Chem. 253 – 5/6 Lecture
Announcements
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Return HW and Group Assignments
Turn in Green Chemistry HW
Today’s Group Assignment mostly on Green Chemistry
Today: completion of Biofuels and then on Toxicology
(some part will be covered next week)
Reading for Toxicology - Girard, Principles of
Environmental Chemistry, 2nd Edition – Chapter 16;
photocopy placed in folder in main office
Homework Questions Posted (Subset 3.4 – only 3 to
turn in)
Last Lecture + Group Assignment – Next Week
Will Have some time to Review for Final Exam
Green Chemistry
- Review
Rationale
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Improved design of compounds involving increased
efficiency, less waste of resources including energy, and
decreased toxicity
Can also be applied to new product production (e.g.
pesticide examples)
Main Principles:
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See 12 Principles
Atom Economy:
% atom economy
= (molar mass of atoms utilized/total molar mass of all
reactants)*100
Hazard Assessment (will get to this more later today)
Green Chemistry
- Review
Changes Resulting in Improvements
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More effective products (narrowly targeted pesticide
examples)
Solvents (move from VOCs to water-based, HFCs, CO2, or
ionic liquids)
Use of Renewable Feedstocks (e.g. from petroleum based
to plant based)
Energy Requirements (lower temperatures or more
efficient heating)
Other Methods of Reducing Waste (the three Rs:
recovery, reuse/recycle, regenerate)
Energy Use and Fuels
- Biofuels - Overview
Main Rationale for Use
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Q. While all carbon-based fuels will release CO2, what is the
advantage with respect to controlling CO2 concentrations to using a
bio-based fuel?
A. The main advantage is if the carbon originates from plant
material, when plants regrow, they will reabsorb emitted CO2. In
principle, this would mean there is no net CO2 production.
Limits to Use
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Plants fix carbon dioxide using sunlight to produce organic
compounds
CO2 + H2O → CH2O (biomass) + O2 (unbalanced)
The above reaction converts sunlight to chemical energy, but is not
super efficient (power density = 0.6 W m-2)
A very significant fraction of the Earth’s surface would need to be
devoted to biofuel needs to meet total transportation demand
Energy Use and Fuels
Biofuels - Overview
Main Types
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Direct use Fuels:
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Combustion of wood for heating, cooking or electricity production
Limited Practical Use (due to pollution and limited resources)
Sugar Based Fuels (main base unit = glucose)
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Ethanol
Ethanol
Ethanol
Related
from Sugar
from Starch
from Cellulose
fuels
Lipid Based Fuels
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OH
O
OH
OH
HO
OH
O
Direct use of oils
Biodiesel
R
O
H3C
O
-
H3C
+
+
O
H3C
OH
R'
O
O
R"
O
OH
O
R'
O
R
O
+
O
H3C
OH
R"
O
O
Energy Use and Fuels
Biofuels - Overview
Secondary Advantages
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Oxygen Content
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A small increase in oxygen content (especially in
petroleum/biofuel blends) improves combustion and reduces
pollutants (e.g. CO)
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Although, this reduces energy density (carbon is already
partially oxidized)
Reduction in Toxicity
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Biofuels start with reduced sulfur, fewer aromatics than diesel
and gasoline
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A fraction of fuel source is waste material (e.g. used
cooking oil) or has co-generation products
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Some of these advantages are good when use is low
Biofuels
- Sugar Based Fuels
Ethanol as a Fuel
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It can easily be added to gasoline (good oxygenate and
octane booster, but requires fuel “reformulation”)
Harder to use at higher concentrations
Additional disadvantages from lower energy density and from
ability to absorb water
Ethanol Production – from sugars and starches
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Technology for producing ethanol has been around for a long time
Once small sugars (mono- or di-saccharides) are present, yeast
enzymes convert sugars to ethanol in water (with carbon dioxide as
waste product)
This results in ~10 to 15% ethanol maximum (yeast don’t tolerate
higher ethanol conditions)
Biofuels
- Sugar Based Fuels – cont.
Ethanol Production – from sugars and starches
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Besides application to sugar cane/sugar beets (sucrose feedstock), it
is easily applied to starch sources (source for many alcoholic
beverages) using other enzymes to depolymerize starch
A major inefficiency in ethanol production is in separating ethanol
from water (distillation requires energy), although production from
sugarcane is more efficient than production from corn
Due to inefficiencies in harvesting and processing, ethanol production
is barely beneficial in reduction of greenhouse gases (and may be
harmful if considering N2O production)
Biofuels
- Sugar Based Compound
Ethanol Production – from cellulose
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Because sugar and starch have food value, there is a competitive
disadvantage to using theses sources for fuels
Much of harvested plant waste (e.g. corn cobs) is cellulose
Depolymerization of cellulose is more difficult
Technology (enzymatic or acid catalyzed) for converting cellulose into
sugar is still maturing
Related Fuels
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Besides yeast, other organisms can convert sugar into better
fuels (e.g. butanol – worse to drink but better alone or with
gasoline)
Biofuels
- Lipid Based Fuels
Vegetable Oil and Meat Fat as a Source
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Fats (triglycerides) are high energy content fuels (used for
long term fuel storage in organisms)
Oils can be used directly as fuel, but have low volatility
More common use is through conversion to biodiesel (typically
methyl esters of fatty acids)
Besides transesterification, production also involves clean up
to remove unreacted constituents, waste glycerin, and other
contaminants
Overall energy required for fuel production is lower than for
ethanol from sugars
Biofuels
- Lipid Based Fuels
Biodiesel as a Fuel
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In many regards, biodiesel is a cleaner burning fuel
(lower particulates, low volatility)
The one exception is NOX formation (higher in
biodiesel)
The other issues are fuel stability (oxidation from
unsaturated fatty acids, while saturated fatty acids
precipitate easily) and effects of contaminants and
aged fuel on engines
As with ethanol, blends generally are less
problematic
Biofuels
Renewable Fuels – Using Fischer-Tropsch Process
I know about this through a contract with
Greyrock Energy (Sacramento-Based Fuel
Company)
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Fuel production is through a two step process
First step is heating biomass under reduced oxygen:
CH2O (biomass) → CO + H2
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Then, the CO and H2 recombine with catalysts
making CH2 radicals (and H2O). Depending on
catalysts and conditions, products can range from
methanol to synthetic gasoline to synthetic diesel
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•
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Biofuels
Renewable Fuels – Using Fischer-Tropsch Process
Example chromatograph from synthetic diesel
(top) vs. petroleum diesel (bottom)
FID1 B, (TODD\11121303.D)
Most “tall”
peaks are
linear alkanes
0
FID1 B, (Y VONNE\08211302.D)
25
min
25
min
Biofuels
Questions I
1.
2.
3.
List one advantage to biofuels other
than reduction of CO2 emissions.
Why is it better to think of biofuels as
useful for a reduction in as opposed to
a replacement of petroleum fuels?
If lipids and carbohydrates can be used
to produce fuel, why not proteins?
Biofuels
Questions II
4.
5.
6.
The stoichiometry for ethanol combustion is:
C2H6O + 3O2 → 2CO2 + 3H2O. What does this
say about energy efficiency (by comparing to
fossil fuels)?
Although ethanol production from cellulose is
not currently cost effective, why is it considered
advantageous to producing ethanol from
starch?
Air pollution control districts often have
summer fuel blends to reduce ozone
production. Why might there be more
restrictions on biodiesel use in the summer?
Toxicology
- Overview
A.
B.
C.
D.
Exposure
Dose/Response
Fate of Toxic Substances in the Body
Types of Effects – to cover later
Toxicology
- Exposure
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The degree to which a toxic substance
will cause health problems will depend
on the following conditions:
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Concentration of substance
Form of substance
Route of entry to body
Time period in which body is exposed
Body’s “reaction” to toxic substance (only above are
considered exposure)
Toxicology
- Exposure
Form of substance:
- The form of the substance will affect how toxic
compounds pass through barriers (skin, GI tract,
airways)
Some examples:
- mercury (methyl mercury vs. inorganic mercury)
- aerosol particles (coarse vs. fine; acidic vs. neutral)
- compounds in specific solvents (e.g. dimethylsulfoxide
vs. water)
Any form that makes barrier passage easier increases
toxicity
Toxicology
- Exposure
Routes of exposure
1. Percutaneous (through skin)
basis:
- diffusion (pure compounds) – very fast for
gases; very slow for solids; faster for smaller
molecules
- polarity (faster for non-polar compounds)
- solvent effects (solutes in certain solvents like
DMSO and acetonitrile have increased hazards)
- people with dermatitis or abrasions are
affected at lower concentrations
Examples: Worker retrieving tool dropped in vat,
contact with pesticides when harvesting crops
Toxicology
- Exposure
2. Inhalation
- gases diffuse to surfaces
(reversible absorption)
- water soluble gases tend
to be absorbed more
efficiently but often before
the lungs
- lungs tend to be most
sensitive organ of airways
(large surface area and
designed for diffusion to
blood).
- Effects can be felt quickly
Toxicology
- Exposure
Inhalation (continued)
- aerosol particles tend to deposit on surfaces irreversibly
- coarse particles can’t follow bends; fine particles go to
lungs; ultra-fine particles diffuse to surfaces
Air passage
Mean gas trajectory
Gas or ultrafine particle
Particle trajectory
Random motion brings ultra-fine particle to wall
Toxicology
- Exposure (Inhalation)
Airways have defense mechanisms (mucous and
cilia to remove particles)
Toxic response can be due to passage to blood
and rest of body (pulmonary problems) or to
lung cell damage (e.g. asbestos)
People with asthma can suffer at much lower
doses than others
Respiration affects exposure. Heavy work or
exercise in poor air quality can be harmful.
Break for Group Activity
Toxicology
- Exposure
3. Oral
- Absorption occurs in the gastrointestinal tract (GI tract)
- Less polar compounds are preferentially absorbed
- For acids and bases, absorption of non-ionized species
is much faster
- Absorption also depends on pH of organ (~2 for
stomach vs. ~6 for intestines)
- Exposure can occur from contaminated foods (e.g. with
pesticide or natural toxin present) or from incidental
ingestion (e.g. lead in toys or paint flakes, chemistry lab
student eating cheetos, my son spraying my toothbrush
with insect repellent)
Toxicology
- Exposure
• Minimization of Exposure
– Use of protective equipment:
• Gloves, protective clothes, goggles (dermal)
• Masks or respirators (inhalation)
– Use of equipment to keep chemicals out of
contact
• Use of fume hoods
• Segregation of work space into different regions
Toxicology
- Some questions I
1.
2.
3.
4.
Besides concentrations, list three other factors that
affect how toxic a substance is
In which form is capsaicin (a moderate sized
compound of weak polarity) absorbed better into the
skin? a) As solid powder
b) in water c) in
acetonitrile
Which form of lead in the environment is most likely to
cause acute exposure problems: a) solid lead, b)
tetraethyl lead, c) lead sulfate (moderately soluble in
water), d) lead phosphate (very insoluble in water)
A researcher found that SO2 inhalation causes more
damage after patients drank lemonade or other acidic
drinks. Explain why?
Toxicology
- Some questions II
5.
6.
7.
A lawyer argues that arsenic in aerosols emitted from
an incinerator has the same concentration as aerosols
produced from soil dust in natural dust storms. Does
this make the incinerator safe? Why or why not? What
else should a safety expert know?
Which part of the GI tract would the following
compound be absorbed in: a) nitrous acid (pKa = 3.1),
b) aniline (pKa of base cation = 4.6)?
Chelating ligands like EDTA are administrated to
remove toxic metals. Based on pH considerations and
on movement across the GI tract in reverse, will
ligands be more effective in the stomach or intestines?
Toxicology
- Dose - Response Relationship
The concentration of a toxic substance in a body
(e.g. mg of toxin per kg body weight) is related
to the response of the body
Numerous responses are possible (e.g. from
inhibition of specific enzyme to organ failure to
death)
Common responses examined are effective dose
(ED), toxic dose (TD) and lethal dose (LD)
Relationship between dose and response is
generally better behaved for acute toxicity
Toxicology
- Dose - Response Relationship
Plots are made showing
onset of response vs.
concentration.
From plots LD50 or ED50 can
be determined.
Log conc. vs. %death on
probit scale typical
(1 probit unit = 1σ)
From Casarett and Duol’s
Toxicology (2nd Ed.)
Toxicology
- Dose - Response Relationship
• Different compounds can have
different response curves.
• Compounds with shallow
slopes mean large variability in
effects (often MORE
hazordous)
• Compounds with low LD50s are
more toxic
• Drugs that have LD range
overlapping with ED range
need close monitoring
From Casarett and Duol’s
Toxicology (2nd Ed.)
Toxicology
- Redistribution in Body
• Movement to target organs/tissue (e.g. Hg to
nerve tissue)
• Storage Tissue/Organs
– fats (for compounds with large Kows)
– bones (for certain inorganic compounds)
• Organs with High Concentrations:
– Liver + Kidneys
– Normal because these organs used for chemical
transformation (liver) or excretion (kidney)
Toxicology
- Fate of Substances
Toxic compounds in the body can be: 1) excreted or 2)
transformed
More water soluble compounds tend to be excreted
more quickly, while lipid soluble compounds can
have long lifetimes (months)
A common transformation is enzymatic oxidation in the
liver (particularly for lipid soluble compounds)
Oxidation can lead to decreases or increases in
toxicity, but usually leads to faster excretion due to
increase in polarity
Toxicology
- Fate of Substances
• Some Common
Transformations:
– Hydroxylation
– Dealkylation (alkyl
RNHCH3
groups attached to N,
O, or S)
RCH3
– Oxidation
RCH=CH2
– Epoxidation
– Glucuronic Acid
Addition
+
O
H
RNH2 + CH2O
RCH2OH
RCH2O
O
RC(OH)HCH2OH
RCH--CH2
OH
H
OH H
OH
HO
HO
OH
H
OH
OH
O
H
OH
H
OH H
OH
HO
O
H
OH
Toxicology
- Fate of Substances
• Hypothetical Example
– Moderately polar compound (compound A) is slowly
eliminated and transformed to product (compound B)
– Compound B is eliminated faster than compound A
(Only reaches low concentration)
Conc.
A – elimination only
A – both losses
A – transformation only
Compound B
Time
Toxicology
- Removal of Substances
• Polar/Water soluble compounds are often
eliminated through urination
• Volatile compounds can be eliminated by
exhalation
• Less polar compounds can be removed from
liver through bile (goes back to GI tract)
• Other routes
– GI tract
– Sweat
Toxicology
- Biotracer Studies
• Exposure is often difficult to assess accurately
• An alternative approach is to directly measure
concentrations of toxin or metabolites in urine
• Factors affecting exposure then can be studied
by comparing environmental concentrations with
detected amounts