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organic

Organic Chemistry Hydrocarbons

The Alkanes

Topics

• Definition: hydrocarbons• The alkanes• Common alkanes, nomentclature• Some physical characteristics of alkanes• Other families of hydrocarbons• Structural Isomers• Alkane chemistry – reactions• Hydrocarbons and the economy• Sources of alkanes• Petroleum and natural gas• Petroleum and natural gas formation

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Topics (Continued)• Energy flow• Time scale• The Hubbert Curve• Petroleum deposits• World oil consumption• From the deposits to the consumer• Petroleum refining• Gasoline• Octane ratings• Internal Combustion Engine Video• The Combustion Reaction- Balancing Act

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Topics (Continued)

• Heats of Combustion• Unintended consequences• Climate Change• Some Environmental Changes• An Expanded Example – Tundra• Petroleum Toxicity• The Clean-up• Cleaning Action of a Soap, a Dispersant• Bio-degradation of Alkanes and Dispersants• Conclusion

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Hydrocarbon Molecules

• Contain only carbon and hydrogen• Important fuels• Base stock for the synthesis of many useful

compounds• Familiar examples: methane, propane,

butane and octane• There are several families of hydrocarbons• The major sources are natural gas and

petroleum• We’ll first focus on the alkanes

The Saturated Hydrocarbons, the Alkanes

• Contain only hydrogen and carbon• Only single covalent bonds• Methane’s molecular formula, CH4 (g)

• Octane’s molecular formula, C8H18 (l)

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Common Alkanes

• Alkanes all fit this formula scheme:• CnH2n+2 where n can be any whole number

• Methane, CH4 fuel, major component of natural gas

• Ethane, C2H6 fuel, component of natural gas

• Propane, C3H8 fuel, LPG bottled gas

• Butane, C4H10 fuel, cigarette lighters

• Pentane, C5H12 fuel, component of gasoline

• Hexane, C6H14 fuel, component of gasoline7

Common Alkanes

• Heptane, C7H16 fuel, component of gasoline

• Octane, C8H18 fuel, major component of gasoline

• Nonane, C9H20 fuel, component of gasoline

• Decane, C10H22 fuel, component of gasoline

• Hexadecane C16H34 fuel, component of diesel and heating oil

• You’ll see that the prefixes, meth, eth, prop, etc mean 1, 2, 3, carbons etc. These prefixes carry on to other organic compound names such as ethanol.

• Ethanol has the formula C2H5OH

• How many carbons would be in propanol?• Answer 3

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Common Alkanes in the Home

• Paraffin wax refers to the solids with 20 ≤ n ≤ 40

• White, odorless, tasteless, waxy solid, with a typical melting point between about 47 °C and 64 °C ( 117°F to 147°F)

• Uses: Candles, drywall, thermostats

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Common Alkanes in the Home

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Mineral Oil refers to liquid alkanes in the range typically - 25.

Common Alkanes in the Home

• Petroleum Jelly: Semi-solid; C range greater than 25; FDA approved; one of the first alkane products

• Improper uses• Fresh Burns• Nasal congestion• or dryness• Sexual Lubricant

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Alkanes MP’s and BP’s

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Temperature Celsius

Number of Carbon Atoms

B.P.

M.P.

Solids

LiquidsGases

At room temperature, 25 C, how many alkanes (C1 –C14) are gases?At 25 C, how many are liquids? Solids?

Room Temp

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Some Other Families of Hydrocarbons

• Cycloalkanes CnH2n

• Alkenes CnH2n Unsaturated hydrocarbons

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Cyclohexane, C6H12

Ethene, C2H2

Some Other Families of Hydrocarbons

• Aromatics (arenes) (Only responsible for benzene)

• Ring compounds with alternating single• (C-C) and double (C=C) carbon to carbon bonds.

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Structural Isomers

• Compounds that have the same molecular formulas but different structural formulas.

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butaneMethylpropane (isobutane)

B.P. -11.7 CB.P. -.5 C

Isomers of C5H12

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As branchingincreaseswhat happens To the boiling points of these isomers?

Number of Isomers

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Crude Oil (Petroleum)

• Crude oil is a complex, highly variable mixture of hydrocarbons.

• Including: alkanes,• Cycloalkanes,• Alkenes, and • Aromatic hydrocarbons

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From Simple to Complex

• These compounds vary from very small molecules to large, complex ones, such as the arene on the right.

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Alkane Reactions

• The most important alkane reaction is combustion. Otherwise, alkanes are relatively stable chemically.

• Combustion refers to the burning of a substance.• Methane + oxygen produces carbon dioxide,

water, and lots of energy (heat and light)• CH4 +O2 CO2 + H2O + Energy (unbalanced)

This is an exothermic process• Recall that energy is the ability to do work• This energy drives our economy

Top Five Global Corps. ($ millions) 2009

• 1 Royal Dutch Shell Revenues Profits• $ 458,361 $26,277• 2 Exxon Mobil • $442,851 $45,220• 3 Wal-Mart Stores• $405,607 $13,400• 4 BP• $ 367,053 $21,157• 5 Chevron $263,159 $23,931

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Sources of Alkanes

• The major sources are natural gas and petroleum (coal too, especially methane)

• Other sources are methanogen bacteria (produce swamp or marsh gas) and cattle

• Biologically produced short chained alkanes are referred to as “biogas”.

• Petroleum is a complex mixture of alkanes and other hydrocarbons

• Petroleum deposits vary in their mixtures of hydrocarbons

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Petroleum and Natural Gas• These are classified as fossil fuels because

the preponderance of evidence suggests that they were formed from microscopic phytoplankton and zooplankton in ancient marine and freshwater environments.

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Anoxic Environment

• Petroleum and NG form under anoxic conditions when dead plankton drift to the ocean bottom (benthos) and are covered by sediments. The organic molecules are deprived of oxygen (anoxic). Over time these organic compounds are gradually converted to alkanes. Pressures and temperatures are high.

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Conversion of Sugar to Methane and Carbon Dioxide

• Example: sugar, under high pressure and temperature, anoxically decomposes to carbon dioxide and methane.

• Sugar carbon dioxide and methane

Energy + C6H12O6 CO2 + CH4

Balanced:

Energy + C6H12O6 3 CO2 + 3 CH4

This is an endothermic process (energy input required)

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The Energy Flow

• Sun Phytoplankton sugar methane available for work

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Photons arrive from the sun (8 minutes)

Photosynthesis converts photon energyto chemical bond energy (millisecond to second time scale)

Chemical bond energyStored in sugar molecules

Sugar’s energytransferred toMethane over millions of years

Time Scale

• From the former slide, you call see that the time scales for the energy flow range from less than a second (photosynthesis) to millions of years (formation of fossil fuels).

• The preponderance of evidence suggests that the world’s consumption of petroleum and natural gas is out pacing it’s natural rate of production. In other words we are rapidly running out of these resources.

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Hubbert Curve (1956)

• A model for predicting the explotation of geological resources.

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Hubbert Prediction vs. US Data

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Petroleum Deposits

• Plankton biomass accumulates constantly on the bottom of the world’s oceans. However the distribution is not even, nor are the physical requirements for the conversion of this biomass to petroleum always present.

• Rates of• Photo-• synthesis

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Anticline

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Impervious rock layer

Oil

Petroleum is formed in an “oil window” of favorable temperatureAnd pressure in the sedimentary rock below the oil deposit.

Petroleum - Complex Mixtures

• Petroleum is a complex mixture of alkanes, cycloalkanes, unsaturated hydrocarbons, as well as other carbon compounds. These deposits will often contain (1) an upper layer of gases,(2) a middle layer of liquid/solid materials (mostly organic compounds) with (3) a lower layer of saline water.

• These mixtures have names such as West Texas Intermediate (WTI), Tapis, and Brent Blend

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Asphalt Deposits

• Sometimes the cap rock is eroded away• The lighter (volatile) compounds evaporate• Leaving behind very heavy semisolid

material - asphalt

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Brea Tar PitsLos Angeles

World Oil Consumption (2007)

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Oil Consumption > Thousand barrels daily (most recent) by country

• Rank   Countries  Amount • # 1   United States: 20,517  • # 2   China: 6,684  • # 3   Japan: 5,288  • # 4   Germany: 2,625  • # 5   Russia: 2,574  • # 6   India: 2,555  • # 7   Korea, South: 2,280  • # 8   Canada: 2,206  • # 9   France: 1,975  • # 10   Mexico: 1,896 

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From the Deposit to the Consumer

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Petroleum Refining

36Oil Refinery, Washington State, USA

Three Approaches to Petroleum Refining

• (1) Fractional distillation: Relies on differences in boiling points to separate compounds from the petroleum mixture

• (2) Hydrocarbon Cracking: Using energy and catalysts, large molecules are broken down into smaller molecules.

• (3) Organic synthesis: Special products called petroleum derivatives are produced using specific chemical processes.

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Fractional Distillation

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Based on boiling points, molecules are separated from a complex mixture.

Hydrocarbon Cracking

• “Hydrocarbon cracking is the process of breaking long chain hydrocarbons into short ones.” Wikipedia

• C6H14g(Hexane) --> C3H8g (Propane)+ C3H6g(Propene)

• A large molecule is “cracked” into two smaller molecules.

• Depending on the demand, products are provided to the market by balancing these two processes as well as others.

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Organic Synthesis

• Here’s an example: The hydration (addition of water) to ethene (C2H4) results in the production of ethanol (drinking alcohol)

• C2H4(g) + HOH(g) CH3CH2OH(l)

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catalyst

ethanol

ethene

Gasoline

• A mixture of alkanes, usually in the range of C4 to C10

• These molecules can be “straight” chains or “branched”

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n-heptane, C7H16Octane rating, zero

2,2,4 – trimeythlpentaneOctane rating, 100

Two common examples: there are many more possibilities.

Octane Rating

• Octane Rating is a measure of the “auto-ignition” properties of a fuel in a spark - ignition internal combustion engine. In other words, the fuel’s “anti-knock” characteristics.

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Octane Ratings

• Fuels are compared to 2,2,4-trimethyl pentane (iso-octane) 100 octane and n-heptane zero octane

• What is compared? The anti-knock characteristics of the fuel

• If a fuel performs as does a mixture of 90% 2,2,4 trimethylpentane (iso-octane) and 10% n-heptane, then the fuel is rated as 90 octane and so on….

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Octane Ratings

• Research Octane Number (RON): most common number used internationally

• Motor Octane Number (MON): Also known as the “aviation lean octane rating”

• Trends 8-10 points below the RON for any given fuel

• (R+M)/2) = the average value and is reported in the U.S.A as the octane rating

• All the same: Road Octane Number (RdON), Pump Octane Number (PON), or

(R+M)/2. 44

Internal Combustion Engine Video

• http://www.youtube.com/watch?v=wRIKJ6Av5zo

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The Combustion Reaction

• Combustion of alkanes• Alkane(g) + Oxygen(g) Carbon dioxide (g) Water vapor• CnH2n+2 + O2(g) CO2(g) + H2O(g) + energy (mostly heat)

• The reaction must be balanced with coefficients.• Balance carbons first:• C5H12(g) + O2(g) 5 CO2(g) + H2O(g) + Energy

• Balance hydrogen next:• C5H12(g) + O2(g) 5 CO2(g) + 6 H2O(g) + Energy

• Now balance the oxygen:• C5H12(g) + 8 O2(g) 5 CO2(g) + 6 H2O(g) + Energy

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Another Example

• Butane + Oxygen Carbon dioxide + Water + Energy

• C4H10 + O2 4 CO2 + 5 H2O + Energy

• Note that there are 13 atoms of oxygen on the right side, so we’ll use (13/2) as our coefficient for the oxygen molecule on the left side to temporarily balance the equation.

• C4H10 + 13/2 O2 4 CO2 + 5 H2O + Energy

• Sometimes you’ll see the equation left as is, but most often it will be “cleaned up” by multiplying everything by a factor of two. This removes the fractional coefficient for the oxygen.

• 2 C4H10 + 13 O2 8 CO2 + 10 H2O + Energy47

Heats of Combustion

• These combustion reactions are extremely important.

• “The combustion of carbon compounds, especially hydrocarbons, has been the most important source of heat energy for human civilizations throughout recorded history.” http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/funcrx1.htm

• Recall that the U.S’s daily consumption of petroleum is about 21,000 thousand barrels per day. That’s 21 million barrels per day!!!

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Unintended Consequences

• Every gallon of gasoline consumed produces about 19 pounds of carbon dioxide gas.

• Humans are shifting the carbon balance on a massive scale from the geologic carbon “sinks” to the atmosphere.

• Carbon dioxide is a greenhouse gas. Greenhouse gases absorb infrared light (heat) and the result is an increase in atmospheric temperature. This leads to climate change.

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Recent Data

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Geologic Time Data

51http://www.pir.sa.gov.au/__data/assets/image/0009/51102/cc_figure_16.jpg

Global Temperature Anolmaly, 1850-2010

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Climate Change

• From the EPA:• “Many elements of human society and the

environment are sensitive to climate variability and change. Human health, agriculture, natural ecosystems, coastal areas, and heating and cooling requirements are examples of climate-sensitive systems.”

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Some Environmental Changes

• “Some observed changes include:• (1) shrinking of glaciers• (2) thawing of permafrost• (3) later freezing and earlier break-up of ice

on rivers and lakes• (4) lengthening of growing seasons • (5) shifts in plant and animal ranges• (6) earlier flowering of trees “

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http://www.epa.gov/climatechange/effects/index.html

An Expanded Example

• Thawing of Permafrost• The Arctic is expected to experience the greatest

rates of warming compared with other world regions• As permafrost melts, methane and CO2 are released

from the frozen soil.• Methane is a greenhouse gas (25 times more potent

than CO2)

• The permafrost system seems to be in a positive feedback mode (higher temperatures increase the melting and release of more GHG’s higher temperatures and so on)

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Global Warming Potential (GWP)

• “For example, the GWP for methane over 100 years is 25 and for nitrous oxide 298. This means that emissions of 1 million metric tonnes of methane and nitrous oxide respectively is equivalent to emissions of 25 and 298 million metric tonnes of carbon dioxide.”

• http://en.wikipedia.org/wiki/Carbon_dioxide_equivalent

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Petroleum Toxicity

• Alkanes have relatively low toxicity• Aromatic hydrocarbons (arenes) have

relatively high toxicity• Aromatics are components of petroleum.

Benzene, C6H6, is an example of an aromatic hydrocarbon.

• Benzene is one of the• 20 most widely used • chemicals in the • United States.

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Benzene Toxicity

• Benzene is classified as a carcinogen by the National Toxicology Program because it has been known to cause cancer. Long-term exposure to high levels of benzene can cause leukemia. 

• Short-term exposure to high levels of benzene by breathing or eating affects the central nervous system, and can cause paralysis, coma, convulsions, dizziness, sleepiness, rapid heart rate, tightness of the chest, tremors, and rapid breathing.

• http://toxtown.nlm.nih.gov/text_version/chemicals.php?id=5

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Methane Clathrate (Hydrate)

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Methane clathrateclogs containmentdome.

Clean up• Combustion

• Pick up

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The Clean-up

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• Dispersants

How do Dispersants Work?

• Soaps are dispersants.• Soaps are compounds which are made by

heating fats or oils, from animal or vegetable sources, with lye, a strongly basic compound. A typical soap molecule has the formula:

• Long alkane – like nonpolar tail• CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CO2

-1 Na+1

Polar end

Polar tail dissolves in oils and the polar end dissolves in water

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Cleaning Action of a Soap, a Dispersant

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• The large oil drops are reduced to micro- droplets by the action of the

• soap or detergent – dispersed.

Detergents

• A detergent is a similar kind of molecule, that is made from petroleum products. A typical formula is:

• Nonpolar alkane-like tail

• CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2OSO3-1 Na+1

• Polar head

• Where do we source detergents? Take a guess- petroleum!• So we don’t really remove the oil from the water; it’s still

there. So what happens to it and the detergent?

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Bio-degradation of Alkanes

• Certain types of bacteria can metabolize alkanes: they prefer even-numbered carbon chains as they are easier to degrade than odd-numbered chains.

• The steps start with the oxidation of one end of the chain to form an alcohol and then proceed step-wise to end up with CO2 and H2O plus metabolic energy.

• Laboratory experiments suggest that microbial communities can adapt to an alkane diet.

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Biodegradation of Dispersants

• “The two dispersants used by BP, Corexit EC9500A and Corexit EC9527A, are either comparable or 10 to 20 times more toxic than 12 other dispersants on the EPA’s approved list. “

• http://www.csmonitor.com/USA/2010/0520/EPA-scolds-BP-in-Gulf-oil-spill-dispersant-is-too-toxic-change-it/(page)/2

• The two dispersants used are produced by Nalco Holding Company, NYSE, NLC. Website: http://www.nalco.com

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Nalco Response

• Nalco Releases Additional Technical Information About COREXIT

• COREXIT 9500, the only dispersant Nalco is manufacturing to help break up the oil spilling into the Gulf of Mexico, is a simple blend of six well-established, safe ingredients that biodegrade, do not bioaccumulate and are commonly found in popular household products, the company said today. The COREXIT products do not contain carcinogens or reproductive toxins. All the ingredients have been extensively studied for many years and have been determined safe and effective by the EPA.

Biodegradation• A March, 1994, report created by France’s Institut National de L’Enviroenment Industriel et des Risques indicated that COREXIT 9500 largely biodegraded in 28 days. COREXIT oil dispersant was first applied to the Gulf oil slick on April 23.

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Nalco Response

• Bioaccumulation

• Based on modeling using US EPA software (as part of the EPI Suite v4.0, 2009), none of the COREXIT product components pose a risk of bioaccumulating.

• • At 840,000 gallons, the amount of dispersant in the region of the 3,850 square-mile slick represents an average concentration of about 30 parts per billion to the 10 meters of depth the dispersant will go – even without factoring in that a substantial portion of the product has already biodegraded.

• By comparison, the EPA allows drinking water to contain non-biodegradable contaminants -- including carcinogens and reproductive toxins -- that exceed the level of biodegradable chemicals present in COREXIT in the Gulf.

• http://www.nalco.com/news-and-events/4279.htm69

The Future?

• Uncertain: first time that dispersants have been used at a wellhead.

• Plumes of hydrocarbons/dispersants present• In deep water• Bacteria “eat” some of the hydrocarbons but

reduce the oxygen levels in doing so; this will likely impact many marine ecosystems throughout the Gulf.

• Heavier petroleum consonants remain as “tar balls”

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“Even with leak stopped, Gulf's pain may last years”

• Over time tar balls can lose their lighter materials, become denser and sink below the surface to resurface after storms.

• "It could show up in Miami next spring," he said. "It is likely that the heavier oils ... will continue to wash in for several years.“

• said Tony Wood, director of the National Spill Control School at Texas A&M-Corpus Christi.

• http://hosted.ap.org/dynamic/stories/U/US_GULF_OIL_SPILL_FOR_HOW_LONG?SITE=FLTAM

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Florida beach visitors soak up sun, ignore occasional tar ball

• http://www.cnn.com/2010/TRAVEL/06/20/florida.tourism.oil.disaster/index.html

• Massive Gulf of Mexico oil spill• http://postpix.palmbeachpost.com/

mycapture/folder.asp?event=991197&CategoryID=50973&ListSubAlbums=0

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Predictions

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Here is a good interactive map…..http://map.floridadisaster.org/gator/

Some Final Comments

• From the preceding slides, you can begin to understand the important role of hydrocarbons in our biosphere.

• From the concept of hydrocarbons, one can also begin to understand how petroleum is connected to products, that a first, may seem totally unrelated. A couple of examples:

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Functional Group Substitution

• Alcohols are derivatives of hydrocarbons as we saw with the synthesis of ethanol from ethene and water.

• C2H4 + HOH CH3CH2OH (ethanol)

• Think of the carbon chain (in this case, C-C) as derived from ethane (C-C chain or backbone). The only difference in the number and types of atoms is that a H atom has been substituted with a –OH functional group (called a hydroxyl group). Note: Technically the C2H4 reaction with water is called an addition reaction.

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• Continuing with this concept of substitution, we have,

• CH2OHCH2OH (a diol, ethane-1,2-diol) recall that di refers to two. In this case, two hydroxyl groups attached ,one to each carbon).

• The common name for this compound is ethylene glycol, or antifreeze, a toxic liquid.

• Precursor to polymers• “In the plastics industry, ethylene glycol is important precursor to

polyester fibers and resins. Polyethylene terephthalate, used to make plastic bottles for soft drinks, is prepared from ethylene glycol.” Wikipedia

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A Series of Substitutions

• Ethane - fuel • Remove H• and add OH• Ethanol – drinking alcohol, solvent, fuel• Remove H• and add another OH• ethane-1,2-diol – antifreeze and precursor for

plastics, etc

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A Word from The Graduate

• Youtube:

• http://www.youtube.com/watch?v=PSxihhBzCjk

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“Everybody's plastic, but I love plastic. I want to be plastic.“ Andy Warhol

• http://www.whatisplastic.com/?page_id=599• Plastics is divided into 2 major categories -

thermoplastics and thermosets.

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can recycle Can not recycle

Vulcanized Rubber Urea Formaldehyde (UF)

Polyethylene (PE)Polyvinyl Chloride (PVC)

Glycerol to Triose, a Sugar• Consider glycerol (glycerine), CH2OHCH2OHCH2OH

• What changes were• made to derive• this triose, D-aldotriose• (a sugar)? It is a precursor• to lactic acid.• C3H6O3 Answer: remove

• 2H’s from C #1 and double

• bond the oxygen.

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C #1C #2 C #3

C #1

C #2

C #3

Triose is a biologically

important sugar.

Conclusion

• Hydrocarbons are arguably the most important source of energy and chemical base stock in recorded history.

• Hydrocarbons makeup the “backbones” of biologically important compounds such as alcohols, sugars, lipids, and amino acids.

• A knowledge of hydrocarbons is absolutely necessary to help one understand the complexities of the biosphere, as well as, economics in the 21st century.

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