon on aromatic ring, C H
Tolu e n e
H
H C H
H
H
H C C C C
H H
H
H C H
H C H
H
M ethyl group, CH3
H
C H
H
Ethyl group, C 2H5
3-Eth yl -3-me th yl pen tan e
H Cl H H
H C C C C H
H H Cl H
H
C
Cl
Cl
Cl
2,3-Dich lorobu tan e
5.4. Functional Groups
Organo-oxygen compounds
O
H C
H
H H
C H H C C OH
H H
H
Eth yl en e oxi de
H O H
H H H O
H C C C H H C C C C OH
H
H
H H H
Eth an ol (alcoh ol)
Ace ton e (k e ton e )
Bu tyri c aci d
(carboxyli c aci d)
H
H C H H
H
C H Me th yl te rti arybu tyl e th er, MTBE (an e th e r)
H C O C
H
H C H H
H
Ethylene oxide is a toxic sweet-smelling, colorless, flammable,
explosive gas used as a chemical intermediate, sterilant, and fumigant.
Ethanol is an alcohol, in which the -OH group is bonded to an alkane
or alkene (attachment of the -OH group to an aromatic hydrocarbon
molecule gives a phenolic compound).
Organo-oxygen Compounds (Cont.)
Acetone is a ketone, a class of compounds that has the C=O
functional group in the middle of a hydrocarbon chain.
Butyric acid, which occurs in butter, is an organic carboxylic acid, all
of which contain the functional group,
O
C
OH
Methyltertiarybutyl ether, MTBE, formerly used as a gasoline
additive, is an ether in which an O atom connects 2 C atoms.
Aldehydes
O
H O
H C H
Form al de hyde
H C
H
C H
Ace talde hyde
Organo-oxygen Compounds (Cont.)
Esters are formed by the reaction of an alcohol and an acid
O H
H H H
H C C C OH + HO C C H
H
H H H
Propyl alcoh ol
Ace tic acid
H H H
O H
H C C C O C C H + H2O
Propyl ace tate e s te r H H H
H
(5.4.1)
Organonitrogen Compounds
Methylamine is a colorless, highly flammable, toxic irritant gas with
a strong odor.
H
H
H
C
Me th yl amin e
N
H
H
Nitromethane is used in chemical synthesis and racing car fuel.
H
H
C
NO2 Ni trome th an e
H
Dimethylnitrosamine is an N-nitroso compound, all of which
contain the N-N=O functional group, and many of which are
carcinogenic.
O
H
H N
H
C
C
H
N
H
H Di me thyl nitros amine
Organohalide Compounds
Cl
Cl
C Cl
Cl
Cl
F C F
Cl
C arbon te trach loride
Dich lorodiflu orom eth an e
(Both of the s e compoun ds are alk yl h ali des .)
H
C
H
Cl
Cl
C
Cl
C
H
C
Cl
H
Vi n yl ch loride
Trich l oroe th yle n e
(Th e s e com pou n ds are alk e n yl hal ide s .)
Cl
Cl
Cl
Cl
Cl
Cl
C h l orobe nz e n e
A pol ych l ori n ate d biph e n yl (PC B)
(Th e s e com pou n ds are aromatic h al ide s.)
Organosulfur and Organophosphorus Compounds
Most common examples are thiols, noted for their foul odors
H
H C SH Me thane thiol
H
H
H
H C S C H
H
H
Di me thyls ul fi de
Organophosphorus Compounds
Most notable examples are organophosphates
S
C2H5 O P O
Parath ionO
C2H5
H O
H C C O C2H5
S
NO2 H3C O P S C H
Mal ath ion O
C O C2H5
CH3
O
Many organophosphates are acetylcholinesterase enzyme inhibitors
that disrupt nerve function.
Parathion and malathion are insecticides. Parathion is now banned
because of its toxicity whereas malathion is a relatively safe
insecticide because mammals can metabolize it to relatively nontoxic
products
The military poison nerve gases, such as sarin, are organophosphates.
5.5. GIANT MOLECULES FROM SMALL ORGANIC
MOLECULES
Synthetic polymers are produced when small molecules called
monomers bond together to form a much smaller number of very
large molecules.
F
F
C
F
F
C +
F
F
C
F
C +
F
F
F
C
F
F
C +
C
F
F
F
C +
F
....
Man y te trafl u oroe th yl en e mon ome r mole cu le s
....
F F F F F F
C C C C C C
F F F F F F
n
....
Polyme r con tai n in g m an y u n its of
tetraflu oroeth yle n e pe r mol e cu l e,
wh e re n i s a very l arge n u m be r
Many natural products, such as cellulose, are polymers (biopolymers).
Polymers (Cont.)
Many of the hazards from the polymer industry arise from the
monomers used as raw materials.
Many monomers are reactive and flammable, with a tendency to form
explosive vapor mixtures with air.
All monomers used to make synthetic polymers have a certain degree
of toxicity; vinyl chloride used to make polyvinyl chloride plastic is a
known human carcinogen.
Polymers made from toxic monomers are not toxic.
Some Typical Polymers Made Synthetically
Mon ome r
Mon ome r form u la
H
H
H3C C C
H
P ropylene
(polypropylene)
Vinyl chloride
(polyvinyl chloride)
H
H
C C
Cl
H
H
Styrene
(polystyrene)
H
C C
H
Acrylonitrile
(polyacrylonit rile)
H
H
C C
H
CN
H2C
CH2
Isoprene
(polyisoprene)
C C
H3C
H
Pol yme r
H H
C C
H3C H
H H
C C
Cl H
Appli cation s
Applications requiring
harder plastic, luggage,
bot t les, out door carpet
n
T hin plastic wrap, hose,
flooring, P VC pipe
n
H H
C C
H
n
P lastic furniture, plast ic
cups and dishes, blown
t o produce Styrofoam
plast ic products
n
Synt het ic fabrics
(Orlon, Acrilan,
Creslan), acrylic
paints
H H
C C
CN H
H
H
C
C
H C C H
H3C
H
Natural rubber
n
5.6. LIFE CHEMICALS
Biochemistry is the chemistry of life processes.
Living organisms produce biochemicals
• Proteins • Carbohydrates • Lipids • Nucleic acids
Many biochemicals are large macromolecules
5.7. CARBOHYDRATES
Biomolecules consisting of carbon, hydrogen, and oxygen
Glucose is a monosaccharide
Table sugar, C12H22O11 is a disaccharide
Starch is a polysaccharide, a biopolymer of glucose
Generation of glucose by
photosynthesis:
6CO2 + 6H2O 
C6H12O6 + 6O2
Carbohydrates and green
chemistry
• Capture of solar energy
CH 2 OH
C
O
H
H H
C OH H C
HO
OH
C
C
H
OH
CH 2 OH
C
O
H H
H H
C OH H C C
O
O
C
C
H
OH
Gl u cos e
CH 2 OH
C
O
H H
H
C C
OH H
O
C
C
H
OH
CH 2 OH
C
O
H
H
C
OH H
O
C
C
H
OH
Th re e u n i ts of th e s tarch macromole cu le
• Solar energy to chemical energy • Glucose fermentation to ethanol
• Glucose as raw material for chemical synthesis
5.8. PROTEINS
Proteins composed of nitrogen, carbon, hydrogen, oxygen, some sulfur
Proteins are macromolecules composed of polymers of many amino
acids
The example below shows polymerization of three amino acids:
H O
H2N C C OH
H
Gl yci n e
H O
H O
H2N C C OH
H2N C C OH
C yste in e
H C H
H C H
SH
H H O H H O H H O
N C C N C C N C C
H
H C H H C H
SH
OH
OH
Tyrosi n e
Proteins (Cont.)
Protein structure
Loss of protein structure, such as is caused by some toxic substances,
is denaturation
Two major categories of proteins
• Fibrous proteins (hair, muscles) • globular proteins (hemoglobin)
Functions of proteins include
• Nutrient proteins (casein in milk)
• Structural proteins (collagen)
• Contractile proteins (muscle)
• Regulatory proteins (insulin)
5.9. LIPIDS: FATS, OILS, AND HORMONES
Lipids are biomolecules soluble in organic solvents
Many lipids, such as animal fats, are triglycerides of fatty acids
H
O H H H H H H H H H H H H H H H H H
H C O C C C C C C C C C C C C C C C C C C H
H H H H H H H H H H H H H H H H H
O H H H H H H H H H H H H H H H H H
H C O C C C C C C C C C C C C C C C C C C H
H H H H H H H H H H H H H H H H H
O H H H H H H H H H H H H H H H H H
H C O C C C C C C C C C C C C C C C C C C H
H
H H H H H H H H H H H H H H H H H
Tri glyce ri de of ste ari c aci d, C
H H2 ) 16 C (O )O H
3 (C
Other kinds of lipids consist of waxes and steroids, such as
cholesterol
• Steroids act as hormones (chemical messengers)
Lipids and green chemistry
• Poorly biodegradable substances may bioaccumulate in lipids
• Lipids can be valuable raw materials and fuels that can be cultivated
as renewable resources
5.10. NUCLEIC ACIDS
The fundamental nucleotide units of nucleic acids:
Th e se n i trogen ou s bas es occur in both DNA an d R NA
NH2
NH2
O
H
C
H
C
N
H
C
N
N
C
N
C
N
C
C H
C H
C
C
C
C
C
C
O
N
H
H
N
N
H2 N
N
N
H C ytos i ne
Ade n inHe
G u an i nHe
Thymine H
N
(DNA only)
O
O P O CH2
O-
C
H
O
C
O
C
N
O
C
C
CH3
H
O
H
C
C
H
H
C
H 2-Deoxy- -Dribof uranos e
O
O P
H
C
H
N
C
Uracil (RNA
C
C
onl y)
N
O
H
O CH2 O
O-
C
H
-D-Ribof uranose
H
C
H
C
C
H
OH
Nu cle oti de of DNA
Un i t of RNA polyme r
Dash e d l in e s s h ow bon ds to n e xt n u cl e otide u n i t.
Nucleic Acids (Cont.)
Nucleic acids are biological macromolecules that store and pass on
the genetic information that organisms need to reproduce and
synthesize proteins.
-helix structure by Watson and Crick
Nucleic acids and green chemistry
• Hazards of chemical substances to DNA, including cancer
• Genetic engineering and recombinant DNA technology
• Transgenic organisms to produce crops with unique
characteristics, synthesize pharmaceuticals, and make a variety of
useful raw materials